The use of nerve stimulation for treating and controlling a variety of medical, psychiatric, and neurological disorders has seen significant growth over the last several decades, including for treatment of heart conditions. In particular, stimulation of the vagus nerve (the tenth cranial nerve, and part of the parasympathetic nervous system) has been the subject of considerable research. The vagus nerve is composed of somatic and visceral afferents (inward conducting nerve fibers, which convey impulses toward the brain) and efferents (outward conducting nerve fibers, which convey impulses to an effector to regulate activity such as muscle contraction or glandular secretion).
The rate of the heart is restrained in part by parasympathetic stimulation from the right and left vagus nerves. Low vagal nerve activity is considered to be related to various arrhythmias, including tachycardia, ventricular accelerated rhythm, and rapid atrial fibrillation. Stimulation of the vagus nerve has been proposed as a method for treating various heart conditions, including atrial fibrillation and heart failure. By artificially stimulating the vagus nerves, it is possible to slow the heart, allowing the heart to more completely relax and the ventricles to experience increased filling. With larger diastolic volumes, the heart may beat more efficiently because it may expend less energy to overcome the myocardial viscosity and elastic forces of the heart with each beat.
Atrial fibrillation (AF) is a condition in which the atria of the heart fail to continuously contract in synchrony with the ventricles of the heart. During fibrillation, the atria undergo rapid and unorganized electrical depolarization, so that no contractile force is produced. The ventricles, which normally receive contraction signals from the atria (through the atrioventricular (AV) node), are inundated with signals, typically resulting in a rapid and irregular ventricular rate. Because of this rapid and irregular rate, the patient suffers from reduced cardiac output, a feeling of palpitations, and/or increased risk of thromboembolic events.
Current therapy for atrial fibrillation includes cardioversion and rate control. Cardioversion is the conversion of the abnormal atrial rhythm into normal sinus rhythm. This conversion is generally achieved pharmacologically or electrically. Rate control therapy is used to control the ventricular rate, while allowing the atria to continue fibrillation. This is generally achieved by slowing the conduction of signals through the AV node from the atria to the ventricles.
Bilgutay et al., in “Vagal tuning: a new concept in the treatment of supraventricular arrhythmias, angina pectoris, and heart failure,” J. Thoracic Cardiovas. Surg. 56(1):71-82, July, 1968, which is incorporated herein by reference, studied the use of a permanently-implanted device with electrodes to stimulate the right vagus nerve for treatment of supraventricular arrhythmias, angina pectoris, and heart failure. Experiments were conducted to determine amplitudes, frequencies, wave shapes and pulse lengths of the stimulating current to achieve slowing of the heart rate. The authors additionally studied an external device, triggered by the R-wave of the electrocardiogram (ECG) of the subject to provide stimulation only upon an achievement of a certain heart rate. They found that when a pulsatile current with a frequency of ten pulses per second and 0.2 milliseconds pulse duration was applied to the vagus nerve, the heart rate could be decreased to half the resting rate while still preserving sinus rhythm. Low amplitude vagal stimulation was employed to control induced tachycardias and ectopic beats. The authors further studied the use of the implanted device in conjunction with the administration of Isuprel, a sympathomimetic drug. They found that Isuprel retained its inotropic effect of increasing contractility, while its chronotropic effect was controlled by the vagal stimulation: “An increased end diastolic volume brought about by slowing of the heart rate by vagal tuning, coupled with increased contractility of the heart induced by the inotropic effect of Isuprel, appeared to increase the efficiency of cardiac performance” (p. 79).
Svedjeholm R et al., in “Predictors of atrial fibrillation in patients undergoing surgery for ischemic heart disease,” Scand Cardiovasc J 34:516-21 (2000), which is incorporated herein by reference, analyze risk factors for postoperative AF in a uniformly managed cohort of patients. The authors report that the incidence of AF was 29.1% in patients undergoing isolated CABG and 48.6% after CABG+valve procedures.
Cummings J E et al., in “Preservation of the anterior fat pad paradoxically decreases the incidence of postoperative atrial fibrillation in humans,” J Am Coll Cardiol 43(6):994-1000 (2004), which is incorporated herein by reference, describe a study they performed to determine if parasympathetic nerves in the anterior fat pad can be stimulated at the time of coronary artery bypass graft (CABG) surgery, and if dissection of this fat pad decreases the incidence of postoperative atrial fibrillation (AF). The authors report that direct stimulation of the anterior epicardial fat pad slows sinus cycle length, and that this parasympathetic effect is eliminated with fat pad dissection. They conclude that the preservation of the human anterior epicardial fat pad during CABG surgery decreases the incidence of postoperative AF.
