Circulation: Arrhythmia and Electrophysiology On the Beat April 2018


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Dr. Paul Wang: Welcome to the monthly podcast On the Beat for Circulation Arrhythmia and Electrophysiology. I'm Dr Paul Wang, editor-in-chief, with some of the key highlights for this month's issue. We'll also hear from Dr. Suraj Kapa reporting on new research from the latest journal articles in the field.

In our first article, Barry Maron associates report on the long term clinical course of hypertrophic cardiomyopathy patients following ICD therapy for ventricular arrhythmias. They studied a cohort of 486 high-risk hypertrophic cardiomyopathy patients with ICDs from eight international centers. Of these 486 patients over 6.4 years, 94 patients or 19% experienced appropriate ICD interventions, terminating VT or VF. Of the 94 patients receiving appropriate ICD therapy, 87 were asymptomatic or only mildly symptomatic at the time of appropriate ICD interventions. Of these 87 patients, 74 or 85% remained in classes one or two without significant change in clinical status of the subsequent 5.9 years up to 22 years. Among the 94 patients, there was one sudden death in three patients who died from non arrhythmic hypertrophic cardiomyopathy related processes. Post ICD intervention, freedom from hypertrophic cardiomyopathy, mortality was 100% at one year, 97% at five years, and 92% at 10 years, distinctly lower than the risk of ischemic or non ischemic cardiomyopathy in ICD trials.

Hypertrophic cardiomyopathy patients with ICDs interventions reported the heightened anxiety and expectation of future shocks. However, they did not affect general psychological well-being or quality of life. The authors concluded that in hypertrophic cardiomyopathy, unlike ischemic heart disease, prevention of sudden death with ICD therapies unassociated with a significant increase in cardiovascular morbidity and mortality, nor transformation into heart failure deterioration, ICD therapy does not substantially impair overall psychological and physical well-being. In our next article, Abdulla Damluji and associates examined the cost of hospitalizations for cardiac arrest using the US nationwide inpatient sample from 2003 to 2012. Using the log transformation of inflation adjusted costs the authors examined 1,387,396 patients who were hospitalized after cardiac arrest. They had a mean age of 66 years. Inpatient procedures included coronary angiography in 15%, PCI in 7%, intra-aortic balloon pump in 4.4%, therapeutic hypothermia in 1.1%, and mechanical circulatory support in 0.1% of patients.

Notably the rates of therapeutic hypothermia increased from 0 in 2003 to 2.7 in 2012, p less than 0.001. Both hospital charges inflation adjusted costs linear increased over time. In a multi-variant analysis predictors of inflation adjusted costs included large hospitals size, urban teaching hospital, and length of stay. Among co-morbidities, atrial fibrillation or fluid and electrolytes imbalance were the most common associated with cost. The authors found that during the period between 2003 and 2012 post cardiac arrest, hospitalizations had a steady rise and associated healthcare costs likely related to increase length of stay, medical procedures and systems of care.

In our next paper, Peter Huntjens and associates examined intrinsic interventricular dyssynchrony as a predictor of human dynamic response to cardiac resynchronization. The authors use a cardiovascular computational model CircAdapt to characterize the isolated effect of intrinsic interventricular or intraventricular activation on resynchronization therapy response that is the change in LV dP/dt max. The simulated change in LV dP to dt max had a range of 1.3 to 26.5% increased considerably with increasing inter ventricular dyssynchrony. In contrast, the isolated effect of intra ventricular dyssynchrony was limited with the change in the LV dP/dt max range and the left ventricle from 12.3 to 18.3% in the right ventricle from 14 to 15.7%.

Secondly, electrocardiographic imaging derived activation characteristics of 51 CRT candidates were used to create individual models of ventricular activation in CircAdapt. The model predicted change in LV dP/dt max was close to the actual value in left bundle branch block patients with 2.7% difference between measured and simulated when only intrinsic interventricular dyssynchrony was personalized. Among non left bundle branch block patients a change in LV dP/dt max was systematically over predicted by CircAdapt with a 9.2% difference between measured and simulated. Adding intra ventricular activation to the model did not improve the accuracy of response prediction. The authors found that computer revealed intrinsic interventricular dyssynchrony is the dominant component of the electrical substrate driving the response to CRT.

In the next paper Kenji Kuroki and associates examined the use of voltage limit adjustment of substrate mapping and fast Fourier transform analysis of local ventricular bipolar electrograms during sinus rhythm to predict VT isthmuses. They performed these studies and nine post infarction patients who underwent catheter ablation for total of 13 monomorphic ventricular tachycardias. Relatively higher voltage areas on electroanatomical map or defined as high voltage channels, which were further classified as full or partial if the entire or more than 30% of the high voltage channel was detectable. 12 full high voltage channels were identified in seven of nine patients. Relatively higher fast Fourier transform areas were defined as high frequency channels, which were located on seven of 12 full high voltage channels. Five VT isthmuses or 71% were included in the seven full high voltage channels positive in high frequency channel positive sites.

While no VT isthmuses were found in five full high voltage channel positive but high frequency channel negative sites, high frequency channels were identical to 9 out of 16 partial high voltage channels. Eight VT isthmuses or 89% were included in nine partial high voltage channel positive in high frequency channel positive sites, whereas no VTs isthmuses were found in the seven partial high voltage channel positive and high frequency channel negative sites.

All high voltage channel positive in high-frequency channel positive sites predicted VT isthmus with a sensitivity of 100% and specificity of 80%. The authors concluded that based on this small series that combined use of voltage, limited adjustment and fast Fourier transform analysis may be useful method to detect VT isthmuses.

In the next study, John Whitaker and associates examined the use of lesion index, LSI index, a proprietary algorithm combining contact force, radio-frequency application duration, and RF current. Cardiac CT was used to assess atrial tissue thickness. Ablation lines two to three per animal were created in the right atrium in seven mini pigs with point lesions using 25 watts of energy. Two weeks after the ablation, serial sections of targeted atrial tissue or examine histologically to identify gaps and transmural ablation. LSI guidelines had a lower incidence of histological gaps. Four gaps in the 69 catheter moved or 5.8% compared to ablation using LSI plus two millimeter lines in which there is seven gaps in 33 catheter moves or 21.2% and using LSI plus four millimeter lines in which there are 15 gaps in 23 moves or 65.2% p less than 0.0. The change in LSI was calculated retrospectively is a distance between two adjacent lesions above the mean LSI of the two lesions. Changing LSI values of 1.5 or less were associated with no gaps in transmural ablation.

