Method and apparatus for evaluating ventricular performance during isovolumic contraction

A method of operating an implantable medical device having a plurality of leads and having an implantable medical device circuit enclosed within a hermetically sealed housing, the method comprising:

• implanting a first lead bearing a first sonomicrometer crystal at a first location of the heart;
• implanting a second lead bearing a second sonomicrometer crystal at a second location of the heart, the first and second locations spanning a portion of the left ventricle;
• coupling the first and second leads to the implantable medical device circuit and implanting the housing in a patient;
• and
• operating the implantable medical device by:
• during one or more heart cycles, periodically energizing one of the first and second sonomicrometer crystals to emit an ultrasonic frequency emitted signal that causes the other of the first and second sonomicrometer crystals to develop an ultrasonic frequency sense signal;
• determining the distance between the first and second sonomicrometer crystals as a function of the time delay between emission of the emitted signal and sensing of the respective sense signal;
• measuring at least one of the following values:
• a) premature shortening (PS) of the ventricular dimension signal,
• the value of PS being equal to the decrease in the ventricular dimension signal
• from a first local maximum value that occurs at or near an end of the ventricular filling phase of the cardiac cycle, to a relative minimum value or inflection point that occurs during a transition from the ventricular filling phase to the ventricular ejection phase of the cardiac cycle;
• and
• b) isovolumic lengthening (IL) of the ventricular dimension signal,
• the value of IL being equal to the increase in the ventricular dimension signal
• from the relative minimum value or inflection point that occurs during the transition from the ventricular filling phase to the ventricular ejection phase of the cardiac cycle, to a second local maximum value that occurs at or near a beginning of the ventricular ejection phase of the cardiac cycle;
• comparing the at least one measured value of PS or IL with at least one reference value or at least one other measured value of PS or IL;
• and
• adjusting the operation of the implantable medical device.

An implantable medical device (IMD) for evaluating ventricular performance of a heart comprising:

• a plurality of leads and an implantable medical device circuit enclosed within a hermetically sealed housing;
• a first lead bearing a first sonomicrometer crystal adapted to be positioned at a first location of the heart;
• a second lead bearing a second sonomicrometer crystal adapted to be positioned at a second location of the heart, the first and second locations spanning a portion of the left ventricle, the first and second leads adapted to be coupled to the IMD circuit, the housing of the IMD adapted to be implanted in a patient, and the IMD capable of:
• periodically energizing one of the first and second sonomicrometer crystals during one or more heart cycles to emit an ultrasonic frequency emitted signal that causes the other of the first and second sonomicrometer crystals to develop an ultrasonic frequency sense signal;
• determining the distance between the first and second sonomicrometer crystals as a function of the time delay between emission of the emitted signal and sensing of the respective sense signal;
• measuring at least one of the following values:
• a) premature shortening (PS) of the ventricular dimension signal,
• the value of PS being equal to the decrease in the ventricular dimension signal
• from a first local maximum value that occurs at or near an end of the ventricular filling phase of the cardiac cycle, to a relative minimum value or inflection point that occurs during a transition from the ventricular filling phase to the ventricular ejection phase of the cardiac cycle;
• and
• b) isovolumic lengthening (IL) of the ventricular dimension signal,
• the value of IL being equal to the increase in the ventricular dimension signal
• from the relative minimum value or inflection point that occurs during the transition from the ventricular filling phase to the ventricular ejection phase of the cardiac cycle, to a second local maximum value that occurs at or near a beginning of the ventricular ejection phase of the cardiac cycle;
• comparing the at least one measured value of PS or IL with at least one reference value or at least one other measured value of PS or IL;
• and
• adjusting the operation of the implantable medical device.