Does ventricular fibrillation cause myocardial stunning during defibrillator implantation?

Induction of ventricular fibrillation (VF) is an important part of the process of inserting implantable cardioverter defibrillators (ICDs), allowing the measurement of defibrillation thresholds. However, animal studies have revealed that repeated cycles of VF and defibrillation result in depressed left ventricular (LV) function and reduced cardiac output. Short intervals of VF do not affect myocardial contractility but longer periods produce heart failure. Induced VF was used in a canine model to study profound myocardial stunning leading to heart failure, as well as the therapeutic potential of the phosphodiesterase inhibitor, amrinone (combined with epinephrine and norepinephrine). Amrinone was found to significantly (p < 0.05) increase contractility when added to a stable preparation supported by epinephrine and norepinephrine infusion; amrinone or catecholamines alone had no effect. In the clinical setting, the following factors may affect LV contractility during ICD surgery: catecholamines released as a result of hypotension; negative VF; ischemia; antiarrhythmic drugs; anesthetics; and bradycardia after device testing. Patients (n = 125) have tolerated ICD insertion well. Early data reveals no significant changes in ejection fraction. Though rare, death due to myocardial stunning and LV power failure can occur during ICD insertion. It may be possible to use arterial pressure monitoring to predict this event in vulnerable patients.