The authors concluded that in this mod of chronic atrial ablation delivery of uninterrupted transmural linear lesions may be facilitated using LSI to guide catheter movement. When change in LSI between adjacent legions is 1.5 millimeters or lower, no gaps in atrial linear lesions should be expected.

In our next paper, Matthew Bennett and associate examined whether their response to antitachycardia pacing in patients with ICD could further discriminate ventricular from super ventricular arrhythmias in patients receiving ATP in the RAFT trial. The RAFT trial randomized 1,798 patients with New York Heart Association class two or three heart failure, left ventricular ejection fraction less than or equal to 30%, in QRS duration 120 millisecond or greater, to an ICD plus or a minus cardiac resynchronization. Beginning with 10,916 ATP attempts for 8,150 tachycardia episodes in 924 patients, the author's excluded tachycardias where ATP terminated the episode or were the specific etiology tachycardia was uncertain. In this study, they analyzed 3,676 ATP attempts delivered to 2,046 tachycardia episodes in 541 patients. The authors found that a shorter difference between the post pacing interval is PPI minus TCL, was more likely to be associated with VT than SVT, mean of 138.1 milliseconds for VT and 277.4 milliseconds for SVT p, less than 0.001. A PPI minus TCL value of less than or equal to 300 milliseconds had a sensitivity in 97.4% and a specificity of 28.3% for VT.

The authors concluded that specifically the PPI minus TCL following antitachycardia pacing may help distinguish ventricular from supraventricular arrhythmias.

In the next study, Shailee Shah and Amr Barakat and associates examined the outcomes after repeat AF ablation. The authors examined 137 patients out of a total of 10,378 patients undergoing Afib ablation who had had initial long-term success defined from recurrent arrhythmias for greater than 36 months off anti-arrhythmic drugs in subsequent underwent repeat ablation for recurrent atrial fibrillation. The median arrhythmia free period that define long-term success was 52 months. In redo-ablations reconnection of at least one of the pulmonary veins was found in 111 or 81% of patients. Additional non PV ablations were performed in 127 or 92.7% of patients. After a mean follow-up of 17 months, 103 patients or 75% were arrhythmia-free, 79 off anti-arrhythmics, and 24 on arrhythmics. The authors found that repeat ablations with re-isolation to the point of veins and modifying the atrial substrate had a good success rate.

In the next article Qiongling Wang and associates hypothesized that genetic inhibition of CaMKII oxidation in a mouse model of Duchenne muscular dystrophy can alleviate abnormal calcium homeostasis thus preventing ventricular arrhythmias. The authors tested whether the selective loss of oxidation of the CaMKII effects ventricular arrhythmias in the mouse model of Duchenne muscular dystrophy. Genetic inhibition of ox-CaM kinase II by knocking replacement of the regulatory domain methionines with valines, which we'll call MMVV, prevented ventricular tachycardia in the mdx mice. Confocal calcium imaging of ventricular myocytes, isolated from the mdx MMVV mice revealed normalization of intra-calcium release events compared to myocytes from the mdx mice. Abnormal action potentials as assessed by optical mapping mdx were also alleviated by genetic inhibition of ox-CaMK II. Knockout of the NADPH oxidase regulatory sub-unit P 47 Fox normalized elevated ox-CaMK II, repaired intracellular calcium hemostasis and rescued inducible ventricular arrhythmias in the mdx mice. The authors concluded that inhibition of ROS or ox-CaMK II protects against pro-arrhythmic intracellular calcium handling, preventing ventricular arrhythmias in a mouse model of Duchenne muscular dystrophy.

In the next article, Kyohei Marume and Teruo Noguchi and associates examined whether the combination of QRS duration of 120 milliseconds or greater in late gadolinium enhancement is a precise prognostic indicator for the primary endpoint of all cause death and a composite of sudden cardiac death or aborted sudden cardiac death in 531 patients with dilated cardiomyopathy. They also analyzed the association between the combination of late gadolinium enhancement and increased QRS duration in these end points among patients with a class one indication for implantable defibrillator. The author's divided study patients in three groups according to late gadolinium enhancement in QRS duration. Two negative indices that is late gadolinium enhancement negative and narrow QRS, one positive index with either late gadolinium enhancement positive or wide QRS or two positive indices late gadolinium positive and wide QRS and followed them for 3.8 years. Multiple variable Cox regression analysis identified to positive indices as significant predictors of all cause death. A hazard ratio of 4.29 p equals 0.026. Among the 317 patients with a class one indication for ICD, the five year event rate of sudden cardiac death or aborted sudden cardiac death was lowest in the two negative indices groups, 1.4%. With propensity score matching cohorts the two negative indices group had a significant lower event rate of sudden cardiac death or aborted sudden cardiac death than to two other groups hazard ratio 0.2, p equals 0.046.

The authors concluded that the combination of late gadolinium enhancement in wide QRS provides additional prognostic stratification compared to late gadolinium enhancement status alone.

In the next study, Matthew Sulkin and associates examined whether a novel local impedance measurement on an ablation catheter identifies catheter tissue coupling and is predictive of lesion formation. The author's first studied explanted hearts, 10 swine, and then in vivo 10 swine, using an investigational electro anatomical mapping system that measures impedance from an ablation catheter with mini electrodes incorporated into the distal electrode. Rhythmia and Intellanav, Boston Scientific.

Explanted tissue was placed in a warmed 37 degree celsius saline bath mounted on a scale, and the local impedance was measured 15 millimeters away from the tissue to five millimeters of catheter tissue compression at multiple catheter angles. Lesions were created for 31 and 50 watts from 5 to 45 seconds for an N of 70. During in vivo valuation of the local impedance measurements of the myocardium 90 and blood pool 30 were guided by intracardiac ultrasound while operators were blinded to the local impedance data. Lesions were created with 31 and 50 watts for 45 seconds in the ventricle with an n of 72. The local impedance of myocardium, which was 119.7 ohms, was significantly greater than in blood pool 67.6 ohms the p of less than 0.01. Models that incorporate local impedance drop to predict lesion size had better performance that models incorporate force time integral r squared of 0.75 versus r squared of 0.54 and generator impedance drop r squared of 0.2 versus r squared of 0.58. Steam pops displayed a significantly higher starting local impedance and a larger change in local impedance compared to successful RF applications, p less than 0.01.

