Symposium on Cardiac Rhythm Disturbances I

The Tachycardia-Bradycardia Syndrome Benjamin M. Kaplan, M.D. *

Paroxysmal atrial fibrillation, flutter, or tachycardia followed by sinoatrial block or sinus arrest, resulting in Stokes-Adams attacks, characterizes the tachycardia-bradycardia syndrome':

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Figure 4. Monitored chest lead. (A CA continuous strip.) Sudden cessation of atrial fibrillation with a fast ventricular response standstill ()f atria and ventricles for more than 4.5 seconds. The cause is not sinoatrial block but (average rate 130) is followed by standstill()f general pacemaker depression as revealed by the gradual shortening of the emerging sinus cycles and by the absence of escapes of subsidiary junctional pacemakers during the long sinus intervals. Times are in hundredths of a second.

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Figure 5. (Same patient as Fig. 4) On March 25 there is repetitive escape of a temporary demand pacemaker set to a cycle length of 0.80 sec (rate 75), about 0.08 sec shorter than the slightly uneven sinus cycles. This results in incomplete atrioventricular dissociation in which two or three successive sinus impulses succeed in capturing the ventricles entirely or partially (cf. fusion beat in the middle of lead 11). On March 27 when the pacemaker was temporarily turned off, the atrial (and ventricular) rate dropped to one half revealing the tendency to (a) spontaneous 2: 1 sinoatrial block, (b) absence of subsidiary atrioventricular junctional pacemaker escapes, and thus the need for permanent pacing.

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Figure 6. Continuous monitored chest lead. The last two ventricular complexes of each strip are reproduced as the first two on the next strip. Demand pacing of the right ventricle prevents cardiac arrest following a bout of atrial fibrillation. In the bottom strip sinus activity has resumed, first at a slow rate (cycle length 2.00 to 2.04 sec) alternating with paced beats. The latter disappear when in the last part of the record the sinus cycle abruptly doubles. Thus, on this day, a sinoatrial block is revealed as the cause of the atrial standstill and of the subsequent slow atrial rate.

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heart action in describing the syndrome of "alternating bradycardiatachycardia." He pointed out that "a means of maintaining auricular fibrillation for these individuals would be invaluable." Subsequently Birchfield et a1. aP7 demonstrated the failure of atropine to increase the sinus rate in a patient who experienced sinus bradycardia, asystole with More recently Lown45 . 46 coined syncope, and transient atrial fibrillation. lVIore the term "sick sinus syndrome" for those patients who experienced little or erratic atrial activity (sinoatrial block or sinoatrial arrest) after electrical countershock for atrial fibrillation. He, like Short,66 indicated that atrial fibrillation "was a blessing for individuals with arrhythmias of the Parkinson-Papp-Evans54 variety, and these patients should not be reverted." Today's extensive interest in the sick sinus syndrome can be at24 -- 26 Her comprehensive publications, as well as the tributed to Ferrer.24 one of Rubenstein et a1. 62 have detailed the various clinical components of this entity and have emphasized the significance of the interrelationship of atrial excitability and sinus node function in the production of the cardiac arrhythmias (including the tachycardia-bradycardia syndrome.) Numerous authors have reported on the effectiveness of pacemaker treatment and/or drug therapy for the tachycardia-bradycardia syndrome.3. 4. 9.10.14.15.17.28.36.37.38.59.65.73 9. 10. 14. 15. 17.28.36.37.38.59.65.73

MECHANISMS AS REVEALED BY THE ELECTROCARDIOGRAM Ventricular standstill may occur after a bout of ventricular tachycardia or ventricular fibrillation in. in the presence of a high degree or complete atrioventricular block. 54 In an analogous manner, a period of atrial asystole may be noted following termination of paroxysmal atrial tachycardia, flutter or fibrillation in patients with sinoatrial block. The failure of the sinus node or atrioventricular junction, or both, to begin to function promptly may be due to either vagal effects, drugs, intrinsic disease, or depression of function of the pacemaker tissue. It has been demonstrated in human beings and in animals that the inherent automaticity of the sinus pacemaker could be transiently inhibited, or conduction of its -the rapid ectopic impulse depressed, by a single premature systole or by a ral?id 31. 40. 47. 49. 51, 53. 56 The length of the "pre-automatic "pre~automatic tachycardia. 2. 5. 8. 30. 31, pause" was most marked when the preceding rate was the th.e most rapid. Others12 . 21, 23 have shown that rapid atrial and ventricular stimulation in patients with a high degree of atrioventricular block and qnd the StokesAdams syndrome produced a similar phenomenon of "depression" of the subsidiary pacemaker escape mechanisms. The degree of depression of the atrioventricular junction was further increased by administration of digitalis, but was reduced by isoproterenol or epinephrine. The mechanisms of spontaneous pacemaker failure fail~re are: (1) depression of impulse formation (arrest) (Figs. 3 and 4); (2) depression of impulse conduction (exit block) (Figs. 5 and 6); and (3) combination of (1) and (2).