An article by Moreira et al., entitled, “Chronic rapid atrial pacing to maintain atrial fibrillation: Use to permit control of ventricular rate in order to treat tachycardia induced cardiomyopathy,” Pacing Clin Electrophysiol, 12(5):761-775 (May 1989), which is incorporated herein by reference, describes the acute induction of atrial fibrillation with rapid atrial pacing, and an associated reduction in ventricular rate with digitalis therapy. Different treatment protocols are described to induce and maintain atrial fibrillation, in order to bring a patient with NYHA class III-IV congestive heart failure to a more moderate NYHA class II.
An article by Preston et al., entitled, “Permanent rapid atrial pacing to control supraventricular tachycardia,” Pacing Clin Electrophysiol, 2(3):331-334 (May 1979), which is incorporated herein by reference, describes a patient who had continuous supraventricular tachycardia with a ventricular rate of about 170. The arrhythmia was refractory to drugs and DC countershock, and did not convert with atrial pacing. Rapid atrial stimulation (pacing at 300-400/min) controlled the ventricular rate by simulating trial fibrillation. This therapy was used on a permanent basis for more than five months.
An article by Lindmark S. et al., entitled, “Does the autonomic nervous system play a role in the development of insulin resistance? A study on heart rate variability in first-degree relatives of type 2 diabetes patients and control subjects.” Diabet Med 20:399-405, 2003, which is incorporated herein by reference, describes how vagal activity is correlated with insulin resistance.
U.S. Pat. No. 6,473,644 to Terry, Jr. et al., which is incorporated herein by reference, describes a method for treating patients suffering from heart failure to increase cardiac output, by stimulating or modulating the vagus nerve with a sequence of substantially equally-spaced pulses by an implanted neurostimulator. The frequency of the stimulating pulses is adjusted until the patient's heart rate reaches a target rate within a relatively stable target rate range below the low end of the patient's customary resting heart rate.
The effect of vagal stimulation on heart rate and other aspects of heart function, including the relationship between the timing of vagal stimulation within the cardiac cycle and the induced effect on heart rate, has been studied in animals. For example, Zhang Y et al., in “Optimal ventricular rate slowing during atrial fibrillation by feedback AV nodal-selective vagal stimulation,” Am J Physiol Heart Circ Physiol 282:H1102-H1110 (2002), describe the application of selective vagal stimulation by varying the nerve stimulation intensity, in order to achieve graded slowing of heart rate. This article is incorporated herein by reference.
The following articles and book, which are incorporated herein by reference, may be of interest:    Levy M N et al., in “Parasympathetic Control of the Heart,” Nervous Control of Vascular Function, Randall W C ed., Oxford University Press (1984)    Levy M N et al. ed., Vagal Control of the Heart: Experimental Basis and Clinical Implications (The Bakken Research Center Series Volume 7), Futura Publishing Company, Inc., Armonk, N.Y. (1993)    Randall W C ed., Neural Regulation of the Heart, Oxford University Press (1977), particularly pages 100-106.    Armour J A et al. eds., Neurocardiology, Oxford University Press (1994)    Perez M G et al., “Effect of stimulating non-myelinated vagal axon on atrioventricular conduction and left ventricular function in anaesthetized rabbits,” Auton Neurosco 86 (2001)    Jones, J F X et al., “Heart rate responses to selective stimulation of cardiac vagal C fibres in anaesthetized cats, rats and rabbits,” J Physiol 489 (Pt 1):203-14 (1995)    Wallick D W et al., “Effects of ouabain and vagal stimulation on heart rate in the dog,” Cardiovasc. Res., 18(2):75-9 (1984)    Martin P J et al., “Phasic effects of repetitive vagal stimulation on atrial contraction,” Circ. Res. 52(6):657-63 (1983)    Wallick D W et al., “Effects of repetitive bursts of vagal activity on atrioventricular junctional rate in dogs,” Am J Physiol 237(3):H275-81 (1979)    Fuster V and Ryden L E et al., “ACC/AHA/ESC Practice Guidelines—Executive Summary,” J Am Coll Cardiol 38(4):1231-65 (2001)    Fuster V and Ryden L E et al., “ACC/AHA/ESC Practice Guidelines—Full Text,” J Am Coll Cardiol 38(4):1266i-12661xx (2001)    Morady F et al., “Effects of resting vagal tone on accessory atrioventricular connections,” Circulation 81(1):86-90 (1990)    Waninger M S et al., “Electrophysiological control of ventricular rate during atrial fibrillation,” PACE 23:1239-1244 (2000)    Wijffels M C et al., “Electrical remodeling due to atrial fibrillation in chronically instrumented conscious goats: roles of neurohumoral changes, ischemia, atrial stretch, and high rate of electrical activation,” Circulation 96(10):3710-20 (1997)    Wijffels M C et al., “Atrial fibrillation begets atrial fibrillation,” Circulation 92:1954-1968 (1995)    Goldberger A L et al., “Vagally-mediated atrial fibrillation in dogs: conversion with bretylium tosylate,” Int J Cardiol 13(1):47-55 (1986)    Takei M et al., “Vagal stimulation prior to atrial rapid pacing protects the atrium from electrical remodeling in anesthetized dogs,” Jpn Circ J 65(12):1077-81 (2001)    Friedrichs G S, “Experimental models of atrial fibrillation/flutter,” J Pharmacological and Toxicological Methods 43:117-123 (2000)    Hayashi H et al., “Different effects of class Ic and III antiarrhythmic drugs on vagotonic atrial fibrillation in the canine heart,” Journal of Cardiovascular Pharmacology 31:101-107 (1998)    Morillo C A et al., “Chronic rapid atrial pacing. Structural, functional, and electrophysiological characteristics of a new model of sustained atrial fibrillation,” Circulation 91:1588-1595 (1995)    Lew S J et al., “Stroke prevention in elderly patients with atrial fibrillation,” Singapore Med J 43(4):198-201 (2002)    Higgins C B, “Parasympathetic control of the heart,” Pharmacol. Rev. 25:120-155 (1973)    Hunt R, “Experiments on the relations of the inhibitory to the accelerator nerves of the heart,” J. Exptl. Med. 2:151-179 (1897)    Billette J et al., “Roles of the AV junction in determining the ventricular response to atrial fibrillation,” Can J Physiol Pharamacol 53(4)575-85 (1975)    Stramba-Badiale M et al., “Sympathetic-Parasympathetic Interaction and Accentuated Antagonism in Conscious Dogs,” American Journal of Physiology 260 (2 Pt 2):H335-340 (1991)    Garrigue S et al., “Post-ganglionic vagal stimulation of the atrioventricular node reduces ventricular rate during atrial fibrillation,” PACE 21(4), 878 (Part II) (1998)    Kwan H et al., “Cardiovascular adverse drug reactions during initiation of antiarrhythmic therapy for atrial fibrillation,” Can J Hosp Pharm 54:10-14 (2001)    Jidéus L, “Atrial fibrillation after coronary artery bypass surgery: A study of causes and risk factors,” Acta Universitatis Upsaliensis, Uppsala, Sweden (2001)    Borovikova L V et al., “Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin,” Nature 405(6785):458-62 (2000)    Wang H et al., “Nicotinic acetylcholine receptor alpha-7 subunit is an essential regulator of inflammation,” Nature 421:384-388 (2003)    Vanoli E et al., “Vagal stimulation and prevention of sudden death in conscious dogs with a healed myocardial infarction,” Circ Res 68(5):1471-81 (1991)    De Ferrari G M, “Vagal reflexes and survival during acute myocardial ischemia in conscious dogs with healed myocardial infarction,” Am J Physiol 261(1 Pt 2):H63-9 (1991)    Li D et al., “Promotion of Atrial Fibrillation by Heart Failure in Dogs: Atrial Remodeling of a Different Sort,” Circulation 100(1):87-95 (1999)    Feliciano L et al., “Vagal nerve stimulation during muscarinic and beta-adrenergic blockade causes significant coronary artery dilation,” Cardiovasc Res 40(1):45-55 (1998)    Lindmark S et al., “Does the autonomic nervous system play a role in the development of insulin resistance? A study on heart rate variability in first-degree relatives of type 2 diabetes patients and control subjects,” Diabet Med 20:399-405 (2003)    Takayama S et al., “A possible involvement of parasympathetic neuropathy on insulin resistance in patients with type 2 diabetes,” Diabetes Care 24:968-969 (2001)
A number of patents describe techniques for treating arrhythmias and/or ischemia by, at least in part, stimulating the vagus nerve. Arrhythmias in which the heart rate is too fast include fibrillation, flutter and tachycardia. Arrhythmia in which the heart rate is too slow is known as bradyarrhythmia. U.S. Pat. No. 5,700,282 to Zabara, which is incorporated herein by reference, describes techniques for stabilizing the heart rhythm of a patient by detecting arrhythmias and then electronically stimulating the vagus and cardiac sympathetic nerves of the patient. The stimulation of vagus efferents directly causes the heart rate to slow down, while the stimulation of cardiac sympathetic nerve efferents causes the heart rate to quicken.
