Atrial synchronized ventricular pacing system using intracardiac pacemaker and extracardiac atrial sensing

1. An implantable medical device system, comprising:

a leadless extracardiac sensing device comprising:

a housing;

a plurality of housing-based electrodes positioned along the housing;

a sensing module enclosed by the housing and configured to sense a P-wave attendant to an atrial activation of a patient's heart via only the housing-based electrodes of the extracardiac sensing device;

a trigger signal generator; and

a control module configured to control the trigger signal generator to transmit a trigger signal in response to the sensing module sensing the P-wave; and

an intracardiac pacemaker comprising;

a power source comprising at least one battery;

a trigger signal detector;

a pacing pulse generator coupled to the power source for providing power to the pacing pulse generator for generating pacing pulses, the pacing pulse generator comprising a charging circuit and a pacing capacitor coupled to the charging circuit for generating the pacing pulses; and

a control module configured to schedule a pacing pulse in response to the trigger signal detector detecting the trigger signal.

2. The system of claim 1 , wherein the sensing device control module is further configured to:

receive a P-wave sensed event signal from the sensing module;

detect an R-wave attendant to a ventricular depolarization of the heart;

set a P-wave sensing window in response to detecting the R-wave;

verify sensing of a P-wave preceding the detected R-wave by determining that the P-wave sensed event signal was received during the P-wave sensing window; and

enable the trigger signal generator to send the trigger signal in response to verifying the sensing of the preceding P-wave.

3. The system of claim 2 , wherein:

the pacemaker further comprises:

a sensing module configured to sense the R-wave;

a wireless signal generator configured to transmit a wireless signal in response to the sensing module sensing the R-wave; and

the extracardiac sensing device comprises a signal detector configured to detect the R-wave by detecting the wireless signal transmitted from the-wireless signal generator of the pacemaker.

4. The system of claim 2 , wherein the sensing device control module is further configured to automatically adjust a P-wave sensing control parameter in response to not sensing the preceding P-wave during the P-wave window.

5. The system of claim 2 , wherein the sensing device control module is further configured to:

determine a P-R interval between the preceding sensed P-wave and the detected R-wave;

set a pacing interval based at least in part on the P-R interval; and

schedule the trigger signal to be sent at the expiration of the pacing interval.

6. The system of claim 5 , wherein the sensing device control module is further configured to:

detect a second R-wave during the pacing interval; and

cancel the trigger signal in response to detecting the second R-wave during the pacing interval.

7. The system of claim 6 , wherein:

the pacemaker further comprises:

a sensing module configured to sense the second R-wave;

a wireless signal generator configured to transmit a wireless signal in response to the pacemaker sensing module sensing the second R-wave; and

the sensing device further comprises a signal detector configured to detect the second R-wave by detecting the wireless signal transmitted from the wireless signal generator of the pacemaker.

8. The system of claim 2 , wherein the housing of the sensing device is an angular housing comprising a bend and the housing-based electrodes comprise a first electrode along a first end of the angular housing, a second electrode along a second end of the angular housing, and a third electrode along the bend;

wherein the sensing module is configured to:

sense the P-wave by a first pair of the housing-based electrodes defining a first sensing vector angle; and

detect the R-wave from a cardiac electrical signal received by a second pair of the housing-based electrodes different than the first pair and defining a second sensing vector angle that is different than the first sensing vector angle.

9. The system of claim 1 , wherein:

the pacemaker further comprises a sensing module configured to sense an R-wave;

the pacemaker control module is further configured to:

schedule the pacing pulse by setting a pacing interval in response to detecting the trigger signal; and

cancel the scheduled pacing pulse in response to the sensing module sensing the R-wave during the pacing interval.

10. The system of claim 9 , wherein:

the pacemaker further comprises a ventricular event signal generator configured to send a wireless ventricular event signal to the extracardiac sensing device in response to the R-wave sensed during the pacing interval;

the extracardiac sensing device further comprising a signal detector configured to detect the ventricular event signal;

the sensing device control module is further configured to set a P-wave sensing blanking interval in response to detecting the ventricular event signal.

