Carotid Sinus Syndrome: Treatment by Carotid Sinus Denervation HUGH H. TROUT, III, M.D.,* LYLE L. BROWN, M.D., JESSE E. THOMPSON, M.D.
Hypersensitive carotid sinus is a rare cause of spontaneous syncopal attacks. It must be differentiated from the other more common causes, such as intrinsic cardiac disease, vasovagal responses, postural hypotension and cerebrovascular insufficiency, although it may accompany these conditions. The definition of carotid sinus syncope is syncope elicited by stimulation of a hypersensitive carotid sinus. Nineteen patients with carotid sinus syncope were treated by carotid sinus denervation. Ages ranged from 48 to 83 with a mean of 65.5 years. Syiwptoms of marked dizziness or syncope were reproduced by gentle compression over the carotid bifurcation, while ECG monitoring revealed bradycardia or transient asystole. Seventeen patients had carotid arteriograms, eleven of which were normal. One patient had stenosis of the external carotid artery, while five had stenosis of the internal carotid. The right carotid sinus was involved in ten patients, the left in three and both sides in six. All patients underwent unilateral or bilateral carotid sinus denervation. Five patients with internal carotid stenosis had concomitant carotid endarterectomy. Complete relief of symptoms or marked improvement was noted in all but one patient. Postoperative follow-up ranged up to 15 years. Carotid sinus denervation is a simple, effective method of treating this disorder. FOR CENTURIES WARRIORS AND PHYSICIANS have
recognized that an effective method of inducing loss of consciousness is deliberate carotid artery compression. Indeed the etymology of the word carotid is founded on the understanding of the consequences of carotid occlusion. In contrast to deliberate occlusion, however, on rare occasions inadvertent gentle carotid manipulation elicited by neck massage, turning the head, or even by a tight collar may produce similar symptoms of dizziness or syncope. In these situations the decreased cerebral blood flow is not caused by Presented at the Annual Meeting of the Southern Surgical As-
sociation, December 4-6, 1978, Hot Springs, Virginia. * Current address: Department of Surgery, George Washington University Medical Center, Washington, D.C. 20037. Reprint requests: Jesse E. Thompson, M.D., Suite 505, 3600 Gaston Avenue, Dallas, Texas 75246. Submitted for publication: December 7, 1978.
From the Department of General Surgery, Baylor University Medical Center, Dallas, Texas
occlusion of a carotid artery but instead is produced by stimulation of a hypersensitive carotid sinus resulting in systemic hypotension or cardiac arrhythmia. Patients with syncope whose symptoms are reproduced by gentle neck massage are said to have carotid sinus syndrome. Nineteen such patients have been treated since 1959. This report summarizes our experience with these patients. Methods and Materials Fifteen male and four female patients presented with numerous symptoms which always included snycope or marked dizziness. These symptoms were invariably reported during gentle unilateral carotid sinus massage during careful EKG monitoring. There were five episodes of such prolonged asystole that resuscitative maneuvers were required. Figure 1 depicts a typical EKG tracing of asystole following unilateral carotid sinus stimulation. The age of patients at the time of evaluation ranged from 48 to 83 with an average of 65.6 years. Arteriograms were performed on 17 patients, and 11 of these were normal. One patient had stenosis of the external carotid artery, while five had stenoses of the internal carotid. The criteria used for determining operability were reproduction of the patient's symptoms, with concomitant demonstration of a hypersensitive carotid sinus. A hypersensitive carotid sinus was defined for this purpose as a sinus which when stimulated by gentle neck massage resulted in asystole for more than two seconds, a bradycardia of more than 30% of control or a drop in systolic blood pressure of more than 30 mm Hg. Table 1 includes the operations performed for treatment of carotid sinus syndrome.
0003-4932/79/0500/0575 $00.80 © J. B. Lippincott Company
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576
Ann. Surg. * May 1979
FIG. 1. EKG tracing during carotid sinus massage (arrow) showing asystole of 4.8 seconds after stimulation of right carotid sinus.
The technique for carotid sinus denervation is as follows: The patient is placed on the operating table in a supine position with a sheet beneath the shoulders and the head resting on a doughnut-shaped support and turned away from the side to be operated upon. Preoperative atropine is given, and with constant EKG and blood pressure monitoring, excessive manipulation is avoided during positioning and endotracheal intuba-
tion in order to prevent inducing the reflex. Following satisfactory induction of endotracheal anesthesia, an incision is chosen according to whether or not a concomitant carotid endarterectomy is to be performed. If so, then the incision is the usual carotid endarterectomy incision, a curvilinear incision along the anterior border of the sternocleidomastoid muscle.17 If an endarterectomy is not planned, a transverse in-
TABLE 1. Summary of Data on Patients with Carotid Sinus Syndrome
Patient
Sex
Age
I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
M F F M M M F M M M M F M M M M M M M
68 62 80 63 74 62 68 59 79 48 66 83 64 60 65 60 61 52 71
Preop Symptoms S S S S S S S S S D S S D S S S S S S
Operation RCD LCD LCD RCD RCD RCD RCD RCD RCD RCD
RCD, LCD RCD, LCD RCD, LCD RCD, LCD RCD&E RCD&E LCD&E RCD, LCD&E RCD&E, LCD&E
* = dead, S = syncope, D = dizziness, I = improved, = residual left hand paresis, RCD = right carotid denervation, LCD = left
Result
I, rarely mild dizziness Relieved Relieved Relieved I, rarely mild dizziness Relieved I, orthostatic hypotension Relieved I, mild dizziness Relieved Developed heart block Relieved Relieved Relieved
Relievedt Relieved Relieved Relieved Relieved
Follow-up (mo.) 56* 185 66 10 55 52 121* 29 83 144 116 38* 11* 156* 81 24 35* 131 48*
carotid denervation, RCD&E = right carotid denervation and endarterectomy, LCD&E = left carotid denervation and endarterectomy.
