Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-04-27
2004-06-22
Bennett, Henry (Department: 3742)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S014000, C607S004000, C607S005000
Reexamination Certificate
active
06754529
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to implantable medical devices and methods of cardiac stimulus. More particularly, the present invention pertains to implantable medical pacing devices and methods that employ ventricular safety pacing (VSP) in cardiac stimulation.
BACKGROUND OF THE INVENTION
Generally, in the heart, the sinus (or sinoartrial (SA)) node typically located near the junction of the superior vena cava and the right atrium) constitutes the primary natural pacemaker by which rhythmic electrical excitation is developed. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers (or atria) at the right and left sides of the heart. In response to excitation from the SA node, the atria contract, pumping blood from those chambers into the ventricles through the atrioventricular (AV) node, and via a conduction system comprising the bundle of His, or common bundle, the right and left bundle branches, and the Purkinje fibers. The transmitted impulse causes the ventricles to contract with the right ventricle pumping unoxygenated blood through the pulmonary artery to the lungs. The blood oxygenated by the lungs is carried via the pulmonary veins to the left atrium. The left ventricle then pumps oxygenated (arterial) blood through the aorta and the lesser arteries throughout the body.
The above action is repeated in a rhythmic cardiac cycle in which the atrial and ventricular chambers alternately contract and pump, and then relax and fill. One-way valves, between the atrial and ventricular chambers on the right and left sides of the heart, and at the exits of the right and left ventricles, prevent backflow of the blood as it moves through the heart and the circulatory system. This sinus node is spontaneously rhythmic, and the cardiac rhythm it generates is termed sinus rhythm. This capacity to produce spontaneous cardiac impulses is called rhythmicity. Some other cardiac tissue possess rhythmicity and hence constitute secondary natural pacemakers, but the sinus node is the primary natural pacemaker because it spontaneously generates electrical pulses at a faster rate. The secondary pacemakers tend to be inhibited by the more rapid rate at which impulses are generated by the sinus node.
Disruption of the natural pacemaking and propagation system as a result of aging or disease is commonly treated by artificial cardiac pacing, by which rhythmic electrical discharges are applied to the heart at a desired rate from an artificial pacemaker. A pacemaker is a medical device which delivers electrical pulses to an electrode that is implanted adjacent to or in the patient's heart to stimulate the heart so that it will contract and beat at a desired rate. If the body's natural pacemaker performs correctly, blood is oxygenated in the lungs and efficiently pumped by the heart to the body's oxygen-demanding tissues. However, when the body's natural pacemaker malfunctions, an implantable pacemaker often is required to properly stimulate the heart.
Implantable pacemakers are typically designed to operate using various different response methodologies, such as, for example, nonsynchronous or asynchronous (fixed rate), inhibited (stimulus generated in the absence of a specified cardiac activity), or triggered (stimulus delivered in response to a specific hemodynamic parameter). Generally, inhibited and triggered pacemakers may be grouped as “demand”-type pacemakers, in which a pacing pulse is only generated when demanded by the heart. To determine when pacing is required by the pacemaker, demand pacemakers may sense various conditions such as heart rate, physical exertion, temperature, and the like. Moreover, pacemaker implementations range from the simple fixed rate, single chamber device that provides pacing with no sensing function, to highly complex models that provide fully-automatic dual chamber pacing and sensing functions. For example, such multiple chamber pacemakers are described in U.S. Pat. No. 4,928,688 to Mower entitled “Method and Apparatus for Treating Hemodynamic Dysfunction,” issued May 29, 1990; U.S. Pat. No. 5,792,203 to Schroeppel entitled “Universal Programmable Cardiac Stimulation Device,” issued Aug. 11, 1998; U.S. Pat. No. 5,893,882 to Peterson et al. entitled “Method and Apparatus for Diagnosis and Treatment of Arrhythmias,” issued Apr. 13, 1999; and U.S. Pat. No. 6,081,748 to Struble et al. entitled “Multiple Channel, Sequential Cardiac Pacing Systems,” issued Jun. 27, 2000.
For example, a DDD pacer paces either chamber (atrium or ventricle) and senses in either chamber. Thus, a pacer in DDD mode, may pace the ventricle in response to electrical activity sensed in the atrium. Further, for example, a pacer operating in VVI mode, paces and senses in the ventricle, but its pacing is inhibited by spontaneous and electrical activity of the ventricle (i.e., intrinsic ventricular activity or events, wherein the ventricle paces itself naturally).
As such, it may be desired to sense in one cardiac chamber (e.g., detect electrical activity represented of contraction of a chamber and referred to as a “sensed event”) and, in response, pace (referred to as a “paced event”) in the same or different chamber. It also may be desired to pace at two electrode locations following a sensed event at one of the pacing electrodes or at a different electrode. For example, patients are often treated with pacemakers that include an electrode in each of the two atrial chambers and a third electrode in the right ventricle. Both atrial chambers usually are paced following a sensed event in either chamber.
Further, bi-ventricular pacing devices are also used for treatment of patients. For example, in such a bi-ventricular pacing apparatus, multiple implantable leads having electrodes associated with a part thereof are implanted to the respective chambers of a patient's heart and coupled to respective circuitry for forming multiple channels for pacing and sensing, e.g., left ventricular channel, right atrial channel, etc. Such an exemplary implantable, four-channel cardiac pacemaker is described in U.S. Pat. No. 6,070,101 to Struble et al. entitled “Multiple Channel, Sequential Cardiac Pacing Systems,” issued May 30, 2000. For example, the distal end of a right atrial lead is attached to the right atrial wall and a right ventricular lead is passed through a vein into the right atrial chamber of the heart and into the right ventricle where its distal electrodes are fixed. Another lead is passed through a vein into the right atrial chamber of the heart, into the coronary sinus (CS), and then inferiorly into the great vein to extend a distal pair of left ventricular pace/sense electrodes alongside the left ventricular chamber and leave a proximal pair of left atrial pace/sense electrodes adjacent the left atrium. With such electrode placement, pacing and sensing can be performed in each chamber of the heart, enabling bi-ventricular pacing. For example, such bi-ventricular pacing may be performed following atrial sensed events or atrial paced events.
Typically in such types of pacing apparatus, if an intrinsic or pacing pulse occurs in one of the chambers, for example, the atrium, then this activity may be erroneously sensed in the other chambers due to cross-talk. In order to eliminate this type of error, in the past, pacemakers have been provided with blanking periods for blanking the sensor in one channel after a pacing pulse occurs in the other. This blanking period is usually referred to as the cross-channel blanking period. Following the blanking period, an alert period is normally designated during which the cardiac chamber of interest is monitored for intrinsic activity. If no such activity is sensed by the end of this alert, then a pacing pulse is applied to the chamber. However, one problem with such pacemakers and the use of blanking channels has been selecting the duration of the blanking period for a particular channel properly. If the blanking period is too short, a cross-channel artifact could be interpr
Bennett Henry
Dahbour Fadi H.
McDowall Paul H.
Medtronic Inc.
Wolde-Michael Girma
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