Myocardial Infarction: Causes, Symptoms, Diagnosis & Rx

Definition and epidemiology

Myocardial infarction is defined by acute myocardial injury with clinical evidence of ischemia and elevated cardiac troponin, along with at least one of: ischemic symptoms, new ECG changes, imaging evidence of new loss of viable myocardium, or intracoronary thrombus. MI is classified into STEMI (ST-elevation MI) and NSTEMI (non-ST-elevation MI) based on ECG findings, which guide management urgency.

MI remains a leading cause of mortality worldwide, with approximately 800,000 cases annually in the United States. Incidence increases sharply with age, and men are affected 2–3 times more frequently than premenopausal women. The gap narrows after menopause. Mortality has declined over recent decades due to improved reperfusion strategies and secondary prevention, but in-hospital mortality for STEMI remains 5–10%.

High-yield for exams

STEMI = ST elevation ≥1 mm in ≥2 contiguous leads or new LBBB; requires immediate reperfusion (PCI or fibrinolysis).
Troponin is the gold standard biomarker; rises 3–4 hours post-MI, peaks 24–48 hours, elevated 7–14 days.
Aspirin is the single most important immediate treatment; give chewable aspirin immediately in suspected MI.
Anterior MI (V1–V4) = LAD occlusion; carries highest risk of heart failure and cardiogenic shock.
Right ventricular infarction: ST elevation in V4R, hypotension, elevated JVP, clear lungs; treat with IV fluids, avoid nitrates.
Ventricular free wall rupture, VSD, and papillary muscle rupture occur 1–5 days post-MI; all cause acute decompensation.
Post-MI secondary prevention: dual antiplatelet therapy ×12 months, aspirin indefinitely, high-intensity statin, beta-blocker, ACE inhibitor.
Dressler syndrome: fever, pleuritic chest pain, friction rub weeks to months post-MI; treat with NSAIDs or colchicine.

Etiology and risk factors

The overwhelming majority of MIs result from acute atherosclerotic plaque rupture or erosion with superimposed thrombosis in a coronary artery. Less common causes include coronary artery spasm (Prinzmetal angina), coronary embolism, dissection, vasculitis, cocaine use, and supply-demand mismatch (type 2 MI) in the setting of severe anemia, hypotension, tachyarrhythmia, or hypoxia.

Major modifiable risk factors:

Smoking (most potent modifiable risk)
Hypertension
Diabetes mellitus
Dyslipidemia (elevated LDL, low HDL)
Obesity and metabolic syndrome
Physical inactivity

Non-modifiable risk factors:

Age (men ≥45, women ≥55)
Male sex
Family history of premature coronary disease
Genetic predisposition

Additional factors include chronic kidney disease, autoimmune disease, obstructive sleep apnea, psychosocial stress, and cocaine or amphetamine use.

Pathophysiology

Atherosclerotic plaques develop over years through endothelial injury, lipid deposition, inflammation, and fibrous cap formation. Acute MI typically occurs when a vulnerable plaque—characterized by a thin fibrous cap and large lipid core—ruptures or erodes. This exposes thrombogenic material to circulating blood, triggering platelet aggregation and thrombus formation.

The thrombus partially or completely occludes the coronary artery, causing downstream myocardial ischemia. If occlusion persists, ischemia progresses to irreversible necrosis within 20–40 minutes. Necrosis begins in the subendocardium (most vulnerable due to highest oxygen demand and lowest perfusion pressure) and extends transmurally over hours if flow is not restored.

STEMI vs NSTEMI:

STEMI: Complete occlusion causes transmural ischemia, manifesting as ST-segment elevation on ECG. Urgent reperfusion is critical.
NSTEMI: Partial occlusion or transient occlusion results in subendocardial ischemia, causing ST depression, T-wave inversion, or no ECG changes. Troponin is elevated.

Myocardial necrosis triggers an inflammatory response. Neutrophils infiltrate within hours, followed by macrophages. Over weeks, granulation tissue forms, and eventually a collagen scar replaces necrotic tissue. Adverse remodeling—ventricular dilatation and dysfunction—can follow large infarcts.

