and the Beginnings of Direct Arrhythmia Surgery Will C. Sealy, M.D.

Transcription

1 The Wolff -ParkinsonWhite Syndrome and the Beginnings of Direct Arrhythmia Surgery Will C. Sealy, M.D. ABSTRACT The bundle of Kent, one of the two pathways involved in the reentry tachycardia of the Wolff- Parkinson-White syndrome, was identified and then interrupted fifteen years ago. This marked the beginning of direct arrhythmia surgery. The patient was a 31-year-old man with a right free wall pathway and persistent tachycardia refractory to medical treatment. In the present report, the historical landmarks in the description of the morphology of the conduction system are reviewed. Current methods of interrupting the Kent bundle, based on experience with more than 200 surgical patients, are discussed. Included is the newer method of simplifying the surgical procedure with cryothermia. Speculation about the future of direct arrhythmia surgery is given in the concluding remarks. Fifteen years ago, a 31-year-old fisherman with the Wolff-Parkinson-White (WPW) syndrome went to Duke Hospital to seek help for an almost continuous tachycardia refractory to all medications. Electrophysiological studies pointed to a right free wall Kent bundle as the cause of the reentry tachycardia. It was decided that operative intervention was the only way to correct the problem. The surgical strategy was to try to find the bundle of Kent by epicardial mapping and then divide it. If that failed, the His bundle would be divided. The Kent bundle was found and interrupted [l], and the man was cured. This operation marked the beginning of direct arrhythmia surgery. Some of my thoughts and experiences that evolved directly from this event are related here. In an article by Wiggers [2], I found a quotation from Barthold G. Nieburh: He who calls departed ages back again in being, /Enjoys a bliss like that of creating. This is a pleasant reason for reading history. It is much better than the one most frequently used that threatens dreadful consequences if we do not learn how to avoid them by studying history. I now will review some of the events that led to our understanding of the conduction system. Historical Background Walter Holbrook Gaskell [3] of Cambridge, England, is credited with proving in the early 1880s that conduction *Professor Emeritus of Thoracic Surgety, Duke University School of Medicine, Durham, NC. From 202 Selkirk Dr, Durham, NC Accepted for publication Feb 20, 1984 of impulses from the atrium to the ventricle was by myocardium and not by nerves. Gaskell s experiments were done on the turtle s heart and could be called experimental surgical studies. In one such study, the atrioventricular (AV) junction was divided in stages with pacing of the atrium at each stage. As the connecting myocardial strand became thinner from staged division, the paced atrial beats were conducted to the ventricle in a ratio of 2 to 1 at first and then 3 to 1. Does this not suggest the possible application of this observation to the AV node and bundle in enhanced AV node conduction? Gaskell was the pupil and later colleague of the founder of the Cambridge school of physiology, Robert Foster [4]. Wilhelm His, Jr. [5], son of one of the great anatomists and embryologists of all time, is eponymously credited with showing that in mammals, AV conduction is by a small myocardial band. Appropriately, the discovery came from the younger His s observations of the chick embryo, observations proving that AV conduction takes place well before cardiac innervation develops. Later, with a series of what I know from experience to be frustrating experiments, His produced heart block in one rabbit after twenty-three tries. A few months ahead of His, Stanley Kent [6], who provided the eponym for the Kent bundle, found that AV conduction was myogenic in mammals. He believed that the normal connections were multiple, which we now know is incorrect. However, in patients with the WPW syndrome, anomalous pathways of AV conduction have been found on the right lateral wall, as Kent [7] noted. His incorrect observations did point the way to the discovery of the anomalous pathways; perhaps he deserves the eponym. On the other hand, in the story of the anatomy of the conduction system, there are examples of unused but deserved eponyms. The AV node is rarely called Tawara s node. During his five years in Aschoff s laboratory in Germany, this Japanese pathologist described the AV node and detailed the ventricular conduction system [8]. Tawara, in the idiom of today, put it all together. The sinoatrial node was the last structure in the conduction system to be found. It seldom is called the node of Keith and Flack [9], the names of its discoverers. Arthur Keith was a distinguished English anatomist of the first half of the twentieth century. Martin Flack, who later became a fine cardiologist, was a medical student and country neighbor of Keith. This brief discussion has not included contemporary anatomists, such as the late Raymond Truex, Maurice Lev, Robert Anderson, Anton Becker, Wallace McA1- pine, and Thomas James. These men identified the 176

