The Effect of Exercise on the Timing of Aortic Valve Closure with Respect to the ECG Tracing
Objective: The temporal relationship between electrical repolarization of the heart and mechanical relaxation is not well quantified. In this study we examined the timing of the aortic valve (AoV) closure with respect to the electrical repolarization at rest and following exercise in young healthy subjects.
Methods: We measured the period from the apex of the T wave (aT) to the beginning of the second heart sound (S2-aT) and the period from the apex of the T wave to the end of the T wave (eT-aT).
Results: At rest, AoV closure occured immediately after the end of the T wave as evidenced by a ratio of (S2-aT)/(eT-aT) greater than 1. The mean time delay between the end of the T wave and AoV closure was 15.5ms which was only 4% of the QT interval duration. After exercise, AoV closure occured just before the end of the T wave (but after the peak of the T wave) as evidenced by the ratio of (S2-aT)/(eT-aT) being between 0 and 1. The mean time difference between the end of the T wave and AoV closure was - 4.4ms, which was only 1% of the QT interval duration. In combination, the QT and RR intervals account for some of the inter-subject variability.
Conclusions: AoV closure closely approximates the end of T wave in healthy subjects indicating existence of electromechanical coupling during left ventricular relaxation. Clinically the end of T wave could, therefore, be used as a surrogate for AoV closure in healthy subjects.