Method and apparatus for monitoring myocardial conduction velocity for diagnostics of therapy optimization

#The present invention relates generally to an implantable cardiac stimulation device and, more specifically, to a method for storing a long-term average myocardial conduction velocity as a diagnostic measure of the physiological condition of the heart for use in monitoring heart disease or optimizing a delivered therapy.

#In a normal human heart, the sinus node, generally located near the junction of the superior vena cava and the right atrium, constitutes the primary natural pacemaker initiating rhythmic electrical excitation of the heart chambers. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers, causing a depolarization known as a P-wave and the resulting atrial chamber contractions. The excitation pulse is further transmitted to and through the ventricles via the atrioventricular (A-V) node and a ventricular conduction system causing a depolarization known as an R-wave and the resulting ventricular chamber contractions.

#The intrinsic heart rate is primarily controlled by the sympathetic and parasympathetic components of the autonomic nervous system. Both components have nerve fibers terminating on the sinus node. Increased sympathetic activation (increased sympathetic tone) increases the heart rate as well as the conduction velocity of action potentials through the heart. Increased parasympathetic tone, also referred to as “vagal tone” since the parasympathetic nerves enter the heart via the vagus nerve, decreases the heart rate and decreases conduction velocity through the heart. Other factors such as circulating hormones and heart wall stretch will also influence heart rate and conduction. Though not fully understood, cardiovascular diseases and other physiological states may alter sympathetic tone, parasympathetic tone, and circulating hormonal levels and thus alter the heart tissue conduction velocity.

#The various features of the present invention and the manner of attaining them will be described in greater detail with reference to the following description, claims, and drawings, wherein reference numerals are reused, where appropriate, to indicate a correspondence between the referenced items, and wherein:

#FIG. 1 is a simplified, partly cutaway view illustrating an implantable stimulation device in electrical communication with at least three leads implanted into a patient's heart for delivering multi-chamber stimulation and shock therapy;

#FIG. 2 is a functional block diagram of the multi-chamber implantable stimulation device of FIG. 1, illustrating the basic elements that provide pacing stimulation, cardioversion, and defibrillation in four chambers of the heart;

#The following description is of a best mode presently contemplated for practicing the invention. This description is not to be taken in a limiting sense but is made merely for the purpose of describing the general principles of the invention. In the description of the invention that follows, like numerals or reference designators will be used to refer to like parts or elements throughout. The present invention is directed at providing a long-term running average of the myocardial conduction velocity of an evoked response for the purposes of monitoring disease progress or optimizing a medical or stimulation therapy. A general cardiac stimulation device will be described in conjunction with FIGS. 1 and 2, in which the features included in the present invention could be implemented. It is recognized, however, that numerous variations of such a device exist in which the methods included in the present invention could be implemented without deviating from the scope of the present invention.

#FIG. 1 illustrates a stimulation device 10 in electrical communication with a patient's heart 12 by way of three leads 20, 24 and 30 suitable for delivering multi-chamber stimulation and shock therapy. To sense atrial cardiac signals and to provide right atrial chamber stimulation therapy, the stimulation device 10 is coupled to an implantable right atrial lead 20 having at least an atrial tip electrode 22, which typically is implanted in the patient's right atrial appendage. The right atrial lead 20 may also have an atrial ring electrode 23 to allow bipolar stimulation or sensing in combination with the atrial tip electrode 22. In the present invention, right atrial stimulation is preferably delivered using the atrial tip electrode 22, and the propagating evoked response is sensed using the atrial ring electrode 23.

#To sense the left atrial and ventricular cardiac signals and to provide left-chamber stimulation therapy, the stimulation device 10 is coupled to a “coronary sinus” lead 24 designed for placement in the “coronary sinus region” via the coronary sinus ostium so as to place a distal electrode adjacent to the left ventricle and additional electrode(s) adjacent to the left atrium. As used herein, the phrase “coronary sinus region” refers to the venous vasculature of the left ventricle, including any portion of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.