Ventricular Arrhythmias in Patients With Implanted Defibrillators

Abstract

Ventricular tachycardia (VT) and ventricular fibrillation (VF) are important causes of mortality and morbidity in a wide variety of heart diseases. Implantable cardioverter-defibrillators (ICDs) are now widely used in patients who survive sustained VT or VF that is not attributable to a transient correctable cause, or who are at high risk for recurrent arrhythmia.1,2 ICDs are dramatically effective for terminating VT and VF. The extent to which VT termination extends survival, however, depends on the severity of the underlying heart disease and associated comorbidities.3–6 The occurrence of VT or VF is associated with increased mortality and heart failure hospitalizations in ICD patients, despite effective termination of the arrhythmia.7 VT or VF is associated with heart disease severity and, in some patients, is a marker for deterioration or intercurrent illness. Whether short VT or VF episodes and the hemodynamic and neurohormonal responses they may elicit contribute directly to adverse outcomes is not known.7,8 Frequent or incessant VT can cause hemodynamic deterioration, and death from uncontrollable VT occasionally occurs. ICD shocks in response to VT can damage myocardial cells and elicit sympathetic responses.8 ICD shocks have been associated with mortality in post hoc analyses of ICD trials, but whether there is a direct causal relationship of shocks to cardiac mortality and heart failure remains a controversial topic.8,9 A patient who reports arrhythmia symptoms or a perceived shock should be promptly evaluated with an ICD interrogation to determine whether the event was truly a ventricular arrhythmia, rather than an inappropriate ICD therapy in response to rapid atrial fibrillation, or electric noise from a lead malfunction, which warrants further intervention.10 Those who have had VT or VF will broadly fall into 1 of 3 groups. The first are typically …