SAN FRANCISCO – Declaring a patient ‘cured’ of atrial fibrillation on the basis of a lack of symptoms following atrial fibrillation ablation is definitely jumping the gun, the DISCERN AF study indicates.
Implantable loop recorders used in DISCERN AF (Discerning the Incidence of Symptomatic and Asymptomatic Episodes Post Radiofrequency Ablation of AF) clearly documented that the proportion of AF episodes that are asymptomatic markedly increases after ablation, Dr. Atul Verma reported at the annual meeting of the Heart Rhythm Society.
"There is something about the postablation state that is making patients less able to detect their arrhythmia," observed Dr. Verma, DISCERN AF principal investigator and an electrophysiologist at Southlake Regional Health Center in Newmarket, Ont.
DISCERN AF was an eight-center, prospective Canadian study in which 50 patients with symptomatic AF received a Medtronic Reveal XT insertable cardiac monitor at least 3 months before they underwent a standard first-time AF ablation procedure. Eighty percent of participants had paroxysmal AF. The subjects’ mean left atrial size was 41 mm. Dr. Verma presented the study results through 18 months of postablation follow-up, but there will be a subsequent report, because the devices will be left in place for a total of 30 months post ablation.
Patients kept a detailed standardized diary to record the exact times of onset and end of their arrhythmic symptoms. Every 3 months the implantable loop recorder data were downloaded, and all recorded episodes were blindly adjudicated and compared to entries in the symptom diaries.
Radiofrequency ablation (RF) effectively reduced total AF burden. Indeed, the total AF/atrial flutter burden decreased from a mean of 2 hours per day per patient preablation to 0.3 hours per day per patient post ablation, an 86% reduction. But while 52% of all AF/flutter episodes preablation were asymptomatic, that proportion climbed to 79% post ablation. The ratio of asymptomatic-to-symptomatic AF episodes preablation was 1.1:1; postablation, it jumped to 3.7:1.
Similarly, 36% of the total AF/flutter burden patients shouldered preablation consisted of asymptomatic arrhythmias, while postablation 68% of the burden was asymptomatic. The ratio of asymptomatic-to-symptomatic AF/flutter burden preablation was 0.6:1; postablation, it was 2:1.
Patient self-reports corresponded to an implantable loop recorder–documented episode of AF only 47% of the time.
On the basis of self-reported symptoms only, 58% of patients were free of AF postablation. However, the implantable monitor data showed that the true figure was 46%. In other words, after AF ablation 12% of study participants had AF recurrences that were exclusively asymptomatic, Dr. Verma continued.
Asymptomatic episodes were shorter than symptomatic ones, lasting 4 and 6 hours, respectively. They also involved a significantly lower heart rate and less heart rate variability. In a multivariate analysis, all three of these factors were independent predictors of asymptomatic AF recurrences. But postablation recurrences were a threefold more powerful predictor of lack of symptoms than any of the other three predictors.
One plausible explanation for the increased proportion of asymptomatic AF episodes postablation is that the procedure results in denervation, although this hypothesis requires further investigation, according to the cardiologist.
Discussant Dr. Michael R. Gold called the finding that the proportion of asymptomatic episodes increases following AF ablation "very intriguing."
In addition, DISCERN AF made a point very similar to the key message of the Catheter Ablation vs. Antiarrhythmic Drug Therapy for AF (CABANA) pilot study presented at the 2010 annual meeting of the American College of Cardiology in Atlanta: "We’re not as good as we thought we were in terms of ablating AF," observed Dr. Gold, professor of medicine, chief of cardiology, and medical director of the heart and vascular center at the Medical University of South Carolina, Charleston.
Dr. Gold noted that in the CABANA pilot study, 66% of patients had experienced asymptomatic and/or symptomatic recurrences of AF, atrial flutter, or tachycardia at 12 months of follow-up postablation. That wasn’t significantly different from the 72% recurrence rate in patients assigned to drug therapy.
"The harder you look, the more arrhythmias you find," Dr. Gold observed. "Clearly, DISCERN AF and the CABANA pilot study point to the need for large-scale studies with long-term follow-up to help us understand the best long-term clinical strategies, such as anticoagulation, as well as how well we’re doing with ablation."
One such study is the full-scale CABANA trial, sponsored by the National Heart, Lung, and Blood Institute; St. Jude Medical; and Biosense Webster. It will involve 3,000 patients and 5 years of follow-up.
The DISCERN AF study was supported by Medtronic. Dr. Verma disclosed that he serves as an adviser to Medtronic and half a dozen other medical device and pharmaceutical companies.