The authors concluded that local impedance recorded for miniature electrodes provides a valuable measure of catheter tissue coupling and the change in local impedance is predictive of lesion formation during RF ablation.

In the next paper, Boaz Avitall and associates found that the rising impedance recorded from a ring electrode placed two millimeters from the cryoballoon signifies ice formation covering the balloon surface and indicates ice expansion. The authors studied 12 canines in a total of 57 pulmonary veins, which were targeted for isolation. Two cryoapplications were delivered per vein with a minimum of 90 and a maximum 180 second duration. Cryoapplications was terminated upon reaching a 500 ohm change from baseline. Animals recovered 38 plus or minus six days post procedure, and the veins were assessed electrically for isolation. Heart tissue was histological examined. Extra cardiac structures were examined for damage. Pulmonary vein isolation was achieved in 100% of veins if the impedance reached 500 ohms in 90 to 180 seconds. When the final impedance was between 200 and 500 ohms within 180 seconds of freeze time, pulmonary vein isolation was achieved in 86.8%. For impedance of less than 200 ohms pulmonary vein isolation was achieved in 14%. No extra cardiac damage was recorded. The authors found that impedance rise of 500 ohms at less than 90 seconds with a freeze time of 90 seconds resulted in 100% pulmonary vein isolation.

In our final papers Sally-Ann Clur and associates examined left ventricular isovolumetric relaxation time as the potential diagnostic marker for fetal Long QT Syndrome. Left ventricular isovolumetric contraction time, ejection time, left ventricular isovolumetric relaxation time, cycle length, and fetal heart rate were measured using pulse doppler wave forms in fetuses. Time intervals were expressed as percentage of cycle length, and the left ventricular myocardium performance index was calculated. Single measurements were stratified and compared between Long QT Syndrome fetuses and controls. Receiver operator curves were reformed for fetal heart rate in normalized left ventricular isovolumetric relaxation time. A linear mixed effect model including multiple measurements was used to analyze fetal heart rate, the left ventricular iso volume metric relaxation time, and the left ventricular myocardial performance index. There were 33 Long QT fetuses in 469 controls. In Long QT fetuses the left ventricular isovolumetric relaxation time was prolonged in all groups, p less than 0.001, as was the left ventricular isovolumetric relaxation time.

The best cutoff to diagnose Long QT syndrome was the normalized left ventricular isovolumetric relaxation time greater than equal to 11.3 at less than or equal to 20 weeks, giving a sensitivity in 92% and a specificity of 70%. Simultaneous analysis of the normalized left ventricular isovolumetric relaxation time and fetal heart rate improved the sensitivity and specificity of Long QT Syndrome, AUC of 0.96. The normalized left ventricular isovolumetric relaxation time, the left ventricular myocardial performance index, and fetal heart rate trends differed significantly between Long QT Syndrome fetuses and controls throughout gestation.

The authors concluded that left ventricular volumetric relaxation time is Prolonged QT fetuses. Findings of a prolonged normalize left ventricular isovolumetric relaxation time, and sinus bradycardia can improve the prenatal detection of fetal Long QT Syndrome.

That's it for this month, but keep listening. Suraj Kapa will be surveying all journals for the latest topics of interest in our field. Remember to download the podcasts On the Beat. Take it away Suraj.

Suraj Kapa: Thank you, Paul and welcome back to On the Beat were we will be summarizing hard-hitting articles across the entire electrophysiologic literature. Today we'll be starting within the realm of atrial fibrillation where we're review an article within the realm of anticoagulation and stroke prevention. Quon et al. published in last month's issue of JACC cardiac electrophysiology on anticoagulant use and risk of ischemic stroke and bleeding in patients with secondary atrial fibrillation. It is well known that use of anticoagulation in atrial fibrillation can reduce overall thromboembolic outcomes. However, its role in secondary atrial fibrillation is unclear. Thus, the authors sought to evaluate the effects anticoagulant use on stroke and bleeding risk. Amongst those where atrial fibrillation occurred in the setting of acute coronary syndrome, pulmonary disease, or sepsis. Amongst around 2300 patients evaluated retrospectively there was no evidence of a lower incidence of ischemic stroke among those treated with anticoagulants compared to those who are not.

However, anticoagulation was associated with a higher risk of bleeding in those with new onset AF associated with acute pulmonary disease. The authors suggest as a result that there is unclear overall benefit for long-term anticoagulation in patients with presumed secondary atrial fibrillation. The difficulty in assessing this is how to define secondary atrial fibrillation. However, in many studies patients who developed in the setting of acute illness still had a high risk of developing quote unquote clinically significant AF in long-term follow-up. However, this was not necessarily absolute as many patients not necessarily develop AF that could be considered clinically significant. Thus, the clinical question that arises is: how long should we treat a patient with anticoagulation when they have presumed secondary atrial fibrillation. These data seem to suggest that there may be no net overall benefits. In other words, all-comers with secondary atrial fibrillation should not necessarily be forever treated with anti-coagulation. However, this slightly requires clinical trials to evaluate further.

Next we delve into the realm of cardiac mapping and ablation where we view an article by Gaita et al. entitled 'Very long-term outcome following transcatheter ablation of atrial fibrillation. Are results maintained after 10 years of follow-up?', published in Europace last month. While pulmonary vein isolation is a widely accepted approach for treatment of atrial fibrillation, most reported studies review outcomes in terms of freedom of AF over a relatively short time period, generally two to five years. However longer term follow up is inconsistently reported. Gaita et al. sought to review 10 year outcomes amongst 255 patients undergoing ablation in a single center. They noted 52% remainder arrhythmia-free amongst a mixed cohort of both paroxysmal and persistent patients while 10% progressed to permanent atrial fiBrillation. They found that absence of increases in blood pressure, BMI, and fasting glucose was protective against an arrhythmia recurrence.

These findings suggest that in a relatively small cohort of patients limited to a single center that even long-term outcomes after pulmonary vein isolation are generally quite good, exceeding 50%. However, future freedom from atrial fibrillation is heavily tied to control of other risk factors. In other words, if a patient is going to have poor control of diabetes, blood pressure, or gain weight, the benefit of their pulmonary vein isolation over long-term follow-up is likely less. These data thus highlight both the potential long-term benefit of PVI, but also the importance of counseling patients regarding the need for continued management and control of future and existing risk factors.

