Monophasic action potential mapping in human subjects with normal electrocardiograms: direct evidence for the genesis of the T wave.

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Abstract
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 function and ECGs with concordant T waves. MAP recordings during constant sinus rhythm or right atrial pacing were analyzed for activation time (AT) = earliest QRS deflection to MAP upstroke, action potential duration (APD) = MAP upstroke to 90% repolarization, and 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 less than .05 to less than .0001). RT was less heterogeneous than APD, and no significant transventricular gradients of RT 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 less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)