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cision is used in a skinfold at the level of the carotid bifurcation. With either incision the carotid bifurcation is exposed, and the sinus is gently infiltrated with 1% plain lidocaine prior to mobilization. The adventitia is stripped from the common carotid artery, the bifurcation, and for about 1 cm up both the external and internal carotid arteries. All nerve fibers entering the crotch of the carotid bifurcation are ligated and divided until the bifurcation is completely free. A small drain is left in place, and the platysma muscle and the skin are closed in layers. The patient remains in bed for 36 hours and then is allowed to walk with assistance until vasomotor stability is assured. The drain is removed the morning after the operation. If a carotid endarterectomy is performed the technique employed is that previously reported.17'18 If no endarterectomy is necessary and the patient is in a high risk category, the surgeon may safely elect to denervate the carotid sinus with the use of local anesthesia. Results (Table 1)
Results of operation have been quite satisfactory. There has been no operative mortality. Fourteen patients have remained completely free of their original symptoms at the time of their last follow-up or at death. Three patients were improved, having occasional mild dizziness. One of these had moderate sensitivity of the unoperated sinus but was not subjected to operation since he developed carcinoma of the prostate, from which he died. One patient was relieved of symptoms for five years and then developed postural hypotenslibn, parkinsonism and organic brain syndrome with recurrence of syncope in the upright position. Another patient was relieved temporarily, only to develop congestive heart failure and complete heart block requiring insertion of a pacemaker. One patient relieved by sinus denervation developed contralateral carotid stenosis and hypersensitive sinus several years later and underwent denervation and endarterectomy with relief. The only serious complication occurred in a patient who had denervation concomitant with endarterectomy; a mild, persistent weakness of the left hand was believed to be secondary to embolism of a platelet aggregation. Follow-up ranged from 10 to 185 months, with an average of 76 months. Seven long-term deaths occurred, two from cardiac causes, two from cerebral causes, two from cancer and one suicide. There has been no evidence of regeneration of nerves in a denervated sinus; this corroborates the results of others who have reported on this operation.
Discussion
Hypersensitive carotid sinus is a rare cause of spontaneous syncopal attacks. It must be differentiated from the other more common causes, such as vasovagal responses, intrinsic cardiac disease, postural hypotension and cerebrovascular insufficiency, although it may accompany these conditions. The two carotid sinuses are located at the bifurcation of each common carotid artery. The nerve fibers supplying the sinuses terminate in the sensory end organs in the walls of the artery and carotid body and are derived from afferent fibers from both the vagus and glossopharyngeal nerves, with efferent connections from the superior cervical ganglion of the sympathetic trunk.20 The principal efferent pathway of the reflex arc is the vagus nerve.'2 The carotid sinus reflex is believed to have fundamental regulatory influences over cardiovascular function. The recognized changes after an increase in intrasinus tension are decrease in systemic blood pressure, bradycardia and slowing of respiration; the opposite effects follow a decrease in tension within the sinus.16 Though the carotid sinus baroreceptor reflex can be demonstrated in man, there is some doubt as to whether the carotid sinus is as powerful a regulator as are the extracarotid baroreceptors.'0 Our clinical impression is that the carotid sinus is a relatively noncritical regulator in the adult human; after either unilateral or bilateral carotid sinus denervation or carotid endarterectdtny, in which carotid sinus denervation is usually performed, the only vasomotor instability has been occasional transient hypertension for a few days postoperatively. Weiss and Baker19 describe three possible responses following stimulation of a hyperactive carotid sinus: 1) the cardioinhibitory type of response with bradycardia or asystole, 2) the vasodepressor type of hypotensive response without cardiac slowing and 3) a primary central cerebral type not accompanied by either systemic hypotension or by bradycardia. Since this was postulated prior to the appreciation of the frequency and extent of extracranial carotid occlusive lesions, it can probably be safely assumed that patients in this third category had syncopal attacks as a result of cerebrovascular insufficiency and not hypersensitive carotid sinUts. Considering this, a reasonable classification would seem to be 1) the cardioinhibitory type, which is by far the more common, and 2) the vasodepressor type. One should keep in mind that either type can coexist with either a hemodynamically important occlusive lesion in one or both carotid arteries or with a clinically significant cardiac conduction defect. A workable definition of what constitutes a hyper-
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active response has been proposed by Franke and is reviewed by Thomas.'6 An abnormal response is one in which cardiac asystole lasts three or more seconds or systolic and diastolic blood pressure drop 50 mmHg or more. A borderline response is one in which asystole lasts two seconds, the heart rate slows by more than 30% or the systolic blood pressure drops by more than 30 mmHg. In our opinion a patient with symptoms of syncope or moderate dizziness reproduced by an abnormal or borderline response to stimulation should be treated. Patients in whom carotid sinus syncope is suspected should have a thorough cardiac evaluation concentrating particularly on cardiac conduction abnormalities. They should also be carefully examined for extracranial cerebral occlusive disease by listening for carotid bruits. A noninvasive test, occuloplethysmography, should, if available, also be performed in an attempt to detect diminished cerebral blood flow.8 If an occlusive lesion is suspected a cerebral arteriogram should be obtained. When provocative carotid sinus stimulation is performed, considerable caution must be exercised since five of our 19 patients required resuscitation following this maneuver. Many methods have been employed, but a satisfactory technique of carotid sinus stimulation is as follows: The patient is placed in a supine position, and, while a second examiner monitors both blood pressure and a continuous EKG tracing, gentle unilateral carotid massage is performed for 10-20 seconds with the head in a relatively neutral position. Both sides are stimulated separately with several minutes' rest between sides. If neither stimulation elicits a response, the same maneuvers may be performed with the patient in a sitting position. The testing should be suspended immediately if a positive response is obtained or if marked dizziness or syncope develops. Simultaneous testing of both sides should never be performed, and testing should be done in an area where complete resuscitative equipment is readily available, such as a cardiac catheterization laboratory. During carotid sinus stimulation the examiner should avoid applying pressure sufficient to occlude the carotid artery. If cerebrovascular occlusive disease is suspected on the basis of physical examination or as a result of the occuloplethysmogram, the patient should be monitored as well with a continuous electroencephalogram during the carotid sinus stimulation. A hyperactive carotid sinus is not a subtle entity; if present, a positive response is quickly apparent. Among our patients elderly males with right-sided hypersensitivity predominated. This same prevalence is noted in almost all reports of carotid sinus syncope. Predisposing factors include generalized arteriosclero-
Ann. Surg. * May 1979
