Diagnosing Myocardial Infarction

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Diagnosing Myocardial Infarction

• Kimberly A. Dovin, MD, PGY3
• Case Conference
• February 18, 2004

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MI Old Definition

• Requires 2 of 3
• Typical Sx
• Enzyme rise
• Typical EKG (Q waves)

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MI Defined 2000

• Acute, evolving or recent MI
• Requires 1 of 2
• Typical rise and gradual fall (troponin) or more
  rapid rise and fall (CK-MB) of markers of
  myocardial necrosis with gt 1 of
• Symptoms
• Q waves
• EKG c/w ischemia
• S/p coronary artery intervention
• Pathologic findings of AMI

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MI Defined 2000

• Established MI
• One or more of
• - new Q waves on EKG
• - pathologic findings of healed/healing MI

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Symptoms of MI

• Chest, epigastric, arm, wrist, jaw pain or
  discomfort w/ exertion or at rest
• Usually lasts 20 min, but may be less
• Associated sx dsypnea, diaphoresis, nausea,
  vomiting, light-headedness
• With or without chest discomfort

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Biochemical markers

• Troponin High sensitivity, high specificity for
  myocardial tissue
• CK-MB less tissue specific, but better
  specificity for irreversible injury
• Myoglobin for rapid diagnosis

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Biochemical Markers II
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Biochemical Markers III

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Non MI Causes of Troponin Elevation

• Tachycardia
• PE w/ Right Vent infarct
• Cardiac failure w/ myonecrosis
• Cardiac surgery
• Myocarditis
• Renal failure

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EKG Findings Ischemia

• Patients with ST segment elevation
• New elevation at the J point in 2 contiguous
  leads
• gt 0.2mV in V1-3
• gt 0.1mV in all others
• Patients without ST segment elevation
• ST segment depression
• T wave abnormalities

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EKG Findings Established MI

• ANY Q waves in V1-3
• Q wave gt .03s in I, II, aVL, aVF, V4-6

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Coronary Angiogram

• Observer variability
• Discordance betw severity of lesion and
  physiologic effects
• Greater stenosis vs more unstable plaques?
• 2-D picture of a 3-D problem
• Diffuse disease may limit estimation of abnormal
  segments
• Missed lesions

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It is now clear that any amount of
myocardial damage, as detected by cardiac
troponins, implies an impaired clinical outcome
for the patient.
A review of currently available data
demonstrates no discernible threshold below which
an elevated value for cardiac troponin would be
deemed harmless.
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Bibliography

• Elliott Antman MD, Jean-Pierre Bassand MD, Werner
  Klein MD, Magnus Ohman MD, Jose Luis Lopez Sendon
  MD, Lars Rydén MD, Maarten Simoons MD and Michal
  Tendera MD Myocardial infarction redefineda
  consensus document of The Joint European Society
  of Cardiology/American College of Cardiology
  committee for the redefinition of myocardial
  infarction Journal of the American College of
  Cardiology Volume 36, Issue 3 , September 2000,
  Pages 959-969
• John K French and Harvey D White Clinical
  implications of the new definition of myocardial
  infarction Heart 20049099-106
• Steven E. Nissen MD, FACC Pathobiology, not
  angiography, should guide managementin acute
  coronary syndrome/nonST-segment elevation
  myocardial infarction1 The non-interventionist's
  perspective Journal of the American College of
  Cardiology Volume 41, Issue 4, Supplement 1 , 19
  February 2003, Pages S103-S112