Clinical features

The hallmark symptom is acute, severe chest pain or pressure, typically substernal, lasting >20 minutes. Pain is often described as crushing, squeezing, or heavy, and may radiate to the left arm, jaw, neck, back, or epigastrium. Associated symptoms include dyspnea, diaphoresis, nausea, vomiting, lightheadedness, and profound anxiety (sense of impending doom).

Atypical presentations are common in women, elderly patients, and those with diabetes. These may include:

Dyspnea without chest pain
Epigastric discomfort or indigestion
Fatigue or weakness
Syncope
Isolated arm or jaw pain

Physical examination may be unremarkable or reveal:

Tachycardia or bradycardia
Hypotension or hypertension
Diaphoresis, pallor
Fourth heart sound (S4) due to decreased ventricular compliance
Third heart sound (S3) if heart failure develops
New systolic murmur (papillary muscle dysfunction or rupture)
Pulmonary crackles if left ventricular failure or pulmonary edema present
Jugular venous distension in right ventricular infarction

Silent MI (no symptoms) occurs in approximately 20–30% of cases, particularly in diabetics with autonomic neuropathy.

Diagnosis

Diagnosis requires integration of clinical presentation, ECG, and cardiac biomarkers.

ECG

Obtain a 12-lead ECG within 10 minutes of presentation. Serial ECGs may be needed if initial findings are non-diagnostic.

STEMI criteria: ST elevation ≥1 mm in two contiguous limb leads or ≥2 mm in two contiguous precordial leads, or new left bundle branch block (LBBB) with typical symptoms.

NSTEMI/unstable angina findings:

ST depression ≥0.5 mm
T-wave inversion ≥1 mm
Dynamic ST-T changes
Non-specific or normal ECG (does not exclude MI)

Localization by ECG leads:

Territory	Leads	Artery
Anterior	V1–V4	LAD
Lateral	I, aVL, V5–V6	LCx
Inferior	II, III, aVF	RCA (or LCx)
Posterior	Tall R in V1–V2, ST depression V1–V3	RCA or LCx
Right ventricular	ST elevation in V4R	Proximal RCA

Cardiac biomarkers

Troponin I or T is the preferred biomarker. Troponin rises within 3–4 hours of infarction, peaks at 24–48 hours, and remains elevated for 7–14 days. High-sensitivity troponin assays detect earlier elevations. Serial measurements (at presentation and 3–6 hours later) improve sensitivity.

Creatine kinase-MB (CK-MB) rises and falls more rapidly than troponin, useful for detecting reinfarction. It is less specific than troponin.

Myoglobin rises earliest but is non-specific.

Imaging

Echocardiography identifies regional wall motion abnormalities, assesses left ventricular function (ejection fraction), and detects mechanical complications. Coronary angiography is diagnostic and therapeutic in STEMI and high-risk NSTEMI, identifying the culprit lesion and guiding percutaneous coronary intervention (PCI). Cardiac MRI or nuclear imaging may be used when diagnosis is unclear.

Differential diagnosis

Acute chest pain has a broad differential. Key considerations include:

Unstable angina: Troponin negative, ischemic symptoms or ECG changes
Aortic dissection: Tearing pain radiating to back, pulse differential, widened mediastinum on imaging
Pulmonary embolism: Pleuritic pain, dyspnea, tachycardia, risk factors for VTE
Pericarditis: Sharp, positional pain relieved by sitting forward; diffuse ST elevation, PR depression
Myocarditis: Viral prodrome, diffuse ST changes, elevated troponin without coronary occlusion
Esophageal rupture (Boerhaave syndrome): Severe pain after vomiting, subcutaneous emphysema
GERD or esophageal spasm: Burning or squeezing pain, relationship to meals, relief with antacids
Pneumothorax: Sudden pleuritic pain, dyspnea, absent breath sounds
Costochondritis: Reproducible tenderness over costochondral junctions
Takotsubo cardiomyopathy (stress cardiomyopathy): Mimics MI, apical ballooning on echo, no coronary occlusion

ECG and troponin are critical to differentiate MI from other causes.