sis, hypertension, coronary artery disease and diabetes mellitus.94 The normal response to carotid sinus massage is sinoatrial slowing with minimal increase in the PR interval.'5 When ventricular asystole occurs following stimulation of a hypersensitive sinus, the usual mechanism of this asystole is sinoatrial arrest with failure of lower escape pacemakers, although occasionally an alternative mechanism is atrioventricular block.6 Hartzler and Maloney6 performed carotid sinus massage on 100 patients undergoing His bundle electrocardiography. Among their patients in whom a hypersensitive carotid sinus was detected, they noted an increased incidence of resting sinus bradycardia, right bundle branch block and mild aortic valve stenosis. Drugs which are said to potentiate carotid sinus hypersensitivity are digitalis,4 methyldopa,1 morphine and thyroid extract.20 Several of our patients were taking digitalis preparations, but we were unable to relate their sinus sensitivity to their medications. As implied above, a hypersensitive carotid sinus reflex following provocative stimulation without spontaneous clinical symptoms does not require treatment. However, the carotid sinus syndrome, which may be defined as syncope or marked dizziness reproduced by a carotid sinus stimulation test, should be treated because of the considerable risk of injury in the elderly patient following a fall. Treatment modalities have included atropine, ephedrine, neck irradiation, glossopharyngeal transsection via a craniotomy, insertion of a cardiac pacemaker and denervation of the carotid sinus. In the cardioinhibitory type of hypersensitive carotid sinus, atropine sulfate, 0.5 mg orally four times a day, may be tried; in the infrequent vasodepressor type, 30 mg of ephedrine two or three times daily may be effective. 16 These measures, however, are rarely beneficial in those patients with obvious carotid sinus syncope, and other therapy is necessary. Though sectioning of the glossopharyngeal nerve has been performed,7'13 this requires an intracranial approach and, given the success with other less extensive procedures, this procedure seems extreme. Three therapeutic modalities which have been reported to be reasonably successful are neck irradiation,5 insertion of a cardiac pacemaker3'11 and denervation of the carotid sinus.12'16'20 Neck irradiation is said to be successful in about two-thirds of those treated, and in elderly high risk patients it may well be a method worth considering. The disadvantages would appear to be that the therapeutic benefit is delayed, that the neck would receive substantial amounts of irradiation and that this method
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CAROTID SINUS SYNDROME
is probably not as effective as the other two. We have had no experience with it, however. Insertion of a cardiac pacemaker is usually successful and may be employed in those patients who have a concomitant conduction defect which itself may benefit by pacing. The disadvantages of cardiac pacing are that, relatively simple as it is to perform, it is more difficult than carotid sinus denervation and it requires more careful long-term follow-up to check on continued correct placement of the catheter and adequate battery charge. Carotid sinus denervation is the modality we have employed. It is simple to perform with minimal risk in the hands of an experienced surgeon, and it may be combined with a carotid endarterectomy in the patient with a stenotic lesion. If the technique for denervation described above is employed, there is no evidence of recurrent sinus reflex activity. Regeneration of nerves does not seem to occur. The only operative complication among our 19 patients was a mild, permanent weakness of the left hand in a patient who had a severe left carotid stenosis with an ulcerated plaque, who had had a carotid endarterectomy at the time of the denervation. This is one of seven mild permanent deficits following carotid endarterectomy in 516 patients operated upon by the senior author (JET). Thus the risk of death or stroke appears to be minimal for denervation alone and 1-2% in those patients in whom both an endarterectomy and denervation are necessary. When bilateral denervation without endarterectomy is warranted, both sides may be operated upon at the same time. If endarterectomy is required on one or both sides, the operations should be staged a week or more apart. Though postural hypotension has been reported following bilateral denervation,2 this complication has not been observed following 264 bilateral cartoid endarterectomies performed by the senior author and his partners, despite the fact that the carotid sinus nerves are usually routinely divided during endarterectomy. We do not attempt preoperative percutaneous anesthetic injection of the carotid sinus, as we believe that this maneuver may provoke an attack. Also, once a patient's symptoms have been reproduced by gentle carotid sinus stimulation, we believe further diagnostic studies are unwarranted and may be dangerous. In that setting we would proceed to carotid sinus denervation or insertion of a cardiac pacemaker depending on the clinical situation. Protocol for Treatment (Table 2) There has been confusion regarding terminology and indications for different types of therapy for the hypersensitive carotid sinus. It has been clearly dem-
579 TABLE 2. Tr-eatmtietit
Hypersensitive Carotid Sinus (HCS) 1. HCS 2. HCS and CDD 3. HCS and CVI
Carotid Sinus Syndrome (CSS) 4. CSS 5. CSS and CDD 6. CSS and CVI
No treatment Cardiac therapy Carotid endarterectomy and CS denervation
CS denervation Cardiac pacemaker Carotid endarterectomy and CS denervation
CDD = cardiac conduction defect, CVI = cerebrovascular insufficiency, CS = carotid sinus.
onstrated by a number of observers that a carotid sinus may be hypersensitive when tested by massage or compression, but the patient may be completely asymptomatic; if this is so and if there are no associated diseases, no treatment is necessary. On the other hand, the patient may have an asymptomatic hypersensitive carotid sinus as well as an associated cardiac problem with a conduction defect or may have symptoms of cerebrovascular insufficiency with extracranial occlusive disease. In the former situation, appropriate cardiac therapy is in order with either drugs or a pacemaker, but carotid sinus denervation is not done. The patient with cerebral symptoms may or may not require carotid endarterectomy; if he does, denervation is done as an accompaniment of the endarterectomy. Carotid sinus syndrome is by definition a symptomatic hypersensitive carotid sinus and occurs spontaneously or is invoked by head turning, tight collars, etc. In its pure form it is unaccompanied by other serious disorders which may cause syncope. If this is the situation, it may be satisfactorily treated by drugs such as atropine; but. true carotid sinus syncope is rarely completely controllable by drugs and usually requires carotid sinus denervation. The syndrome may also occur in patients who have cardiac conduction defects, and, depending upon the clinical situation, proper treatment may be insertion of a pacemaker. Likewise the syndrome may be accompanied by cerebrovascular insufficiency with extracranial occlusive disease. If arteriography demonstrates the appropriate lesions, then the proper treatment is carotid endarterectomy accompanied by sinus denervation. Thus patients with hypersensitive carotid sinus and carotid sinus syndrome must be evaluated carefully in order that the proper therapy be selected for the particular individual. In summary, 19 patients were treated for carotid sinus syncope with carotid sinus denervation alone or in conjunction with carotid artery endarterectomy. This technique was successful in abolishing all further syncopal attacks and in controlling dizziness, except in three patients who had occasional dizzy spells.
Ann. Surg. * May 1979 TROUT, BROWN AND THOMPSON 10. Mancia, G., Ferrari, A., Gregorini, L. et al.: Circulatory ReCarotid sinus denervation is an effective therapeutic flexes from Carotid and Extracarotid Baroreceptor Areas in modality for the patient with carotid sinus syncope. Man. Circ. Res., 41:309, 1977.