Staying within the realm of atrial fibrillation we next review an article by Weng et al. entitled 'Genetic Predisposition, Clinical Risk Factor Burden, and Lifetime Risk of Atrial Fibrillation' published in last month's issue of circulation. The probability of detecting atrial fibrillation in patients based on clinical factors and genetic risk is unknown. Weng et al. sought to clarify whether a combination of clinical and polygenic risk scores could be used to predict risk of developing atrial fibrillation over long-term followup in the Framingham Heart Study. Amongst 4,600 individuals, 580 developed incident atrial fibrillation and had an overall lifetime risk of developing atrial fibrillation of 37%. Those are the lowest risk tertile based on clinical risk factor burden and genetic predisposition had a lifetime risk of 22% versus 48% in the highest. Furthermore, a lower clinical risk factor burden was associated with delayed atrial fibrillation onset. In order to identify patients with atrial fibrillation, before negative sequelae such as stroke occur, patient and physician understanding of risk and monitoring needs is necessary. The fact is that it will be great to identify every single patient who has atrial fibrillation before they have a negative sequela of that atrial fibrillation such as ischemic stroke.

However, performing continuous monitoring of all patients with potential negative sequelae of atrial fibrillation is extraordinarily difficult. The reason is it's excessively costly. We cannot monitor the entire population irrespective of whatever the risk factors are. However, if we're able to identify the highest risk cohorts early on before the atrial fibrillation onsets, this may offer opportunities for use of newer cheaper monitors. The work by Weng et al. suggests one such possible approach combines clinical and polygenic risk scores. Actionability of these data, however, remains to be seen and further validation other cohorts is necessary to clarify generalized ability.

The next article we review is published in last month's issue of the Journal of American College of Cardiology by Lopes at al. entitled 'Digoxin and Mortality in Patients With Atrial Fibrillation. Lopes et al. sought to evaluate the impact of the Digoxin on mortality in patients with atrial fibrillation and the association with the Digoxin serum concentration and heart failure status. They value this association in over 17,000 patients. At baseline 32% were receiving Digoxin. Baseline Digoxin use did not associate with risk of death, but even in these patients a serum concentration of greater than 1.2 nanograms per milliliter was associated with a 56% increase in mortality risk. For each .5 nanogram per milliliter increase in oxygen concentration the hazard ratio increased by 19% for overall mortality. This was irrespective of heart failure status. Furthermore, in patients who are newly started in Digoxin over the follow-up period, the risk and death and sudden death was higher. These data suggests a significant risk associated with Digoxin use for management of atrial fibrillation irrespective of heart failure status. Furthermore, serum valleys above 1.2 require close consideration of dose de-escalation. Whether there is any optimal dose, however, from the study is unclear. These data amongst a host of prior data strongly suggest again strategic use of Digoxin principally for the management of atrial fibrillation.

Moving on within the realm of atrial fibrillation, we review an article published in last month's issue of Circulation Research by Yan et al. entitled Stress Signaling JNK2 Crosstalk with CaMKII Underlies Enhanced Atrial Arrhythmogenesis. In this more acellular based study the mechanism underlying atrial arrhythmogenesis associated with aging was evaluated. Yan et al. sought to figure out whether the stress response JNK in calcium mediated arrhythmias might contribute to atrial arrhythmogenesis in aged transgenic mouse models. They demonstrated significant increased activity of JNK2 and aging atria, those furthermore associated with rhythmic remodeling. This association was mediated through CaMKII and ryanodine receptor channel function, with activation of the former leading to increased calcium leak mediated by the ladder. This in turn related to increase atrial fibrillation likelihood. Identifying novel targets for atrial fibrillation therapy is critical. Given atrial fibrillation is a complex disease process related to a multitude of risk factors it can be assumed that the contribution of any single factor may be mediated through distinct mechanisms.

Aging in particular as well regarded, but considered to be non-modifiable risk factor for atrial fibrillation. Identifying genes or pathways, the immediate aging associated fibrillation, may take the risk of aging as no longer a non-modifiable thing. The finding of the significance of JNK2 and associate downstream effects with AF risks and aging hearts may hold potential in offering unique therapeutic targets.

Finally, within the realm of atrial fibrillation, we're viewing article by Chen et al. in last month's issue of the Journal of the American Heart Association entitled Association of Atrial Fibrillation With Cognitive Decline and Dementia Over 20 Years: The ARIC-NCS Study. Multiple studies have suggested a significant association between atrial fibrillation risk of dementia. However, these studies have limited time follow-up and were often done and predominantly white patients. Thus, the authors sought to use the data from ARIC, the Atherosclerosis Risk in Communities Neurocognitive Study, to assess the risk of cognitive decline associated with atrial fibrillation. Amongst over 12,000 participants, a quarter of whom are black and half of whom are white, they noted 2100 patients developed atrial fibrillation and 1,150 develop dementia over a 20 year follow up period.

There was a significantly greater risk of cognitive decline amongst those who developed atrial fibrillation. In turn incident atrial fibrillation for the follow-up period was associated with a higher risk of dementia even after adjusting for other clinical and cardiovascular risk factors such as incidents that ischemic stroke. These data further strengthened prior evidence of a direct link between atrial fibrillation and risk of cognitive decline and dementia. Understanding this long-term risk raises the need to additionally identify approaches to prevent this occurrence, which in turn is dependent on understanding the underlying mechanisms. The finding that the risk of cognitive decline dementias independent of ischemic stroke events raises concern that either subclinical micro-embolic events or other factors may be playing a role in this risk and in turn raises question as to how best to prevent them. Until better understood, however, the question of whether the association is causal remains to be seen.

Changing gears yet again, we now delve into the realm of ICDs, pacemakers and CRT. Published in last month, issue of Heart Rhythm Tarakji et al. published a paper entitled 'Unrecognized venous injuries after cardiac implantable electronic device transvenous lead extraction.' Overall risk of transvenous lead extraction includes that of potentially fatal venous laceration. The authors sought to evaluate the incidence of venous injury that may be unrecognized based on microscopic study of extracted leads. Amongst 861 leads obtained from 461 patients they noted 80 leads or almost 9%. Amongst 15% of patients showed segments vein on the lead body, most of which were transmural including the tissue layer. However, in terms of clinical significance, only 1% had need for emergent surgical intervention for clinically significant venous laceration. Risk factors for having the entire vein on the lead included age of lead, ICD leads, and the use of the laser sheath.

