Delayed paced ventricular activation in the long QT syndrome is associated with ventricular fibrillation

Background LQTS may cause sudden cardiac death (SCD), but the mechanisms linking gene mutations to ventricular fibrillation (VF) are unclear. Objective To determine whether ventricular activation delays in congenital long QT syndrome (LQTS) are associated with VF and to describe these delays clinically by measuring activation through ventricular myocardium after a premature extrastimulus. Methods Forty-six patients with LQTS, including 16 with VF (LQTS VF) were investigated, and the results were compared with those from 24 patients with hypertrophic cardiomyopathy and VF (HCM VF). Electrograms in response to premature stimuli were analyzed for increases in electrogram duration (ΔED) and the S1S2 coupling intervals at which electrogram latency starts to increase (S1S2 delay ). Two piecewise continuous straight line segments were fitted to the last electrogram deflection as a function of S1S2 interval in the LQTS and HCM VF populations, and the difference in their gradient (α) was taken as an index of the abruptness of the onset of this delay. Results Thirteen LQTS VF and six LQTS non-VF patients had values of ΔED and S1S2 delay comparable to those in HCM VF patients, while the remainder (three LQTS VF and 24 LQTS non-VF) had lower values ( P P Conclusions Large delays in ventricular activation after an extrastimulus occur in patients with the LQTS, especially those with VF. The change in delay is abrupt in the LQTS, indicating sudden block to activation creating a dynamic substrate for arrhythmogenesis.