Frederick O. Bowman

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

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.

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

Fifteen patients with various congenital heart defects were studied during open heart surgery in order to establish the precise mechanism by which a right ventriculotomy causes a right bundle branch block (RBBB) pattern on the scalar electrocardiogram (ECG). All required a right ventriculotomy for the correction of their defects. In each, the right ventriculotomy was carried out in steps, with incisions (3 to 7) of approximately 1 cm in length. Six simultaneous scalar ECG leads were recorded prior to the first incision and following each incision. The QRS duration was then measured and related to the length of the ventriculotomy.Following the right ventriculotomy, 12 of the 15 patients developed an RBBB pattern; the remaining three did not. In all cases, the total increase in QRS duration occurred during one specific incision of the right ventricular free wall and was not related to the total length of the ventriculotomy or to the sequence of the incisions. The site at which incision of the right ventricle caused the RBBB pattern was located at between 40 to 73% of the distance between the pulmonary artery annulus and the inferior border of the heart in nine patients; in three patients the site was higher on the right ventricular free wall.Our results explain why some patients who had a right ventriculotomy during open heart surgery do not develop an RBBB pattern on the scalar ECG. Also, since no relation was found between the length of the incision and the QRS duration, our results suggest that the ventriculotomy-induced RBBB pattern is unlikely to be due to disruption of a continuous Purkinje network but is probably due to disruption of a distal branch or branches of the right bundle.

Etiology of Prolongation of the P-R Interval in Patients with an Endocardial Cushion Defect Further Observations on Internodal Conduction and the Polarity of the Retrograde P Wave

Conduction time from the region of the sinus node to the region of the atrioventricular (A-V) node was studied during open heart surgery in 13 patients with an endocardial cushion type atrial septal defect, eight patients with a secundum type atrial septal defect, one patient with a sinus venosus type atrial septal defect, and eight patients with an intact atrial septum. Internodal conduction time was prolonged by an average of 37 msec (range 15-69 msec) in patients with an endocardial cushion defect when compared with the other three groups of patients. However, when the atria were paced from the A-V nodal region, the resulting P-R intervals in patients with an endocardial cushion defect were similar to those of patients in the other three groups, a fact that indicates normal A-V nodal-His-Purkinje conduction in patients with an endocardial cushion defect. It was therefore concluded that the prolonged P-R interval which patients with an endocardial cushion defect often manifest is due simply to prolonged internodal conduction time. Further, we have suggested that the data from this study support the concept that specialized atrial internodal pathways play an important role in conduction between the sinus and A-V nodes.

Electrophysiologic Identification of the Specialized Conduction System in Corrected Transposition of the Great Arteries

Electrophysiologic identification of the specialized conduction system was performed during open-heart surgery in two cases of corrected transposition of the great arteries (1-TGA) with situs solitus, dextrocardia or dextroversion and membranous ventricular septal defect (VSD). In one case there was accompanying subvalvlar pulmonary stenosis and in the other there was an Ebstein-like deformity of the systemic atrioventricular (A-V) valve. Electrograms were recorded throughout the right atrium and morphologic left ventricle in the case with subvalvar pulmonary stenosis and throughout the left atrium and morphologic right ventricle in the case with the Ebstein-like deformity of the systemic A-V valve. Specialized conduction system electrograms were recorded exclusively at sites anterior to the membranous VSD in both cases and at no other sites in the respective atrium or ventricle studied. There was first degree A-V block in both cases and in each the site within the specialized conduction system of this delay was proximal to the specialized fiber electrogram recording sites and thus probably proximal to the bifurcation of the bundle branches. In addition, on, the Ebstein-like deformity of the systemic A-V valve present in one case was confirmed by directly recording ventricular electrograms in an area of “atrialized-ventricle above the valve.

Management of Total Anomalous Pulmonary Venous Drainage in Early Infancy

Ten consecutive babies ranging in age from two weeks to five months, with total anomalous pulmonary venous drainage and pulmonary artery hypertension, have undergone surgical correction. Seven have survived, including five of six with supracardiac type and two of three with pulmonary venous drainage to the coronary sinus. Six of the last seven operations have been successful, and there have been no late deaths in the series. Factors considered to be important in successful management include: (1) early cardiac catheterization and surgical intervention; (2) high-flow buffered blood perfusion at normothermia; (3) surgical technique aimed at wider common pulmonary vein-left atrial anastomosis; (4) use of indwelling nasotracheal tube with respiratory support for the initial 24 to 48 hours postoperatively; (5) restricted fluid administration in the early postsurgical period; and (6) detailed attention to acid-base balance.

