CHD Electrophysiology Featured Articles of March 2016

1. Electrocardiographic repolarization abnormalities and increased risk of life-threatening arrhythmias in children with dilated cardiomyopathy.

Chen S, Motonaga KS, Hollander SA, Almond CS, Rosenthal DN, Kaufman BD, May LJ, Avasarala K, Dao DT, Dubin AM, Ceresnak SR.

Heart Rhythm. 2016 Mar 2. pii: S1547-5271(16)00184-3. doi: 10.1016/j.hrthm.2016.02.014. [Epub ahead of print]

PMID: 26945851

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Select item 26970963

Take Home Points:

  • Repolarization abnormalities, specifically JTc prolongation and ST segment shifts may be associated with increased risk for LTEs in pediatric cardiomyopathy patients.
  • These findings should be repeated in a larger pediatric population, as the present findings could not be adjusted for other covariates due to the small number of outcomes.
  • Risk stratification for sudden cardiac death in pediatric dilated cardiomyopathy patients remains ill-defined.

J MooreCommentary from Dr. Jeremy Moore (Los Angeles, CA), section editor of Congenital Heart Electrophysiology Journal Watch:  This is a single-center retrospective review of 178 pediatric patients with dilated cardiomyopathy (defined in this study as LVEF <55% and LVEDD z score ≥2) from Stanford University. Given the known risk of electrocardiographic depolarization abnormalities in this population, the authors were interested in examining the independent contribution related to repolarization abnormalities. In order to exclude influence from co-existing QRS prolongation, the corrected JT interval (JTc) was manually calculated (predominantly from lead II) by 3 cardiologists at the study site.

From this cohort of dilated cardiomyopathy patients, the upper 90th percentile for the corrected QT interval (QTc) was 510 ms and for the JTc was 390 ms. A total of 15 life-threatening events (LTE – defined as an episode of ventricular fibrillation or ventricular tachycardia that resulted in syncope or hypotension) occurred during a median follow-up duration of 12 months. The JTc was significantly longer in patients with LTEs versus unaffected dilated cardiomyopathy patients (371 ± 77 ms vs 342 ± 44 ms, p=0.01). Other variables associated with LTE in a Cox proportional hazards model included QRS duration >120 ms, JTc >390 ms, QTc >510 ms, JT dispersion ≥100 ms, QT dispersion >100 ms, T wave inversion, and ST segment depression. No adjustment for multiple comparisons was performed, and multivariable regression was limited to 2 covariates in this small sample population with few clinical outcomes.

 

 

2. Mechanism and outcomes of catheter ablation for ventricular tachycardia in adults with repaired congenital heart disease.

van Zyl M, Kapa S, Padmanabhan D, Chen FC, Mulpuru SK, Packer DL, Munger TM, Asirvatham SJ, McLeod CJ.

Heart Rhythm. 2016 Mar 4. pii: S1547-5271(16)30003-0. doi: 10.1016/j.hrthm.2016.03.002. [Epub ahead of print]

PMID: 26961296

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Select item 26944361

Take Home Points:

  • Catheter ablation of isthmus-dependent VT with subsequent verification of conduction block across the targeted isthmus appears to be highly effective for prevention of recurrent VT in patients with CHD.
  • As many as one-third of patients may have focal VT rather than an isthmus-dependent substrate.
  • A more exhaustive approach to determine the VT mechanism (rather than a substrate-based approach) may be useful to improve procedural outcomes.

Commentary from Dr. Jeremy Moore (Los Angeles, CA), section editor of Congenital Heart Electrophysiology Journal Watch:  This was a retrospective study of 21 patients with repaired congenital heart disease undergoing catheter ablation for clinically-documented ventricular tachycardia (VT) at the Mayo Clinic over a 10-year period spanning 2004 and 2015. The electrophysiologic approach was based on a combination of substrate mapping and entrainment at the site of the suspected critical isthmus, in order to determine the optimal site for catheter ablation. Whenever possible, conduction block was confirmed after lesion placement.

Congenital diagnoses included tetralogy of Fallot in 10, transposition of the great arteries after atrial switch operation in 4, isolated ventricular septal defect in 2, Ebstein anomaly in 2, and 1 each with pulmonary atresia, truncus arteriosus, and congenital aortic valve stenosis. Seven patients (33%) were found to have a focal VT, and 14 (67%) were found to have a conduction isthmus believed to be responsible for the clinical VT. Conduction block was achieved in 8/14 isthmuses (57%). Complete procedural success was achieved in 17 patients (81%). Over a mean follow up of 33 ± 7 months, 18/21 patients were free from VT recurrence. No patient with confirmed conduction block at the targeted isthmus experienced a recurrence.

 

3. Gene-Specific Therapy With Mexiletine Reduces Arrhythmic Events in Patients With Long QT Syndrome Type 3.

Mazzanti A, Maragna R, Faragli A, Monteforte N, Bloise R, Memmi M, Novelli V, Baiardi P, Bagnardi V, Etheridge SP, Napolitano C, Priori SG.

J Am Coll Cardiol. 2016 Mar 8;67(9):1053-8. doi: 10.1016/j.jacc.2015.12.033.

PMID: 26940925 Free PMC Article

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Select item 26950378

Take Home Points:

  • Mexilitine may be an effective therapeutic agent for reduction of cardiac events in LQT3.
  • The clinical efficacy of Mexilitine response may be best gauged by a resultant QTc< 500 ms after initiation of therapy.
  • Further prospective evaluation is warranted.

Commentary from Dr. Jeremy Moore (Los Angeles, CA), section editor of Congenital Heart Electrophysiology Journal Watch:  This is a retrospective study from Italy evaluating the clinical efficacy of Mexilitine in the treatment of long QT syndrome (LQTS) type 3. Although LQTS type 3 is the least prevalent of the major forms of LQTS, clinical events in these patients tend to be the most malignant.

The authors report a total of 34 patients (38% symptomatic and 7/34 with ≥1 cardiac arrest) that were given Mexilitine at an average dose of 8 mg/kg/day. The QTc shortened by a mean of 63 ± 6 ms; and for patients with a QTc >500 ms at baseline, 73% decreased to below this threshold after initiation of therapy. Three infants continued to have significantly prolonged QTc values after initiation of Mexilitine (see figure below) and continued to have clinical cardiac events.

QTc response to Mexilitine therapy. *Patients with ongoing clinical events.

Risk exposure assessment based on the comparison of periods of equal duration (median 35 months) before and after Mexilitine administration was performed in order for the patients to serve as their own controls. There was a significant reduction in the percentage of patients with arrhythmic events (22% to 3%) and mean number of events per patient (0.43 to 0.03) using this methodology.

The authors concluded that not only does Mexilitine shorten the QTc as shown previously, but also results in a clinically meaningful reduction in cardiac events. The only “nonresponders” were those with QTc values that were persistently >500 ms on therapy.

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