U.S. Pat. No. 5,330,507 to Schwartz, which is incorporated herein by reference, describes a cardiac pacemaker for preventing or interrupting tachyarrhythmias and for applying pacing therapies to maintain the heart rhythm of a patient within acceptable limits. The device automatically stimulates the right or left vagus nerves as well as the cardiac tissue in a concerted fashion dependent upon need. Continuous and/or phasic electrical pulses are applied. Phasic pulses are applied in a specific relationship with the R-wave of the ECG of the patient.
European Patent Application EP 0 688 577 to Holmstrom et al., which is incorporated herein by reference, describes a device to treat atrial tachyarrhythmia by detecting arrhythmia and stimulating a parasympathetic nerve that innervates the heart, such as the vagus nerve.
U.S. Pat. Nos. 5,690,681 and 5,916,239 to Geddes et al., which are incorporated herein by reference, describe closed-loop, variable-frequency, vagal-stimulation apparatus for control of ventricular rate during atrial fibrillation. The apparatus stimulates the left vagus nerve, and automatically and continuously adjusts the vagal stimulation frequency as a function of the difference between actual and desired ventricular excitation rates. In an alternative embodiment, the apparatus automatically adjusts the vagal stimulation frequency as a function of the difference between ventricular excitation rate and arterial pulse rate in order to eliminate or minimize pulse deficit.
US Patent Application Publication 2003/0040774 to Terry et al., which is incorporated herein by reference, describes a device for treating patients suffering from congestive heart failure. The device includes an implantable neurostimulator for stimulating the patient's vagus nerve at or above the cardiac branch with an electrical pulse waveform at a stimulating rate sufficient to maintain the patient's heart beat at a rate well below the patient's normal resting heart rate, thereby allowing rest and recovery of the heart muscle, to increase in coronary blood flow, and/or growth of coronary capillaries. A metabolic need sensor detects the patient's current physical state and concomitantly supplies a control signal to the neurostimulator to vary the stimulating rate. If the detection indicates a state of rest, the neurostimulator rate reduces the patient's heart rate below the patient's normal resting rate. If the detection indicates physical exertion, the neurostimulator rate increases the patient's heart rate above the normal resting rate.
US Patent Publication 2003/0045909 to Gross et al., which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes apparatus for treating a heart condition of a subject, including an electrode device, which is adapted to be coupled to a vagus nerve of the subject. A control unit is adapted to drive the electrode device to apply to the vagus nerve a stimulating current, which is capable of inducing action potentials in a therapeutic direction in a first set and a second set of nerve fibers of the vagus nerve. The control unit is also adapted to drive the electrode device to apply to the vagus nerve an inhibiting current, which is capable of inhibiting the induced action potentials traveling in the therapeutic direction in the second set of nerve fibers, the nerve fibers in the second set having generally larger diameters than the nerve fibers in the first set.
US Patent Publication 2003/0229380 to Adams et al., which is incorporated herein by reference, describes techniques for electrically stimulating the right vagus nerve in order to reduce the heart rate of a patient suffering from conditions such as chronic heart failure, ischemia, or acute myocardial infarction. The amount of energy of the stimulation may be determined in accordance with a difference between the patient's actual heart rate and a maximum target heart rate for the patient. Delivery of energy is preferably synchronized with the detection of a P-wave. Automatic adjustment of the target heart rate may be based on current day and/or time of day information, and patient physical activity. The voltage, pulse width, or number of pulses in the stimulation may be controlled.
US Patent Application Publication 2005/0154419 to Whitehurst et al., which is incorporated herein by reference, describes methods for treating a medical condition, including applying at least one stimulus to a target nerve within the patient with an implanted system control unit in accordance with one or more stimulation parameters. The target nerve may include any nerve originating in an upper cervical spine area of the patient or a branch of any nerve originating in the upper cervical spine area of the patient. Medical conditions described include cerebrovascular disease, an autoimmune disease, a sleep disorder (e.g., sleep apnea), an autonomic disorder, a urinary bladder disorder, epilepsy, hyperthyroidism, hypothyroidism, a muscular system disorder, a neuropsychiatric disorder (e.g., depression, schizophrenia, bipolar disorder, autism, personality disorders, and obsessive-compulsive disorder), pain, a gastrointestinal disorder (e.g., a gastrointestinal motility disorder, nausea, vomiting, diarrhea, chronic hiccups, gastroesophageal reflux disease, and hypersecretion of gastric acid), autonomic insufficiency, excessive epiphoresis, excessive rhinorrhea, and a cardiovascular disorder (e.g., cardiac dysrhythmias and arrhythmias, hypertension, and carotid sinus disease).
