PA26.1-10 | Cardiovascular System — Case Study

CLINICAL SCENARIO

A clinical case-study assignment integrating atherogenesis, plaque rupture, coronary territory anatomy, transmural infarct evolution, biomarker/ECG interpretation, and post-MI complications. Covers competencies PA26.1–PA26.10.

1. Atherogenesis and Risk Factor Pathobiology

Mr. Rajan, 58 years old, is a hypertensive, type-2 diabetic smoker with a fasting LDL of 4.8 mmol/L and a 30-pack-year smoking history. He has had no cardiac symptoms until today. Describe the sequence of pathological events — from endothelial injury to advanced vulnerable plaque — that has silently developed in his coronary arteries over the preceding two decades. Explain how each of his risk factors contributes to a distinct step in this sequence.

Guidance: Cover endothelial dysfunction → LDL oxidation → monocyte recruitment/foam cell formation → fatty streak → fibrous cap formation → vulnerable (thin-cap fibroatheroma) plaque. Link hypertension to mechanical endothelial stress, diabetes to AGE-mediated oxidative damage and glycated LDL, smoking to oxidative/inflammatory acceleration, and hyperlipidaemia to lipid core growth. Aim for mechanistic depth (NF-κB, VCAM-1, MMP activity) without exceeding your word allocation.

2. Plaque Rupture and Coronary Occlusion

At 09:15 on the morning of admission, Mr. Rajan experiences the abrupt onset of crushing, vice-like central chest pain radiating to the left jaw and arm, diaphoresis, and nausea. His ECG shows 4 mm ST-elevation in leads II, III, and aVF with reciprocal depression in I and aVL. Explain the pathological event that triggered his symptoms. Identify the coronary artery occluded, the myocardial territory at risk, and the mechanism by which the occlusion becomes complete.

Guidance: Explain thin fibrous cap rupture (MMP-mediated), exposure of subendothelial collagen/tissue factor, platelet adhesion (GP Ib–vWF) → activation → aggregation (GP IIb/IIIa–fibrinogen) → superimposed thrombus. The inferior ST-elevation pattern (II, III, aVF + reciprocal I/aVL) identifies the right coronary artery (RCA) → posterior descending artery territory (inferior and posterior LV walls + posterior septum). Distinguish between erosion and rupture as triggers; state which is more common in diabetics.

3. Gross and Microscopic Evolution of Myocardial Infarction

Mr. Rajan undergoes emergency PCI at 90 minutes. Despite reperfusion, imaging confirms a completed transmural infarct of the inferior LV wall. Construct a timeline of the gross and histological changes that would be found in the infarcted territory at 6 hours, 24 hours, 3–5 days, 10 days, and 6 weeks after the onset of ischaemia. Relate each change to the underlying cellular/tissue mechanism.

Guidance: Timeline: 0–6 h — no gross change; EM: mitochondrial swelling, sarcomere relaxation; LM: wavy fibres, early coagulative necrosis begins. 6–24 h — pallor; neutrophil infiltration peaks. 3–5 d — yellow-tan, soft centre; macrophage/phagocytic phase; risk of rupture highest. 10 d — red-brown hyperaemic border (granulation tissue); collagen deposition begins. 6 wk — grey-white fibrous scar; collagen cross-linking, remodelling. Note reperfusion injury features: contraction bands, haemorrhage. Distinguish transmural vs subendocardial pattern and explain why this case is transmural (total occlusion vs partial).

4. Cardiac Biomarkers and ECG Interpretation

On admission (T=0), troponin I is 0.03 ng/mL (upper limit of normal 0.04). At T+6 h it rises to 18 ng/mL; at T+12 h it peaks at 42 ng/mL; by T+72 h it has fallen to 6 ng/mL. CK-MB follows a similar but earlier-peaking curve. Interpret these kinetics in terms of the underlying cellular pathology. Explain also why the initial ECG showed ST-elevation, and what ECG changes you would expect at 48 hours and at 6 weeks.

Guidance: Troponin I: released from disrupted sarcomeres as myocytes undergo irreversible necrosis; highly specific to cardiac muscle. Initial normal: sampling before detectable release (rises ~3–6 h); peak ~12–18 h (mass release as necrosis completes); prolonged elevation due to structural bound pool. CK-MB peaks earlier (~12 h) and clears faster — useful for re-infarction timing. ECG: acute — hyperacute T → ST elevation (current of injury, K+ leak from ischaemic zone) → Q-wave formation (electrical silence). 48 h: ST settling, T-wave inversion (peri-infarct ischaemia), Q-waves appear. 6 wk: persistent Q-waves (dead tissue); T-wave may normalise or remain inverted.

5. Complications of Acute Myocardial Infarction

On Day 1 post-PCI, Mr. Rajan develops a run of ventricular tachycardia that reverts spontaneously. On Day 4, a new pan-systolic murmur is detected. By Day 14, he is breathless at rest with bilateral basal crepitations and raised JVP. At Week 8, he returns with low-grade fever, pleuritic chest pain, and a pericardial friction rub. Explain the distinct pathological mechanism responsible for each of these four complications, and identify the timing clue that distinguishes them.

Guidance: VT (Day 1): re-entrant arrhythmia at ischaemic/viable border; peak risk 24–72 h; mechanism — heterogeneous conduction velocity. Papillary muscle rupture (Day 4): posterior papillary muscle supplied by RCA alone (single supply); necrotic rupture → acute MR → pan-systolic murmur. Heart failure (Day 14): loss of >25% LV mass → reduced ejection fraction → pulmonary venous hypertension → oedema; also risk of free wall rupture and ventricular septal defect (day 3–7). Dressler syndrome (Week 8): autoimmune pericarditis; anti-myocardial antibodies (anti-cardiac Ag exposed after necrosis); fever + pleuritic pain + rub; treat with NSAIDs/aspirin.

6. Integration: Pathogenesis to Clinical Management Principles

Synthesise what you have learned across sections 1–5. (a) Draw a pathogenetic flow diagram (described in words or as a structured list) connecting Mr. Rajan's risk factors → atherogenesis → plaque rupture → STEMI → complications → heart failure. (b) For each major node in this chain, identify one point of therapeutic intervention and explain the pathological rationale behind it. (c) Reflect on how a different plaque location (e.g., proximal LAD) would have changed the clinical picture.

Guidance: Expected interventions: statins (stabilise plaque, reduce LDL oxidation); antiplatelet therapy (inhibit GP IIb/IIIa and thromboxane A2); primary PCI (restore flow, limit infarct size); beta-blockers (reduce wall stress, anti-arrhythmic); ACE inhibitors (attenuate LV remodelling post-infarct). LAD comparison: anterior STEMI (V1–V4), larger territory, higher risk of cardiogenic shock, LV aneurysm formation, Killip class III/IV; anterior papillary has dual supply → lower rupture risk. Reward students who connect pathology to mechanism-based therapy rather than rote recall.

PEER REVIEW

You will be assigned one classmate's submission to review anonymously. Read their response against each rubric criterion. For each criterion: (1) assign a rating from the rubric (full mark, near-full, partial, minimal, or zero); (2) write 1–2 sentences of specific feedback explaining your rating — cite a pathological detail they included or omitted; (3) end with one constructive suggestion. Your peer review will be graded on specificity and accuracy of feedback, not on how harshly or leniently you score. Avoid vague praise ('Great work!') or unsubstantiated deductions. Submit peer review within 72 hours of the original deadline.