[Experimental left atrial infarct]

Electrical changes produced by an experimental left atrial infarction were studied in 15 mongrel dogs, anesthetized by sodium pentobarbital intravenously and submitted to intratracheal intubation, medical sternotomy and heart exposition without open the pericardial sac. 5 to 8 ml of alcohol 96 degrees were infiltrated into left atrial myocardium by means of a thin needle introduced superficially and parallel to the visceral pericardium. Left atrial damage reduces the electromotive, forces corresponding to the anterolateral portions of the left atrium giving rise to QS or QR slurred P waves with very delayed activation when left portion of interatrial band was damaged. Surface ECG records bimodal wide P waves with or without a qp wave in V2-V4 leads, associated to STa elevation in lead a VL and higher leads in the fourth and third left intercostal spaces at the vertical line of V4. QTac interval is more prolonged in right than in left registries as it was observed in right atrial damage, which implies a more earlier repolarization of left atrium. These data are useful for diagnosis of infarction or myocarditis.