By David C. Fiore, MD

Professor of Family Medicine, University of Nevada, Reno

Dr. Fiore reports no financial relationships relevant to this field of study.

SYNOPSIS: Recognizing the many years of data linking cardiorespiratory fitness to cardiovascular and overall mortality, the American Heart Association says cardiorespiratory fitness should be measured or estimated routinely in patients and added to cardiovascular risk calculators.

SOURCE: Ross R, Blair SN, Arena R, et al. Importance of assessing cardiorespiratory fitness in clinical practice: A case for fitness as a clinical vital sign: A scientific statement from the American Heart Association. Circulation 2016;134:e653-e699.

Cardiovascular disease (CVD) remains the leading cause of death and morbidity in the United States.1 Although it is well established that cardiorespiratory fitness (CRF) is correlated with cardiovascular and all-cause mortality, the Atherosclerotic Cardiovascular Disease (ASCVD) Risk Calculator released jointly by the American College of Cardiology (ACC) and the American Heart Association (AHA) does not include CRF in its calculations. Increasing CRF also has been shown to improve cardiovascular and all-cause mortality. As stated by the researchers, this scientific statement by the AHA attempts to review the “current knowledge related to the association between CRF and health outcomes, increase awareness of the added value of CRF to improve risk prediction, and suggest future directions in research.”2

The first section of the paper examined CRF and its relation to health outcomes. In their review of studies going back to the 1950s, the authors found a consistent correlation between CRF and health outcomes. They found that CRF was as strong a predictor of mortality as diabetes mellitus, smoking, hypertension, and dyslipidemia. The authors also discovered that CRF levels of < 5 METs were associated with a high risk for mortality, and CRF levels > 8 METs were associated with improved survival. Importantly, the authors found that most of the benefit of increased CRF fitness occurred by increasing from the least fit (< 5 METs) to the not least fit (> 8 METs), and that small increases in CRF (1-2 METs) are associated with 10-30% reductions in mortality. The second section looked at CRF as a predictor of other CVD outcomes and found that CRF is a strong predictor of outcomes such as heart failure, stroke, and surgical outcomes.

The authors then reviewed and discussed the application of CRF to reclassification of cardiovascular risk. They reported that adding CRF to traditional risk factors “significantly improves reclassification of risk for adverse outcomes” and that “traditional risk scores (such as Framingham risk score) are enhanced by adding CRF.”

Turning their attention to assessing CRF, the authors reported that cardiopulmonary exercise testing (CPX) is used most frequently in studies, is the ideal testing method, and they believe it is now feasible to do in clinical practice. This typically includes a calculation of peak VO2, which then can be used to determine METs. Because not all practices will be equipped to perform CPX, the authors reviewed other methods of determining CRF. These methods included maximal and sub-maximal exercise stress testing (EST) as well as estimating CRF from non-exercise equations. They concluded that these non-exercise equations may be “reasonably accurate” but should not replace “objective assessment of CRF, especially in some at-risk patient populations” (not defined).

Looking at the effect of exercise on CRF, the report concluded that “a wide variety of endurance-type physical activity regimens produce clinically significant increases in CRF (i.e., 1 MET) in most adults.” The authors also reported that the less fit a person is, the lower the intensity and/or duration of activity needed to produce a clinically significant benefit (1 MET).

The authors concluded that “the inclusion of CRF measurement or estimation in routine practice affords clinicians with a vitally important opportunity to improve patient management and, more importantly, patient health.”

COMMENTARY

Starting when I was in medical school in the 1980s, I’ve been taught “being fit” lowered one’s risk of heart attacks and death. So it’s been puzzling that CRF has not been used in estimates of cardiovascular risk, and this AHA statement is very welcome. After counseling patients that they should exercise more, patients sometimes ask how much is needed to lower their risk of a heart attack. I’ve been unable to answer their question with much confidence. I usually fudge my answer with something like, “We don’t have concise estimates of how much you can lower your cardiovascular risks, but if you exercise regularly, it’s likely to lower your risk as much as medication.” This is consistent with data and conclusions from this report and studies such as the Henry Ford “FIT” project that suggested there is at least a 10% reduction in all-cause mortality for every 1 MET improvement in CRF.3 Looking at it another way, if someone is very fit (> 9 METs), his or her mortality risk is less than half that of a similar person who is unfit (< 6 METS). It’s nice to see that the AHA is finally recognizing this deficit and taking concrete steps to address it. Unfortunately, until risk calculators are developed and validated using CRF as an additional risk factor, clinicians are on their own in figuring out how to use CRF to adjust overall cardiovascular risk.

REFERENCES

  1. Heron M. Deaths: Leading Causes for 2014. Natl Vital Stat Rep 2016;65:1-96.
  2. Ross R, Blair SN, Arena R, et al. Importance of assessing cardiorespiratory fitness in clinical practice: A case for fitness as a clinical vital sign: A scientific statement from the American Heart Association. Circulation 2016;134:e653-e699.
  3. McAuley PA, Blaha MJ, Keteyian SJ, et al. Fitness, fatness, and mortality: The FIT (Henry Ford Exercise Testing) Project. Am J Med 2016;129:960-965.