Page 274 - Concise Pathology for Exam Preparation ( PDFDrive )

11 Disorders of the Heart 259

Evolution of Coronary Arterial Occlusion (Flowchart 11.3)

Acute plaque change

↑ Myocardial Severe coronary Platelet
demand atherosclerosis activation

Haemodynamic Acute transmural Thrombosis
changes MI (or vasospasm)
FLOWCHART 11.3. Evolution of coronary arterial occlusion.

• In 10% cases, MI is not associated with atherosclerosis and is caused by other
mechanisms:
1. Vasospasm: Intense, relatively prolonged, vasospasm with or without coronary ath-
erosclerosis and platelet aggregation can induce acute MI
2. Emboli: May arise from left atrium due to atrial fibrillation, left-sided mural throm-
bosis, vegetative endocarditis, paradoxical embolus from right side of heart or
peripheral veins
3. Unexplained: In one-third patients, small intramural coronary vessel disease (like
vasculitis) or haematological abnormalities, eg, haemoglobinopathies, may lead to
acute coronary episodes

Clinical Features of Acute MI
• Squeezing, constricting or burning type of retrosternal chest pain which most often oc-
curs in the early morning hours (attributed to the increase in catecholamine-induced
platelet aggregation and increased serum concentrations of plasminogen activator in-
hibitor-1 post awakening). The pain may radiate up to the neck, shoulder and jaw and
down to the ulnar aspect of the left arm.
• Dyspnoea due to pulmonary congestion/pulmonary oedema or impaired contractility of
the heart
• Indigestion, feeling of fullness and gas
• Apprehension or anxiety
• Excessive sweating
• Nausea with or without vomiting
• Light headedness with or without syncope
• Cough or wheezing
• Hiccupping (which is thought to be due to irritation of the phrenic nerve or diaphragm)
• Rapid thready pulse
• May be asymptomatic, discovered on ECG (silent MIs are common in underlying dia-
betes mellitus and elderly patients)

Myocardial Response

Decreased blood supply induces profound functional, biochemical and morphologic
changes.
• Biochemical consequences (Flowchart 11.4)

Decreased aerobic glycolysis and onset of anaerobic glycolysis

Inadequate production of high-energy phosphates (creatinine phosphate and ATP)

Lactic acidosis
FLOWCHART 11.4. Biochemical consequences of acute MI.

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