Abstract: An implantable defibrillation system includes a lead system for making electrical contact with a heart, an atrial cardiovertor coupled to the lead system for applying cardioverting electrical energy to that is of the heart, and a ventricular defibrillator coupled to the lead system. The ventricular defibrillator includes a ventricular arrhythmia detector responsive to a control signal for detecting for a ventricular arrhythmia of the heart and a ventricular cardiovertor for cardioverting the ventricles of the heart in response to the ventricular arrhythmia detector detecting a ventricular arrhythmia. A ventricular arrhythmia detector enable stage provides the control signal in response to each application of cardioverting electrical energy to the atria by the atrial cardiovertor.

Abstract: An implantable atrial defibrillator delays therapy intervention for a delay time period after initial detection of fibrillation to provide the atria with an opportunity to spontaneously revert to normal sinus rhythm before cardioversion is attempted. A timer times the delay time period responsive to the first initial detection of fibrillation by a fibrillation detector. After timer time-out, the fibrillation detector redetects for atrial fibrillation. If the atria are still in fibrillation, a cardiovertor cardioverts the atria. If the atria are not in fibrillation, cardioverting therapy is withheld.