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MYOCARDIAL INFARCTION

20-Mark Question Answer | Internal Medicine

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DEFINITION

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EPIDEMIOLOGY

• In the United States, ~605,000 patients experience a new AMI and ~200,000 experience a recurrent AMI each year.
• About half of AMI-related deaths occur before the individual reaches the hospital.
• In-hospital mortality after AMI has declined from 10% to ~5%.
• 1-year mortality rate after AMI is ~15%; fourfold higher in patients >75 years.
• ~10% of MIs occur before age 40; ~45% before age 65.
• Men are at greater risk than women; gap narrows with age. Women are relatively protected during reproductive years due to estrogen; menopause accelerates risk.

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ETIOLOGY & RISK FACTORS

1. Atherosclerosis with acute plaque rupture/erosion — accounts for >90% of MIs
2. Coronary artery vasospasm (Prinzmetal angina)
3. Embolism from mural thrombi or valve vegetations (e.g., atrial fibrillation)
4. Vasculitis, amyloid deposition, sickle cell disease (rare)

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CLASSIFICATION

By Depth:

Universal Classification (4th Universal Definition):

• Type 1 — Spontaneous MI from plaque rupture/erosion with thrombosis
• Type 2 — MI due to supply-demand mismatch (e.g., coronary spasm, severe anemia, tachyarrhythmia)
• Type 3 — MI causing sudden cardiac death before biomarkers obtained
• Type 4a/b — PCI-related MI
• Type 5 — CABG-related MI

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PATHOGENESIS

Step 1 — Coronary Artery Occlusion Sequence:

1. An atheromatous plaque is eroded or suddenly disrupted by endothelial injury, intraplaque hemorrhage, or mechanical forces, exposing subendothelial collagen and necrotic plaque contents to blood.
2. Platelets adhere, aggregate, and are activated, releasing thromboxane A₂, ADP, and serotonin — causing further platelet aggregation and vasospasm.
3. Activation of coagulation by exposure of tissue factor adds to the growing thrombus.
4. Within minutes, the enlarging thrombus completely occludes the coronary artery lumen.
5. Angiography within 4 hours of onset demonstrates thrombosis in almost 90% of cases.

Step 2 — Myocardial Response to Ischemia:

• Within seconds: aerobic metabolism ceases → drop in ATP → accumulation of lactic acid.
• Within minutes: rapid loss of contractility.
• 20–40 minutes: irreversible damage and coagulative necrosis of myocytes.
• Irreversible injury first occurs in the subendocardial zone (most vulnerable — last to receive blood, highest intramural pressure).
• A "wavefront" of cell death moves from subendocardium to epicardium with progressive ischemia.
• Sarcolemmal membrane disruption allows intracellular macromolecules (troponins) to leak into vasculature — basis of biomarker diagnosis.

Glycoprotein IIb/IIIa Receptor:

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ECG CHANGES IN MI (Ganong's Review)

1. Hyperacute T waves — peaked, within minutes
2. ST segment elevation — hallmark of acute STEMI
3. Q wave formation — after days–weeks (electrically silent dead muscle)
4. T wave inversion — subacute phase
5. Non-Q-wave infarcts — less severe but higher incidence of reinfarction

• Inferior MI (RCA): Q waves/ST elevation in leads II, III, aVF
• Anterior MI (LAD): V1–V4
• Lateral MI (LCX): I, aVL, V5–V6
• Posterior MI: tall R waves in V1, ST depression V1–V3

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MORPHOLOGY (Time-Based Evolution)

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CLINICAL FEATURES

Symptoms:

• Severe crushing/squeezing chest pain (substernal) persisting >30 minutes — the cardinal symptom
• Radiation to the left arm, jaw, shoulder, back, or epigastrium
• Diaphoresis (sweating) — strongly suggests STEMI when combined with prolonged chest pain
• Nausea and vomiting (especially inferior MI — vagal stimulation)
• Dyspnea, weakness, fatigue
• Sense of impending doom
• Painless MI (silent MI) — more common in diabetics and elderly

Painless Presentations:

Physical Examination:

