Myocardial Infarction (MI)
Adult Health Nursing | Cardiovascular Disorders
Complete Notes • Clinical Cases • NORCET Revision
25 MCQs | 30-Minute Timed Test
1. Definition
Myocardial infarction (MI) is myocardial cell death caused by prolonged ischemia, usually due to an acute reduction in coronary blood flow. It is commonly associated with atherosclerotic plaque disruption and thrombus formation.
Important terminology
- Myocardial ischemia: Inadequate oxygen supply to the heart muscle.
- Myocardial injury: Cardiac troponin above the assay's 99th-percentile upper reference limit.
- Myocardial infarction: Acute myocardial injury with a rise/fall in cardiac troponin and evidence of acute ischemia.
- ACS: Acute coronary syndrome, including unstable angina, NSTEMI, and STEMI.
- Reperfusion: Restoration of blood flow to ischemic myocardium.
2. Coronary Blood Supply
The coronary arteries arise from the aortic root and deliver oxygenated blood to the myocardium.
- LAD: Supplies much of the anterior left ventricle and interventricular septum.
- LCx: Supplies parts of the lateral left ventricle.
- RCA: Commonly supplies the right ventricle and, in many people, the inferior myocardium and conduction system.
3. Etiology and Risk Factors
Common mechanism
In type 1 MI, rupture or erosion of an atherosclerotic plaque can trigger platelet activation and thrombus formation, reducing or blocking coronary blood flow.
Risk factors
| Non-modifiable | Modifiable |
|---|---|
| Increasing age | Smoking and tobacco exposure |
| Family history of premature CAD | Hypertension |
| Inherited predisposition | Diabetes mellitus |
| High LDL cholesterol | |
| Obesity, physical inactivity, unhealthy diet |
4. Pathophysiology of MI
Atherosclerotic plaque disruption
↓
Platelet activation and thrombus
↓
Reduced / blocked coronary blood flow
↓
Myocardial ischemia
↓
Prolonged ischemia → myocardial necrosis
↓
Reduced cardiac function ± arrhythmias / shock
Clinical significance: Early restoration of coronary blood flow can limit myocardial damage. The amount of myocardium affected depends on the artery involved, duration of ischemia, collateral circulation, and speed of reperfusion.
5. Types of Myocardial Infarction
| Type | Key concept |
|---|---|
| Type 1 MI | Acute atherothrombotic event due to plaque rupture or erosion. |
| Type 2 MI | Ischemic myocardial injury due to oxygen supply-demand imbalance unrelated to acute coronary atherothrombosis, such as severe anemia, hypoxemia, or sustained tachyarrhythmia. |
| STEMI | Acute MI with a diagnostic ST-elevation pattern or recognized equivalent; requires urgent reperfusion assessment. |
| NSTEMI | Acute MI without diagnostic persistent ST elevation; ECG may show ST depression, T-wave inversion, or nonspecific/normal findings. |
Exam point: STEMI and NSTEMI are ECG/clinical categories of acute MI. ST elevation alone is not the complete diagnosis; clinical presentation, ECG criteria, and cardiac biomarkers must be interpreted together.
6. Clinical Manifestations
- Chest pressure, squeezing, heaviness, or discomfort that may persist or recur.
- Pain or discomfort may radiate to one or both arms, shoulder, jaw, neck, back, or upper abdomen.
- Dyspnea, cold sweating, nausea, vomiting, pallor, or marked weakness.
- Palpitations, dizziness, syncope, hypotension, or altered consciousness in severe cases.
- Atypical or silent presentation may occur, particularly in older adults and people with diabetes.
Emergency: Suspected MI is a medical emergency. Activate emergency services / the local ACS pathway immediately. Do not wait for symptoms to resolve, and do not let the patient drive themselves to hospital.
7. Diagnostic Investigations
| Investigation | Important findings / purpose |
|---|---|
| 12-lead ECG | Prompt assessment for ST elevation, ST depression, T-wave changes, and arrhythmias. Repeat if symptoms persist or evolve. |
| High-sensitivity cardiac troponin | Preferred biomarker of myocardial injury; serial measurements help establish acute rise/fall. |
| Echocardiography | Evaluates ventricular function, regional wall-motion abnormalities, and mechanical complications. |
| Coronary angiography | Identifies coronary anatomy and guides PCI when indicated. |
| CBC, renal function, electrolytes, glucose | Assess anemia, renal function, electrolyte disturbances, and comorbidities relevant to treatment. |
| Chest X-ray | May help assess pulmonary edema or alternative causes; it does not rule MI in or out. |
Cardiac biomarkers
- Troponin I / T: Preferred biomarkers. Rise and fall patterns and the clinical context are essential for interpretation.
- CK-MB: Less preferred than high-sensitivity troponin; may sometimes help assess suspected reinfarction in selected settings.
- Myoglobin: Not preferred for routine MI diagnosis because it lacks specificity.
ECG patterns — high-yield overview
| Pattern | Possible interpretation |
|---|---|
| ST elevation in contiguous leads | May indicate acute coronary occlusion; urgent STEMI evaluation is needed. |
| ST depression / T-wave inversion | May indicate ischemia; interpret with symptoms and other findings. |
| Pathological Q waves | May develop after myocardial necrosis; not present in every MI. |
| Normal initial ECG | Does not exclude ACS or MI. |
Important: Do not delay emergency reperfusion in a patient with a diagnostic STEMI pattern while waiting for troponin results.
8. Emergency Medical Management
Treatment is time-critical and depends on the type of MI, blood pressure, oxygenation, bleeding risk, contraindications, and local protocol.
