Restoring sinus rhythm in patients with previous pacemaker implantation submitted to cardiac surgery and concomitant surgical ablation of atrial fibrillation.

OBJECTIVE: Some patients submitted to cardiac surgery have concomitant atrial fibrillation and a previously implanted pacemaker. Because it is unknown if there is any potential for these patients to reassume a regular rate sinus rhythm after ablation of atrial fibrillation, we reviewed the results of all patients with pacemaker enrolled in the Registry of Atrial Fibrillation. MATERIALS: Thirty-six patients were included in this study. Twenty-six had valve disease, seven had coronary disease and three had congenital heart disease. They were submitted concomitantly to ablation of atrial fibrillation using biatrial approaches (seven patients), left sided (27), or right sided (three patients). Thirty-three hospital survivors had a mean follow-up of 18 months, and a maximum of 25 months. RESULTS: At 1 year (n=21), patients' rhythm was sinus non-pacing dependent (52%), sinus pacing-dependent (14%), and atrial fibrillation (14%). At 2 years (n=14), patients' rhythm was sinus non-pacing dependent (57%) and atrial fibrillation (43%). The only factor that may have had impact on the recovery of sinus rhythm at 1 year was the small size of the left atrium (p=0.05). CONCLUSIONS: We conclude that in a significant number of patients, having a pacemaker before surgery does not preclude sinus rhythm recovery after a cardiac operation and ablation for concomitant atrial fibrillation.

Atrial ablation for the surgical treatment of atrial fibrillation: principles and limitations.

This article reviews the development of procedures designed to eradicate atrial fibrillation by creating nonincisional lesions in the atria. Percutaneous interventional and surgical data are reviewed and analyzed. A major limitation of the surgical approaches, which utilize a variety of energy sources, appears to be the difficulty in achieving transmurality in all patients. A second limitation is related to a poor understanding of the underlying mechanisms of atrial fibrillation, and the consequent uncertainty as to the ideal lesion configurations necessary to counter these mechanisms. The article also discusses the various types of clinical atrial fibrillation, and discusses the differences between endocardial and epicardial application of thermal energy sources. Finally, atrial contractility is addressed, and the authors conclude that the ideal procedure will achieve a balance between conversion to normal sinus rhythm and the preservation of atrial contractility.

Intra-atrial temperatures in radiofrequency endocardial ablation: histologic evaluation of lesions.

BACKGROUND: Because of the limited information on the effects of ablation in human tissues, we studied intra-atrial temperatures during endocardial radiofrequency applications. We correlated the intra-tissue temperatures with the tissue thickness and with the histologic appearance of the lesions. METHODS: Radiofrequency currents were delivered to human atrial tissue, simulating conditions in endocardial ablation during surgery at set temperature of 70 degrees and 80 degrees C, and intra-tissue temperatures were measured with thermocouples. Radiofrequency applications at 70 degrees C were performed in patients undergoing mitral valve surgery and biopsy specimens were obtained. Samples from in vitro studies and from patients were assessed histologically. RESULTS: The subepicardial temperatures were usually over 60 degrees C in applications in vitro at 70 degrees C and over 70 degrees C in applications at 80 degrees C. Values were higher when the interior of the tissue was warmer than its surface as a result of consecutive radiofrequency applications over the same area. Histologic examination of 12 in vitro samples showed that 10 had transmural lesions. Five of 10 samples from patients with mitral valve surgery had lesions confined to the endocardium, 3 had damaged variable portions of the myocardium, and 2 had transmural lesions. CONCLUSIONS: Although it is possible to obtain transmural lesions in vitro and in vivo with endocardial applications at 70 degrees C, it is significantly more difficult to achieve transmural lesions in patients with mitral valve disease than in normal atrial tissue in vitro. Consecutive applications can raise the intra-tissue temperatures to values significantly higher than those used for application. Our findings suggest that the composition of the endocardium and of the myocardium is a major determinant in lesion formation.