• Patient is anxious, restless, pallid, diaphoretic, with cold extremities
• Anterior MI: Sympathetic hyperactivity → tachycardia + hypertension
• Inferior MI: Parasympathetic hyperactivity → bradycardia + hypotension
• Precordium usually quiet; apical impulse may be impalpable
• S3 and S4 gallop sounds
• Decreased intensity of S1
• Paradoxical splitting of S2
• Transient midsystolic/late systolic murmur (mitral valve dysfunction)
• Pericardial friction rub (transmural MI)
• Carotid pulse decreased (reduced stroke volume)
• Fever up to 38°C within first week

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INVESTIGATIONS

1. ECG

• STEMI: ST segment elevation ≥1 mm in ≥2 contiguous limb leads; ≥2 mm in precordial leads; New LBBB
• NSTEMI: ST depression, T wave changes without ST elevation
• Serial ECGs every 15–30 minutes in evolving MI

2. Cardiac Biomarkers

3. Imaging

• Chest X-ray: Pulmonary edema, cardiomegaly
• Echocardiography (2D echo): Wall motion abnormalities (regional), LV function (EF), pericardial effusion, mechanical complications
• Coronary angiography: Gold standard for coronary anatomy; enables PCI
• Nuclear imaging (SPECT): Viability, perfusion
• Cardiac MRI: Late gadolinium enhancement for scar assessment

4. Non-Specific Indices of Necrosis and Inflammation

• Leukocytosis (10,000–20,000/μL) — appears within a few hours
• Elevated ESR — rises after the first day, peaks at 1 week
• CRP and other acute-phase proteins elevated

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MANAGEMENT

Immediate (Pre-Hospital / ER):

1. MONA (historical mnemonic): Morphine, Oxygen (only if SpO₂ <90%), Nitroglycerin, Aspirin
2. Aspirin 160–325 mg chewed immediately (buccal absorption, inhibits COX-1, reduces TXA₂)
3. Nitroglycerin sublingual 0.4 mg × 3 doses at 5-minute intervals (↓ preload, vasodilates coronary arteries) — avoid if BP <90 mmHg, RV infarction, or PDE-5 inhibitor use within 24 hours
4. Morphine 2–4 mg IV every 5 min — for pain; vagotonic (may cause bradycardia → atropine)
5. Oxygen only if SpO₂ <90%
6. IV Beta-blocker — Metoprolol 5 mg IV every 2–5 min (×3 doses); reduces O₂ demand, prevents VF; avoid in bradycardia, hypotension, HF, PR >0.24s
7. 12-lead ECG within 10 minutes of presentation

Reperfusion Strategy (Time is Myocardium):

• Contraindications: Prior intracranial hemorrhage, aortic dissection, active bleeding, recent surgery, BP >180/110.

Antiplatelet Therapy:

• Aspirin (lifelong)
• P2Y12 inhibitors: Clopidogrel, ticagrelor, or prasugrel (dual antiplatelet therapy — DAPT)
• GP IIb/IIIa inhibitors: Used in high-risk PCI (abciximab, tirofiban, eptifibatide)

Anticoagulation:

• Unfractionated heparin (UFH) or LMWH (enoxaparin)
• Bivalirudin (direct thrombin inhibitor — alternative during PCI)
• Fondaparinux (NSTEMI with medical management)

Long-Term Medical Therapy (POST-MI):

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COMPLICATIONS

Killip Classification (hemodynamic severity):

Mechanical Complications:

Electrical Complications:

• Ventricular fibrillation (VF) — most common cause of pre-hospital death (80–90% of early cardiac deaths in ischemia)
• Ventricular tachycardia (VT)
• Complete heart block / AV block — especially inferior MI (RCA involvement of AV node)
• Sinus bradycardia — inferior MI (vagal)
• Accelerated idioventricular rhythm (AIVR) — reperfusion arrhythmia, usually benign
• AF/supraventricular arrhythmias

Other Complications:

• Pericarditis — Dressler's syndrome (autoimmune, 2–10 weeks post-MI); fever, pleuritic chest pain, friction rub
• LV aneurysm — persistent ST elevation, mural thrombus, arrhythmias
• Mural thrombus → systemic embolism (stroke)
• RV infarction — inferior MI; presents with hypotension, elevated JVP, clear lungs
• Stunned myocardium — reversible post-ischemic dysfunction even after reperfusion
• Heart failure and cardiogenic shock

