Kent Bundles in the Anterior Septal Space Will C. Sealy, M.D.

Transcription

1 Kent Bundles in the Anterior Septal Space Will C. Sealy, M.D. ABSTRACT Kent bundles in the anterior septal area of the heart occupy a region of complex morphology. In this study, the anatomical characteristics of the area were reviewed by the dissection of 12 human hearts and then an analysis was done of the results of operation in 15 patients with Kent bundles in this location. One important anatomical finding was the relationship of the atrial septum, the right fibrous trigone, and the underlying membranous ventricular septum to the atrioventricular node and the His bundle. The normal components of the conduction system are protected from injury at operation by encasement in these structures. At operation, the accuracy with which retrograde endocardial mapping could identify the Kent bundle was demonstrated in 8 patients who had Kent bundles clearly shown to be within 2 to 5 mm of the His bundle. Kent bundle interruption in 13 patients was achieved by a precisely placed incision and dissection, and in 2 patients by cryothermia. In 1 of these 2 patients, both the His bundle and the Kent bundle were interrupted when cryothermia was used at a second operation. This study indicates that a Kent bundle and His bundle can be within 2 mm of each other, judging their positions by retrograde endocardial mapping. Final proof of the Kent bundle s location is demonstrated by interruption. With the protection afforded to the His bundle by encasement in the right fibrous trigone, surgical interruption of the adjacent Kent bundle can be accomplished without injury to the His bundle. Kent bundles in the anterior septal area cause unusual problems in identification and interruption because of the complex morphology of the region [l]. In this report, a description of this area is given based on the dissections of 12 human hearts free from congenital or valvular heart disease. This description is followed by a review of the identification process and From the Division of Thoracic Surgery, Duke University Medical Center, Durham, NC Accepted for publication Sept 30, methods used for interruption in the last 15 patients operated on who had Kent bundles in the anterior septal area. Material and Methods Anatomical Study Kent bundles classified as anterior septal occupy an area along the right anterior atrioventricular (AV) junction that begins at the insertion of the atrial septum into the right fibrous trigone and then extends anteriorly and laterally to the point where the right coronary artery enters the coronary sulcus (Fig 1). This area contains a portion of the infundibulum of the right ventricle, the right ventricle s attachment to the membranous and muscular ventricular septa, and part of the atrial septum and the right atrium. Thus, there are more possible Kent bundle attachments than those involving septal structures only. However, antegrade epicardial activation sequences of pathways in this area produce similar patterns. The classification is surgically convenient and is based on both physiological and morphological considerations. No pathways have been described in otherwise normal human hearts in the anterior septal area. In the dissection of the hearts, the anterior septal area was approached from the superior aspect of the heart (see Fig 1). The aorta was deflected anteriorly, and the superior vena cava was encircled and displaced posteriorly and laterally. This opened an epicardium-lined sulcus. There was a thin layer of fat beneath the epicardium. The junction of the two atria was not visible above the epicardial reflection because of a thick myocardial band continuous from the right to the left atrium called Bachmann s bundle. The atrial attachment of the epicardium was divided along the right atrium and extended across to the left, thereby exposing the posterior aortic sinus of Valsalva (Fig 2). Then the epicardium was separated over to the right coronary artery to a point just beyond that vessel s emer- 180

2 181 Sealy: Kent Bundles in Anterior Septa1 Space Fig 1. Exposure of the heart from above. The superior vena cava (SVC) is retracted posteriorly as shown by the toumiquet on the vena cava. The medial and lateral limits of the anterior septa1 area are marked by the sets of broken lines. The right coronary artery (RCA) emerges from the aorta (Ao) anteriorly. The atrial septum is not visible, for there is a continuous band of muscle, Bachmann s bundle, from the left atrial appendage to the right atrial appendage. (LA = left atrium; RA = right atrium.) (Used by permission of the Duke University Medical Center.) RFT AS TV Fig 2. If the epicardium is incised along the atrium just below Bachmann s bundle and extended to the free wall on the right and to the left beyond the noncoronary sinus of Valsalva, the junction of the right atrium (RA) and the infundibulum of the right ventricle (RV) is exposed. As the excision is extended to the left, the anterior aspect of the atrial septum (AS) can be identified. Inferiorly, a