Right atrial compression related to defibrillator patches

Acceptable function of an internal defibrillator can be achieved with different patch orientations. For patients requiring defibrillator patches concomitant with a cardiac procedure requiring extracorporeal circulation, application of one of the patches within the pericardium adjacent to the right atrium has provided excellent defibrillation thresholds. We describe 4 such patients in whom a compressing thrombus subsequently developed between the patch and the atrium. The thrombus was small and asymptomatic in 1 patient, but caused localized tamponade requiring reexploration in 2 patients and a fatal superior vena caval obstruction in 1. The precise etiology of this serious complication remains unclear, but its occurrence argues against the application of intrapericardial defibrillator patches in this orientation.