Analysis of surgically-induced right bundle branch block pattern using intracardiac recording techniques

Frequency and significance of conduction defects early after orthotopic heart transplantation

To define the clinical significance of conduction defects after orthotopic heart transplantation sequential electrocardiograms (ECG) of 124 patients were analyzed during their postoperative hospital stay. The first ECG was abnormal in 90 patients (73%), with a predominance of right bundle branch block, and normal in 34 (27%). Sex, age, mean donor ischemic time, duration of aortic cross clamping and use of previous antiarrhythmic therapy were not significantly different in the 2 groups. During hospital follow-up, patients were grouped according to evolution of the initial electrocardiographic abnormalities. In group 1, 25 patients continued to have an initially normal ECG. In groups 2 and 3, 30 and 48 patients, respectively, had evidence of transient and permanent conduction defects. The 21 patients in group 4 showed progressive deterioration of conduction with either a new (9 patients) or worsening preexisting conduction defect (12 patients). The evolution of the initial ECG was strongly dependent on the duration of the donor heart ischemic time and the severity of the in-hospital cardiac rejection. Patients with persistent conduction abnormalities had a statistically longer ischemic time than either patients with normal or transient conduction defects (182 +/- 84 vs 144 +/- 68 and 130 +/- 66 minutes, p = 0.04). Although the overall percentage of patients with histologic evidence of moderate to severe rejection was similar across the groups, 66.6 and 46.1% of patients in groups 3 and 4, respectively, had multiple episodes of rejection compared with 16.6 and 0% in the remaining 2 groups (p = 0.044).(ABSTRACT TRUNCATED AT 250 WORDS)

Radionuclide evaluation of right ventricular wall motion after surgery in tetralogy of Fallot

Regional wall motion patterns in tetralogy of Fallot and its postoperative modifications by electrical and hemodynamic factors were assessed by Fourier analysis of gated radionuclide angiograms in 24 studies performed in children after surgical correction of tetralogy of Fallot. The range of right ventricular (RV) phase angles (standard deviation of the peak [SDP] of RV) as well as the difference between RV and LV (delta MPh) were used as indices of the synchronicity of wall motion and were correlated with RV apical electrical activation time determined by endocardial electrical mapping. Postoperative studies were divided into two groups according to apical activation: (a) those involving right bundle branch block (RBBB) (nine patients), and (b) those involving distal RBBB (15 patients). delta MPh was longer in proximal than in distal RBBB. Best discrimination between the two groups was obtained with SDP of RV (proximal = 24 degrees +/- 3 degrees, and distal = 17 degrees +/- 2 degrees; p less than 0.0001). These results showed that the range of ventricular phases measured by the SD of the phase distribution of the right ventricle is a good index for distinguishing between proximal and distal RBBB after cardiac surgery.

Frequency of ventricular late potentials and fractionated right ventricular electrograms after operative repair of tetralogy of Fallot

This study was conducted to assess the incidence of abnormalities of ventricular depolarization in sinus rhythm after repair of tetralogy of Fallot and their relation to spontaneous ventricular arrhythmias. Forty-four patients were studied, 10 before surgery (mean age 6.9 years) and 34 after repair (mean age 8.1 years, mean age at surgery 6.5 years, mean interval between surgery and evaluation 11 months). Evaluation was performed by means of body surface and intracavitary signal-averaging techniques, by recording local right ventricular (RV) electrograms at several sites and by 24-hour Holter monitoring (n = 28). No electrophysiologic abnormality was observed in children before surgery. Ventricular late potentials were detected in 18 patients (53%) after repair. Body surface detection of ventricular late potentials was frequently masked by the postoperative right bundle branch block pattern. Local RV electrograms were fractionated in 11 cases (32%) (mean duration 103 +/- 33 ms), most often in the RV outflow tract (n = 9), but no relation was found between fragmentation of RV electrograms and the presence of ventricular late potentials. Spontaneous ventricular arrhythmias occurred in 12 children after repair (43%), but were complex in only 4 patients (14%). There was no correlation between spontaneous ventricular arrhythmias and the presence of ventricular late potentials, presence of fractionated RV electrograms, presence of a proximal right bundle branch block or postoperative hemodynamic status.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic cardiac function before and after surgery in children with atrioventricular canal

