Boston, MA - In patients with permanent atrial fibrillation (AF) undergoing mitral-valve surgery, pulmonary vein isolation with epicardial cryoablation (SurgiFrost, CryoCath Technologies, Montreal, QC), an argon-based cooling system, was more effective than mitral-valve surgery alone for the restoration and maintenance of normal sinus rhythm.

These are the findings of the SWEDMAF study, a randomized, double-blind, multicenter study presented here last week during the late-breaking clinical-trials session at the Heart Rhythm Society 2006 Scientific Sessions. According to Dr Per Blomstrom (University Hospital, Uppsala, Sweden), who presented the results on behalf of the investigators, "Epicardial cryoablation can be recommended as an adjunctive therapy for patients with prevalent atrial fibrillation undergoing mitral-valve surgery."

Simpler procedure than Cox-Maze III

Discussing the study, Blomstrom told the audience that AF is present in a majority of patients undergoing mitral-valve surgery and persists in 80% to 90% of patients after surgery. To combat this, operators can combine a Cox-Maze III procedure with mitral-valve surgery, and this combined technique has been shown to be more effective than mitral-valve surgery alone in eliminating AF. While epicardial cryoablation is simpler than a Cox-Maze procedure, the efficacy of the technique is unknown, she said.

With the cryoablation system, a cryosurgical probe ablates cardiac tissue while a patient is undergoing a primary cardiac surgical procedure, such as coronary artery bypass graft (CABG) surgery or mitral-valve replacement and/or repair. Epicardial linear lesions are applied during cardiopulmonary bypass on the beating heart before aortic cross clamp and cardioplegic arrest. Regarding the ablation technique, SWEDMAF operators created two semicircular linear lesions around each pair of pulmonary veins. In addition, three extra lesion lines were also created, with one connecting the two pulmonary vein circular lesions, a mitral lesion line, and a left atrial appendage line.

Including permanent AF patients with a clinical indication for mitral-valve surgery, the investigators enrolled 70 patients at four Swedish centers. Both patients and cardiologists at the attending follow-up centers blinded to the allocated surgery. The postoperative management of all patients included at least two direct-current cardioversions before hospital discharge, and all patients were prescribed antiarrhythmic drug therapy, class I or class III medications. If normal sinus rhythm was absent at one month, patients again underwent cardioversion, but if it was unsuccessful, no more cardioversions were attempted. Antiarrhythmic drug therapy was stopped after three months.

Five patients were not evaluated. Of these, two died, one patient of heart failure in the ICU after surgery and the other from ovarian cancer. One left-sided superior vena cava, a study protocol violation, and one system dysfunction precluded the evaluation of the other patients. In the remaining 65 patients, investigators report that significantly more patients who underwent cryoablation and mitral-valve surgery were in normal sinus rhythm at six months—the primary study end point—than patients who underwent mitral-valve surgery alone. These results were durable to 12 months.

SWEDMAF: Primary and secondary end points

End point	Cryoablation plus mitral-valve surgery (n=30)	Mitral-valve surgery alone (n=35)	p
Restoration and maintenance of sinus rhythm at six months (%)*	73	46	0.024
Restoration and maintenance of sinus rhythm at 12 months (%)	73	49	0.042

In regression analyses, Blomstrom reported that AF duration and coronary artery disease were independent predictors of outcome. She also noted that the extracorporeal circulation time, the time the patient is connected to the heart-lung machine, was 27 minutes longer in the cryoablation study arm, a statistically significant difference. This difference was largely the result of the time required to complete the ablation procedure, which took on average 21 minutes.

While the study shows that epicardial cryoablation is superior to mitral-valve surgery alone for reducing the recurrence of AF and can be used adjunctively in patients undergoing surgery, Blomstrom said further studies are needed to determine whether the same results can be achieved in other patients, including those undergoing CABG surgery. In addition, longer-term follow-up is also needed to test the efficacy of the procedure out past one year, she said.