chronotropic index
A standardized measure of heart rate response to exercise, calculated as the percentage of heart rate reserve utilized at a given workload.
Full Definition
The chronotropic index quantifies the adequacy of heart rate response during exercise testing by comparing the actual heart rate achieved to the predicted maximal heart rate response. Calculated as [(peak heart rate - resting heart rate) ÷ (220 - age - resting heart rate)] × 100, it normalizes heart rate response for age and resting heart rate. A chronotropic index below 80% at peak exercise suggests chronotropic incompetence, indicating impaired heart rate response that may limit exercise capacity. In sports cardiology, this index helps differentiate between cardiac and non-cardiac causes of exercise intolerance and assists in evaluating the significance of heart rate responses in athletic populations.
Usage
Usage note: Express as percentage; distinguish from other chronotropic measures; specify calculation method.
In Context
- "The athlete's chronotropic index of 65% indicated significant chronotropic incompetence despite achieving excellent exercise capacity through enhanced stroke volume." — Exercise stress test interpretation
- "A normal chronotropic index of 95% helped rule out heart rate limitation as the cause of the runner's reduced performance." — Sports cardiology consultation