580
References 1. Bauernfeind, R., Hall, C., Denes, P. et al.: Carotid Sinus Hypersensitivity with Alpha Methyldopa. Ann. Int. Med., 88: 214, 1978. 2. Capps, R. B. and deTakats, G.: The Late Effects of Bilateral Carotid Sinus Denervation in Man. J. Clin. Invest., 17:385, 1938. 3. Chughtai, A. L., Yans, J. and Kwatra, M.: Carotid Sinus Syncope. JAMA, 237:2320, 1977. 4. Correll, H. L. and Lindert, M. C. F.: Vasovagal Syncope: Report of a Case Apparently Induced by Digitalization. Am. Heart J., 37:446, 1949. 5. Greely, H. P., Smedal, M. I. and Most, W.: The Treatment of the Carotid Sinus Syndrome by Irradiation. N. Engl. J. Med., 252:91, 1955. 6. Hartzler, G. 0. and Maloney, J. D.: Cardioinhibitory Carotid Sinus Hypersensitivity. Arch. Intern. Med., 137:727, 1977. 7. Hemmy, D. C., McGee, D. M. and Larson, S. J.: Carotid Sinus Syndrome: Neurosurgical Management. Wis. Med. J., 74:73 1975. 8. Kartchner, M. M., McRae, L. P. and Morrison, F. D.: Noninvasive Detection and Evaluation of Carotid Occlusive Disease. Arch. Surg., 106:528, 1973. 9. Lown, B. and Levine, S. A.: The Carotid Sinus: Clinical Value of Its Stimulation. Circulation, 23:766, 1961.
DISCUSSION DR. SEYMOUR I. SCHWARTZ (Rochester, New York): My comments are somewhat tangential, since years ago we bilaterally stimulated the carotid sinus nerve with an exogenous electric traffic in order to reduce blood pressure. In the 16 patients who were treated for a long period of time with radiofrequency-induced electric traffic up both nerves, interestingly enough, we had not noted any syncopal episodes. The carotid sinus reflex is a real reflex, and I'd like to speak to this point. As Dr. Thompson's group undoubtedly knows, one of the classic methods of creating hypertension in the animal is to bilaterally transect the sinus nerve of dog, pig, and other species. As an aside, when we were interested in stimulating the nerve, we studied a series of eight young patients who had undergone bilateral neck dissection, with extensive dissection, and transection of the sinus nerves bilaterally, and noted a mean elevation in the diastolic blood pressure of somewhat over 20 mmHg in these patients. I would like to ask the question: Have these patients been studied postoperatively, those who have had bilateral transection, in reference to their diastolic pressure? Has hypertension been seen in patients who are not older, who do not have an atherosclerotic carotid sinus, with bilateral nerve transection? The other point that I would echo is the liberal use of lidocaine in the early part of dissection of Hering's nerve, because we have had experience with very exquisite hypertension when we were placing electrodes, in those cases in which we neglected to anesthetize the nerve. DR. HAROLD C. URSCHEL, JR. (Dallas, Texas): This is one of the most extensive experiences in the literature of carotid sinus denervation for carotid sinus syndrome. But far more important than that for us, I think, is that the authors have carefully defined subsets of the syndrome, which were previously often confused by dumping them all in a wastebasket diagnosis. At the same time,
11. Peretz, D. I., Gerein, A. N. and Miyagishima, R. T.: Permanent Demand Pacing for Hypersensitive Carotid Sinus Syndrome. Can. Med. Assoc. J., 108:1131, 1973. 12. Pick, J.: The Autonomic Nervous System. Philadelphia, J. B. Lippincott Company, 1970. 13. Ray, B. S. and Stewart, H. J.: Role of the Glossopharyngeal Nerve in the Carotid Sinus Reflex in Man: Relief of Carotid Sinus Syndrome by Intracranial Section of the Glossopharyngeal Nerve. Surgery, 23:411, 1948. 14. Rudnikoff, I.: Insulin and the Carotid Sinus. Ann. Intern. Med., 34:1382, 1951. 15. Sigler, L. H.: The Cardioinhibitory Carotid Sinus Reflex: Its Importance as a Vagocardiosensitivity Test. Am. J. Cardiol., 12:175, 1963. 16. Thomas, J. E.: Hyperactive Carotid Sinus Reflex and Carotid Sinus Syncope. Mayo Clin. Proc., 44:127, 1969. 17. Thompson, J. E.: Surgery for Cerebrovascular Insufficiency (Stroke). Springfield, Ill., Charles C Thomas, 1968. 18. Thompson, J. E. and Talkington, C. M.: Carotid Endarterectomy. Ann. Surg., 184:1, 1976. 19. Weiss, S. and Baker, J. P.: The Carotid Sinus Reflex in Health and Disease: Its Role in the Causation of Fainting and Convulsions. Medicine (Baltimore), 12:297, 1933. 20. White, J. C., Smithwick, R. H. and Simeone, F. A.: The Autonomic Nervous System, Third Edition. New York, The MacMillan Company, 1952.
they have provided us a very appropriate road map for the management of each subset; and this, again, is excellent. Our experience has been primarily with patients requiring pacemakers for associated cardiac conduction defects, because of the nature of referral practice. In all of our cases in which carotid sinus denervation has been carried out, we have added a pacemaker-the belt-and-suspenders philosophy in action. Therefore, I'm very much impressed with Dr. Thompson's group of patients that had carotid sinus stimulation alone, and the success that he has had with it. DR. HUGH H. TROUT, III (Closing discussion): Dr. Urschel, thank you for your comments. Dr. Schwartz, though in dogs permanent experimental hypertension may be produced by bilateral carotid sinus nerve resection, Dr. Thompson and his partners have not seen permanent hypertension after 264 staged bilateral carotid endarterectomies in man, in which the carotid sinus nerves are routinely divided. This would support our impression that the extracarotid baroreceptors are more influential than the carotid sinus baroreceptors in man. Thus, this is probably a species difference between man and dog. I would like to reemphasize several points. First considerable caution should be exercised prior to testing for carotid sinus syndrome. Five of our patients have required cardiac resuscitation during provocative carotid sinus stimulation. Careful monitoring of patients undergoing testing is necessary, and this testing should be carried out in an area where resuscitative equipment is available. Second, this is a rare entity. Strict criteria for a positive test for hypersensitive carotid sinus should be met, and the syncopal symptoms should be reproducible with carotid sinus massage before any therapy is instituted. Finally, if done properly, this operative procedure is not technically difficult, and enjoys the advantage of essentially no morbidity, combined with no known regeneration of nerves. Consequently, in the carefully selected patient with this unusual condition, the procedure of carotid sinus denervation is almost always successful in abolishing or substantially ameliorating syncopal symptoms.
