Metabolic equivalents, or METs, are routinely employed as a guide to exercise training and activity prescription and to categorize cardiorespiratory fitness (CRF). There are, however, inherent limitations to the concept, as well as common misapplications. CRF and the patient's capacity for physical activity are often overestimated and underestimated, respectively. Moreover, frequently cited fitness thresholds associated with the highest and lowest mortality rates may be misleading, as these are influenced by several factors, including age and gender. The conventional assumption that 1 MET = 3.5 mL O/kg/min has been challenged in numerous studies that indicate a significant overestimation of actual resting energy expenditure in some populations, including coronary patients, the morbidly obese, and individuals taking β-blockers. These data have implications for classifying relative energy expenditure at submaximal and peak exercise. Heart rate may be used to approximate activity METs, resulting in a promising new fitness metric termed the "personal activity intelligence" or PAI score. Despite some limitations, the MET concept provides a useful method to quantitate CRF and define a repertoire of physical activities that are likely to be safe and therapeutic. In conclusion, for previously inactive adults, moderate-to-vigorous physical activity, which corresponds to ≥3 METs, may increase MET capacity and decrease the risk of future cardiac events.

Despite significant advances in medical technology and pharmacology, cardiovascular disease (CVD) remains a major contributor to health care expenses and the leading cause of death in the United States. Patients with established CVD and their health care providers are challenged with achieving cardiovascular risk reduction to decrease the likelihood of recurrent cardiovascular events. This "secondary prevention" can be achieved, in part, through adherence to prescribed pharmacotherapies that favorably modify major coronary risk factors (ie, hypertension, hypercholesterolemia, diabetes, and obesity). However, lifestyle modification can also be helpful in this regard, providing independent and additive benefits to the associated reductions in cardiovascular morbidity and mortality. Accordingly, physicians and other health care providers should routinely counsel their coronary patients to engage in structured exercise and increased lifestyle physical activity, consume a heart-healthy diet, quit smoking and avoid secondhand smoke, and purposefully address psychosocial stressors that may elevate cardiovascular risk. These lifestyle interventions, either as an adjunct to medication therapy or independently in those patients where medications may be poorly tolerated, cost prohibitive, or ineffective, can significantly decrease cardiovascular mortality and the risk of recurrent cardiac events.

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Unfortunately, too many patients continue to rely on costly coronary revascularization procedures, cardioprotective medications, or both, as first-line strategies to stabilize the course of coronary heart disease. However, these palliative therapies do not address the foundational or most proximal risk factors for coronary disease, that is, unhealthy dietary habits, physical inactivity, and cigarette smoking. Because most acute myocardial infarctions evolve from mild-to-moderate coronary artery stenosis (<70 % obstruction), rather than at the more severe obstructions that are commonly treated with coronary revascularization, these findings help explain the inability to demonstrate a reduction in acute cardiac events in most studies examining coronary artery bypass graft surgery and/or percutaneous coronary interventions. The delivery of comprehensive cardiovascular risk reduction, including exercise-based cardiac rehabilitation as an integral component, offers patients a bona fide treatment intervention to prevent recurrent cardiovascular events and the need for repeated revascularization procedures, while simultaneously providing referring physicians with ongoing surveillance data to potentially enhance their medical management.