Transmurality of lesions may not be essential in epicardial pulmonary vein isolation for atrial fibrillation

Abstract

Background: Surgical pulmonary vein isolation has established itself as an effective treatment modality for patients with concomitant atrial fibrillation (AF). However, several uncertainties persist concerning the appropriate energy source, approach and the need for transmurality of lesions. In this study, we present an in-depth histological investigation of epicardial ablation lesions in 3 patients. Methods: Within a large clinical series of adjective epicardial beating-heart microwave isolation of the pulmonary veins with intra-operative measurement of electrical block, 3 non-ablation related deaths allowed detailed histological investigation of the lesions. Two out of three patients had been in stable sinus rhythm prior to dead, one patient did show several short paroxysms of AF post-operatively. Stained sections from the box lesion encircling the pulmonary veins were microscopically examined for tissue damage, lesion depth, width, transmurality, as well as for signs of ongoing repair. Results: Three out of 13 samples showed transmural lesions. In three sections no histological damage was observed and in the remaining samples transmurality ranged from 48% to 82% (mean 64 13%). Lesions depths varied between 1.2 mm and 5.7 mm (mean 2.6 1.3 mm). The lesion depth did not differ significantly between patients and was not related to the thickness of the epicardial or myocardial layers. Interestingly, several sections showed clear necrosis of nerve branches located in the epicardial tissue. Conclusion: Even in this validated approach of epicardial beating heart ablation with satisfactory clinical results, transmurality can not be assumed. This indicates that complete histological isolation of the pulmonary veins may not be necessary for the treatment of AF. The working mechanism of epicardial pulmonary vein isolation may also involve modification of AF substrate, for instance by epicardial nerve denervation.