Clinical cases of transient and intermittent complete left bundle branch block

Abstract

Introduction: The transient complete left bundle branch block (TCLBBB) represents an important marker of myocardial ischemia. Although its low incidence, it must be distinguished from other similar forms, like: intermittent block (manifested in rest), exercise-induced transient block (block of the 3rd phase of the action potential) which appears at increased heart rate (95-126 contraction/min. in average) and transient block induced by bradycardia (block of the 4th phase of the action potential.) The actual attitude to intraventricular blocks isn’t rigid and doesn’t require an obligatory association of an organic heart disease. Frequently, the coronary angiography and the ventriculography in patients with TCLBBB are normal, although there are cases with significant coronary lesions. In patients with „clean” coronary arteries we can suppose the disparity of the refractory phases of the Hiss bundle branches, the fibrosis of the cardiac conduction system in different infectious diseases. The significance and the prognosis of the intermittent block and the exercise-induced block are controversial. According to the Framingham study, the TCLBBB appears at the same age as the permanent block, presents the same prognosis and can be associated with organic cardiac diseases. There are also numerous scientific papers supporting the absence of organic heart diseases in patients with TCLBBB. Purpose and objectives: The comparative study of the intermittent block and the TCLBBB. Materials and methods: We analyzed 2 cases of complete intermittent block and 2 cases of transient complete left bundle branch block. Results: We observed that the TCLBBB presents the same features (dyspnea, palpitations at moderate exercise, specific ECG changes which resolves at rest). The exercise stress tests were stopped because the block appeared. The 24h ECG monitoring highlighted the appereance of TCLBBB at the heart rate (HR) higher than 65-70 beats/min and it’s solving at a lower HR. In both patients the coronary circulation presents a predominant right type, without stenosis. In one patient, by the retrospective analysis of the coronary CT-perfusion, we detected a complete myocardial bridge on the lower third of the posterior interventricular branch with lower contrasting in the area under the bridge and an incomplete myocardial bridge on the middle third of the first marginal branch. The analysis of intermittent blocks also included two female patients with frequent heart palpitation and regular dyspnea at rest and little exercise. The repeated ECG showed on a background of atrial fibrillation the aparition of QRS series specific for complete blocks followed by normal QRS complexes. The 24h monitoring didn’t show a correlation with the heart rate. * Conclusions: The transient complete left bundle branch block represents a multifactorial entity with a variable prognosis, from marker of myocardial ischemia to manifestation of increased heart rate. The differentiation of different forms of the TCLBBB can be done by 24h ECG monitoring with frequency limits specification and by coronarography to exclude myocardial ischemia.