THE TACHYCARDIA-BRADYCARDIA SYNDROME

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Arrest and exit block of the sinus or subsidiary pacemaker cannot always be distinguished in. the electrocardiogram, particularly when there are P waves of varying contour that suggest a shifting atrial pacemaker. One diagnostic clue to arrest (depression of impulse formation) is the demonstration of gradual acceleration ("warming up") of the returning pacemaker rate (Fig. 3 and 4). However, this observation does not always exclude Type I sinoatrial block (sinoatrial block with Wenckebach periods) as the underlying mechanism. On the other hand, abrupt return of a regular rhythm and/or sudden halving or doubling of any pacemaker rate would point toward the existence of depression of impulse conduction (exit block) (Figs. 5 and 6). Thus, the pause that is seen after cessation of a bout of paroxysmal atrial tachycardia, flutter, or fibrillation may be due to either or both of these mechanisms involving the sinus and/or atrioventricular junctional pacemakers. As the number of ventricular ectopic beats may be increased in the presence of a slow ventricular rate, so may ectopic atrial activity and atrial tachyarrhythmias be more frequent in the presence of sinus bradycardia (Fig. 7).29 However, in one aspect, the disturbance at the atrial level differs fundamentally from that at the ventricular level; whereas ectopic ventricular rhythms endanger the life of the patient, atrial arrhythmias, if they remain permanent, may be beneficial for pa58, 68. tients with the "sick" or "sluggish sinus node."33, 58, 68, 69 69 Thus, unless an artificial pacemaker has been previously inserted, conversion of patients with atrial fibrillation with pre-existing sinus bradycardia or sinoatrial block is undesirable because of the risk of asystole. Unresolved is the clinical paradox of atrial fibrillation, flutter, or tachycardia with a rapid ventricular response, followed or preceded by a prolonged pause resulting from the failure of an atrioventricular junctional escape mechanism (Figs. 1 to 4, and 7). Although the atrioventricular junction transmits impulses well, its automaticity is depressed by ectopic atrial beats or the atrial tachyarrhythmias. This paradox suggests independence of the two atrioventricular junctional functions. The dual role may be explained by the observation that atrioventricular conduction and automaticity appear to be related to different portions of 19 •, 32. 32, 55. 55, 71 the atrioventricular junctional tissues. 19 The tachycardia-bradycardia syndrome is not the only example of such a functional dissociation of atrioventricular junctional tissue. Excessive doses of digitalis also produce two seemingly opposite effects. Too much digitalis may lead to impairment of atrioventricular conduction and slowing of the ventricular rate; however, overdigitalization may also enhance automaticity, as manifested by nonparoxysmal atrioventricular junctional tachycardia. The two rhythm disorders may occur separately or simultaneously, and may cause complete atrioventricular dissociation with or without atrioventricular block. Decreased atrioventricular conduction and increased automaticity of the atrioventricular junction accompany other clinical conditions, such as acute posteroinferior wall myocardial infarction, acute rheumatic myocarditis, or post55 surgical cardiac trauma. 55

Figure 7. Continuous monitored chest lead. Paroxysmal atrial fibrillation develops when atrial premature beats occur 2:11 sinoatrial block. The first two premature beats (the fourth and fifth complexes in the upper strip) appear to increase during 2: the sinoatrial block so that an atrioventricular junctional pacemaker can escape at a slow rate of about 40. The third premature impulse presumably elicits a paroxysm of atrial fibrillation with a rapid ventricular response (at an average rate of 135 per min).

