Myocardial infraction full protocall

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Myocardial Infarction (MI) - Full Clinical Protocol

1. Definition & Classification

Myocardial infarction is ischemic myocardial necrosis resulting from prolonged reduction or cessation of blood supply to the myocardium, most commonly due to atherosclerotic plaque rupture with superimposed thrombosis.

Types by ECG:

STEMI (ST-Elevation MI) - complete occlusion, requires immediate reperfusion
NSTEMI (Non-ST-Elevation MI) - partial occlusion, subendocardial ischemia
Unstable Angina (UA) - no biomarker rise; together with NSTEMI = NSTE-ACS

Universal MI Classification (Types 1-5):

Type	Mechanism
Type 1	Spontaneous - plaque rupture/erosion with thrombus
Type 2	Supply-demand mismatch (e.g., tachyarrhythmia, anemia, spasm)
Type 3	Sudden cardiac death before biomarkers drawn
Type 4a/b	PCI-related / In-stent thrombosis
Type 5	CABG-related

2. Pathophysiology

Atherosclerotic plaque rupture exposes subendothelial collagen and tissue factor
Platelet activation and aggregation - thrombus formation
Complete occlusion leads to transmural ischemia (STEMI) within 20-40 minutes
Irreversible necrosis begins at 20-40 min and is complete within 4-6 hours if untreated
Reperfusion injury can occur when flow is restored (calcium overload, free radicals)
Complications: arrhythmias, pump failure, mechanical complications, remodeling
Robbins & Kumar Basic Pathology, p. 465

3. Clinical Presentation

Symptoms:

Chest pain/pressure - crushing, squeezing, "elephant on chest" - radiating to left arm, jaw, neck, back
Diaphoresis, nausea, vomiting
Dyspnea, fatigue
"Silent MI" in diabetics, elderly, women (atypical presentations)

Signs:

Tachycardia, diaphoresis, pallor
New S3/S4 gallop
Signs of heart failure (JVD, crackles, hypotension)
Killip Classification (see below)

Killip Classification:

Class	Features	Mortality
I	No HF signs	~6%
II	Mild HF (S3, basal crackles)	~17%
III	Pulmonary edema	~38%
IV	Cardiogenic shock	~67%

4. Diagnosis

ECG (12-lead within 10 minutes of presentation)

STEMI criteria: ST elevation ≥1 mm in 2+ contiguous limb leads OR ≥2 mm in 2+ contiguous precordial leads; or new LBBB
NSTEMI/UA: ST depression, T-wave inversions, or normal ECG
Right-sided leads (V4R): For suspected RV infarction in inferior MI
Posterior leads (V7-V9): For posterior wall MI

ECG localization:

Territory	Leads	Artery
Anterior	V1-V4	LAD
Lateral	I, aVL, V5-V6	LCx
Inferior	II, III, aVF	RCA
Posterior	Reciprocal ST depression V1-V3	RCA/LCx
Right Ventricular	V1, V4R	RCA

Biomarkers

Troponin I or T (preferred): Rises 3-6 h, peaks 12-24 h, elevated for 7-14 days (highly sensitive cTn rises in 1-3 h)
CK-MB: Rises 4-6 h, returns to normal in 48-72 h (useful for reinfarction)
Myoglobin: Earliest (1-4 h) but nonspecific
Serial troponins at 0, 1-3 h, and 6 h recommended

Echocardiography

Wall motion abnormalities confirm ischemia/infarction
Assess EF, mechanical complications (MR, VSD, free wall rupture)
Evaluate for pericardial effusion

Coronary Angiography

Gold standard for defining anatomy and guiding revascularization
Urgent in STEMI and high-risk NSTEMI

5. STEMI Protocol

5a. Time Targets (ACC/AHA 2025 Guidelines)

First medical contact (FMC) to ECG: ≤10 minutes
FMC to device (primary PCI): ≤90 minutes (door-to-balloon)
FMC to fibrinolysis: ≤30 minutes (door-to-needle) if PCI not available
PCI after fibrinolysis: 3-24 hours after successful lysis (pharmaco-invasive strategy)

The 2025 ACC/AHA ACS Guidelines supersede prior versions (PMID: 40014670).

