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

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 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 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 < .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.

Measuring the T Wave of the Electrocardiogram; The How and Why

“…The available, which is in fact the reason for the ongoing discussion on this topic mentioned in the introduction. However, the results were in agreement with those from the sparse invasive studies available [35,36]. Moreover, the results are in full qualitative agreement with those observed, by means of essentially the same method, when applied to several healthy individuals.…”

Genesis of the T wave as based on an equivalent surface source model

“…£ is a measure of the local duration of the transmembrane potential, the action potential duration (APD) [20]. We take This value is incorporated in the scaling of A, and so a normalized (dimensionless) maximum value of 1 can be used for the local source strength around the nodes, the value shown in Fig.…”

In vivo induction of "focal" triggered ventricular arrhythmias and responses to overdrive pacing in the canine heart.

“…[24][25][26] The catheters were introduced through stab wounds in the LV free wall, and the recording tips were placed against the endocardial surfaces, one on the LV side of the intraventricular septum and the other on the posterior LV free wall. The catheters were secured by mechanical support.…”