In 8 healthy males, the QT variability index consistently reflected stroke volume and acceleration indices during progressive bicycle exercise, serving as a reliable measure of ventricular function.
Observational (n=8)
Does progressive bicycle exercise alter the relationship between electrocardiographic RR/QT interval variabilities and indices of ventricular function in healthy subjects?
The QT variability index (QTVI) is a consistent measure of cardiac ventricular function that remains stable during physical exercise in healthy subjects.
To date there has been no simultaneous characterization of the influence of physical exercise on cardiac ventricular function and cardiac electrical variability. Consequently, little is known about the relationship between the ventricular function and either heart rate (RR) or repolarization (QT) variability. In particular, the relationship between the QT variability index (QTVI) and ventricular function would be of clinical interest. Eight males of similar age (20.7 +/- 0.4 years (mean +/- SD)), mass (78.4 +/- 7.7 kg) and aerobic fitness (50.7 +/- 4.9 ml kg(-1) min(-1)) undertook progressive bicycle exercise. A three-lead Holter ECG was recorded continuously during pre-exercise, exercise and recovery, and mean values of RR and QT, their variabilities (RMSSD and SDNN) and their relative variability (QTVI) were determined. Traditional indices of ventricular function were determined beat to beat via impedance cardiography, and beat-to-beat blood pressure was recorded via photoplethysmography. Multiple linear regression analysis using the stepwise method resulted in significant models for each of the dependent variables (RR, QT, RR and QT variabilities, QTVI), using indices of the ventricular function as predictor variables. Notably, the QTVI reflected both the stroke volume index (SVI) and the acceleration index (ACI), which are measures of cardiac 'output' per contraction and the force of contraction, respectively. This relationship was largely unperturbed by physical exercise, in contrast with the results for all other dependent variables. We conclude that the QTVI is a reasonably consistent measure of the cardiac ventricular function, and as such is a more useful index than other parameters based on RR or QT interval alone.
Lewis et al. (Mon,) conducted a observational in Healthy subjects (n=8). Progressive bicycle exercise was evaluated on Relationship between QT variability index (QTVI) and indices of ventricular function. In 8 healthy males, the QT variability index consistently reflected stroke volume and acceleration indices during progressive bicycle exercise, serving as a reliable measure of ventricular function.
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