U.S. Pat. No. 6,526,318 to Ansarinia, which is incorporated herein by reference, describes a method for the suppression or prevention of pain, movement disorders, epilepsy, cerebrovascular diseases, autoimmune diseases, sleep disorders, autonomic disorders, urinary bladder disorders, abnormal metabolic states, disorders of the muscular system, and neuropsychiatric disorders in a patient. The method comprises positioning at least one electrode on or proximate to at least one of the patient's sphenopalatine ganglia (“SPG”), sphenopalatine nerves (“SPN”), or vidian nerves (“VN”), and activating the at least one electrode to apply an electrical signal to at least one of the SPG, SPN, or VN. In a further embodiment, a method is described to treat the same conditions, and the electrode used is capable of dispensing a medication solution or analgesic which is applied via an electrode to at least one of the SPG, SPN, or VN. A method is also provided for surgically implanting an electrode on or proximate to at least one of the SPG, SPN, or VN of a patient. A method for treating hiccups is also described.
US Patent Application Publication 2005/0080458 to Ehlinger, Jr. et al., which is incorporated herein by reference, describes a device for the treatment of hiccups, and more specifically, a method and apparatus for the treatment of hiccups involving galvanic stimulation of the superficial phrenic and vagus nerves using an electric current.
U.S. Pat. No. 5,188,104 to Wernicke et al., which is incorporated herein by reference, describes a method for treating patients with compulsive eating disorders includes the steps of detecting a preselected event indicative of an imminent need for treatment of the specific eating disorder of interest, and responding to the detected occurrence of the preselected event by applying a predetermined stimulating signal to the patient's vagus nerve appropriate to alleviate the effect of the eating disorder of interest. For example, the preselected event may be a specified level of food consumption by the patient within a set interval of time, or the commencement of a customary mealtime according to the patient's circadian cycle, or the passage of each of a sequence of preset intervals of time, or the patient's own recognition of the need for treatment by voluntarily initiating the application of the stimulating signal to the vagus nerve. In cases in which the disorder is compulsive eating to excess, the stimulating signal is predetermined to produce a sensation of satiety in the patient. The occurrence of the preselected event is detected by summing the number of swallows of food by the patient within the set interval of time. In cases where the disorder is compulsive refusal to eat (anorexia nervosa), the stimulating signal is predetermined to produce a sensation of hunger or to suppress satiety in the patient.
U.S. Pat. No. 5,540,734 to Zabara, which is incorporated herein by reference, describes the treatment, control or prevention of medical, psychiatric or neurological disorders accomplished by application of modulating electric signals to one or both of a patient's trigeminal and glossopharyngeal nerves. The disorders treatable, controllable or preventable by such nerve stimulation are described as including voluntary and involuntary disorders, migraine, epileptic seizure, motor disorders, Parkinson's disease, cerebral palsy, spasticity, chronic nervous illnesses and involuntary movement; pancreatic endocrine disorders including diabetes and hypoglycemia; dementia including cortical, subcortical, multi-infarct, Alzheimer's disease and Pick's disease; sleep disorders including central sleep apnea, insomnia and hypersomnia; eating disorders including anorexia nervosa, bulimia and compulsive overeating; and neuropsychiatric disorders including schizophrenia, depression and borderline personality disorder.
PCT Patent Publication WO 2001/85094 to Shalev et al., which is incorporated herein by reference, describes apparatus for modifying a property of a brain of a patient is provided, including one or more electrodes, adapted to be applied to a site selected from a group of sites consisting of: a sphenopalatine ganglion (SPG) of the patient and a neural tract originating in or leading to the SPG. A control unit is adapted to drive the one or more electrodes to apply a current to the site capable of inducing (a) an increase in permeability of a blood-brain barrier (BBB) of the patient, (b) a change in cerebral blood flow of the patient, and/or (c) an inhibition of parasympathetic activity of the SPG.
U.S. Pat. No. 5,203,326 to Collins, which is incorporated herein by reference, describes a pacemaker which detects a cardiac abnormality and responds with electrical stimulation of the heart combined with vagus nerve stimulation. The vagal stimulation frequency is progressively increased in one-minute intervals, and, for the pulse delivery rate selected, the heart rate is described as being slowed to a desired, stable level by increasing the pulse current.
U.S. Pat. No. 6,511,500 to Rahme, which is incorporated herein by reference, describes various aspects of the effects of autonomic nervous system tone on atrial arrhythmias, and its interaction with class III antiarrhythmic drug effects.
U.S. Pat. No. 5,199,428 to Obel et al., which is incorporated herein by reference, describes a cardiac pacemaker for detecting and treating myocardial ischemia. The device automatically stimulates the vagal nervous system as well as the cardiac tissue in a concerted fashion in order to decrease cardiac workload and thereby protect the myocardium.