wide fibrous band beneath the posterior aortic sinus becomes visible. This is the aortic annulus at the junction with the right fibrous trigone (RFT). (Ao = aorta; TV = tricuspid valve annulus.) (Used by permission of the Duke University Medical Center.) gence from the aorta. The epicardium and the fat underneath it were separated easily from the surrounding structures. In Figure 2, the annulus of the tricuspid valve is shown as a welldefined band inserting into the right fibrous trigone. The annulus was remarkably distinct in all specimens when viewed from the epicardial side. The aortic annulus and the right fibrous trigone were also thick and easily exposed. Medially, the junction of the right and left atria was identified as decussating myocardial bands that extended superiorly for 1.0 to 1.5 cm, at which point the septum was lost in Bachmann s bundle. The atrial septum could be followed inferiorly into the right fibrous trigone. The left atrium after it left the anterior atrial septum was no longer opposite the left ventricle or ventricular septum and thus could not harbor a Kent bundle. As the dissection was extended across the tricuspid valve annulus, the infundibulum of the right ventricle was found to be directed superiorly. The right ventricle s attachment to the ventricular septum was marked by the right fibrous trigone and the annulus of the aortic valve. Underneath the attachment of the right ventricle to the septum was the crista supraventricularis (Fig 3). That structure, a muscle ridge coursing from the superior papillary muscle to the pulmonary valve ring, belonged to the muscular septum for only a part of its course, for the subvalvular aspect of the infundibulum was a muscular tube. The right atrium was opened in a manner similar to that used in the operation (Fig 4). The coronary sinus and atrial extension of the membranous ventricular septum, which is the inferior part of the right fibrous trigone, were identified first. The membranous ventricular septum ranged from 8 to 10 mm by 5 to 8 mm, with the tricuspid valve attachment separating the atrial extension of the membranous ventricular septum from the ventricular part. The tricuspid annulus, after leaving the right fibrous trigone superior to the membranous septum, runs first anteriorly and then laterally to the free wall. The tendon of Todaro, which was found in 8 hearts, is shown in Figure 4. Its connection to the membranous ventricular septum is always superior to the AV node. In Figure 4, the AV

3 182 The Annals of Thoracic Surgery Vol 36 No 2 August 1983 RF1 LA PV Cr S S PM Fig 3. lnfundibulum of the right ventricle has been removed (the division occurring where the ventricle joined the membranous and muscular ventricular septa) and the right corona y arte y divided, exposing the right side of the muscular ventricular septum. The superior papilla y muscle (SPM) is shown with the crista supraventricularis (CrS) extending to the pulmonary valve (PV). Kent bundles leaving the atrium adjacent to the right fibrous trigone (RFT) would cause an activation wave front that might move along the infundibulurn and septum; if the mapping probe cannot be placed on the crossing point because of the pericardial reflection, an early area might be found anyplace along the infundibulurn. (LA = left atrium; RA = right atrium.) (Used by permission of the Duke University Medical Center. ) node, penetrating His bundle, and right bundle branch are shown diagrammatically. Their positions were determined from a study of serial sections made available to me by the Department of Pathology at Duke University Medical Center as well as reference to the work of Becker and Anderson [2]. The AV node and His bundle are actually in the posterior septal area with the compact AV node enclosed in the posterior aspect of the atrial septum just posterior to the membranous ventricular septum and actually below the crest of the muscular ventricular septum. The mitral annulus at this point may be as much as 5 to 8 mm superior to the tricuspid annulus. The penetrating His bundle enters the right fibrous trigone and courses through the membranous ventricular septum. The course is posterior to the attachment of the atrial septum to the anterior aspect of the right fibrous trigone. Based on this anatomical information, one possible Kent bundle connection in the septal area could be from the anterior edge of the atrial septum to the muscular ventricular septum, skirting the anterior edge of the right fibrous RA trigone. The other course from the right atrium to the right ventricle could be a point anterior to the right fibrous trigone to the arbitrary line separating the anterior septal area from the right free wall. Clinical Studies The group reviewed in this study comprised 15 patients with anterior septal Kent bundles and included only patients with one pathway. Two patients, operated on without success early in my series of 190 patients with Kent bundles, were excluded because of the uncertainty about the location of the pathways. The 15 patients