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Rapid atrial stimulation: Successful method of conversion of atrial flutter and atrial tachycardia
Rapid Atrial Stimulation: Successful Method of Conversion of Atrial Flutter and Atrial Tachycardia
DAVID E. PITTMAN, MD JASBIR S. MAKAR, MD KlAN S. KOOROS, MD CLAUDE R. JOYNER, MD, FACC
Pittsburgh, Pennsylvania
Atrial flutter and atrial tachycardia frequently pose difficult therapeutic problems. The established methods of treatment use various antiarrhythmic drugs or precordial countershock, or both. More recently, rapid atrial stimulation has been advocated as an alternative mode of conversion of these tachycardias. Most reports have shown a satisfying rate of conversion. Our experience represents the second largest reported series of patients to undergo cardioversion by this method. In all but 3 of 32 patients who underwent the procedure, either the atrial tachyarrhythmia was converted to sinus rhythm or the flutter-tachycardia was terminated with resultant atrial fibrillation. In 23 patients sinus rhythm was eventually established after atrial stimulation. This technique is confirmed as a safe and reliable method of terminating atrial flutter and atrial tachycardia. Reasons for preferring this mode of cardioversion of atrial tachycardia-flutter over direct-current countershock are discussed. Particular consideration should be given to conversion by rapid atrial stimulation in patients with possible digitalis toxicity and in all patients who have atrial flutter, atrial tachycardia or junctional tachycardia after open heart surgery.
Transthoracic external cardioversion has become a well established method of terminating various supraventricular tachyarrhythmias. 1-s However, this procedure is not without hazard. Complications are especially likely to occur in patients receiving digitalis before electric countershock. 5-s Rapid atrial stimulation has also been reported to be a useful technique for terminating atrial flutter, atrial tachycardia and reciprocating tachycardias. 9-17 However, Rosen et al. is recently reported failure in 15 consecutive patients who underwent rapid atrial stimulation in an a t t e m p t to terminate atrial flutter. Since the results reported by Rosen's group are in conflict with earlier reports and our experience, this report presents a series of 32 patients who underwent rapid atrial stimulation as a method of cardioversion. Atrial stimulation was initially at t em pt ed in these patients in preference to precordial shock since most of the subjects were thought to be in a high risk group for complications from external countershock. Many had recently undergone open heart surgery, and most were receiving digitalis. From the Division of Cardiology, Allegheny General Hospital and The Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pa. Manuscript accepted May 9, 1973. Address for reprints: David E. Pittman, MD, Allegheny General Hospital, 320 East North Ave., Pittsburgh, Pa. 15212.
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Method Patients: Fifteen of the 32 patients were in the postoperative state after aortocoronary bypass graft surgery (Table I). Fourteen had atrial flutter, and one had atrial tachycardia. The arrhythmia developed from several hours to 1 week postoperatively. All but one of these patients had received digitalis before atrial stimulation. None had a history of supraventricular tachycardia before operation.
The American Journal of CARDIOLOGY
Volume 32
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITFMAN ET AL.
TABLE I Pertinent Clinical Data After Coronary Arterial Surgery
Case no.
Age (yr) & Sex
CardiacArrhythmia
1
47M
Atrial flutter
2
55M
3
60F
4 5 6 7
56M 60M 50M 54M
Atrial flutter (recurrent) Atrial flutter (recurrent) Atrial tachycardia Atrial flutter Atrial flutter Atrial flutter
8 9 10 11 12 13
59M 58M 56M 47M 60M 59M
Atrial Atrial Atrial Atrial Atrial Atrial
14
59M
Atrial flutter
15
49F
Atrial flutter
flutter flutter flutter flutter flutter flutter
Medications
Rate of Pacemaker Stimulation (per min)
Results
Digoxin, quinidine Digoxin, propranolol Digoxin
220
A Fib--~ NSR
50O
A Fib
150
NSR
Digoxin None Digoxin Digoxin, quinidine, propranolol Digoxin Digoxin Digoxin Digoxin Digoxin Digoxin, quinidine Digoxin, propranolol Digoxin
150 6OO 54O 4OO
NSR Unchanged A Fib--~ NSR A Fib --~ Junctional (atrial pacing --* NSR)
800 Mech. stim. 800 500 800 700
NSR NSR Unchanged A Fib A Fib NSR
400
NSR
400
NSR
A Fib -----atrial fibrillation; mech. stim = mechanical stimulation; NSR = normal sinus rhythm;--~ = spontaneously converted to.
Of the remaining 17 patients, 4 were in the immediate postoperative period after valvulotomy or prosthetic valve replacement, and 1 had atrial flutter which developed 2 years after mitral commissurotomy; 12 patients had arteriosclerotic heart disease or myocardiopathy (Table II). All but 2 of these 17 patients were receiving drug therapy at the time of atrial stimulation. Two patients (Cases 6 and 21) were considered to have digitalis toxicity. Diagnosis of atrial flutter or tachycardia: Diagnosis of the tachycardia could usually be made by the accepted electrocardiographic criteria. However, accurate classification of the tachyarrhythmia in some patients was possible only when an intraatrial electrocardiogram was obtained. An intraatrial electrocardiogram was recorded for confirmation of the rhythm in all patients before atrial stimulation. The majority of the patients with atrial flutter had 2:1 atrioventricular (A-V) block, but one (Patient 27) had atrial flutter with 1:1 conduction. The four patients who had atrial tachycardia had 1:1 A-V conduction. Rapid atrial stimulation: In most of the postoperative patients cardioversion was attempted with transthoracic atrial pacing wires that had been implanted during thoracotomy. Although several of these attempts proved successful, it became apparent that the success rate was less with transthoracic pacing wires than with an intraatrial pacing catheter. In 85 percent of" the postoperative patients in whom use of the transthoracic wire had failed, successful termination of the tachyarrhythmia followed atrial stimulation with a pacing catheter inserted in the right atrium. It appears that proper placement of the atrial transthoracic wire at operation is a major factor in success if this wire is to be used for atrial stimulation. In a majority of the patients a Cordis 4F bipolar or 5F USCI bipolar pacemaker wire was inserted percutaneously
by way of the subclavian vein or by a basilic vein cutdown procedure. Passage of the wire into the right atrium was usually performed under fluoroscopic control although in several instances the catheter was passed "blindly" with electrocardiographic monitoring from the distal electrode. When fluoroscopy was used, proper apposition of the tip of the electrode t o the upper to mid-portion of the right atrial wall was easily assured. In the cases performed with electrocardiographic monitoring, proper position was assumed by recording the large P waves characteristic of the intracavitary right atrial electrocardiogram. Prestimulation intraatrial leads (Fig. 1A) were recorded from all patients. A standard lead was employed for continuous electrocardiographic monitoring during atrial stimulation. Stimulation of the atrium was accomplished by using a battery-powered external pacemaker designed to pace up to 800 beats/min with a maximum of 25 milliamperes (Medtronic unit model 5800). The stimulation rate was progressively increased from 150 beats/min and the milliamperes (ma) increased from 5 ma until capture of the atrium was accomplished, termination of the tachycardia occurred, or maximal rate and milliamperage were reached without change in the cardiac rhythm. Ten minutes of stimulation at the maximal rate and milliamperage setting was usually performed before failure was accepted. Although a few patients had a sensation of the electrical impulse with high milliamperage and rate settings, the discomfort was not severe enough to cause us to abandon the procedure. After termination of the atrial stimulation, another intraatrial electrocardiogram was recorded to document the rhythm (Fig. 1, B and C). Results
In 17 of t h e 32 p a t i e n t s in t h e series conversion to n o r m a l sinus r h y t h m was d i r e c t (Fig. 2 to 4, T a b l e
October 1973
The American Journal of CARDIOLOGY
Volume 32
701
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
TABLE II Pertinent Clinical Data Rate of
Pacemaker Stimulation
Case no.
