Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-10-30
2004-09-21
Layno, Carl H. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S018000, C600S513000, C600S515000
Reexamination Certificate
active
06795732
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to implantable medical devices (IMDs) that deliver therapies to the heart and/or monitor cardiac physiologic parameters that, in particular, involves implantation of sonomicrometer piezoelectric crystals in or in relation to the heart chambers to detect occurrence of and magnitudes of the mechanical movements of the heart chambers.
BACKGROUND OF THE INVENTION
A wide variety of IMDs have been developed over the years or are proposed that provide cardiac rhythm management of disease states manifested by cardiac rhythm disorders and heart failure. Implantable pacemakers have been developed that monitor and restore heart rate and rhythm of hearts that suffer bradycardia (too-slow or irregular heart rate), tachycardia (regular but excessive heart rate) and heart failure (the inability of the heart to maintain its workload of pumping blood to the body). Implantable cardioverter-defibrillators (ICDs) have been developed that deliver programmed cardioversion/defibrillation energy level shocks to the atria in response to detection of atrial fibrillation (rapid, uncontrolled heartbeats in the atria) or to the ventricles in response to life-threatening, ventricular tachyarrhythmias. Typically, single and dual chamber bradycardia pacing systems are also incorporated into ICDs. Implantable diagnostic and monitoring systems are targeted for an emerging field that may change the way medicine is practiced. These systems typically monitor patients in their home environments, providing treating physicians with more complete information about their patients changing cardiac conditions. Proposals have been made to incorporate capabilities of pervasive computing into such therapy delivery and monitoring IMDs and the external medical devices employed to communicate with the Ms and remote locations via the worldwide web.
These cardiac IMDs have traditionally employed capabilities of sensing the electrogram of the heart manifested by the cyclic PQRST waveform at one or more location principally to detect the contraction of the atria as evidenced by a P-wave meeting P-wave detection criteria of an atrial sense amplifier and/or the contraction of the ventricles as evidenced by an R-wave meeting R-wave detection criteria of a ventricular sense amplifier. The timing of detected atrial and ventricular sense events is used to ascertain normal sinus rhythm or the presence of bradycardia, tachycardia or tachyarrhythmia in the monitoring and therapy delivery contexts.
Among the earliest developed cardiac rhythm management IMDs were simple, single chamber, fixed rate pacing systems comprising an implantable pulse generator (IPG) and a lead bearing one or more pace/sense electrode adapted to be placed in contact with the heart chamber to be paced (commonly referred to as pacemakers) that provided fixed rate pacing to a single heart chamber when the heart rate fell below a lower rate limit. The earliest ICDs delivered a defibrillation shock to the ventricles when heart rate and regularity or morphology criteria were met. It was proposed that blood pressure sensors or accelerometers be incorporated so that the absence of mechanical heart function during fibrillation could also be detected to confirm the tentative determination of fibrillation before a shock therapy was delivered, but suitable sensors were not available.
Over the years, such pacemakers and ICDs evolved in complexity and capabilities as described in greater detail herein. Increasingly complex signal processing algorithms were developed and implemented in the effort to glean as much information as possible about the instantaneous state of the heart in order to provide the appropriate therapy to restore heart rhythm and to avoid mis-delivery of a therapy that would potentially harm the patient.
The accuracy of detection of atrial and ventricular sense events by sense amplifiers can deteriorate due to a wide variety of effects that distort the signal applied to the sense amplifiers such that the P-wave or R-wave is either not detected (an “undersensing” condition) or an atrial or ventricular sense event is mistakenly declared (an “oversensing” condition). The ability to distinguish a true sense event in a distorted signal is also complicated by the necessity of protecting sense amplifier circuitry following delivery of a pacing pulse or cardioversion/defibrillation shock. Conventionally, the sense amplifier circuits are disconnected from the sense electrodes during a blanking time period timed out following delivery of a pacing pulse or cardioversion/defibrillation shock to protect the circuitry. Longer refractory time periods are also timed out following delivery of a pacing pulse or cardioversion/defibrillation shock during which any sense event is declared to be refractory to avoid inappropriately restarting timing periods.
It has been recognized that other indicators of heart function, particularly indicators related to mechanical heart function, would be of great value in augmenting the algorithms that process atrial and ventricular sense events in order to resolve ambiguities that can inherently arise. It is also desirable to be able to ascertain whether a delivered pacing pulse has “captured” the heart, i.e., caused the heart chamber to contract. Further more, it is desirable to be able to rapidly determine that a delivered cardioversion/defibrillation shock has effectively terminated a tachyarrhythmia and that the heart has returned to normal sinus rhythm.
There are other situations where indicators related to mechanical heart function incorporated into pacing systems would be useful. Patients suffering from chronic heart failure or congestive heart failure (CHF) manifest an elevation of left ventricular end-diastolic pressure, according to the well-known heterometric autoregulation principles espoused by Frank and Starling. This may occur while left ventricular end-diastolic volume remains normal due to a decrease in left ventricular compliance concomitant with increased ventricular wall stiffness. CHF due to chronic hypertension, ischemia, infarct or idiopathic cardiomyopathy is associated with compromised systolic and diastolic function involving decreased atrial and ventricular muscle compliance. These may be conditions associated with chronic disease processes or complications from cardiac surgery with or without specific disease processes. Most heart failure patients suffer from symptoms which may include a general weakening of the contractile function of the cardiac muscle, attendant enlargement thereof, impaired myocardial relaxation and depressed ventricular filling characteristics in the diastolic phase following contraction. Pulmonary edema, shortness of breath, and disruption in systemic blood pressure are associated with acute exacerbations of heart failure.
These disease processes lead to insufficient cardiac output to sustain mild or moderate levels of exercise and proper function of other body organs, and progressive worsening eventually results in cardiogenic shock, arrhythmias, electromechanical dissociation, and death. In order to monitor the progression of the disease and to assess efficacy of prescribed treatment, it is necessary to obtain accurate measures of the heart geometry, the degree of heart enlargement, and the mechanical pumping capability of the heart, e.g., ejection fraction, under a variety of metabolic conditions the patient is likely to encounter on a daily basis. These parameters are typically measured through the use of external echocardiogram equipment in the clinical setting. However, the measurement procedure is time consuming to perform for even a resting patient and cannot be practically performed replicating a range of metabolic conditions. Typically, the echocardiography procedure is performed infrequently and months or years may lapse between successive tests, resulting in a poor understanding of the progress of the disease or whether or not intervening drug therapies have been efficacious. Quite often, only anecdotal evidence from the
Combs William J.
Lipson David
Stadler Robert W.
Layno Carl H.
Medtronic Inc.
Soldner Michael C.
Wolde-Michael Girma
LandOfFree
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