Background: The use of beta-adrenergic blockade (BB) therapy is common among patients with coronary heart disease (CHD), and as a result, these patients often undergo exercise testing while taking these medications. However, evaluation of maximal voluntary effort during exercise testing is often in question because current equations to predict maximum heart rate (HR(max); eg, 220 - age) are based on subjects without heart disease or BB therapy. The purpose of this study was to develop and validate an age-specific equation to predict HR(max) in patients with CHD who are receiving BB therapy.
Methods: We queried the Henry Ford Preventive Cardiology Outcomes database for patients with a history of myocardial infarction or revascularization procedure; preserved left ventricular function; age, 40 to 80 years; sinus rhythm; and a graded treadmill test with a respiratory exchange ratio > or =1.10. Data were split, based on date, such that tests performed between November 1996 and April 2001 were used as the BB prediction equation development group (n = 334; 73% men) and those performed between May 2001 and April 2002 were used as the BB cross-validation group (n = 94; 84% men). Linear regression was used to develop the equation to predict HR(max), based on age, and to calculate the correlation coefficient of the prediction equation among the cross-validation group.
Results: The resultant prediction equation was HR(max) = 164 - 0.7 x age (r2 = 0.13), with a standard error of the estimate of 18 per minute. Among the cross-validation group, mean predicted HR(max) was not significantly different from mean measured HR(max) (P = .7). The mean error of prediction was -0.4 +/- 2.0 per minute (mean +/- SEM), and the correlation was r = 0.38.
Conclusions: This new equation provides a better estimate of HR(max) for patients with CHD receiving BB therapy than previously reported equations. Additional variables may improve the equation but may not be as convenient to use.