This study published in JAMA Cardiology looked at risk factors for mortality and concluded that exercise recovery is helpful in predicting mortality. The study further investigated whether exercise and other clinical variables have differential associations with mortality outcomes in men and women and assesses whether sex-specific risk scores better estimate all-cause mortality among patients undergoing treadmill testing.
Blood pressure was measured during every stage of the test. Heart rate was recorded from an electrocardiogram printed every minute during the test. Peak estimated metabolic equivalents of task (METs) were calculated from treadmill speed and grade at peak exercise. Chest discomfort during the test was recorded as none, nonlimiting chest pain, or test-limiting chest pain. Rate-pressure product (RPP) was calculated as the product of heart rate and systolic blood pressure. A ΔRPP was calculated as RPP at peak exercise minus RPP at rest. Heart rate recovery (HRR) was calculated as peak exercise heart rate minus heart rate at 1 minute after exercise.
Patients were given a standard walking recovery for tests involving electrocardiography only, technetium imaging, or metabolic stress testing. For patients undergoing stress echocardiography, a supine recovery immediately after exercise was used. Therefore, HRR at 1 minute was classified as abnormal if 12 or fewer beats/min for patients undergoing upright recovery and abnormal if 18 or fewer beats/min in patients undergoing stress echocardiography.5,11,12 Chronotropic reserve index was calculated as (Peak heart rate – resting heart rate)/[(220 – age) – resting heart rate] and was considered abnormal if no greater than 0.8 for patients not taking a β-blocker and abnormal if at least 0.62 for patients taking a β-blocker. In patients who did not undergo a Bruce protocol, the estimated METs achieved by each patient were converted to minutes per the Bruce protocol before calculation of the DTS. The DTS was calculated as Exercise time – (5 × maximum ST-segment depression) – (4 × treadmill chest pain index). Treadmill chest pain was scored from 0 to 2, with 0 representing no chest pain; 1, nonlimiting chest pain; and 2, chest pain for which the exercise test was terminated.2
In a large cohort of patients who underwent treadmill testing, we have demonstrated a differential effect of exercise variables and clinical risk factors on overall mortality according to sex. The sex-specific risk scores outperform previous risk stratification tools and help to identify patients at the highest risk for death. To facilitate clinical use of these sex-specific risk scores, we have developed an online calculator to estimate 10-year mortality (http://www.clevelandclinic.org/lp/hvi-tools/10YearMortality.html). Even when accounting for multiple comorbidities, exercise capacity was still the predominant risk factor in men and women. This online calculator can be used by physicians and patients to not only assess prognosis but also emphasize the importance of exercise, even in the presence of other cardiovascular risk factors.