Interactions between pharmacologic and nonpharmacologic antiarrhythmic therapy.

Whether patients with serious ventricular arrhythmias should be treated first with antiarrhythmic drugs or an implantable cardioverter-defibrillator (ICD) is not known. Many patients are ultimately treated with both an antiarrhythmic drug and on ICD. Early studies reported that 40-70% of patients who received an ICD were ultimately treated with an antiarrhythmic drug, although fewer patients are now being treated with both modalities. The beneficial interactions between antiarrhythmic drugs and an ICD are slowing of ventricular tachycardia, which yields improved hemodynamic tolerance; improved antitachycardia pacing and low energy cardioversion success; lowering of antiarrhythmic drug doses, which reduces the risk of side effects; limiting the number of arrhythmia episodes, which minimizes patients discomfort and prolongs ICD battery life; and preventing or slowing supraventricular tachyarrhythmias, which reduces the number of inappropriate shocks from the ICD. The disadvantages of combining pharmacologic therapy and the use of an ICD are the cost and side effects of both therapies. Adverse interactions between an ICD and antiarrhythmic drugs include slowed ventricular tachycardia, which may lead to failure to detect the arrhythmia; increased defibrillation and pacing thresholds; worsened hemodynamic tolerance of ventricular tachycardia; lengthened PR, QRS, or QT intervals causing multiple counting; and decreased size of the intracardiac electrogram, leading to failure to detect the ventricular tachycardia or fibrillation. Caution must be used when combining pharmacologic therapy with an ICD. Repeat electrophysiologic testing is frequently necessary after the initiation of antiarrhythmic drug therapy in a patient with an ICD to ensure successful therapy with the ICD.