Fitness, Exercise, and Coronary Calcification
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Article, see p 1888
Both higher coronary artery calcification (CAC) scores and reduced cardiorespiratory fitness (CRF) are independently strong predictors of future cardiovascular events. CAC is a direct measure of coronary atherosclerosis, the cause of most cardiovascular events. CRF, often measured by exercise treadmill time, is an estimate of maximal oxygen uptake and a surrogate measure of cardiac stroke volume. Rearranging the Fick equation demonstrates that maximal oxygen uptake is the product of cardiac output (heart rate × stroke volume) and the arterial-venous O2 difference. Because heart rate is largely age-determined and the arterial-venous O2 difference varies little among healthy individuals, maximal oxygen uptake, and therefore CRF, are proxies for stroke volume and cardiac performance.
Consequently, it is not surprising that Radford and colleagues1 in this issue of Circulation demonstrate that higher levels of CRF are associated with decreased cardiovascular events across the spectrum of CAC scores. These authors followed 8425 men without cardiovascular disease, who had CRF and CAC scores determined at baseline and followed for an average of 8.4 years. Both total cardiovascular events (cardiovascular death, myocardial infarction, stroke, and coronary revascularization) as well as “hard” cardiovascular events (death, myocardial infarction, and stroke) were analyzed. This is an important issue in CAC studies because high CAC scores could prompt testing and revascularization procedures. Subjects were divided into 4 groups based on CAC Agatston unit scores of 0, 1 to 99, 100 to 399, and ≥400. Only the results for men were analyzed because too few cardiovascular events occurred in women. CRF was measured in metabolic …