New MI diagnosis criteria, same old risk

The traditional diagnosis of myocardial infarction (MI) used the World
Health Organization definition and required the concentration of a
cardiac biomarker to be above twice the upper limit of normal.
However, more recent guidelines have defined a troponin level above
the 99th percentile of normal as being diagnostic of MI.

Using data from the AMIS (Acute Myocardial Infarction in Switzerland)
registry, Urban investigated the outcomes of those patients with the
“classic” definition of MI (CK or CK-MB above the upper limit of
normal, or troponin T [TnT] >0.1μg/L) compared to those with the
“new” definition of myocardial infarction (TnT>0.01μg/L).

Overall 489 patients were diagnosed with the new criteria (a “new”
MI) and 8701 with the old (a “classic” MI).  In-hospital mortality
was 3.5% in the “new” group and 6.7% in the “classic” group
(p=0.004).  In as subset of patients with a longer follow-up,
mortality at 3 and 12 months was 1% for “new” compared to 1.6% for
“classic” at 3 months, and 5.6% compared to 4% at 12 months (p=NS).

By lowering the troponin threshold needed for the diagnosis of MI, the
number of patients with this diagnosis will increase.  In this study
this population was represented by the “new” cases, and despite
less aggressive treatment in hospital they had a better short term
prognosis than “classic” cases.  However, the 3- and 12-month risk
was the same in both patients, suggesting that even a minor
troponin leak identifies a group of patients at high-risk in the long
term.

·      Urban P, Radovanovic D, Erne P, Stauffer JC, Pedrazzini G,  
Windecker S, et al. Impact of changing definitions for myocardial  
infarction: A report from the AMIS registry. Am J Med 2008, Dec; 
121(12):1065-71.