Approach
• Noninvasive eval for CAD is done in the ED for pts after “r/o MI”
• It should not be done on pts w/ high-risk ACS, ongoing CP
Indications
• Dx CAD, assess Δ clinical status in pt w/ known CAD, localize ischemia
Contraindications
• Absolute: Severe acute illness – AMI w/i 48 h, high-risk UA, PE/aortic dissection/pericarditis, CHF, arrhythmias – or underlying, severe AS
• Relative: Inability to exercise, high-degree AVB, severe HTN, LM CAD, mod valvular stenosis, HCMP, severe electrolyte abnl
Findings
• HR: A “diagnostic” exercise test requires minimum 85% of max predicted HR (220 – age)
• METS (max exercise capacity), also displayed in minutes
• ECG changes: Downsloping or flat ST ↓ predicts CAD, but does not localize dz; ST ↑ an even better predictor
• Duke Treadmill Score (NEJM 1991;325:848) = Duration of exercise in minutes – (5 × max ST dev, in mm) – (4 × angina index*)
*Angina index: 0 none, 1 nonlimiting, 2 limiting:
Score >+5 → predicted 4-yr survival 98%; average annual mortality 0.25%
Score –10 to 4 → predicted 4-yr survival 94%; average annual mortality 2–3%
Score <–10 → predicted 4-yr survival 81%; average annual mortality 5%
• Imaging: Either radionucleotide defect or echo wall motion abnlty; reversible defect → ischemia; fixed defect → infarct
• Myocardial viability: To find cardiac muscle that can be “saved” by intervention. Can be done w/ multiple modalities: MRI (sens >95%, spec ∼70%), PET (sens ∼90%, spec ∼75%), dobutamine stress echo (sens ∼70%, spec ∼85%), rest redistribution thallium (sens ∼90%, spec ∼55%).
• CT/MR coronary angiography
• Coronary calcium score: Evaluate for CAD & estimate plaque burden based on quantifying coronary artery calcification
• Can assess significant stenosis w/ sens/spec >85% w/ 64-slice CT, but limited by a large portion of nonevaluable artery segments (as much as 30%); requires relative bradycardia (often βB); b/c high NPV → useful for r/o (1) obstructive CAD in pts w/ anginal sxs, (2) CAD in pts w/ intermed & low pretest probability w/ nl serial ECGs/biomarkers (NEJM 2001;345:1863; JAMA 2006;296:403; JACC 2006;48:1475; Circulation 2006;114:1761).
Disposition
• For adequate study (HR, METS achieved) & no e/o ECG changes, sxs, or imaging abnormalities, pt may be discharged home w/ PCP/cards f/u. If low pretest probability, & nondiagnostic test, pt may be discharged home w/ close f/u & 2nd testing modality done as outpt.
• For adequate study w/ high-risk test results, consider coronary angiography, ± admission depending on clinical presentation
Pearl
• Remember that +stress test indicating CAD in a pt who presented to ED w/ CP does not necessarily mean that CP was caused by CAD. Conversely, most of these tests are poorly sens/spec, so a negative result should not be particularly reassuring, esp in high-risk &/or high-PreTP pts.