2 177 Sealy: WPW Syndrome and Direct Arrhythmia Surgery guideposts that have made direct arrhythmia surgery possible. The physiologists and cardiologists who made great contributions to the field of arrhythmia surgery are too numerous to include here. Four, however, must be mentioned: Dr. Willem Einthoven, Sir Thomas Lewis, Dr. Frank Wilson, and Dr. Dirk Durrer. Dr. Einthoven s application of the string galvanometer for recording the heart s electrical activity on the body surface marked the beginning of clinical cardiac electrophysiology [ 101. Sir Thomas Lewis ranks next to Einthoven for both his experimental and clinical contributions [ll]. Dr. Frank Wilson of Ann Arbor was the person most responsible for the wide clinical application of electrocardiography. Dr. Wilson and his colleagues [12], including Dr. John Alexander, did an early map, published in 1928, of the epicardial activation sequences of the ventricle in human beings. The last person, Dr. Dirk Durrer of Amsterdam, is the father of modern clinical electrophysiology [13]. It was his teaching that guided us in our efforts to cure the fisherman with the fast pulse. In the second decade of this century, Dr. Paul Dudley White, a great clinical cardiologist and teacher of cardiologists, collected a series of unusual electrocardiograms. These tracings were from young patients whose condition was normal except for paroxysmal tachycardia and preexcitation of the ventricles. On a trip to England, he found that Dr. Parkinson, an English physician, had a group of similar patients. Dr. Wolff, a fellow of Dr. White s, combined their data and reported their observations [14]. No one could explain the peculiar ECGs in these patients until Drs. Wolferth and Wood [15] published their observations on a young man with paroxysmal tachycardia and electrocardiographic changes similar to those noted by Dr. White. Dr. Wood and his colleagues came to the conclusion that the abnormalities were due to conduction from the atrium to the ventricle by a pathway other than the AV node-his bundle. The patient died. Having based their hypothesis on what Kent thought was normal AV conduction in human beings on the right free wall, Dr. Wood and colleagues [16] directed their anatomical studies to the right lateral free wall and thus found the anomalous pathway. Had Kent not published what are now considered to Se incorrect observations, Wood and colleagues might never have found the right free wall pathway. Had the fisherman s anomalous pathway been anyplace other than the right free wall, I would not likely have found it at operation. Clinical Considerations The Pathways The anomalous pathways are congenital, and thud WPW syndrome is a congenital heart disease. The path& is almost always just a strand or two of working myocardium. This strand, 1 to 2 mm in diameter, is the remnant of the sheet of myocardium that, in the embryo, once connected the atrium and ventricle as a broad sheet. The pathways can be multiple. Because of this mode of development, it is not surprising that pathways can be found anywhere on the right or left annulus fibrosus except where the left atrium is attached to the aortic annulus. There is still a scarcity of information on the morphology of the Kent bundle, not only because it is an uncommon anomaly but because the job of finding a strand a millimeter in diameter in the coronary sulcus fat is formidable. As my experience increased, I assumed that the pathways could be anywhere on the annulus fibrosus and based this assumption on embryology, the 18 reported examples I could find in the literature, and my surgical experience to that time. Subsequent clinical observations confirmed the assumption. I classified the pathways into right and left free wall, posterior septal, and anterior septal. Peculiar to each type of pathway are surgical problems as well as characteristic ECGs. The most common arrhythmia caused by a Kent bundle is a reentry arrhythmia involving the Kent and His bundles and creating a narrow QRS tachycardia. A less common arrhythmia, usually occurring in combination with reentry tachycardia, is a malignant ventricular arrhythmia. It is found in about 25% of patients referred for operation. The malignant arrhythmia is due to a Kent bundle with a short effective refractory period that permits 1:l conduction of the impulses of an atrial tachycardia to the ventricle. The reentry tachycardia is usually triggered by an extra beat, most frequently in the atrium, which finds the Kent pathway nonexcitable because of its long effective refractory period. This is the functional status of 75% of my surgical patients. During the time it takes for the