Medical device

Details Medical device Medical device

1998-11-13

2001-07-10

Getzow, Scott M. (Department: 3737)

Surgery: light, thermal, and electrical application

Light, thermal, and electrical application

Electrical therapeutic systems

C607S017000

Reexamination Certificate

active

06259948

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to implantable medical devices for managing cardiac rhythm. More particularly the invention relates to a device which alters its operation based upon measured sensor variance. The invention is illustrated in the context of a pacemaker for treating episodes of vasovagal syncope.
BACKGROUND OF THE INVENTION
A prolonged period of asystole is an unambiguous indication for pacing. The more complex issue is what pacing rate is appropriate for the heart and when and under what circumstances should the pacing therapy stop. The traditional demand pacemaker sensed R-wave intervals on a beat-to-beat basis and paced only when the underlying rhythm was below a so called escape interval. Modern therapies for bradycardia are much more complex. Many modern pacemakers have sensors. These sensors provide more information about the cardiovascular state of the patient and efforts are being made to use this additional information to improve the efficacy of pacing therapy. These improvements also expand the indications for pacing. At present, pacing therapies have been proposed for treating vasovagal syncope.
Vasovagal syncope, also called neurally-mediated or neurocardiogenic syncope, is a relatively common entity. It also goes by the name “common faint.” For most individuals who are subject to this entity, it occurs very infrequently and can be managed by sitting or lying down when warning symptoms, such as lightheadedness, sweating and nausea, occur. When individuals experience repeated episodes without the usual warning signs, then pharmacologic or pacing therapy is required.
The common “faint” is an example of an interaction between the automatic nervous system and the cardiovascular system. There are several types of faints of which vasovagal syncope is one. Within vasovagal syncope, there are subsets which differ in detail. The typical episode involves a concurrent and precipitous drop in both blood pressure and heart rate. For an ambulatory subject, the resultant sudden loss of cardiac output can result in a potentially injurious fall.
Drugs have been considered the first line of therapy for many of these patients. However the chronic use of drugs for rare episodes of vasovagal syncope is problematic. More recently pacing therapies have been proposed for these patients. For example DDI pacing with hysteresis has been explored as a therapy for this patient group. With DDI hysteresis pacing, a patient with normal sinus function can remain in sinus rhythm most of the time. Vasovagal events which trigger the hysteresis escape interval result in pacing at a relatively high rate to compensate for both asystole and vasodilatation.
It is also possible to trigger a pacing therapy based upon a disease specific rate drop algorithm. See for example U.S. Pat. No. 5,501,701 to Shelton et al. and U.S. Pat. No. 5,501,701 to Markowitz et al. As taught by the patents, a drop in heart rate over a relatively short interval invokes pacing at a programmed higher pacing rate. However, the conventional rate drop algorithm requires several beats before the pacemaker intervenes which is undesirable for a presyncopal patient. Both conventional DDI with hysterisis pacing and the rate drop algorithm are unable to reliably distinguish pathologic from physiologic rate drops. Therefore, the prior pacemakers may pace inappropriately under some circumstances which is undesirable.
SUMMARY OF THE INVENTION
In the present invention certain sensor variance data is used to guide therapy and to alter the behavior of the device to treat vasovagal syncope. This is one example of a broader invention which uses sensor variance data from one or more sensors to control the device. The illustrative pacemaker of this invention uses both measured heart rate and an independent physiologic sensor operating together to determine the occurrence of vasovagal syncope. If an episode of a treatable syncope is detected, the pacemaker quickly elevates the pacing rate to support the patient during the episode.
In operation, the device immediately intervenes to pace the heart at a selected rate if the patient exhibits asystole while the patient's physical activity index indicates a normal physical activity state. This response provides sufficient cardiac output to interrupt the episode. In this illustrative embodiment, two criteria must be met before the therapy is invoked. The first criteria is a characteristic low heart rate derived from the pacemakers sense amplifier and escape interval timer structures. The second criteria is normal patient activity derived from a complimentary physiologic sensor such as physical activity.
The illustrative pacemaker monitors the intrinsic heart rate with the escape interval timer and sense amplifier. The device monitors the metabolic state of the patient by measuring the variance of the patient's activity level. If the pacemaker “escapes” and generates a pace event, then the patient is experiencing asystole which is one example of a sufficiently low heart rate. Next, the pacemaker interrogates the sensor variance. If the sensor variance measurement indicates a normally active patient, then the pacemaker intervenes at a selected rate to treat the declared vasovagal event. In the preferred method, the pacemaker tests the patient activity state after the escape interval times out. However, this desirable sequence is not critical. The principle advantage of the use of the sense amplifier and escape interval timer as one element of the method is that these structures measure the adequacy of the heart rate on a beat-to-beat basis. The principle advantage of the use of sensor variance as an indicator of metabolic state is the high specificity of the measure in distinguishing slowly varying low activity periods like sleep from other more ambiguous metabolic states. Together sensor variance and sensed heart rate permit a rapid accommodation of a “fainting” spell.
Although measured intrinsic heart rate and patient activity variance are used to illustrate this invention, other complementary sensor pairings are contemplated within the scope of the invention as well.
Exemplary pairings include sensors for patient position combined with heart rate and blood pressure combined with heart rate. It should also be understood that the method can be extended to more than one sensor and the method can be used to alter other therapeutic aspects of the device to treat other disorders. It should also be noted that sensor variance can alter other therapy or device parameters. The examples of rate selection and A-V delay interval should not be regarded as limiting.


REFERENCES:
patent: 5342404 (1994-08-01), Alt et al.
patent: 5417714 (1995-05-01), Levine et al.
patent: 5464434 (1995-11-01), Alt
patent: 5472453 (1995-12-01), Alt
patent: 5476483 (1995-12-01), Bornzin et al.
patent: 5501701 (1996-03-01), Markowitz et al.
patent: 5514162 (1996-05-01), Bornzin et al.
patent: 5593431 (1997-01-01), Sheldon
patent: 5676483 (1997-10-01), Koubek
patent: 5891176 (1999-04-01), Bornzin
P.A. Levine, M.D. “New Algorithms: Automatic Mode Switching Neurocardiogenic, Syncope, Sleep Mode, AV/PV Hysteresis, Autocapture, and Others,” pp. 1-12, Pacesetter, Inc., a St. Jude Medical Company, (Mar. 1997).*
A. Fitzpatrick, et al “Recurrent Symptoms after Ventricular Pacing In Unexplained Syncope,” pp. 619-624, PACE, vol. 13 (5/1990).*
A. Fitzpatrick, et al “Dual-Chamber Pacing Aborts Vasovagal Syncope Induced by Head-Up 60 Degree Tilt,” pp. 13-19,PACE, vol. 14(1/1991).*
D. Samoil, et al “Comparision of Single and Dual Chamber Pacing Techniques in Prevention of Upright Tilt Induced Vasovagal Syncope,” pp. 36-41, EUR.J.C.P.E., vol. 3, No. 1 (1993).*
S.S. Jasbir, M.D., et al. “Comparision of Cardiac Pacing with Drug Therapy in the Treatment of Neurocardiogenic (Vasovagal) Syncope with Bradycardia or Asystole,” pp. 1085-1090, The New England Journal of Medicine, vol. 328 (4/1993).*
W.N. Kapoor, et al “Upright tilt Testing in Evaluating Syncope: A Comprehensive Literature Review,” pp. 78-88, The American

Affiliated with

Also associated with

Rating

Medical device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Medical device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Medical device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2478181