Mitral Isthmus Ablation Tied to Subclinical Circumflex Artery Injury

A new study has found that acute subclinical circumflex injury following mitral isthmus (MI) ablation is not uncommon, and identifies several risk factors.

Researchers at the Oxford Heart Center (United Kingdom) followed 54 patients who underwent catheter ablation procedures that included MI ablation for treatment of atrial fibrillation. Irrigated ablation catheters were used at the endocardial surface and the coronary sinus (CS). Coronary angiography was performed pre- and post-ablation and analyzed by two cardiologists with quantitative coronary angiography. In all, MI block was achieved in 89% of patients, 60% of whom required CS ablation.

The results showed that 15 patients (28%) had angiographic changes following ablation; 8 had midcircumflex narrowing only, one had circumflex and obtuse marginal (OM) artery narrowing, one had OM narrowing only, and five had distal circumflex occlusion and narrowing. Five patients had significant narrowing (50% - 84%), which was resolved with intracoronary glycerine trinitrate. Fourteen (93%) of the patients with circumflex injury had CS ablation and a longer mean CS ablation time. There were no electrocardiographic or echocardiographic abnormalities and no angina symptoms during follow-up.

The researchers identified several risk factors for acute circumflex injury after MI ablation. One is ablation within the coronary sinus; all but one patient with this injury had this risk factor. In addition, patients with acute circumflex injury had a longer mean coronary sinus ablation time (5.0 versus 2.6 minutes). Other significant risk factors were that patients with distal circumflex occlusion had significantly smaller vessel diameter; a shorter distance between the circumflex and the CS was also associated with circumflex injury. The study was published in the March 25, 2011, issue of the European Heart Journal.

"Operators should exercise caution during mitral isthmus ablation and consider performing coronary angiography in patients who have had extensive ablation, especially in the coronary sinus," concluded lead author Timothy Betts, MD, and colleagues.

MI ablation is technically challenging, requiring long endocardial ablation times and frequently CS ablation. Since the circumflex artery lies in the epicardium in close proximity to the CS, the mitral annulus may potentially be injured during the radiofrequency ablation procedure.

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