Ann Thorac Surg 2002;74:550-555
© 2002 The Society of Thoracic Surgeons
Original article: cardiovascular
Shallow stitching close to the rim of the ventricular septal defect eliminates injury to the right bundle branch
Toyoki Fukuda, MD*a,
Takaaki Suzuki, MDa,
Ichiro Kashima, MDa,
Masaaki Sato, MDa,
Yukihiko Morikawa, MDa
a Departments of Cardiovascular Surgery, Pediatric Cardiology, and Pathology, Tokyo Metropolitan Kiyose Children‘s Hospital, Tokyo, Japan
Accepted for publication April 8, 2002.
* Address reprint requests to Dr Fukuda, Director, Cardiovascular Surgery, Tokyo Metropolitan Kiyose Children’s Hospital, 1-3-1 Umezono, Kiyose-shi, Tokyo 204-8567 Japan
e-mail: fukuda{at}chp-kiyose-tokyo.jp
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Abstract
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Background. Complete right bundle branch block carries a deleterious effect on the long-term outcome of patients who undergo surgical treatment of the perimembranous ventricular septal defect. We describe a novel suturing method to reduce the prevalence of complete right bundle branch block.
Methods. From March 1996 through December 2000, 48 consecutive patients with perimembranous ventricular septal defect underwent patch closure using shallow stitches placed close to the rim (group 1). The same number of patients was randomly selected from those who had previously undergone surgery using deep stitches placed distant from the rim (group 2). Postoperative electrocardiograms were reviewed to compare the prevalence of complete right bundle branch block between groups. A morphologic study of the conduction system was performed to identify the vulnerable segment of the right bundle branch where the surgical damage tended to occur. Additional analyses were made to determine whether younger age and right ventriculotomy increased the prevalence of complete right bundle branch block.
Results. The prevalence of complete right bundle branch block in group 1 (6.3%) was significantly (p < 0.0001) lower than in group 2 (43.8%). The result was consistent with the morphologic finding that stitches of group 2 tended to damage the right bundle branch and those of group 1 did not. The younger age and right ventriculotomy did not increase the prevalence of complete right bundle branch block.
Conclusions. Shallow stitches placed close to the rim of the perimembranus ventricular septal defect eliminate injury to the right bundle branch.
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Introduction
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Despite intricate modifications of the suturing method for patch closure of the perimembranous ventricular septal defect (VSD), the likelihood of postoperative complete right bundle branch block (CRBBB) remains high with a reported prevalence of 20% to 62% [1–8]. In the conventional suturing method, stitches are placed distant or approximately 5 mm away from the posterior and inferior rim where the His bundle is believed to course along the left ventricular aspect. In fact this method has reduced the postoperative prevalence of complete atrioventricular block. However, against our expectation that this method would equally affect the right bundle branch (RBB) in a favorable fashion, earlier attempts have failed to reduce the prevalence of CRBBB to an acceptable level [1–8]. To delineate the reason for the surgical injury to RBB, we performed a morphologic study of the specialized conduction system of this subset of VSD. The result showed a crucial area in the right side of the ventricular septum where RBB was vulnerable to the surgical manipulation and led us to devise a novel suturing method with which we could eliminate injury to RBB.
In this study we describe our experience of the novel suturing method together with a comparative study of the prevalence of postoperative CRBBB between patients who were treated by the novel suturing method and others who had been treated previously by the conventional suturing method. Additional analyses were made to determine whether the younger age of the patient and right ventriculotomy increased the prevalence of CRBBB.
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Material and methods
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Morphologic features of RBB
Three autopsy specimens of the perimembranous VSD were subjected to the morphologic study of the specialized conduction system. Methods of the histologic study were similar to those described by Lev and associates [9, 10]. Our findings were consistent with the earlier view [11–18] that the His bundle penetrated the central fibrous body and reached to the left ventricular aspect of the ventricular septum, with subsequent ramification of both bundle branches (Fig 1).
At the level of the posterior and inferior rim, RBB took an intramural course keeping a maximal depth of 1 to 1.5 mm from the right surface of the septum and went across the septum in the direction of the right side of the septum (Fig 2).