Hypersensitive carotid sinus is a rare cause of spontaneous syncopal attacks. It must be differentiated from the other more common causes, such as intrinsic cardiac disease, vasovagal responses, postural hypotension and cerebrovascular insufficiency, although it may accompany these conditions. The definition of carotid sinus syncope is syncope elicited by stimulation of a hypersensitive carotid sinus. Nineteen patients with carotid sinus syncope were treated by carotid sinus denervation. Ages ranged from 48 to 83 with a mean of 65.5 years. Syiwptoms of marked dizziness or syncope were reproduced by gentle compression over the carotid bifurcation, while ECG monitoring revealed bradycardia or transient asystole. Seventeen patients had carotid arteriograms, eleven of which were normal. One patient had stenosis of the external carotid artery, while five had stenosis of the internal carotid. The right carotid sinus was involved in ten patients, the left in three and both sides in six. All patients underwent unilateral or bilateral carotid sinus denervation. Five patients with internal carotid stenosis had concomitant carotid endarterectomy. Complete relief of symptoms or marked improvement was noted in all but one patient. Postoperative follow-up ranged up to 15 years. Carotid sinus denervation is a simple, effective method of treating this disorder. FOR CENTURIES WARRIORS AND PHYSICIANS have
recognized that an effective method of inducing loss of consciousness is deliberate carotid artery compression. Indeed the etymology of the word carotid is founded on the understanding of the consequences of carotid occlusion. In contrast to deliberate occlusion, however, on rare occasions inadvertent gentle carotid manipulation elicited by neck massage, turning the head, or even by a tight collar may produce similar symptoms of dizziness or syncope. In these situations the decreased cerebral blood flow is not caused by Presented at the Annual Meeting of the Southern Surgical As-
sociation, December 4-6, 1978, Hot Springs, Virginia. * Current address: Department of Surgery, George Washington University Medical Center, Washington, D.C. 20037. Reprint requests: Jesse E. Thompson, M.D., Suite 505, 3600 Gaston Avenue, Dallas, Texas 75246. Submitted for publication: December 7, 1978.
From the Department of General Surgery, Baylor University Medical Center, Dallas, Texas
occlusion of a carotid artery but instead is produced by stimulation of a hypersensitive carotid sinus resulting in systemic hypotension or cardiac arrhythmia. Patients with syncope whose symptoms are reproduced by gentle neck massage are said to have carotid sinus syndrome. Nineteen such patients have been treated since 1959. This report summarizes our experience with these patients. Methods and Materials Fifteen male and four female patients presented with numerous symptoms which always included snycope or marked dizziness. These symptoms were invariably reported during gentle unilateral carotid sinus massage during careful EKG monitoring. There were five episodes of such prolonged asystole that resuscitative maneuvers were required. Figure 1 depicts a typical EKG tracing of asystole following unilateral carotid sinus stimulation. The age of patients at the time of evaluation ranged from 48 to 83 with an average of 65.6 years. Arteriograms were performed on 17 patients, and 11 of these were normal. One patient had stenosis of the external carotid artery, while five had stenoses of the internal carotid. The criteria used for determining operability were reproduction of the patient's symptoms, with concomitant demonstration of a hypersensitive carotid sinus. A hypersensitive carotid sinus was defined for this purpose as a sinus which when stimulated by gentle neck massage resulted in asystole for more than two seconds, a bradycardia of more than 30% of control or a drop in systolic blood pressure of more than 30 mm Hg. Table 1 includes the operations performed for treatment of carotid sinus syndrome.
0003-4932/79/0500/0575 $00.80 © J. B. Lippincott Company
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Ann. Surg. * May 1979
FIG. 1. EKG tracing during carotid sinus massage (arrow) showing asystole of 4.8 seconds after stimulation of right carotid sinus.
The technique for carotid sinus denervation is as follows: The patient is placed on the operating table in a supine position with a sheet beneath the shoulders and the head resting on a doughnut-shaped support and turned away from the side to be operated upon. Preoperative atropine is given, and with constant EKG and blood pressure monitoring, excessive manipulation is avoided during positioning and endotracheal intuba-
tion in order to prevent inducing the reflex. Following satisfactory induction of endotracheal anesthesia, an incision is chosen according to whether or not a concomitant carotid endarterectomy is to be performed. If so, then the incision is the usual carotid endarterectomy incision, a curvilinear incision along the anterior border of the sternocleidomastoid muscle.17 If an endarterectomy is not planned, a transverse in-
TABLE 1. Summary of Data on Patients with Carotid Sinus Syndrome
Patient
Sex
Age
I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
M F F M M M F M M M M F M M M M M M M
68 62 80 63 74 62 68 59 79 48 66 83 64 60 65 60 61 52 71
Preop Symptoms S S S S S S S S S D S S D S S S S S S
Operation RCD LCD LCD RCD RCD RCD RCD RCD RCD RCD
RCD, LCD RCD, LCD RCD, LCD RCD, LCD RCD&E RCD&E LCD&E RCD, LCD&E RCD&E, LCD&E
* = dead, S = syncope, D = dizziness, I = improved, = residual left hand paresis, RCD = right carotid denervation, LCD = left
Result
I, rarely mild dizziness Relieved Relieved Relieved I, rarely mild dizziness Relieved I, orthostatic hypotension Relieved I, mild dizziness Relieved Developed heart block Relieved Relieved Relieved
Relievedt Relieved Relieved Relieved Relieved
Follow-up (mo.) 56* 185 66 10 55 52 121* 29 83 144 116 38* 11* 156* 81 24 35* 131 48*
carotid denervation, RCD&E = right carotid denervation and endarterectomy, LCD&E = left carotid denervation and endarterectomy.
