Question

A histology slide of myocardium is taken from a patient who died 1-3 days after an acute myocardial infarction. Which of the following cellular changes is MOST characteristic of this time interval?

• A. Dense neutrophilic (polymorphonuclear) infiltration of necrotic myocardium
• B. Coagulative necrosis with wavy fibres and contraction bands only
• C. Macrophage infiltration with phagocytosis of dead myocytes
• D. Dense collagenous scar with few cells

Hint:

Acute inflammation dominates the first few days - think which white cell arrives first.

Answer 1

The Correct Option is A

Step 1: Recall the timeline of histological changes after MI.
The microscopic evolution of a myocardial infarct follows a well-defined sequence. In the first 0-4 hours there are usually no light-microscopic changes. From 4-12 hours, early coagulative necrosis, oedema and haemorrhage begin, and wavy fibres and contraction bands may appear. From 12-24 hours, coagulative necrosis becomes prominent with marked nuclear changes.

Step 2: Identify the 1-3 day window.
Between roughly 1 and 3 days (24-72 hours), there is established coagulative necrosis accompanied by a brisk acute inflammatory response - the necrotic myocardium is heavily infiltrated by neutrophils (polymorphonuclear leukocytes). This is the hallmark of the slide shown.

Step 3: Why the other options are wrong.
Option 2 (wavy fibres/contraction bands alone) is an earlier finding (4-24 hours). Option 3 (macrophage infiltration clearing debris) typically peaks at day 3-7 onward, after the neutrophilic phase wanes. Option 4 (dense collagenous scar) is the late healed phase, occurring after about 2-8 weeks.

Key fact: Neutrophilic infiltration of necrotic myocardium is the characteristic histology of a 1-3 day old myocardial infarct.