Age (yr) & Sex
16
59M
Cardiomyopathy
Atrial flutter
17
45M
18
57M
19
65M
20
51M
21
59M
Post-aortic valve replacement Post-mitral valve replacement Post-mitral valve replacement Post-aortic valve replacement ASH D
22
59F
ASHD
23
57M
24 25 26 27 28 29
74M 59M 69F 77M 58M 42F
30
75M
Idiopathic, ? ASHD ASHD ASHD ASHD ASHD ASHD Mitral commissurotomy (2 yr postop) ASHD
31
55F
32
60F
Origin of Arrhythrnia
Postop bivalve replacement ASHD, chronic lung disease
Cardiac Arrhythmia
Medications
(per min)
Results
300
NSR
Atrial flutter
Digoxin, quinidine None
300
A Fib
Atrial flutter
Digoxin
300
A Fib--~ NSR
Atrial flutter
Digoxm
300
A Fib--~ NSR
Atrial flutter
Digoxm
150
NSR
Atrial tachycardia (recurrent) Atrial flutter (recurrent) Atrial flutter
Digoxm
3OO
NSR
Digoxm
3OO
NSR
Digoxm
150
A Fib--~ NSR
Atrial Atrial Atrial Atrial Atrial Atrial
Digoxm None None Digoxin Digoxin Digoxin
3OO 54O 160 300 3O0 3OO
A Fib NSR NSR NSR NSR A Fib
Digoxin, quinidine Digoxin
350
NSR
800
Unchanged
Digoxin, quinidine
800
NSR
flutter flutter tachycardia tachycardia tachycardia flutter
Atrial flutter Atrial tachycardia Atrial flutter
ASH D = arteriosclerotic heart disease; postop = postoperative. Other abbreviations as in Table I.
III). The effective stimulation rate ranged between 150 to 800/min. Post-coronary arterial surgery: The following results were obtained in the 15 patients studied in the early postoperative period after bypass graft surgery. In seven the arrhythmia was converted directly to normal sinus rhythm and in six atrial flutter was converted to atrial fibrillation. Spontaneous reversion to normal sinus rhythm then occurred in three of these six, whereas atrial fibrillation persisted in the other three subjects. Rapid atrial stimulation was unsuccessful in altering the atrial flutter in two patients. Post-valvular surgery: In the five patients who had atrial tachyarrhythmias after valve replacement the following results were obtained with atrial stimulation. In two patients atrial flutter was directly converted to normal sinus rhythm, and in two patients atrial flutter was converted to atrial fibrillation with subsequent spontaneous reversion to normal sinus rhythm. In one patient with atrial tachycardia the arrhythmia was refractory to several attempts at
702
October 1973
The American Journal of CARDIOLOGY
atrial stimulation; although cardioversion to sinus rhythm was accomplished with precordial countershock, atrial tachycardia returned within 24 hours in spite of treatment with digitalis and quinidine. In another patient who had atrial flutter 2 years after mitral commissurotomy (Patient 29) rapid atrial stimulation converted the flutter to atrial fibrillation. Later, external precordial shock was twice used to establish sinus rhythm, but on both occasions was followed by a return to atrial fibrillation. Arteriosclerotic heart disease: In the 10 patients with suspected or confirmed arteriosclerotic heart disease the following results were obtained with rapid atrial stimulation. In eight patients, atrial tachycardia or atrial flutter was terminated with immediate conversion to normal sinus rhythm; in one patient atrial flutter was converted to atrial fibrillation with subsequent spontaneous reversion to normal sinus rhythm; in one patient atrial flutter was converted to persistent atrial fibrillation. In Patient 9 atrial flutter was converted to normal sinus rhythm by mechanical stimulation of the right atrial wall by
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RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
the catheter tip before electrical stimulation was applied. The rates at which cardioversion was accomplished, the drugs the patient received and the prestimulation rhythms are shown in Tables I and II. In two patients with atrial flutter and in one patient with atrial tachycardia the arrhythmias were refractory to change to sinus rhythm or atrial fibrillation. In six patients, atrial flutter was transformed to atrial fibrillation with later (30 minutes to 24 hours) spontaneous reversion to normal sinus rhythm. Five patients continued to manifest atrial fibrillation with ventricular rates controlled by digitalis. External countershock cardioversion was not attempted during their hospitalization. In one patient (Case 29) atrial flutter was converted to atrial fibrillation which shortly thereafter was converted by direct-current shock to sinus rhythm. In one patient (Case 7) the arrhythmia was converted to atrial fibrillation which in several minutes reverted to sinus rhythm (Fig. 4). This event was followed by sinus arrest and a slow junctional escape rhythm. The patient underwent atrial pacing for 48 hours until sinoatrial nodal function returned and stable normal sinus rhythm was established. Cardioversion by this method was not followed by ventricular or junctional tachyarrhythmias in any patient.
