[Study of myocardial perfusion by means of scintigraphy with thallium-210 in left bundle branch block induced by exertion].

Myocardial perfusion scintigraphy with 201-TL was performed in a group of subjects affected by exercise-induced, rate-dependent left bundle branch block (LBBB). The aim of the study was: to define the significance of the exercise-induced conduction abnormality: "primitive" or "ischemic". 14 patients, aging 28-58 years (x = 42), 8 with chest pain (4 typical angina, 4 atypical angina) and 6 without any symptoms were studied. None had history of prior myocardial infarction or clinical and echocardiographic signs of heart disease. LBBB appeared at a heart rate ranging from 70 to 160 beats/min. 6 patients showed repolarization abnormalities (ST changes, deep and negative T wave) suggestive for ischemia, during successive QRS normalization. 201-TL-uptake was normal in 5 subjects; in the remaining 9 ones reversible TL defects were demonstrated in the septum (6), in the septum and apex (2), in the septum and inferior-apical wall (1). No patients had irreversible impaired perfusion. All the patients had normal coronary angiography, with negative ergonovine test for coronary artery spasm. In conclusion, in the majority of our subjects (64%) with exercise-induced LBBB, a reversible TL-uptake defect, usually located in the septum without diagnostic value of obstructive CAD, has been observed. Further studies will establish if the TL-defect is only an "apparent phenomenon" due to contraction abnormality secondary to LBBB, or, on the contrary, an expression of myocardial ischemia with normal coronary vessels as a consequence of the LBBB.