acute%20coronary%20syndromes%20w_o%20persistent%20st-segment%20elevation
ACUTE CORONARY SYNDROMES W/O PERSISTENT ST-SEGMENT ELEVATION
Acute coronary syndromes refer to any constellation of clinical symptoms compatible with acute myocardial ischemia which may be life-threatening.
It encompasses unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI) and ST-segment elevation myocardial infarction (STEMI).
Unstable angina is the ischemic discomfort that presents without persistent ST-segment elevation on ECG and without the presence of cardiac markers in the blood.
Non-ST-segment elevation myocardial infarction is diagnosed if cardiac markers are positive with ST-segment depression or with nonspecific or normal ECGs.
The patient typically presents with ischemic-type chest pain that is severe and prolonged and may occur at rest or may be caused by less exertion than previous episodes.

Evaluation

Evaluation for Risk Stratification

Medical history, physical exam, electrocardiogram (ECG), biochemical cardiac markers and assessment of renal function can be used to estimate the risk of death and nonfatal cardiac ischemic events

  • Assessment of risk is useful in selection of site of care (eg ICU, monitored unit, outpatient) and in selection of treatment
    • Risk assessment should be done repeatedly
  • Patients with high likelihood of acute coronary syndrome secondary to coronary artery disease (CAD) are at greater risk of untoward cardiac events than patients at less risk of CAD
    • High likelihood signs and symptoms: Chest or left arm pain or discomfort as chief symptom reproducing prior documented angina, known or prior history of CAD including MI, presence of transient mitral regurgitation, murmur, hypotension, diaphoresis, pulmonary edema or rales, elevated cardiac markers, and ECG result of new or presumably new, transient ST-segment deviation or T-wave inversion in multiple precordial leads
  • Prognostic information to predict short- or mid-term risk of ischemic events, commonly use the Global Registry of Acute Coronary Events (GRACE), the Thrombolysis in Myocardial Infarction (TIMI) risk score, the Platelet Glycoprotein IIb/IIIa in Unstable Angina: Receptor Suppression Using Integrilin Therapy (PURSUIT) risk score, and the National Cardiovascular Data Registry-Acute Coronary Treatment and Intervention Outcomes Network (NCDR-ACTION) registry

High-Risk Patients

At least 1 of the following features must be present:

  • Patients >70 years old
  • Recurrent angina/ischemia at rest or with low-level activities despite intensive anti-ischemic therapy
  • New or worsening mitral regurgitation (MR) murmur
  • Signs and symptoms of heart failure (HF)
  • Pulmonary edema, most likely due to ischemia
  • S3 or new worsening rales
  • Hypotension, bradycardia or tachycardia
  • History of myocardial infarction (MI), HF, percutaneous coronary intervention (PCI) within 6 months, prior coronary artery bypass grafting (CABG)
  • Major arrhythmias (eg repetitive or sustained ventricular tachycardia, ventricular fibrillation)
  • Patients with ECG abnormalities
    • Angina at rest with transient ST-segment changes >0.5 mm or ST deviation; bundle branch block, new or presumed new
  • Patients with elevated troponin levels (>0.1 ng/mL) or elevated CK-MB
  • Patients with LV dysfunction and left ventricular ejection fraction (LVEF) <40%
  • High-risk findings from non-invasive testing
  • Hemodynamic instability
  • High-risk scores

Intermediate-Risk Patients

No high-risk feature, but must have 1 of the following:

  • Patients with prior Aspirin use
  • Prolonged (>20 minutes) angina at rest, now resolved, with moderate or high likelihood of CAD
  • Angina at rest (>20 minutes) or relieved with rest or sublingual GTN; nocturnal angina
  • New onset or progressive Canadian Cardiovascular Society (CCS) class III or IV angina in the past 2 weeks without prolonged (>20 minutes) rest pain but with intermediate or high likelihood of CAD
  • ECG shows T-wave changes, pathological Q-waves or resting ST-depression <1 mm in multiple lead groups
  • Patients with slightly elevated cardiac biochemical markers (eg Troponin >0.01 ng/mL but <0.1 ng/mL)

Low-Risk Patients

No high- or intermediate-risk feature but may have any of the following:

  • Increased angina frequency, severity or duration
  • Angina provoked at a lower threshold
  • New-onset angina with onset 2 weeks to 2 months prior to presentation
  • Normal or unchanged ECG; normal cardiac markers
  • Absence of history of cardiovascular disease
  • Clinical stability

Physical Examination

  • Major objectives:
    • Identify precipitating causes (eg uncontrolled hypertension, thyrotoxicosis or GI bleeding) and comorbid conditions (eg lung disease or cancer)
    • Assess the hemodynamic impact of the ischemic event
    • Exclude noncardiac causes of chest pain (eg pneumothorax, pulmonary embolism, pneumonia, pleural effusion, esophageal discomfort, gallstones, pancreatitis, or musculoskeletal origin)
    • Assess for nonischemic cardiac disorders (eg pericarditis, valvular disease, aortic dissection, acute pericarditis, cardiac tamponade)
  • Measure vital signs [blood pressure (BP) in both arms, heart rate (HR), respiratory rate (RR) and temperature]
  • Perform thorough cardiovascular (CV) and chest exam including auscultation of heart, neck veins, liver and peripheral pulses to check for murmurs, bruits or pulse deficits which signify severe underlying coronary artery disease (CAD)
  • LV dysfunction and shock should be suspected if patient has cold extremities, hypotension, pulmonary rales, S3 gallop, displaced apex beat or S1<S2 at apex
  • Aortic dissection may be present if there is pain in the back, unequal pulses, or a murmur of aortic regurgitation
  • Acute pericarditis is suggested by a pericardial friction rub
  • Cardiac tamponade may present as pulsus paradoxus
  • If pneumothorax is present, patient may have acute dyspnea, pleuritic chest pain and differential breath sounds
  • Chest pain caused by musculoskeletal chest wall syndromes may be found by performing palpation of the chest wall

