[Etiological study of 23 cases of complete block of the left branch of the bundle of His, in the absence of myocardial infarction].

An aetiological study was performed in 23 asymptomatic patients with left bundle branch block (LBBB) which included Thallium 201 myocardial scintigraphy on effort and, in 15 cases, cardiac catheterisation and coronary angiography. Thallium fixation was abnormal in all patients, but the cause of LBBB was attributed to cardiomyopathy in 9 cases, and to coronary artery disease in 2 cases. Cardiac catheterisation was normal in 4 cases. The hypofixation of Thallium 201 in LBBB can be explained either by an abnormality of left ventricular contraction due to heterotopic propagation of the depolarisation or by the unusually high incidence of the association of LBBB and left main coronary artery stenosis and/or a dominant left coronary artery. The practical implication of this study is that Thallium 201 myocardial scintigraphy is of little value in patients with LBBB.