Chronic performance of a novel radiofrequency ablation device on the beating heart: Limitations of conduction delay to assess transmurality

Abstract

Objective The creation of consistenly transmural lesions with epicardial ablation on the beating heart has represented a significant challenge for current technology. This study examined the chronic performance of the AtriCure Coolrail™ device, an internally cooled, bipolar radiofrequency ablation device designed for off-pump, epicardial ablation. It also examined the reliability of using acute intraoperative conduction delay to evaluate lesion integrity. Methods Seven swine underwent median sternotomy. The right atrial appendage and inferior vena cava were isolated with a bipolar radiofrequency clamp. Linear ablation lines were created between these structures with the AtriCure Coolrail™. Paced activation maps were recorded with epicardial patch electrodes acutely before and after ablation and after surviving the animals for four weeks. The conduction time across the linear ablation was calculated from these maps. The lesions were histologically evaluated with trichrome staining. Results Only 76% of cross sections of Coolrail™ lesions were transmural, and only one of twelve ablation lines was transmural in every cross section examined. Mapping data were available in five of the animals. Significant conduction delay was present after the creation of each line of ablation acutely; however, after 4 weeks, conduction time returned to pre-ablation values, demonstrating lack of transmurality. Conclusion The AtriCure Coolrail™ failed to reliably create transmural lesions. While it was able to create acute conduction delay, its failure to transmurally ablate the atrial myocardium left gaps along the length of the lesion which resulted in neither chronic conduction block nor delay across any line of ablation.

New Technologies and Hybrid Surgery for Atrial Fibrillation

“…The group of Damiano demonstrated in an animal model the potential risk of incomplete lesions using these devices 13. Our clinical experience confirmed their findings: in 23% of patients, the epicardial lines created with these linear ablation devices were not transmural and necessitated an endocardial touch-up ablation, demonstrating the importance of power application and mapping during the catheter treatment of atrial fibrillation 14.…”

Performance of a Novel Bipolar/Monopolar Radiofrequency Ablation Device on the Beating Heart in an Acute Porcine Model

“…17 In a chronic study with this device, only 8% of the lesions were transmural along their entire length, and no lesion was able to create lasting conduction block. 18 Microwave epicardial ablation devices also were tested on the beating heart in acute animals, creating transmural lesions only 36% and 38% of the time, respectively. 17, 19 The poor efficacy of these devices is one of the factors which have contributed to the often disappointing results with minimally-invasive, off-pump surgical approaches for AF.…”

Surgical ablation in atrial fibrillation: in which patients?

“…On the catheter ablation side, new tools such as endocardial multiple radiofrequency tip catheters may provide more consistency to ablation lines, but a similar path has been followed in the surgical field with transpolar radiofrequency technology demonstrating inconsistency when reaching transmurality 19. The cryoballoon opens a new window in endocardial ablation technology, but it seems far from being able to perform ablations beyond pulmonary vein isolation, and therefore may be insufficient for persistent and longstanding persistent AF patients.…”