Heart attack mbbs

Reading File

Finding Sources

Searching PubMed

"myocardial infarction"[MeSH Terms] AND "management"[MeSH Terms]

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Finding Sources

Loading Image

I now have comprehensive textbook content and images. Let me compile the full MBBS-level answer on Myocardial Infarction (Heart Attack):

Myocardial Infarction (Heart Attack) - MBBS Notes

1. Definition

Myocardial infarction (MI) is necrosis of cardiac muscle resulting from ischemia. The 2018 joint task force (US and European Cardiology) defines it as "acute myocardial injury detected by abnormal cardiac biomarkers in the setting of evidence of acute myocardial ischemia."

Robbins & Kumar Basic Pathology, p. 353

2. Epidemiology & Risk Factors

MI can occur at virtually any age; frequency rises with age
~10% occur before age 40; ~45% before age 65
Men are at greater risk, but the gap narrows with age
Women are relatively protected during reproductive years; risk rises post-menopause (declining estrogen)
Risk factors: Atherosclerosis (main cause), hypertension, diabetes, hyperlipidemia, smoking, obesity, family history

3. Pathogenesis

The vast majority (>90%) are caused by acute coronary thrombosis. The sequence:

An atheromatous plaque is eroded or disrupted by endothelial injury, intraplaque hemorrhage, or mechanical forces - exposing subendothelial collagen and necrotic plaque contents
Platelets adhere, aggregate, and are activated - releasing thromboxane A2, ADP, and serotonin, causing further platelet aggregation and vasospasm
Coagulation is activated by exposure of tissue factor - adding to the growing thrombus
Within minutes, the enlarging thrombus completely occludes the coronary lumen

In ~10% of transmural MIs, no occlusive atherosclerosis is found - these are due to vasospasm, embolism (e.g., from AF, valve vegetations), or small vessel disease (vasculitis, amyloid, sickle cell).

Robbins & Kumar Basic Pathology, pp. 353-354

4. Coronary Artery Territories

Artery	Territory	Infarct Location
LAD (most common)	Anterior LV, anterior septum, apex	Anterior MI
RCA	Posterior LV, posterior septum, RV, SA/AV nodes	Inferior/posterior MI
LCx	Lateral LV	Lateral MI

5. Types of MI

Based on depth:

Transmural infarction: Full thickness of ventricle wall; caused by epicardial vessel occlusion with thrombosis → associated with STEMI on ECG
Subendocardial infarction: Limited to inner third of myocardium; occurs when thrombus is lysed before necrosis becomes transmural, or from global hypoperfusion → associated with NSTEMI

Based on ECG:

STEMI (ST-elevation MI): Complete occlusion, transmural ischemia
NSTEMI (Non-ST-elevation MI): Partial occlusion or spontaneous thrombolysis

6. Myocardial Response to Ischemia

Within seconds: Loss of contractile function (stunning)
At 20-40 minutes: Irreversible cell death begins in the subendocardium (most vulnerable - farthest from epicardial vessels, highest oxygen demand, compressed during systole)
Necrosis then spreads outward as a "wavefront" toward epicardium over hours

The heart needs ~1.3 mL O2/100g/min just to survive; normal delivery is ~8 mL O2/100g/min. If 15-30% of normal flow is maintained, muscle may survive.

Progression of myocardial necrosis from subendocardium outward after coronary occlusion

Fig. 9.8 - Progression of necrosis from subendocardium outward over 24 hrs (Robbins Basic Pathology)

Guyton & Hall Textbook of Medical Physiology, p. 271

7. Morphology - Timeline (VERY HIGH YIELD)

Time	Gross Features	Light Microscopy	Key Feature
0 - 30 min	None	None	Reversible - EM shows mitochondrial swelling, glycogen loss
30 min - 4 hr	None	Usually none; wavy fibers at border	Sarcolemmal disruption (irreversible begins)
4-12 hr	Occasionally dark mottling	Coagulative necrosis begins; edema, hemorrhage
12-24 hr	Dark mottling	Coagulative necrosis; pyknotic nuclei; hypereosinophilic myocytes; early neutrophils	TTC stain shows pale area
1-3 days	Mottling with yellow-tan center	Full coagulative necrosis; loss of nuclei/striations; peak neutrophils
3-7 days	Hyperemic border; yellow-tan softening	Dying neutrophils; macrophages begin phagocytosis	Risk of rupture highest
7-10 days	Maximally yellow-tan and soft	Active phagocytosis; early granulation tissue at margins
10-14 days	Red-gray depressed borders	Well-developed granulation tissue; new vessels; collagen deposition
2-8 weeks	Gray-white scar	Dense collagenous scar
>2 months	Complete scar	Complete fibrosis

Key stain: Triphenyl tetrazolium chloride (TTC) - infarcted area appears pale/unstained (LDH leaks out), healthy muscle stains deep red.

Histological progression of MI from coagulative necrosis (A) to neutrophil infiltration (B) to macrophage phagocytosis (C) to granulation tissue (D) to collagen scar (E)

Fig. 9.11 - Microscopic stages of MI healing (Robbins Basic Pathology)

Robbins & Kumar Basic Pathology, p. 357

8. Clinical Features

Symptoms:

Severe, crushing/squeezing central chest pain - often radiating to left arm, jaw, neck, back
Pain lasts >30 minutes (unlike angina which resolves with rest/nitrates)
Nausea, vomiting, sweating (diaphoresis)
Dyspnea (from acute LV failure/pulmonary congestion)
Sense of impending doom
Silent MI (no pain) - common in diabetics and elderly

Signs:

Pallor, sweating, clammy skin
Tachycardia or bradycardia
Hypotension (cardiogenic shock if extensive)
S3/S4 gallop
Mitral regurgitation murmur (papillary muscle ischemia)