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CAROTID SINUS SYNDROME
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cision is used in a skinfold at the level of the carotid bifurcation. With either incision the carotid bifurcation is exposed, and the sinus is gently infiltrated with 1% plain lidocaine prior to mobilization. The adventitia is stripped from the common carotid artery, the bifurcation, and for about 1 cm up both the external and internal carotid arteries. All nerve fibers entering the crotch of the carotid bifurcation are ligated and divided until the bifurcation is completely free. A small drain is left in place, and the platysma muscle and the skin are closed in layers. The patient remains in bed for 36 hours and then is allowed to walk with assistance until vasomotor stability is assured. The drain is removed the morning after the operation. If a carotid endarterectomy is performed the technique employed is that previously reported.17'18 If no endarterectomy is necessary and the patient is in a high risk category, the surgeon may safely elect to denervate the carotid sinus with the use of local anesthesia. Results (Table 1)
Results of operation have been quite satisfactory. There has been no operative mortality. Fourteen patients have remained completely free of their original symptoms at the time of their last follow-up or at death. Three patients were improved, having occasional mild dizziness. One of these had moderate sensitivity of the unoperated sinus but was not subjected to operation since he developed carcinoma of the prostate, from which he died. One patient was relieved of symptoms for five years and then developed postural hypotenslibn, parkinsonism and organic brain syndrome with recurrence of syncope in the upright position. Another patient was relieved temporarily, only to develop congestive heart failure and complete heart block requiring insertion of a pacemaker. One patient relieved by sinus denervation developed contralateral carotid stenosis and hypersensitive sinus several years later and underwent denervation and endarterectomy with relief. The only serious complication occurred in a patient who had denervation concomitant with endarterectomy; a mild, persistent weakness of the left hand was believed to be secondary to embolism of a platelet aggregation. Follow-up ranged from 10 to 185 months, with an average of 76 months. Seven long-term deaths occurred, two from cardiac causes, two from cerebral causes, two from cancer and one suicide. There has been no evidence of regeneration of nerves in a denervated sinus; this corroborates the results of others who have reported on this operation.
Discussion
Hypersensitive carotid sinus is a rare cause of spontaneous syncopal attacks. It must be differentiated from the other more common causes, such as vasovagal responses, intrinsic cardiac disease, postural hypotension and cerebrovascular insufficiency, although it may accompany these conditions. The two carotid sinuses are located at the bifurcation of each common carotid artery. The nerve fibers supplying the sinuses terminate in the sensory end organs in the walls of the artery and carotid body and are derived from afferent fibers from both the vagus and glossopharyngeal nerves, with efferent connections from the superior cervical ganglion of the sympathetic trunk.20 The principal efferent pathway of the reflex arc is the vagus nerve.'2 The carotid sinus reflex is believed to have fundamental regulatory influences over cardiovascular function. The recognized changes after an increase in intrasinus tension are decrease in systemic blood pressure, bradycardia and slowing of respiration; the opposite effects follow a decrease in tension within the sinus.16 Though the carotid sinus baroreceptor reflex can be demonstrated in man, there is some doubt as to whether the carotid sinus is as powerful a regulator as are the extracarotid baroreceptors.'0 Our clinical impression is that the carotid sinus is a relatively noncritical regulator in the adult human; after either unilateral or bilateral carotid sinus denervation or carotid endarterectdtny, in which carotid sinus denervation is usually performed, the only vasomotor instability has been occasional transient hypertension for a few days postoperatively. Weiss and Baker19 describe three possible responses following stimulation of a hyperactive carotid sinus: 1) the cardioinhibitory type of response with bradycardia or asystole, 2) the vasodepressor type of hypotensive response without cardiac slowing and 3) a primary central cerebral type not accompanied by either systemic hypotension or by bradycardia. Since this was postulated prior to the appreciation of the frequency and extent of extracranial carotid occlusive lesions, it can probably be safely assumed that patients in this third category had syncopal attacks as a result of cerebrovascular insufficiency and not hypersensitive carotid sinUts. Considering this, a reasonable classification would seem to be 1) the cardioinhibitory type, which is by far the more common, and 2) the vasodepressor type. One should keep in mind that either type can coexist with either a hemodynamically important occlusive lesion in one or both carotid arteries or with a clinically significant cardiac conduction defect. A workable definition of what constitutes a hyper-
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active response has been proposed by Franke and is reviewed by Thomas.'6 An abnormal response is one in which cardiac asystole lasts three or more seconds or systolic and diastolic blood pressure drop 50 mmHg or more. A borderline response is one in which asystole lasts two seconds, the heart rate slows by more than 30% or the systolic blood pressure drops by more than 30 mmHg. In our opinion a patient with symptoms of syncope or moderate dizziness reproduced by an abnormal or borderline response to stimulation should be treated. Patients in whom carotid sinus syncope is suspected should have a thorough cardiac evaluation concentrating particularly on cardiac conduction abnormalities. They should also be carefully examined for extracranial cerebral occlusive disease by listening for carotid bruits. A noninvasive test, occuloplethysmography, should, if available, also be performed in an attempt to detect diminished cerebral blood flow.8 If an occlusive lesion is suspected a cerebral arteriogram should be obtained. When provocative carotid sinus stimulation is performed, considerable caution must be exercised since five of our 19 patients required resuscitation following this maneuver. Many methods have been employed, but a satisfactory technique of carotid sinus stimulation is as follows: The patient is placed in a supine position, and, while a second examiner monitors both blood pressure and a continuous EKG tracing, gentle unilateral carotid massage is performed for 10-20 seconds with the head in a relatively neutral position. Both sides are stimulated separately with several minutes' rest between sides. If neither stimulation elicits a response, the same maneuvers may be performed with the patient in a sitting position. The testing should be suspended immediately if a positive response is obtained or if marked dizziness or syncope develops. Simultaneous testing of both sides should never be performed, and testing should be done in an area where complete resuscitative equipment is readily available, such as a cardiac catheterization laboratory. During carotid sinus stimulation the examiner should avoid applying pressure sufficient to occlude the carotid artery. If cerebrovascular occlusive disease is suspected on the basis of physical examination or as a result of the occuloplethysmogram, the patient should be monitored as well with a continuous electroencephalogram during the carotid sinus stimulation. A hyperactive carotid sinus is not a subtle entity; if present, a positive response is quickly apparent. Among our patients elderly males with right-sided hypersensitivity predominated. This same prevalence is noted in almost all reports of carotid sinus syncope. Predisposing factors include generalized arteriosclero-
Ann. Surg. * May 1979
