Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2002-01-03
2004-07-27
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06768924
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to the field of cardiac rhythm/function management devices, and more particularly relates to cardiac rhythm/function management devices that automatically determine whether or not a pacing stimulus to the atrium(s) and/or ventricle(s) results in capture. The cardiac device of the present invention is suitable for use in either a unipolar or bipolar pacing/sensing configuration and may be utilized to verify either atrial or ventricular capture in a heart having either normal or abnormal intrinsic conduction.
II. Background of the Prior Art
In a normal heart, the sino-atrial (SA) node initiates the myocardial stimulation of the atrium. The SA node comprises a bundle of unique cells disposed within the roof of the right atrium. The SA node cells are in electrical communication with the surrounding atrial muscle cells such that the depolarization of the SA node cells causes the adjacent atrial muscle cells to depolarize. The depolarization causes the atria to contract forcing blood into the ventricles. The depolarization of the SA node is further communicated to the atrio-ventricular (AV) node. The AV node communicates the depolarization impulse to the ventricles sequentially through the Bundle of His and Purkinje fibers. The time for the depolarization impulse to travel from the AV node through the Bundle of His and Purkinje fibers results in a brief delay for ventricular contraction. Therefore, ventricular contraction or systole lags behind atrial systole. The sequential contraction of the atria and ventricles allows the atria to fill the ventricles before the ventricles pump the blood through the body and lungs. Atrial and ventricular diastole follow wherein the heart muscle or myocardium is re-polarized and relaxed prior to the next contraction.
When the intrinsic stimulation system fails or functions abnormally an implanted pacing device may be needed to deliver an electrical (pacing) stimulus to the heart. When the strength of the stimulus is sufficient, the artificial electrical stimulus can cause the muscle cells surrounding the electrode to depolarize. This depolarization will spread out through the entire chamber or chambers of the heart and result in contractions. Thus, electrical stimulation, when applied at the appropriate time and location, can maintain the proper heart rate and/or efficient contraction. This typically is the purpose of a cardiac rhythm/function management device. Further, certain conditions result in heart fibrillation and require a significant electrical stimulus to defibrillate the heart.
Cardiac rhythm/function management devices are widely used for supplanting the heart's natural pacing functions and for defibrillating the heart. The devices may be used to correct various abnormalities, including total or partial heart block, arrhythmias, myocardial infarctions, congestive heart failure, congenital heart disorders, and various other rhythm disturbances within the heart. A cardiac rhythm/function management device typically includes a pulse generator to generate an electrical stimulus and at least one lead to transfer the electrical stimulus to the heart. The electrical stimulus or pacing stimulus may be directed to one or more of the atria and/or ventricles. Further, the leads may also be used to sense for electrical impulses in one or more of the atria and/or the ventricles. A ventricular lead of the cardiac rhythm/function management device may also be used in a defibrillation mode to defibrillate the heart. The cardiac rhythm/function management device typically includes a pacing output circuit designed to selectively deliver stimulus pulses through the lead to one or more electrodes. The pacing output circuit includes a power supply, switches, a pacing charge storage capacitor, and a coupling capacitor, all of which cooperatively operate under the direction of a controller to perform a charging cycle, a pacing cycle, and a recharging cycle.
Regardless of the particular device's configuration (ie: ventricular pacing, atrial pacing, multi-chamber pacing, etc.), cardiac rhythm/function management devices generally operate by stimulating the muscle cells adjacent to the pacing electrode or set of electrodes. The devices provide one or more particular stimuli to the heart that overcomes the abnormality and/or confers an appropriate rhythm. When the strength of the pacing stimulus meets or exceeds a threshold level, the resulting depolarization propagates through the heart. A pacing stimulus that initiates a propagated depolarization is said to have “captured” the heart.
Thus, the success of a pacing stimulus in capturing the heart depends on whether or not the current of the pacing stimulus to the myocardium exceeds the threshold value. The threshold value, frequently referred to as the capture threshold, is related to the electrical field intensity required to alter the permeability of the myocardial cells to thereby initiate cell depolarization. If the local electrical field associated with the pacing stimulus does not exceed the capture threshold, then the permeability of the myocardial cells will not be altered sufficiently to initiate depolarization. If, on the other hand, the local electrical field associated with the pacing stimulus exceeds the capture threshold, then myocardial cell permeability will be sufficiently altered to propagate depolarization.
The capture threshold may vary over time. Changes in the capture threshold may be detected by monitoring the efficacy of stimulating pulses at a given energy level. If capture does not occur at a particular stimulation energy level which previously was adequate to effect capture, then it can be surmised that the capture threshold has increased and that the stimulation energy should be increased. On the other hand, if capture occurs consistently at a particular stimulation energy level over a relatively large number of successive stimulation cycles, then it is possible that the capture threshold has decreased such that the stimulation energy is being delivered at a level higher than necessary to effect capture.
The ability of a pacing device to detect capture is desirable in that delivering stimulation pulses having energy far in excess of the patient's capture threshold is wasteful of the limited power supply. In order to minimize current drain on the power supply, it is desirable to automatically adjust the device to deliver the lowest energy level that will reliably capture the heart. To accomplish this, a process known as “capture verification” must be performed wherein the device monitors to determine whether an evoked depolarization occurs in the pre-selected heart chamber following the delivery of each pacing stimulus pulse to the chamber.
In many cardiac rhythm/function management devices, the device does not determine whether or not a pacing stimulus or set of stimuli have promoted the heart to contract. Efforts have been made to develop a cardiac rhythm/function management device that verifies capture. For example, special sensing amplifiers and algorithms have been added to the device to detect evoked potential presented in an electrode after a stimulus is delivered to that electrode. However, it has been found that such capture verification is difficult due to polarization voltages or “after-potential” which develop at the heart tissue/electrode interface following the application of the stimulation pulses.
The ability to verify capture is further affected by other variables, including patient activity, body position, drugs, lead movement, noise, etc. Because of the multiplicity of variables, the algorithms used to determine capture are frequently complex. The complexity adds to the costs and the likelihood of errors in the software. Also, adding specialized components to verify capture increases the cost and complexity of the pacing apparatus. Therefore, a need exists for an apparatus for sensing ventricular capture that does not require specialized components, such as s
Ding Jiang
Spinelli Julio C.
Yu Yinghong
Zhu Qingsheng
Cardiac Pacemakers Inc.
Layno Carl
Nikolai Thomas J.
Nikolai & Mersereau , P.A.
Webb B.
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