The hemodynamic determinants of myocardial oxygen utilization were ascertained in the isolated, metabolically supported, nonfailing canine heart. The primary determinant was found to be the total tension developed by the myocardium as indicated by the area beneath the systolic pressure curve (Tension-Time Index). The significance of these findings for the understanding of the low efficiency of the failing heart and the consequently increased importance of Laplace's law are discussed.

New criteria for the electrocardiographic recognition of right atrial enlargement, left atrial enlargement, and combined atrial enlargement were studied in 110 patients with congenital and acquired heart disease. Precise physiologic data weife available in all cases.The method of analysis was designed for application to conventional scalar electrocardiography and hence can be used without modification for routine clinical purposes.THE current criteria for the electrocardiographic diagnosis of atrial enlargement are seldom adequate for the recognition of even moderate increases in chamber size that may be detectable radiologically. Analysis of tracings has principally considered the configuration, amplitude, and duration of I' waves. Although prolongation of P-R interval has also been observed in severe pulmonic stenosis,' atrial septal defect,2 Ebstein's disease,3 and atrioventricularis communis,4 attention thus far has not specifically been directed toward the P-R segment (time between end of electric atrial systole and onset of electric ventricular systole). This communication proposes a new basis for the diagnosis of atrial enlargement based upon the relation b)etween the durations of P wave, P-R segment, and P-R interval. MATERIALS AND METHODSThe electrocardiograms of 62 normal adults and 110 patients with congenital or acquired heart disease were analyzed.This case material is summarized in table 1.The patients were divided into 2 groups-those with diseases in which an increase in left atrial size might be expected and those with diseases in which an increase in right atrial size might be expected. These will subsequently be designated "left atrial group" and "right atrial group."The width of the P wave and the durations of P-R interval and P-R segment were each measured in lead II according to the following criteria. When the P-R segment was flat, it was measured from the end of the P wave to the onset of the QRS complex. Occasionally the P-R segment was From the Laboratory of Cardiovascular Physiology, National Heart Institute, Bethesda, Md. 882found to slope downwards to the QRS complex, and in this case the onset of the P-R segment was considered to be the point where a line extended from the T-P segment intersected the descending limb of the P wave. The P-R interval was measured from the onset of the P wave to the onset of the QRS complex. Width of the P wave was measured from the onset of the P wave to the onset of the P-R segment. In coIiventional single channel scalar electrocardiography, the most accurate P-R interval is the sum of the maximum P wave duration (in any lead) plus the minimum P-R segment duration (in any lead). This largely obviates the need for simultaneous leads. When this method was applied to our tracings, it was determined that lead II reflected the correct P-R interval with sufficient frequency to warrant its selection for the type of analyses described in this study. ' The evaluation of all patients included fluoroscopy, x-ray, electrocardiogram, and right heart catheteriz...

These results suggest an important role of HT in the treatment of CCHD. There was a low frequency of T cruzi infection reactivation and no signs of recurrence of the disease in the allograft. The surprisingly decreased rejection incidence and severity require further studies for elucidation.

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