impulse to pass through the AV node and His bundle, the Kent bundle becomes excitable. The impulse then reenters the atrium and initiates the circusmovement tachycardia. Rarely, the atrial reentry is by the His bundle and AV node, and thus ventricular entry is over the Kent bundle. This type produces a wide QRS tachycardia. However, such a tachycardia frequently points to the presence of a second Kent bundle, the two bundles composing the circuit. The characteristics of the pathways may differ. Some conduct only retrograde but can be associated with a reentry tachycardia that can be difficult to control. Others have only antegrade function and can cause a malignant arrhythmia but seldom are associated with a reentry tachycardia. Some behave as if composed of AV nodal tissue. Considerations before Operation The first manifestation of WPW syndrome may be in infancy. Babies with anomalous pathways may be troubled with recurrent tachycardias. Although most such arrhythmias can be controlled with digitalis, the drug can have a lethal effect on adults with WPW syndrome. Some children in the series had had incessant junctional reentry tachycardia from infancy and required operation. It is not unusual for patients to have their first

3 178 The Annals of Thoracic Surgery Vol38 No 2 August 1984 symptoms when they are 40 to 60 years old. Perhaps this is because extra beats tend to be more common at that age. The additive effect of the tachycardia on other cardiac problems, such as Ebstein s anomaly, cardiomyopathy, and valvular and coronary artery disease, make the episodes of tachycardia more frequent and less tolerable, and may make interruption of the pathway necessary. Without a doubt, the patient whose pathway has the potential to cause a malignant ventricular arrhythmia is a candidate for operation. This group of patients is selected by two methods: a history of episodes of malignant ventricular tachycardia and the finding at electrophysiological study that on induced atrial fibrillation, a rapid ventricular rate ensues. It is difficult to distinguish the young person at the right time. Sometimes the malignant arrhythmia is the first symptom of the disorder. In my opinion, any young patient known to have preexcitation on an ECG should at least undergo induced atrial fibrillation through an esophageal electrode to determine whether a malignant ventricular arrhythmia is likely to develop. Another factor that helps distinguish those patients who are candidates for operation is age. A young person who requires daily medication should undergo an operation. A lifetime of medication is too great a burden and too great a potential risk to impose on a young patient. An older patient in whom the tachycardia cannot be controlled also should have an operation. The selection process includes a careful preoperative physiological study. Sometimes a short PR interval is caused by an AV connection bypassing the AV node; or, preexcitation from a His bundle can cause a connection to go directly to the ventricle and bypass the bundle branches. Occasionally, it is discovered that the tachycardia is not caused by the Kent bundle at all, even though preexcitation is present. When done carefully, such a study can identify multiple pathways in almost every instance; they were found in nearly 20% of my patients. Electrophysiological studies in patients with reentry supraventricular arrhythmias but no preexcitation may detect an unsuspected Kent bundle with only retrograde function. The incidence of this was about 15% in the series. In fact, 30 to 40% of reentry supraventricular tachycardias are due to Kent bundles that can conduct only retrograde. A careful cardiac evaluation of patients with WPW syndrome is needed to exclude other heart problems. Three of the patients in the series who died had an unrecognized cardiomyopathy, severe idiopathic hypertrophic subvalvular aortic stenosis. Ebstein s deformity was present in about 15% of the 200 patients in my series. Division of the Kent bundle should be done with a guide to identify it at operation, for the bundle is neither visible nor palpable. This is accomplished by a procedure called mapping, an electrophysiological study performed in the operating room. It should be noted, however, that in more than 90% of patients, the preoperative study localizes the pathway well enough to act as a guide in case the pathway is obtunded by manipulation at operation. Surgical Technique In planning the surgical strategy, observations during operation are of help in defining the surgical anatomy, even though the Kent bundle is not visible. In left free wall pathways, for example, such observations led to the following conclusions. I decided that pathways in the free wall were external to the annulus fibrosus. Their course could be close to the annulus or out in the coronary sulcus fat at varying distances from the annulus fibrosus