Myocardial Infarction (MI)

Definition

• Robbins & Kumar Basic Pathology, p. 353

Pathogenesis - How It Happens

1. Plaque disruption - An atheromatous plaque is eroded or suddenly ruptured by endothelial injury, intraplaque hemorrhage, or mechanical forces. This exposes subendothelial collagen and necrotic plaque contents to circulating blood.
2. Platelet activation - Platelets adhere, aggregate, and release thromboxane A₂, ADP, and serotonin, causing further platelet aggregation and vasospasm.
3. Coagulation cascade - Tissue factor exposure activates the coagulation system, adding to the growing thrombus.
4. Total occlusion - Within minutes, the thrombus can completely occlude the coronary artery lumen.

• Robbins & Kumar Basic Pathology, p. 353-354

What Happens to the Heart Muscle

• Within seconds: aerobic metabolism ceases; ATP drops; lactic acid accumulates.
• Within minutes: contractility is lost (reversible at this stage).
• After 20-40 minutes of sustained ischemia: irreversible damage and coagulative necrosis of myocytes begins.
• The earliest sign of necrosis is disruption of the sarcolemmal membrane, allowing intracellular enzymes (troponin, CK-MB) to leak into blood - the basis of biomarker testing.

• Has the highest oxygen consumption
• Is the last region to receive blood from epicardial vessels
• Is exposed to high intramural pressures during systole

• Guyton and Hall Medical Physiology, p. 271
• Robbins & Kumar Basic Pathology, p. 354-355

Coronary Artery Territory - Where Infarcts Occur

• Robbins & Kumar Basic Pathology, p. 355

Types of MI

• Frameworks for Internal Medicine, p. 33

Symptoms

• Chest pain/pressure - crushing, squeezing, or burning; often radiating to the left arm, jaw, or epigastrium
• Diaphoresis (heavy sweating)
• Nausea and vomiting
• Dyspnea (shortness of breath)
• Syncope or near-syncope
• Fatigue

Important: Women, diabetics, and post-operative patients often present atypically (without classic chest pain), more commonly with dyspnea, fatigue, or back pain.

• Frameworks for Internal Medicine, p. 32

Diagnosis

1. ECG - obtained immediately. Key findings:
   • STEMI: ST elevation in ≥2 contiguous leads; hyperacute (tall, broad-based, symmetrical) T-waves early on; later Q waves
   • NSTEMI/UA: ST depression or T-wave inversions
2. Cardiac biomarkers - Troponin I or T (most sensitive and specific); CK-MB. Rise and fall pattern is characteristic of MI.
3. Coronary angiography - confirms occlusion and guides intervention

Causes of Death in Acute MI

1. Decreased cardiac output (cardiogenic shock) - non-contracting myocardium; paradoxical systolic stretch worsens dysfunction
2. Pulmonary edema - blood dams in the pulmonary vasculature
3. Ventricular fibrillation - most common cause of sudden death; ischemia creates electrical instability. In 80-90% of out-of-hospital MI deaths, ventricular fibrillation is the terminal event.
4. Cardiac rupture - rare but catastrophic; occurs in the first 1-2 weeks

• Guyton and Hall Medical Physiology, p. 271

Complications

• Arrhythmias (ventricular fibrillation, heart block)
• Heart failure / cardiogenic shock
• Mechanical complications: papillary muscle rupture (mitral regurgitation), ventricular septal defect, free wall rupture
• Pericarditis (Dressler syndrome)
• Ventricular aneurysm
• Mural thrombus with embolism
• Reperfusion injury - restoring blood flow can paradoxically worsen damage via reactive oxygen species and inflammatory mediators ("stunned myocardium")

Treatment

• Primary PCI (percutaneous coronary intervention) - preferred for STEMI if available within 90 minutes; involves balloon angioplasty and stenting
• Fibrinolytic therapy (thrombolytics) - used when PCI is not available within a timely window
• Antiplatelet agents - aspirin + P2Y12 inhibitor (clopidogrel, ticagrelor, prasugrel)
• Anticoagulants - heparin
• Beta-blockers - reduce myocardial oxygen demand, prevent arrhythmias
• ACE inhibitors - limit ventricular remodeling
• Statins - plaque stabilization and secondary prevention
• Nitrates - for pain and vasodilation

• Robbins & Kumar Basic Pathology
• Frameworks for Internal Medicine

Pathology Illustration (Stages After MI)

Hospital Biomedical Waste - Color-Coded Bin Guide

India - Bio-Medical Waste Management Rules 2016

🟡 YELLOW Bin / Yellow Non-Chlorinated Plastic Bag

🔴 RED Bin / Red Non-Chlorinated Plastic Bag (≥50 micron thickness)

⬜ WHITE Bin / White Translucent Puncture-Proof Container

The CDC estimates ~385,000 needlestick injuries occur in hospital workers annually - proper white bin use is the primary prevention tool.

