Thirty-eight direct electrocardiographic records have been obtained by applying an exploring electrode directly to the epicardium after incision of the pericardium in the case of seven patients subjected to thoracotomy for various forms of heart surgery. These cases include three individuals with the tetralogy of Fallot, one with mitral stenosis, one with coarctation of the aorta, one with probable pulmonary atresia and one with a patent ductus arteriosus. This exploration has permitted us to study the patterns obtained in different regions of the right and left ventricular epicardial surfaces in four patients with right ventricular hypertrophy, two patients with left ventricular hypertrophy, and one patient with a heart whose left ventricle-right ventricle ratio was probably little disturbed.IT IS now well recognized that certain characteristic modifications of the QRS complex in unipolar precordial leads will result from right or left ventricular hypertrophy, respectively. However, there have not yet appeared any reports concerning the form of QRS in direct epicardial leads in such cases in man. Recently, we were afforded an opportunity to obtain such information in four instances of right ventricular hypertrophy (three due to tetralogy of Fallot and one to mitral stenosis) and in two instances of left ventricular hypertrophy (one due to a coarctation of the aorta and one due to an obscure type of anomaly associated with pulmonary atresia). In the present communication, it is our purpose to describe the findings thus obtained and to correlate the QRS pattern in direct epicardial leads with that in unipolar precordial leads in right and left ventricular hypertrophy, respectively. METHODAfter the heart was exposed and the pericardium incised during operation for the treatment of the cardiovascular anomalies already described, direct unipolar leads were obtained by the application of an electrode directly upon various sites on the ventricular epicardium. The type of electrocardiograph available at the time of these studies did not permit the simultaneous registration of a lead on the body surface. The instrument was standardized to one-half of the usual sensitivity. The exploring electrode consisted of a polished silver disk measuring 13 mm. in diameter and 1 mm. in thickness. To one edge was attached a long handle, which facilitated its application. The disk was pliable and could be bent easily and made to conform to the cardiac surface being explored. This electrode could be introduced easily through the rent in the pericardium and could be held in contact with the visceral epicardium without the aid of absorbent cotton or other substance. The sites selected for the application of the exploring electrode were noted and charted, so that appropriate correlations could be made. Comparisons were then made in the same (Text continued on page 56) FIG. 1. A comparison of the QRS pattern in conventional unipolar precordial leads with that in direct unipolar epicardial leads in a patient with tetralogy of Fallot, who h...

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