Intraventricular trifascicular blocks. Review of the literature and classification

Argentina's most important contributions in the field of electrophysiology

Latin American electrocardiology emerged internationally thanks to the Argentine School of Electrocardiology. All started when the idea of a different anatomy of the conduction system was not only necessary to change the paradigm of a bifascicular system, but also to question diagnostic electrocardiographic criteria adopted by the scientific community without dispute. Almost every scientific contribution coming from the Argentine School of Electrocardiology represented a significant step forward in the understanding of the electrophysiology of the heart and its electrocardiographic counterpart. There is another reason that increases their value: the noticeable simplicity of the technical facilities with which these studies were done from the modest laboratory in Argentina, whose production was purely and genuinely Latin American. In the following lines we summarize what we consider to be the greatest contributions of the Argentine school to world electrophysiology.

Fascicular heart blocks and risk of adverse cardiovascular outcomes: Results from a large primary care population

BACKGROUND

Fascicular heart blocks can progress to complete heart blocks, but this risk has not been evaluated in a large general population.

OBJECTIVE

The purpose of this study was to investigate the association between various types of fascicular blocks diagnosed by electrocardiographic (ECG) readings and the risk of incident higher degree atrioventricular block (AVB), syncope, pacemaker implantation, and death.

METHODS

We studied primary care patients referred for ECG recording between 2001 and 2015. Cox regression models were used to estimate hazard ratios (HRs) as well as absolute risks of cardiovascular outcomes.

RESULTS

Of 358,958 primary care patients (median age 54 years; 55% women), 13,636 (3.8%) had any type of fascicular block. Patients were followed up to 15.9 years. We found increasing HRs of incident syncope, pacemaker implantation, and third-degree AVB with increasing complexity of fascicular block. Compared with no block, isolated left anterior fascicular block (LAFB) was associated with 0%-2% increased 10-year risk of developing third-degree AVB (HR 1.6; 95% confidence interval [CI] 1.25-2.05), whereas right bundle branch block combined with LAFB and first-degree AVB was associated with up to 23% increased 10-year risk (HR 11.0; 95% CI 7.7-15.7), depending on age and sex group. Except for left posterior fascicular block (HR 2.09; 95% CI 1.87-2.32), we did not find any relevant associations between fascicular block and death.

CONCLUSION

We found that higher degrees of fascicular blocks were associated with increasing risk of syncope, pacemaker implantation, and complete heart block, but the association with death was negligible.

Human ventricular activation sequence and the simulation of the electrocardiographic QRS complex and its variability in healthy and intraventricular block conditions

Aims

To investigate how variability in activation sequence and passive conduction properties translates into clinical variability in QRS biomarkers, and gain novel physiological knowledge on the information contained in the human QRS complex.

Methods and results

Multiscale bidomain simulations using a detailed heart-torso human anatomical model are performed to investigate the impact of activation sequence characteristics on clinical QRS biomarkers. Activation sequences are built and validated against experimentally-derived ex vivo and in vivo human activation data. R-peak amplitude exhibits the largest variability in terms of QRS morphology, due to its simultaneous modulation by activation sequence speed, myocardial intracellular and extracellular conductivities, and propagation through the human torso. QRS width, however, is regulated by endocardial activation speed and intracellular myocardial conductivities, whereas QR intervals are only affected by the endocardial activation profile. Variability in the apico-basal location of activation sites on the anterior and posterior left ventricular wall is associated with S-wave progression in limb and precordial leads, respectively, and occasional notched QRS complexes in precordial derivations. Variability in the number of early activation sites successfully reproduces pathological abnormalities of the human conduction system in the QRS complex.

Conclusion

Variability in activation sequence and passive conduction properties captures and explains a large part of the clinical variability observed in the human QRS complex. Our physiological insights allow for a deeper interpretation of human QRS biomarkers in terms of QRS morphology and location of early endocardial activation sites. This might be used to attain a better patient-specific knowledge of activation sequence from routine body-surface electrocardiograms.

A new terminology for describing left and right ventricular conduction abnormalities

The words we use to describe a medical condition should match our knowledge of it. Unfortunately, at times, the words we used long ago persist after new knowledge of the subject has become apparent; so it is with left and right ventricular conduction system abnormalities. The words left or right bundle-branch block no longer reflect our knowledge of the condition. Accordingly, this essay describes a new terminology that more accurately describes the numerous abnormalities that compose left and right ventricular conduction system block as well as their numerous subsets. A brief account of the cardiac conditions associated with the conduction defects is also presented.

