Patent ID: 7532928

Claim:
An atrial defibrillator comprising: at least one stimulation pulse generator to generate pacing pulses for at least a ventricle of a heart; at least one sensing stage for sensing of intrinsic ventricular events, said intrinsic ventricular event being an R-wave having an amplitude; a defibrillation shock generator to generate an atrial defibrillation shock; an atrial fibrillation detector adapted to detect an atrial fibrillation; a control unit connected to the stimulation pulse generator, the sensing stage, the atrial fibrillation detector and the defibrillation shock generator, said control unit being adapted to trigger an atrial defibrillation shock after detection of an atrial fibrillation and synchronous with a sensed or a paced ventricular event, wherein the control unit is adapted to compare a sensed R-wave amplitude with a reference R-wave amplitude and synchronize an atrial defibrillation shock with either a paced ventricular event or a sensed ventricular event if said sensed ventricular event is an R-wave having an amplitude of at least 60% of the magnitude of the reference amplitude; and an impedance sensor connected to an impedance evaluation unit adapted to detect ventricular contractions by evaluating an intracardiac impedance signal, wherein the control unit is connected to the impedance evaluation unit and is adapted to evaluate an actual intracardiac impedance signal by comparing said actual intracardiac impedance signal with a stored reference intracardiac impedance signal, and wherein the control unit is adapted to form a difference area between an actual impedance signal and a stored reference impedance signal and to compare the difference area to a stored reference area, said stored reference area representing the area defined by the reference impedance signal.