Management

Management depends on MI type (STEMI vs NSTEMI) and time from symptom onset.

Immediate general measures (all MI)

Aspirin (chewable, loading dose) immediately unless contraindicated
Oxygen if hypoxic (SpO2 <90%); avoid routine supplemental oxygen
Nitroglycerin sublingually for ongoing pain, avoid if hypotensive or right ventricular infarction
Morphine for pain unresponsive to nitroglycerin
Continuous ECG monitoring

STEMI management

Goal: Reperfusion as rapidly as possible. Door-to-balloon (PCI) time ≤90 minutes or door-to-needle (fibrinolysis) ≤30 minutes.

Reperfusion strategy:

Primary PCI (preferred if available within 120 minutes of first medical contact): emergent coronary angiography with stenting of culprit lesion
Fibrinolytic therapy (if PCI not available within 120 minutes and <12 hours from symptom onset): agents include alteplase, tenecteplase, reteplase. Contraindications: prior intracranial hemorrhage, ischemic stroke within 3 months, active bleeding, suspected aortic dissection

Adjunctive pharmacotherapy:

Dual antiplatelet therapy: Aspirin plus a P2Y12 inhibitor (clopidogrel, prasugrel, or ticagrelor)
Anticoagulation: Heparin (unfractionated or low-molecular-weight) or bivalirudin during PCI
Beta-blocker: Oral within 24 hours if hemodynamically stable
ACE inhibitor or ARB: Start within 24 hours, especially if anterior MI, heart failure, or ejection fraction <40%
Statin: High-intensity statin regardless of baseline LDL

NSTEMI/unstable angina management

Risk stratification using scores (e.g., GRACE, TIMI) guides timing of invasive strategy.

Pharmacotherapy:

Aspirin plus P2Y12 inhibitor
Anticoagulation (heparin, enoxaparin, fondaparinux, or bivalirudin)
Beta-blocker
Statin
Consider glycoprotein IIb/IIIa inhibitors in high-risk patients undergoing PCI

Invasive strategy timing:

Immediate (<2 hours): Hemodynamic instability, refractory angina, life-threatening arrhythmias
Early (<24 hours): High-risk features (elevated troponin, dynamic ECG changes, GRACE score >140)
Elective (<72 hours): Intermediate risk
Conservative (medical management): Low-risk patients, extensive comorbidities, patient preference

Long-term secondary prevention

Dual antiplatelet therapy for at least 12 months post-stent
Aspirin indefinitely
High-intensity statin
Beta-blocker, especially if reduced ejection fraction
ACE inhibitor or ARB if ejection fraction <40%, diabetes, or hypertension
Aldosterone antagonist (spironolactone, eplerenone) if ejection fraction <40% and heart failure or diabetes
Cardiac rehabilitation
Lifestyle: smoking cessation, diet, exercise, weight control, diabetes and blood pressure management

Complications and prognosis

Complications may occur acutely (within hours to days) or later (weeks to months).

Acute complications

Arrhythmias: Ventricular fibrillation and ventricular tachycardia are leading causes of sudden death in the first 24–48 hours. Bradyarrhythmias and heart block may occur, especially with inferior MI (RCA involvement).

Cardiogenic shock: Results from severe left ventricular dysfunction, mechanical complications, or right ventricular infarction. Occurs in 5–10% of STEMI; mortality exceeds 40%.

Acute heart failure and pulmonary edema: Due to left ventricular dysfunction. Classified by Killip class (I–IV).

Right ventricular infarction: Presents with hypotension, elevated JVP, clear lungs. Avoid nitrates and diuretics; treat with IV fluids.

