Etiology of Right Bundle-Branch Block in Patients Undergoing Total Correction of Tetralogy of Fallot

Abstract

The electrocardiographic (ECG) pattern of right bundle-branch block (RBBB) occurs routinely in patients after open-heart surgery for tetralogy of Fallot (TF). To determine the etiology of the RBBB pattern, 14 patients with TF, seven with ventricular septal defects (VSD), and one with pulmonary stenosis (PS) were studied during and after cardiac surgery. Bipolar electrograms from 10 selected right ventricular epicardial sites were recorded simultaneously with an ECG. Records were obtained before and immediately after vertical right ventriculotomy, after infundibular resection, and after repair of a ventricular septal defect (VSD). The vertical ventriculotomy alone was always associated with significant prolongation of the time of epicardial activation only to the recording sites lateral to the incision with prolongation of the QRS complex by an average of 39 msec, and with the appearance of an RBBB ECG pattern. Infundibular resection and VSD repair were not associated with any changes in the electrophysiologic parameters measured. A retrospective analysis of 251 patients with TF, VSD, and PS revealed a 100% incidence of RBBB pattern in the electrocardiograms of only those who had undergone ventriculotomy. It can be concluded that the RBBB pattern seen postoperatively in patients with TF is due to changes in right ventricular activation secondary to the vertical ventriculotomy.Additional Indexing Words: Vertical ventriculotomy Right ventricular activation time Specialized conduction system T HE electrocardiographic pattern of right bundle-branch block (RBBB) invariably follows total surgical correction of tetralogy of Fallot (TF).1 4 However, to date there is no direct physiologic evidence concerning the etiology of this RBBB pattern. RBBB has also From the Congenital heart disease Cardiac surgery been noted after surgical correction of ventricular septal defects (VSD )4-6 and infundibular pulmonic stenosis (PS ) 7 Investigators have attributed the RBBB pattern observed following surgical repair of VSD to operative trauma to the right main bundle branch.6

Late results in patients with tetralogy of Fallot repaired during infancy.

“…The AH interval was prolonged in two patients, and the HV interval was prolonged in three. Delayed right ventricular apex activation was observed in 22 patients, consistent with "central" right bundle branch block.27 28 Symptomatic arrhythmias/late death. None (table 3).…”

Further Observations on the Etiology of the Right Bundle Branch Block Pattern Following Right Ventriculotomy

“…If and when such injury to the proximal part of the right bundle branch occurs, it might not always be detected with the epicardial recording technique previously used, 13 25 we feel that the disruption of the right bundle branch at the level of the moderator band is of clinical importance. This is so mainly because it is a major fascicle of the right bundle branch and disruption occurs prior to its insertion into right ventricular myocardium.…”

“…In their study Gelband et al 13 demonstrated that, on completion of the ventriculotomy, right ventricular activation was delayed at sites lateral to the ventriculotomy. Since activation time did not change medial to the ventriculotomy following infundibular resection and VSD closure, they assumed "that no further injury occurred with further procedures.…”

“…8 13 This has been shown to be equally true for canines."' 12 The finding that this conduction disturbance can be explained by a similar cause in humans also,8-10, 13 has been recently questioned, however, because some patients do not develop an RBBB pattern following a right ventriculotomv. '7 Our results show that in 12 of 15 patients studied in whom an RBBB developed following surgery the development of this pattern was associated with the right ventriculotomy.…”

“…'1-3 Although injury to the proximal part of the right bundle branch can occur during open-heart surgery,'-3 the electrocardiographic pattern of RBBB has been shown recently by Gelband and associates to occur immediately following the right ventricular incision, and prior to closure of the ventricular septal defect or pulmonary infundibular resection. 13 At the end of the surgical procedure and following the closure of the ventriculotomy, several measurements were obtained in order to identify precisely the location of the ventriculotomy on the right ventricular free wall, and its relation to the various structures on the cardiac surface. These measurements were as follows: the distance from the 1) pulmonary artery annulus to the diaphragmatic surface of the heart (length of the heart) 2) pulmonary artery to the upper margin of the ventriculotomy; 3-5) left anterior descending coronary artery to the upper, middle, and lower parts of the ventriculotomy; and 6) total length of the ventriculotomy.…”