B.8 STEMI Etiology, Pathophys, DX Flashcards
B.8 STEMI Etiology, Pathophys, DX
Define STEMI
Acute myocardial ischemia that is severe enough to result in ST-segment elevations on an ECG.
B.8 STEMI Etiology, Pathophys, DX
Clinical
- Angina at rest or with minimal exertion
- New-onset angina
- Severe, persistent, or worsening angina (crescendo angina)
- Autonomic symptoms that may occur include diaphoresis, syncope, palpitations, nausea, and/or vomiting.
B.8 STEMI Etiology, Pathophys, DX
Cardiac Biomarker
Cardiac biomarkers are typically elevated (e.g., troponin).
B.8 STEMI Etiology, Pathophys, DX
Pathophysi
Primary Cause: Often results from unstable plaque and subsequent rupture, but can also occur due to vasospasms and embolism.
-Inflammatory Processes:
- Macrophages in the plaque secrete matrix metalloproteinases, leading to the breakdown of extracellular matrix.
- The degradation of the fibrous cap triggers minor stress or exposes the underlying lipid core, resulting in thrombus formation that may block coronary arteries.
Complete Coronary Artery Occlusion
Effects:
- Impaired myocardial blood flow can lead to sudden death of myocardial cells.
- The occlusion can compromise the entire thickness of the myocardium (transmural infarction).
- Clinical Manifestation: Typically presents as ST-Elevation Myocardial Infarction (STEMI).
B.8 STEMI Etiology, Pathophys, DX
DX
An ECG should be performed immediately upon suspicion of Acute Coronary Syndrome (ACS), followed by the measurement of cardiac biomarkers.
Additional diagnostic evaluations, such as echocardiography, will depend on the initial assessment results and further risk stratification.
B.8 STEMI Etiology, Pathophys, DX
ECG
ECG
- A 12-lead ECG is the most reliable initial test.
- Dynamic changes require serial ECG evaluations.
- Comparison to prior ECGs is beneficial if available.
Types of ECG changes:
Acute Stage: Myocardial damage evident
- ST elevations in two contiguous leads with reciprocal ST depressions.
- Pathological T waves (“peaked T waves”).
Intermediate Stage: Myocardial necrosis present
- Pathological Q waves.
- T-wave inversions.
Chronic Stage: Permanent scarring
- Persistent, broad, and deep Q waves.
- Often incomplete recovery of T waves.
- Permanent T-wave inversion may occur.
The progression of ECG changes over several hours includes: hyperacute T waves → ST elevation → pathological Q wave → T-wave inversion → ST normalization → T-wave normalization.
An acute LBBB accompanied by symptoms of ACS is also regarded as a STEMI since ST elevations cannot be accurately assessed in the presence of an LBBB.
B.8 STEMI Etiology, Pathophys, DX
Localization on ECG
proximal left anterior descending artery (LAD) - When the leads V1 to V6 show extensive anterior changes, it typically indicates involvement of the
.
antero-septal region, also associated with the LAD. - If the leads V1 and V2 are affected, the infarct is often located in the
The antero-lateral area - can be identified when leads V3 and V4 display changes, which point to the diagonal branch of the distal LAD.
For the lateral region, changes in leads V5 and V6 suggest involvement of the left circumflex artery (LCX).
When leads I and aVL are affected, it indicates an inferior infarct, generally associated with the right coronary artery (RCA), although this is less common.
In contrast, inferior changes in leads II, III, and aVF signify involvement of the RCA.
changes in leads V7 to V9 suggest a posterior or postero-lateral infarction, which is related to the posterior descending artery, originating from either the RCA or LCX.
An ST elevation in aVR and lead I, along with diffuse ST depression in all other leads, may indicate the possibility of left main stenosis.
B.8 STEMI Etiology, Pathophys, DX
Labs
Laboratory Findings
- Increase in Troponin T/I and CK-MB
- Elevated LDH
- Increased WBC and CRP
- Elevated BNP, particularly in cases of heart failure
Serum troponin T is considered the most specific marker for cardiac injury and can typically be detected 3–4 hours after the onset of a myocardial infarction (MI). CK-MB levels correlate with the size of the infarct and usually peak around 12–24 hours post-MI, then normalize within 2–3 days, making CK-MB a reliable marker for assessing reinfarction.
B.8 STEMI Etiology, Pathophys, DX
Coronary Angiography
Coronary Angiography
- Gold standard for diagnosing acute occlusion
- Enables both diagnosis and immediate intervention
- Capable of identifying the location and extent of vessel blockage
The most frequently occluded coronary arteries are: LAD > RCA > LCX.
B.8 STEMI Etiology, Pathophys, DX
TTE
Transthoracic Echocardiography (TTE)
- Identifies any wall motion abnormalities and assesses left ventricular (LV) function
- Crucial for risk assessment; in STEMI, the strongest predictor of survival is LVEF
- Evaluates for complications such as aneurysms, mitral valve regurgitation, pericardial effusion, and free wall rupture
B.8 STEMI Etiology, Pathophys, DX
Cardiac CT
Cardiac CT
- Can be used as an alternative to invasive coronary angiography for patients with an intermediate risk of acute coronary syndrome (ACS)
- Facilitates noninvasive visualization of the coronary arteries
- Contraindications include arrhythmias and tachycardia
