Percutaneous Epicardial Mapping and Ablation of a Posteroseptal Accessory Pathway
A 20-year-old man with no past medical history experienced a syncopal episode. He was found to be pulseless, and cardiopulmonary resuscitation was initiated. When emergency medical service arrived, rhythm strip showed an irregular wide-complex tachycardia consistent with preexcited atrial fibrillation with cycle length as short as 180 ms (333 beats per minute) (Figure 1A). He was defibrillated successfully into sinus rhythm. A 12-lead ECG showed sinus rhythm with PR interval of 110 ms, delta waves and pseudo-infarct pattern in the inferior leads consistent with a posteroseptal accessory pathway (Figure 1B). He was referred to us for an electrophysiology study.
During the procedure, extensive mapping in the right atrium, the coronary sinus (CS) and its branches, and the left atrium (via transseptal approach) was performed. A CS angiogram showed the presence of a diverticulum. The area of earliest ventricular activation was localized to the posteroseptal region in the proximal CS near the os. Radiofrequency applications in this area failed to eliminate the preexcitation pattern on surface ECG. At this point, a cryoablation catheter was used to create more lesions in the proximal CS, but these applications were also unable to eliminate preexcitation. At the end of this initial procedure, the accessory pathway remained intact.
The patient returned to the electrophysiology laboratory 1 week later for a repeat mapping and ablation procedure. Subxiphoid percutaneous epicardial access was obtained, and extensive endocardial and epicardial mapping was performed. The earliest ventricular activation was mapped to the epicardial surface in the posteroseptal region (Figure 2B through 2D). Preprocedural computed tomographic imaging of the heart demonstrated the course of the right coronary artery and its branches along the inferoposterior surface (Figure 2A). Because of the epicardial ablation target, a coronary angio-gram was performed to ensure that the ablation catheter was not in close proximity to one of the epicardial coronary arteries (Figure 2B). The accessory pathway was eliminated after 6.5 seconds of radiofrequency application (25 Watts, maximum temperature 44°C) in the area (Figure 3).
Successful epicardial mapping and ablation of difficult accessory pathways have been previously reported,1–4 with the majority being in the posteroseptal area. Because of the thickness of the myocardium in this area, energy delivered from endocardial ablation often may not reach the epicardial location of the accessory pathway. In this case, the epicardial ablation lesions were clearly at a distance away from the sites of attempted endocardial ablation (Figure 4A and 4B). For this reason, epicardial approach should be considered when repeated attempts of endocardial ablation fail to terminate accessory pathway conduction.