Discussion The use of rapid atrial stimulation to terminate supraventricular arrhythmias has been well documented. ~-~7 The poor result recently reported by Rosen et al. ~s is contrary to findings in previous reports. In attempting to analyze the possible causes of the difference in their results from our satisfying experience, one might mention the slightly different patient population. The group of Rosen et al. included only two patients who had undergone cardiac surgery, whereas 21 of the 32 patients in our series were treated in the postoperative period after surgery for coronary artery or valvular heart disease. Their group included three patients with "primary myocardial disease," only one patient in our group had this lesion. However, cardioversion was successful in our single patient with a cardiomyopathy. The remainder of their group, representing patients with hypertensive cardiovascular disease or arteriosclerotic heart disease, was comparable to our patient population. Actually, our patients with arteriosclerotic heart disease fared much better than those having other cardiac diagnoses. It therefore is difficult to explain the marked difference in effectiveness of this procedure on the basis of patient selection. The description of Rosen et al. of their technique of catheter placement and stimulation of various locations within the right atrium is similar to the technique used in our laboratory. However, there is a definite difference between the maximal rate of stimulation employed in their study and in our series. Only one patient in the study of Rosen et al. underwent atrial stimulation at a rate greater than 400 beats/min. In our experience, 8 patients needed between 500 to 800 stimuli/min to terminate atrial October
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FIGURE 1. Illustrative electrocardiograms. A, u p p e r t r a c i n g , supraventricular tachycardia suggesting atrial flutter with 2:1 block, L o w e r t r a c i n g , intraatrial electrocardiogram in the same patient defining P waves very clearly, confirming rhythm to be atrial flutter with an atrial rate of 320/rain and a ventricular rate of 160/min. B, u p p e r t r a c i n g , rhythm strip from lead II electrocardiogram obtained from a patient after conversion from atrial flutter with use of rapid atrial stimulation. L o w e r t r a c i n g , Intraatrial electrocardiogram confirming the return of normal sinus rhythm. C, intraatrial electrocardiogram taken after rapid atrial stimulation showing characteristic appearance of atrial fibrillation. The patient had had atrial flutter before atrial stimulation.
TABLE III Summary
of Results
of Atrial Stimulation (32 P a t i e n t s ) Patients
1973
Result of Stimulation
no.
% Total
Direct conversion to normal sinus rhythm Conversion from atrial flutter to atrial fibrillation Subsequent spontaneous reversion from atrial fibrillation to normal sinus rhythm Persistent atrial fibrillation (with controlled ventricular rate) Subsequent conversion by direct.current shock before discharge Rhythm unaffected Atrial stimulation successful in terminating atrial flutter or tachycardia
17
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12
37.5
6 of 12
18.8
5 of 12
15.6
2 of 12
6.3
3 29
9.1 90.9
The American
Journal of CARDIOLOGY
Volume 32
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RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
flutter. It would seem reasonable not to accept failure unless the maximal rate of pacing has been accomplished. Another possible reason for their unusual rate of failure may be their unwillingness to exceed a maximum of 15 ma. Our external atrial stimulator has a maximal output of 25 ma. This maximal level was required in a significant number of our patients. Conversion of a t r i a l flutter to fibrillation and its m a n a g e m e n t : In the experience of Rosen et al. conversion of flutter to fibrillation was considered a failure. In many of our cases atrial fibrillation was eventually followed by spontaneous reversion to
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sinus rhythm. Atrial stimulation changed atrial flutter to atrial fibrillation in six cases in the series of Rosen et al. In these patients conversion was accomplished by use of direct-current shock if spontaneous reversion to sinus rhythm had not occurred within 1 hour. In our series four of the patients continued to have atrial fibrillation for several hours before spontaneous conversion to sinus rhythm occurred. It thus appears incorrect to assume that sinus rhythm will not return if it does not appear within 1 hr. In the study of Rosen et al. patients were returned to medical wards after cardioversion; in such instances, it would seem justifiable to proceed with precordial shock. However, if patients are adequately monitored, it would appear best not to consider precordial shock for at least 24 hours after conversion from atrial flutter to fibrillation. Even if sinus rhythm does not occur, we believe that atrial fibrillation is preferable to atrial tachycardia, atrial flutter or reciprocating tachycardia since the ventricular rate is usually controlled easily with digitalis or a combination of digitalis a n d propranolol. In our series of patients, it did not seem wise to attempt further change in rhythm by precordial shock until some later date when maintenance of sinus r h y t h m could be better assured.2 Recurrence r a t e after conversion: Atrial tachyarrhythmias, especially atrial flutter, are notorious for their tendency to recur after conversion. Three of our patients had recurrent atrial flutter which was easily terminated by repeat atrial stimulation. This
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FIGURE 2. Case 32. A, upper tracing, lead II electrocardiogram showing saw-tooth-like base line with regular ventricular response characteristic of atrial flutter with 2:1 block. Lower tracing, intraatrial electrocardiogram taken with bipolar transvenous pacemaker wire showing very prominent waves confirming diagnosis of atrial flutter with 2:1 block. B, upper tracing, lead II electrocardiogram taken during rapid atrial stimulation at rate of 800/rain, 24 ma. Note transient termination of atrial flutter in mid-portion of strip with an atrial capture beat followed by a sinus conducted beat. Subsequent return to atrial flutter is shown in the latter portion of strip. Lower tracing, first portion of the tracing shows continued rapid atrial stimulation at rate of 800/min and 24 ma with termination of flutter and return of normal sinus rhythm on cessation of pacing. Note the high voltage peaked P waves suggesting right atrial hypertrophy in this patient with a diagnosis of chronic pulmonary disease. C, intraatrial electrocardiogram taken after lower strip of B, confirming a change of rhythm to normal sinus rhythm when compared to previous intraatrial electrocardiogram (A).
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FIGURE 3. Case 28. A, upper tracing, lead II electrocardiogram showing suprav~ntricular tachycardia at rate of 160/min with no consistent definable P waves. Lower tracing, intraatrial electrocardiogram showing P waves with a 1:1 conduction ratio (carotid massage resulted in a transient increase in atrioventricular block, thus confirming the atrial tachycardia and ruling out the possibility of sinus rhythm with a prolonged P-R interval). B, upper tracing, lead II electrocardiogram after attempted conversion at rate of 150/min showing continuation of atrial tachycardia. Lower lracing, lead II electrocardiogram taken during rapid atrial stimulation at rate of 300/min showing atrial capture with 2;1 atrioventricular conduction and return of normal sinus rhythm on termination of atrial pacing.
Volume 32
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
finding illustrates the efficacy of leaving the pacemaker wire in place within the atrium or having a properly placed epicardial atrial wire. Our follow-up studies of this patient group were not designed to determine accurately the rate of recurrence of arrhythmia, but we had the impression that our incidence of recurrence was much less than would have been anticipated. Administration of antiarrhythmic drugs before and after conversion may have helped suppress recurrence of the arrhythmia once conversion was accomplished. The tendency for recurrence depends upon the many factors influencing the integrity of the cardiac conductive and pacing systems.