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STUNNED vs. HIBERNATING MYOCARDIUM

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PROGNOSIS & RISK STRATIFICATION

• TIMI Risk Score — used to stratify NSTEMI/STEMI
• Left ventricular ejection fraction (LVEF) is the single most important determinant of long-term prognosis
• LVEF <40% → high risk for sudden cardiac death → consider ICD
• Post-MI rehabilitation, lifestyle modification, and strict secondary prevention are essential

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DIFFERENTIAL DIAGNOSIS

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SUMMARY TABLE

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⚠️ Important Note on Sources: The medical library available contains Harrison's Principles of Internal Medicine 22E (2025) and Goldman-Cecil Medicine (International Edition). Golwala's Medicine and Davidson's Principles & Practice of Medicine are not available in the library. Goldman-Cecil Medicine is used as the closest international medicine textbook equivalent in content and scope. Key points from Golwala and Davidson's tradition are incorporated from general medical knowledge where directly relevant. Also note: regarding "homeopathic management of Yama" — "Yama" does not correspond to any recognized medical or homeopathic term or entity. If you meant "Arrhythmia" or a specific homeopathic remedy/condition, please clarify. The homeopathic section below covers management of the cardiac/MI condition itself.

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MYOCARDIAL INFARCTION

Comprehensive 20-Mark Notes

Sources: Harrison's Principles of Internal Medicine 22E · Goldman-Cecil Medicine (International Edition) · Robbins & Kumar Basic Pathology

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1. DEFINITION

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2. EPIDEMIOLOGY

• ~605,000 new AMIs and 200,000 recurrent AMIs per year in the USA
• ~50% of AMI deaths occur before reaching hospital
• In-hospital mortality has fallen from 10% → ~5%
• 1-year mortality post-AMI: ~15%
• Mortality ~4× higher in patients >75 years

• Cardiovascular disease = #1 cause of death in USA — 690,000 deaths in 2020 (21% of all deaths)
• ~600,000 first acute MIs, 200,000 recurrent MIs, ~170,000 "silent" MIs annually
• ~365,000 Americans die from coronary heart disease per year
• ST-elevation MI now comprises ≤25% of acute coronary syndromes (shifted to NSTEMI pattern)
• STEMI rates have fallen by two-thirds since 2008
• All modifiable risk factors together account for >90% of population-attributable risk globally
• Genetic contribution to CAD risk: ~40%; polygenic risk scores provide supplementary prognosis

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3. RISK FACTORS

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4. CLASSIFICATION

A. Universal Classification (4th Universal Definition):

B. By Depth:

• STEMI (Transmural): ST elevation; profound transmural ischaemia; complete coronary occlusion
• NSTEMI (Subendocardial): No ST elevation; incomplete blockage; biomarker rise without Q waves
• Unstable Angina: Same presentation as NSTEMI but no biomarker rise

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5. PATHOPHYSIOLOGY

A. Coronary Artery Occlusion — Harrison's 22E:

"STEMI usually occurs when coronary blood flow decreases abruptly after a thrombotic occlusion of a coronary artery previously affected by atherosclerosis… STEMI occurs when the surface of an atherosclerotic plaque becomes disrupted either through erosion or rupture, exposing its contents to the blood."

• Rich lipid core with thin fibrous cap (key feature)
• Expansive remodeling
• Neovascularisation (angiogenesis)
• Plaque haemorrhage
• Adventitial inflammation
• "Spotty" pattern of calcification

B. Sequence of Coronary Occlusion:

1. Plaque disruption — erosion, rupture, or fracture of calcified nodule exposes thrombogenic plaque core
2. Platelet activation — collagen, ADP, epinephrine, serotonin promote platelet activation → thromboxane A₂ released → further aggregation + vasoconstriction
3. GP IIb/IIIa receptor activation → high affinity for fibrinogen → platelet cross-linking
4. Coagulation cascade — tissue factor exposed in damaged endothelium → Factor VII + X activated → prothrombin → thrombin → fibrinogen → fibrin
5. Complete occlusion within minutes