Mechanical complications (1–5 days post-MI):

Ventricular free wall rupture: Sudden cardiovascular collapse, cardiac tamponade; often fatal
Ventricular septal rupture (VSD): New harsh holosystolic murmur, step-up in oxygen saturation from right atrium to right ventricle
Papillary muscle rupture: Acute severe mitral regurgitation, pulmonary edema, new systolic murmur

Pericarditis (acute post-MI pericarditis): Chest pain, friction rub; typically occurs 2–4 days post-MI. Treat with high-dose aspirin. Avoid other NSAIDs and corticosteroids, as they interfere with myocardial scar formation and increase the risk of ventricular free wall rupture.

Subacute and late complications

Left ventricular thrombus: Risk highest with anterior MI and apical akinesis. May embolize, causing stroke. Anticoagulation recommended if detected.

Dressler syndrome (post-MI syndrome): Autoimmune pericarditis occurring weeks to months post-MI. Fever, pleuritic chest pain, friction rub, elevated inflammatory markers. Treat with NSAIDs or colchicine.

Ventricular aneurysm: Persistent ST elevation on ECG, dyskinetic bulge on echo. Risk of thrombus, arrhythmia, and heart failure.

Chronic heart failure: Due to extensive myocardial loss and adverse remodeling.

Prognosis

In-hospital mortality for STEMI is 5–10%, for NSTEMI 3–5%. Prognosis depends on infarct size, left ventricular function, completeness of revascularization, and adherence to secondary prevention. One-year mortality post-MI is approximately 10%. Major predictors of poor outcome include age, heart failure (Killip class), anterior location, ejection fraction <40%, diabetes, and chronic kidney disease. Early reperfusion and guideline-directed medical therapy substantially improve survival.

Mnemonic

MONA for acute MI initial management: Morphine, Oxygen (if hypoxic), Nitroglycerin, Aspirin.

Practice questions

1. A 58-year-old man with a history of hypertension and smoking presents to the emergency department with 2 hours of severe, crushing substernal chest pain radiating to his left arm. He is diaphoretic and anxious. Vital signs: BP 160/95 mmHg, HR 102/min, RR 22/min, SpO2 94% on room air. ECG shows ST-segment elevation of 3 mm in leads V2–V5. Which of the following is the most appropriate immediate management?

Answer: C. This patient presents with STEMI (ST elevation ≥2 mm in contiguous precordial leads V2–V5, indicating LAD occlusion). The most appropriate immediate action is to administer aspirin and arrange emergent PCI with a goal door-to-balloon time of ≤90 minutes. Aspirin is given immediately to all suspected MI patients unless contraindicated. Nitroglycerin alone is inadequate. Waiting for biomarkers or echocardiography delays life-saving reperfusion. Fibrinolytic therapy is reserved for settings where PCI cannot be performed within 120 minutes; in a hospital setting, PCI is preferred.

2. A 65-year-old woman with diabetes and hyperlipidemia is admitted with acute chest pain. Troponin I is elevated at 8.5 ng/mL (normal <0.04). ECG shows ST-segment depression of 2 mm in leads V4–V6 and T-wave inversion in leads I and aVL. She is hemodynamically stable. Which of the following best describes the next step in management?

Answer: C. This patient has NSTEMI (elevated troponin with ischemic ECG changes but no ST elevation). She is hemodynamically stable, so emergent PCI within 90 minutes (indicated for STEMI or very high-risk NSTEMI) is not required. Fibrinolysis is contraindicated in NSTEMI. The appropriate management is aspirin, a P2Y12 inhibitor (e.g., ticagrelor), anticoagulation (e.g., enoxaparin), and risk stratification using a score such as GRACE or TIMI to determine timing of invasive strategy (angiography ± PCI), typically within 24–72 hours for high-risk NSTEMI. Discharge or mere observation would be inappropriate given her elevated troponin and dynamic ECG changes.

3. A 70-year-old man undergoes successful percutaneous coronary intervention with stent placement for acute inferior STEMI. On day 3 of hospitalization, he develops sudden hypotension (BP 85/60 mmHg), elevated jugular venous pressure, and clear lung fields. Cardiac auscultation reveals a new loud holosystolic murmur at the left lower sternal border. Echocardiography is most likely to show which of the following?

