Myocardial infarction

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Myocardial infarction
Diagnosis in short

Contraction band necrosis - a finding of MI. H&E stain.

LM early to late: wavy fibers, myocyte necrosis with loss of cross striations, contraction bands, edema, hemorrhage, neutrophilic infiltrate, pyknosis of nuclei, loss of nuclei (karyolysis), macrophage and mononuclear infiltration, fibrovascular response, granulation tissue, myocardial fibrosis
LM DDx cardiac amyloidosis for old infarct, myocarditis
Gross early to late: myocardial pallor, hyperemia (redness), yellow lesion with hyperemic border, white (fibrosis)
Site heart

Associated Dx coronary artery atherosclerosis+/-plaque rupture, +/-thrombosis, cocaine use
Signs +/-tachycardia, +/-diaphoresis (sweating), +/-hypotension
Symptoms classic findings: retrosternal chest pain +/- with radiation down the arms, nausea +/- vomiting, +/-shortness of breath
Blood work elevated troponin, CK-MB
Prognosis dependent on extent
Other abnormal EKG - especially ST elevation
Clin. DDx varies by presentation - usu. aortic dissection, angina, acute infectious pneumonia, pulmonary embolism, pericarditis, chest wall pain, anxiety, GI disease, others

Myocardial infarction, abbreviated MI, is death of cardiac muscle due to a compromised blood supply. In the context of pathology, they are occasionally seen at autopsy.

The lay term for MI is heart attack.

General

Clinical

  • Usually diagnosed clinically - with blood work (troponin, CK-MB) or EKG.
  • MI may be precipitated by cocaine use... and further exacerbated by treatment with a beta-blocker.[1]
  • Acute myocardial infarction (abbreviated AMI) = MI < 6 hours old.[2]
    • Usually no PMN infiltrate.

Classic symptoms:

  • Retrosternal chest pain +/- with radiation down the arms.
  • Nausea & vomiting.
  • Diaphoresis.

Enzymatic tests:[3]

  • CK: peaks at day 1, resolves after 2-3 days.
  • AST: peaks close to day 2, resolves after 4-5 days.
  • LDH: peaks day 2, resolves after ~6 days.

Complications

Complications of MI:[4]

  • Contractile dysfunction.
  • Cardiac arrhythmia.
  • Aneurysm formation, e.g. left ventricular aneurysm.
  • Ventricular rupture:
    • Ventricular free wall rupture.
    • Ventricular septal rupture.
  • Fibrinous pericarditis.
    • Dressler's syndrome AKA postmyocardial infarction syndrome[5]; pericarditis post-myocardial infarction +/- pericardial effusion (clinically tamponade).
  • Mural thrombosis.
  • Extension of MI.

Gross

Sequence:[6]

  • 18-24 hours - myocardial pallor.
  • 1-3 days - pallor, moderate hyperemia (redness due to congestion with blood).
  • 3-7 days - yellow lesion with hyperemic border.
  • 10-21 days - maximally yellow.
  • 6 weeks - white (fibrosis).

Image

Microscopic

Sequence:[7]

  • 1-3 hours - Wavy (myocardial) fibers
  • 4-12 hours - Coagulative necrosis & loss of cross striations, contraction bands, edema, hemorrhage, PMN infiltrate.
  • 18-24 hours - Coagulative necrosis, pyknosis of nuclei, and marginal contraction bands.
  • 1-3 days - Loss of nuclei (karyolysis), loss of striations, abundant PMNs.
  • 3-7 days - Macrophage and mononuclear infiltration, fibrovascular response.
  • 10-21 days - Fibrovascular response, prominent granulation tissue.
  • 6 weeks - Fibrosis.

Images

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Contraction band necrosis

General:

  • Mediated by catecholamines.[8]
  • Thought to arise in reperfusion from hypercontraction.

Microscopic:

  • Thick intensely eosinophilic staining bands (on H&E) ~ typically 4-5 micrometres wide
    • Span the short axis of myocyte.
    • Can be thought of bunched-up striae.

Notes:

  • Better seen with special stains (Masson or Gomori trichrome).[9]

Images

See also

References

  1. Mohamad T, Kondur A, Vaitkevicius P, Bachour K, Thatai D, Afonso L (2008). "Cocaine-induced chest pain and beta-blockade: an inner city experience". Am J Ther 15 (6): 531-5. doi:10.1097/MJT.0b013e3181758cfc. PMID 19127137.
  2. Senter, S.; Francis, GS. (Mar 2009). "A new, precise definition of acute myocardial infarction.". Cleve Clin J Med 76 (3): 159-66. doi:10.3949/ccjm.75a.08092. PMID 19258462.
  3. URL: http://pro2services.com/Lectures/Fall/CardEnz/a6mienz.gif. Accessed on: 27 April 2012.
  4. Mitchell, Richard; Kumar, Vinay; Fausto, Nelson; Abbas, Abul K.; Aster, Jon (2011). Pocket Companion to Robbins & Cotran Pathologic Basis of Disease (8th ed.). Elsevier Saunders. pp. 293. ISBN 978-1416054542.
  5. Hutchcroft BJ (July 1972). "Dressler's syndrome". Br Med J 3 (5817): 49. PMC 1788531. PMID 5039567. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1788531/.
  6. http://library.med.utah.edu/WebPath/TUTORIAL/MYOCARD/MYOCARD.html
  7. http://library.med.utah.edu/WebPath/TUTORIAL/MYOCARD/MYOCARD.html
  8. Hopster DJ, Milroy CM, Burns J, Roberts NB (May 1996). "Necropsy study of the association between sudden cardiac death, cardiac isoenzymes and contraction band necrosis". J. Clin. Pathol. 49 (5): 403–6. PMC 500481. PMID 8707956. //www.ncbi.nlm.nih.gov/pmc/articles/PMC500481/.
  9. Hopster DJ, Milroy CM, Burns J, Roberts NB (May 1996). "Necropsy study of the association between sudden cardiac death, cardiac isoenzymes and contraction band necrosis". J. Clin. Pathol. 49 (5): 403–6. PMC 500481. PMID 8707956. //www.ncbi.nlm.nih.gov/pmc/articles/PMC500481/.