Atypical atrioventricular Wenckebach periodicity caused by conduction through triple atrioventricular junctional pathway as a probable mechanism

Electrocardiograms were taken from an 84-year-old man with right bundle branch block in whom atypical atrioventricular Wenckebach periodicity was frequently occurred. The electrocardiographic findings as mentioned below suggested that the atypical periodicity was caused by conduction through triple atrioventricular junctional pathways as a probable mechanism. When a P wave was blocked after a markedly prolonged PR interval of 0.64 s, the RP interval containing this blocked P wave ranged between 0.84 s and 0.86 s, and the next P wave was followed by a QRS complex of the same configuration, with the PR interval of 0.35 s. On the other hand, when a P wave was blocked after a PR interval of 0.49 s or 0.52 s, the RP interval containing this blocked P wave was comparatively long, ie, 0.95 s or 0.98 s, and the next P wave was followed by a QRS complex of somewhat different configuration showing borderline left axis deviation, with a shorter PR interval of 0.21 s or 0.23 s. These findings suggest that longitudinal dissociation occurred not only in the atrioventricular junction but also in the His bundle. This is the first report suggesting triple atrioventricular junctional pathways probably associated with longitudinal dissociation in the His bundle.

Analysis of the hypoplastic right ventricle utilizing electrocardiographic body surface potential mapping (BSPM)

The authors present electrocardiographic body surface potential maps (BSPMs) of 11 patients with hypoplastic right ventricle (HRV) of three types: type I, HRV with pulmonary atresia; type II, HRV with tricuspid atresia; and type III, HRV with tricuspid artesia and transposition of the great arteries. The BSPMs of all 11 patients demonstrated evidence for epicardial right ventricular breakthrough, indicating conduction through an intact right bundle branch and Purkinje system. Nonetheless, the BSPMs strongly suggested profound morphological, probably embryological, differences among the right ventricles of the three groups. The four patients with type I HRV had no evidence for conduction abnormality. The five patients with type II, HRV however, had very marked conduction abnormality. In four of these five, the standard ECG and VCG had initial forces suggesting left lateral wall myocardial infarction. The BSPMs showed no evidence for infarction but demonstrated very complicated slow initial activation, explaining why the initial QRS vector was to the right and posterior before extending leftward. In addition, in all five the initial positive potentials were unusually inferior and the initial negative potentials unusually superior. After the evidence for epicardial right ventricular breakthrough, the positive and negative potentials rapidly changed positions so that the positive potentials were unusually superior and the negative potentials unusually inferior, consistent with the BSPM of endocardial cushion defects. In four of these five there was marked delay of total ventricular activation time. Of the two patients with type III HRV, one had an initial QRS similar to that of type II. Neither had rapid change of inferior and superior positive and negative potentials after right ventricular breakthrough, and both had intraventricular slowing, one with partial left bundle branch block.

Complete right bundle branch block (CRBBB) with three different mean frontal plane QRS axes--a case report

A routine ECG of a seventy-year-old man, who had been followed for five years because of complete right bundle branch block (CRBBB) with first-degree atrioventricular (AV) block, showed CRBBB and three different mean frontal plane QRS axes suggesting normal conduction, bradycardia-dependent left anterior hemiblock, and tachycardia-dependent left posterior hemiblock--all within the same tracing. Holter recording demonstrated transient advanced AV block, and a permanent pacemaker was implanted.

Criteria for intraventricular conduction disturbances and pre-excitation. World Health Organizational/International Society and Federation for Cardiology Task Force Ad Hoc

In an effort to standardize terminology and criteria for clinical electrocardiography, and as a follow-up of its work on definitions of terms related to cardiac rhythm, an Ad Hoc Working Group established by the World Health Organization and the International Society and Federation of Cardiology reviewed criteria for the diagnosis of conduction disturbances and pre-excitation. Recommendations resulting from these discussions are summarized for the diagnosis of complete and incomplete right and left bundle branch block, left anterior and left posterior fascicular block, nonspecific intraventricular block, Wolff-Parkinson-White syndrome and related pre-excitation patterns. Criteria for intraatrial conduction disturbances are also briefly reviewed. The criteria are described in clinical terms. A concise description of the criteria using formal Boolean logic is given in the Appendix. For the incorporation into computer electrocardiographic analysis programs, the limits of some interval measurements may need to be adjusted.

