*See MDCalc.com for the HEART, TIMI, and GRACE risk stratification tools.

Acute Coronary Syndrome

Definitions

Acute coronary syndrome encompasses the spectrum of diseases which cause a sudden reduction in blood flow to the heart, leading to myocardial injury or ischemia. The 2023 ESC Guidelines focus on management of the ACS spectrum from unstable angina to STEMI (Byrne, 2023). The 2021 ACC/AHA Guidelines focus on risk stratification of patients with chest pain into low, intermediate, or high-risk categories (Gulati, 2021). Based on this initial risk assessment, patients may require further evaluation in line with the ESC Guidelines.

The 2021 ACC/AHA Guidelines for Evaluation and Diagnosis of Chest Pain recommend using broad terminology such as “chest discomfort” (as opposed to “chest pain”)  to describe patients who may be having an ischemic event. Additionally, they recommend against the term “atypical chest pain,” which is vague and misleading, in favor of the more precise “cardiac,” “possibly cardiac,” or “noncardiac” to describe chest discomfort (Gulati, 2021).

History and Physical

Some features which suggest chest discomfort is ischemic in nature are if it is central, pressure-like, squeezing, gripping, a heaviness, tightness, exertional, or retrosternal. Conversely, words such as sharp, fleeting, shifting, pleuritic, or positional, suggest alternative etiologies (Gulati, 2021).

In considering alternative etiologies, Dr. Francis recommends vigilance for “can’t miss” diagnoses, including pulmonary embolism and acute aortic syndrome. Once these have been ruled out, consider the patient’s risk factors for acute coronary syndrome, including hypertension, hyperlipidemia, diabetes, a family history, and tobacco use disorder.

Contrary to the old dogma that women present differently from men with ACS, recent studies suggest that women and men present with similar symptoms (Lichtman, 2019; Hermal, 2017). Of note, the guidelines recommend cultural competency training to improve outcomes of patients presenting from diverse backgrounds (Gulati, 2021).

Regarding the physical exam, Dr. Francis recommends doing a brief, complete cardiac assessment of the patient. This should include auscultation for carotid bruits: the carotids are the most easily accessible vessels for auscultation, so if a bruit is heard, it signifies that this patient has atherosclerosis, and may have a higher likelihood for coronary atherosclerosis (expert opinion). Dr. Francis also recommended checking for symmetry of pulses to ensure that an acute aortic syndrome is not missed.

ECG and Biomarkers

ECG

Any patient presenting to the ER with chest discomfort should have a 12-lead ECG performed within 10 minutes of arrival (Gulati, 2021; Byrne, 2023). A non-diagnostic ECG does not rule out acute coronary syndrome in all cases: for example, dynamic changes on repeat ECGs may reveal evolving ischemia, and additional precordial leads may reveal a posterior myocardial infarction (MI) (Gulati, 2021; Byrne, 2023).

Dr. Francis reviewed the following ECG findings and ranked them from most to least concerning:

• ST Elevation: ST elevations in a territorial distribution suggest myocardial injury and should prompt a decision on cath lab activation or administering thrombolytics for immediate reperfusion.
• Left Bundle Branch Block (LBBB): New LBBB is considered a STEMI equivalent in someone with acute chest discomfort. If you are uncertain as to whether a LBBB in a patient with ischemic symptoms is new, assume it is new to ensure proper evaluation.
• Q waves: similar to ST elevations, Q waves in a coronary territory indicate ischemia has occurred. Q waves can form within hours of an ischemic event and can exist concurrently with ST segment changes.
• ST depression: Deeper and more downsloping ST depressions, especially in a coronary territory, are worrisome for ischemia. Diffuse ST depressions combined with ST elevation in lead aVR suggest global ischemia (Nabati, 2016).
• Right Bundle Branch Block (RBBB): New RBBB is not considered a STEMI equivalent, but could mask other ischemic findings, so further work-up typically required (Byrne, 2023).
• T wave abnormalities: T wave abnormalities are common but non-specific. Peaked or deep T waves or dynamic changes should prompt further evaluation.
• Unremarkable ECG: A normal ECG does not rule out ischemia, for example, early on in ACS, or in a posterior infarction (Gulati, 2021; Byrne, 2023).

