Relationship Between Percent Heart Rate Reserve and Percent MET Reserve in Patients with Heart Disease on Beta Blockade Therapy

Abstract

In the absence of appropriate heart rate (HR) data to prescribe exercise due to a change in beta blocker therapy, an acceptable alternative is to utilize MET levels. It has been reported that percent Heart Rate Reserve (HRR) closely approximates the same percentage for both the % VO2 reserve and % MET reserve in individuals with and without heart disease during an exercise test. However, the relationship of % MET reserve to % HRR during actual exercise training in patients taking a beta-adrenergic blocking agent is unknown. PURPOSE: To test the hypotheses that % MET reserve and % HRR during exercise training are significantly and meaningfully related in patients with heart disease on beta blockade. METHODS: A retrospective assessment of patients (n=39; 92% male, 46% Caucasian, age 53± 5 years) who participated in cardiac rehabilitation (CR) was completed by conducting a manual chart review. Included in the study were men and women age 40–60 yr with a history of heart disease and on beta blockade therapy. Peak MET and HR were measured during a symptom limited maximal stress test. Percent MET reserve was calculated based on the exercise training work rates measured in CR within two weeks of the stress test which was performed at a similar time of day as their exercise in CR. Linear regression was used to evaluate the relationship between % MET and % HRR reserve. RESULTS: Mean peak MET and peak HR were 6.2± 1.3 and 128± 21beats/min, respectively. The correlation between % MET reserve and % HRR reserve was calculated at r=0.66 (p<0.01). The standard error of the estimate (SEE) was 14% (e.g., a workload set at 60% MET reserve would result in a HRR of 46–74%). CONCLUSION: Contrary to our hypothesis, % MET reserve and % HRR during exercise training, although significantly related, may not be clinically meaningful based on the large SEE. This supports the importance of also using rating of perceived exertion when guiding exercise intensity. A prospective trial is needed to better define the MET reserve/HRR relationship and identify sources of variability, before it is used as a method to prescribe exercise in patients with heart disease on beta blockade therapy.