DESCRIPTION 
- Cardiac testing is indicated for emergency patients at risk for heart failure (HF) or acute coronary syndrome (ACS).
- These pathologies may be thought of as a spectrum: Unstable angina can evolve into MI, which in turn can cause HF:
- ~20% of ED malpractice claims are due to missed diagnosis of ACS.
- ~2% of patients with ACS are inappropriately discharged from an ED.
- History, physical exam, and ECG are the critical elements in working up chest pain and ACS/HF.
- History, physical, and ECG nevertheless miss 1–4% of all heart attacks.
- Additional tools include imaging modalities and blood tests (e.g., cardiac biomarkers).
ETIOLOGY
ACS is caused by atherosclerotic narrowing of coronary vessels or by coronary vasospasm.
Pregnancy Considerations
In the pregnant patient with chest pain and ischemic changes on ECG, also consider spontaneous coronary artery dissection.
[Outline]
SIGNS AND SYMPTOMS
History
- Anginal symptoms usually are produced by bodily stresses, including exertional and emotional events, and relieved by rest.
- ACS is less likely when chest pain is sharp, stabbing, pleuritic, or reproducible with palpation.
- Ischemia is still diagnosed in 13% of pleuritic chest pain and in 7% of chest pain reproducible with palpation.
- Nitroglycerin may relieve cardiac ischemia, but can also relieve pain in GI and aortic pathology.
- A "GI cocktail" of lidocaine and Maalox, or a proton-pump inhibitor such as omeprazole, may relieve GI pathology, but can also relieve cardiac ischemia.
- Anginal symptoms often last < 20 min but > 5 min
- AMI and UA should be considered if symptoms last > 20 min.
Physical Exam
Often unremarkable
ESSENTIAL WORKUP
EKG:
- Per ACC/AHA guidelines, a 12-lead ECG should be performed on a patient with chest pain within 10 min of arrival to the ED:
- A single ECG will miss ~50% AMI.
- Hyperacute T-waves (tall, broad-based, especially in anterior leads) may be the earliest and only sign of AMI.
- During an MI, the ECG may evolve. Continuous ECG monitoring can identify an additional 16% of acute MIs not seen on initial ECGs. Absent continuous monitoring, consider a repeat EKG 15–60 min after the initial ECG.
- New ST-segment changes or T-wave inversions are suspicious for ischemia.
- ST depressions of 1 mm are characteristic of ischemia; or, could be reciprocal changes, so check other leads.
- STEMI: ST-elevation of > 1–2 mm in ≥2 contiguous leads.
- New left bundle branch block (LBBB) is suggestive of AMI:
- Old LBBB makes diagnosing AMI difficult: Apply Sgarbossa criteria: AMI is likely if LBBB and > 1 mm ST-elevation concordant with QRS, or ST depression > 1 mm in leads V1, V2, or V3.
- Current ACCF/AHA guidelines advise that LBBB "not known to be old" in isolation is not diagnostic of AMI, and should be further evaluated with serum biomarkers and immediate cardiac consultation for consideration of echocardiography and invasive angiography.
- Additional-lead EKGs: Standard 12 leads often miss infarcts in the posterior, right, and high lateral walls.
- Right-sided EKG:
- Move lead V4 to the right side of chest, midclavicular line, 5th intercostal space, and repeat EKG, to capture infarct in right ventricle.
- A right-sided EKG is often performed in the setting of a STEMI in inferior leads (II, III, aVF) to diagnose a right ventricular (RV) infarct.
- Posterior EKG:
- Leads V7, V8, V9 are placed posterior thorax along 5th intercostal space: V7 at posterior axillary line, V8 at inferior angle of scapula, V9 paraspinal.
- Performed in setting of inferior or lateral wall MI; or if ST depression in V1–V3. May identify a lateral or left circumflex infarct.
- EKG may be helpful in diagnosing other etiologies of chest pain:
- Pericarditis is suggested by diffuse ST-elevations followed by T-wave inversions and P-R depression.
- Pulmonary embolism is suggested by unexplained tachycardia, signs of right heart strain (RVH, RBBB, "p" pulmonale), new-onset atrial fibrillation, or rarely with S1, Q3, T3 pattern.
DIAGNOSIS TESTS & INTERPRETATION
Lab
- Cardiac biomarkers:
- Indicated if the history is suspicious for ACS.
- Should not be elevated in stable angina and may be normal in unstable angina.
- Troponin T and I: Starts to rise 2–3 hr after onset of chest pain of ACS and peaks in 8–12 hr. Remains elevated 7–14 days:
- A single troponin has low sensitivity for ACS (1 study of low-risk chest pain in patients with negative initial troponin: 2.3% rate of AMI and 1% rate of death at 30 days).
- Timing of biomarker testing is critical: ACEP endorses with "moderate clinical certainty" that a single negative troponin can rule out AMI if drawn 8–12 hr after onset of symptoms. However, uncertainty in time of symptom onset, unreliable history, and possibility of preinfarction angina complicates utilizing single troponin.
- Newer, more sensitive assays may in the future eliminate the need for a 2nd troponin.
- Minor troponin elevations may occur with renal failure, structural heart disease, CHF (acute or chronic), cardiac pacing, pulmonary embolism, sepsis, stroke.
- Lack of standardization between assays (particularly with troponin I) means values from 1 lab cannot always be simply compared to values from another.
