Method and apparatus for optimizing cardiac resynchronization therapy

#The present invention relates generally to medical devices for treating cardiac dysfunction and more particularly to a device and method for optimizing cardiac resynchronization therapy acutely and/or chronically based on a hemodynamic surrogate measurement for stroke volume.

#Evaluation of left ventricular function is of interest for both diagnostic and therapeutic applications. During normal cardiac function the cardiac chambers observe consistent time-dependent relationships during the systolic (contractile) phase and the diastolic (relaxation) phase of the cardiac cycle. During cardiac dysfunction associated with pathological conditions or following cardiac-related surgical procedures, these time-dependent mechanical relationships are often altered. This alteration, when combined with the effects of weakened cardiac muscles, reduces the ability of the ventricle to generate contractile strength resulting in hemodynamic insufficiency.

#Ventricular dyssynchrony following coronary artery bypass graft (CABG) surgery is a problem encountered relatively often, requiring post-operative temporary pacing. Atrio-biventricular pacing has been found to improve post-operative hemodynamics following such procedures. See Weisse et al., Thorac. Cardiovasc. Surg. 2002;41:131-135. A widely accepted, standardized method for selecting pacing sites and pacing intervals that provide the greatest hemodynamic benefit to the patient during the critical recovery phase, however, has not been available.

#FIG. 1 depicts an implantable, multi-chamber cardiac pacemaker in communication with a patient's heart by way of three leads.

#FIG. 2 is a schematic block diagram of the exemplary multi-chamber pacemaker of FIG. 1 that provides delivery of cardiac resynchronization therapy and is capable of processing physiological signal input.

#FIG. 3 is a schematic block diagram of an alternative embodiment of multi-chamber pacemaker that includes an implantable sensor for monitoring arterial pressure.

#As indicated above, the present invention provides a method for optimizing cardiac resynchronization therapy (CRT). Optimal CRT pacing intervals, which can include a right and/or left atrial-ventricular (A-V) interval and an interventricular (V-V) interval, collectively referred to herein as “A-V-V intervals”, are selected based on a surrogate measure of stroke volume. Methods included in the present invention may be implemented in an external device or “programmer” that is in telemetric communication with an implanted multi-chamber pacemaker for acute optimization procedures performed in association with an external pressure measurement device. Methods included in the present invention may additionally or alternatively be implemented in the implantable multi-chamber pacemaker for chronic optimization procedures performed in association with an implantable sensor of aortic or arterial pressure or a correlate thereof.

#FIG. 1 depicts an implantable, multi-chamber cardiac pacemaker 14 in communication with a patient's heart 10 by way of three leads 16, 32 and 52. The heart 10 is shown in a partially cut-away view illustrating the upper heart chambers, the right atrium (RA) and left atrium (LA), and the lower heart chambers, the right ventricle (RV) and left ventricle (LV), and the coronary sinus (CS) extending from the opening in the right atrium laterally around the atria to form the great cardiac vein 48, which branches to form inferior cardiac veins. The pacemaker 14, also referred to herein as the “implantable pulse generator” or “IPG,” is implanted subcutaneously in a patient's body between the skin and the ribs. Three endocardial leads 16, 32 and 52 connect the IPG 14 with the RA, the RV and the LV, respectively. Each lead has at least one electrical conductor and pace/sense electrode. A remote indifferent can electrode 20 is formed as part of the outer surface of the housing of the IPG 14. The pace/sense electrodes and the remote indifferent can electrode 20 can be selectively employed to provide a number of unipolar and bipolar pace/sense electrode combinations for pacing and sensing functions. The depicted positions of leads 16, 32 and 52 and associated electrodes in or about the right and left heart chambers are merely exemplary. Moreover other leads and pace/sense electrodes that are adapted to be placed at electrode sites on or in or relative to the RA, LA, RV and LV may be used instead of the depicted leads and pace/sense electrodes.

#The depicted bipolar endocardial RA lead 16 is passed through a vein into the RA chamber of the heart 10, and the distal end of the RA lead 16 is attached to the RA wall by an attachment mechanism 17. The bipolar endocardial RA lead 16 is formed with an in-line connector 13 fitting into a bipolar bore of IPG connector block 12 that is coupled to a pair of electrically insulated conductors within lead body 15 and connected with distal tip RA pace/sense electrode 19 and proximal ring RA pace/sense electrode 21 provided for achieving RA pacing and sensing of RA electrogram (EGM) signals.