Bradyarrhythmias: clinical significance and management

Clinicians have long recognized the potentially serious manifestations of extreme bradycardia. However, even marked bradycardia can often be physiologic, and in the presence of impaired ventricular function may offer important compensatory hemodynamic effects. Disorders of the sinoatrial node producing bradycardia include failure of impulse formation, sinoatrial conduction block, concealed sinus-perinodal reentry, carotid sinus hypersensitivity and the constellation of brady- and tachyarrhythmias that compose the "sick sinus syndrome." Bradycardia can also result from intraatrial block, atrioventricular nodal block or infranodal block. In addition, paroxysmal supraventricular tachyarrhythmias may produce concealment into the atrioventricular junction and simultaneous suppression of sinus node rhythmicity, resulting in long pauses. Pseudobradycardias manifesting as slow peripheral pulse rates can result from frequent, nonconducted early atrial premature beats, from ventricular bigeminy or runs of ventricular extrasystoles or from mechanical alternans. Cardiac pacemakers play an important role in the management of patients with severe symptoms attributable to bradyarrhythmias. However, excessive use of pacemakers and the inappropriate selection of physiologically unfavorable pacemaker systems should be avoided. Frequently, patients who are only mildly symptomatic with bradycardia should not receive a cardiac pacemaker because the prognosis is favorable. Patients with the tachy-bradycardia syndrome often require both pharmacologic and pacemaker therapy. In selected patients electrophysiologic testing may be helpful, but the majority of patients are best managed by careful attention to the history, electrocardiogram and ambulatory electrocardiographic recordings.

Transient tachycardia- and bradycardia-dependent left anterior and left posterior hemiblocks. Effects of isoproterenol

Tachycardia- and bradycardia-dependent, left anterior and left posterior hemiblocks as transient phenomena were registered in two patients spontaneously, and especially as a consequence of isoproterenol infusion. A chronic trifascicular type of A-V block was present in the first case, whereas in the second case a bradycardia-dependent left posterior hemiblock was registered during an acute myocardial infarction. In the first patient the isoproterenol effects were: (1) a shortening of the refractoriness and an increase of the conduction velocity in the injured fascicle, (2) an increase in the slope of phase-4 depolarization on the left posterior fascicle, and (3) a presumably shifting toward zero of threshold potential on the left anterior fascicle. Isoproterenol effects disappeared from 30 to 40 min after it was discontinued. In the second case the bradycardia-dependent left posterior hemiblock was registered during very fast heart rates (150 beats min). This finding supports the view that enhanced phase-4 depolarization is the main factor in the development of bradycardia-dependent intraventricular blocks in the course of acute myocardial ischemia.

Effects of left anterior fascicular block on the depolarization process as depicted by total body surface mapping

To examine the effects of left anterio fascicular block (LAFB) on the depolarization process as manifested on the body surface, 142 lead maps were recorded in 25 subjects with LAFB. Three abnormalities were detected: (1) In the early and mid portion of QRS, twenty of 25 subjects showed abnormal anterior superior positivity, starting in the precordial area and proceeding toward the left subclavicular area. The explanation was thought to be the relatively delayed, dysynchronous, and superiorly directed altered sequence of depolarization of the anterior left ventricle. (2) All the subjects showed left lower abnormal negativity. This was thought to represent the unopposed receding activation front after the left ventricular breakthrough posteroinferiorly and also the negative aspect of the abnormally directed superior positivity. (3) Eleven subjects showed abnormal negative potentials at the right lower chest. This was thought to represent the partially unopposed activation fronts of the right ventricular free wall seen after right ventricular epicardial breakthrough, because of the absence of the usually cancelling normal forces from the anterior portion of the left ventricle. Additionally, the surface manifestation of the septal depolarization was found to be indistinguishable from nornal. This study further enhances our understanding of the altered sequence of depolarization in LAFB, as manifested on the body surface instant-by-instant.

