Rhythm control was not a superior treatment strategy compared with rate control for patients with atrial fibrillation (AF), according to analyses of the ORBIT-AF registry, published in JACC: Clinical Electrophysiology.1In addition, higher body mass index (BMI) was associated with similar or better outcomes compared with normal BMI.2
The registry was designed to examine differences between rhythm and rate control in various cardiovascular outcomes, as well as the effect of BMI on AF.1,2
A total of 10 135 patients were enrolled between June 2010 and August 2011 from 176 US practices. After adjusting for exclusion criteria (eg, patients with <6 months life expectancy or AF due to reversible causes), 6988 patients were included in the first analysis.1 Follow-up data were collected every 6 months and continued through 24 to 36 months for those patients.
The primary outcomes were defined as all-cause death, cardiovascular death, first cardiovascular hospitalization, cardiovascular hospitalization or death; first stroke, non-central nervous system (CNS) systemic embolism or transient ischemic attack (TIA); composite of death, stroke, non-CNS embolism and TIA; new-onset heart failure; and first major bleeding.1
Approximately 41% (n=2858) of patients were treated with rhythm control and 60% (n=4130) with rate control.1 Overall, patients in the rhythm control group were younger and had a slightly lower prevalence of hypertension, diabetes, chronic kidney disease, and vascular disease, among other comorbidities. These patients were also less likely to have implanted pacemakers and have diagnoses of cardiomyopathy. The rhythm control group, however, had a higher proportion of paroxysmal AF, higher European Heart Rhythm Association symptom class, and were more likely to have had previous catheter ablation.1
Patients in the rhythm control group had lower all-cause death (P<.0001), lower cardiovascular death (P=.015), fewer first stroke/non-CNS systemic embolization/TIA (P=.028), and fewer first major bleeding events (P=.0039), in unadjusted analyses. There was no statistical difference in new-onset heart failure between the 2 treatment groups (P=.28). However, the rhythm control group had higher rates of a first cardiovascular hospitalization (P=.0006). This particular clinical outcome was the only statistically significant difference between the 2 groups (hazard ratio [HR]: 1.24; confidence interval [CI]: 1.10-1.39; P=.0003). Meanwhile, the adjusted relative hazard of composite end point of death, stroke, non-CNS embolism, and TIA was 0.90 (CI: 0.77-1.06; P=.20).1
“Rhythm control patients experience more cardiovascular hospitalizations, possibly related to elective hospitalizations for changes in antiarrhythmic drug regimen or procedures (eg, cardioversion, catheter ablation),” researchers wrote. “Therefore, these findings support current guideline recommendations that the primary indication for rhythm control therapy is for the reduction of symptoms and improvement in quality of life.”1
In the BMI analysis, researchers included 9606 patients from the original study population, stratified into 5 categories: underweight (<18.5 kg/m2; <1% of patients), normal weight (18.5 to <25 kg/m2; 22% of patients), overweight (25.0 to <30kg/m2; 33% of patients), class I obese (30.0 to <35 kg/m2; 23% of patients), class II obese (35 to <40 kg/m2; 12% of patients), and class III obese (≥40 kg/m2; 10% of patients).2 These patients were followed up for 2 years. Higher BMI categories had higher incidences of diabetes, hypertension, and obstructive sleep apnea.2
All-cause mortality rates decreased in a near-linear manner across increasing BMI categories, with the highest rate in the normal weight group (8.28 per 100 patient years) and the lowest in the class III obesity group (3.81 per 100 patient years).2 The lowest risk for mortality was observed in the class I obese group, after multivariable adjustment compared with the normal weight group (HR: 0.65; 95% CI: 0.54-0.78). The risk-adjusted hazard of mortality was 7% lower (HR: 0.93; 95% CI: 0.89-0.98) for every 5-kg/m2 increase in BMI.2
Class II and III obese groups also had lower risks for stroke/TIA/non-CNS embolism on unadjusted analysis (class II obese HR: 0.38; 95% CI: 0.24-0.60; class III obese: HR: 0.38; 95% CI: 0.23-0.63).2
Researchers noted that the obesity paradox has been reported in other cardiovascular diseases—heart failure, coronary artery disease, and acute coronary syndromes—but very few studies have examined the association between BMI and AF.2
“[A] potential explanation for the observed obesity paradox is the significant BMI based differences in the proportional use of different AF management strategies in our study population,” researchers wrote. “It is possible that overweight/obese patients with AF present at a younger age, are more symptomatic and thus, more likely to receive and tolerate these evidence-based disease modifying therapies.”2
Both analyses suggest further research is needed to properly assess affects of different AF therapies (eg, catheter ablation vs antiarrhythmic drugs) on different patient populations.1,2
- Noheria A, Shrader P, Piccini JP, et al; for the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) investigators and patients. Rhythm control vs rate control and clinical outcomes in patients with atrial fibrillation: results from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF). JACC Clin Electrophysiol. 2016. doi: 10.1016/j.jacep.2015.11.001.
- Pandey A, Gersh BJ, McGuire DK, et al. Association of body mass index with care and outcomes in patients with atrial fibrillation: results from the ORBIT-AF registry. JACC Clin Electrophysiol. 2016. doi:10.1016/j.jacep.2015.12.001.