It is recommended that patients with myocardial infarction (MI) be prescribed exercise by target heart rate (HR) at the anaerobic threshold (AT) via cardiopulmonary exercise testing (CPX). Although percent HR reserve using predicted HR max (%HRR pred ) is used to prescribe exercise if CPX or an exercise test cannot be performed, %HRR pred is especially difficult to use when patients take β-blockers. We devised a new formula to predict HR at AT (HR AT ) that considers β-blocker effects in MI patients and validated its accuracy. Methods: The new formula was created using the data of 196 MI patients in our hospital (derivation sample), and its accuracy was assessed using the data of 71 MI patients in other hospitals (validation sample). All patients underwent CPX 1 mo after MI onset, and resting HR, resting systolic blood pressure (SBP), and HR AT were measured during CPX.
Results:The results of multiple regression analysis in the derivation sample gave the following formula (R 2 = 0.605, P < .001): predicted HR AT = 2.035 × (≥65 yr:−1, <65 yr:1) + 3.648 × (body mass index <18.5 kg/m 2 :−1, body mass index ≥18.5 kg/m 2 :1) + 4.284 × (β1-blocker(+):−1, β1-blocker(−):1) + 0.734 × (HR rest ) + 0.078 × (SBP rest ) + 36.812. This formula consists entirely of predictors that can be obtained at rest. HR AT and predicted HR AT with the new formula were not significantly different in the validation sample (mean absolute error: 5.5 ± 4.1 bpm). Conclusions: The accuracy of the new formula appeared to be favorable. This new formula may be a practical method for E xercise training is associated with reduced cardiovascular events and mortality after acute myocardial infarction (MI), and many guidelines recommend exercise training for MI patients. 1,2 It is very important to determine the optimum exercise intensity to prescribe safe and effective training. 3 Exercise prescription using target heart rate (HR) at the anaerobic threshold (AT) via cardiopulmonary exercise testing (CPX) is effective and safe for MI patients. [4][5][6] Although prescribing exercise intensity based on the AT measured by CPX is desirable, it is not yet widely available. It has been recommended to determine the target HR range by 40-70% HR reserve (HRR) using predicted maximum HR (HRR pred ) if gas-exchange analysis data or exercise test data cannot be obtained. 2,7 However, a recent study reported that 41% of patients had their AT identified outside of the 40-70% HRR pred exercise training zone. 8 In addition, HRR pred is considered difficult to use if patients are undergoing β-blocker treatment because β-blockers affect calculations by reducing HR responses at rest and during incremental exercise. 9-11 Thus, it is necessary to establish a practical method to predict HR AT that considers the effects of β-blockers in MI patients.Although both α β-blockers and β1-blockers are frequently prescribed for MI patients due to their effectiveness, 12-14 our previous studies suggested that only β1-blockers strongly decrease HR response during incremental CPX in MI ...