Pacing mode switching in a ventricular pacemaker

1. A medical device, comprising:

a motion sensor configured to sense a motion signal;

a pulse generator configured to deliver ventricular pacing pulses; and

a control circuit configured to:

determine a first patient physical activity metric from the motion signal;

determine an actual ventricular rate based on a plurality of ventricular pacing pulses delivered by the pulse generator, each of the plurality of ventricular pacing pulses being delivered by the pulse generator in response to an atrioventricular pacing interval expiring;

determine that first pacing mode switching criteria are met based on the first patient physical activity metric and the actual ventricular rate by:

setting a threshold rate based on the actual ventricular rate;

determining a sensor indicated pacing rate based on the first patient physical activity metric; and

determining that the sensor indicated pacing rate is greater than the threshold rate set based on the actual ventricular rate; and

control the pulse generator to deliver ventricular pacing pulses according to a ventricular lower rate in response to the first pacing mode switching criteria being met.

2. The medical device of claim 1 , wherein the control circuit is configured to set the ventricular lower rate based on the first patient physical activity metric.

3. The medical device of claim 1 , further comprising a cardiac electrical signal sensing circuit configured to sense intrinsic ventricular electrical events;

wherein the control circuit is configured to determine the actual ventricular rate based on the plurality of ventricular pacing pulses and at least one intrinsic ventricular electrical event sensed by the cardiac electrical signal sensing circuit.

4. The medical device of claim 1 , wherein the control circuit is configured to:

sense an atrial event from the motion signal; and

set the atrioventricular pacing interval in response to sensing the atrial event from the motion signal.

5. The medical device of claim 1 , wherein the control circuit is configured to:

set the atrioventricular pacing interval during an atrial tracking ventricular pacing mode; and

switch from the atrial tracking ventricular pacing mode to a non-atrial tracking ventricular pacing mode in response to the first pacing mode switching criteria being met.

6. The medical device of claim 1 , wherein the control circuit is further configured to:

determine that the first pacing mode switching criteria are met by determining that the first patient activity metric is greater than a threshold patient activity level.

7. The medical device of claim 1 , wherein the control circuit is further configured to:

determine a rate smoothing interval based on the actual ventricular rate; and

deliver the ventricular pacing pulses according to the ventricular lower rate by:

initially setting a ventricular pacing interval to the rate smoothing interval; and

adjusting the ventricular pacing interval toward the sensor indicated pacing rate.

8. The medical device of claim 1 , further comprising:

a housing enclosing the motion sensor, the pulse generator and the control circuit; and

a pacing electrode pair carried by the housing and coupled to the pulse generator for delivering the ventricular pacing pulses.

9. A medical device, comprising:

a motion sensor configured to sense a motion signal;

a pulse generator configured to deliver ventricular pacing pulses; and

a control circuit configured to:

determine a first patient physical activity metric from the motion signal;

determine an actual ventricular rate based on a plurality of ventricular pacing pulses delivered by the pulse generator, each of the plurality of ventricular pacing pulses being delivered by the pulse generator in response to an atrioventricular pacing interval expiring;

determine that first pacing mode switching criteria are met based on the first patient physical activity metric and the actual ventricular rate; and

control the pulse generator to deliver ventricular pacing pulses according to a ventricular lower rate in response to the first pacing mode switching criteria being met, wherein the control circuit is further configured to:

control the pulse generator to generate the ventricular pacing pulses according to the ventricular lower rate for a minimum mode switch time interval;

determine that the minimum mode switch time interval is expired;

determine a second patient activity metric from the motion signal;

after the minimum mode switch time interval is expired, determine that second pacing mode switching criteria are met based on the second patient activity metric; and

switch to an atrioventricular tracking pacing mode in response to the second pacing mode switching criteria being met.

10. A method, comprising:

sensing a motion signal;

determining a first patient physical activity metric from the motion signal;

determining an actual ventricular rate based on a plurality of ventricular pacing pulses, each of the plurality of ventricular pacing pulses being delivered in response to an atrioventricular pacing interval expiring;

determining that first pacing mode switching criteria are met based on the first patient physical activity metric and the actual ventricular rate by:

setting a threshold rate based on the actual ventricular rate;

determining a sensor indicated pacing rate based on the first patient physical activity metric; and

determining that the sensor indicated pacing rate is greater than the threshold rate set based on the actual ventricular rate; and

delivering ventricular pacing pulses according to a ventricular lower rate in response to the pacing mode switching criteria being met.

11. The method of claim 10 , comprising setting the ventricular lower rate based on the first patient physical activity metric.

12. The method of claim 10 , comprising:

sensing intrinsic ventricular electrical events; and

determining the actual ventricular rate based on the plurality of ventricular pacing pulses and at least one sensed intrinsic ventricular electrical event.

13. The method of claim 10 , comprising:

sensing an atrial event from the motion signal; and

setting the atrioventricular pacing interval in response to sensing the atrial event from the motion signal.

14. The method of claim 10 , comprising:

setting the atrioventricular pacing interval during an atrial tracking ventricular pacing mode; and

switching from the atrial tracking ventricular pacing mode to a non-atrial tracking ventricular pacing mode in response to the first pacing mode switching criteria being met.

15. The method of claim 10 , wherein determining that the first pacing mode switching criteria are met comprises determining that the first patient activity metric is greater than a threshold patient activity level.

16. The method of claim 10 , comprising:

determining a rate smoothing interval based on the actual ventricular rate; and

delivering the ventricular pacing pulses according to the ventricular lower rate by:

initially setting a ventricular pacing interval to the rate smoothing interval; and

adjusting the ventricular pacing interval toward the sensor indicated pacing rate.

17. A method, comprising:

sensing a motion signal;

determining a first patient physical activity metric from the motion signal;

determining an actual ventricular rate based on a plurality of ventricular pacing pulses, each of the plurality of ventricular pacing pulses being delivered in response to an atrioventricular pacing interval expiring;

determining that first pacing mode switching criteria are met based on the first patient physical activity metric and the actual ventricular rate;

delivering ventricular pacing pulses according to a ventricular lower rate in response to the pacing mode switching criteria being met delivering the ventricular pacing pulses according to the ventricular lower rate for a minimum mode switch time interval;

determining that the minimum mode switch time interval is expired;

determining a second patient activity metric from the motion signal;

after the minimum mode switch time interval is expired, determining that second pacing mode switching criteria are met based on the second patient activity metric; and

switching to an atrioventricular tracking pacing mode in response to the second pacing mode switching criteria being met.

18. A non-transitory, computer-readable medium storing a set of instructions, which, when executed by a control circuit of a medical device, cause the medical device to:

sense a motion signal;

determine a patient physical activity metric from the motion signal;

determine an actual ventricular rate based on a plurality of ventricular pacing pulses, each of the plurality of ventricular pacing pulses being delivered in response to an atrioventricular pacing interval expiring;

determine that first pacing mode switching criteria are met based on the first patient physical activity metric and the actual ventricular rate by:

setting a threshold rate based on the actual ventricular rate;

determining a sensor indicated pacing rate based on the first patient physical activity metric; and

determining that the sensor indicated pacing rate is greater than the threshold rate set based on the actual ventricular rate; and

deliver ventricular pacing pulses according to a ventricular lower rate in response to the pacing mode switching criteria being met.