U.S. Pat. Nos. 5,334,221 to Bardy and 5,356,425 to Bardy et al., which are incorporated herein by reference, describe a stimulator for applying stimulus pulses to the AV nodal fat pad in response to the heart rate exceeding a predetermined rate, in order to reduce the ventricular rate. The device also includes a cardiac pacemaker which serves to pace the ventricle in the event that the ventricular rate is lowered below a pacing rate, and provides for feedback control of the stimulus parameters applied to the AV nodal fat pad, as a function of the determined effect of the stimulus pulses on the heart rate.
U.S. Pat. No. 5,522,854 to Ideker et al., which is incorporated herein by reference, describes techniques for preventing arrhythmia by detecting a high risk of arrhythmia and then stimulating afferent nerves to prevent the arrhythmia.
U.S. Pat. No. 6,434,424 to Igel et al., which is incorporated herein by reference, describes a pacing system with a mode switching feature and ventricular rate regularization function adapted to stabilize or regularize ventricular heart rate during chronic or paroxysmal atrial tachyarrhythmia.
US Patent Application Publication 2002/0120304 to Mest, which is incorporated herein by reference, describes a method for regulating the heart rate of a patient by inserting into a blood vessel of the patient a catheter having an electrode at its distal end, and directing the catheter to an intravascular location so that the electrode is adjacent to a selected cardiac sympathetic or parasympathetic nerve.
U.S. Pat. Nos. 6,006,134 and 6,266,564 to Hill et al., which are incorporated herein by reference, describe an electro-stimulation device including a pair of electrodes for connection to at least one location in the body that affects or regulates the heartbeat.
PCT Publication WO 02/085448 to Foreman et al., which is incorporated herein by reference, describes a method for protecting cardiac function and reducing the impact of ischemia on the heart, by electrically stimulating a neural structure capable of carrying the predetermined electrical signal from the neural structure to the “intrinsic cardiac nervous system,” which is defined and described therein.
U.S. Pat. No. 5,243,980 to Mehra, which is incorporated herein by reference, describes techniques for discrimination between ventricular and supraventricular tachycardia. In response to the detection of the occurrence of a tachycardia, stimulus pulses are delivered to one or both of the SA and AV nodal fat pads. The response of the heart rhythm to these stimulus pulses is monitored. Depending upon the change or lack of change in the heart rhythm, a diagnosis is made as to the origin of the tachycardia.
U.S. Pat. No. 5,658,318 to Stroetmann et al., which is incorporated herein by reference, describes a device for detecting a state of imminent cardiac arrhythmia in response to activity in nerve signals conveying information from the autonomic nerve system to the heart. The device comprises a sensor adapted to be placed in an extracardiac position and to detect activity in at least one of the sympathetic and vagus nerves.
U.S. Pat. No. 6,292,695 to Webster, Jr. et al., which is incorporated herein by reference, describes a method for controlling cardiac fibrillation, tachycardia, or cardiac arrhythmia by the use of a catheter comprising a stimulating electrode, which is placed at an intravascular location. The electrode is connected to a stimulating means, and stimulation is applied across the wall of the vessel, transvascularly, to a sympathetic or parasympathetic nerve that innervates the heart at a strength sufficient to depolarize the nerve and effect the control of the heart.
U.S. Pat. No. 6,134,470 to Hartlaub, which is incorporated herein by reference, describes an implantable anti-arrhythmia system which includes a spinal cord stimulator coupled to an implantable heart rhythm monitor. The monitor is adapted to detect the occurrence of tachyarrhythmias or of precursors thereto and, in response, trigger the operation of the spinal cord stimulator in order to prevent occurrences of tachyarrhythmias and/or as a stand-alone therapy for termination of tachyarrhythmias and/or to reduce the level of aggressiveness required of an additional therapy such as antitachycardia pacing, cardioversion or defibrillation.
US Patent Application Publication 2003/0181958 to Dobak, which is incorporated herein by reference, describes a method for the treatment of obesity or other disorders, by electrical activation or inhibition of the sympathetic nervous system. This activation or inhibition is achieved by electrically stimulating the greater splanchnic nerve or another portion of the sympathetic nervous system using an implantable pulse generator. This nerve activation is described as possibly resulting in reduced food intake and increased energy expenditure. Reduced food intake is described as possibly occurring through a variety of mechanisms that reduce appetite and cause satiety. Increased adrenal gland hormone levels are described as resulting in increased energy expenditure. Fat and carbohydrate metabolism, which are described as being increased by sympathetic nerve activation, are described as accompanying the increased energy expenditure.
