Cardiology · Acute Coronary Syndrome
The facts most likely to be tested
The diagnostic ECG criteria for STEMI require new ST-segment elevation at the J-point in at least two contiguous leads of ≥1 mm in all leads other than V2-V3, where specific age- and sex-dependent thresholds apply.
Primary percutaneous coronary intervention (PCI) is the preferred reperfusion strategy and must be performed within a door-to-balloon time of 90 minutes at a PCI-capable facility.
Fibrinolytic therapy is indicated for patients presenting to a non-PCI-capable facility if the door-to-needle time can be achieved within 30 minutes and the patient presents within 12 hours of symptom onset.
Inferior wall STEMI involving leads II, III, and aVF requires immediate right-sided ECG (V4R) to evaluate for right ventricular infarction, which presents with hypotension and clear lungs.
Nitrates and diuretics are strictly contraindicated in right ventricular infarction due to the patient's profound dependence on preload to maintain cardiac output.
Dual antiplatelet therapy (DAPT) consisting of aspirin and a P2Y12 inhibitor (e.g., ticagrelor or prasugrel) must be administered immediately to prevent further thrombus propagation.
New left bundle branch block (LBBB) in the setting of ischemic chest pain is considered a STEMI equivalent and warrants immediate reperfusion therapy.
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A 62-year-old male presents to the emergency department with 90 minutes of crushing substernal chest pain radiating to his left jaw. His medical history is significant for hypertension and hyperlipidemia. Physical examination reveals a diaphoretic patient with a blood pressure of 88/50 mmHg and clear lung fields on auscultation. An ECG shows ST-segment elevation in leads II, III, and aVF. A right-sided ECG confirms ST-segment elevation in lead V4R.
Which of the following medications is most likely to cause a precipitous drop in blood pressure in this patient?
Nitroglycerin
The patient has an inferior STEMI with right ventricular involvement, making him preload-dependent; nitrates reduce preload and can cause severe hypotension in this clinical scenario.
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High yield triage
Etiology / Epidemiology
Caused by complete coronary artery occlusion due to plaque rupture. Smoking, HTN, DM, and dyslipidemia are primary risk factors.
Clinical Manifestations
Presents as Levine's sign with substernal chest pain radiating to the jaw/arm. Diaphoresis and syncope are high-risk indicators.
Diagnosis
ECG showing ST-segment elevation >1mm in ≥2 contiguous leads. Troponin I/T is the gold-standard biomarker.
Treatment
Immediate PCI within 90 minutes. Administer Aspirin and Heparin; avoid nitrates in RV infarction.
Prognosis
Risk of ventricular arrhythmia is highest in the first 24 hours. Left ventricular failure is the leading cause of death.
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Epidemiology & Etiology
STEMI results from acute thrombotic occlusion of an epicardial coronary artery. Male gender, age >45, and family history are non-modifiable risks. Smoking remains the most significant modifiable risk factor for early-onset disease.
Pertinent Anatomy
The Left Anterior Descending (LAD) artery supplies the anterior wall (leads V1-V4). The Right Coronary Artery (RCA) supplies the inferior wall (leads II, III, aVF) and often the right ventricle.
Pathophysiology
Plaque rupture exposes the subendothelial matrix, triggering platelet aggregation and the coagulation cascade. This creates a fibrin-rich thrombus that completely obstructs blood flow. Myocardial necrosis begins within 20-40 minutes, leading to myocardial stunning and eventual irreversible cell death.
Clinical Manifestations
Patients report crushing substernal pressure often associated with nausea, vomiting, and dyspnea. Physical exam may reveal an S4 gallop or a new mitral regurgitation murmur. Silent ischemia is common in patients with Diabetes Mellitus.
Diagnosis
The ECG is the definitive diagnostic tool. Look for ST-segment elevation or a new Left Bundle Branch Block (LBBB). Troponin I/T levels rise within 3-6 hours and remain elevated for 7-10 days.
Treatment
Primary PCI is the preferred reperfusion strategy. If unavailable, administer Fibrinolytics (e.g., alteplase) within 30 minutes. Contraindications to fibrinolytics include active internal bleeding or history of intracranial hemorrhage.
Prognosis
Early mortality is driven by ventricular fibrillation. Long-term outcomes depend on the extent of myocardial remodeling and the development of congestive heart failure.
Differential Diagnosis
Aortic Dissection: tearing chest pain radiating to the back
Pericarditis: diffuse ST elevation with PR depression
Pulmonary Embolism: tachycardia and hypoxia with clear lungs
GERD: burning pain relieved by antacids
Tension Pneumothorax: absent breath sounds and tracheal deviation