In vivo validation of the coincidence of the peak and end of the T wave with full repolarization of the epicardium and endocardium in swine.
OBJECTIVE
Previous in vitro studies have suggested full repolarization of the epicardium coincides with the peak of the T wave (T(peak)) and that of the M cells coincides with the end of the T wave (T(end)). However, in vivo validation of the theory is lacking.


METHODS
Monophasic action potentials (MAPs) were recorded using the CARTO mapping system from 51 +/- 10 epicardial sites and 64 +/- 9 endocardial sites of the left ventricle in 10 pigs and from 41 +/- 4 epicardial sites and 53 +/- 2 endocardial sites of the right ventricle in two of the 10 pigs. End of repolarization (EOR) times over the epicardium (EOR(epi)), endocardium (EOR(endo)), and over both (EOR(total)) were obtained. QT(peak) and QT(end) intervals were measured from simultaneously recorded 12-lead ECG.


RESULTS
Minimal and maximal EOR(total) were observed in the left ventricle in all pigs. Minimal EOR(total) was on the epicardium in five pigs, and maximal EOR(total) was on the endocardium in nine pigs. Minimal, mean, and maximal QT(peak) intervals all were significantly smaller than maximal EOR(epi) (322 +/- 23 ms, P <.01). No significant difference was found between maximal QT(end) interval (338 +/- 30 ms) and maximal EOR(endo) (339 +/- 24 ms, difference = 1 +/- 19 ms, P =.92), between maximal QT(end) interval and maximal EOR(total) (341 +/- 24 ms, difference = 2 +/- 18 ms, P =.69), or between minimal QT(peak) interval (283 +/- 28 ms) and minimal EOR(total) (282 +/- 20 ms, difference = 0 +/- 15 ms, P =.95).


CONCLUSIONS
In in vivo pig models, T(peak) does not coincide with full repolarization of the epicardium but coincides well with the earliest EOR, whereas the T(end) corresponds with the latest EOR. These findings suggest that not only the transmural gradients but also the apicobasal repolarization gradients contribute to genesis of the T wave.
Xia
Yunlong
Y
Department of Cardiology, University Hospital, Lund, Sweden.
Liang
Yanchun
Y
Kongstad
Ole
O
Liao
Qiuming
Q
Holm
Magnus
M
Olsson
Bertil
B
Yuan
Shiwen
S
D000200:Action Potentials; D000818:Animals; D004562:Electrocardiography; D004699:Endocardium / Q000502:physiology*; D010496:Pericardium / Q000502:physiology*; D013552:Swine; D016276:Ventricular Function