C. Myocardial Response to Ischaemia:

• Seconds: Aerobic metabolism ceases → ATP drops, lactic acid accumulates
• Minutes: Rapid loss of contractility (reversible)
• 20–40 minutes: Irreversible necrosis begins — point of no return
• Sarcolemmal disruption → intracellular macromolecules (troponin, CK-MB) leak → biomarker basis
• Subendocardial zone is first and most vulnerable (highest intramural pressure, most distal from epicardial supply)
• Wavefront phenomenon: Necrosis spreads from subendocardium → epicardium over time

D. Types of Necrosis:

• Coagulative necrosis — classic; main pattern
• Contraction band necrosis — reperfusion injury; hypercontracted sarcomeres
• Myocytolysis — chronic ischaemia, subendocardial

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6. MORPHOLOGY (Time-Based Evolution)

• Infarcted area = pale/unstained (LDH enzyme leaked out)
• Normal myocardium = brick red (LDH intact)
• Useful from 3 hours post-infarction

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7. CLINICAL FEATURES

Symptoms — Harrison's 22E:

"Substernal chest pain persisting for >30 minutes and diaphoresis strongly suggests STEMI."

• Chest pain: Severe, crushing, pressing, heavy, "like a vice" — substernal
• Radiation: Left arm, jaw, neck, shoulder, back, epigastrium
• Duration: >30 minutes (differentiates from angina)
• Diaphoresis (cold sweating) — prominent
• Nausea and vomiting — especially inferior MI (vagal)
• Dyspnoea — from pump failure
• Profound weakness, fatigue
• Sense of impending doom (angor animi)

• Diabetics (autonomic neuropathy)
• Elderly patients
• Women
• May present as: sudden dyspnoea, arrhythmia, confusion, syncope, unexplained hypotension, peripheral embolism

Physical Signs — Harrison's 22E:

"Most patients are anxious and restless, attempting unsuccessfully to relieve the pain by moving about in bed, altering their position, and stretching."

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8. INVESTIGATIONS

A. ECG (Serial — every 15–30 min)

• ST elevation ≥1 mm in ≥2 contiguous limb leads
• ST elevation ≥2 mm in ≥2 contiguous precordial leads
• New LBBB

1. Tall/peaked (hyperacute) T waves (earliest)
2. ST segment elevation
3. Q wave development (pathological Q = >1 mm wide, >2 mm deep)
4. T wave inversion
5. Return of ST to baseline

B. Cardiac Biomarkers

C. Imaging

D. Blood Tests

• FBC: Leukocytosis (10,000–20,000/μL) within hours
• ESR: Rises after 1st day; peaks at 1 week
• CRP / acute-phase proteins: Elevated
• Blood glucose: Hyperglycaemia (stress response); important to monitor in diabetics
• Serum lipids: Baseline; drops within 24 h — measure early or wait 3 months
• Renal function / electrolytes: Baseline; hypomagnesaemia → arrhythmia risk
• Coagulation screen: Pre-thrombolysis

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9. MANAGEMENT

A. Immediate/Emergency (First 10 Minutes)

"Aspirin is essential in the management of patients with suspected STEMI and is effective across the entire spectrum of acute coronary syndromes. Rapid inhibition of cyclooxygenase-1 in platelets followed by a reduction of thromboxane A₂ levels is achieved by buccal absorption of a chewed 160–325-mg tablet."

• SBP <90 mmHg
• Clinical suspicion of RV infarction
• PDE-5 inhibitor use within 24 hours (sildenafil etc.)

"May reduce sympathetically mediated arteriolar and venous constriction, and the resulting venous pooling may reduce cardiac output and arterial pressure. Morphine also has a vagotonic effect and may cause bradycardia → treat with atropine 0.5 mg IV."

• Reduces O₂ demand
• Prevents VF and reinfarction
• Avoid if: HR <60, SBP <100, PR >0.24s, signs of HF, severe bronchospasm

B. Reperfusion Strategy — "Time is Myocardium"

• Streptokinase (non-fibrin specific; antigenic)
• Alteplase/tPA (fibrin-specific)
• Tenecteplase/TNK-tPA (fibrin-specific; single bolus — easiest to use)
• Reteplase (double bolus)

• Prior intracranial haemorrhage (any time)
• Known structural cerebrovascular lesion
• Ischaemic stroke within 3 months
• Active internal bleeding
• Suspected aortic dissection
• Significant closed-head trauma within 3 months

C. Antiplatelet and Anticoagulant Therapy

D. Long-Term Secondary Prevention (POST-MI)

"Sacubitril/valsartan was not more effective than an ACE inhibitor in preventing the development of incident HF in patients early post-MI."

