Pathophysiologic correlations in two cases of split His bundle potentials

Review of His-Purkinje System Abnormality with Case Studies

A single beat arising as extra systole within the His-Purkinje system or from ventricle or even atrium based on conduction timing can invoke delayed conduction or block within intra-Hisian or infra-Hisian sites. This may be either manifested in the form of premature atrial or ventricular complexes or concealed as with His extra systoles. It appears commonly there is disease within the His-Purkinje system.

Intra-His bundle block corresponds with interruption of the branching portion of the His bundle

We compared His-bundle electrograms with pathological findings of the atrioventricular conduction system in four patients with complete atrioventricular intra-His block with narrow QRS complexes on ECG. Split His electrograms were recorded at the time of electrophysiological study. The patients died from noncardiac causes at 10 days, 1 year, 4 years, and 9 years, respectively, after the pacemaker implantation. Serial sections through the atrioventricular conduction system revealed strictly localized more than 50% reduction of conducting cells replaced by fibrosis at the branching portion of His bundle. The proximal portions of the bundle branches also exhibited decrease of the conducting cells showing a rough positive relation with the patient's age. Therefore, we considered that the H1 spikes seen on His-bundle electrograms originated from the penetrating portion of His, which was virtually intact in our cases, and that the H2 spikes originated from the right side of the distal branching portion of His.

Anatomy, histology, and pathology of the cardiac conduction system--Part V

Although morphologic findings in many of the cardiac arrhythmias of acute and chronic disease have been elusive, the correlates of heart block (particularly atrioventricular block) are abundant. Pathologic features of sinoatrial, atrioventricular, and bundle-branch block are reviewed. Lev and Lenegre diseases (idiopathic bilateral bundle-branch fibrosis) are also reviewed.

Prevalence and clinical correlates of non-Wenckebach, narrow-complex second-degree atrioventricular block detected by ambulatory ECG

Among 113 patients with transient, narrow-complex second-degree atrioventricular (AV) block detected by ambulatory ECG, there were 20 with non-Wenckebach behavior. Based on the presence or absence of PR interval shortening after single blocked complexes, patients with narrow-complex non-Wenckebach patterns could be separated into a pseudo-Mobitz II group of 16 patients (greater than or equal to 20 msec of PR shortening after the blocked complex) and a classic Mobitz II group of four patients (constant PR interval). These groups had additional distinct ECG and clinical features. Patients with the pseudo-Mobitz II pattern had a 44% prevalence of associated Wenckebach block during the same ambulatory recording, whereas Wenckebach behavior did not occur in patients with classic Mobitz II block. Pseudo-Mobitz II block occurred at significantly longer cycle lengths (876 vs 585 msec) and with significantly longer PR intervals (225 vs 165 msec) preceding the blocked complex than did classic Mobitz II block. Syncope was the presenting symptom in 38% of patients with pseudo-Mobitz II block and in all patients with classic Mobitz II block. Patients with pseudo-Mobitz II block had a 56% prevalence of associated coronary disease and a 44% prevalence of congestive heart failure; the mortality rate was 38% in this group over 4 years of follow-up, but in all instances death was due to associated disease rather than to conduction itself. In contrast, patients with classic Mobitz II block had hypertensive or valvular disease but no evidence of coronary disease or congestive failure; all are alive with pacemakers after 3 years of follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognosis in patients with intra-Hisian conduction disturbances

Intra-Hisian delay is usually associated with fascicular conduction abnormalities. We report our experience in 23 patients who had intra-Hisian delay as their only conduction defect. First-degree intra-Hisian delay (His bundle deflection greater than or equal to 30 msec) was present in 17 patients, 5 of whom also had split His potentials. Three of these patients received permanent pacemakers, all of whom had a history of syncope. Higher degrees of intra-Hisian delay were observed either spontaneously or in response to atrial pacing in 6 patients. Five of these patients were treated with permanent pacing, 4 of whom had symptomatic bradyarrhythmias and/or syncope. No patient has had a recurrence of symptoms following pacemaker insertion during the mean 31-month follow-up. No patient with first-degree intra-Hisian delay not receiving a pacemaker developed symptomatic bradyarrhythmias or syncope during a mean follow-up of 21 months.

