BOSTON — Researchers recently devised a way to visualize fibrotic tissue within the left atrial wall noninvasively with MRI. Results from a new study that took this analysis a step further showed that patients with atrial fibrillation whose left atrium had high levels of fibrosis also faced a significantly increased risk of failing treatment by pulmonary vein isolation and septal debulking and revert to fibrillation.
The new method of left atrial assessment with delayed-enhancement (DE) MRI may identify patients at the highest risk of early recurrence of atrial fibrillation following a noninvasive, pulmonary-vein isolation procedure, Dr. Saul Kalvaitis said at the Heart Rhythm Society's annual meeting.
Although this early finding needs replication by other groups, it has significant therapeutic implications, said Dr. Melvin M. Scheinman, professor and cardiac electrophysiologist at the University of California, San Francisco. The report suggests that DE MRI may identify patients with atrial fibrillation who are not good candidates for ablation therapy because of high fibrosis content within the atrial wall. Recent research findings by other groups suggest that certain drug treatments reverse fibrosis. If such treatments prove effective, potentially nonresponsive atrial fibrillation patients might benefit from ablation, he added.
DE MRI is now a standard method for assessing ventricular scar tissue, but Dr. Kalvaitis and his coworkers at the University of Utah, Salt Lake City, are the first to apply the method to left atrial assessment, Dr. Scheinman said in an interview. A published report of the Utah group's success with DE MRI for left atrial assessment appeared earlier this year (Circulation 2009;119:1758-67). DE MRI involves infusing gadolinium contrast into the patient. Uptake of the contrast into fibrotic tissue occurs at a different rate compared with its entry into healthy tissue, and this difference allows assessment of the amount and location of fibrotic scar within the heart wall.
In the new study, Dr. Kalvaitis and his associates performed DE MRI exams on 62 patients with atrial fibrillation scheduled to undergo pulmonary vein antrum isolation and atrial septum debulking. Their average age was 64 (range 23-84), and two-thirds were men. On average for the entire group, structural modeling affected 17% of the left atrium.
The researchers divided the patients into three subgroups based on the extent of their left atrial remodeling ratio: less than 15% (27 patients), 15%-35% (28 patients), and more than 35% (7 patients). The amount of left atrial fibrosis closely correlated with the ratio of left atrial remodeling, ranging from a mean of 8% fibrosis in patients with the least remodeling to 46% in patients with the most. (See box.).
The incidence of an early recurrence of atrial fibrillation, defined as atrial fibrillation recurring within 3 months of the ablation procedure, closely correlated with the extent of left atrial fibrosis. The early recurrence rate was 19% in the subgroup with the lowest level of atrial fibrosis and 39% and 40%, respectively, in the two subgroups with higher amount of fibrosis.
In a multivariate analysis that controlled for baseline differences among the patients, the subgroup assignment of left atrial remodeling ratio and left atrial fibrosis was the only significant determinant of recurrence risk, increasing the risk by more than twofold, Dr. Kalvaitis reported.
Expressed another way, patients with an early recurrence of atrial fibrillation after ablation had an average 24% left atrial remodeling ratio prior to ablation treatment, compared with an average 14% ratio among those who did not have an early recurrence.
This method for defining recurrence risk may identify patients who would benefit from treatment with an antiarrhythmic drug ablation, Dr. Kalvaitis said. He said that he and his associates had no financial disclosures.
Source Elsevier Global Medical News
Delayed-enhancement MRI images of left atria show fibrotic tissue as green and healthy tissue as blue.
Source Courtesy Dr. Nassir F. Marrouche