Thirty-two children with atrioventricular (AV) canal underwent electrophysiologic studies: 18 underwent preoperative studies at a median age of 3 years (range 6 months to 16 years); 14 underwent postoperative studies at a median age of 4 years (range 2 to 19); and 2 underwent both preoperative and postoperative matched studies. In the preoperative group the following abnormalities were observed: first-degree AV block in 5 patients (due to internodal conduction delay in 1, AV nodal conduction delay in 2 and normal intracardiac intervals in 2); internodal conduction delay but normal PR interval in 4; and disease of the sinus node in only 1. In the postoperative group the following abnormalities were observed: first-degree AV block in 9 (due to AV nodal conduction delay in 2, His-Purkinje system conduction delay in 1, upper normal intracardiac intervals in 3 and unidentified in 3); prolongation of the right ventricular apical activation time in 11 of 13 with right bundle branch block; abnormal sinus node function in 3; and abnormal AV nodal function in 4 (1 of whom had associated sinus node disease). Atrial and ventricular functions were normal in all preoperative and postoperative patients. Electrophysiologic dysfunction is rare in preoperative patients with AV canal; in postoperative patients electrophysiologic abnormalities occur in 38% and involve the sinus and AV nodes in 19 and 25%, respectively.

Local abnormalities of right ventricular depolarization after repair of tetralogy of Fallot: a basis for ventricular arrhythmia

Ventricular arrhythmia is common after repair of tetralogy of Fallot (TF) and may cause sudden death. To explore the mechanisms, ambulatory electrocardiographic monitoring and electrophysiologic studies were undertaken, without the use of provocative tests, in 22 patients 5 to 24 years (mean 13) after repair. His-Purkinje and right ventricular (RV) apical activation times were measured to assess conduction. Endocardial mapping of the right ventricle was performed, with additional recordings from the left ventricle in 10 patients, to detect abnormalities of local depolarization and repolarization. Local RV electrograms were fractionated or delayed in 12 patients (55%) at 1 or more RV sites (septum in 7 patients, outflow in 7, free wall in 2 and apex 1 patient), reflecting disordered depolarization, but left ventricular recordings were normal in all. Ventricular arrhythmia out of hospital was more common (p less than 0.05) and more severe (p less than 0.01) in the patients with depolarization abnormalities than in those with normal electrographic findings. In contrast, there was no association between ventricular arrhythmia and conduction disturbances. Abnormalities of RV repolarization, consisting of low-frequency signals after the T wave, were observed in 17 patients (77%), but were not associated with arrhythmia. Thus, ventricular arrhythmia during daily life was associated with fractionated depolarization at multiple sites in the right ventricle. This suggests that there are widespread areas of RV myocardial damage that provide substrates for ventricular tachycardia.

Intraventricular conduction disturbances after correction of tetralogy of Fallot: can bifascicular and trifascicular block be diagnosed from the surface ECG?

To determine the origin of conduction disturbances commonly seen in the ECG after correction of Fallot's tetralogy, 36 children underwent electrophysiologic studies; these included endocardial recordings of right ventricular (RV) and left ventricular (LV) apical activation and His-bundle recordings. The surface ECG showed a pattern of complete right bundle branch block (RBBB) in 22, and RBBB with left-axis deviation (LAD)--so-called bifascicular block--in nine; the remaining five had RBBB, LAD, and a long PR interval, often considered as indicating trifascicular block. Eight of 22 patients with RBBB and normal axis had delayed RV apical activation (36%), indicating a proximal lesion. Of nine patients with RBBB and LAD, four only had delayed RV apical activation (44%); in the other five, therefore, the RBBB pattern was due to a peripheral lesion (ventriculotomy); they cannot be considered as having true bifascicular block. LV activation was not delayed in any case. In five cases, the surface ECG suggested trifascicular block (long PR in the presence of RBBB and LAD). His-bundle recordings showed the HV interval to be prolonged in only two cases, at the upper limit of normal in two, and short in one. The AH interval was prolonged in all and was mainly responsible for the long PR interval. Thus, the surface ECG is not a reliable tool for making a diagnosis of true bifascicular block and trifascicular damage after correction of Fallot's tetralogy. This may explain controversies existing about the prognosis of such conduction abnormalities.

