Relation of human cardiac action potential duration to the interval between beats: implications for the validity of rate corrected QT interval (QTc).

Abstract

Fourteen patients undergoing routine cardiac catheterisation were paced at a steady frequency; after this test, stimuli were introduced with a variable preceding interval (test pulse interval). The QT interval of the electrocardiogram and the duration of the monophasic action potential of the right ventricle were measured. QT interval is a function of action potential duration; the two variables were very closely correlated in this study. Both these variables increased in duration with increasing test pulse interval. A biphasic response, as previously reported, was not seen. An increase in steady state pacing frequency caused QT interval and action potential duration to decrease for any given R-R interval. When frequency of stimulation was suddenly increased and then maintained, there was an immediate action potential shortening followed by a further more gradual shortening occurring over several minutes. These results imply that a simple correction of QT interval for heart rate (QTc) is inadequate. It is concluded that the relation between action potential duration (or QT interval) and heart rate depends on both the instantaneous interval between beats and the duration of the prevailing heart rate.

Role of α₁-Blockade in Congenital Long QT Syndrome

“…Shortening of the QT interval with increased HR is a normal response, 30 but the QT interval is modulated by a number of additional factors [31][32][33] and correction by the Bazett formula might result in some limitations. [34][35][36] Recently, Kligfield et al reported that the QT interval and heart rate (or cycle length) during exercise testing were linearly correlated.…”

Pathogenesis of the Novel Autoimmune-Associated Long-QT Syndrome

“…36,37 Because it is generally accepted that the QT interval is a function of ventricular APD and that the 2 variables are very closely correlated in humans 38,39 and animals, 40 the combined in vitro and in vivo data from this study provided important clues to the relationship among ion channel block, APD lengthening, and QT interval prolongation. Abnormal QTc interval prolongation is known to predispose to ventricular arrhythmias known as Torsades de Pointes via early afterdepolarization-induced triggered activity.…”

Prediction of Ventricular Tachyarrhythmias by Intracardiac Repolarization Variability Analysis

“…Experiments have shown that QT interval measured on NF RV EGM corresponds to the action potential duration. 13,14 We speculate that the NF EGM performs well because it is more closely associated with local action potential and is less affected by geometric considerations.…”