Diagnosis of left anterior hemiblock and left posterior hemiblock in the presence of inferior wall myocardial infarction.

THERE are several ways to prove that a given electrocardiographic pattern is due to a block in one of the subdivisions of the left branch (hereby designed as left anterior hemiblock (LAH) and left posterior hemiblock (LPH) respectively).' One useful approach is, of course, extrapolation from animal experiments. However, the history of left hemiblocks has shown that their clinical recognition was greatly delayed by trying to apply information obtained from dogs, since in these ani-mals complete right bundle-branch block (CRBBB), LAH, and LPH produce electrocardiographic changes different from those in man.2 Re-cently reported a better correlation between man and lower species when the experiments were performed in baboons.2 Another way to study the hemiblock problem is through analysis of QRS changes produced by the inadvertent section of the conducting tracts during intracardiac surgery. According to Rosenbaum al. constitutes the in vivo counterpart of the animal experiments.3 beat-to-beat a of several days, to evaluate the natural history of the conduction distur-bances.' the induction of left hemiblocks by coupled atrial pacing with the of simultaneous recordings of the intraventricular conducting tissues) corroborated the assumptions postulated by extrapolating from animal experiments surgically induced abnormalities, sequential changes, and deductive reasoning.4