Electrophysiological Delineation of the Specialized A-V Conduction System in Patients with Congenital Heart Disease II. Delineation of the Distal His Bundle and the Right Bundle Branch

The course of the distal His bundle and the right bundle branch was electrophysiologically delineated during open heart surgery in nine patients with tetralogy of Fallot and in six other patients with various forms of congenital heart disease. In patients with tetralogy of Fallot, right bundle branch electrograms were usually recorded up to 25 mm from the plane of the tricuspid valve annulus and only rarely beyond this site, indicating that the electrical activity in the right bundle branch was isolated from right ventricular myocardium to a site 25 mm away from the tricuspid annulus in the patients studied. In one patient with right bundle branch block pattern on the electrocardiogram induced by a ventriculotomy, the right bundle branch was traced to the Purkinje fiber-ventricular muscle junction, supporting the observation that a right bundle branch block pattern induced by ventriculotomy does not indicate that injury to the proximal part of the right bundle branch occurred.In five patients with various forms of congenital heart disease we did not record electrical activity from the distal His and right bundle branch. The anatomic and functional reasons for this failure are discussed. In one patient with a common ventricle, the identification of the specialized atrioventricular (A-V) conduction system allowed for total surgical correction of this anomaly without injury to the conduction system. The electrophysiological delineation of the specialized atrioventricular conduction system is suggested for all patients undergoing open heart surgery who have complicated congenital heart disease on which no data are available regarding the exact location of the specialized atrioventricular conduction system, for patients with unusual ventricular anatomy, and for patients in whom the hemodynamic and angiographic studies do not correlate well with the electrocardiogram.

Atrial Standstill Secondary to Atrial Inexcitability (Atrial Quiescence): Recognition and Treatment following Open-Heart Surgery

Atrial standstill secondary to atrial inexcitability or atrial quiescence was diagnosed in 11 patients and atrial standstill, in which atrial excitability was still present though depressed, was diagnosed in two patients during the immediate period following open-heart surgery. Atrial quiescence was successfully treated in six patients and atrial standstill with depressed excitability in both patients by the infusion of small doses of isoproterenol. Atrial quiescence was not treated in the other five patients and reverted spontaneously within 24 hours after surgery. It is suggested that atrial quiescence results from relative depolarization of the atrial membrane and that the success of therapy with isoproterenol results from hyperpolarization of the atrial membrane by this drug.

New Method to Delineate Myocardial Damage at Surgery

A technique is described for obtaining unipolar and bipolar ventricular electrograms at surgery. The alterations in the form of the electrogram in various pathologic states are consistent, reliable, and reproducible. The method has advantages over dye technique for delineating areas of damaged myocardium and has been used in a clinical series of 12 patients undergoing cardiac surgery.

Total Correction of Tetralogy of Fallot in Adolescents and Adults

Sixty-four cyanotic patients over 15 years of age with tetralogy of Fallot have undergone total correction. Fifty-one patients had previous shunting procedures. The established intracardiac technique for total repair was used throughout. In 11% (7 of 64) of patients reconstruction of the pulmonary outflow tract was required. Follow-up extends from six months to ten years. Operative mortality was 6.25% (4 of 64). There was one late death. All deaths were technically related and none could be correlated with patient age. Bilaterally functioning Blalock shunts and Potts anastomoses contributed significantly to operative mortality. Abundant collateral circulation exists in older patients with tetralogy of Fallot, and increased bleeding in this series was reflected in a 20.3% (13 of 64) reoperation rate. Survivors represent 92.2% (59 of 64) of the group and all are completely asymptomatic. Approximately one-half of the surviving patients have undergone postoperative catheterization. Of those patients studied, 93.4% (29 of 31) have a good to excellent hemodynamic result following correction. All patients with outflow-tract patches subsequently developed pulmonary insufficiency and right-heart failure. These patients were easily managed on a cardiotonic regimen, however, and digitalis was discontinued in each case by the end of the third postoperative month. These mortality and survivor figures parallel those obtained in our total experience of 250 tetralogy repairs. We believe all patients with tetralogy of Fallot should undergo total correction. Advanced age is no contraindication to surgery. Shunting procedures, when indicated, are to be considered only a preliminary to full correction.

Systemic-Pulmonary Arterial Shunts in the First Year of Life

Results of systemic to pulmonary arterial shunts during the first year of life are reported in 86 infants under one year of age. Survival rates were highest in older patients and among infants whose basic cardiac defects were considered to be eventually amenable to surgical repair. Persistent hypoxia accounted for the majority of deaths. Congestive heart failure secondary to too large anastomoses occurred in 32.5% of Waterston shunts, but could be successfully managed medically in the majority of patients. Surgical revision of the shunt was accomplished successfully in two infants with subsequent alleviation of symptoms. Congestive heart failure occurred in only one of 26 patients after a Blalock shunt. Ten of the twelve patients in this series survived open-heart repair for cardiac lesions. It will eventually be necessary to compare these data with the results of single stage corrective surgery in the infant group.