Impact of Utilizing a Women-Based Formula for Determining Adequacy of the Chronotropic Response During Exercise Treadmill Testing

Background: A women-based formula for calculation of age-predicted maximum heart rate [age-predicted maximum heart rate=206-(0.88×age)] was established in asymptomatic volunteer women undergoing treadmill exercise tolerance testing (ETT). We sought to perform a comparison of the performance of this women-based formula for prediction of peak heart rate to the traditional formula [220-age] and our own database-generated prediction formula in a large database of women undergoing ETT. Methods: We performed a retrospective analysis of all consecutive women who underwent symptom-limited Bruce protocol ETT at the Mayo Clinic from 1994 to 2010. Women with known cardiovascular disease or those using beta blockers, calcium channel blockers, or digitalis were excluded. Separate analyses were performed according to symptomatic status. Results: The study included 11,029 women (89.4% Caucasian) with a mean age 52±12 years; 3,632 (33%) were referred specifically for evaluation of symptoms. Age-predicted maximum heart rate calculated by the traditional formula was achieved by 49.7% of women versus 69.9% by the women-based formula with most of the underestimation observed in older women. Average absolute deviation between achieved and predicted peak heart rate (HR) was 10.85±9.18bpm for traditional versus 11.98±9.00 for women-based formulas (dependent t=-16.64, p<0.0001). The linear regression line calculated from our population [HR=201-(0.67×age)] was closer to the women-based formula, both in terms of intercept and slope than the traditional formula. Peak HR was shown to be slightly affected (-2.5bpm) by symptom status at referral, whereas smoking and diabetes more significantly reduced achieved peak HR. Conclusions: The women-based formula underestimated peak HR, especially in older women, but was observed to be closer in both intercept and slope to the regression line determined from our study in this large population of female patients. These sex-unique observations should be taken into account when determining adequacy and targets for ETT in women.