Left axis deviation: a reassessment

This report deals with the ramifications of the concept of left axis deviation. In early life, the leftward shift of the frontal plane QRS axis is determined chiefly, if not solely, by the relative weights of the ventricles. Once adult ventricular weight ratios are reached, there is a long period of axis stability, then a gradual leftward drift of the QRS, governed principally by left anterior fascicular conduction. Thus, the normal QRS axis is age-dependent, and left axis deviation must be considered accordingly.

Pure anterior conduction delay: a variant "fascicular" defect

Based upon electrocardiographic studies of conduction disturbances, the human intraventricular conduction system has been considered trifascicular: a right bundle and a bidivisional left bundle. Right bundle branch block, left anterior hemiblock, and left posterior hemiblock have been described. Microscopic and endocardial mapping studies, however, do not demonstrate a corresponding anatomical basis of this useful functional concept. Atrial premature beats in our two cases resulted in ventricular aberrancy which strongly suggests an additional form of a functional conduction delay. Such delay is manifest as a narrow QRS with anterior displacement in the horizontal plane but no axis shift in the frontal plane. This aberrancy is important to recognize because it can mimic the ECG findings of true posterior myocardial infraction. We do not postulate, however, a specific fascicle of the left bundle as the anatomic substrate for this recently recognized effect.

A prospective study of sudden death in "high-risk" bundle-branch block

We prospectively followed 257 patients with bifascicular and trifascicular conduction-system disease and intact atrioventricular conduction who had undergone His-bundle studies. Forty-seven per cent had associated coronary-artery disease, and 23 per cent primary conduction-system disease. His-ventricular interval was moderately prolonged in 43 per cent and markedly prolonged in 12 per cent. During an average follow-up period of 25 months 50 patients died. However, death was sudden in only 27, and 17 of the sudden deaths were not due to bradyarrhythias. Actuarial analysis showed an overall mortality rate (mean +/- S.E.) of 19 +/- 2.6 per cent at two years, mortality from sudden death being 10 +/- 2.6 per cent. Permanent heart block occurred in 12. No clinical symptoms (including syncope), electrocardiographic findings, electrophysiologic data or their combination identified patients at high risk of sudden death. Sudden death due to bradyarrhythmia is uncommon in patients with bundle-branch block and intact atrioventricular conduction. Therefore, routine prophylactic use of permanent pacemakers in all such patients is inappropriate. Pacemaker implantation should be reserved for those with documented symptomatic bradyarrhythmias.

Fascicular block within the His bundle

The findings in a patient with complete atrioventricular block and normal morphology and duration of the QRS complex are presented. A His bundle electrogram was obtained, which led to the location of the atrioventricular block within the His bundle. A careful review of the electrocardiograms obtained during the seven years preceding the onset of complete atrioventricular block showed a QRS complex with the features of left anterior hemiblock and a progressive impairment of atrioventricular conduction. From these data, we inferred that the different degrees of atrioventricular block and the left anterior hemiblock were caused by lesions within the His bundle involving the fibers destined for the left anterior division of the left branch. After the onset of complete atrioventricular block, with the subsidiary pacemaker located in the His bundle distal to the lesions, the QRS complex became normal, indicating the integrity of the bundle branches and fasciculi. The atrial and proximal His potential intervals and those between distal His and ventricular potentials were normal.

A study on electrocardiographic changes during long-term cardiac pacing

This report describes the clinical evaluation of chest wall stimulation (CWS) follow-up studies in patients implanted with pacemakers and the value of this method for the observation of intrinsic rhythm. The CWS method was used to periodically check the intrinsic rhythm in 25 long-term pacemaker cases with atrioventricular block. After an average of 26.6 months, an improvement of conduction disturbance was seen in four cases (16 per cent), aggravation was noted in 11 cases (44 per cent), and no change was found in 10 cases (40 per cent). In five patients exhibiting aggravation, no intrinsic rhythm could be detected. Improvement was noted only in atrioventricular and not in intraventricular conduction. Six generators with demand failures were also detected during the course of this study.

Studies of acute myocardial infarction with intermittent bundle branch and hemiblock

Two cases of transient hemiblock occurring during the course of acute myocardial infarction are reported. The transient manifestation permits the accurate evaluation of the diagnostic features of the hemiblocks as modified by acute infarction. One case reflects the development of left bundle branch block due to bilateral post-divisional block which inter alia permits the study of left bundle branch block in the presence of acute myocardial infarction.

