[Experimental subendocardial postero-inferior infarctions].

In 30 mongrel dog hearts, epicardial and thoracic unipolar records were obtained after myocardial damage was produced by infiltration of 96% alcohol in the postero-inferior free left ventricular wall. Necrosis was transmural in 5 cases, subendocardial in 11 and intramural in 10. In 4 dogs, intramural unipolar and bipolar leads were recorded in order to determine the electrical subendocardium and its relation to potentials of Purkinje's fibres. At the end of each experiment, left posterior subdivision block (LPSB) was provoked. In 90% of the cases, direct epicardial records were QS in transmural infarction, qrS or less frequently QRS in subendocardial ones, and rS or qRS in the presence of intramural necrosis. In several cases myocardial necrosis was located in the middle third instead of the inferior third, but the direct registries were similar. Nevertheless the surface leads (II, III and aVF) did not show abnormal Q waves or greater voltage of Q and S, but there were RS complexes in V1 and V2. In 80% of the cases, transmural necrosis of inferior third was manifested by QS complexes and subendocardial necrosis by rS or qRS complexes with increased Q and S waves and reduced R waves. LPSB masked the signs of necrosis. There is no justification for speaking of myocardial infarction with or without abnormal Q waves, because it does not add more precision. Moreover these expressions can create confusion in cases of middle or high posterior myocardial necrosis, revealed by RS complexes in V1 and V2.