🔵 BLUE Bin / Blue-Marked Puncture-Proof Box

Quick Reference Summary Table (India BMW Rules 2016)

US/International (OSHA & WHO Standards)

What Should NOT Go in Biomedical Bins

• General paper/packaging waste - goes in regular general waste bins
• Food waste - general waste
• E-waste (batteries, circuit boards) - separate e-waste rules (E-waste Management Rules 2016)
• Radioactive waste - governed by Atomic Energy Act; separate handling entirely
• Liquid waste - sewage and liquid effluents treated in ETP (effluent treatment plant), not in color-coded bags

Key Rules to Remember

1. Segregation happens at the point of generation - at the bedside, in the OT, in the lab
2. Never mix categories - a yellow bag contaminated with sharps creates a serious safety hazard
3. Bags should not be overfilled - fill only up to 3/4 capacity
4. Label all bags with date, ward, and hospital name before transport
5. Sharps never go in soft bags - always in rigid, puncture-proof white containers
6. Chemotherapy waste always goes in yellow (incineration) - autoclaving does NOT destroy cytotoxic drugs

DMO Interview Preparation - Inpatient Ward (No Emergency/Casualty)

1. Role Understanding & Responsibilities

Expected answer: Reviewing all admitted patients each shift, checking vitals charts, reviewing nursing notes, countersigning/updating medication orders, updating progress notes, calling consultants when required, declaring patients fit for procedures or discharge, documenting in medical records, and handover to the next DMO.

DMO manages day-to-day ward monitoring and implements treatment plans already made by the consultant. The consultant makes definitive treatment decisions; the DMO executes and watches for changes in patient condition.

Hand over all unstable or flagged patients verbally AND in writing - cover current vitals, recent changes, pending investigations, and any expected events. Use SBAR (Situation, Background, Assessment, Recommendation) format.

Patients who deteriorated overnight, those with abnormal vitals, post-operative patients in the first 24-48 hours, patients awaiting urgent reports, and those scheduled for procedures or discharge today.

2. Clinical Monitoring & Vitals

Go immediately, put the patient on oxygen (start with nasal prongs at 2-4 L/min, escalate to face mask/NRM if needed), check RR, HR, BP, auscultate chest, check if new onset or gradual, review current medications (sedatives?), call for ABG if available, and escalate to the consultant if no improvement.

Temperature, pulse, blood pressure, respiratory rate, SpO₂, urine output (in relevant patients), pain score, GCS (if neurological case), wound condition (if post-op), and input/output charts.

It's a scoring system based on 6-7 vital parameters. A rising score (typically ≥5) triggers escalation. It helps identify patients deteriorating before a crisis happens.

When there is: persistent hypoxia not responding to supplemental oxygen, hemodynamic instability (BP not responding to fluids), falling GCS/altered consciousness, worsening sepsis criteria, or any condition requiring invasive monitoring or ventilatory support.

3. Medication Management

Assess urgency - if it's a critical drug (e.g., insulin, anticoagulant, antiepileptic), escalate immediately to pharmacy and nursing in-charge. Document the issue. If unavailable, contact the consultant for an alternative. Never skip documentation.

Stop the suspected drug, assess severity (mild/anaphylaxis), give treatment accordingly (antihistamine, steroids, adrenaline for anaphylaxis), document in the patient's file, fill the ADR reporting form (Yellow Card / Pharmacovigilance), and inform the consultant.

Right Patient, Right Drug, Right Dose, Right Route, Right Time. (Some add: Right Documentation and Right Reason.)

Hold warfarin, inform consultant, monitor closely for signs of bleeding, check for interacting drugs/diet changes, and repeat INR. Vitamin K may be given per consultant advice.

