Chronic stable angina risk assessment in patients with an intermediate or high probability of coronary artery disease
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Based on the ACC/AHA guidelines, the pretest probability of underlying coronary artery disease (CAD) can be classified into low (less than 10%-20%), intermediate (between 20%-80%) and high probability (more than 80%-90%). All patients with intermediate to high probability of CAD need to undergo exercise stress testing to stratify the risk of subsequent coronary events and hence determine the appropriate diagnostic and therapeutic interventions. Bruce protocol and DUKE score are widely adopted methods for exercise stress testing. The exercise capacity, clinical, hemodynamic and electrocardiographic responses must be considered while interpreting the results of exercise treadmill test.
Exercise Treadmill Test Interpretation
- Angina: If occurred during or after exercise, particularly if it forces to stop the test.
- ST segment changes if occurred during or after exercise. Factors that indicate high probability of underlying CAD include:
- Hemodynamic responses like changes in heart rate or blood pressure with exercise
- Workload in metabolic equivalents (METs)
- In a 40-year old man weighing 70kg, 1 MET refers to the resting volume oxygen consumption per minute (VO2).
- 1 MET = 3.5 mL/min/kg of body weight
Methods to Assess Exercise Treadmill Test
- Bruce protocol is most widely used and has seven stages, with a complete 21-minute exercise and each stage lasting for 2-minutes.
- The result is satisfactory when a patient completes of 9-12minutes of exercise or 85% of the maximum predicted changes in heart rate.
|Stage 1||0-3 min||1.7 mph||10% grade||5.0 METS|
|Stage 2||3-6 min||2.5 mph||12% grade||6.8 METS|
|Stage 3||6-9 min||3.4 mph||14% grade||9.4 METS|
|Stage 4||9-12 min||4.2 mph||16% grade||13.3 METS|
|Stage 5||12-15 min||5.0 mph||18% grade||16.6 METS|
|Stage 6||15-18 min||5.5 mph||20% grade||19.5 METS|
|Stage 7||18-21 min||6.0 mph||22% grade||22.7 METS|
|CAD risk probability (DTS)||4-year survival||Annual mortality|
|Low probability (more than 5 DTS)||99%||0.25%|
|Moderate probability (-10 to 4 DTS)||95%||1.25%|
|High probability (less than -10 DTS)||79%||5%|
ACC/AHA Guidelines- Risk Assessment and Prognosis in Patients With an Intermediate or High Probability of CAD (DO NOT EDIT)
|"1. Patients undergoing initial evaluation. (Exceptions are listed below in classes IIb and III) (Level of Evidence: B)"|
|"2. Patients after a significant change in cardiac symptoms. (Level of Evidence: C)"|
|"1. Patients with severe comorbidity likely to limit life expectancy or prevent revascularization. (Level of Evidence: C)"|
|"1. Patients with the following ECG abnormalities:|
|a. Preexcitation (Wolff-Parkinson-White syndrome). (Level of Evidence: B)|
|b. Electronically paced ventricular rhythm. (Level of Evidence: B)|
|c. More than 1 mm of rest ST segment depression. (Level of Evidence: B)|
|d. Complete left bundle-branch block. (Level of Evidence: B)"|
|"2. Patients who have undergone cardiac catheterization to identify ischemia in the distribution of a coronary lesion of borderline severity. (Level of Evidence: C)"|
|"3. Post-revascularization patients who have a significant change in anginal pattern suggesting ischemia. (Level of Evidence: C)"|
- Gibbons RJ, Chatterjee K, Daley J, Douglas JS, Fihn SD, Gardin JM et al. (1999) ACC/AHA/ACP-ASIM guidelines for the management of patients with chronic stable angina: executive summary and recommendations. A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients with Chronic Stable Angina). Circulation 99 (21):2829-48.  PMID: 10351980
- Mark DB, Shaw L, Harrell FE, Hlatky MA, Lee KL, Bengtson JR et al. (1991) Prognostic value of a treadmill exercise score in outpatients with suspected coronary artery disease. N Engl J Med 325 (12):849-53. DOI:10.1056/NEJM199109193251204 PMID: 1875969
- Mark DB, Hlatky MA, Harrell FE, Lee KL, Califf RM, Pryor DB (1987) Exercise treadmill score for predicting prognosis in coronary artery disease. Ann Intern Med 106 (6):793-800. PMID: 3579066
- Johnson GG, Decker WW, Lobl JK, Laudon DA, Hess JJ, Lohse CM et al. (2008) Risk stratification of patients in an emergency department chest pain unit: prognostic value of exercise treadmill testing using the Duke score. Int J Emerg Med 1 (2):91-5. DOI:10.1007/s12245-008-0031-5 PMID: 19384658