Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-07-31
2002-08-13
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06434428
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to implantable cardiac stimulation devices, including bradycardia and antitachycardia pacemakers, defibrillators, cardioverters and combinations thereof that are capable of measuring physiological data and parametric data pertaining to implantable medical devices. Particularly, this invention relates to a system and method for automating detection of atrial capture in an implantable cardiac stimulation device using far-field signal detection. More specifically, this invention provides for the automatic optimization of far-field R-wave sensing by switching electrode polarity during atrial capture verification.
BACKGROUND OF THE INVENTION
Implantable medical devices, such as pacemakers, defibrillators, and cardioverters (collectively referred to herein as implantable cardiac stimulating devices), are designed to monitor and stimulate the heart of a patient that suffers from a cardiac arrhythmia. Using leads connected to a patient's heart, these devices typically stimulate the cardiac muscles by delivering electrical pulses in response to measured cardiac events that are indicative of a cardiac arrhythmia. Properly administered therapeutic electrical pulses often successfully reestablish or maintain the heart's regular rhythm.
Implantable cardiac stimulating devices can treat a wide range of cardiac arrhythmias by using a series of adjustable parameters to alter the energy, shape, location, and frequency of the therapeutic pulses. The adjustable parameters are usually defined in a computer program stored in a memory of the implantable device. The program (which is responsible for the operation of the implantable device) can be defined or altered telemetrically by a medical practitioner using an external implantable device programmer.
Modern programmable pacemakers, the most commonly used implantable devices, are generally of two types: (1) single-chamber pacemakers, and (2) dual-chamber pacemakers. In a single-chamber pacemaker, the pacemaker provides stimulation pulses to, and senses cardiac activity within, a single-chamber of the heart (e.g. either the right ventricle or the right atrium). In a dual-chamber pacemaker, the pacemaker provides stimulation pulses to, and senses cardiac activity within, two chambers of the heart (e.g. both the right atrium and the right ventricle). The left atrium and left ventricle can also be paced, provided that suitable electrical contacts are effected therewith.
In general, both single and dual-chamber pacemakers are classified by type according to a three letter code. In this code, the first letter identifies the chamber of the heart that is paced (i.e. the chamber where a stimulation pulse is delivered)—with a “V” indicating the ventricle, an “A” indicating the atrium, and a “D” (dual) indicating both the atrium and ventricle. The second letter of the code identifies the chamber where cardiac activity is sensed, using the same letters to identify the atrium or ventricle or both, and where an “O” indicates that no sensing takes place.
The third letter of the code identifies the action or response that is taken by the pacemaker. In general, three types of action or responses are recognized: (1) an Inhibiting (“I”) response, where a stimulation pulse is delivered to the designated chamber after a set period of time unless cardiac activity is sensed during that time, in which case the stimulation pulse is inhibited; (2) a Trigger (“T”) response, where a stimulation pulse is delivered to the designated chamber of the heart a prescribed period after a sensed event; or (3) a Dual (“D”) response, where both the Inhibiting mode and Trigger mode are evoked, inhibiting in one chamber of the heart and triggering in the other.
A fourth letter, “R”, is sometimes added to the code to signify that the particular mode identified by the three letter code is rate-responsive, where the pacing rate may be adjusted automatically by the pacemaker based on one or more physiological factors such as blood oxygen level or the patient's activity level.
Modem pacemakers also have a great number of adjustable parameters that must be tailored to a particular patient's therapeutic needs. One adjustable parameter of particular importance in pacemakers is the pacemaker's stimulation energy. “Capture” is defined as a cardiac response to a pacemaker stimulation pulse. When a pacemaker stimulation pulse stimulates either a heart atrium or a heart ventricle during an appropriate portion of a cardiac cycle, it is desirable to have the heart properly respond to the stimulus provided. Every patient has a “capture threshold” which is generally defined as the minimum amount of stimulation energy necessary to effect capture. Capture should be achieved at the lowest possible energy setting yet provide enough of a safety margin so that, should a patient's threshold increase, the output of an implantable pacemaker, i.e. the stimulation energy, will still be sufficient to maintain capture. Dual-chamber pacemakers may have differing atrial and ventricular stimulation energy that correspond to atrial and ventricular capture thresholds, respectively.
The earliest pacemakers had a predetermined and unchangeable stimulation energy, which proved to be problematic because the capture threshold is not a static value and may be affected by a variety of physiological and other factors. For example, certain cardiac medications may temporarily raise or lower the threshold from its normal value. In another example, fibrous tissue that forms around pacemaker lead heads within several months after implantation may raise the capture threshold.
As a result, some patients eventually suffered from loss of capture as their pacemakers were unable to adjust the pre-set stimulation energy to match the changed capture thresholds. One attempted solution was to set the level of stimulation pulses fairly high so as to avoid loss of capture due to a change in the capture threshold. However, this approach resulted in some discomfort to patients who were forced to endure unnecessarily high levels of cardiac stimulation. Furthermore, such stimulation pulses consumed extra battery resources, thus shortening the useful life of the pacemaker.
When programmable pacemakers were developed, the stimulation energy was implemented as an adjustable parameter that could be set or changed by a medical practitioner. Typically, such adjustments were effected by the medical practitioner using an external programmer capable of communication with an implanted pacemaker via a magnet applied to a patient's chest or via telemetry. The particular setting for the pacemaker's stimulation energy was usually derived from the results of extensive physiological tests performed by the medical practitioner to determine the patient's capture threshold, from the patient's medical history, and from a listing of the patient's medications. While the adjustable pacing energy feature proved to be superior to the previously known fixed energy, some significant problems remained unsolved. In particular, when a patient's capture threshold changed, the patient was forced to visit the medical practitioner to adjust the pacing energy accordingly.
To address this pressing problem, pacemaker manufacturers have developed advanced pacemakers that are capable of determining a patient's capture threshold and automatically adjusting the stimulation pulses to a level just above that which is needed to maintain capture. This approach, called “autocapture”, improves the patient's comfort, reduces the necessity of unscheduled visits to the medical practitioner, and greatly increases the pacemakers battery life by conserving the energy used to generate stimulation pulses.
However, many of these advanced pacemakers require additional circuitry and/or special sensors that must be dedicated to capture verification. This requirement increases the complexity of the pacemaker system and reduces the precious space available within a pacemaker&apo
Levine Paul A.
Sloman Laurence S.
Pacesetter Inc.
Schaetzle Kennedy
LandOfFree
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