1999.05.17 Risk Stratification in Heart Disease: The Exercise Stress Test
Risk stratification is a major task in the medical management of coronary heart disease. A recent review by David A. Driggers and David Marchant (Postgrad Med, 1-May-1999;105:53) discusses important ways to make the most out of the exercise treadmill test (ETT). First of all, patient selection is important. The treadmill test generally should not be used in patients with:
1. Baseline ECG abnormalities, e.g. bundle branch block
2. Patients on digoxin or beta blockers
3. Patients unable to exercise adequately
It should be noted that just like every other test, the ETT works best in patients with an intermediate probability of disease. It performs poorly when the likelihood of disease is less than 20% or greater than 80%. Indications for further testing include:
Evidence of myocardial ischemia, e.g. exercise induced angina, ST segment depression with exercise (1 mm of depression 0.08 sec beyond the J point), a blood pressure drop with exercise ( > 20 mm SBP ), or an inability to exercise to 85% of the maximum predicted heart rate.
A Duke exercise treadmill score of -11 or lower. The Duke exercise treadmill score is calculated as: exercise time (minutes)- (5 x maximum ST segment depression in mm) - (4 x the angina index). The angina index is 0 for no angina, 1 for typical angina, and 2 for angina that terminates testing. Note: an angina index of 1 or 2 would in itself be a criteria for further testing.
The test is generally considered adequate if the patient achieves a) stage 4 of the Bruce protocol, b) a double product of 20,000 or greater (SBP x max HR), or c) 85% of the maximum predicted heart rate (220 - age in years).
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