Atrial fibrillation is associated with increased morbidity and mortality, in part because AF is a marker for other cardiovascular risk factors such as hypertension, valvular disease and left ventricular dysfunction. AF is also deleterious in its own right, due to the rapid, irregular heart rate, loss of atrial systole and atrial thromboembolism. Thus, there is a long history of attempting to restore and maintain normal sinus rhythm through cardioversion and anti-arrhythmic drug therapy.
More recently, several large trials have found no mortality benefit to the rhythm approach over the rate approach (anticoagulating and controlling ventricular rate), and the pendulum has started to swing towards rate control. However, an analysis of one of these trials suggested that there was, in fact, a benefit to sinus rhythm which may have been offset by mortality associated with anti-arrhythmic drug therapy. It is speculated that if sinus rhythm could be maintained without resorting to antiarrhythmics, the rhythm control approach might be beneficial after all. Thus the potential appeal of catheter-based ablation of atrial fibrillation which does not rely so much on anti-arrhythmic drugs.
In today’s NEJM, Hsu et al from Bordeaux, France investigate catheter ablation of atrial fibrillation in congestive heart failure. They studied 58 consecutive patients with at least class II CHF and echocardiographically documented ejection fractions less than 45%, who were undergoing catheter-based ablation of AF. Ejection fraction, symptoms and exercise capacity before and up to one year after the procedure were studied. These patients were also compared to 58 matched controls with normal ejection fractions undergoing the same procedure.
The authors observed substantial improvement in ejection fraction after ablation, from a mean of 36% before the procedure to 57% at one year post-procedure. NYHA class improved from 2.3 to about 1.5. Bicycle ergometer exercise time increased from 11 minutes to 14 minutes (in the control group without CHF, it increased from 14 to 16 minutes).
The authors also looked at their results among patients with adequate vs inadequate rate control before the procedure (average HR 72 vs 103). The ejection fraction improved by 23% in patients with poor rate control and by 17% in those with good rate control. In the absence of structural heart disease, EF increased by 24%; in patients with structural heart disease it increased by 16%.
The authors conclude:
Restoration and maintenance of sinus rhythm by catheter ablation without the use of drugs in patients with congestive heart failure and atrial fibrillation significantly improve cardiac function, symptoms, exercise capacity and quality of life.
I have some reservations about this study. First of all, it is not clear to me how exactly to evaluate a comparison of an ejection fraction in atrial fibrillation (the baseline) with one obtained in normal sinus rhythm. The EF is difficult to measure accurately in fibrillation; furthermore, the decrease in EF in atrial fibrillation which is due in part to tachycardia, in part to the absence of atrial contraction may not exactly reflect the actual decrease in LV contractility. Thus, I am not as impressed by the large increase in ejection fraction as I would have been if the before and after measurements had been taken in sinus rhythm.
Second, the rise in ejection fraction was less among patients with inadequate rate control before the procedure, but the authors do not state how the functional improvements (exercise time and functional status) fared in these two groups. Were they substantially less in those patients with adequate rate control?
Finally, as the authors themselves note, this was not a trial designed to evaluate mortality. But they go on to state that
Since a reduced left ventricular ejection fraction is an important predictor of mortality, the significant improvement in left ventricular function after ablation could be important in improving survival.
I would emphasize the word could here.
Note: there are three other atrial fibrillation articles in this issue. In an editorial, Stevenson and Stevenson summarize nicely the status of catheter ablation for atrial fibrillation and the potential problems and future approaches. Page reviews the approach to newly diagnosed atrial fibrillation. And there is an article on outpatient treatment of recent-onset AF with the “pill-in-the-pocket” approach.