4. Common Ward Scenarios

Call for help immediately, check for responsiveness and breathing, start BLS if no pulse/breathing, call for crash cart, attach defibrillator, follow ACLS protocol, inform consultant and senior, document time of events.

Wind, Water, Wound, Walking, Wonder drugs (the "5 Ws"):

• Day 1-2: Wind - atelectasis, pneumonia
• Day 3-5: Water - UTI, IV line infection
• Day 5-7: Wound - surgical site infection
• Day 7+: DVT/PE Examine accordingly, send cultures if indicated, review antibiotics with consultant.

If conscious and able to swallow - give 15g oral glucose (juice/glucose tablets). Recheck in 15 minutes. If unconscious - IV 25 mL of 50% dextrose (D50) or 150 mL of 10% dextrose, then start 10% dextrose infusion. Identify the cause (excess insulin? missed meal?), adjust insulin orders, and inform consultant.

Check hydration status and IV fluid input, check if catheter is blocked (flush/replace if catheterized), palpate for bladder distension, review medications (opioids cause urinary retention), check electrolytes/creatinine - if still no output after correcting factors, inform consultant, consider catheterization if not already done.

Listen respectfully to the family's concerns, explain the medical necessity of continued admission in simple language, involve the consultant in the conversation, document the discussion. If they insist on leaving against medical advice (LAMA), explain risks clearly, have them sign the LAMA form, and document thoroughly.

5. Documentation & Legal Aspects

Date and time, doctor's name and signature, patient's current complaints, examination findings, investigation results reviewed, assessment (diagnosis/changes), plan (medication changes, orders, referrals), and whether consultant was informed.

Confirm death (check for pulse, breathing, pupil response), note the time of death, inform the consultant, inform the family with empathy, complete the Death Certificate (if the cause is known and not suspicious), hand over the body to the mortuary as per hospital protocol, document everything, and inform the ward in-charge/nursing staff.

Leave Against Medical Advice. Document the patient's stated reason, risks explained to them, names of witnesses, and get the patient's signature on the LAMA form. A patient has the legal right to leave as long as they have decision-making capacity.

When the death is sudden/unexplained, within 24 hours of admission, post-operative death (especially within 24-48 hours), suspicious/medicolegal circumstances, injury-related death, or poisoning. In these cases, refer to the Medical Superintendent and/or police for medico-legal autopsy.

6. Infection Control & Hospital Protocols

Isolate the patient if indicated (e.g., MRSA, C. difficile), send appropriate cultures, review antibiotic policy with the consultant/microbiologist, report to the hospital infection control committee, implement contact precautions, and educate nursing staff on hand hygiene.

Gloves and gown at minimum. Add a mask if respiratory precautions apply. Remove PPE before leaving the patient's room and perform hand hygiene with soap and water or sanitizer.

Wash the wound immediately with soap and water (do not suck the wound), report to the occupational health/nodal officer, get baseline serology (HIV, HBV, HCV) for both source patient and injured staff, start PEP (Post-Exposure Prophylaxis) within 2 hours for HIV risk, document in the incident report.

7. Communication & Team Work

Use SBAR format:

• Situation: "Dr. X, patient in Bed 12, Mr. Y, is deteriorating."
• Background: "He was admitted 3 days ago with pneumonia, on IV antibiotics."
• Assessment: "His SpO₂ has dropped to 90% on 4L O₂, RR is 28, BP 90/60."
• Recommendation: "I think he may need ICU transfer. Can you please come and review?"

Remain calm and professional, focus on the patient's best interest, clarify your clinical reasoning, escalate to the consultant if the disagreement affects patient safety, and document the exchange.

8. Personal & Situational Questions

Focus on: interest in inpatient clinical medicine, desire to develop systematic patient monitoring skills, building clinical decision-making in a structured ward environment.

Prioritize by acuity using vitals flags. Delegate appropriate tasks to nursing staff. Use a structured checklist. Communicate early if the workload is unsafe. Document as you go rather than at the end of the shift.

Use a STAR answer (Situation, Task, Action, Result). Be specific, honest, and focus on what you learned.

Never act beyond your competence level. Call the consultant or senior on call. It is better to make one call and be corrected than to miss something serious. Document that you consulted.

Key Topics to Revise Before the Interview