Background: We previously reported that peak exercise-heart rate (HR) is related to exercise capacity and prognosis in patients with atrial fibrillation (AF). The aim of the study was to investigate the clinical characteristics and prognostic value of the slope of HR versus work load (HR-WR slope) as a parameter for chronotropic ability.
Methods: We analyzed 341 male patients with AF from our observational cohort who performed symptom-limited maximal cardiopulmonary exercise testing. Divided them into two groups by median value of HR-WR slope, we compared the clinical characteristics and the prognosis. The endpoint was set as cardiovascular (CV) events; cardiovascular death, hospitalization for heart failure (HF), acute coronary syndrome and cerebral infarction (CI).
Results: HR-WR relationship was linear and HR-WR slope was calculated as the slope of linear regression line between HR and WR during exercise. HR-WR slope was normally distributed and positively associated with % predicted peak VO2. Organic heart disease was more prevalent in the lower HR-WR slope. During the median follow up period of 3 years, the CV events were observed in 35 patients; 7 CV death, 21 HF hospitalization, 1 ACS and 6 CI. The incidence of CV events was negatively associated with HR-WR slope. Kaplan-Meier curve showed that the binary HR-WR slope well discriminated the risk (Figure). Multivariate Cox regression analysis showed the strong relation of binary HR-WR slope to the endpoint independently of age, HR lowering drugs and the presence of organic heart disease.
Conclusions: HR-WR slope would be a feasible prognostic predictor in AF even when maximal exercise test is not applied.