Exercise capacity at submaximal heart rate and prognosis.

Area of Science:

• Cardiology
• Exercise Physiology
• Preventive Medicine

Background:

• Submaximal exercise testing is valuable for patients unable to perform maximal tests.
• Previous research indicated a potential link between low workload at 100 beats/minute heart rate (HR(100)) and increased cardiovascular (CV) mortality risk.
• This study investigated the prognostic significance of METs achieved at HR(100) (METs(100)) in patients referred for treadmill testing.

Purpose of the Study:

• To evaluate the prognostic value of METs(100) in predicting cardiovascular mortality.
• To compare the predictive power of METs(100) with maximal exercise capacity and Duke Treadmill Score (DTS).

Main Methods:

• A cohort of 1446 patients (56+/-12 years, 76% female) without heart failure or beta-blocker treatment was studied between 1997 and 2004.
• Cardiovascular mortality was tracked over a mean follow-up of 7.0+/-2.3 years.
• Cox regression models were used to assess predictors of CV mortality.

Main Results:

• During follow-up, 35 (2.5%) patients died from CV causes. Non-survivors were older, with higher rates of diabetes, coronary artery disease, and stroke.
• Non-survivors exhibited lower DTS and maximal exercise capacity (METs).
• METs(100) and %HR reserve achieved at HR(100) were higher in non-survivors, but age-adjusted METs(100) was not a significant predictor of CV mortality. Each one MET increase in exercise capacity was associated with a 17% increase in survival (HR=0.83).

Conclusions:

• In this patient population, METs at HR(100) did not emerge as a significant predictor of cardiovascular mortality.
• Maximal exercise capacity and DTS demonstrated significant prognostic value for CV mortality.
• Submaximal measures at a fixed heart rate may not be as reliable as maximal exercise capacity for risk stratification.