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FIGURE 4. Case 7. A, upper tracing, lead II electrocardiogram showing regular rhythm (rate of 140//rain) which would be almost impossible to define as atrial flutter. With position of the P waves (arrow) and the relatively slow ventricular rate it is difficult to differentiate the rhythm from sinus tachycardia. Lower tracing, intraatrial electrocardiogram showing the P wave not only on the T wave but also embedded in the initial portion of the QRS complex. This is diagnostic of atrial flutter with rate of 280//rain and 2:1 atrioventricular block. B, upper tracing, taken during rapid atrial stimulation of 400/rain. Middle tracing, continuation of strip with resulting rhythm suggesting atrial fibrillation at termination of atrial stimulation. Lower tracing, intraatrial lead taken immediately after previous strip, showing rapid atrial depolarization at a rate of 400/rain representing a definite change from the lower tracing of A. C, upper tracing, taken several minutes after B following spontaneous termination of atrial fibrillation with complete silencing of sinoatrial nodal function, and resultant slow junctional or Purkinje rhythm. Lower tracing, atrial pacing accomplished with intraatrial pacing wire previously used for atrial stimulation and left in place in upper right atrium. Note the pacemaker spike (arrow) followed by atrial depolarization and QRS complex.
Although the low incidence of recurrence in our series is encouraging, we have no evidence that it is related to our method of cardioversion. M e c h a n i s m s of a t r i a l stimulation: There are probably several mechanisms by which atrial stimulation can effectively terminate many kinds of supraventricular tachyarrhythmias.9,11,14-17 The precise electrophysiologic mechanism of atrial flutter has not been fully defined, but the circus movement theory is supported by most clinical and experimental d a t a } 9 Other supraventricular arrhythmias may also represent reentry rhythms produced by circus movements in the atrioventricular conduction system. 9,20 Unless slowed or controlled, atrial flutter or atrial tachycardia can often precipitate or complicate severe hemodynamic alterations in the presence of myocardial or valvular heart disease. Atrial stimulation vs. e x t e r n a l countershock: Cardioversion using transthoracic direct-current countershock has been very successful, but can be hazardous to patients receiving digitalis. 5-s In such patients there is reason for concern that use of external countershock may uncover latent digitalis toxicity and precipitate disruptive ventricular arrhythmias. The negligible incidence of post-conversion ventricular arrhythmias in our patients should be emphasized. We had no incidence of significant postconversion ventricular or junctional arrhythmias. We had only one case of significant post-conversion bradyarrhythmia, and this seemed definitely related to the administration of antiarrhythmic drugs. It thus seems safer to attempt conversion with rapid atrial stimulation as the initial procedure, utilizing precordial shock only if absolutely necessary. Direct application of electricity to the ventricular muscle is avoided, and the use of relatively small amounts of electrical energy minimizes the chances of precipitating serious dysrrhythmias. General anesthesia, usually administered for cardioversion induced by precordial shock, may be an additional hazard. Therefore, another advantage of our method is that it avoids the requirement for general anesthesia. It is also a simple matter, once cardioversion has been accomplished, to leave the atrial pacing wire in position for repeated cardioversions in cases of recurrent supraventricular tachycardias. The catheter can also be utilized for atrial pacing if desired for "overdriving" a tachyarrhythmia or pacing the heart if a bradyarrhythmia develops. Intraatrial vs. atrial epieardial stimulation: This method provides a rapid and relatively safe method of terminating supraventricular tachyarrhythmias occurring after cardiac surgery. If an atrial epicardial wire has been properly attached by the surgeons, an excellent method is afforded for both diagnosing the arrhythmia and attempting cardioversion. Unfortunately, in our study we were not assured of proper attachment of the epicardial wire inserted at operation. This was indicated by several cases in which success with intraatrial catheter pacing followed failure of stimulation with transthoracic wires.
October 1973
The American Journal of CARDIOLOGY
Volume 32
705
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN
Acknowledgment We.express our appreciation to Mrs. Jacqueline Soltis for her technical and secretarial assistance, to Drs. Suren-
ET A L
dra Sethi and Mohan Chhabra, Cardiovascular Fellows, who participated in several of the reported cases, and to Dr. George Magovern whose postoperative patients represented a large component of this study.
References 1. Halmos PB: Direct conversion of atrial fibrillation. Brit Heart
2.
3. 4. 5. 6. 7. 8. 9. 10.
706
J 28:302-308, 1966 Morris JJ, Peter RH, Mclntosh HD: Electrical conversion of atrial fibrillation and immediate and long-term results and selection of patients. Ann Intern Mad 65:216-231, 1966 Thind GS, Blakemore WS, Zinseer HF: Direct current cardioversion in digitalized patients with mitral valve disease. Arch Intern Mad (Chicago) 123:156-159, 1969 Resnekov L, McDonald L: Appraisal of electroconversion in treatment of cardiac dysrrhythmias. Brit Heart J 30: 786810, 1968 Kleiger R, Lown B: Cardioversion and digitalis. II. Clinical studies. Circulation 33:878-887, 1966 Szekely P, Wynne NA, Pearson DT, et ah Direct current shock and digitalis. A clinical and experimental study. Brit Heart J 31:91-96, 1969 Rabbino MD, Likoff W, Dreifus LS: Complications and limitations of direct current countershock. JAMA 190:792-796, 1964. Yang SS, Moranhao V, Manheit R, et ah Cardioversion following open-heart valvular surgery. Brit Heart J 31:91-96, 1969 Massumi RA, Kistin AD, Towakkol AA: Termination of reciprocating tachycardia by atrial stimulation. Circulation 36:637-643, 1967 Haft JI, Kosowsky BD, Lau SH, et ah Termination of atrial flutter by rapid electrical pacing of the atrium. Amer J Cardiol 20:239-344, 1967
