Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (35 page)

   
Exercise treadmill testing
should be considered first, particularly in lowrisk groups; low sensitivity, predictive value, and inability to identify and quantify ischemic areas when compared with imaging modalities; cannot interpret ECG if LBBB, ventricular paced rhythm, LVH hypertrophy, and conduction abnormalities. Duke prognostic treadmill score establishes the risk of death from CAD; combined with imaging (SPECT, MRI, or echo) to improve sensitivity and specificity in women and those with confounding baseline ECGs.

   The advantage of echocardiography over SPECT (single-photon emission computed tomography) is lack of radiation exposure but carries higher false-negative results at submaximal heart rates. SPECT has higher positive-negative predictive values over treadmill testing alone.

   
Cardiac MRI
has excellent spatial resolution without radiation; similar to SPECT, may assess myocardial viability (unlike SPECT can differentiate pericarditis). Stress MRI can be performed with dobutamine or adenosine; difficulty imaging irregular heart rhythms and patients with metal implants. No large comparative studies published yet.

   
Cardiac CT
(64 slice) has excellent negative predictive value (>90%), slightly diminished positive predictive value (80%). Rapid acquisition but requires lower heart rates for image analysis with a tendency to overestimate disease severity; provides only anatomic, not functional information (i.e., culprit lesion). At present, no consensus for use of CT as a “triple rule out”—CAD, aortic dissection, PE in the rapid assessment of chest pain.

Suggested Readings

Anderson JL, Adams CD, Antman EM, et al. ACC/AHA 2007 guidelines for the management of patients with unstable angina/non–ST elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines.
J Am Coll Cardiol.
2007;50:e1–e157.

Body R, Carley S, McDowell G, et al. Rapid exclusion of acute myocardial in patients with undetectable troponin using a high-sensitivity assay.
J Am Coll Cardiol.
2011;58:1332–1339.

McCaig L, Burt C. National Hospital Ambulatory Medical Care Survey: 2003 Emergency Department Summary. In:
Advance Data from Vital and Health Statistics
. Atlanta, GA: Centers for Disease Control and Prevention, 2005.

Than M, Cullen L, Aldous S, et al. 2-Hour accelerated diagnostic protocol to assess patients with chest pain syndromes using contemporary troponins as the only biomarker: the ADAPT trial.
J Am Coll Cardiol.
2012;59:2091–2098.

Thygesen K, Alpert JS, White HD; on behalf of the Joint ESCIACCFI AHA/WHF Task Force for the Redefinition of Myocardial Infarction. Universal definition of myocardial infarction.
J Am Cardiol.
2007;50:2173–2195.

CHEST PAIN: NONATHEROSCLEROTIC ISCHEMIA

   Definition

   Approximately 5% of patients with acute myocardial infarction do not have atherosclerotic coronary disease, increasing to 20% in patients under the age of 35. Necropsy studies in these individuals often demonstrate luminal narrowing, leading to ischemia via several mechanisms: internal narrowing by obstructions or encroachment by adjacent structures.

   Ischemia may also result from dynamic changes in an otherwise normal arterial wall (spasm and anomalous arteries) or an imbalance in oxygen supply and demand (type 2 MI).

   Over 50% of fatal MIs without coronary disease likely represent coronary vasospasm.

   Who Should Be Suspected?

   Diagnosis is often made by exclusion via cardiac imaging due to overlap of symptom presentation with ACS.