Furthermore, on the way toward the right ventricular apex, RBB approached to the right surface of the septum approximately 5 mm inferior to the inferior rim (Fig 2).
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Fig 1. A histologic section of a heart with the perimembranous ventricular septal defect at the level of the posterior ventricular septum shows leftward deviation of the His bundle, ramification of the left bundle branch (thin arrows) and the right bundle branch (thick arrow). The displaced His bundle keeps straddling the septal myocardium. (MV = mitral valve; TV = tricuspid valve.)
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Fig 2. A section at the level of the inferior rim shows the intramural and subendocardial segments, or the second and third portions of Lev’s classification of the right bundle branch (thick arrows). The intramural segment is sandwiched between the septal myocardium and septomarginal trabeculation (SMT), with the latter structure separating this segment from the right surface of the septum. The distance between the rim of ventricular septal defect (VSD) and the third portion measures 5 mm. The maximal depth of the second portion measures 1.5 mm. (Thin arrows = left bundle branch.)
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Patients
The present study comprised two groups of the patients who underwent surgical repair of the perimembranous VSD at the age of 2 years or less. Group 1 comprised 48 consecutive patients who were operated on using the novel suturing method between March 1996 and December 2000. Group 2 comprised 48 randomly selected patients from those who had been operated on using the conventional suturing method between January 1990 and February 1996. Primary closure of the defect was achieved in 42 patients of group 1 and 45 patients of group 2, with the remaining patients undergoing the staged repair subsequent to banding of the pulmonary artery.
Clinical records
Medical records, operative notes, all available electrocardiograms (ECG), echocardiogaphy reports, and cardiac catheterization reports were retrospectively reviewed. In ECG analysis, CRBBB was considered present if QRS duration was 
0.10 seconds with a wide and slurred S wave in leads I and V6. The left axis deviation (LAD) was defined as the deviation of QRS axis between -30 and -90 degrees in the frontal plane.
Surgical technique
Patients of both groups underwent bicaval and aortic cannulation and were perfused with moderate hypothermia of 32°C. Myocardial protection was achieved with repeated infusion of cold blood cardioplegia into the aortic root and topical cooling. Transatrial repair of the defect was performed on 41 patients of group 1 and 33 patients of group 2, while a combination of transatrial and transventricular repair was performed on 7 patients of group 1 and 15 patients of group 2. A 0.4 mm Gore-Tex patch (W. L. Gore and Associates, Flagstaff, AZ) was fixed with pledget-supported mattress sutures in 18 patients of group 1 and all patients of group 2, while with continuous running sutures in the recent 30 patients of group 1. Patients who underwent the right ventriculotomy included those having the Eisenmenger type VSD and others who had the defect extended to the outlet. In these patients a vertical incision of less than 3 cm was made in the infundibulum of the right ventricle with subsequent reconstruction with a patch.
Based on the revised knowledge of the specialized conduction system, patients of group 1 underwent patch closure with the novel suturing method. In this method the first stitch of the double-armed 5-0 monofilament polypropylene suture was placed anterior to the medial papillary muscle or at the anterior-inferior rim of the defect. The ensuing stitch was directed counterclockwise toward the septal leaflet of the tricuspid valve and was passed through the annulus terminating at the right atrial surface. The sutures were snugged-up as the patch was lowered into position. Working then with the other limb, stitches on the inferior rim were placed shallow and close to the rim, or less than 1.5 mm in depth and less than 4 mm away from the rim (Fig 3).
Provided the medial papillary muscle stood in the way of the suture line, one or two stitches were passed through the base of the papillary muscle. At the posterior rim, shallow stitches were placed more than 5 mm away. The suture was then passed into the right atrium through the nearby annulus of the tricuspid valve. The ensuing stitches were taken between the patch and annulus until the two limbs met at the atrial side of the annulus.
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Fig 3. A schematic drawing of the inferior rim of the perimembranous ventricular septal defect viewed from the posterior right ventricular cavity. The septum is divided at the level where the right bundle branch takes off from the His bundle. Two stitches are shown on the right side of the septum, with the upper and lower ones indicating those of the novel and conventional suturing methods, respectively.