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The American Journal of C A R D I O L O G Y
11. Hunt NC, Cobb DR, Waxman MD, et al: Conversion of supraventricular tachycardias with atrial stimulation. Evidence of re-entry mechanisms. Circulation 38:1060-1064, 1968 12. Lister JW, Cohen LS, Bernstein EH, et ah Treatment of supraventricular tachycardias by rapid atrial stimulation. Circulation 38:1044-1059, 1968 13. Barold SS, Linhart JW, Samet P, et ah Supraventricular tachycardias initiated and terminated by a single electrical stimulus. Amer J Cardiol 24:37-41, 1969 14. Barold SS, Linhart JW: Recent advances in the treatment of ectopic tachycardias by electrical pacing. Amer J Cardiol 25:698-706, 1970 15. Zeft JH, Cobb FR, Waxman MD, et ah Right atrial stimulation in the treatment of atrial flutter. Ann Intern Med 70:447-456, 1969 16. Pittman DE, Makar JS: Atrial tachyarrhythmias: conversion by means of rapid atrial stimulation: report of two cases. Allegheny General Hosp Bull 2:30-37, 1972 17. Vergara GS, Hildner FJ, Schoenfeld CB, et ah Conversion of supraventricular tachycardias with rapid atrial stimulation. Circulation 54:788-793, 1972 18. Rosen KM, Sinno MZ, Gunnar RM, et ah Failure of rapid atrial pacing in the conversion of atrial flutter. Amer J Cardiol 29:524-528, 1972 19. Rytand DA: The circus movement (entrapped circuit wave) hypothesis and atrial flutter. Ann Intern Mad 65:125-159, 1966 20. Han J: The mechanism of paroxysmal atrial tachycardia: sustained reciprocation. Amer J Cardiol 26:329-330, 1970
Volume 32
DAVID E. PITTMAN, MD JASBIR S. MAKAR, MD KlAN S. KOOROS, MD CLAUDE R. JOYNER, MD, FACC
Pittsburgh, Pennsylvania
Atrial flutter and atrial tachycardia frequently pose difficult therapeutic problems. The established methods of treatment use various antiarrhythmic drugs or precordial countershock, or both. More recently, rapid atrial stimulation has been advocated as an alternative mode of conversion of these tachycardias. Most reports have shown a satisfying rate of conversion. Our experience represents the second largest reported series of patients to undergo cardioversion by this method. In all but 3 of 32 patients who underwent the procedure, either the atrial tachyarrhythmia was converted to sinus rhythm or the flutter-tachycardia was terminated with resultant atrial fibrillation. In 23 patients sinus rhythm was eventually established after atrial stimulation. This technique is confirmed as a safe and reliable method of terminating atrial flutter and atrial tachycardia. Reasons for preferring this mode of cardioversion of atrial tachycardia-flutter over direct-current countershock are discussed. Particular consideration should be given to conversion by rapid atrial stimulation in patients with possible digitalis toxicity and in all patients who have atrial flutter, atrial tachycardia or junctional tachycardia after open heart surgery.
Transthoracic external cardioversion has become a well established method of terminating various supraventricular tachyarrhythmias. 1-s However, this procedure is not without hazard. Complications are especially likely to occur in patients receiving digitalis before electric countershock. 5-s Rapid atrial stimulation has also been reported to be a useful technique for terminating atrial flutter, atrial tachycardia and reciprocating tachycardias. 9-17 However, Rosen et al. is recently reported failure in 15 consecutive patients who underwent rapid atrial stimulation in an a t t e m p t to terminate atrial flutter. Since the results reported by Rosen's group are in conflict with earlier reports and our experience, this report presents a series of 32 patients who underwent rapid atrial stimulation as a method of cardioversion. Atrial stimulation was initially at t em pt ed in these patients in preference to precordial shock since most of the subjects were thought to be in a high risk group for complications from external countershock. Many had recently undergone open heart surgery, and most were receiving digitalis. From the Division of Cardiology, Allegheny General Hospital and The Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pa. Manuscript accepted May 9, 1973. Address for reprints: David E. Pittman, MD, Allegheny General Hospital, 320 East North Ave., Pittsburgh, Pa. 15212.
700
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Method Patients: Fifteen of the 32 patients were in the postoperative state after aortocoronary bypass graft surgery (Table I). Fourteen had atrial flutter, and one had atrial tachycardia. The arrhythmia developed from several hours to 1 week postoperatively. All but one of these patients had received digitalis before atrial stimulation. None had a history of supraventricular tachycardia before operation.
The American Journal of CARDIOLOGY
Volume 32
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITFMAN ET AL.
TABLE I Pertinent Clinical Data After Coronary Arterial Surgery
Case no.
Age (yr) & Sex
CardiacArrhythmia
1
47M
Atrial flutter
2
55M
3
60F
4 5 6 7
56M 60M 50M 54M
Atrial flutter (recurrent) Atrial flutter (recurrent) Atrial tachycardia Atrial flutter Atrial flutter Atrial flutter
8 9 10 11 12 13
59M 58M 56M 47M 60M 59M
Atrial Atrial Atrial Atrial Atrial Atrial
14
59M
Atrial flutter
15
49F
Atrial flutter
flutter flutter flutter flutter flutter flutter
Medications
Rate of Pacemaker Stimulation (per min)
Results
Digoxin, quinidine Digoxin, propranolol Digoxin
220
A Fib--~ NSR
50O
A Fib
150
NSR
Digoxin None Digoxin Digoxin, quinidine, propranolol Digoxin Digoxin Digoxin Digoxin Digoxin Digoxin, quinidine Digoxin, propranolol Digoxin
150 6OO 54O 4OO
NSR Unchanged A Fib--~ NSR A Fib --~ Junctional (atrial pacing --* NSR)
800 Mech. stim. 800 500 800 700
NSR NSR Unchanged A Fib A Fib NSR
400
NSR
400
NSR
A Fib -----atrial fibrillation; mech. stim = mechanical stimulation; NSR = normal sinus rhythm;--~ = spontaneously converted to.
