Post myocardial infarction, left ventricular dysfunction, and the expanding role of cardiac implantable electrical devices.

Abstract

In patients post myocardial infarction (MI) at risk for fatal ventricular arrhythmias, cardiac implantable devices offer a means of preventive therapy that complements optimal pharmacologic therapy. In patients with depressed ejection fractions, prophylactic implantable cardioverter defibrillators (ICDs) significantly improve survival. The efficacy of ICDs in the primary prevention of sudden cardiac death in patients post MI has been examined in a number of major primary prevention trials. These trials demonstrated as much benefit as some secondary prevention trials, which were conducted in high-risk patients who already had a spontaneous sustained ventricular tachyarrhythmia. In patients who are candidates for an ICD, best medical therapy for left ventricular dysfunction should be in place for some time before implanting. This waiting period could mean avoiding the implantation of a device in a patient who would heal sufficiently with pharmacologic therapy alone. In New York Heart Association (NYHA) class III and IV, patients with heart failure, and QRS intervals > or = 120 ms, cardiac resynchronization therapy (CRT) in combination with a defibrillator is a valuable addition to optimal pharmacologic therapy. Recent studies have demonstrated improved survival with CRT as well as improved quality of life. The high cost of cardiac implantable devices has led the Centers for Medicare and Medicaid Services to impose strict indications for use. However, it is likely that indications will be broadened for ICDs to include selected patients with left ventricular ejection fraction up to 40%, compared with the current indication of < or = 30%. Implanted devices must be followed up appropriately, with periodic interrogation and program adjustment to reduce the risk for pacing-induced desynchronization and to optimize hemodynamic benefit.