- CK/CK-Mb: Less sensitive than troponin, rises more slowly. Little gained by using both CK-Mb and troponin assays. Obtain CK-Mb if
- Renal failure is present (Tn less accurate)
- Recent prior infarct
- Myoglobin: Rises faster than standard troponin assays and thus able to detect AMI sooner, but max. sensitivity is 70%.
- B-type natriuretic peptide (BNP):
- Release and synthesis activated by diastolic ventricular stretch.
- Useful for detecting HF.
- A cutoff of > 100 pg/mL diagnosed HF with a sensitivity of 90% and specificity of 76%.
- Unclear significance of elevated BNP in setting of ACS.
Imaging
- CXR:
- Rest echocardiography:
- May identify ACS or AMI based on wall motion abnormalities; also can detect pump failure and valvular abnormalities.
- Rest echo has a sensitivity of 70% and specificity of 87% for ACS.
- Rest echo has a sensitivity of 93% and specificity of 66% for AMI.
- Technetium99m sestamibi:
- Radioactive IV dye taken up by myocardium, and detected by single photon emission CT (SPECT) imaging. (Also known as myocardial perfusion imaging.)
- Can be imaged at rest to detect low- or no-flow areas of myocardium; can also be imaged after exercise or pharmacologic stress.
- Per 2009 AHA/ACC guidelines, reserve for intermediate- to high-risk patients.
- Has a sensitivity of 81% and specificity of 73% for ACS.
- Has a sensitivity of 92% and specificity of 67% for AMI.
- CT coronary angiography (CTCA):
- Imaging to evaluate degree of coronary artery stenosis and calcium deposits
- Negative predictive value between 97% and 100%, accuracy comparable to stress testing
- Recent NEJM article suggests CTCA decreases ED length of stay but leads to further downstream testing, radiation exposure, and no decrease in cost of care.
- Exercise stress testing (ETT):
- May help establish diagnosis of angina, provide prognostic information.
- 1-mm depression of the ST-segment in 3 consecutive beats and 2 consecutive leads is characteristic of cardiac ischemia.
- Early positive (within 3 min) stress tests are worrisome for unstable angina.
- 6 min of exercise using a standard Bruce protocol suggests an excellent prognosis.
- Exercise stress testing with EKG alone has a sensitivity of 68% and specificity of 77%.
- Exercise stress testing with echo has a sensitivity of 85% and specificity of 77%.
- Exercise stress testing with technetium99m sestamibi has a sensitivity of 87% and specificity of 64%.
- Cardiac catheterization:
- Considered the gold standard for evaluating coronary arteries.
- A history of a recent negative catheterization does not fully exclude AMI, i.e., in cases of vasospasm or cocaine use.
Diagnostic Procedures/Surgery
EKG, cardiac enzymes, echo, stress testing
DIFFERENTIAL DIAGNOSIS
See ACS chapters.
[Outline]
PRE-HOSPITAL
- Cardiac monitoring
- Out-of-hospital EKG:
- Alone has a sensitivity of 76% and specificity of 88% for ACS.
- Alone has a sensitivity of 68% and specificity of 97% for AMI.
INITIAL STABILIZATION/THERAPY
- Cardiac monitoring
- Oxygen saturation
ED TREATMENT/PROCEDURES
- See "Acute Coronary Syndrome: Stable Angina"; "Acute Coronary Syndrome: Unstable Angina"; and "Acute Coronary Syndrome: MI" for more detail.
- Guidelines for cardiac testing
- History suggestive of ACS:
- Obtain ECG and 1st troponin (or other cardiac biomarkers).
- ECG or 1st troponin abnormal:
- Admit; consider cardiology consult.
- Ongoing chest pain or pressure:
- Obtain sestamibi or echo.
- Consider serial EKGs
- Sestamibi, serial EKG or echo abnormal:
- Admit or cardiology consult.
- Second troponin (or other cardiac biomarkers) abnormal:
- Admit; consider cardiology consult.
- Ancillary testing:
- For low- to moderate-risk patients: standard exercise testing (ETT).
- If low-risk patient with good follow-up, ACC/AHA guidelines allow for outpatient stress testing within 72 hr.
- Per 2007 AHA/ACC guidelines CTCA "reasonable alternative" to stress testing.
- For abnormal or uninterpretable EKG: Stress echo or sestamibi.
- For patient unable to exert self: Pharmacologic ETT (i.e., dobutamine stress or dipyridamole sestamibi).
- Ancillary testing abnormal:
- Cardiology consult or admit.
MEDICATION
Patient should not be started on new antianginal medication before stress testing in the ED.
[Outline]
DISPOSITION
Admission Criteria
- History suggestive of cardiac etiology for chest pain and ED observation for serial testing unavailable
- Abnormal or changed EKG and ED observation unavailable
- Positive cardiac biomarkers
- Positive rest imaging
- If the diagnosis is unclear, admission to the hospital or an ED observation unit may be useful for serial cardiac biomarkers, EKGs, and further ancillary testing.
- Early positive stress test:
- If the patient has a positive stress test, the decision for admission should be made in consultation with the primary care physician or cardiologist.
Discharge Criteria
Patients who meet the following criteria are safe to discharge:
- History not suggestive of cardiac etiology for chest pain
- Normal ECG
- Normal cardiac testing
FOLLOW-UP RECOMMENDATIONS
- Abnormal stress test will require close follow-up with cardiology or PCP.
- Undifferentiated CP should have ED stress testing unless clear follow-up is available.
[Outline]