These findings suggest that there may be a high incidence of subclinical venous injury after lead extraction though rarely resulting clinically apparent sequelae. As would be expected, venous injury, including transmural removal of portions of the vein traversed by the lead, was more common amongst older leads, which generally more often require laser sheets and ICD leads. The question is however, whether this carries any direct clinical implications. One they may be considered is the potential additive risk of an advancing new lead through the same venous channel, particularly in the setting of potential transmural venous injury that already exists.

Next in last month's issue of Heart Rhythm we review an article by Sharma at al. entitled 'Permanent His-bundle pacing as an alternative to biventricular pacing for cardiac resynchronization therapy: A multicenter experience.' The use of resynchronization therapy for treatment of patients with heart failure and wide QRS has been shown to offer morbidity and mortality benefits. However, many patients maybe non-responders, and recent studies on His bundle pacing of suggested potential clinical benefits. His bundle pacing essentially only requires one pacing catheter attached within the region of the His bundle Sharma et al. sought to evaluate the safety and success rates of His bundle pacing for patients who have either failed standard resynchronization therapy or in whom most tried as a primary intervention. They noted His bundle pacing was successful in 90% of patients with reasonable myocardial and His bundle capture thresholds. Patients in both groups exhibits significant narrowing of QRS morphology and improvement in left ventricular ejection fraction from a mean of 30 to 43%. However, a total of seven patients had lead related complications.

These database on a retrospective analysis of two types of patients, those failing standard biventricular therapy, and those on whom his bundle pacing was attempted as a primary modality suggest overall safety and efficacy in a handful of experienced centers. The promise of His bundle pacing is that a may allow for more effective resynchronization than standard approaches. The high rate of success suggests that His bundle pacing maybe both safe and reasonable to pursue. However randomized trials across more centers are needed to fully prove its benefit, particularly as a primary modality of treatments.

Next we review ICDs and chronic kidney disease. In last month's issue of JAMA cardiology by Bansal at al. entitled 'Long-term Outcomes Associated With Implantable Cardioverter Defibrillator in Adults With Chronic Kidney Disease.' While the benefit of ICDs in patients with low EF is widely recognized, modifying factors that may increase risk of death are not as well defined. These include things like advanced age and chronic kidney disease. Bansal et al. sought to evaluate long-term outcomes and ICD therapy in patients with chronic kidney disease. In retrospective study of almost 5,900 ambulatory patients amongst whom 1550 had an ICD, they found no difference in all cause mortality. However, ICD placement was associated with an increased risk of subsequent hospitalization due to heart failure or any cause hospitalization.

In light of recent studies such as DANISH the robust sense of ICD benefit is being questioned. One of the thoughts for the absence of similar benefit to prior studies lies in the improving care of ambulatory heart failure patients. In patients with chronic kidney disease several questions rises to the risk with ICD, including infectious risk in dialysis patients and the concomitant mortality risk with renal dysfunction. The author suggested in retrospective study, no incremental benefit of ICDs in patients with chronic kidney disease and perhaps some element of added risk is related to hospitalization. However, this study has several limitations. It is retrospective and many patients received ICDs may have been perceived to be sicker in some way. Thus care must be taken in interpretation, but consideration of randomized studies to adjudicate benefit are likely necessary.

Finally, within the realm of devices, we reviewed an article by Tayal et al. entitled "Cardiac Resynchronization Therapy in Patients With Heart Failure and Narrow QRS Complexes.' publishing the Journal of American College of Cardiology last month. Several parameters have been stressed to identify benefit of resynchronization therapy in patients with wide QRS include cross correlation analysis with tissue doppler imaging. However, many patients may have evidence in mechanical dyssynchrony even in the absence of an apparent wide QRS thus Tayal et al. sought to evaluate the benefit of resynchronization therapy amongst 807 patients with heart failure and a narrow QRS mean criteria in a randomized study. Of the 807 46% had delayed mechanical activation. Those without delay mechanical activation had underwent we standardization therapy and were associated with worse overall outcomes likely due to new delayed mechanical activation potentially related to CRT pacing. These data support the absence of a role for resynchronization therapy in patients with a narrow QRS. This is expected as resynchronization therapy likely offers the most benefit in patients with mechanical dyssynchrony that results from electrical dyssynchrony.

Since by its very nature resynchronization therapy relies on non physiologic cardiac pacing thus compared to normal cardiac activation the nature of resynchronization pacing is desynchronization. These data support the absence of a role for resynchronization therapy in patients with heart failure and narrow QRS complexes.

Moving on to cellular electrophysiology we review an article by Kozasa et al. published in last month's issue of Journal of Physiology entitled 'HCN4 pacemaker channels attenuate the parasympathetic response and stabilize the spontaneous firing of the sinoatrial node.' Heart rate is controlled by an interplay between sympathetic and parasympathetic components. In turn HCN4 abnormalities have been implicated in congenital sick sinus syndrome. The authors sought to clarify the contribution of HCN4 to sinus node autonomic regulation. They created a novel gain-of-function mouse where the HCN4 activity could be modulating from zero to three times normal. They then evaluated ambulatory heart-rate variability and responsive heart rate to vagus nerve stimulation. They found HCN4 over-expression did not increase heart rate, but attenuated heart-rate variability. It also attenuated bradycardic response to vagus nerve stimulation. Knockdown of HCN4 in turn lead to sinus arrhythmia and enhanced parasympathetic response. These data suggest HCN4 attenuates sinus node response to vagal stimuli thus stabilizing spontaneous firing of the node. The clinical application of this remain to be seen but are maybe important in that they highlight a mechanism for a heretofore poorly understood mechanism for how exactly HCN4 abnormalities may lead to sick sinus syndrome.