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The conventional suturing method of group 2 contrasted with the novel one in that stitches were placed distant, approximately 5 mm or more, from the posterior and inferior rim and passed deep through the septum (Fig 3).
Data analysis
Continuous variables, expressed as the mean ± standard deviation, were analyzed using the unpaired Student’s t test. Categorical variables, expressed as absolute values and percentages, were analyzed with the 
2 test or Fisher’s exact test as appropriate. In the separate analyses, the entire group of patients was divided into the two age groups, those 6 months of age or younger and others older than 6 months, and also into the two surgical groups with and without the right ventriculotomy. The prevalence of CRBBB during the postoperative period was then compared between the two age groups and two surgical groups. A p value less than 0.05 was considered statistically significant.
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Results
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There was no early or late postoperative death and no reoperation for the residual defect in either of the groups. There was no significant difference between groups with respect to age, weight, and size of VSD (Table 1).
Postoperative examination
The follow-up was complete in both groups. Time to follow-up of groups 1 and 2 ranged from 12 to 66 months (median 41.0) and from 68 to 138 months (median 97.5), respectively. Thirty patients of group 1 have so far undergone postoperative catheter examination with none of these showing the residual VSD. The remaining 18 patients, including 3 patients who await catheter examination, were followed up by repeated cross-sectional and Doppler echocardiography with 6 of these revealing a small, hemodynamically insignificant residual shunt at hospital discharge. The residual shunt, however, disappeared spontaneously in 4 of the patients by 12 months after the surgery.
ECG analysis
Preoperatively all patients of both groups showed regular sinus rhythm and normal duration of the QRS complex. Postoperatively none of the patients in either of the groups developed complete atrioventricular block. CRBBB occurred in 3 patients of group 1 (6.3%) compared with 20 patients of group 2 (41.7%), with a significant difference (p < 0.0001) between groups (Table 2). LAD developed solely among patients with CRBBB and occurred in 1 patient of group 1 (2.1%) compared with 11 patients of group 2 (22.9%), with a significant difference (p = 0.002) between groups (Table 2). The reduction of the prevalence of CRBBB in group 1 occurred irrespective of the type of VSD (Table 3).
In the separate analyses right ventriculotomy and younger age of the patient did not correlate with the postoperative development of CRBBB (Table 4).
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Table 4. Prevalence of Complete Right Bundle Branch Block (CRBBB) Based on Right Ventriculotomy and Age: Analysis of Patients of Groups 1 and 2
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Comment
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Although the postoperative development of CRBBB is known to carry a deleterious effect on the long-term outcome of patients with the perimembranous VSD [3], earlier efforts have failed to reduce the prevalence of CRBBB to an acceptable level [1–8]. Currently most surgeons employ the conventional suturing method in which stitches on the posterior and inferior rim of VSD are placed deep into the septum and distant from the defect. The primary concept of this method is to make stitches firm enough to secure the patch and to keep stitches distant from the left ventricular aspect of the rim where the His bundle and the takeoff of RBB are known to indwell [19]. However, the high prevalence of CRBBB, comparable with that seen in the earliest experience [20], raises a question as to whether the conventional suturing method fulfills the need for protection of RBB against surgical injury. A morphologic study of the specialized conduction system was therefore made to investigate the anatomical substrate predisposing to such injury. The morphologic feature of the His bundle was consistent with the earlier view [11–18] that the bundle penetrated the central fibrous body and reached to the left ventricular aspect of the septum (Figs 1 and 2). Likewise, the cardinal morphologic feature of RBB was consistent with the earlier view of Lev and associates [9, 10] that it comprised three portions, where the second portion was intramural and the third portion was subendocardial (Fig 2).