An unusual mechanism of initiation of circus movement tachycardia in a patient with concealed Wolff-Parkinson-White syndrome

Infranodal conduction delay is an uncommon mechanism of initiation of circus movement tachycardia in the Wolff-Parkinson-White syndrome. A patient with a concealed left free wall atrioventricular accessory pathway who underwent electrophysiological study is presented. During atrial extrastimulus testing, a pattern of alternating bundle branch block was observed and was most marked after the administration of intravenous procainamide. Conversion from right bundle branch block to left bundle branch block was reproducibly associated with the initiation of circus movement tachycardia utilizing the normal conducting system antegradely and the accessory pathway retrogradely. Initiation of tachycardia was critically related to the increase in the HV interval associated with left bundle branch block. Of interest, conduction in the right bundle branch became progressively slower as the prematurity of the atrial extrastimulus increased, whereas conduction time through the left bundle branch remained fixed prior to block. Implications of these findings are discussed. To our knowledge, this is the first report of alternating bundle branch block during atrial extrastimulus testing as a mode of initiation of circus movement tachycardia in the Wolff-Parkinson-White syndrome.

Electrophysiologic and histologic correlations in chronic complete atrioventricular block

Electrophysiologic studies using the His bundle electrogram (HBE) and histologic studies of serial sections of the conduction system were correlated in two groups of deceased patients. Group 1 consisted of five patients with chronic complete atrioventricular block (CAVB) who had narrow QRS complexes and AH block (block proximal to the His bundle deflection). Group 2 consisted of four patients with chronic CAVB who had wide QRS complexes and HV block (block distal to the His bundle deflection). In group 1, the sites of the main lesion were not located in the approaches to the atrioventricular (AV) node or the AV node, but were found in the penetrating portion of the His bundle in one patient and in the branching portion of the His bundle in three patients. In the remaining patient, the main site of block could not be demonstrated histologically in the AV conduction system, but marked fibrosis of the approaches to the sinoatrial node and surrounding atrial muscle was found. In all patients of group 2, the site of the main lesion was located in the bilateral bundle branches, and thus was compatible with so-called trifascicular block. This correlation study between the His bundle electrogram and histologic findings of the AV conduction system showed that in some cases, CAVB presenting as AH block on the HBE can be associated with a lesion in the branching portion of the His bundle (distal His), and that CAVB presenting as HV block on the HBE is associated with a bilateral lesion of the bundle branches.

His bundle in electrocardiographic semantics of AV block. Anatomoclinical considerations

The AV conducting system was examined histologically in 13 selected human hearts (7 control and 6 AV block specimens), focusing attention upon normal His bundle (HB) structure, and upon the histopathologic basis of intrahisian block, with supraventricular QRS configuration. HB revealed a poor morphologic identity, often failing to represent the "undivided stem" of the AV pathway, either due to an early partition into separate longitudinal fascicles, or to varied types and sites of bifurcation, without any definite boundary between nonbranching and branching portions. Split His potentials, the distal component of which has been suggested as arising in the proximal bundle branch system, has been found in a case free of HB histologic abnormality. Supraventricular QRS configuration in escape rhythm was observed in two cases of AV block, not withstanding destruction of the entire His bifurcation, and in experimental bilateral bundle branch block. Pertinent explanations have been suggested. The overall semantic value and usefulness of the current HB nomenclature do not seem to imply, as yet, a precise and constant anatomoclinical correlation.

Disappearing His deflection. Electrophysiological evidence for conduction defect within the His bundle

A change in the voltage and character of the His bundle deflection following premature atrial stimuli was observed and analysed in 5 of 95 patients having intracardiac conduction studies because of AV conduction disturbances. Of these 5 patients, 3 had spontaneous block within the His bundle, 2 of them showing block in other segments of the conduction system. With increasing prematurity of programmed atrial stimuli, there was a progressive decrease in the voltage of the His deflection, followed by a split His deflection, and finally disappearance of the His deflection. The voltage of the His deflection was also reduced in sinus beats following spontaneous His bundle premature beats. Similarly, during atrial stimulation at increasing rates, the His deflection decreased in voltage, split, and finally disappeared, but when Wenckebach periods appeared the His deflection reappeared in the first paced beat after the dropped beat. The preceding H-H interval was the only electrophysiological variable consistently related to the changes in the His deflection. These changes in His deflection can be explained electrophysiologically as the result of a conduction disturbance within the His bundle. The clinical significance of the phenomenon is discussed. The occurrence of this phenomenon during a conduction study makes it difficult or even impossible to localise the AV block precisely.

