Epicardial Left Lateral Accessory Pathways: An Uncommon Cause of Ablation Failure – Insights from a Case Series

Background Catheter ablation is the treatment of choice for patients with recurrent, symptomatic accessory pathway (AP)-related tachycardias and for asymptomatic patients with high-risk pathways. Catheter ablation is associated with high success rates and low risk of complications, particularly when the pathway is located at the mitral annulus. Epicardial left lateral APs are rare but can account for ablation failures, posing a significant therapeutic challenge. Case summary We report two young patients with recurrent paroxysmal supraventricular tachycardias related to a left lateral AP. In both cases, endocardial ablation targeting the lateral mitral annulus failed. Subsequent mapping of the coronary sinus and its branches revealed earliest activation sites consistent with an epicardial course of the APs. Subsequent deployment of radiofrequency (RF) energy lesions within the coronary venous system using an irrigated-tip catheter resulted in immediate and durable AP elimination. Discussion Epicardial left lateral APs are an uncommon but important cause of failed ablation. Ablation within the coronary venous system, particularly when guided by three-dimensional electroanatomic mapping and performed with irrigated-tip catheters, can be both effective and safe. However, meticulous mapping and targeted energy delivery are necessary to prevent potential complications, such as venous stenosis, thrombosis vascular injury and perforation.