Exercise Capacity in Patients With Coronary Artery Disease: Does Revascularization Status Matter?

Editor's Note: Commentary based on Hung RK, Al-Mallah MH, McEvoy JW, et al. Prognostic value of exercise capacity in patients with coronary artery disease: the FIT (Henry Ford ExercIse Testing) project. Mayo Clin Proc 2014;89:1644-54.

Background

Cardiorespiratory fitness is strongly associated with lower lifetime risk for cardiovascular morbidity and mortality among healthy adults as well as patients with known coronary artery disease (CAD).1-3 However, the extent to which revascularization status modifies the prognostic value of cardiorespiratory fitness in these patients is not well understood. In this peer-reviewed publication, Hung and colleagues4 report the interaction between cardiorespiratory fitness and revascularization status on cardiovascular outcomes in a cohort of CAD patients referred for exercise testing in routine clinical practice.

Methods

The study included patients with known CAD from the Henry Ford Exercise Testing (FIT) Project who were referred for stress testing between 1991 and 2009. Primary exposure variables of interest included baseline revascularization status and cardiorespiratory fitness estimated in metabolic equivalents (METs) using a treadmill stress test. The primary outcomes of interest included all-cause mortality, myocardial infarction (MI) and downstream revascularization. The investigators used multivariable adjusted Cox regression analysis to calculate the adjusted hazard ratios (HR) for outcomes across different patient groups stratified by baseline revascularization status and cardiorespiratory fitness level.

Results

The study included 9,852 patients (mean age = 61 + 12 years, 31% women), of which 46% were nonrevascularized at baseline. The investigators observed a consistent, inverse association between cardiorespiratory fitness and mortality across all revascularization groups. After multivariable adjustment, one unit greater cardiorespiratory fitness in METs was associated with a significant reduction in mortality risk among both nonrevascularized [HR (95% confidence interval [CI]): 0.87 (0.85 – 0.89)] as well as revascularized patients [HR (95% CI) for percutaneous coronary intervention (PCI): 0.87 (0.85 – 0.90); HR (95% CI) for coronary artery bypass graft (CABG): 0.86 (0.84 – 0.89). In contrast, cardiorespiratory fitness was associated with a lower risk for MI only in the revascualrized group [HR per 1-MET increase (95% CI) PCI: 0.88 (0.84 – 0.92); CABG: 0.93 (0.90 – 0.97)] but not in the nonrevascularized group [HR per 1-MET increase (95% CI): 0.98 (0.96 – 1.01)]. Furthermore, in each MET category, the nonrevascularized group had similar mortality risk but higher MI risk as compared to the PCI and CABG group (P <0.05)

Conclusion

Cardiorespiratory fitness is a strong determinant of survival in this cohort of patients with CAD irrespective of their revascularization status.

Commentary/Perspective

The data presented by Hung and colleagues confirms the strong, inverse association between cardiorespiratory fitness and survival among patients with CAD.3,5,6 The magnitude of reduction in mortality risk associated with 1 unit greater cardiorespiratory fitness in METs (13%) observed in this study is comparable to that reported previously in healthy individuals as well as patients with CAD.3 These findings reinforce the importance of cardiorespiratory fitness as a prognostic indicator as well as a therapeutic target in patients with stable CAD.

A more interesting finding observed in this study was the interaction between cardiorespiratory fitness and baseline revascularization status on risk for MI. The investigators observed a significant reduction in risk of MI with higher levels of cardiorespiratory fitness only in revascularized patients (PCI and CABG groups) and not in nonrevascularized groups. The mechanism underlying this lack of association in the nonrevascularized group is unclear. It is plausible that in patients with less severe coronary disease, the cardiovascular benefits of higher levels of cardiorespiratory fitness may be more related to its favorable effects on cardiac structure and function and not on recurrent MI.7 This is supported by recent studies from our group that have shown a stronger association between fitness and heart failure risk as compared with MI risk among healthy individuals.1 Furthermore, recent studies from the Coronary Artery Risk Development in Young Adults Study (CARDIA)8 and Cooper Center Longitudinal Study9 have not shown significant association between cardiorespiratory fitness and coronary artery calcium among healthy individuals, the latter of which has been associated with MI.10

Taken together, the present study confirms the central prognostic role of cardiorespiratory fitness in patients with CAD and provides additional support for the role of cardiac rehabilitation in this patient population. Furthermore, it also provides additional evidence in support of the hypothesis that lower mortality risk associated with higher levels of cardiorespiratory fitness may be mediated by nonatherosclerotic mechanisms.

References

  1. Berry JD, Pandey A, Gao A, et al. Physical fitness and risk for heart failure and coronary artery disease. Circ Heart Fail 2013;6:627-34.
  2. Gupta S, Rohatgi A, Ayers CR, et al. Cardiorespiratory fitness and classification of risk of cardiovascular disease mortality. Circulation 2011;123:1377-83.
  3. Myers J, Prakash M, Froelicher V, et al. Exercise capacity and mortality among men referred for exercise testing. N Engl J Med 2002;346:793-801.
  4. Hung RK, Al-Mallah MH, McEvoy JW, et al. Prognostic value of exercise capacity in patients with coronary artery disease: the FIT (Henry Ford ExercIse Testing) Project. Mayo Clin Proc 2014;89:1644-54.
  5. Vanhees L, Fagard R, Thijs L, Staessen J, Amery A. Prognostic significance of peak exercise capacity in patients with coronary artery disease. J Am Coll Cardiol 1994;23:358-63.
  6. Keteyian SJ, Brawner CA, Savage PD, et al. Peak aerobic capacity predicts prognosis in patients with coronary heart disease. Am Heart J 2008;156:292-300.
  7. Brinker SK, Pandey A, Ayers CR, et al. Association of cardiorespiratory fitness with left ventricular remodeling and diastolic function: the Cooper Center Longitudinal Study. JACC Heart Fail 2014;2:238-46.
  8. Lee CD, Jacobs DR, Jr., Hankinson A, Iribarren C, Sidney S. Cardiorespiratory fitness and coronary artery calcification in young adults: The CARDIA Study. Atherosclerosis 2009;203:263-8.
  9. DeFina L, Radford N, Leonard D, Gibbons L, Khera A. Cardiorespiratory fitness and coronary artery calcification in women. Atherosclerosis 2014;233:648-53.
  10. McEvoy JW, Blaha MJ, DeFilippis AP, et al. Coronary artery calcium progression: an important clinical measurement? A review of published reports. J Am Coll Cardiol 2010;56:1613-22.

Clinical Topics: Cardiac Surgery, Diabetes and Cardiometabolic Disease, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Aortic Surgery, Cardiac Surgery and Heart Failure, Acute Heart Failure, Interventions and Coronary Artery Disease

Keywords: Adult, Confidence Intervals, Coronary Artery Bypass, Coronary Artery Disease, Coronary Disease, Exercise Test, Female, Heart Failure, Longitudinal Studies, Metabolic Equivalent, Metabolic Syndrome X, Myocardial Infarction, Regression Analysis, Research Personnel, Percutaneous Coronary Intervention


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