Assessing the requirement for the 6-hour interval between specimens in the American Heart Association Classification of Myocardial Infarction in Epidemiology and Clinical Research Studies.
BACKGROUND
The American Heart Association (AHA) case definition for acute myocardial infarction (AMI) requires an "adequate set" of biomarkers: 2 measurements of the same marker at least 6 h apart. A sensitive troponin assay might detect significant changes in concentration earlier. We determined AMI prevalence, using protocols with shorter intervals between measurements, with and without incorporating the time from onset of symptoms.


METHODS
The AHA case definition was used to retrospectively assign a diagnosis in 258 patients presenting to the emergency department with symptoms of cardiac ischemia. AMI was diagnosed if either specimen in an adequate set had a cardiac troponin I (cTnI) above the 99th percentile (AccuTnI >0.04 microg/L; Beckman Coulter) with a > or =20% change in concentration between specimens. We assessed positivity for AMI after progressively decreasing the time interval between specimens in specimen sets. In addition, for each patient, 2 additional specimen pairs were selected: pairs collected at least 1 h apart with 1 specimen being either > or =3 h after onset or > or =6 h after onset.


RESULTS
When we used the AHA definition, the AMI prevalence was 35.7%. Prevalence was not significantly diminished when the interval between specimens was > or =5, > or =4, or > or= 3 h (36.4%, 34.5%, and 33.7%, respectively) compared with the AHA > or =6 h interval. When the time from onset of symptoms was included in the specimen selection algorithm, a 1-h interval was sufficient provided that at least one specimen was collected > or =6 h after onset (prevalence, 34.1%; P = 0.48 vs AHA definition).


CONCLUSIONS
A sensitive cTnI assay in specimen sets with time intervals > or =3 h, or having one specimen > or =6 h after onset, gave an AMI prevalence equivalent to the AHA definition.
The Research Institute at Lakeridge Health, Oshawa, ON, Canada.
Andrew R
AR
Macrae
Peter A
PA
Kavsak
Viliam
V
Lustig
Rakesh
R
Bhargava
Rudy
R
Vandersluis
Glenn E
GE
Palomaki
Marie-Jeanne
MJ
Yerna
Allan S
AS
Jaffe
D000572:American Heart Association; D015415:Biomarkers / Q000097:blood; D001800:Blood Specimen Collection; D006801:Humans; D009203:Myocardial Infarction / Q000145:classification / Q000175:diagnosis* / Q000453:epidemiology*; D017410:Practice Guidelines as Topic; D015995:Prevalence; D012189:Retrospective Studies; D013997:Time Factors; D019210:Troponin I / Q000097:blood
D015415:Biomarkers; D019210:Troponin I