Within the realm of ventricular arrhythmias we highlighted a number of articles published this past month. The first article we review was published in last month's issue of JACC clinical electrophysiology, entitled characterization of the electrode atomic substrate and cardiac sarcoidosis: correlation with imaging findings of scarring inflammation published by [inaudible 00:41:40] et al. In patients with cardiac sarcoidosis one of the questions is how to define the electronic atomic substrate, particularly before we entered the electrophysiology laboratory. Both active inflammation and replacement fibrosis maybe be seen in patients. The authors evaluated in 42 patients with cardiac sarcoidosis, the association between an abnormal electrograms and cardiac imaging findings including PET and Computed Tomography, as well as Cardiac MRI. They noted that amongst these 40 patients, a total of 21,000 electrograms were obtained, and a total of 19% of these were classified as abnormal. Most of the abnormalities occurred in the basal paravalvular segments and intraventricular septum. They further noted that many of these abnormalities in terms of electrograms were located outside the low voltage areas, particularly as it relates to fractionation. In about 90% of patients they notice late gadolinium enhancements and they noted abnormal FDG uptakes suggesting active inflammation in about 48%.

However, it should be noted that only 29 of the 42 patients underwent cardiac imaging. Segments with abnormal electrograms tended to have more late gadolinium enhancement evidence scar transmurality, and also they noted that the association of abnormal PET scan did not necessarily occur with abnormal electrograms. Thus, they concluded that in patients with cardiac sarcoidosis and ventricular tachycardia pre-procedural imaging with cardiac MRI could be useful in detecting electroanatomic map abnormalities that may in turn be potential targets for substrate ablation. However, they were more likely associated with more scar transmurality and lower degrees of inflammation on PET scanning. These data are important in that they highlight potential non-invasive means by which to understand where substrate might occur in patients with the cardiac sarcoidosis. It is well recognized that cardiac sarcoidosis is associated with increased risk of ventricular arrhythmias. These risks have increased ventricular arrhythmias, might be targetable with ablation. Newer therapies might even offer non invasive means by which to perform ablation in patients best. Thus if we could identify non based on mechanisms of identifying the substrate, this will be even more critical.

The critical findings of this particular paper lie in noting that most of the abnormalities still is in intra ventricular sePtum in basal segments, and also that it is MRI in late gadolinium enhancement and associates more with the abnormal electrograms. Interestingly, the absence of inflammation correlating with the presence of more abnormal electrograms suggests that it is not so much the act of inflammation as being reflected in the endocardial map, but the existence of scar.

Next, again within JACC clinical electrophysiology we review an article by Porta-Sánchez et al. entitled 'Multicenter Study of Ischemic Ventricular Tachycardia Ablation With Decrement Evoked Potential Mapping With Extra Stimulus.' The authors sought to conduct a multicenter study of decrement evoked potential base functional tech ventricular tachycardia substrate modification to see if such mechanistic and physiologic strategies could result in reduction in VT burden. It is noted that really only a fraction of the myocardium in what we presume to be substrate based on the presence of low voltage areas are actually involved in the initiation and perpetuation of VT. Thus if we can identify the critical areas within the presumed substrate for ablation, this would be even a better way of potentially honing in on our targets. They included 20 consecutive patients with ischemic cardiomyopathy. During substrate mapping fractionated late potentials were targeted and an extra stimulus was provided to determine which display decrements. All patients underwent DEEP focus ablation with elimination being correlated with VT non-inducibility after radio-frequency ablation. Patients were predominantly male, and they noted that the specificity of these decrement evoked potentials to detect the cardiac isthmus for VT was better than that of using late potentials alone. They noted 15 of 20 patients were free of any VT after ablation of these targets over six months of follow-up, and there was a strong reduction in VT burden compared to six months pre ablation.

They concluded that detriment evoked potential based strategies towards ablation for ventricular tachycardia might identify the functional substrate and those areas most critical to ablation. They in turn regarded that by its physiologic nature it offers greater access to folks to ablation therapies.

This publication is important in that it highlights another means by which we can better hone in on the most critical regions for substrate evaluation in patients with ventricular tachycardia. The fact is more extensive ablation is not necessarily better and might result in increased risk of harm if we think about the potential effects of longer ablations or more ablation lesions. Thus if we could identify ways of only targeting those areas that are most critical to the VT circuits, we could perhaps short and ablation procedural time, allow for novel ways of approaching targeted ablation with limited amounts of ablation performed, or perhaps even improve overall VT outcomes by knowing the areas that are most critical to ensure adequate ablation therapy provided. However, we need to understand that this is still a limited number of patients evaluated in a non randomized manner. Thus whether or not more extensive ablation performed might have been better is as of yet unclear

Staying within the realm of ventricular tachycardia we review an article published in last month's issue of Heart Rhythm by Winterfield et al. entitled the 'Impact of ventricular tachycardia ablation on healthcare utilization.' Catheter ablation of atrial tachycardia has been well accepted to reduce recurrent shocks in patients with ICDs. However, this is a potentially costly procedure, and thus effect on overall long-term health care utilization remains to be seen. The authors sought to evaluate in a large scale real world retrospective study the effect of VT ablation on overall medical expenditures in healthcare utilization. A total 523 patients met study inclusion criteria from the market scan database. After VT ablation median annual cardiac rhythm related medical expenditures actually decreased by over $5,000. Moreover the percentage of patients with at least one cardiac rhythm related hospitalization an ER visit decreased from 53 and 41% before ablation respectively, to 28 and 26% after ablation. Similar changes we're seeing in number of all cause hospitalizations and ER visits. During the year before VT ablation interestingly there was an increasing rate of healthcare resource utilization, but a drastic slowing after ablation.

These data suggests that catheter ablation may lead to reduced hospitalization in overall healthcare utilization. The importance of these findings lies in understanding why we do the things we do. We can provide a number of therapies to patients, but we seek two different effects. One is the individual effect of improving their particular health. The second thing is trying to avoid increasing healthcare expenditures on a population level and making sure resources are utilized. If we can reduce recurrent hospitalizations and overall healthcare expenditure in patients by providing a therapy in addition to provide individual benefit, this is the optimal situation. These data suggests that VT ablation might provide such a benefits, that in fact it reduces overall healthcare utilization while improving overall outcomes.