Of the remaining 17 patients, 4 were in the immediate postoperative period after valvulotomy or prosthetic valve replacement, and 1 had atrial flutter which developed 2 years after mitral commissurotomy; 12 patients had arteriosclerotic heart disease or myocardiopathy (Table II). All but 2 of these 17 patients were receiving drug therapy at the time of atrial stimulation. Two patients (Cases 6 and 21) were considered to have digitalis toxicity. Diagnosis of atrial flutter or tachycardia: Diagnosis of the tachycardia could usually be made by the accepted electrocardiographic criteria. However, accurate classification of the tachyarrhythmia in some patients was possible only when an intraatrial electrocardiogram was obtained. An intraatrial electrocardiogram was recorded for confirmation of the rhythm in all patients before atrial stimulation. The majority of the patients with atrial flutter had 2:1 atrioventricular (A-V) block, but one (Patient 27) had atrial flutter with 1:1 conduction. The four patients who had atrial tachycardia had 1:1 A-V conduction. Rapid atrial stimulation: In most of the postoperative patients cardioversion was attempted with transthoracic atrial pacing wires that had been implanted during thoracotomy. Although several of these attempts proved successful, it became apparent that the success rate was less with transthoracic pacing wires than with an intraatrial pacing catheter. In 85 percent of" the postoperative patients in whom use of the transthoracic wire had failed, successful termination of the tachyarrhythmia followed atrial stimulation with a pacing catheter inserted in the right atrium. It appears that proper placement of the atrial transthoracic wire at operation is a major factor in success if this wire is to be used for atrial stimulation. In a majority of the patients a Cordis 4F bipolar or 5F USCI bipolar pacemaker wire was inserted percutaneously
by way of the subclavian vein or by a basilic vein cutdown procedure. Passage of the wire into the right atrium was usually performed under fluoroscopic control although in several instances the catheter was passed "blindly" with electrocardiographic monitoring from the distal electrode. When fluoroscopy was used, proper apposition of the tip of the electrode t o the upper to mid-portion of the right atrial wall was easily assured. In the cases performed with electrocardiographic monitoring, proper position was assumed by recording the large P waves characteristic of the intracavitary right atrial electrocardiogram. Prestimulation intraatrial leads (Fig. 1A) were recorded from all patients. A standard lead was employed for continuous electrocardiographic monitoring during atrial stimulation. Stimulation of the atrium was accomplished by using a battery-powered external pacemaker designed to pace up to 800 beats/min with a maximum of 25 milliamperes (Medtronic unit model 5800). The stimulation rate was progressively increased from 150 beats/min and the milliamperes (ma) increased from 5 ma until capture of the atrium was accomplished, termination of the tachycardia occurred, or maximal rate and milliamperage were reached without change in the cardiac rhythm. Ten minutes of stimulation at the maximal rate and milliamperage setting was usually performed before failure was accepted. Although a few patients had a sensation of the electrical impulse with high milliamperage and rate settings, the discomfort was not severe enough to cause us to abandon the procedure. After termination of the atrial stimulation, another intraatrial electrocardiogram was recorded to document the rhythm (Fig. 1, B and C). Results
In 17 of t h e 32 p a t i e n t s in t h e series conversion to n o r m a l sinus r h y t h m was d i r e c t (Fig. 2 to 4, T a b l e
October 1973
The American Journal of CARDIOLOGY
Volume 32
701
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
TABLE II Pertinent Clinical Data Rate of
Pacemaker Stimulation
Case no.
Age (yr) & Sex
16
59M
Cardiomyopathy
Atrial flutter
17
45M
18
57M
19
65M
20
51M
21
59M
Post-aortic valve replacement Post-mitral valve replacement Post-mitral valve replacement Post-aortic valve replacement ASH D
22
59F
ASHD
23
57M
24 25 26 27 28 29
74M 59M 69F 77M 58M 42F
30
75M
Idiopathic, ? ASHD ASHD ASHD ASHD ASHD ASHD Mitral commissurotomy (2 yr postop) ASHD
31
55F
32
60F
Origin of Arrhythrnia
Postop bivalve replacement ASHD, chronic lung disease
Cardiac Arrhythmia
Medications
(per min)
Results
300
NSR
Atrial flutter
Digoxin, quinidine None
300
A Fib
Atrial flutter
Digoxin
300
A Fib--~ NSR
Atrial flutter
Digoxm
300
A Fib--~ NSR
Atrial flutter
Digoxm
150
NSR
Atrial tachycardia (recurrent) Atrial flutter (recurrent) Atrial flutter
Digoxm
3OO
NSR
Digoxm
3OO
NSR
Digoxm
150
A Fib--~ NSR
Atrial Atrial Atrial Atrial Atrial Atrial
Digoxm None None Digoxin Digoxin Digoxin
3OO 54O 160 300 3O0 3OO
A Fib NSR NSR NSR NSR A Fib
Digoxin, quinidine Digoxin
350
NSR
800
Unchanged
Digoxin, quinidine
800
NSR
flutter flutter tachycardia tachycardia tachycardia flutter
Atrial flutter Atrial tachycardia Atrial flutter
ASH D = arteriosclerotic heart disease; postop = postoperative. Other abbreviations as in Table I.
III). The effective stimulation rate ranged between 150 to 800/min. Post-coronary arterial surgery: The following results were obtained in the 15 patients studied in the early postoperative period after bypass graft surgery. In seven the arrhythmia was converted directly to normal sinus rhythm and in six atrial flutter was converted to atrial fibrillation. Spontaneous reversion to normal sinus rhythm then occurred in three of these six, whereas atrial fibrillation persisted in the other three subjects. Rapid atrial stimulation was unsuccessful in altering the atrial flutter in two patients. Post-valvular surgery: In the five patients who had atrial tachyarrhythmias after valve replacement the following results were obtained with atrial stimulation. In two patients atrial flutter was directly converted to normal sinus rhythm, and in two patients atrial flutter was converted to atrial fibrillation with subsequent spontaneous reversion to normal sinus rhythm. In one patient with atrial tachycardia the arrhythmia was refractory to several attempts at
702
October 1973
The American Journal of CARDIOLOGY
atrial stimulation; although cardioversion to sinus rhythm was accomplished with precordial countershock, atrial tachycardia returned within 24 hours in spite of treatment with digitalis and quinidine. In another patient who had atrial flutter 2 years after mitral commissurotomy (Patient 29) rapid atrial stimulation converted the flutter to atrial fibrillation. Later, external precordial shock was twice used to establish sinus rhythm, but on both occasions was followed by a return to atrial fibrillation. Arteriosclerotic heart disease: In the 10 patients with suspected or confirmed arteriosclerotic heart disease the following results were obtained with rapid atrial stimulation. In eight patients, atrial tachycardia or atrial flutter was terminated with immediate conversion to normal sinus rhythm; in one patient atrial flutter was converted to atrial fibrillation with subsequent spontaneous reversion to normal sinus rhythm; in one patient atrial flutter was converted to persistent atrial fibrillation. In Patient 9 atrial flutter was converted to normal sinus rhythm by mechanical stimulation of the right atrial wall by
Volume 32
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
the catheter tip before electrical stimulation was applied. The rates at which cardioversion was accomplished, the drugs the patient received and the prestimulation rhythms are shown in Tables I and II. In two patients with atrial flutter and in one patient with atrial tachycardia the arrhythmias were refractory to change to sinus rhythm or atrial fibrillation. In six patients, atrial flutter was transformed to atrial fibrillation with later (30 minutes to 24 hours) spontaneous reversion to normal sinus rhythm. Five patients continued to manifest atrial fibrillation with ventricular rates controlled by digitalis. External countershock cardioversion was not attempted during their hospitalization. In one patient (Case 29) atrial flutter was converted to atrial fibrillation which shortly thereafter was converted by direct-current shock to sinus rhythm. In one patient (Case 7) the arrhythmia was converted to atrial fibrillation which in several minutes reverted to sinus rhythm (Fig. 4). This event was followed by sinus arrest and a slow junctional escape rhythm. The patient underwent atrial pacing for 48 hours until sinoatrial nodal function returned and stable normal sinus rhythm was established. Cardioversion by this method was not followed by ventricular or junctional tachyarrhythmias in any patient.
