PATH - Myocardial Infarction

Question 1

Myocardial infarction

Answer 1

Most often acute thrombosis due to rupture of coronary artery atherosclerotic plaque. 

Commonly occluded coronary arteries: LAD > RCA > circumflex.

SX
diaphoresis, nausea, vomiting, severe retrosternal pain, pain in left arm and/or jaw,
shortness of breath, fatigue

cardiac biomarkers (CK-MB, troponins) are diagnostic
-Cardiac troponin I rises after 4 hours (peaks at 24 hr) and is  for 7–10 days; more specific
than other protein markers
-CK-MB rises after 6–12 hours (peaks at 16–24 hr)Useful in diagnosing reinfarction following acute MI because levels return to normal after 48 hours.

Question 2

ST-segment elevation MI (STEMI)

Answer 2

Transmural infarcts

Full thickness of myocardial wall involved

ST *elevation
*Q waves

Question 3

Non–ST-segment elevation MI (NSTEMI)

Answer 3

Subendocardial infarcts

Subendocardium (inner 1⁄3) especially vulnerable to ischemia

ST *depression

Question 4

0–24 hr

Answer 4

GROSS
Dark mottling; pale with
tetrazolium stain

LIGHT MICROSCOPE

• Early coagulative necrosis, release of necrotic cell contents into blood
• edema, hemorrhage, wavy fibers.
• Neutrophils appear.
• Reperfusion injury, associated with generation of free radicals, leads to hypercontraction of myofibrils

COMPLICATIONS
Ventricular arrhythmia
HF
cardiogenic shock

Question 5

1–3 days

Answer 5

GROSS
Hyperemia

LIGHT MICROSCOPE

• Extensive coagulative necrosis.
• Tissue surrounding infarct shows acute inflammation with neutrophils.

COMPLICATIONS
Postinfarction fibrinous pericarditis

Question 6

3–14 days

Answer 6

GROSS
Hyperemic border; central yellow-brown softening maximally yellow and soft by 10 days

LIGHT MICROSCOPE
Macrophages, then granulation
tissue at margins

COMPLICATIONS
-Free wall rupture-->tamponade
-papillary muscle rupture-->mitral regurgitation
-interventricular septal rupture
due to macrophage-mediated
structural degradation.
-LV pseudoaneurysm

Question 7

2 weeks to several months

Answer 7

GROSS

• Recanalized artery
• Gray-white

LIGHT MICROSCOPE
Contracted scar complete

COMPLICATIONS
Dressler syndrome, HF, arrhythmias, true ventricular
aneurysm (risk of mural
thrombus).