MCQ Pathology Answer 29

The correct Answer is B

Transmural infarct - usually involves the LV or in 15-30% it may involve septum with extension into the RV. Isolated infarcts of RV and right atrium are extremely rare. Infarct is within area fed by one coronary vessel.
Pathogenesis of transmural infarcts (most common type of MI)

a. Occlusive coronary thrombus overlying an ulcerated or fissured stenotic plaque causes 90% of transmural AMI.
b. Vasospasm with or without coronary atherosclerosis and possible association with platelet aggregation.
c. Emboli from left sided mural thrombi, vegetative endocarditis, or paradoxic emboli from the right side of heart through a patent foramen ovale.

• macroscopically, transmural infarct not identifiable less than 12 hours from time of onset

• takes about 24 hours for damage to travel from the endocardium to epicardium
• after 24 hours infarct can be recognised by pallor or by reddish-blue colour (due to congestion)
• after 3 – 5 days, infarct is mottled and more sharply outlined with a central pale yellowish necrotic region bordered by a hyperaemic zone
• by 2 – 3 weeks, infarct usually depressed and soft with gelatinous appearance
• older infarcts are firm and have pale grey appearance (scar tissue)

Transmural infarction produces changes in both myocardial depolarization (QRS complex) and myocardial repolarization (ST-T complex.)

The earliest changes seen with an acute transmural infarction occur in the ST-T complex. There are two sequential phases to these ST-T changes seen with MI: the acute phase and the evolving phase. The acute phase is marked by the appearance of ST segment elevations and sometimes tall positive (hyperacute). T waves in certain leads. The evolving phase (occurring after hours or days) is characterized by the appearance of deep T wave inversions in those leads that previously showed ST elevations.

Transmural MI can also be described in terms of the location of the infarct: anterior means involving the anterior and/or lateral wall of the left ventricles (chest leads V₁ to V₆, limb leads 1 and aV_L): inferior means involving the inferior (diaphragmatic) wall of the left ventricle.(leads II, III and aV_F). For example, with an acute anterior wall MI the ST segment elevations and tall hyperacute T waves appear in one or more of the anterior leads.

Category: Pathology MCQs