Heart-rate dependency of QRS-microvariability during atrial pacing

Patients with ventricular tachyarrhythmias show an increased beat-to-beat microvariability of the QRS. The authors evaluated the dependency of QRS duration variability (QDV) on heart rate and heart rate variability (HRV). ECGs were analyzed during sinus rhythm and during right atrial pacing (80 ppm, 105 ppm, 130 ppm). QRS duration of each individual beat was measured and QDV was calculated as standard deviation of the QRS duration of consecutive normal beats. QDV during sinus rhythm did not differ from QDV during 80 ppm atrial stimulation (Delta -0.01±0.58 ms) indicating that QDV is present at zero heart rate variation. With increasing pacing rates VT patients showed a significant increase of QDV from 0.52±0.06 ms to 1.84±1.10 ms (ANOVA p<0.013) not present in healthy subjects. It is concluded that QDV is independent from heart rate variability. Patients with malignant arrhythmias show a heart rate dependent increase of beat-to-beat QRS variability indicating stress dependent anisotropic conduction