The implantable cardioverter defibrillator

Overview of randomized trials of antiarrhythmic drugs and devices for the prevention of sudden cardiac death

BACKGROUND

Sudden cardiac death is a prominent feature of the natural history of heart disease. The efficacy of antiarrhythmic drugs and devices in preventing sudden death and reducing total mortality is uncertain.

METHODS

We reviewed randomized trials and quantitative overviews of type I and type III antiarrhythmic drugs. We also reviewed the randomized trials of implantable cardioverter defibrillators and combined these outcomes in a quantitative overview.

RESULTS

Randomized trials of type I antiarrhythmic agents used as secondary prevention after myocardial infarction show an overall 21% increase in mortality rate. Randomized trials of amiodarone suggest a 13% to 19% decrease in mortality rate, and sotalol has been effective in several small trials. Trials of pure type III agents, however, have shown no mortality benefit. An overview of implantable defibrillator trials shows a 24% reduction in mortality rate (CI 15%-33%) compared with alternative therapy, most often amiodarone.

CONCLUSION

Amiodarone is effective in reducing the total mortality rate by 13% to 19%, and the implantable defibrillator reduces the mortality rate by a further 24%.

Role of transvenous implantable cardioverter-defibrillators in preventing sudden cardiac death in children, adolescents, and young adults

OBJECTIVE

To evaluate the indications, underlying cardiac disorders, efficacy, and complications involved with transvenous implantable cardioverter-defibrillators (ICDs) in pediatric patients at the Mayo Clinic.

PATIENTS AND METHODS

The records of all patients aged 21 years or younger who underwent transvenous ICD placement at the Mayo Clinic, Rochester, Minn, were reviewed retrospectively.

RESULTS

Between March 1992 and September 2000, 16 patients (7 females; mean age, 15.4 years; range, 10-21 years) underwent transvenous ICD placement. The ICD was implanted for primary prevention of sudden cardiac death in 7 and for secondary prevention in 9. The underlying cardiac disorders included hypertrophic cardiomyopathy in 6 patients and congenital long QT syndrome in 6 patients. The mean +/- SD follow-up was 36+/-29 months (range, 5-108 months). There was no mortality. Seven patients (44%) received appropriate ICD therapy, including 6 of 9 who had ICDs placed for secondary prevention. Median time free from appropriate ICD discharge was 3 years (range, 0.2-9 years). Three patients (19%) experienced inappropriate ICD discharge. Two patients needed device replacement because of technical problems (lead fracture and device malfunction). Two patients developed pocket infection that required removal and reimplantation of the ICD.

CONCLUSION

In adolescents and young adults, transvenous ICDs may prevent sudden death but are not free of complications. Forty-four percent of this cohort received potentially life-saving ICD therapy, including two thirds who received an ICD for secondary prevention.

Should all implantable cardioverter defibrillators for ventricular arrhythmias be dual-chamber devices?

The advantages of a dual-chamber implantable cardioverter defibrillator (ICD) over a single-chamber ICD include physiologic pacing capability, atrial electrogram storage, enhanced arrhythmia discrimination algorithms, and a potential to treat atrial arrhythmia by pacing or defibrillation. Current evidence supports the supposition that dual-chamber ICDs are definitely indicated in patients who have a concomitant indication for physiologic pacing, such as bradycardia or bradycardia-dependent ventricular tachyarrhythmias. Refined dual-chamber arrhythmia discrimination algorithms and enhanced atrial therapies are probably required for patients with frequent supraventricular arrhythmias. Furthermore, in patients with systolic heart failure, low ejection fraction, and intraventricular conduction delay, triple-chamber ICDs with biventricular pacing may improve their functional status and prevent sudden arrhythmic death. Careful patient selection is required to optimize the cost-effectiveness of these sophisticated technologies.

Are drugs and catheter ablation effective for treating ventricular arrhythmias in populations that cannot afford implantable cardioverter defibrillators?

Despite recent advances, ventricular arrhythmias continue to pose a therapeutic challenge, especially to the clinician in the developing world. Although the implantable cardioverter defibrillator (ICD) has improved survival in both primary and secondary prevention trials, it still remains a costly modality for the developing world. Even though certain subgroups stand to benefit unequivocally in survival from the ICD, there are others in whom this therapy may not offer a survival benefit over empiric antiarrhythmic drug therapy with amiodarone. The utility of optimized drug therapy (including either amiodarone or sotalol, b-blockers, and angiotensin-converting enzyme inhibitors) needs to be compared with the ICD in a randomized manner in these lower-risk patients with ventricular arrhythmias. The role of conventional catheter ablation techniques is mostly adjunctive to drugs and ICDs, although the newer mapping and ablation techniques may offer greater promise in the future.