A maximal exercise test is often not available for patients in cardiac rehabilitation (CR) and many programs determine a target heart rate (THR) using equations to estimate maximum heart rate (HRmax). The purpose of this study was to describe the % of patients in which a THR based on an estimated HRmax would result in a heart rate (HR) that is consistent with guidelines (i.e., 50%–80% HR reserve) in patients with heart disease (HD) on beta-blockade therapy.
This was a secondary analysis of the iATTEND study; a randomized trial of facility-based only CR vs. hybrid CR. Subjects included in the present analysis had a history of myocardial infarction, coronary revascularization procedure, or heart failure; beta-blockade therapy; and sinus rhythm. Exclusion criteria were heart transplant, atrial fibrillation, implanted pacemaker, and exercise-induced ischemia. Measured HR reserve (maximum - rest) was determined from a symptom-limited maximal exercise test with gas exchange performed on a treadmill. Estimated HRmax was determined using (a) 220 age and (b) a published equation based on patients with HD with beta-blockade (HD BB; 164-0.72xage). % measured HR reserve associated with 60% and 85% estimated HRmax using each equation was compared to guideline recommended intensity of 50%–80% measured HR reserve. Paired sample t-tests were used to compare measured HRmax to the 2 estimates of HRmax.
Among 166 subjects (68% male; age= 59±11 yr [mean±SD]) measured HRmax was 133±21 min 1. Compared to measured, estimated HRmax using 220-age was significantly higher (161±11 min- 1; p<.001) and estimated HRmax using HD-BB was significantly lower (121±8 min-1; p<.001). At 60% of 220-age, 19% of subjects would have been provided a THR that was consistent with guidelines; 72% would have been too low. At 60% of HD-BB, 1% of subjects would have been provided a THR that was consistent with guidelines; 99% would have been too low. At 85% of 220-age, 16% of subjects would have been provided a THR that was consistent with guidelines; 84% would have been too high. At 85% of HD-BB, 36% of subjects would have been provided a THR that was consistent with guidelines; 15% would have been too high.
THR based on % estimated HRmax from 220-age and HD-BB do not provide an exercise training HR target that is consistent with guideline recommendations, thus should not be used to prescribe an exercise intensity in patients with HD on BB therapy.
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