Repolarization abnormality in idiopathic ventricular fibrillation: assessment using 24-hour QT-RR and QaT-RR relationships

We evaluated the characteristics of QT-RR and QaT (apex of T wave)-RR relationships in patients with idiopathic ventricular fibrillation (IVF) compared with control subjects. We hypothesized that IVF patients have unique repolarization dynamics related to a reduced fast Na current and a prominent transient outward current. The study group consisted of 9 men (age 47 +/- 10 years) with IVF (6 with Brugada type and 3 with non-Brugada type) who had experienced nocturnal episodes of VF. The control group consisted of 28 healthy age-matched men (age 44 +/- 12 years). The relationships between QT and RR intervals and between QaT and RR intervals were analyzed from 24-hour Holter ECG data using an automatic measurement system. Both QT and QaT at RR intervals of 0.6, 1.0, and 1.2 seconds were determined from QT-RR and QaT-RR linear regression lines. Both QT-RR and QaT-RR slopes were lower in the IVF group than in the control group (QT-RR: 0.092 +/- 0.023 vs 0.137 +/- 0.031, P < 0.001; QaT-RR: 0.109 +/- 0.025 vs 0.153 +/- 0.028, P < 0.001). QT at an RR interval of 0.6 second did not differ between two groups, but QT at RR intervals of either 1.0 or 1.2 seconds was significantly shorter in the IVF group than in the control group (RR 1.0 s: 0.384 +/- 0.018 vs 0.399 +/- 0.017, P < 0.05; RR 1.2 s: 0.402 +/- 0.019 vs 0.426 +/- 0.020, P < 0.01). QaT at RR intervals of either 1.0 or 1.2 seconds also was shorter in the IVF group (RR 1.0 s: 0.289 +/- 0.022 vs 0.312 +/- 0.021, P < 0.01; RR 1.2 s: 0.311 +/- 0.024 vs 0.343 +/- 0.024, P < 0.01). In four patients, oral administration of disopyramide (300 mg/day) was effective in suppressing VF episodes and increased slopes of QT-RR and QaT-RR relationships. IVF patients had lower slopes of QT-RR and QaT-RR regression lines and impaired prolongation of QT and QaT at longer RR intervals compared with control subjects. These unique repolarization dynamics may be related to the frequent occurrence of VF episodes at night.