in this study underwent operation at a later time than those 2 with an uncertain diagnosis. The 15 patients had no other cardiac anomalies, although l had sick sinus syndrome. All of the patients had preoperative electrophysiological studies by the Department of Medicine at Duke University Medical Center as described in a previous report [3]. From this investigation, the pathways were believed to be in the anterior septal area in 14 of the 15 patients. The error was in placing one pathway in the posterior septal area. The operative procedure consisted of first confirming the location of the pathway by measuring the activation sequence of the atria and the ventricles with techniques in many ways similar to those used for the preoperative electrophysiological study. The technique of epicardial mapping has been described in another report from Duke University Medical Center [4]. The pathway in Patient 8 was made functionless by manipulation before the mapping; thus, the interruption of the pathway was guided by the preoperative electrophysiological study (Table). Patient 12 had a pathway that functioned intermittently, and reentry tachycardia could not be induced. Eventually both the His and Kent bundles were ablated. Six patients had pathways with only retrograde function. The epicardial and right atrial endocardia1 maps were done whenever possible. Antegrade epicardial activation measurements in the 9 patients with bidirectional pathways, done with atrial pacing or occasionally during sinus rhythm, had the earliest activation over the infundibulum of the right ventricle. Retrograde

4 183 Sealy: Kent Bundles in Anterior Septa1 Space Fig 4. (A) Right atrium opened for division of an anterior septa1 Kent bundle. The AV node (AVN) and penetrating His bundle (broken lines) are shown in relationship to the right fibrous trigone and the atrial extension of the membranous ventricular septum (AMS). The tendon of Todaro (dark line) extends from the eustachian valve of the coronay sinus to the right fibrous trigone superior to the AV node. The conduction system is both concentrated and protected by the structures that make up the right fibrous trigone. (B) lncision (broken line) for Kent bundle interruption begins at the anterior extent of the AMS and extends laterally and posteriorly to the junction with the free wall. (C) lncision has been completed and the subepicardial fat separated from the infundibulum of the right ventricle (RV). The right atrium (RA), freed of fat, is pulled toward the left, exposing the annulus of the tricuspid valve (TV). (FO = fossa ovalis.) (Used by permission of the Duke University Medical Center.) earliest epicardial activation, determined during either reentry tachycardia or ventricular pacing, was described in 14 of the patients as being on the anteromedial aspect of the right atrium. To complete the mapping process, cardiopulmonary bypass was started and a right atriotomy was made. The retrograde endocardial maps done during either reentry tachycardia or ventricular pacing turned out to be the most helpful. First, the His bundle electrogram was sought and was always found, as expected, over the atrial extension of the membranous ventricular septum. Then the Kent bundle s po- sition on the right atrium was identified and its relation to the His bundle noted. In the 11 patients in whom it was possible to do retrograde endocardial maps, the Kent bundle, as indicated by the early atrial activation point, was found in 8 patients to be 5 mm or less anterior to the His bundle electrogram. In 3 patients, the Kent bundle was 1 cm or more anterior to the His bundle electrogram. One of the 3 had a pathway at the junction with the right free wall. After the crossing point of the Kent bundle was found, the procedure for division was begun. An endocardial right atrial incision was made 3 to 4 mm above the annulus, thereby exposing the subepicardial fat, as shown in Figure 4. The incision began at the anterior edge of the atrial septum and extended to the right free wall. This exposed the epicardial side of the right atrial wall, the infundibulum of the right ventricle, and the anterior aspect of the atrial septum at its insertion into the right fibrous trigone. The surfaces were thoroughly cleaned of all subepicardial fat. Then the superficial fibers of ventricular myocardium entering the annulus of the tricuspid valve were divided. After this, the bands of muscle and fibrous tissue on the atrial septum and the right fibrous trigone were divided. Keeping the dissection on the epicardial side of the atrial septum, right