to points just beneath the epicardium. Since the coronary sinus has atrial muscle in its wall, this structure could be the atrial origin of a pathway. A drawing of the interruption of a left free wall pathway demonstrates how these suppositions were put into practice (Figure). The His bundle and AV node must always be considered in planning and performing the operation for tachycardia due to a Kent bundle. The His bundle is one of the two arms of the reentry circuit, and its division will cure the tachycardia. However, if the reason for operation is to repair a potentially malignant arrhythmia, then interruption of only the Kent bundle will suffice. His bundles and Kent bundles can be close together. In posterior pathways, both may have to be interrupted owing to the inability to separate them. On the other hand, an anterior septal Kent bundle and the His bundle have been judged by mapping to be within 2 to 3 mm of each other. By careful placement of the incision, the Kent bundle alone can be interrupted and the His bundle spared. Also, the His bundle is well protected by the membranous ventricular septum. The relationship of the Kent bundle to the His bundle and the multiple courses the Kent bundle can follow in the posterior septal area are complex. Mapping is difficult because of the relationship of the Kent bundles to the two atria, the coronary sinus, the ventricular and atrial septa, and the right fibrous trigone, which is composed, in part, of the membranous ventricular septum. The His bundle penetrates the right fibrous trigone. To give some perspective on the boundaries of this area, I have likened it to a three-sided pyramid toppled on its side. The right fibrous trigone is its apex; the epicardium of the crux and a part of the coronary sinus make up the base; and the right atrium, the left atrium, and the combination of the septum and the posterior process of the left ventricle constitute the three sides. This arrangement prevents accurate epicardial mapping because the right atrium overlaps the left ventricle. Two other structural arrangements make mapping difficult: the superior position of the left annulus fibrosus over the right and the obliquity of the atrial septum from its insertion in the right fibrous trigone to the crux. These relationships have led me to believe that a patient whose surface map shows earliest activation of the ventricle just to the left of the crux or over the interventricular groove should have an extensive dissection not

4 179 Sealy: WPW Syndrome and Direct Arrhythmia Surgery / The approach to a left free wall pathway. (Upper left) A left atriotomy similar to that used for a mitral valve replacement is done. The suture marks the site of the connection of the pathway to the atrium, as determined by mapping at operation. A long incision including a2- most all of the free wall is made. (A) The fat in the coronary sulcus is separated from the atrium and ventricle. (B) Extent of the dissection. (C) The vey superficial fibers of the ventricle are separated from the external surface of the annulus. These steps take care of all possible routes the Kent bundle may take from the atrium to the ventricle. only of the pyramidal septal space but a right and left atriotomy as well. The latter can be avoided in some patients by substituting cryothermic ablation. When the early ventricular activation site is found to the right of the crux, then only a right atriotomy and posterior septal dissection are needed. Last, the His and Kent bundles may be adjacent to each other. Problems with interruption have occurred more frequently with pathways here in the posterior septal area than anywhere else. The possibility of interrupting the Kent bundle without an atriotomy and even without cardiopulmonary bypass has now been realized by my approach recently to three right free wall pathways and by the external approach of Guiraudon* to left free wall pathways. The cryoprobe is used for this purpose. Guiradon G: Personal communication, At operation to control the reentry tachycardia in WPW syndrome, the surgeon has the option to interrupt conduction over the His bundle. Early in my experience, I used this method occasionally because I was not able to find the Kent bundle. Recently, I have elected to interrupt the His bundle only in patients with associated severe cardiomyopathies in whom the Kent bundle was on the left side or in the posterior septal area. The results of operation involving the arrhythmia associated with WPW are excellent. In my experience with more than 200 patients, only patients with serious associated diseases, including idiopathic hypertrophic subvalvular aortic stenosis, Ebstein s anomaly, and ischemic heart disease, have died. With our current knowledge, success in identifying the pathway and then interrupting it should be nearly 100%. Are there methods that promise to reduce the complexity of the procedure? A cardiac catheter electrode attached to a direct-current defibrillator and introduced through the venous system can now be used to interrupt the His bundle [17,18]. When control of the extent of the burn caused by this method can be obtained so as to avoid injury to the coronary arteries, then the technique might be more widely used in the ablation of Kent bundles. Closing Remarks In closing, I will raise some points about the future of direct arrhythmia surgery. The surgical approaches to

