Circulation: Arrhythmia and Electrophysiology january 2019 Issue

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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 from this month's issue.

Koji Miyamoto and associates conducted the AD-Balloon Study, which investigates the ideal number of free cycles during second-generation cryoballoon pulmonary vein isolation. In a prospective, multicenter, randomized clinical trial, the authors compared in 110 patients the addition of a three minute freeze after pulmonary vein isolation had been achieved to pulmonary vein isolation alone. Delayed-enhancement magnetic resonance imaging was also performed one to two months after the pulmonary vein isolation to assess the ablation lesions. The freedom from atrial arrhythmias at one year was similar. Log rank test, P equals 0.78 in the two groups, 87.3% in the extra three-minute freeze group, and 89.1% in the pulmonary vein isolation group. There was no significant difference in the frequency of gaps on the pulmonary vein isolation lines in the delayed-enhancement magnetic resonance imaging. The authors conclude that an insurance freeze after achieving pulmonary vein isolation may be unnecessary and time consuming.

In our next study, Robert Sheldon and associates examined the genetic basis of vasovagal syncope. They studied 160 subjects in 9 kindreds comprising 82 fainters and 78 controls. Common genetic variants were genotype for 12 genes for vascular signaling, potassium channels, the serotonin 5-HT1A receptor, the serotonin transporter and catecholamine-O-methyltransferase or COMT. They found that in 9 of 12 variants, there was no significant association between genotype and phenotype. However, the serotonin 5-HT1A receptor, HTR1-A G alleles were associated with syncope in males but not in females. P equals 0.005. The men with serotonin 5-HT1 receptor C alleles had a 9% likelihood of syncope while Gg males had a 77% likelihood of syncope. The SL6A4 promoter L alleles were associated with decreased syncope in males but increase in females. P equals 0.059. The Ll males had a 25% syncope likelihood and Ss males had a 47% syncope likelihood. The COMT A alleles were associated with decreased syncope in males but increased in females. P equals 0.017. The Gg males had a 50% syncope likelihood and A males had a 15% syncope likelihood. The Gg females had 52% syncope likelihood and the Aa females had a 73% syncope likelihood. The authors concluded that there is a sex-dependent effect of alleles of serotonin signaling in vasovagal syncope, supporting the serotonin hypothesis of the physiology of vasovagal syncope.

In the next study, Michael Barkagan and associates sought to examine whether the standard criteria for mitral line block with endocardial and epicardial activation mapping may not distinguish from slow conduction or conduction via epicardial bridging connections. In 56 patients, the authors creates a posterior mitral line using radiofrequency ablation. Mitral block determined by pacing with conduction block defined as trans-isthmus time of 100 milliseconds or greater in reversal of coronary sinus activation during pacing from the left atrial appendage was achieved in 51 out of 56 or 91% of patients. In 11 of 51 or 22% of patients, high-resolution activation mapping, using Rhythmia, of the endocardium and epicardium via the coronary sinus demonstrated residual endocardial in 27% or residual epicardial in 73% connections. Epicardial bridging connections were distant from the line, 2.4 plus or minus 1.6 centimeters, inserting laterally at the proximal-mid coronary sinus and septally at the left atrial ridge. Patients with residual conduction were prone to complex circuits involving the epicardium in 7 of 11 patients. Mitral line block was achieved in 75% by targeting these insertion sites. The trans-isthmus time had limited predictive value for distinguishing block from pseudoblock. The authors concluded the connections are a frequent cause of complex circuits, and their insertion sites can be targeted for ablation.

In our next paper, Santiago Rivera and associates examined the causes of QRS variability in Papillary muscle arrhythmias usually attributed to anisotropy. In 33 patients with papillary muscle arrhythmias prospectively undergoing cardiac resonance imaging, papillary muscle connections away from the papillary muscle base were identified. Arrhythmogenic papillary muscles, N equals 35, exhibited a higher number of papillary muscle connections, 72 versus 18, P equals 0.01. Patients with inconsistent QRS precordial transition and inconsistent QRS access exhibited a 100% prevalence of papillary muscle connections. Those with consistent precordial transition and consistent QRS access showed 40% and 26% prevalence of papillary muscle connections respectively. Inconsistent QRS precordial transition and inconsistent QRS access predicted the presence of papillary muscle connections with 59% or 28% sensitivity and 100% specificity respectively. Those papillary muscles exhibiting clinical recurrence after ablation presented a higher prevalence of papillary muscle connections, 91% versus 60%, P=0.04.

In our next paper, Jason Coult and associates examined the quantitative measures of the electrocardiogram waveform during ventricular fibrillation to assess myocardial physiology and predict cardiac arrest outcomes. They collected five second ventricular fibrillation ECG segments with and without chest compressions prior to 2,755 defibrillation shocks from 1,151 out of hospital cardiac arrest patients. 24 individual measures and 3 combination measures were optimized to predict functionally intact survival using 460 training cases. Measures predicted functionally intact survival in 691 independent test cases with an area under the receiver operating curve (AUC) ranging from 0.56 to 0.75 without chest compressions and 0.53 to 0.75 with compressions, P less than 0.001. Of all measures evaluated, the support vector machine model ranked highest both without chest compressions, AUC equals 0.75, and with compressions, AUC equals 0.75. The authors concluded the waveform measures predict functionally intact survival when calculated during chest compressions, but prognostic performance is generally reduced compared to analysis without compressions. Support vector machine models exhibited similar performance with and without compressions while also achieving the highest area under the curve.

In our last paper, Hailey Jansen, Martin Mackasey and associates examined the effective natriuretic peptides in the specific natriuretic peptide receptor NPR-C on angiotensin II-mediated atrial fibrillation. The authors examined wild-type and NPR-C knockout mice to investigate the effects of angiotensin II administered three milligrams per kilo per day for three weeks on atrial fibrillation susceptibility and atrial function. In wild-type mice, angiotensin II increased susceptibility to atrial fibrillation and associated with a prolonged P wave duration, increased atrial refractory period, and slowed atrial conduction. These effects were exacerbated in angiotensin II-treated NPR-C knockout mice. Angiotensin II prolonged action potential duration and reduced action potential upstroke velocity. Angiotensin II also increased fibrosis in the atria in wild-type mice while angiotensin II-treated NPR-C knockout mice exhibited substantially higher atrial fibrosis. Co-treating wild-type mice with angiotensin II and the NPR-C agonist cANF, those dependently reduced atrial fibrillation inducibility by preventing some of the angiotensin II-induced changes in atrial myocyte electrophysiology and preventing atrial fibrosis. The authors suggested that the NPR-C receptor may represent a new target for the prevention of angiotensin II-induced atrial fibrillation via protective effects on atrial, electrical and structural remodeling.

That's it for this month! We hope that you'll find the journal to be the go-to place for everyone interested in the field. See you next time! This program is copyright American Heart Association 2019.

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