Introduction: Prior to ablation, predicting the site of origin (SOO) of outflow tract ventricular arrhythmia (OTVA), can inform patient consent and facilitate appropriate procedural planning. We set out to determine if OTVA variability can accurately predict SOO. Methods: Consecutive patients with a clear SOO identified at OTVA ablation had their prior 24-hour ambulatory ECGs retrospectively analysed (derivation cohort). Percentage ventricular ectopic (VE) burden, hourly VE values, episodes of trigeminy/bigeminy, and the variability in these parameters were evaluated for their ability to distinguish right from left sided SOO. Effective parameters were then prospectively tested on a validation cohort of consecutive patients undergoing their first OTVA ablation. Results: High VE variability (coefficient of variation ≥ 0.7) and the presence of any hour with < 50 VE, were found to accurately predict RVOT SOO in a derivation cohort of 40 patients. In a validation cohort of 29 patients, the correct SOO was prospectively identified in 23/29 patients (79.3%) using CoV, and 26/29 patients (89.7%) using VE < 50. Including current ECG algorithms, VE < 50 had the highest Youden Index (78), the highest positive predictive value (95.0%) and the highest negative predictive value (77.8%). Conclusion: VE variability and the presence of a single hour where VE < 50 can be used to accurately predict SOO in patients with OTVA. Accuracy of these parameters compares favourably to existing ECG algorithms.

Aims: To investigate the utility of adenosine administration to test the durability of cavotricuspid isthmus (CTI) block after radiofrequency (RF) catheter ablation for typical atrial flutter. Methods: Adenosine 10mg was administered by bolus injection through a femoral sheath at 5 minutes after apparent completion of CTI ablation in consecutive patients, and its effect on CTI conduction was recorded. Conduction in both directions across the CTI was tested repeatedly until 20 minutes after the last energy delivery. Results: Among 132 patients treated with a Blazer 10mm (n=126) or 8mm (n=6) ablation catheter, bidirectional block of the CTI was achieved in all cases. Adenosine administration was followed by a transient recurrence of conduction in 3 cases (2.3%); in all of these, a persistent recurrence of CTI conduction was observed within the waiting period. Persistent recurrence of CTI conduction occurred within the waiting period in 3 patients (2.3%) whose adenosine test had been negative. In all cases, further RF delivery achieved CTI block that persisted to the end of a 20-minute waiting period. During 38 months of follow-up, 131 patients (99.2%) remained free of clinical recurrence of typical flutter. Conclusion: Administration of adenosine 10mg at 5 minutes after RF delivery reveals latent conduction in the CTI in some but not all cases that are revealed by a 20-minute wait. At this dosage and at this time-point, adenosine testing is not an adequate substitute for a waiting period.