5 180 The Annals of Thoracic Surgery Vol38 No 2 August 1984 reentry ventricular tachycardia are now well established. Direct operation on the AV node is possible. This node is relatively large, and conduction through it is slow. By means that are not known, the node filters excessive numbers of impulses from the atrium, thereby protecting the ventricle from a fast, intolerable rate. Sometimes these two peculiar mechanisms malfunction. Would a graded division of the AV node or nodal approaches increase this capacity of the node for filtering the excess impulses resulting from a tachycardia? The AV node is sometimes found to be divided into two physiologically different pathways. In 1 patient with AV nodal tachycardia, partial division of the AV node served to interrupt a reentry circuit using these two physiologically distinct conduction pathways, and thus cured the tachycardia [19]. In disorders that arise because the sinoatrial node fails in its function as the heart s pacemaker, would elimination of this node allow a lower atrial pacemaker to become dominant? If so, would it be reliable? Animal studies have shown that the pacemaker is in the region of the coronary sinus. More experimental studies are required, for it appears that a large volume of atrium needs to be in continuity with the substitute pacemaker for the pacemaker to assume dominance [20]. This may explain the problems with pacemakers after extensive atrial operations when the sinoatrial node is preserved but the surrounding right atrium is partially destroyed or excluded. The fisherman with the fast pulse started me on an interesting trip. There are many miles left to travel. I am thankful to have been in at the start. References 1. Sealy WC, Hattler BG Jr, Blumenschein SD, Cobb FR Surgical treatment of Wolff-Parkinson-White syndrome. Ann Thorac Surg 8:1, Wiggers CJ: Some significant advances in cardiac physiology during the nineteenth century. Bull Hist Med 34:1, Gaskell WH: On the innervation of the heart, with especial reference to the heart of the tortoise. J Physiol 4:43, Geison GL: Michael Foster and the Cambridge School of Physiology. Princeton, NJ, Princeton University Press, His W Jr: Activity of the embryonic human heart and the significance for the understanding of the heart movement in the adult. J Hist Med Allied Sci 4:289, Kent AFS: Researches on the structure and function of the mammalian heart. J Physiol 14233, Kent AFS: A conduction path between the right auricle and the external wall of the right ventricle in the heart of the mammal. J Physiol 4857, Aschoff KAL: A discussion on some aspects of heart-block. Br Med J 2:1103, Keith A, Flack MW The auriculo-ventricular bundle of the human heart. Lancet 2:359, Shapiro E: Willem Einthoven s fortuitous invention. Am J Cardiol40:987, Callahan JA, Keys JD, Keys TA: Sir Thomas Lewis. Mayo Clin Proc 56749, Barker PS, MacLeod AG, Wilson FN, Alexander J: The excitatory process observed in the exposed human heart. Am Heart J 5:720, Durrer D, Roos JP: Epicardial excitation of the ventricles in a patient with Wolff-Parkinson-White syndrome (type 9): temporary ablation at surgery. Circulation 3535, Wolff L, Parkinson J, White PD Bundle branch block with short P-R interval in healthy young people prone to paroxysmal tachycardia. Am Heart J 5:685, Wolferth CC, Wood FC: The mechanism of production of short P-R intervals and prolonged QRS complexes in patients with presumably undamaged hearts: hypothesis of an accessory pathway of auriculo-ventricular conduction (bundle of Kent). Am Heart J 8:297, Wood FC, Wolferth CC, Geckeler GD: Histologic demonstration of accessory muscular connections between auricle and ventricle in a case of short P-R interval and prolonged QRS complex. Am Heart J 25:454, Gonzalez R, Scheinman M, Margotten W, Rubinstein M: Closed chest electro-catheter technique for His bundle ablation in dogs. Am J Physiol 241:283, Gallagher JJ, Svenson RH, Kasell J, et al: Catheter technique for closed chest ablation of atrioventricular conduction system. New Engl J Med 306:194, Pritchett EL, Anderson RW, Benditt DG, et al: Re-entry within the atrioventricular node: surgical cure with preservation of atrioventricular conduction. Circulation 60:440, Sealy WC, Seaber AV: Cardiac rhythm following exclusion of the sinoatrial node and most of the right atrium from the remainder of the heart. J Thorac Cardiovasc Surg 77:436, 1979