sis, hypertension, coronary artery disease and diabetes mellitus.94 The normal response to carotid sinus massage is sinoatrial slowing with minimal increase in the PR interval.'5 When ventricular asystole occurs following stimulation of a hypersensitive sinus, the usual mechanism of this asystole is sinoatrial arrest with failure of lower escape pacemakers, although occasionally an alternative mechanism is atrioventricular block.6 Hartzler and Maloney6 performed carotid sinus massage on 100 patients undergoing His bundle electrocardiography. Among their patients in whom a hypersensitive carotid sinus was detected, they noted an increased incidence of resting sinus bradycardia, right bundle branch block and mild aortic valve stenosis. Drugs which are said to potentiate carotid sinus hypersensitivity are digitalis,4 methyldopa,1 morphine and thyroid extract.20 Several of our patients were taking digitalis preparations, but we were unable to relate their sinus sensitivity to their medications. As implied above, a hypersensitive carotid sinus reflex following provocative stimulation without spontaneous clinical symptoms does not require treatment. However, the carotid sinus syndrome, which may be defined as syncope or marked dizziness reproduced by a carotid sinus stimulation test, should be treated because of the considerable risk of injury in the elderly patient following a fall. Treatment modalities have included atropine, ephedrine, neck irradiation, glossopharyngeal transsection via a craniotomy, insertion of a cardiac pacemaker and denervation of the carotid sinus. In the cardioinhibitory type of hypersensitive carotid sinus, atropine sulfate, 0.5 mg orally four times a day, may be tried; in the infrequent vasodepressor type, 30 mg of ephedrine two or three times daily may be effective. 16 These measures, however, are rarely beneficial in those patients with obvious carotid sinus syncope, and other therapy is necessary. Though sectioning of the glossopharyngeal nerve has been performed,7'13 this requires an intracranial approach and, given the success with other less extensive procedures, this procedure seems extreme. Three therapeutic modalities which have been reported to be reasonably successful are neck irradiation,5 insertion of a cardiac pacemaker3'11 and denervation of the carotid sinus.12'16'20 Neck irradiation is said to be successful in about two-thirds of those treated, and in elderly high risk patients it may well be a method worth considering. The disadvantages would appear to be that the therapeutic benefit is delayed, that the neck would receive substantial amounts of irradiation and that this method
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is probably not as effective as the other two. We have had no experience with it, however. Insertion of a cardiac pacemaker is usually successful and may be employed in those patients who have a concomitant conduction defect which itself may benefit by pacing. The disadvantages of cardiac pacing are that, relatively simple as it is to perform, it is more difficult than carotid sinus denervation and it requires more careful long-term follow-up to check on continued correct placement of the catheter and adequate battery charge. Carotid sinus denervation is the modality we have employed. It is simple to perform with minimal risk in the hands of an experienced surgeon, and it may be combined with a carotid endarterectomy in the patient with a stenotic lesion. If the technique for denervation described above is employed, there is no evidence of recurrent sinus reflex activity. Regeneration of nerves does not seem to occur. The only operative complication among our 19 patients was a mild, permanent weakness of the left hand in a patient who had a severe left carotid stenosis with an ulcerated plaque, who had had a carotid endarterectomy at the time of the denervation. This is one of seven mild permanent deficits following carotid endarterectomy in 516 patients operated upon by the senior author (JET). Thus the risk of death or stroke appears to be minimal for denervation alone and 1-2% in those patients in whom both an endarterectomy and denervation are necessary. When bilateral denervation without endarterectomy is warranted, both sides may be operated upon at the same time. If endarterectomy is required on one or both sides, the operations should be staged a week or more apart. Though postural hypotension has been reported following bilateral denervation,2 this complication has not been observed following 264 bilateral cartoid endarterectomies performed by the senior author and his partners, despite the fact that the carotid sinus nerves are usually routinely divided during endarterectomy. We do not attempt preoperative percutaneous anesthetic injection of the carotid sinus, as we believe that this maneuver may provoke an attack. Also, once a patient's symptoms have been reproduced by gentle carotid sinus stimulation, we believe further diagnostic studies are unwarranted and may be dangerous. In that setting we would proceed to carotid sinus denervation or insertion of a cardiac pacemaker depending on the clinical situation. Protocol for Treatment (Table 2) There has been confusion regarding terminology and indications for different types of therapy for the hypersensitive carotid sinus. It has been clearly dem-
579 TABLE 2. Tr-eatmtietit
Hypersensitive Carotid Sinus (HCS) 1. HCS 2. HCS and CDD 3. HCS and CVI
Carotid Sinus Syndrome (CSS) 4. CSS 5. CSS and CDD 6. CSS and CVI
No treatment Cardiac therapy Carotid endarterectomy and CS denervation
CS denervation Cardiac pacemaker Carotid endarterectomy and CS denervation
CDD = cardiac conduction defect, CVI = cerebrovascular insufficiency, CS = carotid sinus.
onstrated by a number of observers that a carotid sinus may be hypersensitive when tested by massage or compression, but the patient may be completely asymptomatic; if this is so and if there are no associated diseases, no treatment is necessary. On the other hand, the patient may have an asymptomatic hypersensitive carotid sinus as well as an associated cardiac problem with a conduction defect or may have symptoms of cerebrovascular insufficiency with extracranial occlusive disease. In the former situation, appropriate cardiac therapy is in order with either drugs or a pacemaker, but carotid sinus denervation is not done. The patient with cerebral symptoms may or may not require carotid endarterectomy; if he does, denervation is done as an accompaniment of the endarterectomy. Carotid sinus syndrome is by definition a symptomatic hypersensitive carotid sinus and occurs spontaneously or is invoked by head turning, tight collars, etc. In its pure form it is unaccompanied by other serious disorders which may cause syncope. If this is the situation, it may be satisfactorily treated by drugs such as atropine; but. true carotid sinus syncope is rarely completely controllable by drugs and usually requires carotid sinus denervation. The syndrome may also occur in patients who have cardiac conduction defects, and, depending upon the clinical situation, proper treatment may be insertion of a pacemaker. Likewise the syndrome may be accompanied by cerebrovascular insufficiency with extracranial occlusive disease. If arteriography demonstrates the appropriate lesions, then the proper treatment is carotid endarterectomy accompanied by sinus denervation. Thus patients with hypersensitive carotid sinus and carotid sinus syndrome must be evaluated carefully in order that the proper therapy be selected for the particular individual. In summary, 19 patients were treated for carotid sinus syncope with carotid sinus denervation alone or in conjunction with carotid artery endarterectomy. This technique was successful in abolishing all further syncopal attacks and in controlling dizziness, except in three patients who had occasional dizzy spells.
Ann. Surg. * May 1979 TROUT, BROWN AND THOMPSON 10. Mancia, G., Ferrari, A., Gregorini, L. et al.: Circulatory ReCarotid sinus denervation is an effective therapeutic flexes from Carotid and Extracarotid Baroreceptor Areas in modality for the patient with carotid sinus syncope. Man. Circ. Res., 41:309, 1977.