The spectrum of right bundle branch block as manifested in electrocardiographic body surface potential maps

A wide spectrum of types of right bundle branch block (RBBB) were studied utilizing the body surface potential maps (BSPMs) of 37 children. Although the spectrum varied from very advanced RBBB to minimal partial RBBB, a common diagnostic feature was the absence of evidence for right ventricular breakthrough in the maps of all patients. Evidence for left ventricular breakthrough was usually seen, the exceptions being five patients with partial RBBB and one of 29 with advanced RBBB. The appearance of evidence for activation of the right ventricle by way of the septum was late in onset. In addition, especially in advanced RBBB, the BSPM pattern reflecting right ventricular activation was prolonged in such a manner that it appeared that utilization of right ventricular Purkinje tissue was minimal and inefficient. The BSPMs during ST-T, which were of inverse polarity, reflect repolarization that is determined by the sequence of depolarization to a greater degree than in the normal. In general, the more extensive the surgery, the more advanced the RBBB (as reflected in the BSPM), although there were exceptions. The one parameter that linked all patients with RBBB together was the absence of evidence for right ventricular epicardial breakthrough.

Site of conduction delay in children with catheter-induced right bundle branch block

Eight cases of catheter-induced right bundle branch block (RBBB) in children during electrophysiologic studies are presented. Recording of right ventricular apical activation time (V-RVA) before and during the conduction delay allowed localization of the block along the course of the right bundle branch system. In the majority of patients, a significant lengthening of V-RVA was observed, indicating that proximal right bundle branch block is the most commonly induced type of conduction delay. Block was transient in all patients and terminated several minutes to 24 hours after its induction.

Electrophysiologic residua and sequelae of surgery for congenital heart defects

Postoperative arrhythmias may occur in any patient who undergoes intracardiac surgery for a congenital heart defect. The correction of certain intracardiac heart defects predisposes to a large incidence of cardiac arrhythmias. Ventricular arrhythmias and conduction disturbances are seen after correction of tetralogy of Fallot, ventricular septal defect and atrioventricular canal defect. Supraventricular arrhythmias and sinus nodal dysfunction may be seen after surgery for transposition of the great arteries or atrial septal defect. The identification, evaluation and treatment of these patients are discussed.

Cardiac pacing in children

Twenty patients aged between 12 months and 13 years underwent permanent pacemaker implantation. The main indication for pacing was post-surgical atrioventricular block. The complication rate was high and related mainly to infections and lead system problems. The use of small multiprogrammable pacemakers is expected to reduce the reoperation rate for system malfunction and elective replacement. Newer methods of electrode insertion and active fixation devices in smaller diameter leads make endocardial pacing a practical alternative to epicardial pacing in the larger child who did not require a pacing system at the time of surgery.

Arrival of excitation at the left ventricular apical endocardium in Wolff-Parkinson-White syndrome type B

Electrograms were recorded from the His bundle area, right ventricular apex, right ventricular inflow tract, and left ventricular apical endocardium in four patients (aged, 1, 1, 1.5, and 16 years) with Wolff-Parkinson-White syndrome type B. In beats without preexcitation: (a) delayed activation of the right ventricular inflow tract reflected the occurrence of a conduction disturbance through the "distal" or "peripheral" ramifications of the right bundle branch; and (b) the slightly earlier activation of the left ventricular apical endocardium (in reference to the right ventricular apex) may have been due to an earlier emergence from the divisions of the left bundle branch, presumably due to the greater length of the right bundle branch. In beats with preexcitation: (a) the "incomplete" right bundle branch block pattern was concealed because the right ventricular inflow tract was activated before the right ventricular apex; (b) the delta-right ventricular apical intervals were shorter than those of adults with Wolff-Parkinson-White type B; and (c) arrival of excitation at the left ventricular endocardium was a function, either of the impulse emerging from the left bundle branch, or of that propagating from the preexcited site. Therefore, the delta-left ventricular apical endocardial intervals were considered to have represented conduction time from preexcited region to endocardium of left ventricle only when it could be proven that the conduction time (from atrial site of origin to left ventricular apical endocardium) was shorter through the right sided accessory pathway than through the normal pathway. This study suggests that some beats, which may be interpreted as representing "pure" Wolff-Parkinson-White type B complexes from epicardial maps, may in reality be "fusion" complexes.

Right ventricular apical activation time in children. Reference standards for clinical use

To differentiate proximal from peripheral right bundle-branch block, several investigators have used the right ventricular apical (RVA) activation time, but there is a lack of reference standards for infants and other children. Using intracardiac electrography, His bundle and RVA electrograms were recorded in 123 children before surgery for various types of congenital cardiac malformations. None had evidence of conduction defects on their surface ECG. The average RVA activation time was 15 +/- 7 msec (+/- SD) linearly increasing with age from infancy to adolescence. The values found in this large population may be useful as reference standards for right bundle-branch conduction times in other infants and children.