Discussion The use of rapid atrial stimulation to terminate supraventricular arrhythmias has been well documented. ~-~7 The poor result recently reported by Rosen et al. ~s is contrary to findings in previous reports. In attempting to analyze the possible causes of the difference in their results from our satisfying experience, one might mention the slightly different patient population. The group of Rosen et al. included only two patients who had undergone cardiac surgery, whereas 21 of the 32 patients in our series were treated in the postoperative period after surgery for coronary artery or valvular heart disease. Their group included three patients with "primary myocardial disease," only one patient in our group had this lesion. However, cardioversion was successful in our single patient with a cardiomyopathy. The remainder of their group, representing patients with hypertensive cardiovascular disease or arteriosclerotic heart disease, was comparable to our patient population. Actually, our patients with arteriosclerotic heart disease fared much better than those having other cardiac diagnoses. It therefore is difficult to explain the marked difference in effectiveness of this procedure on the basis of patient selection. The description of Rosen et al. of their technique of catheter placement and stimulation of various locations within the right atrium is similar to the technique used in our laboratory. However, there is a definite difference between the maximal rate of stimulation employed in their study and in our series. Only one patient in the study of Rosen et al. underwent atrial stimulation at a rate greater than 400 beats/min. In our experience, 8 patients needed between 500 to 800 stimuli/min to terminate atrial October
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TABLE III Summary
of Results
of Atrial Stimulation (32 P a t i e n t s ) Patients
1973
Result of Stimulation
no.
% Total
Direct conversion to normal sinus rhythm Conversion from atrial flutter to atrial fibrillation Subsequent spontaneous reversion from atrial fibrillation to normal sinus rhythm Persistent atrial fibrillation (with controlled ventricular rate) Subsequent conversion by direct.current shock before discharge Rhythm unaffected Atrial stimulation successful in terminating atrial flutter or tachycardia
17
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18.8
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15.6
2 of 12
6.3
3 29
9.1 90.9
The American
Journal of CARDIOLOGY
Volume 32
703
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
flutter. It would seem reasonable not to accept failure unless the maximal rate of pacing has been accomplished. Another possible reason for their unusual rate of failure may be their unwillingness to exceed a maximum of 15 ma. Our external atrial stimulator has a maximal output of 25 ma. This maximal level was required in a significant number of our patients. Conversion of a t r i a l flutter to fibrillation and its m a n a g e m e n t : In the experience of Rosen et al. conversion of flutter to fibrillation was considered a failure. In many of our cases atrial fibrillation was eventually followed by spontaneous reversion to
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sinus rhythm. Atrial stimulation changed atrial flutter to atrial fibrillation in six cases in the series of Rosen et al. In these patients conversion was accomplished by use of direct-current shock if spontaneous reversion to sinus rhythm had not occurred within 1 hour. In our series four of the patients continued to have atrial fibrillation for several hours before spontaneous conversion to sinus rhythm occurred. It thus appears incorrect to assume that sinus rhythm will not return if it does not appear within 1 hr. In the study of Rosen et al. patients were returned to medical wards after cardioversion; in such instances, it would seem justifiable to proceed with precordial shock. However, if patients are adequately monitored, it would appear best not to consider precordial shock for at least 24 hours after conversion from atrial flutter to fibrillation. Even if sinus rhythm does not occur, we believe that atrial fibrillation is preferable to atrial tachycardia, atrial flutter or reciprocating tachycardia since the ventricular rate is usually controlled easily with digitalis or a combination of digitalis a n d propranolol. In our series of patients, it did not seem wise to attempt further change in rhythm by precordial shock until some later date when maintenance of sinus r h y t h m could be better assured.2 Recurrence r a t e after conversion: Atrial tachyarrhythmias, especially atrial flutter, are notorious for their tendency to recur after conversion. Three of our patients had recurrent atrial flutter which was easily terminated by repeat atrial stimulation. This
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FIGURE 3. Case 28. A, upper tracing, lead II electrocardiogram showing suprav~ntricular tachycardia at rate of 160/min with no consistent definable P waves. Lower tracing, intraatrial electrocardiogram showing P waves with a 1:1 conduction ratio (carotid massage resulted in a transient increase in atrioventricular block, thus confirming the atrial tachycardia and ruling out the possibility of sinus rhythm with a prolonged P-R interval). B, upper tracing, lead II electrocardiogram after attempted conversion at rate of 150/min showing continuation of atrial tachycardia. Lower lracing, lead II electrocardiogram taken during rapid atrial stimulation at rate of 300/min showing atrial capture with 2;1 atrioventricular conduction and return of normal sinus rhythm on termination of atrial pacing.
Volume 32
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN ET AL.
finding illustrates the efficacy of leaving the pacemaker wire in place within the atrium or having a properly placed epicardial atrial wire. Our follow-up studies of this patient group were not designed to determine accurately the rate of recurrence of arrhythmia, but we had the impression that our incidence of recurrence was much less than would have been anticipated. Administration of antiarrhythmic drugs before and after conversion may have helped suppress recurrence of the arrhythmia once conversion was accomplished. The tendency for recurrence depends upon the many factors influencing the integrity of the cardiac conductive and pacing systems.
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FIGURE 4. Case 7. A, upper tracing, lead II electrocardiogram showing regular rhythm (rate of 140//rain) which would be almost impossible to define as atrial flutter. With position of the P waves (arrow) and the relatively slow ventricular rate it is difficult to differentiate the rhythm from sinus tachycardia. Lower tracing, intraatrial electrocardiogram showing the P wave not only on the T wave but also embedded in the initial portion of the QRS complex. This is diagnostic of atrial flutter with rate of 280//rain and 2:1 atrioventricular block. B, upper tracing, taken during rapid atrial stimulation of 400/rain. Middle tracing, continuation of strip with resulting rhythm suggesting atrial fibrillation at termination of atrial stimulation. Lower tracing, intraatrial lead taken immediately after previous strip, showing rapid atrial depolarization at a rate of 400/rain representing a definite change from the lower tracing of A. C, upper tracing, taken several minutes after B following spontaneous termination of atrial fibrillation with complete silencing of sinoatrial nodal function, and resultant slow junctional or Purkinje rhythm. Lower tracing, atrial pacing accomplished with intraatrial pacing wire previously used for atrial stimulation and left in place in upper right atrium. Note the pacemaker spike (arrow) followed by atrial depolarization and QRS complex.