Recent studies investigating the embryological development of the specialized conduction system [21, 22] reported that, in the early stage of development of the heart, bilateral bundle branches were spread over the surface of the apical interventricular myocardium. The key to solving the enigma concerning the subsequent developmental mechanism as to how the second portion submerged into the myocardium was provided by an earlier study of Kurosawa and associates [16]. In that study they claimed that, during the process of development, the septomarginal trabeculation extended posterior and hung over the interventricular myocardium in a manner as to separate the His bundle and second portion of RBB from the right surface of the septum (Fig 2). Their concept implicated further that plastering of the septomarginal trabeculation over the right side of the septum displaced the His bundle toward the left ventricular aspect. Indeed, our study supported this view with the finding that the displaced His bundle kept straddling the septal myocardium with RBB being sandwiched between the myocardium and septomarginal trabeculation (Fig 2). Taking all these findings together, it is conceivable that the extent of hypertrophy and inferior extension of the septomarginal trabeculation determine the distances between the right surface and second portion and between the inferior rim of the defect and third portion.
The course of RBB along the right surface of the septum varies according to the type of the defect and is roughly divided into two forms [12–18]. One of these courses posterior to the defect in an oblique fashion and the other skirts along the posterior and inferior rim in a manner as to approach the medial papillary muscle and then turns downward terminating at the moderator band. The former course is frequently seen in the trabecular or outlet type of VSD [12, 13, 18] whereas the latter in the inlet type [11, 12]. In view of the fact that the prevalence of CRBBB of group 1 was reduced irrespective of the type of VSD, it is conceivable that RBB near the rim is usually intramural regardless of the type of the defect. This result suggests that the upper and lower margins of the "safe area" on the right surface of the septum are composed of the inferior rim of the defect and a semicircular line running parallel the inferior rim at a distance of 5 mm, respectively (Fig 4).
However, it is difficult to define precisely the safe area along the posterior rim as the septomarginal trabeculation diminishes near the posterior rim with an extreme form of denudation of RBB [16]. Therefore, it is our current practice to place stitches more than 5 mm away from the posterior rim.
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Fig 4. Surgeon’s view of the perimembranous ventricular septal defect through the right atrium. Double lines indicate the course of the His bundle and the right bundle branch. Double dotted lines include the intramural segment of the right bundle branch and double solid lines indicate the subendocardial segment. The upper and lower margins of the "safe area" for suturing are composed of the inferior rim of the defect and a dotted line running parallel to the inferior rim at a distance of 5 mm, respectively.
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Although our result shows that the novel suturing method is promising in terms of eliminating injury to RBB, concern may be raised as to whether shallow stitches are firm enough to secure the patch against dehiscence. However, the favorable result of group 1 with a minimal incidence of the residual shunt seems to support the validity and certainty of this method.
There has been a longstanding controversy regarding the role of the right ventriculotomy as a risk factor of CRBBB. Earlier reports claimed that a vertical incision to the infundibulum of the right ventricle tended to jeopardize the peripheral branches of RBB with subsequent development of CRBBB [1, 2, 4, 6, 7, 23, 24]. Conversely, other reports argued that the right ventriculotomy was not responsible for the postoperative CRBBB provided that the incision was small and horizontal [1, 6]. In our series, patients who underwent right ventriculotomy included those having the Eisenmenger type VSD, in which the potential narrowing of the right ventricular outflow tract was pointed out recently [25], and others who had the defect extending to the outlet. Our result shown in Table 4 endorses the latter view in the context that the right ventriculotomy was not the contributing factor for the postoperative development of CRBBB.
Younger age of patients has also been considered as a risk factor of CRBBB, with some reports claiming that infants aged 6 months or younger were prone to develop CRBBB [4, 6]. However, a favorable result among young infants of group 1 (Table 4) indicates that younger are not a risk factor of CRBBB.
There are several limitations of this study. First, the number of patients enrolled in this study was small. Although we are aware that the sample size of this study is not large enough, to be conclusive, our experience implies that, should a larger series of patients be investigated, the validity of the novel suturing method could be verified. Second, this investigation was not a randomized study of patients who were treated during the same period of time. However, that the surgeons and the technique of the cardiopulmonary bypass and myocardial protection were identical, would offset the drawback of the protocol.
In conclusion, our novel suturing method in which stitches are placed shallow and close to the inferior rim of the perimembranous VSD reduced the prevalence of postoperative CRBBB. By contrast, the conventional suturing method, in which the stitches were placed deep and distant from the rim, could potentially damage the second and third portion of RBB. The younger age of the patient and a small vertical incision of the right ventricle did not increase the prevalence of CRBBB.
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Abstract
Introduction