Long-term evaluation (12 to 22 years) of open heart surgery for tetralogy of Fallot

Four hundred seventy-five patients underwent repair of tetralogy of Fallot from 1955 to 1964; 396 of these were hospital survivors and were followed up for 12 to 22 years. An excellent late clinical result was maintained by 87 percent of the 396 hospital survivors. A less than excellent result in the remaining 13 percent of hospital survivors was caused by late mortality in 7 percent (sudden death in 3 percent, death due to cardiac causes in 2 percnt and death due to noncardiac causes in 2 percent), required reoperation in 4 percent (mainly because of residual ventricular septal defect) and development of symptoms in 2 percent. Postoperative cardiomegaly (cardiothoracic ratio greater than 0.55) was observed in 60 (25 percent) of 246 patients who had a follow-up chest roentgenogram, and was more common among those who died late or remained symptomatic. Among the few patients with inadequate surgical relief of right ventricular hypertension who did not have transanular patch repair, the hypertension did not tend to decrease progressively, whereas it did decrease in patients who had patch repair. No late sudden deaths were encountered in 20 patients shown to have postoperative right bundle branch block plus left axis deviation (bifascicular block pattern). Pulmonary valve incompetence appeared to have relatively little harmful influence on the late result, causng cardiac disability in 1 percent of the patients and appeared to be the main contributing factor of postoperative cardiomegaly in 13 (5 percent) of the 246 patients who had a follow-up chest roentgenogram. Most late deaths and complicatins appeared within 2 years of operation, and accelerating deterioration in late results did not occur as the follow-up extended beyond 2 decades.

Right ventricular apical activation times in patients with conduction disturbances occurring during acute transmural myocardial infarction

His bundle and right ventricular apical electrograms were recorded in 18 patients with acute transmural myocardial infarction in whom catheter insertion was considered necessary for clinical reasons. The V-RVA and H-V intervals were of normal duration (5 to 30 and 35 to 55 msec, respectively) in five patients (Group 1) with persistently narrow (less than 100 msec) QRS complexes. In contrast, 13 patients (Group 2) who manifested a "complete" right bundle branch block pattern within 96 hours after admission had prolonged V-RVA intervals (range 50 to 80 msec, mean 59.2 msec) and H-V intervals that were at the upper limits of normal or prolonged (range 55 to 90 msec, mean 63 msec). In 6 of these 13 patients, the duration of the V-RVA interval became normal when the "complete" right bundle branch block pattern disappeared and was replaced by a "complete" left bundle branch block pattern in three patients and by narrow QRS complexes in the three other patients. This study showed that transmural myocardial infarction in itself did not increase the duration of the V-RVA interval even when "complete" left bundle branch block was present. Moreover, a prolonged V-RVA interval coexsting with a "complete" right bundle branch block pattern was not due to distal right bundle branch block but resulted from a conduction disturbance located in the proximal portions of the right bundle, or perhaps, even within the His bundle itself.

His bundle electrogram after intracardiac repair of tetralogy of Fallot. Analysis of data in 59 patients

His bundle electrograms were recorded in 59 patients after intracardiac repair of tetralogy of Fallot and were correlated with the postoperative electrocardiogram. Except for five patients with first degree atrioventricular block postoperatively all patients in Group A (those with either a normal electrocardiogram or solitary right bundle branch block) had a normal A-H interval (77.7 +/- 21.6 msec) (mean +/- standard deviation); all had a normal H-V interval (39.5 +/- 7.2 msec). Patients in Group B (bifascicular block) tended to have a normal A-H interval (97.2 +/- 26.2 msec) with a prolonged H-V interval (48.8 +/- 10.7 msec). Patients in Group C (trifascicular block) had prolongation of both the A-H (160.0 +/- 32.4 msec) and the H-V interval (58.8 +/- 10.6 msec) by comparison with control values. Patients in Group D (transient complete heart block) had a normal A-H interval (79.5 +/- 28.2 msec) but a prolonged H-V interval (57.8 +/- 16.4 msec), similar to that in Group C. A good hemodynamic result was associated with a normal H-V interval; a prolonged interval accompanied a poor result.