Cardiorespiratory fitness and heart rate recovery predict sudden cardiac death independent of ejection fraction.

OBJECTIVE: To evaluate whether cardiorespiratory fitness (CRF) and heart rate recovery (HRR) associate with the risk of sudden cardiac death (SCD) independently of left ventricular ejection fraction (LVEF).
METHODS: The Finnish Cardiovascular Study is a prospective clinical study of patients referred to clinical exercise testing in 2001-2008 and follow-up until December 2013. Patients without pacemakers undergoing first maximal or submaximal exercise testing with cycle ergometer were included (n=3776). CRF in metabolic equivalents (METs) was estimated by achieving maximal work level. HRR was defined as the reduction in heart rate 1 min after maximal exertion. Adjudication of SCD was based on death certificates. LVEF was measured for clinical indications in 71.4% of the patients (n=2697).
RESULTS: Population mean age was 55.7 years (SD 13.1; 61% men). 98 SCDs were recorded during a median follow-up of 9.1 years (6.9-10.7). Mean CRF and HRR were 7.7 (SD 2.9) METs and 25 (SD 12) beats/min/min. Both CRF and HRR were associated with the risk of SCD in the entire study population (HRCRF0.47 (0.37-0.59), p<0.001 and HRHRR0.57 (0.48-0.67), p<0.001 with HR estimates corresponding to one SD increase in the exposure variables) and with CRF, HRR and LVEF in the same model (HRCRF0.60 (0.45-0.79), p<0.001, HRHRR0.65 (0.51-0.82), p<0.001) or adjusting additionally for all significant risk factors for SCD (LVEF, sex, creatinine level, history of myocardial infarction and atrial fibrillation, corrected QT interval) (HRCRF0.69 (0.52-0.93), p<0.01, HRHRR0.74 (0.58-0.95) p=0.02).
CONCLUSIONS: CRF and HRR are significantly associated with the risk of SCD regardless of LVEF. © Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.