Prognostic significance of isolated left anterior hemiblock and left axis deviation in the course of acute myocardial infarction

In 700 patients with acute myocardial infarction admitted to the intensive coronary care unit of our hospital, the incidence and significance of left anterior hemiblock and left axis deviation has been studied in the acute phase of disease. In 102 (14.6%) of the 700 patients, isolated left axis deviation (mean QRS axis-45 degrees) was found and 69 of them (9.9%) met the criteria of left anterior hemiblock. Of the 69 patients with left anterior hemiblock, 61 had acute anterior myocardial infarction, 5 had inferior infarction, and 3 had subendocardial infarction. The anterior hemiblock was transient in 5 patients, but persisted in 64. All patients with and without isolated left anterior hemiblock and left axis deviation were compared statistically with reference to mortality rate and the incidence of arrythmias; no significant difference was noted. However, in patients over the age of 65 and also in those with hypertension, the incidence of left axis deviation was significantly higher (P less than 0.05 and P less than 0.001, respectively). It was concluded that isolated left anterior hemiblock and left axis deviation occurring in the course of acute myocardial infarction no influence on the prognosis of acute myocardial infarction.

Prognostic value of infranodal conduction time in patients with chronic bundle branch block

His bundle recordings were obtained in 121 patients with chronic bundle branch block and the patients were followed for a mean period of 18 months. Seventy-nine patients had an infranodal conduction time (H-Q) less than 70 msec while 42 had H-Q greater than or equal to 70 msec. There was no significant difference in mean age, smoking history, diabetes, syncope, dizziness, blood pressure, and serum cholesterol or triglyceride levels between the two groups. There was a significantly greater incidence of progresssion to second degree or third degree atrioventricular block (9/42, 21%), and of severe congestive heart failure (16/42, 38%) in patients with H-Q greater than or equal to 70 compared with those with H-Q less than 70 (1/79, 1.3%; and 13/79, 16%, respectively). The risk of sudden death was significantly greater only in the group with H-Q greater than or equal to 70 and severe congestive heart failure. There was no correlation between the presence of first degree atrioventricular block and/or any particular type of bundle branch block pattern with sudden death and/or progression to second degree or third degree atrioventricular block. Analysis of the surface electrocardiogram is only of limited value in predicting high risk patients with chronic bundle branch block. Electrophysiologic studies are of greatest value in patients with bundle branch block with transient neurologic symptoms in whom no cause for the symptoms is evident.

Chronic bilateral bundle-branch block. Long-term observations in ambulatory patients

During a period of 28 months, all patients (79) who presented with bilateral bundle-branch block were selected for study from a private practice outpatient population. They were followed prospectively from the date of entry into the study and their charts were reviewed retrospectively. The average age of the participants was 73-3 years and they were observed clinically for a cumulative period of 4237 months (353-08 years). A high incidence of severe heart disease and death was noted among the study group. Twenty-four (30-3%) had a New York Heart Association functional classification of 3 or 4. Eight (10-1%) died. Only one patient died suddenly and he had had a stable electrocardiographic pattern of bilateral bundle-branch block for a period of 118 months (9 years 10 months). Seven patients required permanent pacemakers. In 6 instances death resulted from pump failure; in one it was the result of lung cancer. In none of these 7 individuals did rhythm disturbances contribute to death. In most cases vertigo was not of cardiac origin (88-2%). Eight patients had 11 major surgical procedures with no significant cardiac sequelae. Our observations suggest that elderly patients with chronic bilateral bundle-branch block should be managed conservatively. The prognosis in these patients appears primarily to be related to the degree of myocardial disease rather than to the conduction disorder.

Bradycardia-related (phase 4) left anterior hemiblock

A case is presented in which left anterior hemiblock (LAH) appeared transiently after the pause terminating atrial pacing, after atrial premature beats and during the slowing of sinus rhythm induced by carotid sinus massage. The transient LAH is attributed to phase-4 block, and is reported in order to add weight to the hypothesis that phase-4 block is a significant factor in the genesis of discrete conduction blocks in the human heart.

Transient unifascicular, bifasicular and trifascicular block: electrophysiologic correlations in a patient with rate-dependent left bundle branch block and transient right bundle branch block

Correlations of the His to ventricular (H-V) conduction time were made with the surface electrocardiogram during normal intraventricular conduction, unifascicular block (right bundle branch block), bifascicular block (left bundle branch block) and trifascicular block (right and left bundle branch block) in a patient with rate-dependent left bundle branch block who had transient right bundle branch block during recording of the His bundle electrogram. The results provide a functional confirmation of the theory that a prolonged H-V time is a manifestation of trifascicular disease.

