Monitoring activation times for use in determining pacing effectiveness

1. An implantable medical device for tracking effectiveness of pacing therapy to a patient comprising:

a therapy delivery module configured to deliver pacing therapy to a patient's heart using at least a first electrode;

a sensing module configured to sense electrical activity of the patient's heart using a second electrode during the delivery of pacing therapy using at least the first electrode; and

a control module coupled to the therapy delivery module and to the sensing module and configured to:

measure an activation time for each of a plurality of heart beats between the delivery of a pacing stimulus of the pacing therapy using the first electrode and a selected fiducial point of the sensed electrical activity resulting from the delivered pacing stimulus of the pacing therapy;

determine beat-to-beat data representative of whether the pacing stimulus of the delivered pacing therapy for each heart beat of the plurality of heart beats was effective or ineffective based on the measured activation times, wherein the determination of whether the pacing stimulus of the delivered pacing therapy for each heart beat was effective or ineffective is indicative of whether capture occurred as a result of the delivered pacing stimulus; and

use the beat-to-beat data to determine if the pacing therapy was effective or ineffective for the patient, wherein to use the beat-to-beat data to determine whether the delivered pacing therapy was effective or ineffective, the control module is further configured to:

classify, for each heart beat, the measured activation time as being characteristic of one of a plurality of types of pacing therapy and an intrinsic activation; and

determine that the delivered pacing therapy was ineffective if the classification is not the same as the pacing therapy programmed to be delivered.

2. A method of tracking effectiveness of pacing therapy provided using an implantable medical device, wherein the method comprises:

delivering pacing therapy to a patient's heart using at least a first electrode of an implantable medical device, wherein the pacing therapy is delivered over a plurality of heart beats;

sensing electrical activity of the patient's heart using at least a second electrode of the implantable medical device during the delivery of the pacing therapy using at least the first electrode;

measuring an activation time for each of a plurality of heart beats between the delivery of a pacing stimulus of the pacing therapy using the first electrode and a selected fiducial point of the sensed electrical activity resulting from the delivered pacing stimulus of the pacing therapy;

determining beat-to-beat data representative of whether the pacing stimulus of the delivered pacing therapy for each heart beat of the plurality of heart beats was effective or ineffective based on the measured activation times, wherein determination of whether the pacing stimulus of the delivered pacing therapy for each heart beat was effective or ineffective is indicative of whether capture occurred as a result of the delivered pacing stimulus; and

using the beat-to-beat data to determine if the pacing therapy was effective or ineffective for the patient, wherein using the beat-to-beat data to determine whether the delivered pacing therapy was effective or ineffective for the patient comprises:

classifying, for each heart beat, the measured activation time as being characteristic of one of a plurality of types of pacing therapy and an intrinsic activation; and

determining that the delivered pacing therapy was ineffective if the classification is not the same as the pacing therapy programmed to be delivered.