Although the low incidence of recurrence in our series is encouraging, we have no evidence that it is related to our method of cardioversion. M e c h a n i s m s of a t r i a l stimulation: There are probably several mechanisms by which atrial stimulation can effectively terminate many kinds of supraventricular tachyarrhythmias.9,11,14-17 The precise electrophysiologic mechanism of atrial flutter has not been fully defined, but the circus movement theory is supported by most clinical and experimental d a t a } 9 Other supraventricular arrhythmias may also represent reentry rhythms produced by circus movements in the atrioventricular conduction system. 9,20 Unless slowed or controlled, atrial flutter or atrial tachycardia can often precipitate or complicate severe hemodynamic alterations in the presence of myocardial or valvular heart disease. Atrial stimulation vs. e x t e r n a l countershock: Cardioversion using transthoracic direct-current countershock has been very successful, but can be hazardous to patients receiving digitalis. 5-s In such patients there is reason for concern that use of external countershock may uncover latent digitalis toxicity and precipitate disruptive ventricular arrhythmias. The negligible incidence of post-conversion ventricular arrhythmias in our patients should be emphasized. We had no incidence of significant postconversion ventricular or junctional arrhythmias. We had only one case of significant post-conversion bradyarrhythmia, and this seemed definitely related to the administration of antiarrhythmic drugs. It thus seems safer to attempt conversion with rapid atrial stimulation as the initial procedure, utilizing precordial shock only if absolutely necessary. Direct application of electricity to the ventricular muscle is avoided, and the use of relatively small amounts of electrical energy minimizes the chances of precipitating serious dysrrhythmias. General anesthesia, usually administered for cardioversion induced by precordial shock, may be an additional hazard. Therefore, another advantage of our method is that it avoids the requirement for general anesthesia. It is also a simple matter, once cardioversion has been accomplished, to leave the atrial pacing wire in position for repeated cardioversions in cases of recurrent supraventricular tachycardias. The catheter can also be utilized for atrial pacing if desired for "overdriving" a tachyarrhythmia or pacing the heart if a bradyarrhythmia develops. Intraatrial vs. atrial epieardial stimulation: This method provides a rapid and relatively safe method of terminating supraventricular tachyarrhythmias occurring after cardiac surgery. If an atrial epicardial wire has been properly attached by the surgeons, an excellent method is afforded for both diagnosing the arrhythmia and attempting cardioversion. Unfortunately, in our study we were not assured of proper attachment of the epicardial wire inserted at operation. This was indicated by several cases in which success with intraatrial catheter pacing followed failure of stimulation with transthoracic wires.
October 1973
The American Journal of CARDIOLOGY
Volume 32
705
RAPID ATRIAL PACING FOR TACHYARRHYTHMIA--PITTMAN
Acknowledgment We.express our appreciation to Mrs. Jacqueline Soltis for her technical and secretarial assistance, to Drs. Suren-
ET A L
dra Sethi and Mohan Chhabra, Cardiovascular Fellows, who participated in several of the reported cases, and to Dr. George Magovern whose postoperative patients represented a large component of this study.
References 1. Halmos PB: Direct conversion of atrial fibrillation. Brit Heart
2.
3. 4. 5. 6. 7. 8. 9. 10.
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J 28:302-308, 1966 Morris JJ, Peter RH, Mclntosh HD: Electrical conversion of atrial fibrillation and immediate and long-term results and selection of patients. Ann Intern Mad 65:216-231, 1966 Thind GS, Blakemore WS, Zinseer HF: Direct current cardioversion in digitalized patients with mitral valve disease. Arch Intern Mad (Chicago) 123:156-159, 1969 Resnekov L, McDonald L: Appraisal of electroconversion in treatment of cardiac dysrrhythmias. Brit Heart J 30: 786810, 1968 Kleiger R, Lown B: Cardioversion and digitalis. II. Clinical studies. Circulation 33:878-887, 1966 Szekely P, Wynne NA, Pearson DT, et ah Direct current shock and digitalis. A clinical and experimental study. Brit Heart J 31:91-96, 1969 Rabbino MD, Likoff W, Dreifus LS: Complications and limitations of direct current countershock. JAMA 190:792-796, 1964. Yang SS, Moranhao V, Manheit R, et ah Cardioversion following open-heart valvular surgery. Brit Heart J 31:91-96, 1969 Massumi RA, Kistin AD, Towakkol AA: Termination of reciprocating tachycardia by atrial stimulation. Circulation 36:637-643, 1967 Haft JI, Kosowsky BD, Lau SH, et ah Termination of atrial flutter by rapid electrical pacing of the atrium. Amer J Cardiol 20:239-344, 1967
October 1973
The American Journal of C A R D I O L O G Y
11. Hunt NC, Cobb DR, Waxman MD, et al: Conversion of supraventricular tachycardias with atrial stimulation. Evidence of re-entry mechanisms. Circulation 38:1060-1064, 1968 12. Lister JW, Cohen LS, Bernstein EH, et ah Treatment of supraventricular tachycardias by rapid atrial stimulation. Circulation 38:1044-1059, 1968 13. Barold SS, Linhart JW, Samet P, et ah Supraventricular tachycardias initiated and terminated by a single electrical stimulus. Amer J Cardiol 24:37-41, 1969 14. Barold SS, Linhart JW: Recent advances in the treatment of ectopic tachycardias by electrical pacing. Amer J Cardiol 25:698-706, 1970 15. Zeft JH, Cobb FR, Waxman MD, et ah Right atrial stimulation in the treatment of atrial flutter. Ann Intern Med 70:447-456, 1969 16. Pittman DE, Makar JS: Atrial tachyarrhythmias: conversion by means of rapid atrial stimulation: report of two cases. Allegheny General Hosp Bull 2:30-37, 1972 17. Vergara GS, Hildner FJ, Schoenfeld CB, et ah Conversion of supraventricular tachycardias with rapid atrial stimulation. Circulation 54:788-793, 1972 18. Rosen KM, Sinno MZ, Gunnar RM, et ah Failure of rapid atrial pacing in the conversion of atrial flutter. Amer J Cardiol 29:524-528, 1972 19. Rytand DA: The circus movement (entrapped circuit wave) hypothesis and atrial flutter. Ann Intern Mad 65:125-159, 1966 20. Han J: The mechanism of paroxysmal atrial tachycardia: sustained reciprocation. Amer J Cardiol 26:329-330, 1970
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