Newer Diagnostic Tests for MI
                       =============================
þ Troponin
 - Consists of three subunits: Troponin-C, Troponin-T, Troponin-I
 - Found in skeletal muscle, too -- but the cardiac Troponin-T and -I are
   encoded by different genes, so can be distinguished from skeletal
 - Troponin-I most sensitive in early hours

þ Troponin-T
 - more sensitive than CPK-MB;
 - peaks at 14 hours and 3-5 days in acute MI;
 - can be released from ischemic and not-yet infarcted tissue (reversible
   ischemic damage)
   [Hamm CW, et al. The prognostic value of single troponin T in unstable
   angina. N Engl Med J 1992;327(3):146-9.]
 - can last for 2-3 weeks.
   [Antman EM, Grudzien C, Sacks DB. Evaluation of a rapid bedside assaay for
   detection of serum cardiac troponin T.]
 - what level is positive?
  + 0.1
    [Ohman EM, et al [for the Gusto-IIa investigators]. Cardiac Troponin T
    levels for risk stratification in acute myocardial ischemia. N Engl J Med
    1996;335(18):1333-1341.]
    [Van de Werf F. Cardiac troponins in acute coronary syndromes [editorial].
    N Engl J Med 1996;335(18):1388-1389.]
  + 0.2-0.4 (commmon clinical practice)
 - are bedside qualitative assays useful in the ED?
  + maybe (but this study has problems with selection bias; only patients
    admitted to CCU):
    [Antman EM, Grudzien C, Sacks DB. Evaluation of a rapid bedside assaay for
    detection of serum cardiac troponin T.]
 - Troponin T may be falsely elevated in those with renal failure.
   [Antoinette Mangione, MD, PharmD, FACEP, 1998 PaACEP conference]

þ Mercy (and Mercy Prov)
 - used to use Troponin-T, revised 1/97 to detect level as low as 0.08 ng/ml,
   is a qualitative test.
 - now uses quantitive Troponin-I level (must go in red top or similar, purple
   top not acceptable) as of Dec 1 1998

þ Troponin-I
 - upslope similar to CPK-MB; usually positive starting about 4-8 hours after
   pain (per Mercy lab); both MB and cTnI (cardiac Troponin-I) peak at about
   18 hours
 - stays elevated longer than CPK-MB (good substitute for LDH isos); CPK-MB
   usually gone in 48-72 hours but cTnI may stay elevated for up to 9 days
   (per Mercy lab)
 - not routinely elevated in dialysis patients
 - no "background level" as with CPK
 - Hennepin Co. Medical Center has converted to troponin-I
   <C-MI-TrA.TXT>
   [Antman EM, et al [including Eugene Braunwald]. Cardiac specific Troponin I
   levels to predict the risk of mortality in patients with acute coronary
   syndromes. New Engl J Med 1996;335(18):1342-1349.]

þ Myoglobin
 - only present after MI for about 2 hours, so not very useful in ED.
 - found to be better than Troponin T or CPK-MB in one study
   [Bakker AJ, Koelemay MJW, Gorgels JPMC, van Vlies B, Smits R, Tussen JGP,
   Haagen FDM. Troponin T and myoglobin at admission; value of early diagnosis
   of acute myocardial infarction. Eur Heart J 1994;15:45-53.]
   Poor study; no gold standard:
   [Davis CP, Barrett K, Torre P, Wacasey K. Serial myoglobin levels for
   patients with possible myocardial infarction. Acad Emerg Med
   1996;3(6):590-597.]
 - Need to do serial levels ("nurse, draw blood every 30 minutes"?!?):
   [Tucker JF, et al. Value of serial myoglobin levels in the early diagnosis
   of patients admitted for acute myocardial infarction. Ann Emerg Med
   1994;24(4):704-708.]
 - elevated in trauma patients, those with renal failure. If exclude those
   patients, false + rate is acceptable.

þ CPK-MB Isoforms
 - cleavage of CPK-MB results in isoforms CPK-MB1 and CPK-MB2.
 - ratio of 1/2 changes even before total CPK-MB elevates
 - research only at present (1998)

þ Echos:
 - 93% sensitive, 57% specific; if discharged patients with normal echo and
   normal EKG would have missed 2 MIs out of 202 ED patients. [Sabia et al.
   Circ 1991;84(suppl):85.]

þ Sestamibit imaging:
 - small study suggests normal scan rules out MI. [Varetto et al. J Amer
   Coll Cardiol 1993;22:1804.]
 - larger study seemed to confirm. [Tatum et al. Ann Emerg Med 1997;29:116/]