Electrophysiological studies in patients with rate-related intermittent left bundle-branch block

Rate-related left bundle branch block and cardiac memory in a patient with bradycardia: Case report and literature review

Rate-related left bundle branch block (LBBB) is a well-studied phenomenon. Cardiac memory is another physiologic phenomenon in which T-wave abnormalities occur in the absence of ischemia. The association between these 2 phenomena has been described in several case reports. A literature review was performed through Ovid and PubMed, where at total of 93 cases of rate-related LBBB were identified. Cases were reviewed, and data were collected on rates of appearance and disappearance as well as the presence or absence of cardiac memory. There is some overlap in the rate at which LBBB appears. Cardiac memory is associated with rate-related LBBB in several cases, but its true prevalence is unknown. Cardiac memory is a phenomenon that is well described in the literature but is often underrecognized in clinical practice. As a consequence of overlooking this phenomenon and not including cardiac memory in the differential when T-wave abnormalities are observed, patients may be subjected to unnecessary invasive diagnostic testing.

Left bundle branch block, an old-new entity

Left bundle branch block (LBBB) is generally associated with a poorer prognosis in comparison to normal intraventricular conduction, but also in comparison to right bundle branch block which is generally considered to be benign in the absence of an underlying cardiac disorder like congenital heart disease. LBBB may be the first manifestation of a more diffuse myocardial disease. The typical surface ECG feature of LBBB is a prolongation of QRS above 0.11 s in combination with a delay of the intrinsic deflection in leads V5 and V6 of more than 60 ms and no septal q waves in leads I, V5, and V6 due to the abnormal septal activation from right to left. LBBB may induce abnormalities in left ventricular performance due to abnormal asynchronous contraction patterns which can be compensated by biventricular pacing (resynchronization therapy). Asynchronous electrical activation of the ventricles causes regional differences in workload which may lead to asymmetric hypertrophy and left ventricular dilatation, especially due to increased wall mass in late-activated regions, which may aggravate preexisting left ventricular pumping performance or even induce it. Of special interest are patients with LBBB and normal left ventricular dimensions and normal ejection fraction at rest but who may present with an abnormal increase in pulmonary artery pressure during exercise, production of lactate during high-rate pacing, signs of ischemia on myocardial scintigrams (but no coronary artery narrowing), and abnormal ultrastructural findings on myocardial biopsy. For this entity, the term latent cardiomyopathy had been suggested previously.

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.

Effect of rate-dependent left bundle branch block on global and regional left ventricular function

Seven subjects with rate-dependent left bundle branch block (RDLBBB) and 13 subjects with normal conduction (control group) underwent upright bicycle exercise radionuclide angiography to determine the effects of the development of RDLBBB on global and regional left ventricular function. Six of the seven subjects with RDLBBB had atypical chest pain syndromes; none had evidence of cardiac disease based on clinical examination and either normal cardiac catheterization or exercise thallium-201 scintigraphy. Radionuclide angiograms were recorded at rest and immediately before and after RDLBBB in the test group, and at rest and during intermediate and maximal exercise in the control group. The development of RDLBBB was associated with an abrupt decrease in left ventricular ejection fraction (LVEF) in six of seven patients (mean decrease 6 +/- 5%) and no overall increase in LVEF between rest and maximal exercise (65 +/- 9% and 65 +/- 12%, respectively). In contrast, LVEF in the control group was 62 +/- 8% at rest and increased to 72 +/- 8% at intermediate and 78 +/- 7% at maximal exercise. The onset of RDLBBB was associated with the development of asynchronous left ventricular contraction in each patient and hypokinesis in four of seven patients. All patients in the control group had normal wall motion at rest and exercise. These data indicate that the development of RDLBBB is associated with changes in global and regional ventricular function that may be confused with development of left ventricular ischemia during exercise.

Chest pain and rate-dependent left bundle branch block in patients with normal coronary arteriograms

A triad of exertional chest discomfort, transient rate-dependent left bundle branch block (LBBB), and normal coronary arteries is presented in seven consecutive patients. Although the clinical symptoms resembled effort angina, qualities atypical of classic angina pectoris were commonly noted: 1) the onset was always abrupt; and 2) the pain was local, never radiating; 3) palpitation; and 4) "walk through" phenomenon were often present. The abrupt pain took place simultaneously with the appearance of LBBB induced by physical exercise in all seven patients. Atrial pacing or spontaneous resting heart rate changes produced similar sensations and LBBB in four of the five patients examined in this way. Similarly, in the same four patients kinetocardiographic recordings disclosed a sudden occurrence of paradoxic cardiac movement at the moment LBBB and chest pain appeared. The paradoxic systolic motion disappeared at reversion to normal conduction.

Effect of intermittent left bundle branch block on left ventricular performance in the normal heart

The effect of left bundle branch block on left ventricular performance was studied in a patient with rate-dependent left bundle branch block and an otherwise normal heart. The timing of left heart events, hemodynamic pressures and indexes of left ventricular contractility were determined during normal intraventricular conduction and during left bundle branch block. The results indicate that in the normal heart left bundle branch block has no significant effect on left ventricular performance.

Case studies: Simultaneous intermittent intraatrial and intraventricular conduction defects mimicking trifascicular conduction delay

Both intermittent rate related left bundle branch block and intermittent rate related trifascicular conduction delay (left bundle branch block with marked H-V interval prolongation) have been previously described. However intermittent rate related intraatrial block with left bundle branch block has not. No only does the case presented herein reveal intermittent rate related intraatrial block with left bundle branch block, but also PR prolongation secondary to the intraatrial block. This combination mimicked intermittent trifascicular conduction delay. Electrophysiological testing allowed differentiation of this pseudotrifascicular defect from true trifascicular conduction delay.

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.