11. The system of claim 1 , wherein:

the pacemaker further comprises:

a sensing module configured to sense an R-wave;

a signal generator configured to send an R-wave signal from the pacemaker to the extracardiac sensing device in response to the pacemaker sensing module sensing the R-wave;

the sensing device further comprising a signal detector configured to detect the R-wave signal sent by the pacemaker; and

the extracardiac sensing device control module further configured to:

set an R-wave window in response to a P-wave sensed by the sensing module of the extracardiac sensing device; and

enable the trigger signal to be sent in response to the R-wave signal being detected during the R-wave window.

12. The system of claim 1 , wherein:

the extracardiac sensing device is further configured to send a P-wave signal from the sensing device to the pacemaker in response to sensing the P-wave;

the pacemaker further comprises a signal detector configured to detect the P-wave signal;

the pacemaker control module configured to:

determine a P-R interval in response to the detected P-wave signal; and

schedule the pacing pulse by setting a pacing interval based at least in part on the P-R interval.

13. The system of claim 1 , wherein:

the plurality of housing-based electrodes comprises a first pair of electrodes defining a first sensing vector and a second pair of electrodes defining a second sensing vector, the second sensing vector at an angle of at least 45 degrees to the first sensing vector;

the sensing module configured to select one of the first sensing vector and the second sensing vector for sensing the P-wave.

14. The system of claim 1 , wherein the sensing module senses the P-waves when the sensing device is implanted above the fourth intercostal space.

15. The system of claim 1 , wherein the pacemaker control module is further configured to:

determine an RR interval from one of an R-wave sensed by the pacemaker and a previously delivered ventricular pacing pulse to the scheduled pacing pulse;

compare the RR interval to a minimum interval; and

cancel the scheduled pacing pulse in response to the RR interval being less than the minimum RR interval.

16. An implantable medical device system, comprising:

a leadless extracardiac sensing device comprising:

a housing comprising a pair of housing-based electrodes positioned along the housing;

a first sensing module enclosed by the housing and configured to sense a P-wave attendant to an atrial activation of a patient's heart via only the pair of housing-based electrodes;

a trigger signal generator; and

a first control module configured to control the trigger signal generator to transmit a trigger signal in response to the first sensing module sensing the P-wave; and

an intracardiac pacemaker comprising;

a power source;

a trigger signal detector;

a pacing pulse generator coupled to the power source to provide power the pacing pulse generator for generating pacing pulses, the pacing pulse generator comprising a charging circuit and a pacing capacitor coupled to the charging circuit for generating the pacing pulses;

a second sensing module configured to sense an R-wave; and

a second control module configured to:

schedule a pacing pulse by setting a pacing interval in response to the trigger signal detector detecting the trigger signal; and

cancel the scheduled pacing pulse in response to the second sensing module sensing the R-wave during the pacing interval.

17. An implantable medical device system, comprising:

an extracardiac sensing device comprising:

a housing carrying a plurality of housing-based electrodes;

a first sensing module enclosed by the housing and configured to sense a plurality of P-waves via the housing-based electrodes, each P-wave attendant to an atrial activation of a patient's heart;

a trigger signal generator; and

a first control module coupled to the sensing module and the trigger signal generator;

an intracardiac pacemaker comprising;

a power source comprising at least one battery;

a trigger signal detector;

a second sensing module configured to sense an R-wave attendant to a ventricular activation of the patient's heart;

a pacing pulse generator coupled to the power source for providing power to the pacing pulse generator for generating pacing pulses, the pacing pulse generator comprising a charging circuit and a pacing capacitor coupled to the charging circuit for generating the pacing pulses; and

a signal generator configured to send an R-wave signal from the intracardiac pacemaker to the extracardiac sensing device in response to the second sensing module sensing the R-wave; and

a second control module coupled to the trigger signal detector, the pacing pulse generator and the second sensing module;

the extracardiac sensing device further comprising a signal detector configured to detect the R-wave signal sent from the intracardiac pacemaker;

the first control module configured to:

set an R-wave window in response to a first P-wave sensed by the first sensing module;

detect the R-wave signal sent from the intracardiac pacemaker during the R-wave window;

enable triggered pacing in response to detecting the R-wave signal during the R-wave window;

control the trigger signal generator to transmit a trigger signal in response to the first sensing module sensing a second P-wave after triggered pacing is enabled; and

the second control module configured to schedule a pacing pulse in response to the trigger signal detector detecting the trigger signal.