U.S. Pat. No. 5,335,657 to Terry, Jr. et al., which is incorporated herein by reference, describes techniques for treating and controlling sleep disorders by detecting the presence of the sleep disorder under treatment, and, in response, selectively applying a predetermined electrical signal to the patient's vagus nerve for stimulation thereof to alleviate the sleep disorder under treatment. The method and apparatus includes several techniques for detecting the presence of the sleep disorder under treatment, such as sensing the patient's EEG activity in the case of insomniac and hypersomniac patients, or detecting a sudden nodding of the head in the case of narcoleptic patients, or sensing the cessation of respiration in the case of sleep apnea patients.
PCT Publication WO 04/078252 to Karashurov, which is incorporated herein by reference, describes an implanted system for treatment of human diseases by electric stimulation and/or electric blocking of the body tissues, comprising sensor and/or biosensor means for measuring variables in the body, processor means connected to the sensors and biosensors for processing the measured variables and for deciding in real time whether to apply an electric signal to the body tissues, and electrode means implanted at predefined locations and connected to the processor means, for applying the stimulation and/or electric blocking signals to the body tissues.
U.S. Pat. No. 6,668,191 to Boveja, which is incorporated herein by reference, describes apparatus for neuromodulation adjunct (add-on) therapy for atrial fibrillation, refractory hypertension, and inappropriate sinus tachycardia, comprising an implantable lead-receiver and an external stimulator. Neuromodulation is performed using pulsed electrical stimulation. The external stimulator contains a primary coil which inductively transfers electrical signals to the implanted lead-receiver, which is also in electrical contact with a vagus nerve. The external stimulator emits electrical pulses to stimulate the vagus nerve according to a predetermined program. In a second mode of operation, an operator may manually override the predetermined sequence of stimulation.
A number of patents and articles describe other methods and devices for stimulating nerves to achieve a desired effect. Often these techniques include a design for an electrode or electrode cuff.
US Patent Publication 2003/0050677 to Gross et al., which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes apparatus for applying current to a nerve. A cathode is adapted to be placed in a vicinity of a cathodic longitudinal site of the nerve and to apply a cathodic current to the nerve. A primary inhibiting anode is adapted to be placed in a vicinity of a primary anodal longitudinal site of the nerve and to apply a primary anodal current to the nerve. A secondary inhibiting anode is adapted to be placed in a vicinity of a secondary anodal longitudinal site of the nerve and to apply a secondary anodal current to the nerve, the secondary anodal longitudinal site being closer to the primary anodal longitudinal site than to the cathodic longitudinal site.
U.S. Pat. Nos. 4,608,985 to Crish et al. and 4,649,936 to Ungar et al., which are incorporated herein by reference, describe electrode cuffs for selectively blocking orthodromic action potentials passing along a nerve trunk, in a manner intended to avoid causing nerve damage.
PCT Patent Publication WO 01/10375 to Felsen et al., which is incorporated herein by reference, describes apparatus for modifying the electrical behavior of nervous tissue. Electrical energy is applied with an electrode to a nerve in order to selectively inhibit propagation of an action potential.
U.S. Pat. No. 5,755,750 to Petruska et al., which is incorporated herein by reference, describes techniques for selectively blocking different size fibers of a nerve by applying direct electric current between an anode and a cathode that is larger than the anode. The current applied to the electrodes blocks nerve transmission, but, as described, does not activate the nerve fibers in either direction.
U.S. Pat. No. 6,600,956 to Maschino et al., which is incorporated herein by reference, describes an electrode assembly to be installed on a patient's nerve. The electrode assembly has a thin, flexible, electrically insulating circumneural carrier with a split circumferential configuration longitudinally attached to a lead at the distal end thereof The carrier possesses circumferential resiliency and has at least one flexible, elastic electrode secured to the underside thereof and electrically connected to an electrical conductor in said lead. A fastener serves to close the split configuration of the carrier to prevent separation from the nerve after installation of the electrode assembly onto the nerve. Tear away webbing secured to adjacent serpentine segments of the lead near the carrier enables the lead to lengthen with patient movements.