Assessment of atrioventricular conduction in aortic valve disease

To determine the frequency of atrioventricular conduction disturbances in aortic valve disease, 26 consecutive patients (age 54 +/- 2 years) with symptomatic aortic valve disease were studied by His bundle electrocardiography at the time of cardiac catheterisation and were compared with a group of patients who underwent cardiac catheterisation and were found to have coronary artery or mitral valve disease but no aortic valve disease. Patients with aortic valve disease had significantly longer PR, AH, and HV intervals than cardiac patients not having this abnormality. Patients with aortic stenosis had prolonged HV, 52 +/- 6 vs +/- 42 +/- 2 ms (P = 0.06), whereas patients with chronic aortic regurgitation had prolonged PR, 245 +/- 27 vs 163 +/- 5 ms (P less than 0.001), and prolonged AH, 178 +/- 30 vs 102 +/- ms (P less than 0.001). Patients with combined lesions had significant prolongation of PR, AH, and HV intervals. Three patients with acute aortic regurgitation caused by endocarditis had normal atrioventricular conduction. Though the presence of valvular calcification did not significantly alter the pattern of atrioventricular conduction in these patients, those with calcified aortic valves had longer HV (P less than 0.005) than the control group. In addition, ventricular dysfunction or coronary artery disease did not affect the pattern of atrioventricular conduction in these patients. Thus, atrioventricular conduction disturbances are common in symptomatic aortic valve disease. With aortic stenosis the site of delay occurs more frequently below the His deflection, whereas in aortic regurgitation it is more frequent above the His deflection.

The surface electrocardiogram in complete intra-his heart block

In some cases, the surface ECG may be useful in predicting that the level of heart block is intra-His rather than supra-His. In five patients with third degree heart block the level of block was documented to be within the His bundle. In all five, the surface ECG showed an escape rhythm with QRS complexes of less than 0.10s. duration. The initial QRS forces were abnormal in that "septal" q waves were not present in leads 1 and V6. Two of the five patients had occasional conducted beats with normal "septal" q waves. Thus, heart block associated with an escape rhythm of narrow QRS morphology but abnormal septal depolarization may indicate that the level of the block is intra-His rather than supra-His.

Combined intra-Hisian block and A-V nodal bypass

A patient with first and second degree atrio-ventricular (A-V) block and left bundle branch block was shown on electrophysiological study to have an intra and infra-His bundle branch block. In addition, this patient also had an A-V nodal bypass tract. The intra-Hisian block was concealed on the resting His bundle electrogram and became evident only during atrial pacing. The A-V nodal bypass was masked on the surface electrocardiogram (ECG) by the associated A-V conduction defect. The clinical significance of A-V bypass and combined block below the A-V node is discussed. The diagnostic value of His bundle electrocardiography in a patient with complex electrophysiological abnormalities is stressed.

Intra-His bundle block in acute myocardial infarction. Report of two cases

Two patients with acute intra-His bundle block, both secondary to myocardial infarction, are described. The diagnosis of the block was proved by means of His bundle recordings during the phase of complete atrio-ventricular (A-V) block. Two His bundle potentials, one (H) following each A wave and the other (H') preceding each QRS complex, were detected. In both cases, as well as in the few cases reported in the literature, the site of the infarction was in the inferior wall, an occurrence which shows the functional importance of the posterior blood supply to the His bundle. In both cases the block developed into a chronic form, requiring the implantation of a transvenous pacemaker in one case. This evolution suggests that the post-infarction intra-His bundle block may be due to irreversible anatomic damage.

Chronic His bundle block. Clinical, electrocardiographic, electrophysiological, and follow-up studies on 16 patients

This report describes 16 patients with block within the His bundle seen over a period of 55 months. Ten were women and 6 men, with an average age of 76 years, range, 42 to 98 years. All patients had His bundle recordings showing split His bundle potentials (H and H) (13 patients) or narrow QRS with block distal to the His bundle potential (3 patients). Of the 16 patients, 10 had complete heart block, 4 second degree AV block (2 patients with Mobitz type II, and 2 with 2:1), and 2 first degree AV block. Ten patients had a narrow QRS in the conducted beats or escape rhythms. Intravenous atropine (1 to 2 mg) had a variable effect on AV conduction and the rate of the escape rhythm. Twelve patients have had a permanent pacemaker implanted. During the follow-up period, 10 patients died 1 to 31 months from the time of initial examination. The remaining 6 patients (5 with pacemaker) are alive 3 to 58 months later.