Answer: B. This patient presents with a mechanical complication of inferior MI occurring 1–5 days post-infarction. The triad of hypotension, elevated JVP, and clear lungs with a new harsh holosystolic murmur at the left lower sternal border is classic for ventricular septal rupture (VSD). VSD creates a left-to-right shunt, increasing right heart pressures (elevated JVP) and causing a loud murmur. Severe mitral regurgitation from papillary muscle rupture would cause pulmonary edema, not clear lungs. Pericardial effusion and free wall rupture cause tamponade with muffled heart sounds and pulsus paradoxus, not a loud murmur. Right ventricular infarction would have been present on admission, not a new day-3 complication.

Frequently asked questions

What causes a myocardial infarction?

Myocardial infarction is most commonly caused by rupture or erosion of an atherosclerotic plaque in a coronary artery, leading to thrombus formation and acute arterial occlusion. This blocks blood flow to part of the heart muscle, causing ischemia and necrosis. Risk factors include smoking, hypertension, diabetes, high cholesterol, obesity, and family history. Less common causes include coronary spasm, dissection, embolism, cocaine use, and severe supply-demand mismatch in conditions like anemia or shock.

What are the first symptoms of a heart attack?

The first symptom is typically sudden, severe chest pain or pressure, often described as crushing or squeezing, lasting more than 20 minutes. The pain may radiate to the left arm, jaw, neck, or back. Other early symptoms include shortness of breath, sweating, nausea, lightheadedness, and a sense of impending doom. Women, elderly patients, and diabetics may have atypical presentations such as fatigue, indigestion, or isolated arm or jaw discomfort without classic chest pain.

How is myocardial infarction diagnosed?

Diagnosis requires a combination of clinical symptoms, ECG changes, and elevated cardiac biomarkers, especially troponin. A 12-lead ECG is obtained within 10 minutes of presentation; ST-segment elevation indicates STEMI, while ST depression or T-wave inversion suggests NSTEMI. Troponin levels are measured at presentation and 3–6 hours later. Echocardiography assesses heart function and wall motion abnormalities. Coronary angiography is performed for definitive diagnosis and treatment, especially in STEMI and high-risk NSTEMI.

Is myocardial infarction curable?

Myocardial infarction causes permanent damage to heart muscle; necrotic tissue is replaced by scar and does not regenerate. However, prompt reperfusion therapy (PCI or fibrinolysis) can limit infarct size and preserve heart function. With appropriate acute treatment and lifelong secondary prevention—including medications (aspirin, statins, beta-blockers, ACE inhibitors) and lifestyle changes—many patients live normal or near-normal lives. The key is rapid treatment to minimize damage and prevent recurrence.

STEMI vs NSTEMI — what is the difference?

STEMI (ST-elevation MI) occurs when a coronary artery is completely blocked, causing transmural ischemia and ST-segment elevation on ECG; it requires immediate reperfusion (PCI or fibrinolysis within minutes). NSTEMI (non-ST-elevation MI) results from partial or transient occlusion, causing subendocardial ischemia without ST elevation; ECG may show ST depression, T-wave inversion, or be normal. Both cause elevated troponin, but STEMI is a greater emergency. Management urgency differs: STEMI needs immediate reperfusion, NSTEMI is risk-stratified for early invasive strategy within hours to days.

Key drugs

AspirinClopidogrelTicagrelorPrasugrelHeparinEnoxaparinNitroglycerin MorphineMetoprololAtenololLisinoprilRamiprilAtorvastatin RosuvastatinAlteplaseTenecteplase

Unstable anginaStable angina pectorisAcute coronary syndromeCoronary artery diseaseHeart failureCardiogenic shockVentricular arrhythmiasAortic dissection

Sources and further reading

StatPearls (NCBI Bookshelf)MedlinePlus WHO ICD-10: I21

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.

Myocardial infarction