Conduction disturbances of the left bundle branch system and their relationship to complete heart block. II. A review of differential diagnosis, pathology and clinical significance

Electrocardiographic hypertrophic patterns in hypertensive Nigerians

We studied hypertrophic patterns in the electrocardiograms of 60 Nigerian hypertensives. Thirty were in heart failure and 30 without failure (matched for age and sex). Combined left ventricular and left atrial hypertrophy was the commonest finding occurring in 58.3%, followed by left ventricular hypertrophy alone in 30%. 76.7% and 40% had combined left ventricular and left atrial hypertrophy in the heart failure and the non-heart failure groups, respectively (P less than 0.02). Though these changes increased with increased blood pressure, the latter is similarly severe in both groups. 100% of patients in Class IV failure had combined left ventricular and left atrial hypertrophy. The 3 patients who had additional right atrial hypertrophy were in Class IV failure, 2 of whom died during follow-up. These changes are much more marked at presentation than reprots in caucasians and even in previous reports in Africans. The changes reflect the long-standing nature and severity of the hypertensive process, and point to the fact that the majority of hypertensives in this environment present rather late.

Left bundle branch block: a continuously evolving concept

Eppinger and Rothberger in 1909 and 1910 first acknowledged the importance of the conduction system, yet a confusion of the pattern of left bundle branch block with right bundle branch block resulted which persisted for 25 years. In left bundle branch block, right ventricular endocardial activation begins before, and is often completed before, initiation of left ventricular endocardial activation. Most likely, right to left septal activation then follows, resulting in left ventricular endocardial activation. Although it is hazardous to make definitive diagnoses of infarction in the presence of left bundle branch block, clues do exist. Benign left bundle branch block is rare; usually disease becomes manifest. Electrocardiographic criteria of hypertrophy are not as helpful in older patients with chronic left bundle branch block (mainly because of the very high incidence of left ventricular hypertrophy) as in younger patients with block of nonatherosclerotic origin. Left bundle branch block is often associated with other abnormalities of the conduction system. Fascicular blocks may mask or mimic myocardial infarction. Left posterior fascicular block is most often an indicator of left ventricular myocardial deficit if right ventricular enlargement is eliminated. Mortality is higher in patients with associated left axis deviation than in those with a normal axis, although the incidence of progression of atrioventricular (AV) block is low. In symptomatic patients with prolonged His to ventricular intervals, the incidence of progression of AV block is higher (12%). Preexisting left bundle branch block in the absence of clinical evidence of heart disease is rare, yet carries with it a slightly increased mortality. Newly acquired left bundle branch block carries a 10-fold increase in mortality; the incidence of sudden death as the first manifestation of heart disease is increased 10-fold.

The significance and prognosis of chronic bifascicular block

The clinical course of 303 patients with bifascicular block was reviewed. Initially, 62% of the total group had evidence of heart disease. The highest frequency of heart disease was in patients with left bundle-branch block and first-degree atrioventricular block (78% or 22/28), while the lowest was in those with right bundle-branch block and left axis deviation (56% or 55/98). During the subsequent clinical course the occurrence of cardiovascular morbidity was greatest in patients who had left bundle-branch block and heart disease (55% or 49/89). Complete heart block occurred in only 11 patients. The highest incidence of complete heart block occurred in right bundle-branch block and left axis deviation when associated with heart disease, but the annual rate was only 4%/yr. Mortality was highest in those with left bundle-branch block, first-degree atrioventricular block, and left axis deviation (43%/yr). A one-year mortality of 65% (11/17) was noted for patients who had bifascicular block prior to the time of acute myocardial infarction.

Noninvasive myocardial imaging with potassium-43 and rubidium-81 in patients with left bundle branch block

Noninvasive myocardial imaging with potassium-43 and rubidium-81 has been used successfully to identify areas of infarction and exercise-induced ischemia as regions of decreased radioactivity. The image defects observed are believed to be due to a decreased radionuclide uptake in regions of myocardial scar or to heterogeneous myocardial accumulation of tracer as a result of regional ischemia. Of 27 patients with left bundle branch block studied with noninvasive imaging at rest and during exercise, 25 manifested at rest reduced radioactivity in the region of the interventricular septum. This pattern is similar to that seen in patients with anteroseptal myocardial infarction. Sixteen of the 27 patients underwent diagnostic coronary arteriography and left ventriculography. Only five of these patients had evidence of either previous infarction or significant obstructive coronary artery disease as assessed with clinical or angiographic criteria, or both. Although the image defect was routinely demonstrated at rest in patients with left bundle branch block, this defect was generally normalized or less distinct with exercise in patients with no anatomic heart disease. In contrast, a larger, more distinct or new image defect with exercise correctly identified the presence of significant obstructive coronary artery disease in patients with left bundle branch block. In the clinical application of noninvasive myocardial imaging, these image defects observed at rest can lead to the false pasitive radionuclide interpretation of anteroseptal myocardial infarction.

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.

Cardiac conduction in myotonic dystrophy

Cardiac conduction abnormalities are frequent in myotonic dystrophy and can result in complete heart block. In a study of 26 patients with myotonic dystrophy, first degree heart block was found to precede clinical presentation of the disease in 7 patients. His bundle electrocardiography in 11 patients demonstrated abnormalities throughout the entire conducting system, even in patients with only first degree heart block. In patients with block of the right bundle branch or anterior fascicle of the left bundle branch, slowing in the remaining fascicles was always present. Therapy of myotonia with procainamide significantly lengthened the P-R interval, and treatment with diphenylhydantoin significantly shortened the P-R interval suggesting that diphenylhydantoin may be preferable for therapy of myotonia in patients with myotonic dystrophy.

Left bundle branch block and coronary artery disease

This study tries the concept that left bundle-branch block (LBBB) connotes coronary artery disease (CAD). The findings indicate that prior studies both supporting of and in contradiction to the premise of a positive correlation have been biased by pre-selection of the patients reviewed. The data indicate, therefore, that LBBB is related to multiple entities. The major categories are CAD and/or hypertension myocardiopathy and aortic valvular disease. In addition, LBBB may develop during the acute phase of myocardial infarction. Its existence as a wholly benign entity has been documented as well. Further, this study adds still another group with LBBB. Six of the nine LBBB patients were female. Five of these, in spite of typical anginal histories, had no arteriographically demonstrable CAD. The absence of disease was surprising and the incidence of women with LBBB was greater than anticipated, thus providing some basis for suggesting that these women may be representative of still another group with LBBB. Further, this study supports the findings of Lewis et al by confirming an association between LBBB and a statistically shorter LCA mainstem (p less than 0.001).

Coronary artery anatomy in left bundle branch block

It has previously been reported that the length of the left main coronary artery is short in patients with left bundle branch block (LBBB) and that an unexpectedly large number of LBBB patients had dominant left coronary arterial distribution. The present coronary arteriographic study of 13 patients with LBBB revealed a mean length of the left main coronary artery ( ± 1 sd ) of 10.9 ± 6.0 mm, a measurement which was not significantly different ( P > 0.5) from that of the left coronary arteries in 78 patients in a control group (10.0 ± 3 mm). The arterial distribution patterns showed a contribution of the right coronary artery to the posterior descending artery in 12 of the 13 patients with LBBB. Coronary artery anatomy does not appear related to the presence of LBBB.