5 184 The Annals of Thoracic Surgery Vol 36 No 2 August 1983 Summary of Data on Pathway Mapping and Operation Patient Distance on No. Retrograde Endocardial Map" Comments 1 Close to His (map 1); 5 mm Only retrograde conduction; operation 1, from His (map 2) incision within 1 to 2 mm of RFT; operation 2, 24 hr later, incision extended to RFT 2 5 mm from His AV block for 24 hours; endocardial incision 3 Close to His Only retrograde conduction; antegrade conduction noted 4 yr before 4 3 mm from His Sick sinus syndrome; endocardial incision 5 10 mm from His Only retrograde conduction; cryothermic ablation through atriotomy at point 10 mm from RFT 6 7 Had activation antegrade superiorly over infundibulum; long epicardial incision made first; second attempt, extension to RFT interrupted the Kent Epicardial map: medial aspect of right atrium, retrograde; infundibulum, antegrade 8 Only retrograde conduction; pathway did not function at operation; wide endocardial incision 9 15 mm from His Pathway at junction with free wall; wide endocardial and epicardial incision 10 4 mm from His Only retrograde conduction 11 2 mm from His Only retrograde conduction mm from His Less than 4 mm from His 5 mm from His Intermittent pathway function; mapping unsatisfactory; operation 1, incision to RFT missed; operation 2 in 24 hr, cryothermic ablation of His and Kent bundles First incision 4 mm from His electrogram; then Kent electrogram 1 to 2 mm from RFT; extended incision to include fibers of RFT Endocardial incision Endocardial incision "Distance from Kent bundle to His bundle. RFT = right fibrous trigone; AV = atrioventricular. atrium, and ventricle avoids the AV node and His bundle even when the activation studies place the His bundle within 2 to 3 mm of the Kent bundle. In the patients with early retrograde activation-10 mm or more from the His spike-the surgeon should consider extending the incision to include about one-half of the free wall. This is done by dividing the epicardium at its attachment to the atrium as described for right free wall pathways [5]. This can be extended into the sulcus between the aorta and right atrium in the manner shown in Figure 2. The epicardial incision, which is believed to be essential for the right free wall division, is not usually done when retrograde maps place the Kent bundle less than 10 mm from the recording site of the His bundle electrogram. Cryothermia was successful in interrupting one pathway (Patient 5) that was 1 cm from the His bundle. The method used was similar to that reported for interruption of the His bundle [6, 71. First, the temperature of the tissue over the crossing point was reduced to 0 C by the probe. If this blocked conduction, a cluster of overlapping ice balls (usually five) with a temperature of -60 C was applied for 2 minutes. When pathways are less than 1 cm from the His bundle, the ice balls and thus the destroyed tissue are very likely to include the His bundle, as may have happened in Patient 12. During the open-heart portion of the proce-

6 185 Sealy: Kent Bundles in Anterior Septa1 Space dure, moderate total-body hypothermia to 34 C was employed. In all but 2 patients in whom cardioplegia was employed, the aorta was intermittently clamped and ventricular fibrillation induced for two to three periods of 5- to 10-minute duration. The average pump time, including mapping, was 75 minutes. Mapping required an average of 18 minutes of bypass time, the longest being 35 minutes and the shortest 10 minutes. After division and with the patient still on bypass, another activation sequence was measured to make certain that no other pathways were present. Then incremental atrial and ventricular pacing was done to look for the Wenckebach period. If found, AV or VA conduction was considered to be through the AV node and His bundle. Results The 15 patients survived the operative treatment without serious postoperative complications. The Kent bundle was interrupted in all patients. Two patients (Patients 1 and 12) had to have a second operation, both within 24 hours of the first. In the first operation in Patient 1, the incision was made just to the right fibrous trigone. At the second operation, the His bundle and Kent bundle electrograms during reentry tachycardia were within 3 mm of each other, with the Kent bundle electrogram just at the edge of the atrial septum where it was attached to the right fibrous trigone. The previous endocardial atrial incision was opened and the anterior edge of the atrial septum exposed, and then the fibers on the edge of the septum and adjacent right fibrous trigone were divided. This interrupted the pathway, but avoided injury to the His bundle. In Patient 12, a retrograde map was not done at the first operation. A generous incision was made to include the anterior end of the atrial septum. Conduction returned over the Kent bundle about 8 hours later. The next day the second operation was carried out. With the cryothermia probe over the atrial septum at its junction with the posterior aspect of the right fibrous trigone, conduction over both the Kent and His bundles was blocked when the probe s temperature was reduced to 0 C. Then an area about 10 mm by 15 mm was destroyed by reducing the probe s temperature to - 60 C for 2 min- utes. This was followed by permanent interruption of both the Kent and His bundles. In retrospect, a more extensive dissection along the anterior edge of the atrial septum and the right fibrous trigone might have succeeded, although the incision at