Intraventricular trifascicular block verified by His bundle electrocardiography

A patient with the combination of right bundle branch block and intermittent left anterior and left posterior hemiblock is presented. His bundle recordings proved that this type of intraventricular conduction defect appeared when the two left fascicles were damaged partially, and to a varying degree. The recordings also revealed a Grade 2 A-V block distal to the A-V node. The mechanism is discussed.

ECG and VCG changes in experimental hemiblock and bifascicular block

ECG and VCG changes in QRS configuration before and after left anterior subdivision block (LASB), isolated and combined with right bundle branch block (LASB combined with RBBB), were studied in canine hearts. In another series left posterior subdivision block (LPSB), isolated and combined with right bundle branch block (LPSB combined with RBBB), were also performed. With LASB, the A QRS axis deviated superiorly to the left and the QRS duration showed no significant prolongation. Additional RBBB to the existing LASB, moreover, rotated the A QRS axis counterclockwise, and prolonged the QRS duration significantly. With LPSB, the axis was deviated inferiorly to the right and the QRS duration showed no significant prolongation. Additional RBBB to the existing LPSB rotated the A QRS axis clockwise. The QRS duration showed significant prolongation. Vectorcardiographically, the initial part of the QRS loop did not show any essential changes with either LASB or LPSB. The main and terminal parts of the QRS loop, however, were deviated superiorly and to the left with LASB and inferiorly and to the right with LPSB. No changes were observed in the direction of rotation of QRS loop with either subdivision block. From these results it appears that the changes in the terminal forces are more of importance than the initial forces in the diagnosis of hemiblock.

Reassessment of Q waves in left bundle branch block

This study disputes a number of recent reports claiming that abnormal Q waves or a QS configuration in inferior leads (II, III and AVF) coexisting with left bundle branch block is highly suggestive of, and indeed specific for, myocardial infarction. Five patients reported herein demonstrate disappearance of Q waves in inferior leads on spontaneous reversal of LBBB to normal conduction. This necessitates the conclusion that these Q waves represent a postdivisional conduction variant most closely equivalent to left anterior fascicular block coexisting with predivisional LBBB. Absence of inferior R waves in the five patients demonstrating LBBB is explicable by as little as a 20 msec conduction delay in the posterior fascicle coexisting with a higher grade conduction defect in the anterior fascicle. It is concluded that LBBB with a QS configuration in II, III and AVF cannot be considered diagnostic of inferior wall infarction since it regularly results from impaired conduction of the left anterior and possibly the left posterior fascicle (to a lesser extent), which may be reversible.

Prolonged His-Q interval in chronic bifascicular block. Relation to impending complete heart block

Although prolonged infra-His conduction time in bifascicular block is suspected of denoting trifascicular disease, adquate documentation is lacking concerning the correlation between lengthened His-Q interval (H-Q) and the risk of development of complete heart block (CHB). H-Q in conducted sinus beats in patients with bifascicular block associated with Mobitz II or intermittent CHB represents the approximation of maximal H-Q prolongation prior to onset of trifascicular block. To assess this relationship between prolongation of H-Q and trifascicular block, His bundle electrocardiography (HBE) was performed in 50 patients with chronic bifascicular block exhibiting Mobitz II block or transient CHB. Mobitz II or episodic CHB was shown in all patients: within two days prior to HBE in 45/50 patients; in 39/50 patients during HBE; and following HBE in five patients. In 49/50 patients H-Q was prolonged (greater than 55 msec) and in 47 this interval was substantially lengthened (65 msec or greater). Since marked H-Q prolongation in conducted sinus beats was documented in nearly all patients with bifascicular block associated with intermittent complete trifascicular block, we conclude that a considerably lengthened H-Q interval in bifascicular block is not only a usual prerequisite but strong evidence, for impending complete heart block.

