Implantable defibrillators versus medical therapy for cardiac channelopathies

Sudden cardiac death is a significant cause of mortality in both the US and globally. However, 5% to 15% of people with sudden cardiac death have no structural abnormalities, and most of these events are attributed to underlying cardiac ion channelopathies. Rates of cardiac ion channelopathy diagnosis are increasing. However, the optimal treatment for such people is poorly understood and current guidelines rely primarily on expert opinion.

To compare the effect of implantable cardioverter defibrillators (ICD) with antiarrhythmic drugs or usual care in reducing the risk of all-cause mortality, fatal and non-fatal cardiovascular events, and adverse events in people with cardiac ion channelopathies.

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, 2015, Issue 6), EMBASE, MEDLINE, Conference Proceedings Citation Index - Science (CPCI-S), ClinicalTrials.gov, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) in July 2015. We applied no language restrictions.

We included all randomized controlled trials of people aged 18 years and older with ion channelopathies, including congenital long QT syndrome, congenital short QT syndrome, Brugada syndrome, or catecholaminergic polymorphic ventricular tachycardia. Participants must have been randomized to ICD implantation and compared to antiarrhythmic drug therapy or usual care.

Two authors independently selected studies for inclusion and extracted the data. We included all-cause mortality, fatal and non-fatal cardiovascular events, and adverse events for our primary outcome analyses and non-fatal cardiovascular events, rates of inappropriate ICD firing, quality of life, and cost for our secondary outcome analyses. We calculated risk ratios (RR) and associated 95% confidence intervals (CIs) for dichotomous outcomes, both for independent and pooled study analyses.

From the 468 references identified after removing duplicates, we found two trials comprising 86 participants that met our inclusion criteria. Both trials included participants with Brugada syndrome who were randomized to ICD versus β-blocker therapy for secondary prevention for sudden cardiac death. Both studies were small, were performed by the same investigators, and exhibited a high risk of bias across multiple domains. In the group randomized to ICD therapy, there was a nine-fold lower risk of mortality compared with people randomized to medical therapy (0% with ICD versus 18% with medical therapy; RR 0.11, 95% CI 0.01 to 0.83; 2 trials, 86 participants). There was low quality evidence of a difference in the rates of combined fatal and non-fatal cardiovascular events, and the results were imprecise (26% with ICD versus 18% with medical therapy; RR 1.49, 95% CI 0.66 to 3.34; 2 trials, 86 participants). The rates of adverse events were higher in the ICD group, but these results were imprecise (28% with ICD versus 10% with medical therapy; RR 2.44, 95% CI 0.92 to 6.44; 2 trials, 86 participants). For secondary outcomes, the risk of non-fatal cardiovascular events was higher in the ICD group, but these results were imprecise and were driven entirely by appropriate ICD-termination of cardiac arrhythmias (26% with ICD versus 0% with medical therapy; RR 11.4, 95% CI 1.57 to 83.3; 2 trials, 86 participants). Approximately 25% of the ICD group experienced inappropriate ICD firing, all of which was corrected by device reprogramming. No data were available for quality of life or cost. We considered the quality of evidence low using the GRADE methodology, due to study limitations and imprecision of effects.

Among people with Brugada syndrome who have survived a prior episode of sudden cardiac death, ICD therapy appeared to reduce mortality when compared to β-blocker therapy, but the true magnitude may be substantially different from the estimate of the effect because of study limitations and imprecision. Due to the large magnitude of effect, it is unlikely that there will be additional studies evaluating the role of ICDs for secondary prevention in this population. Further studies are necessary to determine the optimal treatment, if any, to prevent an initial episode of sudden cardiac death in people with cardiac ion channelopathies.