Relationship between age and maximal heart rate in atrial fibrillation

The negative relationship between age and peak exercise heart rate (HR) has been well demonstrated in healthy people with sinus rhythm. The prediction of maximal HR using Astrand’s formula (220 – age) has been widely used as a criterion for achieving maximal exertion in settings of exercise testing or as an indicator of chronotropic incompetence. In terms of atrial fibrillation, however, the maximal predicted HR remains unknown, and the target of end of exercise testing has depended on the tester’s discretion in clinical practice. We previously reported that patients with atrial fibrillation have more increased HR during exercise compared with those with sinus rhythm in symptom-limited maximal exercise testing. Therefore, we assumed that maximal HR in atrial fibrillation should be considered differently from that in sinus rhythm. This study aimed to investigate whether this relationship between age and maximal HR during exercise and its regression equation differs between atrial fibrillation and sinus rhythm. Among 3357 patients who underwent symptom-limited maximal cardiopulmonary exercise testing with ergometer (CPET) at our hospital between 2004 and 2016, excluding patients who had atrioventricular block/sick sinus syndrome/pacemaker (n1⁄4 466), structural heart diseases and/or HR lowering drugs including digitalis/Ca channel blocker/b-blocker (n1⁄4 1722), we analyzed a total of 1169 patients: 163 atrial fibrillation patients and 1006 sinus rhythm patients. None of the patients changed cardiac rhythm during CPET. This study was approved by the Institutional Review Board of the Cardiovascular Institute. CPET was performed using a cycle ergometer and consisted of 4min of rest, 4min of warming up followed by a ramp protocol (10–20W/min), and 6min of recovery. All normally distributed data were expressed as mean standard deviation. Linear regression analyses were performed to determine the associations among variables. The slopes of regression lines were compared using analysis of covariance (ANCOVA). Multivariate regression analysis was used to identify significant independent determinants for the age-related decline in peak exercise HR. To do so, only those variables related to peak exercise HR, age, sex and peak oxygen uptake (VO2) were entered into the model. The statistical significance was set at p< 0.05. The patients with atrial fibrillation were older (60 11 vs. 54 15 years), had a higher body mass index (24.6 3.4 vs. 23.1 3.5), had a lower female proportion (male: 89% vs. 55%), had a lower peak VO2 (21.7 4.1 vs. 23.8 6.6mL kg min), and a higher VE/VCO2 slope (30.4 5.3 vs. 28.8 5.8). The prevalence of hypertension and diabetes mellitus were similar (hypertension; 32% vs. 28%, diabetes 12% vs. 11%). In terms of HR, both resting and peak exercise HRs were higher in patients with atrial fibrillation than those in patients with sinus rhythm (92 21 vs. 76 12 beats/min, 193 33 vs. 150 21 beats/min, respectively). The peak respiratory gas exchange ratio was similar and greater than 1.1 (1.14 0.8 vs. 1.14 0.7), indicating sufficient exercise volume in both rhythms. Negative linear relationships between age and peak HR were found in atrial fibrillation as well as in sinus rhythm (Figure 1). This relationship was significant even after adjusting for sex, exercise capacity (percent predicted peak VO2) (atrial fibrillation: B1⁄4 –0.780, y-intercept1⁄4 189, p1⁄4 0.005; sinus rhythm: B1⁄4 –0.371, y-intercept1⁄4 135, p< 0.0001). Interactions of peak VO2/sex with the relationship between age and peak HR were not found (peak VO2: atrial fibrillation,