The superior QRS axis in ostium primum ASD: a proposed mechanism

The influence of abnormal hemodynamics, ventricular hypertrophy, and right bundle branch block on the AQRS was studied pre- and post-operatively in 29 patients with OPSD. The AQRS markedly diminishes with the surgical correction of abnormal hemodynamics and the subsequent resolution of RVH or BVH. With the persistence of ventricular hypertrophy postoperatively or the surgical induction of RBBB, the AQRS either remains unchanged or, in the latter instance, becomes more superior and rightward. The dependence of the superior AQRS on these factors suggests that a left anterior hemiblock is not responsible for this AQRS. In OPSD early activation of the posterobasal region of the left ventricle through an abnormally short posterior fascicle results in a minimal superior AQRS which is then exaggerated in the presence of abnormal hemodynamics, ventricular hypertrophy, or RBBB. Thus, the superior AQRS in OPSD with associated RBBB does not represent a true bifascicular block and has a different natural history and clinical significance.

His bundle electrogram in trifascicular disease: report of a case studied with His bundle electrograms

His bundle electrograms were performed on a 75 year old female with trifascicular block and digitalis induced junctional block. The usefulness of this technique in understanding the patients' electrocardiographic abnormalities and the relationship to phase-3 and phse-4 block is discussed.

The relative risk of spontaneous complete atrioventricular block in elderly patients with impaired intra-ventricular conduction

We reviewed 144 consecutive patients with symptomatic high grade atrioventricular block. Cases due to congenital heart disease, acute myocardial infarction, cardiac surgery or digitalis toxicity were excluded. Of the remaining, we chose 71 patients in whom atrioventricular conduction was observed either intermittently during complete heart block (CHB) or in electrocardiograms taken within two years prior to documentation of CHB. The mean age was 69 years, with the peak incidence in the seventh decade in 43 men and eight decade in 28 women. Bundle branch block (BBB) was present in 76% of patients as follows: 47% had right BBB (20% with normal QRS axis, 20% with left axis deviation and 7% with right axis deviation), 17% had left BBB (11% with normal QRS axis and 6% with left axis deviation) and 12% had either alternating BBB, right BBB with alternating axis deviation or atypical BBB. "Trifascicular block" patterns accounted for 21% of the total group of CHB. We also studied the prevalence of various patterns of BBB in a group of 2000 random hospital patients of comparable age and sex exclusive of those with acute myocardial infarction and heart surgery. The risk of CHB for the various patterns of BBB was calculated relative to normal intraventricular conduction. All patterns of BBB carried a considerably increased relative risk of CHB, (P smaller than .01). The relative risk was highest for RBBB with left axis deviation and lowest for LBBB with normal or left axis deviation. In the men, 74% had QRS patterns of "bifascicular" or "trifascicular" block during atrioventricular conduction. By contrast, 71% women had atrioventricular beats showing either no BBB or right BBB with normal QRS axis. QRS pattern during CHB was unchanged from that during atrioventricular conduction in 52% if cases (rabge 38%-76% with different QRS patterns) suggesting idiojunctional pacemaker. CHB in these cases was thought to be due probably to coexistent disease in the AV node or His bundle. Although the concept of uni-, bi- and trifascicular block patterns has been useful in identifying patients at greater risk of CHB, the predictability of the electrocardiogram has obvious limitations, particularly in women.

Complete His-Purkinje block produced by carotid sinus massage. Report of a case

A case of complete heart block (CHB), localized in the His-Purkinje system, induced by carotid sinus massage (CSM) is presented. A 63-year-old male with right bundle branch block and left anterior hemiblock was evaluated for recurrent syncope. Right or left CSM produced brief periods of CHB with presyncopal symptoms. His bundle (HB) studies during normal sinus rhythm revealed normal conduction times (A-H interval = 80 msec; H-V interval = 48 msec). Carotid sinus massage produced progressive slowing of the sinus rate, and complete heart block below the HB occurred whenever the sinus rate fell below 42 beats/min. During atrial pacing at 70 beats/min, CSM produced 2:1 block above the HB with an effective rate to the HB of 35 and complete block below the HB. Atrial pacing at rates above 93 beats/min resulted in 2:1 block below the HB. Administration of intravenous atropine produced an apparent junctional tachycardia with 2:1 block below the HB. Thus, complete heart block related to both bradyCardia (phase 4) and tachycardia (phase 3) was demonstrated. The complete heart block induced by CSM was thought to be secondary to bradycardia-induced left posterior fascicular or intra-His block. However, the possibility of a direct vagal effect on ventricular conduction could not be ruled out.