Heart rate recovery, Duke treadmill score, exercise capacity, and chronotropic index are useful prognostically in patients similar to studied populations. Longevity has been found to be related to how well one can exercise, one's ability to increase one's heart rate and blood pressure with exercise and lower one's heart rate and blood pressure quickly after exercise stops because of the restoration of vagal tone. Other factors, such as exercise-induced angina and ST depression are incorporated into the Duke treadmill score.
Normal values for these parameters are indicated on our Sample Stress Echo Report. One minute heart rate recovery, or the fall in heart rate after exercise, should be at least 12 beats per minute during an easy walking cool down or 18 beats per minute if the patient lies supine immediately after stress echocardiography. An attenuated blood pressure response is < 20 to 30 mmHg rise in systolic blood pressure with exercise or ratio of blood pressure at peak exercise to blood pressure at rest of < 1.2.
Other parameters that impact prognosis include increased resting heart rate (>90 bpm), a history of congestive heart failure or myocardial infarction, frequent ventricular ectopy or ventricular tachycardia with exercise, exercise-induced bundle branch block, or a > 10 mm of mercury drop in systolic blood pressure compared to the previous stage or the baseline blood pressure.
The above parameters have been studied in specific groups, which may or may not apply to your patient. Typically, patients have been studied who were being evaluated for possible CAD without a history of previous cardiac catheterization, cardiac surgery, pacemaker, CHF, congenital or valvular disease, uninterpretable EKG or use of digitalis. Use of beta blockers was a reason for exclusion or was a confounding factor in some but not all of the studies. References are listed below are and accessible through the internet for subscribers.
The following definitions are used according to the literature.
Duke Treadmill Score = Exercise time* – 5 X (ST segment deviation#) – 4 X (Angina indexo)
* = Exercise time is based on standard Bruce protocol
# = ST segment deviation is measured 60 to 80 milliseconds after the J point. If the amount of exercise-induced ST-segment deviation is less than 1 mm, the value entered into the score for ST deviation is 0.
o = Angina index is 0 if no exercise angina occurs, 1 if exercise angina occurs, and 2 if angina is the reason the patient stopped exercising.
Interpretation
Score > 5 = Low risk
Score -10 to 4 = Intermediate risk
Score < -10 = High risk
Heart rate reserve = (HR peak – HR rest)/(220-age-HRrest). Normal is > 0.8
Reference List
1. Gibbons et al. ACC/AHA 2002 Guideline Update for Exercise Testing: Summary Article. Circulation 2002;106:1883-1892. www.circulationaha.org
2. Fletcher et al. Exercise Standards for Testing and Training. Circulation 2002;104:1694-1740. www.circulationaha.org
3. Cole et al. Heart-Rate Recovery Immediately After Exercise as a Predictor of Mortality. New Engl J Med 1999:341(18) 1351-1357 www.nejm.org
4. Watanabe et al. Heart Rate Recovery Immediately After Treadmill Exercise and Left Ventricular Systolic Dysfunction as Predictors of Mortality. Circulation 2001;104:1911- 1916. www.circulationaha.org
5. Nishime et al. Heart Rate Recovery and Treadmill Exercise Score as Predictors of Morality in Patients Referred for Exercise ECG. JAMA 2000;284:1932-1398. www.jama.com
6. Lauer et al. Impaired Heart Rate Response to Graded Exercise. Circulation 1996;93:1520- 1526. www.circulationaha.org
7. Myers et al. Exercise Capacity and Mortality Among Men Referred for Exercise Testing. New Engl J Med 2002;346:793-801. www.nejm.org
8. Snader et al. Importance of Estimated Functional capacity as a Predictor of All-Cause Mortality Among Patients Referred for Exercise Thallium Single-Photon Emission Computed Tomography: Report of 3,400 Patients from a Single Center. J Am Coll Cardiol 1997;30:641-648. www.cardiosource.com
9. Lauer et al. Association of Chronotropic Incompetence with Echocardiographic Ischemia and Prognosis. J Am Coll Cardiol 1998;32:1280-1286. www.cardiosource.com
10. McHam et al. Delayed Systolic Blood Pressure Recovery After Graded Exercise. J Am Coll Cardiol 1999;34:754-759. www.cardiosource.com
11. Kristal-Boneh E; Silber H; Harari G; Froom P. The association of resting heart rate with cardiovascular, cancer and all-cause mortality. Eight year follow-up of 3527 male Israeli employees (the CORDIS study) Eur Heart J 2000: 21:116-24
