Aims: Mitral isthmus ablation is technically challenging, often requiring both endocardial and epicardial coronary sinus (CS) ablation. Blood flow in the CS and circumflex artery may act as a 'heat sink' and reduce the efficacy of radiofrequency ablation. This study investigates how the CS and circumflex artery diameters affect mitral isthmus ablation.
Methods and results: Thirty-five patients underwent ablation for atrial fibrillation. Irrigated-tip catheters were used during mitral isthmus ablation with the following settings: endocardial surface (maximum power: 40-50 W at the annular end of line; maximum temperature: 48°C); CS (maximum power: 25-30 W; maximum temperature: 48°C). The absence of block after 10 min of endocardial ablation led to CS ablation for up to 5 min. If there was still no block, further ablation was at the discretion of the physician. Coronary angiography and CS venography were performed and analysed with quantitative coronary angiography. Mitral isthmus block was achieved in 31 patients (89%). Twenty-three patients (74%) required CS ablation to achieve block. These patients were found to have significantly larger CS diameters (6.5 ± 1.2 vs. 5.4 ± 0.5 mm, P< 0.02). Coronary sinus diameter >59 mm predicted the need for CS ablation (specificity: 100%; sensitivity: 78%). Coronary sinus diameter correlated significantly with total mitral isthmus ablation time (r = 0.52, P < 0.003) and CS ablation time (r = 0.59, P < 0.0005), whereas circumflex diameter did not.
Conclusion: Larger-diameter CS is associated with a need for CS ablation during mitral isthmus ablation. Coronary sinus but not circumflex diameter was significantly correlated with total and CS ablation time, supporting the hypothesis that the CS but not the circumflex artery acts as a heat sink.