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THE TACHYCARDIA-BRADYCARDIA SYNDROME

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ANATOMIC BASIS The method of the pathologic examination of the two cases of tachycardia-bradycardia syndrome,35 studied in extensive anatomic detail, included serial section analyses of the sinoatrial and atrioventricular nodes and their approaches, the atrioventricular bundle, and a complete study of the atria. 6,. 41, 41. 42, 42. 61 Disease of both nodal regions and the atria was present in these two patients. Coronary atherosclerosis and the pathologic effects of azotemia were noted in one, while atrial amyloidosis and coronary atherosclerosis were seen in the other. These findings would point toward two correlations: (1) pathologic involvement of both the sinoatrial node and atrioventricular junction is a feature of the tachycardia-bradycardia syndrome; (2) atrial disease is also part of this entity. Anatomic studies of the conduction system of two other documented cases of tachycardia-bradycardia syndrome have been published. In one case Cohn and Lewis 16 observed destruction of the upper end of the sinus node and fibrosis and dilation of the atria. Rasmussen57 reported extensive fibrosis of the sinoatrial node and sinoatrial junction in his case. From the available descriptions there is no assurance that the atria and the conduction systems were properly sampled in either of these two· two cases. Others have studied the cardiac pathologic features of sinus and atrial rhythm disorders. 33, 34, 44, 50, 67, 70, 72 disorders.!.1, 6, 13, 18, 18,33,34,44,50,67,70,72 To date, coronary atherosclerosis, amyloidosis, renal insufficiency with azotemia, and trauma following open heart surgery would all appear to have clinical correlation with the tachycardia-bradycardia 26 lists the following diseases that cause the sick syndrome. Ferrer24 - 26 sinus syndrome: (1) ischemic, sclerotic, and rheumatic diseases; (2) inflammatory diseases; (3) acute and chronic coronary disease, including coronary artery occlusion; (4) pericarditis; (5) cardiomyopathies; (6) Friedreich's ataxia; (7) collagen disease; (8) progressive muscular dystrophy; (9) amyloidosis; (10) hemochromatosis; (11) surgical injury to the sinoatrial node; (12) metastatic disease; (13) fibrotic infiltration of unknown cause; (14) familial sinoatrial nodal disease. Whether the same pathology is present in the tachycardia-bradycardia syndrome as described for the other sinus and atrial disorders of the sick sinus syndrome has not been determined as yet, but it would be reasonable to expect similar anatomic abnormalities in these disorders.

CLINICAL PICTURE Symptomatology The clinical expressions of the tachycardia-bradycardia syndrome are primarily those of cerebral ischemia as a result of the marked bradycardia. Lightheadedness, dizziness, syncope, and convulsions result from the period of asystole that follows the tachycardia. Lesser neurologic manifestations may also be present, but usually do not alert the physician to the diagnosis of the tachycardia-bradycardia syndrome. Palpitations, flushing of the face, pounding of the heart, weakness, retrosternal

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BENJAMIN

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KAPLAN

pressure, all may be presenting complaints caused by the tachycardia. Since the rapid heart action is usually not lengthy, signs of severe coronary insufficiency, hypotension, or acute congestive failure are uncommon. Because sinus bradycardia and/or atrial premature beats often precede the tachycardia-bradycardia syndrome, minor cardiac and/or neurologic complaints may be present for years prior to the onset of the tachycardia-bradycardia syndrome. On the other extreme, death rarely occurs during the first episode of the tachycardia-bradycardia syndrome, unless the latter is associated with an acute myocardial infarction. An increased incidence of valvular (aortic and mitral) heart disease and systemic emboli has been reported in patients with tachycardiabradycardia syndrome. 33 We have not made similar observations. Our experience would indicate that the majority of patients are aged. Some suffer from ischemic heart disease, but very often the etiologic basis for the rhythm disturbance remains unknown during life. The characteristic rhythm disturbance has also been seen following open heart 10 individuals.1O surgery in young individuals.

