PATHOPHYSIOLOGY AND NATURAL HISTORY ELECTROPHYSIOLOGY Monophasic action potential mapping in human subjects with normal electrocardiograms: direct evidence for the genesis of the T wave

T wave concordance in the normal human electrocardiogram (ECG) generally is explained by assuming opposite directions of ventricular depolarization and repolarization; however, direct experimental evidence for this hypothesis is lacking. We used a contact electrode catheter to record monophasic action potentials (MAPs) from 54 left ventricular endocardial sites during cardiac catheterization (seven patients) and a new contact electrode probe to record MAPs from 23 epicardial sites during cardiac surgery (three patients). All patients had normal left ventricular funtion and ECGs with concordant T waves. MAP recordings during constant sinus rhythm or right atrial pacing were analyzed for (1) activation time (AT) = earliest QRS deflection to MAP upstroke, (2) action potential duration (APD) = MAP upstroke to 90% repolarization, and (3) repolarization time (RT) = AT plus APD. AT and APD varied by 32 and 64 msec, respectively, over the left ventricular endocardium and by 55 and 73 msec, respectively, over the left ventricular epicardium. On a regional basis, the diaphragmatic and apicoseptal endocardium had the shortest AT and the longest APD, and the anteroapical and posterolateral endocardium had the longest AT and the shortest APD (p < .05 to < .0001). RT was less heterogeneous than APD, and no significant transventricular gradients ofRT were found. In percent of the simultaneously recorded QT interval,epicardial RT ranged from 70.8 to 87.4 (mean 80.7 + 3.9) and endocardial RT ranged from 80 to 97.8 (mean 87.1 4.4) (p < .001). Plotting of APD as a function of AT, independent of the recording site, revealed a close inverse relationship, such that progressively later activation was associated with progressively earlier repolarization The linear regression slope of this relationship averaged from all 10 hearts was 1.32 + 0.45 (r = .78 + . 10). These data suggest a transmural gradient of repolarization,with earlier repolarization occurring at the epicardium. The negative correlation between AT and APD, which was found at both the endocardial and epicardial surface and had an average slope of greater than unity, may further contribute to a positive ventricular gradient and T wave concordance. Circulation 75, No. 2, 379-386, 1987. IN THE NORMAL electrocardiogram (ECG), the T wave has the same polarity as the QRS complex, although on a cellular level depolarization and repolarization cause deflections of opposite polarities. This paradox of the T wave concordance in the ECG has been explained by assuming that the repolarization wave travels, at least in some part of the ventricle, in a direction opposite to that of depolarization.1 This hypothesis requires that some areas of early activation From the Division of Cardiology and Cardiovascular Surgery, Hannover Medical School, Hannover, German Federal Republic. Address for correspondence: Michael R. Franz, M.D., Cardiology DivisionCVRC 293, Stanford University Medical Center, Stanford, CA 94305. Received April 30, 1986; revision accepted Oct. 9, 1986. Presented in part at the 58th Annual Scientific Sessions of the American Heart Association, Washington, DC, November 1985. Vol. 75, No. 2, February 1987 have longer action potentials than do areas excited later. Direct experimental evidence supporting this hypothesis is scarce. Burgess et al.2 determined the recovery of excitability at different ventricular sites as an indirect index of local repolarization; they found long functional refractory periods in the endocardium and the apex and short functional refractory periods in the epicardium and the base. Spach and Barr3 used implanted electrode arrays in dogs to measure the potential distribution during depolarization and repolarization. They found a relative extracellular positivity on the epicardial surface, suggesting earlier repolarization, and a prolonged negativity at the apical free wall, suggesting delayed repolarization. Cohen et al.4 and Watanabe et al.5 recorded intracellular action poten379 by gest on A ril 2, 2017 http://ciajournals.org/ D ow nladed from