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The possible reasons of limited rate freedom from atrial fibrillation after thoracoscopic microwave

Cardiovascular Surgery, Saint Luc University Hospital, Avenue Hippocrate 10, 1200 Brussels, Belgium

Thoracoscopic microwave ablation of atrial fibrillation

I read with great interest the paper by Koistinen et al. [1]. Only 60% of patients are in documented sinus rhythm at a mean follow-up of 11 months. The reasons for this are unclear. One contributing factor may be the reported non-uniform transmural lesion depth with microwave energy [2]. Indeed, this report histologically demonstrated non-uniform transmurality of microwave lesions despite the fact that patients were clinically treated successfully. The underlying reason for the lack of transmurality in some patients cannot be fully explained. Possible reasons may include: incomplete surface contact of the Flex 10 with the left atrial tissue, a thick and fibrotic left atrial wall, and high cardiac output during ablation causing loss of heat energy [3].

Whether clinical success was determined by the associated partial cardiac denervation, overcoming the shortcoming of a non-transmural lesion set, remains uncertain. However, this theory might be of value since it could potentially explain a relapse of AF during follow-up. Indeed, re-innervation has been suggested [4]. In a study by Kangavari [5], radiofrequency catheter ablation was followed by an elevation in nerve growth factor concentration in peripheral veins. This could explain nerve sprouting, re-innervation and potential recurrence of AF during follow-up. A further understanding and finding decent solutions to these possible limitations may enhance the outcome.

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1. Koistinen J, Valtonen M, Savola J, Airaksinen J. Thoracoscopic microwave ablation of atrial fibrillation. Interact CardioVasc Thorac Surg 2007; 6:695–699.[Abstract/Free Full Text]
2. Accord RE, Van Suylen RJ, Van Brakel TJ, Maessen JG. Post-mortem histologic evaluation of microwave lesions after epicardial pulmonary vein isolation for atrial fibrillation. Ann Thorac Surg Sep 2005; 80:881–887.[Abstract/Free Full Text]
3. Pruit JC, Lazzara RR, Dworkin GH, Badhwar V, Kuma C, Ebra G. Totally endoscopic ablation of lone atrial ffibrillation: initial clinical experience. Ann Thorac Surg Apr 2006; 81:1325–1330. discussion 1330–1331.[Abstract/Free Full Text]
4. Okuyama Y, Pak HN, Miyauchi Y, Liu YB, Chou CC, Hayashi H, Fu K, Kerwin W, Kar S, Hata C. Sympathetic nerve sprouting induced by radiofrequency catheter ablation in dogs. Heart Rhythm 2005; 1:712–717.[CrossRef]
5. Kangavari S, Oh YS, Zhou S, Youn HJ, Lee MY, Jung WS, Rho T, Hong S, Kar S, Kerwin W. Radiofrequency catheter ablation and nerve growth factor concentration in humans. Heart Rhythm 2006; 3:1150–1155.[Medline]

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