Diagnosis The electrocardiogram serves as the only means of making the precise diagnosis of the tachycardia-bradycardia syndrome. Although one may suspect this syndrome from the history and/or physical examination, demonstration of the rhythm disturbance in the resting electrocardiogram or on long-term monitoring establishes the diagnosis. In patients with sinus node disease, intravenous infusion of isoproterenol may precipitate a bout of paroxysmal atrial tachycardia, fibrillation, or flutter. When the drug is withdrawn, a period of asystole may result. Atrial pacing, used in assessing sinus node recovery time,48. 49. 51. 53. 69 has 31 Nevertheless, not been found to be a reliable test for sinus node disease.31 in some patients, cessation of rapid pacing has been followed by a prolonged period of asystole. Either of these provocative techniques (isoproterenol infusion or atrial pacing), may be warranted when one suspects the tachycardia-bradycardia syndrome as the basis of cardiac and/or neurologic symptoms and cannot make the diagnosis by the resting electrocardiogram or long term monitoring. Intraventricular conduction defects including left bundle branch block, right bundle branch block and fascicular blocks have been frequent occurrences in patients with this entity. Other commonly associated electrocardiographic patterns include left ventricular hypertrophy, old myocardial infarction and nonspecific STT abnormalities. Ventricular arrhythmias are rare. Prognosis Since pacemaker implantation combined with pharmacologic therapy has provided a satisfactory means of treatment, the prognosis for life of patients with the tachycardia-bradycardia syndrome is primarily that of the underlying cardiac disorder. Indeed, the presence of severe ischemic heart disease, renal insufficiency, valvular heart disease, ventricular arrhythmias, and/or primary cerebrovascular insuffi-

THE TACHYCARDIA-BRADYCARDIA SYNDROME

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ciency, all worsen the prognosis. The pacemaker, obviously, cannot prevent death from the underlying pathologic disorder. Complications of cardiac pacing, such as displacement of an electrode, generator failure, infection, bleeding, and myocardial perforation, occur with the same frequency as noted in the general pacemaker population. Since many cases of the tachycardia-bradycardia syndrome may go undetected for years, survival statistics after clinical recognition of the rhythm disturbance have limited value.

TREATMENT Drug therapy alone is usually unsatisfactory for patients with the tachycardia-bradycardia syndrome. The medications used to prevent or treat the atrial tachyarrhythmias-namely, quinidine, procainamide, digitalis, and propranolol-are all capable of bringing about sinoatrial block or sinus arrest and depression of lower pacemakers. The dilemma is further complicated, since isoproterenol, useful for the treatment of the sinus nodal disorders, may produce atrial tachyarrhythmias. Furthermore, atropine has usually been found to be ineffective for the treatment of sinoatrial block or sinus arrest. The dilemma can be resolved by the insertion of an artificial pacemaker. With a pacemaker in place, the bradycardia can be treated adequately and the concern of producing asystole by suppressing intrinsic impulse formation with drugs eliminated. At the same time, the rapid ventricular response to recurrent atrial tachyarrhythmias, which are common even after pacemaker implantation, may be treated with digitalis or propranolol, or both, without fear of producing cardiac standstill (Figs. 5, 6, and 8); congestive heart failure, 5,6, if present, may be handled safely with digitalis. Ventricular pacing has been reported to diminish the incidence of recurrent supraventricular tachycardia4,. 14, 15,38,59,73 by increasing the atrial rate (1: 14.15.38,59,73 (1 : 1 ventriculoatrial retrograde conduction). Temporary pacing, instead of permanent pacing, may be preferable if the tachycardia-bradycardia syndrome is due to an acute reversible condition, such as trauma following open heart surgery or a recent myocardial infarction. A period of clinical observati9n is necessary to determine whether the edema and inflammation produced by these conditions will subside and thus eliminate the rhythm disturbance and need for permanent pacing. Corticosteroids have been reported to be of value under such circumstances and merit further study.28 Just as the microscopic findings in our two patients indicated pathologic alterations of the sinus node, atria and atrioventricular junction, physiologic studies52 , 58, 60, 64 in patients with sinus node disorders have demonstrated simultaneous atrioventricular junctional abnormalities and the potential development of complete atrioventricular block. Others24 , 27, 39, 57 have mentioned that the tachycardia-bradycardia syndrome may represent multiple defects in the conduction system of the heart including the atrioventricular junction. Thus, transvenous ven-