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10. COMPLICATIONS

A. Killip Classification (Harrison's 22E)

B. Ventricular Dysfunction and Remodeling — Harrison's 22E:

"After STEMI, the left ventricle undergoes a series of changes in shape, size, and thickness… referred to as ventricular remodeling. Greater dilation follows infarction of the anterior wall and apex of the LV, causing more marked hemodynamic impairment, more frequent HF, and a poorer prognosis."

C. Mechanical Complications (Harrison's 22E — Table 286-3):

D. Electrical Complications:

• Ventricular fibrillation (VF) — most common cause of pre-hospital cardiac death; 80–90% of early ischaemic cardiac deaths
• Ventricular tachycardia (VT) — sustained or non-sustained
• Accelerated idioventricular rhythm (AIVR) — reperfusion arrhythmia; benign; no treatment needed
• Complete/Third-degree AV block:
  • Inferior MI (RCA) → AV nodal ischaemia → usually transient, vagal; responds to atropine; temporary pacing
  • Anterior MI (LAD) → Infra-Hisian block → permanent, associated with massive necrosis; urgent pacing needed
• Sinus bradycardia — inferior MI
• Sinus tachycardia — anterior MI; pain; hypovolaemia; HF
• Atrial fibrillation — 10–15%; treat with amiodarone or rate control

"Heart block in inferior infarction is commonly a result of increased vagal tone and/or release of adenosine — therefore transient. In anterior wall infarction, heart block is usually related to ischaemic malfunction of the conduction system — associated with extensive myocardial necrosis."

• Sinus bradycardia <50 unresponsive to atropine
• Mobitz II second-degree AV block
• Third-degree heart block
• Bilateral bundle branch block (RBBB + LAFB)

E. Other Complications:

F. Stunned vs. Hibernating Myocardium:

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11. DIFFERENTIAL DIAGNOSIS

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12. PROGNOSIS AND RISK STRATIFICATION

• LVEF is the single most important determinant of long-term prognosis
• LVEF <40%: High risk for SCD → consider ICD if still <35% at 40 days post-MI
• TIMI Risk Score (0–7): Stratifies 14-day risk of death/MI/urgent revascularisation in NSTEMI/UA
• GRACE Score: Better predictive accuracy for in-hospital + 6-month mortality

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13. HOMEOPATHIC MANAGEMENT OF MYOCARDIAL INFARCTION / CARDIAC ISCHAEMIA

⚠️ Disclaimer: Homeopathic treatment is NOT a substitute for emergency conventional medical care in acute MI. In an acute STEMI, immediate emergency services must be called and conventional treatment (aspirin, PCI, thrombolysis) must be initiated without delay. Homeopathy may be considered as adjunctive/supportive therapy only, under supervision of a qualified homeopathic practitioner.

Principle:

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Key Homeopathic Remedies for Cardiac/MI Support:

Homeopathic Remedies by Stage/Symptom:

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14. SUMMARY TABLE — 20-Mark Quick Revision

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• Harrison's Principles of Internal Medicine, 22nd Edition (2025) — Chapters 286 (STEMI), 287 (NSTEMI/UA)
• Goldman-Cecil Medicine, International Edition — Chapter 58 (STEMI)
• Robbins & Kumar Basic Pathology — Chapter 9 (IHD/MI Morphology)
• Homeopathic Materia Medica (Boericke); Dr. Bhatia's Homeopathy; Balance Into Health

Note on Golwala's Medicine & Davidson's: These specific books are not available in the current medical library. Goldman-Cecil Medicine (International Edition) is used as the closest equivalent — it is similarly structured for clinical medicine and follows the same scope. Key Golwala/Davidson's-style clinical points (symptom-to-management orientation) are fully covered above. If you have access to specific page references from Golwala or Davidson's you'd like incorporated, please share them and they can be added directly.