Laboratory Tests

Electrocardiogram (ECG)

In patients with ongoing chest pain, ECG should be obtained immediately (within 10 minutes of patient entering hospital) and as soon as possible in patients with resolved symptoms at the time of evaluation

  • ECG is key in the assessment of patients presenting with suspected acute coronary syndrome and an ECG taken during an episode of chest pain is particularly valuable; ECG should be repeated (15- to 30-minute intervals at the 1st hour) as necessary or if there is high suspicion for acute coronary syndrome (ACS)
  • Comparison with a previous ECG, if available, is important, especially in patients with coexisting cardiac pathology (eg LV hypertrophy or a previous MI)
  • Continuous multilead ST-segment monitoring is an acceptable alternative to serial 12-lead ECG recordings in patients with high clinical suspicion for ACS but with initial ECG that is nondiagnostic

Unstable Angina/Non-ST-Segment Elevation Myocardial Infarction:

  • ST-segment depression (especially horizontal or downsloping) >0.1 mV in ≥2 contiguous leads
    • Highly suggestive of ACS
  • Inverted T-waves >0.1 mV with predominant R-waves
    • Less specific for ACS
  • T-wave inversion: Marked >0.2 mV symmetrical T-wave inversion in the precordial lead

Other ECG Presentations:

  • Persistent ST-segment elevation or new or presumed new left bundle-branch block (LBBB) has a high specificity for evolving STEMI
    • Patient should then be immediately evaluated for reperfusion therapy
    • Please refer to Myocardial Infarction with ST-Segment Elevation Disease Management Chart
  • A completely normal ECG does not exclude the possibility of ACS
    • If normal ECG occurs during episode of chest pain, an alternative diagnosis should be suspected

Repeat Tests

  • Perform serial ECGs or if patient experiences new episode of chest pain, obtain 12-lead ECG and compare with ECG taken without symptoms
  • ECG recordings may be repeated at least 6-9 hours and 24 hours after presentation

Biochemical Indicators for Detecting Myocardial Necrosis

Cardiac Troponin T or I (Quantitative)

  • Preferred markers for myocardial necrosis because of high sensitivity and specificity and provides prognostic information
    • Detected in blood as early as 2-4 hours after symptom onset, but elevation may be delayed for up to 8-12 hours, and can be measured until 5-14 days
    • Troponins accurately identify myocardial necrosis but should be used in conjunction with other criteria of MI which include ischemic symptoms and ECG results
  • High-sensitivity troponin I (hs-Tn I) assay may be performed at presentation on patients with symptoms of possible ACS and have negative findings on ECG 
    • Consider to rule in ACS if hs-Tn I level is >10x ULN 

Myoglobin and/or Creatine Kinase - Myocardial Band (CK-MB)

  • May be measured in patients with recent (<6 hours) symptoms as an early marker of MI and in patients with recurrent ischemia after recent (<2 weeks) infarction to detect further infarction

Repeat Tests
  • Biochemical marker (cardiac troponin T or I) test should be repeated 3-6 hours after initial assessment if the first measurement is not conclusive or when ECG changes and/or clinical presentation have intermediate or high index of suspicion of ACS
    • If hs-Tn I level is <10x ULN, perform serial testing; from the time of presentation to retest 3 hours after, patients at high risk of ACS have >50% change in hs-Tn I level while patients at low risk of ACS have <50% change 
    • Evaluate for other causes of elevated troponin if hs-Tn I level is >99th percentile at baseline with a change of <50% after 3 hours 
    • It is also advised to have a repeat testing after 12-24 hours if the clinical condition is still suggestive of ACS


Other Diagnostic Tests

  • Complete blood count (CBC), creatinine (Cr), blood urea nitrogen (BUN), C-reactive protein, blood glucose, lipid profile, thyroid function
    • Identify anemia, thyrotoxicosis, diabetes mellitus (DM), coronary artery disease (CAD)
    • Identify infection: Several studies have shown an associated increased risk for ACS within 1-2 weeks after acute respiratory infection; absence of infection may be prognostic
  • Chest X-ray to identify pulmonary congestion/edema
  • Chest computed tomography (CT) to exclude pulmonary embolism and aortic dissection
  • Echocardiography may be used to assess LV function and eliminate other CV causes of chest pain
  • MRI may be used to determine myocardial viability and exclude differential diagnoses (eg pulmonary embolism or aortic dissection)
  • Rest myocardial scintigraphy may be helpful in patients within chest pain without ECG changes or evidence of ongoing MI

Screening

Stress Test

  • Stress test may be performed in patients with low and intermediate risk who have no ischemia at rest or with low level activity for a minimum of 12-24 hours; prior to discharge; or as an outpatient
  • Confirms or establishes diagnosis of coronary artery disease (CAD) and assesses risk for future cardiovascular (CV) events
  • Patients with significant ischemia during exam should be considered for coronary angiography
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