Atrial defibrillator

1. 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.

2. The atrial defibrillator according to claim 1 , additionally comprising a sensing stage adapted to sense atrial events and being connected to the atrial fibrillation detector.

3. The atrial defibrillator according to claim 2 , wherein the sensing stage for sensing of intrinsic ventricular events comprises a band pass filter having a pass band between 15 Hz and 80 Hz.

4. The atrial defibrillator according to claim 3 , wherein the sensing stage comprises a second filter having a lower cut-off frequency of 22 to 26 Hz for filtering a ventricular signal in order to suppress T-wave sensing.

5. The atrial defibrillator according to claim 4 , wherein the control unit is adapted to synchronize an atrial defibrillation shock with a ventricular event sensed within a ventricular signal having passed the second filter.

6. The atrial defibrillator according to claim 1 , wherein the sensing stage for sensing of intrinsic ventricular events comprises a band pass filter having a pass band between 15 Hz and 80 Hz.

7. The atrial defibrillator according to claim 6 , wherein the sensing stage comprises a second filter having a lower cut-off frequency of 22 to 26 Hz for filtering a ventricular signal in order to suppress T-wave sensing.

8. The atrial defibrillator according to claim 7 , wherein the control unit is adapted to synchronize an atrial defibrillation shock with a ventricular event sensed within a ventricular signal having passed the second filter.

9. The atrial defibrillator according to claim 8 , wherein the control unit is adapted to trigger an atrial defibrillation shock within 30-100 ms after detection of an R-wave having an amplitude with a magnitude of at least 60% of the magnitude of the reference amplitude.

10. The atrial defibrillator according to claim 9 , additionally comprising a memory for storing R-wave amplitudes sensed during episodes of sinus rate.

11. The atrial defibrillator according to claim 7 , additionally comprising a memory for storing R-wave amplitudes sensed during episodes of sinus rate.

12. The atrial defibrillator according to claim 11 , wherein the control unit is connected to the memory and is adapted to generate a mean amplitude value from R-wave amplitude values stored in said memory and to set said mean value as a reference amplitude.

13. The atrial defibrillator according to claim 12 , wherein the memory for storing R-wave amplitudes is operationally connected to the second filter for filtering the R-wave amplitude to be stored in said memory.

14. The atrial defibrillator according to claim 1 , wherein the control unit is adapted to evaluate an intracardiac impedance signal in a time window starting with a sensed ventricular event (R-wave) and ending after 30 to 50 ms and to suppress delivery of an atrial defibrillation shock when the difference area is larger than 10 to 20% of the reference area.

15. The atrial defibrillator according to claim 14 , wherein the control unit is adapted to suppress delivery of an atrial defibrillation shock when the difference area is larger than 15% of the reference area.

16. The atrial defibrillator according to claim 1 , wherein the control unit is adapted to trigger an atrial defibrillation shock within 30-100 ms after detection of an R-wave having an amplitude with a magnitude of at least 60% of the magnitude of the reference amplitude.

17. The atrial defibrillator according to claim 16 , additionally comprising a memory for storing R-wave amplitudes sensed during episodes of sinus rate.