Pocket Medicine

CARDIOLOGY

NONINVASIVE EVALUATION OF CAD

Stress testing (Circ 2007;115:1464; JACC 2012;60:1828)

•  Indications: dx CAD, evaluate Δ in clinical status in Pt w/ known CAD, risk stratify s/p ACS, evaluate exercise tolerance, localize ischemia (imaging required)

•  Contraindications (Circ 2002;106:1883; & 2012;126:2465)

Absolute: AMI w/in 48 h, high-risk UA, acute PE, severe sx AS, uncontrolled HF, uncontrolled arrhythmias, myopericarditis, acute aortic dissection

Relative: left main CAD, mod valvular stenosis, severe HTN, HCMP, high-degree AVB, severe electrolyte abnl

•  Exercise: standard Bruce (↑ speed & incline q3min), modified Bruce (begins w/o treadmill incline), submax (if <3 wk post-MI) or sx-limited; hold nitrates/βB/CCB/ranolazine if trying to dx CAD, but give when assessing if Pt ischemic on meds

•  Pharmacologic: if unable to exer., low exer. tol, or recent MI. Se & Sp  exercise. Preferred if LBBB (requires imaging since ECG not interpretable). Coronary vasodilators (will reveal CAD, but not tell you if Pt ischemic): regadenoson, dipyridamole or adenosine (may precipitate bradycardia and bronchospasm). Chronotropes/inotropes (more physiologic): dobutamine (may precipitate tachyarrhythmias).

•  Imaging: used if uninterpretable ECG (paced, LBBB, resting ST ↓ >1 mm, dig., LVH, WPW), after indeterminate ECG test, pharmacologic tests, or localization of ischemia

SPECT (eg, 99mTc-sestamibi), PET (rubidium-82; usually w/ pharm test), echoMRI

Test results

•  HR (must achieve ≥85% of max pred HR [220-age] for exer. test to be dx), BP response, peak double product (HR × BP; nl >20k), HR recovery (HRpeak – HR1 min later; nl >12)

•  Max exercise capacity achieved (METS or min)

•  Occurrence of symptoms (at what level of exertion and similarity to presenting sx)

•  ECG Δsdownsloping or horizontal ST ↓ (≥1 mm) 60–80 ms after QRS predictive of CAD (but does not localize ischemic territory); however, STE highly predictive & localizes

•  Duke treadmill score = exercise min – (5 × max ST dev) – (4 × angina index) [0 none, 1 nonlimiting, 2 limiting]; score ≥5 → <1% 1-y mort; –10 to + 4 → 2–3%; ≤ –11 → ≥5%

•  Imaging: radionuclide defects or echocardiographic regional wall motion abnormalities

reversible defect = ischemia; fixed defect = infarct; transient isch dilation = severe CAD

false : breast → ant “defect” and diaphragm → inf “defect”

false  may be seen if balanced (eg, 3VD) ischemia (global ↓ perfusion w/o regional Δs)

High-risk test results (PPV ~50% for LM or 3VD, consider coronary angio)

•  ECG: ST ↓ ≥2 mm or ≥1 mm in stage 1 or in ≥5 leads or ≥5 min in recovery; ST ↑;  VT

•  Physiologic: ↓ or fail to ↑ BP, <4 METS, angina during exercise, Duke score ≤ –11; ↓ EF

•  Radionuclide: ≥1 lg or ≥2 mod. reversible defects, transient LV cavity dilation, ↑ lung uptake

Myocardial viability (Circ 2008;117:103; Eur Heart J 2011;31:2984 & 2011;32:810)

•  Goal: identify hibernating myocardium that could regain fxn after revascularization

•  Options: MRI (Se ~95%, Sp ~85%), PET (Se ~90%, Sp ~65%), dobutamine stress

echo (Se ~80%, Sp ~80%); SPECT/rest-redistribution (Se ~85%, Sp ~70%)

In Pts w/ LV dysfxn, viabil. doesn’t predict ↑ CABG benefit vs. med Rx (NEJM 2011;364:1617)

CT & MR coronary angio (NEJM 2008;369:2324; Circ 2010;121:2509; Lancet 2012;379:453)

•  Image quality best at slower & regular HR (? give bB if possible, goal HR 55–60)

•  Calcium generates artifact for CT angiography

•  MRI: angiography, perfusion, LV fxn, enhancement (early = microvasc obstr; late = MI)

Coronary artery calcium score (CACS; Circ 2010;122:e584; NEJM 2012;366:294; JAMA 2012;308:788)

•  Quantifies extent of calcium; thus estimates plaque burden (but not % coronary stenosis)

•  ? Risk strat. (<100 = low; >300 = high) in asx Pts w/ intermed risk (10–20% 10-y risk)

•  ? Value as screening test to r/o CAD in sx Pt (CACS <100 → 3% probability of signif CAD; but interpretation affected by age, gender)