the first operation was deemed adequate. The Kent bundle could have penetrated the membranous septum in a way similar to the His bundle, and, if so, would properly be classed as a posterior septal pathway. In spite of the close proximity of the Kent and His bundles, the His bundle was temporarily blocked in only 1 patient. This patient and the 13 others have normal AV conduction. In 1 patient, a pacemaker was installed because of associated sick sinus syndrome. Comment Anterior septal Kent bundles occupy an area that is not usually exposed during other cardiac operations. This fact, along with the close proximity of the Kent bundle to the His bundle, makes the interruption of the Kent bundle a challenge in surgical anatomy. The first point of interest in this study was the accuracy of the retrograde endocardia1 maps, both during reentry tachycardia and with ventricular pacing, in allowing separation of the His bundle from the Kent bundle when the two were only 2 to 5 mm apart. This is in contrast to the posterior septal Kent bundles. For them, retrograde maps done with ventricular pacing are of little value and those done during reentry tachycardia are of only limited usefulness [8]. In posterior septal pathways with ventricular pacing retrograde, conduction occurs simultaneously over both the Kent and His bundles with the His bundleconducted impulses passing through the AV node to the atria. Although Kent bundle conduction to the atrium is faster than conduction from the His bundle to the AV node to the atrium, fusion still occurs and precise mapping is impossible. In addition, the posterior septal Kent bundle s connection to the atrium can be almost anywhere over the wide expanse of the area and located in places not accessible to the mapping probe. Even though in the anterior septal area the Kent and His bundles are close to the probe, the His bundle electrogram is recorded on the ventricle, while the Kent bundle

7 186 The Annals of Thoracic Surgery Vol 36 No 2 August 1983 electrogram is recorded on the atrium. In this situation the Kent bundle activates the atrium before impulses from the His bundle can penetrate the AV node and fuse with those arriving by the Kent bundle. This allows easy timing and thus separation of the course of the anterior septal Kent bundle from the His bundle during mapping. The Kent bundle can course from the atrium to the ventricle almost within the right fibrous trigone and the membranous ventricular septum, as shown by the mapping and by the results of the surgical dissection. Thus, the trigone and membranous septum serve as an easily recognizable conduit containing the His bundle, which is concentrated in the conduit; these structures also act as a protective shield for the His bundle during operative manipulation of the area. The high incidence of pathways with only retrograde function in this group of patients, 6 of 15, is also of interest. The reasons for this are obscure. In the entire series of patients with Kent bundle, the incidence was about 15%. Another interesting point for future consideration was shown by the 1 patient who had Kent bundle interruption without an intraoperative map. Actually, the preoperative localization was accurate in 14 of the 15 patients. Mapping required 18 to 20 minutes of the cardiopulmonary bypass time. If the patient has a good preoperative study, the intraoperative mapping could be shortened to a quick retrograde endocardia1 recording of the early activation area using ventricular pacing. Now that the anatomical details of the region are better understood, Kent bundles in the anterior septal area have proven to be the easiest and most certain of the pathways to identify and to interrupt. The close proximity of many of the Kent bundles to the His bundle has made the use of a precise surgical incision for interruption mandatory. References 1. Sealy WC, Gallagher JJ: The surgical approach to the septal area of the heart based on the experiences with forty-five patients with Kent bundles. J Thorac Cardiovasc Surg 79:542, Becker AE, Anderson RH: Morphology of the atrioventricular junctional area. In Wellens HJJ, Lie KI, Janse MJ (eds): The Conduction System of the Heart. Philadelphia, Lea & Febiger, 1976, Gallagher JJ, Gilbert M, Sevenson RH, et al: Wolff- Parkinson-White syndrome: the problem, evaluation and surgical correction. Circulation 51:767, Gallagher JJ, Kasell J, Sealy WC, et al: Epicardial mapping in the Wolff-Parkinson-White syndrome. Circulation , Sealy WC: The evolution of the surgical methods for interruption of right free wall Kent bundles. Ann Thorac Surg 35:29, Harrison L, Gallagher JJ, Kasell J, et al: Cryosurgical ablation of the A-V node-his bundle: a new method for producing A-V block. Circulation 55:463, Sealy WC, Gallagher JJ, Kasell J: His bundle interruption for control of inappropriate ventricular responses to atrial arrhythmias. Ann Thorac Surg 32:429, Sealy WC, Mikat E: Anatomical problems with identification and interruption of posterior septal Kent bundles. Ann Thorac Surg (in press, 1983)