9. ECG Changes (High Yield)

Three mechanisms of ECG change (from Ganong's Physiology):

Defect in Infarcted Cells	Current Flow	ECG Change
Rapid repolarization (K+ channels open)	Out of infarct	ST elevation
Decreased resting membrane potential	Into infarct	TQ depression (appears as ST elevation)
Delayed depolarization	Out of infarct	ST elevation

ECG Evolution:

Hyperacute T waves - earliest change (minutes to hours)
ST-segment elevation - classic STEMI, in leads overlying the infarct; reciprocal ST depression in opposite leads
T-wave inversion - develops hours to days
Pathological Q waves - develop over days, persist; indicate transmural necrosis (dead silent tissue)

ECG Localization:

Anterior MI: V1-V4 (LAD occlusion)
Inferior MI: II, III, aVF (RCA occlusion)
Lateral MI: I, aVL, V5-V6 (LCx occlusion)
Posterior MI: Tall R in V1 (mirror image; use V7-V9)
Ganong's Review of Medical Physiology, p. 534

10. Investigations / Diagnosis

Biomarkers (most important):

Marker	Rises	Peaks	Returns to Normal	Notes
Troponin I/T	3-4 hr	24-48 hr	7-14 days	Most sensitive & specific; gold standard
CK-MB	4-6 hr	18-24 hr	48-72 hr	Useful for re-infarction detection
Myoglobin	1-2 hr	6-8 hr	24 hr	Earliest; not cardiac-specific
LDH	24-48 hr	3-6 days	8-14 days	Useful in late presenters

Other investigations:

ECG - serial ECGs
Echocardiography - regional wall motion abnormality
Coronary angiography - confirms and allows PCI
Chest X-ray - pulmonary edema, cardiomegaly
CBC, lipid profile, glucose, renal function

11. Immediate Management ("MONA" + Reperfusion)

Initial stabilization:

Morphine - analgesia, anxiolysis (use cautiously - may worsen outcomes in some studies)
Oxygen - if SpO2 <94%
Nitrates - sublingual GTN for chest pain (contraindicated if hypotensive or RV infarct)
Aspirin 300 mg loading dose - inhibits platelet aggregation (COX-1 pathway, TXA2)
P2Y12 inhibitor - Clopidogrel/Ticagrelor (dual antiplatelet therapy)

Reperfusion (time is myocardium):

Primary PCI (percutaneous coronary intervention) - preferred if available within 90-120 min of first medical contact; stenting + balloon angioplasty
Thrombolysis (streptokinase, tPA/alteplase) - if PCI not available within 120 min; best given within 12 hours; dissolves thrombus by activating plasminogen

Additional drugs:

Beta-blockers (metoprolol) - reduce heart rate, O2 demand; reduce arrhythmia risk
ACE inhibitors - reduce LV remodeling, given within 24 hours
Statins - high-intensity statin therapy (atorvastatin 80 mg)
Anticoagulation - Heparin/LMWH/fondaparinux (adjunct to reperfusion)

"Time is myocardium" - Every minute of delay = ~1.9 million myocytes lost.

Robbins & Kumar Basic Pathology, p. 355

12. Complications

Early (<72 hours):

Arrhythmias (most common - ~90% develop some rhythm disturbance): VF (most dangerous, highest risk in first hour), VT, heart block, AF
Cardiogenic shock: When >40% of LV is infarcted; 10% of transmural MIs; high mortality
Acute LV failure / Pulmonary edema

Day 3-7 (softening phase - danger zone):

Cardiac rupture (free wall rupture → hemopericardium → tamponade; usually fatal)
Interventricular septum rupture → acute VSD
Papillary muscle rupture → acute severe mitral regurgitation

Late (weeks-months):

Pericarditis - appears 2-3 days post-MI (fibrinous pericarditis), friction rub; Dressler syndrome - autoimmune pericarditis weeks later
Ventricular aneurysm - thinned, scarred, non-contractile wall (large anterior infarcts); causes mural thrombus, arrhythmia, heart failure; does NOT rupture
Mural thrombus - risk of systemic embolism
Progressive heart failure / Ischemic cardiomyopathy

13. Reperfusion Injury

Restoration of blood flow, while beneficial, can cause additional injury:

Mitochondrial dysfunction - altered membrane permeability, apoptosis
Myocyte hypercontracture - Ca²+ overload → uncontrolled sarcomere contraction → cell death
Oxidative stress - ROS (O2-, H2O2, OH·) generated within minutes of reperfusion
"No-reflow" phenomenon - leukocyte plugging of microvasculature despite opening the epicardial artery
Contraction band necrosis - pathognomonic histologic feature of reperfused myocardium; intense eosinophilic transverse bands of hypercontracted sarcomeres
Robbins & Kumar Basic Pathology, p. 358

14. Summary Mnemonics

STEMI management: "TIME"

Thrombolysis or PCI (reperfusion)
Infusion of anticoagulant (heparin)
MONA (Morphine, O2, Nitrates, Aspirin)
Extras: Beta-blocker, ACE inhibitor, Statin

Causes of early death in MI (Guyton & Hall):

Decreased cardiac output (cardiogenic shock) - "systolic stretch" of infarcted segments
Pulmonary edema - damming of blood in pulmonary circulation
Ventricular fibrillation - most common cause of sudden cardiac death
Cardiac rupture (rare)

Sources: Robbins & Kumar Basic Pathology (9780323790185); Guyton & Hall Textbook of Medical Physiology (9780443111013); Ganong's Review of Medical Physiology 26th Ed (9781260122404)

This is a shared conversation. Sign in to Orris to start your own chat.