The following articles, which are incorporated herein by reference, may be of interest:    Ungar I J et al., “Generation of unidirectionally propagating action potentials using a monopolar electrode cuff,” Annals of Biomedical Engineering, 14:437-450 (1986)    Sweeney J D et al., “An asymmetric two electrode cuff for generation of unidirectionally propagated action potentials,” IEEE Transactions on Biomedical Engineering, vol. BME-33(6) (1986)    Sweeney J D et al., “A nerve cuff technique for selective excitation of peripheral nerve trunk regions,” IEEE Transactions on Biomedical Engineering, 37(7) (1990)    Naples G G et al., “A spiral nerve cuff electrode for peripheral nerve stimulation,” by IEEE Transactions on Biomedical Engineering, 35(11) (1988)    van den Honert C et al., “Generation of unidirectionally propagated action potentials in a peripheral nerve by brief stimuli,” Science, 206:1311-1312 (1979)    van den Honert C et al., “A technique for collision block of peripheral nerve: Single stimulus analysis,” MP-11, IEEE Trans. Biomed. Eng. 28:373-378 (1981)    van den Honert C et al., “A technique for collision block of peripheral nerve: Frequency dependence,” MP-12, IEEE Trans. Biomed. Eng. 28:379-382 (1981)    Rijkhoff N J et al., “Acute animal studies on the use of anodal block to reduce urethral resistance in sacral root stimulation,” IEEE Transactions on Rehabilitation Engineering, 2(2):92 (1994)    Mushahwar V K et al., “Muscle recruitment through electrical stimulation of the lumbo-sacral spinal cord,” IEEE Trans Rehabil Eng, 8(1):22-9 (2000)    Deurloo K E et al., “Transverse tripolar stimulation of peripheral nerve: a modelling study of spatial selectivity,” Med Biol Eng Comput, 36(1):66-74 (1998)    Tarver W B et al., “Clinical experience with a helical bipolar stimulating lead,” Pace, Vol. 15, October, Part II (1992)    Manfredi M, “Differential block of conduction of larger fibers in peripheral nerve by direct current,” Arch. Ital. Biol., 108:52-71 (1970)
In physiological muscle contraction, nerve fibers are recruited in the order of increasing size, from smaller-diameter fibers to progressively larger-diameter fibers. In contrast, artificial electrical stimulation of nerves using standard techniques recruits fibers in a larger- to smaller-diameter order, because larger-diameter fibers have a lower excitation threshold. This unnatural recruitment order causes muscle fatigue and poor force gradation. Techniques have been explored to mimic the natural order of recruitment when performing artificial stimulation of nerves to stimulate muscles.
Fitzpatrick et al., in “A nerve cuff design for the selective activation and blocking of myelinated nerve fibers,” Ann. Conf. of the IEEE Eng. in Medicine and Biology Soc, 13(2), 906 (1991), which is incorporated herein by reference, describe a tripolar electrode used for muscle control. The electrode includes a central cathode flanked on its opposite sides by two anodes. The central cathode generates action potentials in the motor nerve fiber by cathodic stimulation. One of the anodes produces a complete anodal block in one direction so that the action potential produced by the cathode is unidirectional. The other anode produces a selective anodal block to permit passage of the action potential in the opposite direction through selected motor nerve fibers to produce the desired muscle stimulation or suppression.
The following articles, which are incorporated herein by reference, may be of interest:    Rijkhoff N J et al., “Orderly recruitment of motoneurons in an acute rabbit model,” Ann. Conf. of the IEEE Eng., Medicine and Biology Soc., 20(5):2564 (1998)    Rijkhoff N J et al., “Selective stimulation of small diameter nerve fibers in a mixed bundle,” Proceedings of the Annual Project Meeting Sensations/Neuros and Mid-Term Review Meeting on the TMR-Network Neuros, Apr. 21-23, 1999, pp. 20-21 (1999)    Baratta R et al., “Orderly stimulation of skeletal muscle motor units with tripolar nerve cuff electrode,” IEEE Transactions on Biomedical Engineering, 36(8):836-43 (1989)
The following articles, which are incorporated herein by reference, describe techniques using point electrodes to selectively excite peripheral nerve fibers:    Grill W M et al., “Inversion of the current-distance relationship by transient depolarization,” IEEE Trans Biomed Eng, 44(1):1-9 (1997)    Goodall E V et al., “Position-selective activation of peripheral nerve fibers with a cuff electrode,” IEEE Trans Biomed Eng, 43(8):851-6 (1996)    Veraart C et al., “Selective control of muscle activation with a multipolar nerve cuff electrode,” IEEE Trans Biomed Eng, 40(7):640-53 (1993)
As defined by Rattay, in the article, “Analysis of models for extracellular fiber stimulation,” IEEE Transactions on Biomedical Engineering, Vol. 36, no. 2, p. 676, 1989, which is incorporated herein by reference, the activation function is the second spatial derivative of the electric potential along an axon. In the region where the activation function is positive, the axon depolarizes, and in the region where the activation function is negative, the axon hyperpolarizes. If the activation function is sufficiently positive, then the depolarization will cause the axon to generate an action potential; similarly, if the activation function is sufficiently negative, then local blocking of action potentials transmission occurs. The activation function depends on the current applied, as well as the geometry of the electrodes and of the axon.
For a given electrode geometry, the equation governing the electrical potential is:∇(σ∇U)=4πj, 
where U is the potential, σ is the conductance tensor specifying the conductance of the various materials (electrode housing, axon, intracellular fluid, etc.), and j is a scalar function representing the current source density specifying the locations of current injection.