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tricular demand pacing rather than synchronous (atrial or coronary sinus) pacing is preferred for patients with this syndrome. Demand pacing is safer than fixed-rate pacing; however, the latter has the capability of terminating recurrent reciprocating tachycatdias,72 which occasionally may be part of the tachycardia-bradycardia syndrome. The advantages of both demand and fixed-rate pacing can be gained by the use of a demand pacemaker that can be converted to a fixed-rate pacemaker by the use of an external magnet or by radiofrequency trans63 Bifocal or atrioventricular sequential pacing llll has the 20 .,63 mission. 2o theoretical advantage of providing an improved hemodynamic state. However, with two electrodes (one in the atria and one in the ventricle) and a more complicated generator, the chances for pacemaker malfunction are considerably greater. Again, because of the simplicity of ventricular pacing and less risk for mechanical difficulties, ventricular pacing is considered a better choice. In the rare instance for the patient who requires the atrial contribution to cardiac output (atrial kick), atrioventricular sequential pacing would be justified. All patients with the tachycardia-bradycardia syndrome should receive maintenance doses of digitalis after pacemaker implantation. In addition, supplementary propranolol may be needed to slow the rapid ventricular response of recurrent atrial tachyarrhythmias. In some instances suppression of the ectopic atrial arrhythmias with quinidine, procainamide, or propranolol, singly or in combination, may be desirable.

RELATIONSHIP TO THE SICK SINUS SYNDROME The term "sick sinus syndrome" has been used to include numerous sinus nodal and atrial rhythm disturbances that may produce neurologic 24 26 ., 45. - 26 45, 46. 46, 62 62 All of the following electrocardiograand cardiac symptoms. 24 phic mechanisms have been considered as part of this entity: (1) sinus arrest (including atrial standstill); (2) sinoatrial block not due to drugs; (3) failure of sinus rhythm to follow electroconversion of atrial fibrillation; (4) persistent marked or unexpected sinus bradycardia with or without atrial premature systoles; (5) chronic atrial fibrillation with a slow ventricular rate, not drug produced; (6) repeated episodes of transient atrial fibrillation followed by sinus bradycardia; and (7) tachycardia-bradycardia syndrome. A proposed relationship of the various functional disorders of the atria, sinus node, and atrioventricular junctional tissues resulting in tachycardia-bradycardia syndrome is schematicized in Figure 9. Very often a patient with sinus node and atrial dysfunction will experience multiple sinus and atrial rhythm disturbances during his lifetime; the occurrence of the tachycardia-bradycardia syndrome might be anticipated in such an individual. However, many years may elapse before this rhythm disturbance occurs, or it may never happen at all. Some have used the terms tachycardia-bradycardia syndrome and sick sinus syndrome interchangeably. Their synonymous use may be

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"SICK SINUS SYNDROME"

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TACHYCARDIA - BRADYCARDIA SYNDROME Figure 9. Diagrammatic representation of the multiple factors resulting in the tachycardia-bradycardia syndrome.

hazardous, since the sick sinus syndrome includes a variety of sinus and atrial rhythm disturbances, the treatment of which may differ from that appropriate for the tachycardia-bradycardia syndrome. In addition, pathologic studies of patients who exhibited the tachycardia-bradycardia syndrome during life have shown that the atrioventricular junction-al junctional tissues and atria are just as "sick" as the sinus node. Thus, "sick sinus" does not accurately denote the anatomic abnormalities of the tachycardia-bradycardia syndrome.

SUMMARY The tachycardia-bradycardia syndrome (paroxysmal atrial fibrillation, flutter, or tachycardia followed by sinoatrial block or sinus arrest resulting in Stokes-Adams attacks) is an important clinical entity that requires familiarity by the clinician. Pathologic studies and physiologic mechanisms as revealed in the electrocardiogram indicate multiple disturbances in the conduction system of the heart (sinus node, atria, and atrioventricular junctional tissues). The electrocardiogram establishes the diagnosis. Pacemaker implantation with supplementary drugs has provided a satisfactory means of therapy. With proper treatment the prognosis of patients with the tachycardia-bradycardia syndrome has improved to the extent that the primary determinant of mortality is no longer the arrhythmia, but the underlying cardiac and/or systemic pathology.

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ACKNOWLEDGMENTS

I am indebted to Drs. Richard Langendorf, Maurice Lev, and Alfred Pick for their contributions to the original publication and for reviewing this manuscript. acknowledge permission for use of the figures and portions of the I wish to acknowledge text which appeared in the American Journal of Cardiology, Vol. 31, 497-508, 1973.

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