Guidelines for the treatment of atrial fibrillation (AF) suggest that, where rate control is the preferred management stratey, a resting heart rate of less than 80 bpm and an exercise heart rate of less than 110 bpm should be targeted.  These values are based on the belief that lower heart rates will result in fewer symptoms, are likely to be associated with better cardiovascular function because of longer diastolic filling times and more satisfactory hemodynamics, and are associated with a lower risk of tachycardia-related cardiomyopathy.  While these assumptions may be supported by some epidemiological and echocardiographic data, there is no prospective evidence to guide clinicians and in the RACE (RAte Control Efficacy) II trial the authors set out to explore this question.
In this prospective, multi-centre study, 614 patients with permanent atrial fibrillation were recruited and randomly assigned to either a strict rate control strategy (resting heart rate <80 bpm and heart rate during moderate exercise <110 bpm) or a lenient strategy (resting heart rate <110 beats per minute).  Decisions on therapy were left to individual physicians, but there were high rates of beta-blocker and calcium antagonist use in both groups with individuals in the strict control group generally on higher doses to achieve targets.  The primary outcome was a composite of death from cardiovascular causes, hospitalization for heart failure, and stroke, systemic embolism, bleeding, and life-threatening arrhythmic events after a follow up of at least 2 years and a maximum of 3.
The results showed no benefit from the strict strategy with the incidence of the primary outcome of 14.9% versus 12.9% in the lenient-control group (90% CI, −7.6 to 3.5; P<0.001 for the prespecified noninferiority margin).  The frequencies of the components of the primary outcome were similar in the two groups and symptoms and adverse events were also similar.  Moreover, patients in the lenient-control group met the heart-rate targets with fewer total visits reducing resource use and clinic time.
Whilst there are limitations to the study, including recruitment of a relatively young and fit AF population, a preponderance of men (while women are known to have a greater symptom burden) and also a limited follow-up that may not be able to detect the long term benefits of a strict rate control strategy, this is the first work of its kind to examine an important question in clinical cardiology.

Conclusions:
In this randomised controlled trial, an aggressive rate control regime (resting heart rate <80 bpm) in patients with atrial fibrillation appeared to have no benefits over a more lenient one (resting heart rate <110bpm).

•    Lenient versus strict rate control in patients with atrial fibrillation. Van Gelder IC, Groenveld HF, Crijns HJ, Tuininga YS, Tijssen JG, Alings AM, Hillege HL, Bergsma-Kadijk JA, Cornel JH, Kamp O, Tukkie R, Bosker HA, Van Veldhuisen DJ and Van den Berg MP for the RACE II Investigators N Engl J Med. 2010 Apr 15;362(15):1363-73.