Implantable medical device incorporating integrated circuit...

Details Implantable medical device incorporating integrated circuit... Implantable medical device incorporating integrated circuit...

2000-12-05

2003-03-25

Layno, Carl (Department: 3762)

Surgery: light, thermal, and electrical application

Light, thermal, and electrical application

Electrical therapeutic systems

C607S060000

Reexamination Certificate

active

06539253

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to implantable medical devices (IMDs) having sense amplifiers for sensing physiologic signals and parameters, RF telemetry capabilities for uplink transmitting patient data and downlink receiving programming and interrogation commands to and from an external programmer or other medical device, and other electronic circuitry susceptible to electromagnetic interference (EMI), and more particularly to miniaturized, integrated circuit notch filters for use in such circuitry to reject EMI.
BACKGROUND OF THE INVENTION
A wide variety of IMDs that employ electronic circuitry for providing electrical stimulation of body tissue and/or monitoring a physiologic condition are known in the art. A number of IMDs of various types are known in the art for delivering electrical stimulating pulses to selected body tissue and typically comprise an implantable pulse generator (IPG) for generating the stimulating pulses under prescribed conditions and at least one lead bearing a stimulation electrode for delivering the stimulating pulses to the selected tissue. For example, cardiac pacemakers and implantable cardioverter-defibrillators (ICDs) have been developed for maintaining a desired heart rate during episodes of bradycardia or for applying cardioversion or defibrillation therapies to the heart upon detection of serious arrhythmias. Other nerve, brain, muscle and organ tissue stimulating medical devices are also known for treating a variety of conditions.
There are at least four paramount considerations or goals that are taken into account in the design and fabrication of IMDs. First, the IMD operation must be safe, reliable and effective in delivering a therapy and/or monitoring a physiologic condition. Second, the IMD must be long lived and be cost-effective relative to alternative therapies. Third, the IMD must be reasonably miniaturized so that it can be implanted without being uncomfortable and cosmetically distressing to the patient. Finally, each new generation of IMD must satisfy the first three considerations while providing an ever increasing number of performance features and functions that are clinically beneficial to the patient and useful to the medical community.
For example, over the past 20 years, ICD IPGs have evolved, as described in some detail in commonly assigned U.S. Pat. No. 5,265,588, from relatively bulky, crude, and short-lived ICD IPGs simply providing high energy defibrillation shocks to complex, long-lived, and miniaturized ICD IPGs providing a wide variety of pacing, cardioversion and defibrillation therapies. Numerous improvements have been made in cardioversion/defibrillation leads and electrodes that have enabled the cardioversion/defibrillation energy to be precisely delivered about selected upper and lower heart chambers and thereby dramatically reducing the delivered shock energy required to cardiovert or defibrillate the heart chamber. Moreover, the high voltage output circuitry has been improved in many respects to provide monophasic, biphasic, or multiphase cardioversion/defibrillation shock or pulse waveforms that are efficacious, sometimes with particular combinations of cardioversion/defibrillation electrodes, in lowering the required shock energy to cardiovert or defibrillate the heart.
The first implanted automatic implantable defibrillator (AID) IPG housing disclosed in U.S. Pat. No. 4,254,775 was very large and had to be implanted in a patient's abdominal region. Since that time, the ICD IPGs have been reduced in size while their complexity has been vastly increased. Battery energy requirements for powering both the low voltage integrated circuits (ICs) and for providing the cardioversion/defibrillation shocks have been reduced while battery energy density has been increased and battery configuration made more conforming to the interior space of the ICD IPG housing. Miniaturized, flat high voltage output capacitors that can be shaped to fit the allocated housing space and miniaturized high voltage switching components have been developed and employed. All of these improvements, together with the above-mentioned cardioversion/defibrillation improvements have contributed to a significant reduction in the volume of the ICD IPG housing without sacrificing longevity and capabilities. Similar improvements in reducing housing volume have been made in other IMD IPGs, particularly implantable cardiac pacemakers, nerve stimulators and monitors, over the same time period.
Such ICDs as well as implantable cardiac pacemakers and implantable cardiac monitors have been clinically employed or proposed that include capabilities of sensing one or more physiologic parameter and triggering delivery of a therapy and/or storage of physiologic data. With the exception of certain subcutaneously implanted monitors, all such IMDs comprise a hermetically sealed IPG housing containing the battery and electronic circuitry that is coupled through an elongated lead to a remote sense/stimulation electrode or physiologic sensor located typically in a heart chamber, heart muscle or blood vessel. Such physiologic parameters include electrical heart signals and other physiologic parameters, e.g. blood pressure at various locations of the heart and vascular system, respiration, blood temperature, blood pH, and blood gas concentrations.
The sensing of these physiologic parameters involves the detection of minute electrical signals in an inherently electrically noisy environment including both ambient EMI in the patient's environment as well as electrical signals either generated in the body or in the sensor due to patient motion or respiration or the like. Sources of EMI include metal detectors such as are used in airports, welders, radio transmitters (broadcast and two-way), cellular phones, microwave ovens, electronic article surveillance (EAS) systems, etc. The electrical signals conducted to the implanted device from the electrodes implanted in the heart may thus include EMI superimposed on the heart's natural cardiac signal. In dual chamber cardiac pacing and ICDs, it is necessary to sense and discriminate between P-waves and R-waves despite the presence of EMI and various pathologic cardiac conditions that can cause the sense amplifier to oversense or undersense these particular signals. It is currently the practice to start blanking periods upon delivery of a pacing pulse in one heart chamber to avoid saturating the sense amplifier circuitry and refractory periods that are used to disregard sense events representing artifacts of the induced depolarization or a closely timed depolarization in another heart chamber. To avoid sensing EMI, it has been the practice to low pass filter the sense amplifier input and to programmably adjust the sensitivity of the sense amplifier to a level that renders it insensitive to low level EMI but capable of sensing the peak voltages of the signal of interest. Descriptions of various sensing windows and noise rejection techniques for implantable and external pacemakers that have been employed or proposed are set forth in U.S. Pat. Nos. 4,357,943, 4,390,020, 4,401,119, 4,436,093, 4,596,292, and 5,188,117.
Although the IMD sense amplifiers are filtered to attenuate noise superimposed on a cardiac signal, in some situations the noise component may be such that the filters cannot adequately eliminate the noise. If a patient with an IMD walks through a metal detector, for example, the resulting EMI signal may overwhelm the cardiac signal picked up by the electrodes. Although the IMD may be able to determine that it is receiving an excessive amount of noise, the IMD may be unable to extract the true cardiac signal from the noise. Because the true cardiac electrical signal cannot be accurately ascertained, the IMD's operating system cannot determine when the vulnerable period of each cardiac cycle is occurring. Such implantable cardiac pacemakers and ICDs having a pacing capability are therefore often supplied with a “reversion mode” of operation that will cause no harm to the pa

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