Immediate priorities
- Activate the emergency / ACS pathway and arrange urgent transfer to an appropriate cardiac-care setting.
- Assess airway, breathing, circulation, vital signs, pain, mental status, and oxygen saturation.
- Obtain a 12-lead ECG promptly, ideally within 10 minutes of first medical contact when ACS is suspected.
- Establish IV access, obtain blood samples, and initiate cardiac monitoring as appropriate.
- Give aspirin and other antithrombotic treatment according to protocol and after checking contraindications.
- Provide nitroglycerin for suitable patients when prescribed and safe; avoid it with hypotension and relevant drug interactions.
- Give oxygen for hypoxemia or another clinical indication; routine oxygen is not recommended for normoxemic patients.
- Prepare for reperfusion when indicated and monitor continuously for deterioration.
Medicines used when indicated
- Antiplatelets: Aspirin and a P2Y12 inhibitor when indicated.
- Anticoagulants: Used according to the ACS treatment strategy and patient-specific risk.
- Nitrates: Symptom relief in suitable patients; not appropriate in all cases.
- Statins: High-intensity therapy is commonly indicated after atherosclerotic MI unless contraindicated.
- Beta-blockers: Considered in appropriate patients after evaluating heart rate, blood pressure, heart failure, and contraindications.
- ACE inhibitors / ARBs: Used when indicated, especially in selected patients with left ventricular dysfunction or other relevant conditions.
9. Reperfusion Therapy
| Method | Description |
|---|---|
| Primary PCI | Catheter-based reperfusion, usually involving balloon angioplasty and stent placement. Preferred for STEMI when timely available. |
| Fibrinolytic therapy | Clot-dissolving medication for eligible STEMI patients when timely PCI is unavailable, according to protocol and contraindication screening. |
| CABG | Surgical revascularization for selected coronary anatomy or clinical circumstances. |
Safety point: Fibrinolytics are not used for NSTEMI or unstable angina. They carry major bleeding risks, including intracranial hemorrhage, so eligibility and contraindications must be checked carefully.
10. Nursing Management
Acute phase
- Recognize symptoms and activate the emergency pathway without delay.
- Maintain appropriate positioning and reduce unnecessary exertion.
- Monitor ECG rhythm, heart rate, blood pressure, oxygen saturation, pain, and consciousness.
- Prepare for ECGs, blood sampling, IV treatment, and reperfusion according to protocol.
- Administer prescribed medication safely and observe for adverse effects, bleeding, and hypotension.
- Observe for ventricular arrhythmias, acute heart failure, cardiogenic shock, and recurrent ischemia.
- Document symptom onset, assessment findings, interventions, and response to treatment.
Recovery and rehabilitation
- Progress activity according to clinical stability and the prescribed rehabilitation plan.
- Teach medication adherence and explain the importance of antiplatelet therapy after stent placement.
- Encourage tobacco cessation and control of blood pressure, diabetes, and cholesterol.
- Support heart-healthy eating, appropriate activity, follow-up, and cardiac rehabilitation.
- Provide emotional support and education about warning symptoms and emergency response.
11. Complications of MI
| Complication | Clinical clues |
|---|---|
| Arrhythmias | Palpitations, unstable rhythm, syncope, cardiac arrest. |
| Left ventricular failure / pulmonary edema | Dyspnea, crackles, hypoxemia, respiratory distress. |
| Cardiogenic shock | Hypotension, cool clammy skin, altered consciousness, poor perfusion. |
| Papillary muscle rupture / severe dysfunction | Acute pulmonary edema and new mitral regurgitation murmur. |
| Ventricular septal rupture | Sudden deterioration and a new harsh systolic murmur. |
| Free-wall rupture / tamponade | Sudden collapse, hypotension, and possible tamponade signs. |
| Pericarditis | Pleuritic chest pain or pericardial rub in the appropriate context. |
| Left ventricular aneurysm | Persistent ventricular dysfunction or arrhythmias in selected patients. |
12. Patient Education and Prevention
- Take medicines exactly as prescribed and never stop antiplatelet medicines after a stent without specialist advice.
- Attend follow-up appointments and cardiac rehabilitation when recommended.
- Stop smoking and avoid tobacco exposure.
- Control blood pressure, glucose, cholesterol, and body weight.
- Follow a heart-healthy diet and a clinician-approved activity plan.
- Seek emergency care for new or persistent chest discomfort, severe breathlessness, collapse, or symptoms similar to the original MI.
13. High-Yield NORCET Revision
| Question clue | Answer |
|---|---|
| Preferred biomarker for MI | High-sensitivity cardiac troponin |
| Common mechanism of type 1 MI | Plaque disruption with coronary thrombosis |
| STEMI priority | Urgent reperfusion evaluation |
| First-line cardiac assessment in suspected ACS | Prompt 12-lead ECG and clinical assessment |
| Routine oxygen in normoxemic ACS | Not recommended |
| Major early life-threatening complication | Ventricular arrhythmia |
| Common mechanical complication after MI | Papillary muscle, septal, or free-wall rupture |
| STEMI reperfusion option when timely PCI unavailable | Fibrinolysis in eligible patients after contraindication screening |
| Type 2 MI mechanism | Ischemia due to oxygen supply-demand imbalance |
| Important secondary prevention | Risk-factor control and indicated antiplatelet/statin therapy |
14. MCQ Practice Test — 25 Questions
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Myocardial Infarction Test
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Educational material for nursing students. This content does not replace emergency assessment, clinician advice, or local ACS protocols.