1. Prognosis of heart disease patients is associated not only with their exercise capacity, but also the type of exercise protocol used
Evidence Rating: 2 (Good)
Exercise testing is a common prognostic measurement used to assess heart disease patients. Exercise capacity, which represents oxygen uptake during exertion, is measured in units of estimated metabolic equivalents (METs), which represent oxygen consumption at rest. The standard exercise protocol is known as the Bruce protocol, but when patients are unable to meet the physical demands of this, the less demanding non-Bruce protocols used instead. This retrospective cohort study examined whether METs consistently predict prognosis of all-cause mortality, between Bruce and non-Bruce protocols. In total, 120 705 patients were examined, with 74 953 undergoing the Bruce protocol, and 45 752 undergoing a non-Bruce protocol. Those undergoing a non-Bruce protocol were more likely to be women, and were on average 10 years older than those in a Bruce protocol. After adjusting for METs, the results showed that patients undergoing a Bruce protocol were associated with a lower risk of mortality, in comparison to those undergoing the less demanding non-Bruce protocols (Hazards Ratio of 0.67; 95% CI, 0.64-0.72; P < 0.001). For both types of protocols though, higher METs were predictive of lower all-cause mortality (Hazards Ratio of 0.46; 95% CI, 0.44-0.48; P < 0.001). Overall, this shows that METs are not transferable between Bruce and non-Bruce protocols: When METs are equivalent in two protocols, the patient in the less demanding protocol has a higher risk of all-cause mortality. The main implication of this study is that the prognosis of a heart disease patient should not only be based on the METs measured from the exercise testing, but also based on the type of exercise protocol chosen.
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