5b. Initial Assessment & Stabilization (MONA-B)

M - Morphine (or fentanyl) for refractory pain (use cautiously - may worsen outcomes)
O - Oxygen if SpO2 <90% or respiratory distress (avoid routine oxygen if SpO2 ≥90%)
N - Nitroglycerin 0.4 mg SL q5 min x3 (avoid if RV infarction, hypotension, PDE5 inhibitor use within 24-48 h, severe bradycardia)
A - Aspirin 325 mg (chewed, non-enteric coated) immediately
B - Beta-blocker (oral metoprolol 25-50 mg if hemodynamically stable; avoid IV if LV dysfunction/shock risk)

5c. Antithrombotic Therapy for STEMI

Antiplatelet (Dual Antiplatelet Therapy - DAPT):

Drug	Dose	Notes
Aspirin	162-325 mg loading, then 81 mg/d	Lifelong
Ticagrelor (preferred)	180 mg load, then 90 mg BID	Preferred P2Y12 inhibitor
Prasugrel	60 mg load, then 10 mg/d	Avoid in age >75, <60 kg, prior stroke/TIA
Clopidogrel	600 mg load, then 75 mg/d	If ticagrelor/prasugrel unavailable or fibrinolysis given

Anticoagulation:

Drug	Indication
UFH (Unfractionated Heparin)	Preferred with primary PCI - 60-70 U/kg IV bolus (max 5000 U) + infusion
Enoxaparin	1 mg/kg SC q12h (adjust for renal function); preferred with fibrinolysis
Bivalirudin	Alternative to UFH in primary PCI (lower bleeding risk)
Fondaparinux	Preferred in NSTEMI on conservative therapy; NOT for primary PCI

5d. Reperfusion Strategy

Primary PCI (Preferred):

Door-to-balloon ≤90 min (FMC ≤90 min)
Preferred if available in time
Drug-eluting stent preferred over bare-metal stent
Target only culprit lesion in acute phase (unless cardiogenic shock)
Harrison's Principles, p. 2163

Fibrinolytic Therapy (when PCI unavailable):

Indicated if: onset ≤12 h + STEMI criteria + no absolute contraindications + PCI not available within 120 min
Preferred: Tenecteplase (TNK) single weight-based IV bolus, Alteplase (tPA) accelerated infusion, Reteplase (rPA) double bolus
Not to be used after prior streptokinase if <5 days to 2 years
Harrison's Principles, p. 2161

Absolute Contraindications to Fibrinolysis:

Prior intracranial hemorrhage
Known CNS structural lesion/malignancy
Ischemic stroke within 3 months
Active internal bleeding
Aortic dissection suspected
Significant closed-head or facial trauma within 3 months
Severe uncontrolled hypertension (>180/110 refractory)

Pharmaco-Invasive Strategy:

If fibrinolysis given, transfer ALL patients to PCI-capable center within 24 h
Rescue PCI if: persistent pain + ST elevation >90 min post-lysis
Routine angiography at 3-24 h post-successful fibrinolysis

Reperfusion Decision Algorithm (No PCI):

Symptom onset ≤2 h AND PCI delay >60 min → Fibrinolysis
Symptom onset 2-3 h AND PCI delay >60-120 min → Consider fibrinolysis OR PCI
Symptom onset 3-12 h AND PCI delay <120 min → PCI preferred
Symptom onset >12 h → PCI preferred over fibrinolysis

Rosen's Emergency Medicine, p. 1025

6. NSTEMI/UA Protocol

Risk Stratification

TIMI Risk Score (1 point each):

Age >65
Known CAD (stenosis >50%)
≥2 episodes chest pain in 24 h
ST or T-wave changes
Elevated cardiac biomarkers
Aspirin use in last 7 days
≥3 CAD risk factors

Score 0-2 = low risk; 3-4 = intermediate; 5-7 = high risk

GRACE score better predicts in-hospital and 6-month mortality.

Urgent Invasive Strategy (<2 hours):

Refractory ischemia despite medical therapy
New HF or cardiogenic shock
New MR
New LBBB
Sustained VT/VF

Early Invasive (<24 h): TIMI ≥3, GRACE >140

Conservative (Ischemia-Driven) Strategy: Low-risk patients with TIMI 0-2

Medical Therapy for NSTEMI:

Aspirin + P2Y12 inhibitor (ticagrelor preferred)
Anticoagulation: enoxaparin, fondaparinux, or UFH
Beta-blocker (oral)
High-intensity statin immediately
ACE inhibitor/ARB if EF reduced, hypertension, or diabetes
Nitrates for symptom control

7. In-Hospital Management

Monitoring & Activity

Continuous cardiac monitoring (telemetry) for all ACS patients
Bed rest initially, early ambulation if stable after 24-48 h
ICU/CCU for high-risk: hemodynamic instability, arrhythmias, shock
Transition to step-down unit after 24-48 h if stable
Harrison's Principles, p. 2164

