ROCHESTER, NEW YORK. There is evidence that a large left atrium (LA) is associated with poorer efficacy of antiarrhythmic drugs and poorer outcome of radio frequency catheter ablation for atrial fibrillation (AF). In routine practice the size of the LA is approximated by measuring the LA diameter (LAD) in the parasternal long-axis view using standard transthoracic echocardiography (TTE). A more accurate measurement can be obtained by the use of transesophageal echocardiography (TEE), but the most accurate method of measuring left atrial size (volume) involves the use of 64-slice contrast-enhanced computed tomography (CT).

Researchers at the University of Rochester Medical Center now report that left atrial volume (LAV) measured by CT can predict the risk of recurrence following ablation. Their study included 65 male afibbers and 23 females with an average age of 57 years (range of 30 to 78 years). Sixty percent of the patients had hypertension, and 22% had coronary artery disease or had undergone valve or coronary bypass surgery. At baseline 97% were taking an antiarrhythmic drug and 86% were on beta-blockers. Forty-five percent of study participants had paroxysmal AF, while the remaining 55% had the persistent variety.

All patients underwent an anatomically-guided, wide-area, circumferential pulmonary vein isolation procedure with additional linear lesions at the EP's discretion. Follow-up was at least one year. Success rate for the initial procedure was 55% for paroxysmal afibbers and 50% for persistent afibbers. After an average 1.5 procedures, success rate was 88% for paroxysmal afibbers and 52% for persistent afibbers. Thus, having persistent AF was a strong predictor of the likelihood of AF recurrence during follow-up.

However, the strongest predictor of failure turned out to be LAV as measured by CT prior to the ablation. Patients with a LAV above 130 cc had a 22 times greater risk of recurrence than did those with a smaller LAV. Thus the failure rate for patients with a LAV above 130 cc was more than 90%. LAD as measured by TTE correlated poorly with failure rate, while LAD measured using TEE correlated somewhat better, but not nearly to the extent of the correlation associated with CT. A pre-procedure LAD (measured by TEE) of greater than 4.9 cm and a LAV (measured by CT) greater than 117 cc were both associated with a greater than 30% failure rate.

The researchers conclude that a left atrial volume of 130 cc or larger is associated with a recurrence rate of more than 90%. They suggest that, in the case of such grossly enlarged left atria, the risk of undergoing catheter ablation far outweighs any clinical benefit.

Parikh, SS, et al. Predictive capability of left atrial size measured by CT, TEE, and TTE for recurrence of atrial fibrillation following radiofrequency catheter ablation. PACE, Vol. 33, May 2010, pp. 532-40
Russo, AM. Is atrial fibrillation ablation a futile effort in patients who have markedly enlarged left atria? PACE, Vol. 33, May 2010, pp. 527-31

Editor's comment: Although the patient group in the Rochester study included 22% with underlying heart disease, it is likely that a grossly enlarged left atrium may also be associated with a poorer outcome of ablation in lone afibbers. Certainly it would seem prudent to get in line for a PVI once LAD, as measured by TEE, approaches 5.0 cm.