Cardiorespiratory fitness predicts risk for sudden cardiac death
MedWire News: Low cardiorespiratory fitness is strongly associated with increased risk for sudden cardiac death (SCD) in men, a population study has found.
However, the clinical relevance of the finding is less clear cut, since cardiorespiratory fitness did not improve on the ability of conventional risk factors to predict the likelihood for SCD.
This "well-done but negative study" serves as a "potent reminder of the need for basic, translational, and clinical research to redefine the paradigms for confronting this ongoing public health scourge," said Michael Lauer (National Institutes of Health, Bethesda, Maryland, USA) in an editorial accompanying the study.
The study was undertaken by Jari Laukkanen (University of Eastern Finland, Kuopio) and co-workers and included information on 2368 men aged 42-60 years who were generally healthy at enrolment in a population-based study.
At baseline, the men underwent a symptom-limited exercise tolerance test with direct measurement of respiratory gases. They were then followed-up for 17 years, during which time there were 146 SCDs.
Writing in the Journal of the American College of Cardiology, the authors report that each 1-metabolic equivalent (MET) increase in maximal oxygen consumption predicted a 22% reduction in the risk for SCD. This association was highly statistically significant, with a p-value of <0.001.
The team then scrutinized this relationship further by determining the ability of maximal oxygen consumption to improve SCD risk-prediction when included alongside established risk factors.
They found that maximal oxygen consumption led to a modest, albeit significant, increase in the ability to distinguish between higher- and lower-risk individuals (ie, discrimination), with the C-index increasing from 0.760 to 0.767.
The same was true for the ability to correctly reassign risk (ie, reclassification), with the C-index increasing from 0.760 to 0.766, a nonsignificant change.
Indeed, the team found that including maximal oxygen consumption alongside standard risk factors actually increased the likelihood of misclassifying SCD risk, with a net reclassification index of -0.018.
Laukkanen et al write: "Low levels of cardiorespiratory fitness may provide valuable information when the future risk of SCD is estimated, but may not provide incremental utility over prediction based on traditional risk factors."
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By Joanna Lyford