The clinical spectrum of chronic His bundle block

This report details our total experience with documented chronic His bundle block in 24 patients. Ten patients had second-degree block (eight with 2:1 block and two with type-1 block), and 14 patients had complete heart block. There were 16 women (67 percent) and eight men (33 percent) with ages ranging from 17 to 87 years. Diagnoses were as follows: hypertensive cardiovascular disease, nine patients (38 percent); arteriosclerotic heart disease, six patients (25 percent); aortic valvular disease, three patients (13 percent); primary conduction disease, two patients (8 percent); primary myocardial disease, two patients (8 percent); congenital heart block, one patient (4 percent); and traumatic heart block, one patient (4 percent). Pacing was instituted in 20 patients because of the following; congestive heart failure, seven patients; syncope, seven patients; fatigue, four patients; and recurrent dizziness, two patients. Permanent pacing was indicated within ten days of initial diagnosis in 13 patients, from 20 to 80 days in four patients, and later than 100 days in three patients. An additional two asymptomatic patients were treated with prophylactic pacing.

Pathologic correlations in three cases of bilateral bundle branch disease with unusual electrophysiologic manifestations in two cases

Examination of the conduction system in three patients with bifascicular block who had electrophysiologic studies forms the basis for this report. Patients 1 and 2 had left bundle branch block and Patient 3 right bundle branch block and left axis deviation. The H-V interval was prolonged in each case (70, 65 and 60 msec, respectively). Serial section examination of the conduction system revealed sclerodegenerative involvement of both bundle branches in all cases. In Case 1, atrial extrastimulus testing converted left to right bundle branch block; in Case 2, it delineated a sinus echo zone with repetitive sinus nodal reentrance. In the latter case serial section revealed extensive amyloid infiltration of the approaches to the sinoatrial (S-A) node and the atrial preferential pathways. In Case 3, with right bundle branch block and left axis deviation, serial section revealed greater involvement of the anterior part of the main left bundle branch than of the posterior portion as well as involvement of the second part of the right bundle branch. The study revealed excellent correlation between electrophysiologic and pathologic findings in three cases of intraventricular conduction disease and demonstrated an anatomic basis for the electrophysiologic findings resembling alternating bilateral bundle branch block. Sinus nodal reentrance may be related to disease in the approaches to the S-A node thereby causing delay in perinodal tissue allowing sinus reentrance. Finally in Case 3, the anatomic substrate for left axis deviation may lie in a greater involvement of the anterior portion than of the posterior portion of the main left bundle rather than in the corresponding portions of the periphery.

Pathologic correlations in a case of complete heart block with split His potentials resulting from a stab wound of the heart

A 23 year old previously healthy man was stabbed in the anterior chest. This resulted in a ventricular septal defect and complete atrioventricular (A-V) block. The electrocardiogram revealed complete A-V block with a QRS pattern of right bundle branch block. His bundle recordings 26 days later revealed A-V dissociation with split His potentials (P-H1 interval of 100 msec and H2-V interval of 40 msec). During the study the escape QRS shifted from right to left bundle branch block with H2 potentials still preceding each QRS interval with H2-V intervals of 40 msec. A permanent pacemaker was implanted because of persistent congestive heart failure and bradycardia due to A-V block. The patient subsequently became asymptomatic. He died suddenly 3 1/2 years later. Pathologically there were sizable openings in both the tricuspid and mitral valve substance and a ventricular septal defect involving the pars membranacea and part of the adjacent muscular septum. Serial sections of the conduction system revealed total destruction and fibrous replacement of the bifurcation and beginning of the right and left bundle branches and subtotal fibrous replacement of the branching bundle. Thus, the bifurcation of the bundle of His was totally absent at autopsy despite apparent electrophysiologic evidence of its existence 26 days after the stab wound. A possible explanation for this discrepancy is the subsequent fibrosis of the bifurcation produced by hemodynamic changes at the lower margin of the ventricular septal defect.

Congenital and surgical atrioventricular block within the His bundle

In three patients with congenital heart disease the site of atrioventricular (A-V) block was localized within the His bundle with the aid of His bundle electrograms. In one patient with first degree A-V block and normal QRS configuration, electrophysiologic studies revealed "split" His potentials. The other two patients had complete A-V block, and their His bundle electrograms revealed His spikes both proximal and distal to the site of block. One of the two patients, who had a pattern of left bundle branch block in the electrocardiogram, had surgically induced complete A-V block after repair of an ostium primum atrial septal defect. The other patient with congenital A-V block had a narrow QRS complex and, in addition to complete block within the His bundle, prolonged A-V nodal conduction time but no associated cardiac anomaly. Both patients with complete heart block required pacemaker insertion. The natural history of intra-H-is bundle block is not known, and it is difficult to recommend appropriate therapy. More electrophysiologic studies are needed in patients with A-V block to determine the prognostic significance of such block or conduction delay in the His bundle.