Because dynamic ECG changes can happen within minutes, use repeat ECGs when the diagnosis is uncertain. This information can be particularly valuable while awaiting biomarker results or when there has been a clinical change (Byrne, 2023).

Risk Stratification Scores

Several risk stratification tools to estimate morbidity and mortality from ACS have been developed. All use a combination of history, initial ECG findings, and biomarkers to determine risk.

• HEART Score
• TIMI Risk Score for Unstable Angina and NSTEMI
• GRACE

Imaging

Low-risk patients should receive counseling on risk factor modification and outpatient re-assessment with non-invasive tools like the coronary calcium scores. High-risk patients typically need invasive evaluation with cardiac catheterization. Intermediate-risk patients should undergo anatomic or functional testing tailored to the individual patient: consider their ability to exercise, radiation exposure, body habitus for image capture, and institutional expertise and access (Gulati, 2021).

Anatomic Testing

• Coronary CT Angiography: Coronary CT can diagnose and estimate the extent of coronary artery disease. Dr. Francis highlights its ability to measure fractional flow reserve (FFR), providing an estimate of the severity of disease in a vessel. Contraindications include: iodine allergy, inability to cooperate with instructions, clinical instability, renal impairment,beta blocker and/or nitroglycerin intolerance, marked heart rate variability due to arrhythmia (Gulati, 2021). Dr. Francis notes that  coronary CT angiography is only useful in patients who have not previously undergone revascularization of any kind.
• Invasive Coronary Angiography (catheterization): Catheterization measures the severity of coronary obstruction and allows simultaneous intervention on lesions amenable to angioplasty and/or stenting (Gulati, 2021).

Diagnostic Testing

• Exercise Treadmill Test: An exercise treadmill test can detect ischemic symptoms, ECG changes, or a drop in blood pressure with exercise. Contraindications include: baseline abnormal ECG (especially near ST segment), inability to achieve 5 METs, high-risk unstable angina or acute MI, uncontrolled heart failure, cardiac arrhythmias, severe symptomatic aortic stenosis, severe systemic arterial hypertension, and acute illness (Gulati, 2021).
• Echocardiography: Traditional echocardiography allows evaluation for alternative causes such as aortic dissection, pericardial effusion, stress cardiomyopathy, hypertrophic cardiomyopathy, as well as assessment of left ventricular and right ventricular function (Gulati, 2021). Additionally, it can be helpful in an acute coronary syndrome to assess for wall motion abnormalities and the degree of left ventricular dysfunction (Byrne, 2023).
• Stress echocardiography: Stress echo can be used to define ischemia severity or for risk stratification. Contraindications include: poor windows, inability to reach target heart rate, uncontrolled heart failure, high-risk unstable angina, active ACS, arrhythmias (ventricular arrhythmias, AV block, or uncontrolled AF), respiratory failure, severe COPD, acute PE , severe pulmonary hypertension, contraindications to dobutamine or atropine, critical aortic stenosis, acute illness, hemodynamically significant LV outflow tract obstruction, and severe hypertension (Gulati, 2021).
• Stress Nuclear (PET or SPECT) Myocardial Perfusion Imaging: These tests assess perfusion abnormalities, left ventricular function, and transient ischemic dilation. PET allows calculation of myocardial blood flow reserve, while SPECT MPI does not. Contraindications include: high-risk unstable angina, ACS complicated by arrhythmia or heart failure, contraindications to vasodilators, regadenoson, or adenosine; severe hypotension or hypertension, COPD or asthma, and recent use of dipyridamole or methylxanthines (Gulati, 2021).
• Cardiac MRI: Cardiac MRI assesses global and regional left and right ventricular function, localizes myocardial ischemia or infarction, and measures myocardial viability. MRI can help differentiate acute from chronic ischemia. Contraindications include: reduced GFR, inability to tolerate vasodilators, implanted devices, claustrophobia, and recent caffeine. (Gulati, 2021).

THIS CONCLUDES PART 1