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...http://www.google.de/patents/US5697954?utm_source=gb-gplus-sharePatent US5697954 - Defibrillation system including an atrial defibrillator and ventricular defibrillation backup 
