Cardiorespiratory fitness (CRF) and heart rate recovery (HRR) can be major predictors of sudden cardiac death (SCD) independent of left ventricular ejection factor (LVEF) in patients undergoing clinical exercise testing. They can also be significant prognostic factors for SCD in patients with even slightly reduced or normal LVEF, according to study results published in Heart.
The Finnish Cardiovascular Study was a prospective clinical study of patients who were referred to clinical exercise testing from 2001 to 2008 and who continued follow up until December 2013. The study included 3776 patients without pacemakers who underwent maximal or submaximal exercise testing with cycle ergometers.
The mean age of the study population was 55.7±13.1 years; 60.6% were male. Investigators used a maximal work level to estimate CRF in metabolic equivalents and defined heart rate recovery as the reduction in heart rate 1 minute after maximal exertion. They measured LVEF in 71.4% of the patients for clinical indications and considered SCD the final endpoint of the study, confirmed according to death certificates.
During a median follow-up of 9.1 years, the researchers recorded 534 (14.1%) deaths, with 98 (18.4%) deaths classifiable as SCDs and 436 (81.6%) deaths listed as other causes. They said that both CRF and HRR were associated with the risk for SCD throughout the study population (hazard ratio [HR] 0.47; 95% CI, 0.37-0.59 and HR 0.57; 95% CI, 0.48-0.67, respectively).
Researchers also noted that CRF and HRR are important predictors of SCD regardless of LVEF in patients who were going through the process of clinical exercise testing; CRF and HRR were linked with a risk for SCD in patients with normal or slightly reduced LVEF (>35%).
One limitation of this study is that rather than measuring LVEF systematically at the time of the exercise tests, researchers collected LVEF data only in patients with a clear clinical indication and extracted the information from patients’ records later.
Investigators of the study concluded a significant association exists between CRF and HRR with SCD, and recommended further studies to verify the actual clinical implications of CRF and HRR when considering primary prevention of SCD.
Hernesniemi JA, Sipilä K, Tikkakoski A, et al. Cardiorespiratory fitness and heart rate recovery predict sudden cardiac death independent of ejection fraction [published online August 17, 2019]. Heart. doi:10.1136/heartjnl-2019-315198