Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2002-01-17
2004-09-21
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06795735
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates generally to implantable electronic tissue stimulating systems, and more particularly to a method and apparatus for recording for subsequent read-out physiologic and operational data occurring a predetermined time prior to, during and after detection of a fault condition whereby diagnosis and evaluation of a stimulating system malfunction is enhanced.
II. Discussion of the Prior Art
While the present invention may find application in a variety of implantable medical tissue stimulating systems, the present invention will be described in the environment of cardiac rhythm management devices, including bradycardia and tachycardia pacemakers and automatic implantable defibrillators. However, limitation of the invention to cardiac rhythm management devices should not be inferred in that it may also be used in neural stimulating systems as well.
Pacemakers have advanced from non-programmable, single-chamber, asynchronous devices (VOO) to dual-chamber, multi-mode systems with extensive programmability. For example, state-of-the-art pacemakers include the ability to automatically adjust the pacing rate on the basis of signals that are independent of the intrinsic heart rhythm (DDDR). The analysis/trouble shooting of a pacing system was comparatively easy during the early days of pacing, whereas the challenge in evaluating the modern pacemaker has increased to a degree that is concordant with the sophistication of the current devices.
To facilitate these evaluations, manufacturers have incorporated a multitude of diagnostic tools in their cardiac rhythm management products. The various diagnostic tools commonly complement one another, either eliminating the need for ancillary testing or providing an indication of direction for additional testing. Occasionally, a given feature provides absolute unique information that is not readily available by any other technique. These tools, which are integral to the implanted device, can be accessed by an external programmer, via a telemetry link. To take advantage of these diagnostic features and to determine the appropriate function of a stimulating system, the clinician must have an in-depth knowledge of the system components, including not only the pulse generator employed, but also the medical leads used to couple the pulse generator to the target tissue, programmed parameters, sensors, as well as the patient's physiology.
State-of-the-art implantable medical stimulators commonly incorporate a telemetry link allowing transmission of information or data between the implanted device and an external programmer/monitor. Such a telemetry link provides the ability to non-invasively change the functional parameters of the implanted device by coded commands transmitted to it from the external programmer and the ability of the implanted device to, in turn, transmit operational and physiologic data back to the external programmer/monitor for analysis by trained medical personnel. Bi-directional telemetry allows the implanted unit to be interrogated about its program parameters when the patient is seen during follow-up or is evaluated for suspected pacing system malfunction. Without this feature, there would be no way to determine the current settings of a device for features other than rate and pulse width. It also makes the retrieval of detailed data collected by the pacemaker in its various event counters feasible.
The introduction of dual chamber pacing has significantly increased the level of complexity of the paced rhythm. The interaction between two or more channels of the pacing system with the spontaneous rhythms occurring in either the atria or ventricles added to the potential for confusion. The addition of rate-modulated pacing (i.e., allowing the pacemaker to respond also to one or more sensor signals that are invisible on a surface ECG) further contributes to the challenge of interpreting the paced ECG because these sensor signals are frequently invisible on the surface ECG.
Thus, in current, state-of-the-art cardiac rhythm management devices, interpretation of a paced rhythm requires knowledge of the basic timing intervals. A variety of refractory periods, including post-ventricular atrial refractory period (PVARP), post-ventricular atrial blanking period, ventricular refractory period, ventricular blanking period, and paced and sensed atrioventricular (AV) intervals, must also be considered. Certain of these intervals vary depending on the instantaneous rate. Hence, the clinician needs to be aware of a number of device-specific responses to protect the system from a variety of anticipated, but undesirable behaviors or clinical events. These include cross-talk, a premature ventricular beat initiating a pacemaker-mediated tachycardia, mode switching, and multiblock upper rate behavior.
To facilitate interpretation of the paced rhythm, increasing numbers of pacing systems incorporate the ability to transmit information regarding real-time pacing system behavior to the external programmer on a virtually continual basis and to display this information on a screen or other recording system. Both paced and sensed events are communicated to the programmer. Displayed as a series of positive or negative marks, with or without alpha
umeric annotation, these are generally termed event markers. These event markers are generally superimposed above or below a simultaneously recorded surface ECG. The simultaneous ECG and markers allow the clinician to correlate the behavior of the pacemaker directly with the patient's rhythm to determine whether the system is functioning properly.
Most prior art implantable medical devices having event marker telemetry is limited to real-time recordings. The markers must be telemetered from the implanted device to the programmer while the rhythm is being actively monitored. Neither the pacemaker nor the programmer can retrospectively provide markers for previously recorded rhythms. If the implanted device is responding to events that are not visible on the surface ECG, the event marker simply confirms this fact, but does not identify the specific signal. An evaluation of sensed, but otherwise invisible events, requires electrogram (EGM) telemetry or an invasive procedure to record the signal from the implanted lead. More recently, implantable pacemakers have been introduced that have the capability of storing event markers with or without EGMs. These may be stored by the use of a patient trigger, such as the application of an external magnet proximate the site of the implanted device or a device triggered event.
As those skilled in the art appreciate, the recorded signal that enters the pacemaker's sense amplifier by way of the electrodes located within or on the heart is termed an intracardiac EGM. It is composed of a number of elements. The portion that is sensed by the pacemaker is termed the intrinsic deflection and reflects the rapid deflection that occurs when the wave of cardiac depolarization passes by the electrode. The intrinsic deflection can be characterized by both the amplitude and slew rate. The other portion of the cardiac depolarization, as reflected by the EGM, are termed the extrinsic deflection.
Real-time telemetry of event markers and EGM waveforms only allows the physician to analyze the behavior of the pacing system when the patient is in the physician's office or clinic while these diagnostics are being accessed with the programmer. This is impractical over a long period. Long-term monitoring of pacing system behavior requires either a Holter monitor, which is expensive and cumbersome, or event counter telemetry, depending on the degree of precision that is desired. Implantable medical devices, with microprocessor-based controllers and significant random access memory (RAM), can store selected EGMs as well as event markers when triggered by the patient or by a predefined set of circumstances. However, due to memory size constraints, it is impossible to continuously store EGM waveforms and event marker
Cardiac Pacemakers Inc.
Getzow Scott M.
Nikolai Thomas J.
Nikolai & Mersereau , P.A.
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