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References 1. Bauernfeind, R., Hall, C., Denes, P. et al.: Carotid Sinus Hypersensitivity with Alpha Methyldopa. Ann. Int. Med., 88: 214, 1978. 2. Capps, R. B. and deTakats, G.: The Late Effects of Bilateral Carotid Sinus Denervation in Man. J. Clin. Invest., 17:385, 1938. 3. Chughtai, A. L., Yans, J. and Kwatra, M.: Carotid Sinus Syncope. JAMA, 237:2320, 1977. 4. Correll, H. L. and Lindert, M. C. F.: Vasovagal Syncope: Report of a Case Apparently Induced by Digitalization. Am. Heart J., 37:446, 1949. 5. Greely, H. P., Smedal, M. I. and Most, W.: The Treatment of the Carotid Sinus Syndrome by Irradiation. N. Engl. J. Med., 252:91, 1955. 6. Hartzler, G. 0. and Maloney, J. D.: Cardioinhibitory Carotid Sinus Hypersensitivity. Arch. Intern. Med., 137:727, 1977. 7. Hemmy, D. C., McGee, D. M. and Larson, S. J.: Carotid Sinus Syndrome: Neurosurgical Management. Wis. Med. J., 74:73 1975. 8. Kartchner, M. M., McRae, L. P. and Morrison, F. D.: Noninvasive Detection and Evaluation of Carotid Occlusive Disease. Arch. Surg., 106:528, 1973. 9. Lown, B. and Levine, S. A.: The Carotid Sinus: Clinical Value of Its Stimulation. Circulation, 23:766, 1961.
DISCUSSION DR. SEYMOUR I. SCHWARTZ (Rochester, New York): My comments are somewhat tangential, since years ago we bilaterally stimulated the carotid sinus nerve with an exogenous electric traffic in order to reduce blood pressure. In the 16 patients who were treated for a long period of time with radiofrequency-induced electric traffic up both nerves, interestingly enough, we had not noted any syncopal episodes. The carotid sinus reflex is a real reflex, and I'd like to speak to this point. As Dr. Thompson's group undoubtedly knows, one of the classic methods of creating hypertension in the animal is to bilaterally transect the sinus nerve of dog, pig, and other species. As an aside, when we were interested in stimulating the nerve, we studied a series of eight young patients who had undergone bilateral neck dissection, with extensive dissection, and transection of the sinus nerves bilaterally, and noted a mean elevation in the diastolic blood pressure of somewhat over 20 mmHg in these patients. I would like to ask the question: Have these patients been studied postoperatively, those who have had bilateral transection, in reference to their diastolic pressure? Has hypertension been seen in patients who are not older, who do not have an atherosclerotic carotid sinus, with bilateral nerve transection? The other point that I would echo is the liberal use of lidocaine in the early part of dissection of Hering's nerve, because we have had experience with very exquisite hypertension when we were placing electrodes, in those cases in which we neglected to anesthetize the nerve. DR. HAROLD C. URSCHEL, JR. (Dallas, Texas): This is one of the most extensive experiences in the literature of carotid sinus denervation for carotid sinus syndrome. But far more important than that for us, I think, is that the authors have carefully defined subsets of the syndrome, which were previously often confused by dumping them all in a wastebasket diagnosis. At the same time,
11. Peretz, D. I., Gerein, A. N. and Miyagishima, R. T.: Permanent Demand Pacing for Hypersensitive Carotid Sinus Syndrome. Can. Med. Assoc. J., 108:1131, 1973. 12. Pick, J.: The Autonomic Nervous System. Philadelphia, J. B. Lippincott Company, 1970. 13. Ray, B. S. and Stewart, H. J.: Role of the Glossopharyngeal Nerve in the Carotid Sinus Reflex in Man: Relief of Carotid Sinus Syndrome by Intracranial Section of the Glossopharyngeal Nerve. Surgery, 23:411, 1948. 14. Rudnikoff, I.: Insulin and the Carotid Sinus. Ann. Intern. Med., 34:1382, 1951. 15. Sigler, L. H.: The Cardioinhibitory Carotid Sinus Reflex: Its Importance as a Vagocardiosensitivity Test. Am. J. Cardiol., 12:175, 1963. 16. Thomas, J. E.: Hyperactive Carotid Sinus Reflex and Carotid Sinus Syncope. Mayo Clin. Proc., 44:127, 1969. 17. Thompson, J. E.: Surgery for Cerebrovascular Insufficiency (Stroke). Springfield, Ill., Charles C Thomas, 1968. 18. Thompson, J. E. and Talkington, C. M.: Carotid Endarterectomy. Ann. Surg., 184:1, 1976. 19. Weiss, S. and Baker, J. P.: The Carotid Sinus Reflex in Health and Disease: Its Role in the Causation of Fainting and Convulsions. Medicine (Baltimore), 12:297, 1933. 20. White, J. C., Smithwick, R. H. and Simeone, F. A.: The Autonomic Nervous System, Third Edition. New York, The MacMillan Company, 1952.
they have provided us a very appropriate road map for the management of each subset; and this, again, is excellent. Our experience has been primarily with patients requiring pacemakers for associated cardiac conduction defects, because of the nature of referral practice. In all of our cases in which carotid sinus denervation has been carried out, we have added a pacemaker-the belt-and-suspenders philosophy in action. Therefore, I'm very much impressed with Dr. Thompson's group of patients that had carotid sinus stimulation alone, and the success that he has had with it. DR. HUGH H. TROUT, III (Closing discussion): Dr. Urschel, thank you for your comments. Dr. Schwartz, though in dogs permanent experimental hypertension may be produced by bilateral carotid sinus nerve resection, Dr. Thompson and his partners have not seen permanent hypertension after 264 staged bilateral carotid endarterectomies in man, in which the carotid sinus nerves are routinely divided. This would support our impression that the extracarotid baroreceptors are more influential than the carotid sinus baroreceptors in man. Thus, this is probably a species difference between man and dog. I would like to reemphasize several points. First considerable caution should be exercised prior to testing for carotid sinus syndrome. Five of our patients have required cardiac resuscitation during provocative carotid sinus stimulation. Careful monitoring of patients undergoing testing is necessary, and this testing should be carried out in an area where resuscitative equipment is available. Second, this is a rare entity. Strict criteria for a positive test for hypersensitive carotid sinus should be met, and the syncopal symptoms should be reproducible with carotid sinus massage before any therapy is instituted. Finally, if done properly, this operative procedure is not technically difficult, and enjoys the advantage of essentially no morbidity, combined with no known regeneration of nerves. Consequently, in the carefully selected patient with this unusual condition, the procedure of carotid sinus denervation is almost always successful in abolishing or substantially ameliorating syncopal symptoms.
