QT‐Interval Turbulence Induced by Atrial and Ventricular Extrastimuli in Patients with Ventricular Tachycardia

Atrial and ventricular premature beats (APB, VPB) cause consistent changes in the sinus-cycle length known as heart rate (HR) turbulence. HR turbulence is described by turbulence onset (TO) and turbulence slope (TS). This article investigated into whether specific QT interval changes are associated with HR turbulence and whether these can be assessed using HR turbulence quantifiers. A total of 40 patients (54 +/- 16 years, 34 men) referred for electrophysiological evaluation for ventricular tachycardia (VT) underwent a study protocol prior to programmed electrical stimulation. The protocol consisted of three consecutive series of atrial and ventricular stimulation with single extrastimuli delivered from the high right atrium and the right ventricular apex at a coupling interval decremented from 750 to 400 ms at a 50-ms step. A 20-second period of sinus rhythm was allowed between ES. Turbulence onset and TS after an APB and a VPB were calculated separately using a dedicated computer algorithm. Consistent changes in the QT interval (QT turbulence) were observed immediately after premature beats and were determined using TO. QT TO was calculated as a relative difference between the QT interval of the first sinus cycle after the induced premature beat and the mean of the QT intervals of the two sinus cycles preceding the premature beat. QT turbulence was present following both APBs and VPBs but was less pronounced after an APB. In contrast to negative VPB-induced TO of HR turbulence reflecting early acceleration of the HR, VPB-induced TO of QT turbulence was positive showing lengthening of the QT interval following a VPB. The subgroup analysis has shown that QT turbulence was significantly attenuated in patients with ischemic heart disease and a left ventricular (LV) ejection fraction (EF) </=0.40 compared with those with nonischemic VT and left ventricular ejection fraction >0.40 (after an APB: 0.73 +/- 0.31% vs 2.58 +/- 0.31%, respectively, P = 0.0044; after a VPB: 1.18 +/- 0.29% vs 4.40 +/- 1.38%, respectively, P = 0.0026). Neither APB nor VPB produced late QT dynamics equivalent to TS of HR turbulence. QT-interval turbulence occurs in association with HR turbulence following induced VPB and APB but QT dynamics is opposite to that of HR. It can be expressed as TO but not TS. Patients with ischemic VT and LV dysfunction exhibited significantly lower QT TO values than those with nonischemic VT and normal ventricular function.