Next and finally within the realm of ventricular arrhythmias, we review more on the basic side the role of Titin cardiomyopathy leads to altered mitochondrial energetics, increased fibrosis and long-term life-threatening arrhythmias, published by Verdonschot et al. in last month's issue of European Heart Journal. It is known now that truncating Titin variants might be the most prevalent genetic cause of dilated cardiomyopathy. Thus, the authors sought to study clinical parameters and long term outcomes related to Titin abnormalities in dilated cardiomyopathy. They reviewed 303 consecutive and extensively phenotype dilated cardiomyopathy patients who underwent cardiac imaging, Holter monitoring, and endomyocardial biopsy and in turn also underwent DNA sequencing of 47 cardiomyopathy associated genes. 13% of these patients had Titin abnormalities. Over long-term followup they noted that these patients had increased ventricular arrhythmias compared to other types of dilated cardiomyopathy, but interestingly, they had similar survival rates. Arrhythmias in those Titin abnormal patients were most prominent in those who were subjected to an additional environmental trigger, including viral infection, cardiac inflammation, other systemic disease or toxic exposure. They also noted the cardiac mass was relatively reduced in titan admirable patients.

They felt that all components of the mitochondrial electron transport chain we're simply up-regulated in Titin abnormal patients during RNA sequencing and interstitial fibrosis was also augmented. As a result, they concluded that Titin variant associated dilated cardiomyopathy was associated with an increased risk of ventricular arrhythmias, and also with more interstitial fibrosis. For a long time we have reviewed all non ischemic cardiomyopathy as essentially equal. However, more recent data has suggested that we can actually hone in on the cause. In turn, if we hone in on the cause, we might be able to understand the effects of specific therapies for ventricular arrhythmias based on that underlying cause. Patchy fibrosis might not be as amenable, for example, to ablation as discreet substrate that we might see in infarct related VT. Understanding the relative benefit in very specific types of myopathies might hold benefit in understanding how to, one, risk stratify these patients, and two, understand what type of therapy, whether pharmacologic or ablative, might result in greatest benefit to the patients.

Changing gears entirely now to the role of genetics, we review multiple articles in various genetic syndromes published this past month. First, we reviewed an article by Providência et al. published in the last month's issue of heart entitled 'Impact of QTc formulae in the prevalence of short corrected QT interval and impact on probability and diagnosis of short QT syndrome.' The authors sought to assess the overall prevalence of short corrected QT intervals and the impact on diagnosis of short QT syndrome using different methods for correcting the QT interval. In this observational study they reviewed the sudden cardiac death screening of risk factors cohorts. They then applied multiple different correction formulae to the ECGs. They noted that the prevalence of individuals with the QTc less than 330 and 320 was extremely low, namely less than .07 and .02% respectively. They were also more frequently identified using the Framingham correction. The different QTc correction formulae could lead to a shift of anywhere from 5 to 10% of individuals in the cohort overall.

They further noted, that based on consensus criteria, instead of 12 individuals diagnosed with short gut syndrome using the Bazett equation, a different number of individuals would have met diagnostic criteria with other formulae, 11 using Fridericia, 9 with Hodges, and 16 using the Framingham equation. Thus, they noted that overall the prevalence of short QT syndrome exceedingly low and an apparently healthy adult population. However, reclassification as meeting criteria might be heavily dependent on which QT correction formula is used. The importance of these findings is that not all QTs are created equal.

Depending on how you compute the QT interval in which formula to use may affect how you actually risk characterize a patient. Unfortunately, these data do not necessarily tell us which is the right formula, but this highlights that it might be relevant to in the future evaluate the role of different formulae and identifying which is the most necessary to classify a patient.

Moving on to an article published in last month's issue of the journal of clinical investigation by Chai et al. we review an article entitled 'Physiological genomics identifies genetic modifiers of Long QT Syndrome type 2 severity.' Congenital Long QT Syndrome is a very well recognized, inherited channelopathy associated life-threatening arrhythmias. LQTS type 2 is specifically caused by mutations in casein to encoding the potassium channel hERG. However, even with the mutation not all patients exhibit the same phenotype. Namely some patients are more at risk of life threatening arrhythmias in spite of having the same mutation as others who do not exhibit the same severity phenotype. The authors sought to evaluate whether specific modifiable factors within the remaining genetic code might be modifying the existing mutation. Thus, they sought to identify contributors to variable expressivity in an LQT 2 family by using induced pluripotent stem cell derived cardiomyocytes and whole exome sequencing in a synergistic manner.

They found that patients with severely effected LQT 2 displayed prolonged action potentials compare to sales from mildly effected first-degree relatives. Furthermore, stem cells derived from patients were different in terms of how much L-type calcium current they exhibited. They noted that whole exome sequencing identified variants of KCNK17 and the GTP-binding protein REM2 in those patients with more severe phenotypes in whom greater L-type calcium current was seen. This suggests that abnormalities or even polymorphisms in other genes might be modifying the risk attributed to by mutations in the primary gene. This showcases the power of combining complimentary physiological and genomic analysis to identify genetic modifiers and potential therapeutic targets of a monogenic disorder. This is extraordinarily critical as we understand on one level that when we sequence a monogenic disorder that there might exist variants of uncertain significance, namely they have not been classified as disease causing, but could be. In turn, we also recognize that mutations in a family might effect different relatives differently. However, why this is has been relatively unclear.

If we can understand and identify those patients who are most at risk of dangerous abnormal rhythms, this will be useful in how much to follow them, and what type of therapy to use in them. The fact that other genes might modify the risk even in the absence of specific mutations, suggests that novel approaches to characterizing the risk might help for the risk modified patients classification in general. Clinical use, however, remains to be seen.

Moving on from long QT, we evaluate 'The Diagnostic Yield of Brugada Syndrome After Sudden Death With Normal Autopsy' noted in last month's issue of the Journal of American College of Cardiology and published by Papadakis et al. It is well known, the negative autopsies are not uncommon in patients, however, families might be wondering how at risk they are. Thus, the authors sought to assess the impact of systematic ajmaline provocation testing using high right precordial leads on the diagnostic yield Brugada syndrome in a large cohort of Sudden Arrhythmic Death syndrome families. Amongst 303 families affected by Sudden Arrhythmic Death Syndrome evaluation was done to determine whether or not there was a genetic inherited channelopathy cause. An inherited cardiac disease was diagnosed in 42% of the families and 22% of relatives Brugada syndrome was the most prevalent diagnosis overall amongst 28% of families. Ajmaline testing was required, however, to unmask the Brugada Syndrome in 97% of diagnosed individuals. Furthermore, they use of high right precordial leads showed a 16% incremental diagnostic yield of ajmaline testing for diagnosing Brugada syndrome.

