Abstract Background A recent review of 86 patients with short or long-coupled premature ventricular complex (SLC-PVC) initiating idiopathic ventricular fibrillation (IVF) found high success rate in arrhythmia control with quinidine (QND) (83%) or radiofrequency ablation (RFA) (70.8%). Purpose To compare the efficacy of QND vs. RFA therapy in a large patient cohort with SLC-IVF. Methods THESIS included 287 patients with SLC-IVF screened from 58 centers and 1 multicenter group in 22 countries across 4 continents. The study cohort included 146 (50.9%) males, aged 39+14 years at the time of IVF documentation. Therapy groups were defined according to the first therapy given. Therapy success was defined as no VF recurrence. Results Patients presented after aborted cardiac arrest, ICD shocks, syncope, aborted cardiac arrest + arrhythmic storm, arrhythmic storm, palpitations, seizures or were asymptomatic in 121 (42%), 51(18%), 42(14.6%), 27 (9.4%), 23 (8%), 8 (2.8%), 6 (2.1%) and 9 (3.1%), respectively. Fifty-three patients (18.5%) had a prior history of syncope. Eleven (3.8%) patients required ECMO support. Mean shortest and longest coupling interval which triggered VF in the same patient were 304.9+82ms and 341.2+94.1ms, respectively. VF initiation with "long" coupled PVC (coupling interval &amp;gt;350ms) was observed in 41 (18.1%) patients, and VF initiation with both short and long coupled PVC was documented in 30 (13.2%) others. RFA was performed in 112 patients and QND was given to 68 patients. Patients were followed during a mean follow-up of 84.8+64.5 months. Therapy success was achieved in the RFA or QND group in 69 (62.2%) and 49 (71%) patients, respectively (p=0.29). The RV Purkinje was the main targeted ablation site in 46 (47.4%) patients. Treatment success varied according to the site of origin (SOO) of the PVC which triggered VF. Therapy success was higher with QND when PVC SOO based on ECG, was the RV inflow tract (81.3% vs. 57.7%, p=0.048) or when the SOO was not available (67.9% vs 36.4%, p=0.064), and when the coupling interval/QT ratio was &amp;lt;1 (75.5% vs. 57.5%, p=0.03), Figures 1,2. A higher success rate with ablation compared with QND was seen with LV- SOO compared with RV-SOO (82.1% vs 60.3%, p=0.019). Similarly, successful ablation was achieved in 83.3% (n=24) vs. 55.9% (n=68) patients with LV and RV-SOO respectively; p=0.004. One patient expired of sudden cardiac death due to misdiagnosis, while wearing a subcutaneous -ICD, without any drug or ablation therapy. Conclusions SLC-IVF strikes males and females equally. SLC-PVCs triggering the arrhythmia mainly arise from the RV Purkinje system. QND and RFA have similar efficacy in arrhythmia control. Quinidine has a higher treatment success rate in patients with PVC-SOO in the RV inflow area and in those with coupling interval/QT&amp;lt;1.Figure 1Treatment success by SOOFigure 2Treatment success by CI/QT

THerapy Efficacy in Short or long-coupled idiopathic ventricular fibrillation: an International Survey (THESIS)