Ongoing Medications

Drug	Notes
Aspirin 81 mg/day	Lifelong
P2Y12 inhibitor	12 months minimum post-ACS (ticagrelor or clopidogrel)
Beta-blocker	Start within 24 h if stable; metoprolol succinate preferred
High-intensity statin	Atorvastatin 40-80 mg or rosuvastatin 20-40 mg - start immediately
ACE inhibitor	Start within 24 h, especially if EF <40%, HF, or diabetes
Aldosterone antagonist	If EF <40% + HF symptoms or diabetes (eplerenone/spironolactone)

Echocardiography

All patients should have LV function assessed before or shortly after discharge

8. Complications

Electrical Complications

Complication	Management
VF/pulseless VT	Defibrillation + ACLS
Sustained VT with pulse	Synchronized cardioversion or amiodarone IV
Accelerated idioventricular rhythm	Usually benign, no treatment
Atrial fibrillation	Rate control; anticoagulation if hemodynamically stable
Complete heart block (inferior MI)	Temporary pacing; usually resolves
Complete heart block (anterior MI)	Permanent pacemaker usually needed

Harrison's Principles, p. 2167

Mechanical Complications

Complication	Features	Management
Free wall rupture	Sudden hemopericardium, PEA	Emergency surgery
Ventricular septal defect	Harsh holosystolic murmur, step-up in O2 sat RV	Emergency surgery/percutaneous closure
Papillary muscle rupture	Sudden severe MR, pulmonary edema	Emergency mitral valve surgery
LV aneurysm	Persistent ST elevation, HF, VT	Anticoagulation; surgery if refractory
Mural thrombus	LV thrombus post-large anterior MI	Anticoagulation for 3-6 months

Hemodynamic Complications

Cardiogenic shock: Prompt reperfusion; inotropes (dopamine/dobutamine); IABP or Impella as bridge; prompt PCI even if late
RV Infarction: Volume loading is key; avoid diuretics/nitrates; pacing if bradycardia; do not use preload reducers
Acute HF: Diuresis (furosemide IV), nitrates, ACE inhibitor, oxygen; digoxin has limited role post-MI
Harrison's Principles, p. 2165-2166

Pericarditis (Dressler Syndrome)

Early pericarditis: 1-3 days post-MI (fibrinous, treat with aspirin)
Dressler syndrome: weeks to months later (autoimmune), treat with NSAIDs/colchicine

9. Discharge Planning & Secondary Prevention

Intervention	Target/Dose
Aspirin	81 mg/day - lifelong
P2Y12 inhibitor	12 months (extend if high ischemic, low bleeding risk)
Beta-blocker	Continue ≥3 years; indefinite if LV dysfunction
Statin (high-intensity)	LDL target <55-70 mg/dL (<1.4 mmol/L)
ACE inhibitor/ARB	Indefinite if EF <40%, HF, DM, or HTN
Aldosterone antagonist	If EF <40% + symptoms or DM
Cardiac Rehabilitation	All MI patients - class I recommendation
Smoking cessation	Mandatory
Glycemic control	HbA1c <7-8%
BP control	Target <130/80 mmHg
PCSK9 inhibitor	If LDL target not achieved on max statin + ezetimibe

10. Special Populations

Diabetics: Higher risk, more silent MIs, worse outcomes; SGLT2i and GLP-1 agonists have cardiovascular benefit
Elderly (>75 y): Avoid prasugrel; higher bleeding risk; adjust dosing; higher fibrinolysis complication rate
CKD: Avoid fondaparinux if eGFR <20; adjust enoxaparin; contrast nephropathy prevention
Cardiogenic Shock: Consider mechanical circulatory support (Impella, IABP, ECMO); PCI of culprit-only vessel initially
Pregnancy: Aspirin + UFH (LMWH), avoid fibrinolytics; PCI preferred

11. Key Time Benchmarks Summary

Metric	Target
ECG acquisition	≤10 min from arrival
Door-to-balloon (primary PCI)	≤90 min
Door-to-needle (fibrinolysis)	≤30 min
FMC-to-device (prehospital STEMI)	≤90 min
Early invasive strategy (NSTEMI high-risk)	≤24 h
Urgent invasive (NSTEMI very high-risk)	≤2 h
Angiography post-fibrinolysis	3-24 h

Sources:

Harrison's Principles of Internal Medicine, 22nd Edition (2025) - Chapter 286
Rosen's Emergency Medicine: Concepts and Clinical Practice - Chapter 64
The Washington Manual of Medical Therapeutics - Chapter 4
Robbins & Kumar Basic Pathology - Chapter 4
2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for Management of ACS (PMID: 40014670) - most current guideline

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