Implantable cardiac stimulation device having T-wave discrimination of fusion events during autocapture/autothreshold assessment

A method for discriminating a fusion event from an evoked response in an implantable pacemaker during an autocapture/autothreshold routine, wherein the autocapture/autothreshold routine adjusts the output energy of stimulation pulses in response to sensing and not sensing a response to a stimulation pulse, the method comprising the steps of:

• defining at least one attribute of a reference T-wave wherein the definition includes an acceptable variance in that attribute;
• sensing a first response corresponding to a stimulation pulse delivered during the autocapture/autothreshold routine;
• measuring the same at least one attribute as was defined for the reference T-wave for a T-wave corresponding to the stimulation pulse;
• comparing the at least one attribute of the T-wave to the same at least one attribute of the reference T-wave;
• defining the first sensed response to the stimulation pulse as an evoked response if the measured attribute of the T-wave is within the acceptable variance of the reference T-wave definition;
• and
• defining the first sensed response to the stimulation pulse as a fusion event if the measured attribute of the T-wave is not within the acceptable variance of the reference T-wave definition.

In an implantable pacemaker, a method for classifying a voltage signal sensed in response to a stimulation pulse as an evoked response or a fusion beat, the method comprising the steps of:

• generating stimulation pulses to a patient's heart;
• defining an acceptable value range for at least one attribute of the patient's T-waves, said range extending a predetermined amount above and below a prescribed reference value;
• sensing the voltage signal in response to a stimulation pulse;
• sensing the T-wave that follows the sensed voltage signal;
• measuring the at least one attribute of the sensed T-wave;
• classifying the sensed voltage signal as a fusion beat if the measured attribute of the T-wave is beyond the prescribed acceptable value range;
• and
• classifying the sensed voltage signal as an evoked response if the measured attribute of the T-wave is within the prescribed acceptable value range.

An implantable stimulation device, comprising:

• a pulse generator which generates stimulation pulses at a predetermined rate;
• a timing circuit, triggered by the generation of a stimulation pulse, that defines a first and second detection window;
• a sensing circuit that senses a first response during a first detection window following a stimulation pulse and a second response during the second detection window;
• and
• a processor circuit, coupled to the sensing circuit, that determines if a T-wave which is sensed in the second detection window corresponds to a true evoked response or a fusion beat, the processor circuit further having means for increasing the rate when fusion beats occur, the processor circuit still further having autocapture/autothreshold routine means operative to adjust the output energy of stimulation pulses in response to sensing and not sensing a response to a stimulation pulse.