The Heart

Question 1

Creatine kinase isoenzymes

Answer 1

1. CK1: fast migrating: brain
2. CK2 (MB): skeletal muscle (1% MB) and cardiac muscle (30% MB)
3. CK3 (MM): skeletal muscle (99% MM) and cardiac muscle (70% MM)

Question 2

CK-MB : total CK

Answer 2

The “relative index”

• improves specificity of CK-MB for MI; >5% is suggestive of cardiac source

Question 3

• Macro CK Type 1
• Mitochondrial CK (macro CK type 2)

Answer 3

• Macro CK Type 1: May be found in healthy elderly women
• Macro CK Type 2: may be found in patients with advanced malignancy

Question 4

Answer 4

Question 5

Troponin

• specificity
• Reference intervals
• significance of elevation in nonischemic states
• Analytical false positive

Answer 5

• Highly cardiospecific; has largely replaced CK for MI diagnosis
• Reference interval includes all values up to 99th percentile of healthy adults
• Elevation of Tn in nonischemic states:
  
  1. Pulmonary embolism
  2. Myocarditis
  3. Pericarditis
  4. Heart failure
  5. Intracranial insults
  6. Rhabdomyolysis
  7. Sepsis
  8. Shock
  9. Renal insufficiency
• 1% of healthy adults have TnI > 99th percentile
• Analytical false positives: interferences, e.g., fibrin, heterophile antibodies

Question 6

Universal definition of MI

Answer 6

• Symptoms of ischemia
• New significant ST-T changes or new left bundle branch block
• Development of pathological Q waves
• Imaging showing new loss of viable myocardium or new regional wall motion abnormality
• Identification of an intracoronary thrombus by angiography or autopsy

Question 7

Patients whose initial cTnI value is abnormal

Answer 7

>20% change in cTnI values at 3 or 6 hours indicates myocardial necrosis

This + clinical evidence of ischemia indicates MI

Question 8

• MI evaluation in patients with normal initial cTnI value
• Acute versus chronic elevations

Answer 8

• >50% change in cTnI values at 3 or 6 hours indicates myocardial necrosis if initial value is normal
• The above + clinical evidence of ischemia indicates MI
• Demonstration of a rising and/or falling pattern is needed to distinguish acute from chronic elevations of cTn concentrations (elevations related to chronic renal failure or congestive heart failure do not change acutely)

Question 9

BNP

• source
• synthesis correlates with
• half life
• elevated in what patients

Answer 9

• source = ventricular myocytes
• Synthesis of BNP correlates directly with ventricular wall tension
• Rapidly degraded following production with t_1/2 of 20 minutes; N terminal peptide fragment (NT-proBNP) is more stable (t_1/2 1-2 hours)
• BNP and NT-proBNP are elevated in patients with heart failure