Heart rate turbulence slope reduction in imminent ventricular tachyarrhythmia and its implications

The aim of this study was to see whether heart rate turbulence (HRT) parameters change preceding imminent ventricular tachyarrhythmias (VT/VF).

The Spontaneous Ventricular Tachyarrhythmia Database (Medtronic Version 1.0) consisting of 83 paired (control and pre-VT/VF) sets of 1,000 RR intervals recorded by the Medtronic Jewel Plus ICD was used. Sixty-one control records and 69 pre-VT/VF records had two or more ectopic beats, allowing calculation of six HRT indices: means and standard deviations (SD) of turbulence slope (TS), turbulence onset (TO), and turbulence timing (TT). The only index found to be different between control and pre-VT/VF records was SD of TS (4.2 +/- 3.0 control vs 3.1 +/- 1.9 pre-VT/VF, P < 0.05). Thirty-one datasets classified as having normal HRT in control demonstrated a decrease of both TS mean (P < 0.01) and SD (P < 0.01), and loss of correlation between TS mean and left ventricular ejection fraction (LVEF) preceding VT/VF (P < 0.0001 control, P = 0.8 pre-VT/VF).

Both mean and SD of TS are reduced before VT/VF, but only in patients who have normal baseline HRT, and are capable of manifesting reduction. This may be why previous studies could not agree on pre-arrhythmia characteristics.