They further noted that a spontaneous type 1 regard or pattern or a clinically significant rhythmic event developed in 17% of these concealed regardless syndrome patients. The authors concluded the systematic use of ajmaline testing with high right precordial leads increases the yield of Brugada Syndrome testing in Sudden Arrhythmic Death Syndrome families. Furthermore, they noted that assessments should be performed in expert centers or patients could also be counseled appropriately. These findings are important and one of the big questions always becomes how aggressively to test family members of patients or of deceased individuals who experienced sudden arrhythmic death. Many of these patients have negative autopsies, and genetic autopsy might not be possible due to lack of tissue or blood products that can be adequately tested.

The data here suggest that amongst a group of 303 sudden arrhythmic death, families that Brugada Syndrome is by far the most frequent diagnosis. If an inherited cardiac disease was identified. In turn, it is not ECG alone or echo alone that helps identify them, but requires drug provocation testing in addition to different electrode placements. Whether or not this will consistently offer benefit in patients in general or my result in overcalling remains to be seen next within the realm of genetic predisposition.

We view an area where we don't know if there's a genetic predisposition in article published by Tester et al. entitled Cardiac Genetic Predisposition in Sudden Infant Death Syndrome in last month's issue of the journal of american college of cardiology. Sudden Infant Death Syndrome is the leading cause of post-neonatal mortality and genetic heart diseases might underlie some cases of SIDS. Thus the authors sought to determine the spectrum and prevalence of genetic heart disease associated mutations as a potential monogenic basis for Sudden Infant Death Syndrome. They study the largest cohort to date of unrelated SIDS cases, including a total of 419 individuals who underwent whole exome sequencing and targeted analysis for 90 genetic heart disease susceptibility genes. Overall, 12.6% of these cases had at least one potentially informative genetic heart disease associated variants. The yield was higher in those mixed European ancestry than those of European ancestry.

Infants older than four months were more likely to host a potentially informative gene. Furthermore, they noted that only 18 of the 419 SIDS cases hold a [inaudible 01:01:26] or likely pathogenic variant. So in other words, only 4% of cases really had a variant that they could say was distinctly pathogenic or likely pathogenic. Thus, overall, the minority of SIDS cases have potentially informative variant in genetic heart disease susceptibility gene, and these individuals were mostly in the 4 to 12 month age group. Also, only 4% of cases had immediately clinically actionable variance, namely a variant, which is well recognized as pathogenic and where we could actually say that a specific therapy might have had some effect. These findings can have major implications for how best to investigate SIDS cases in families. It might suggest that SIDS cases where the individual was older, nearly 4 to 12 months of age might have a greater yield in terms of identifying variance.

While this might not affect the deceased in fit, it might affect, families are planning on having another child in whom a variant can be identified.

Finally, within the realm of genetics, we review an article published in last month's issue of Science Advances by Huang. et al. entitled 'Mechanisms of KCNQ1 Channel Dysfunction in Long QT Syndrome Involving Voltage Sensor Domain Mutations'. Mutations that induce loss of function of human KCNQ1 underlie the Long QT Syndrome type 1. While hundreds of mutations have been identified the molecular mechanism by which they result in impaired function are not as well understood. The authors sought to investigate impact of 51 specific variants located within the voltage sensor domain and emphasized effect on cell surface expression, protein folding, and structure. For each variant efficiency of trafficking of the plasma membrane, impact of proteasome inhibition, and protein stability were evaluated. They noted that more than half of the loss of function mutations were seen to destabilized structure of the voltage sensor domain, generally accompanied by mistrafficking and degradation by the proteasome.

They also noted that five of the folding defective Long QT Syndrome mutant sites were located in the S0 helix, where they tend to interact with a number of other loss of function mutation sites in other segments of the voltage sensor domain. They suggested these observations reveal a critical role for the S0 helix as a central scaffold to help organize and stabilized KCNQ1 overall. They also note the importance of these findings is that mutation-induced destabilization of membrane proteins may be a more common cause of disease functioning in humans. The importance of these findings lies in better understanding why specific mutations lead to apparent phenotypes. If we can unDerstand this, we might be able to characterize better variants as they appear where pathologic effects are not as well demonstrated in in vitro assays. Thus variance of uncertain significance might be more easily reclassified if we understand why they occur, where they occur, and how they modulate disease.

Changing gears to our final article of this edition of On the Beat we delve into the realm of syncope and an article published in last month's issue of Circulation Research by van den Berg. et al. entitled 'Mutations in CYB561 Causing a Novel Orthostatic Hypotension Syndrome.' Orthostatic hypotension is a very common clinical problem, but a very difficult one because we don't totally understand the underlying mechanisms. The authors described to families with four patients in total who experienced severe orthostatic hypotension. They noted that concentrations of norepinephrine and epinephrine and these particular patients relatively low. They did molecular genetic analysis to determine if they could identify an underlying genetic cause. They noted that in these two families, abnormalities in genes encoding cytochrome CYB561 were present. They in turn sought to understand what the mechanism of these specific mutations were. They noted that defects in the protein led to a shorted ascorbate inside the catecholamine secretory vesicles linked to a functional dopamine beta hydroxylase deficiency. Concentration and catecholamines and downstream metabolites in turn was measured in brain and adrenal tissue in knockout mice for the same gene. The concentration of norepinephrine and normetanephrine was known to be decreased in whole brain homogenates compared with wild type mice.

They intern treated these patients with L-dihydroxyphenylserine, which can be converted directly to norepinephrine to see if this effected the phenotype and noted that these patients responded favorably. This study is the first one to implicate the cytochrome b561 in orthostatic hypotension diseases. They also suggested the mechanism by which this might occur, namely through some degree of neurotransmitter metabolism. They also suggested treatment in the specific subtype with L-dihydroxyphenylserine. These findings are important in they highlight not all orthostatic hypotension is created equal. Namely, some patients with orthostatic hypertension might have a discrete phenotype. If we can understand the phenotype and understand how best to treat it, we might be able to actually offer targeted personalizable therapies. I appreciate everyone's attention to these key and hard-hitting articles that we have just focused on from this past month of cardiac electrophysiology across literature. Thanks for listening. Now back to Paul.

Thanks, Suraj. You did a terrific job surveying all journals for the latest articles on topics of interest to our field. There's not an easier way to stay in touch with the latest advances. These summaries and a list of all major articles in our field each month can be downloaded from Circulation Arrhythmia and Electrophysiology website. We hope that you'll find the journal to be the go to place for everyone interested in the field. See you next month.

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