To examine the initiating mode of Torsade de Pointes (TdP) in patients with congenital long QT syndrome (LQTS).

We evaluated 111 episodes of TdP recorded on the electrocardiograms of 24 patients with congenital LQTS, and clarified the initiating mode, the three consecutive preceding RR intervals defined as C₂, C₁, and C₀, the timing of initiating premature ventricular contraction (PVC) and the cycle length (CL) of TdP. Three different initiating patterns were observed: (1) a "short-long-short" sequence (SLS) pattern (23 patients, 72 TdP, 65%) defined as one or more short–long cardiac cycles followed by an initiating short-coupled PVC (C₁>C₂ and C₀), (2) an "increased sinus rate" (ISR) pattern (8 patients, 28 TdP, 25%) defined as a gradual increase in sinus rate with or without T-wave alternans (C₂≥C₁≥C₀), and (3) a "changed depolarization" (CD) pattern (5 patients, 11 TdP, 10%) defined as a sudden long-coupled PVC or fusion beat followed by short-coupled PVC. The C₀ was shorter in ISR than SLS and CD (mean C₀: 488 vs. 587 and 603 ms, respectively; P<0.05). Therefore, the initiating PVC appeared near the T-wave peak of the last beat before onset in ISR, while it occurred after the T-wave peak in SLS and CD. The CL of TdP was shorter in ISR than in SLS (256 vs. 295 ms, P<0.05).

Our data show the existence of three predominant initiating modes of TdP in patients with congenital LQTS and suggests a differential mechanism of initiation of TdP for each mode.