michael s
(Michael S)
#1
days. An elevated troponin T has a predictive value for
myocardial ischaemia several times higher than CK-MB mass.
Troponin T as a diagnostic tool
Troponin T can be used both as a diagnostic and a prognostic tool
in the Accident and Emergency Department. Repeated troponin
assays taken 4–6 hours apart have been used to successfully
identify all patients with MI even in the absence of ST
elevation.^1 Individuals who were troponin T negative were shown
to be at low short term risk. Troponin T accurately reflects the
degree of myocardial necrosis with the overall risk of death
following an ACS being directly related to the levels detected.
Data from the Fragmin During Instability in Coronary Artery
Disease trial (FRISC) demonstrated that patients with the highest
levels of troponin T following an ACS carried the highest risk of
death and MI, in contrast to those who were troponin T negative
who were at low risk.^2 A subset from the GUSTO IIa trial had
similar findings for non-ST elevation ACS where troponin T
positive patients had a much higher risk of death and heart failure
than troponin T negative individuals.^3
Risk stratification
The initial step in risk stratification is an ECG. Patients with
acute ST elevation are considered to have an acute MI and
require reperfusion therapy according to local protocols.
Individuals with ST depression are also at high risk and require
admission for further evaluation. The presence of a positive
troponin T in this group further confirms them as high risk. In
situations where patients present either with a normal ECG or
with T wave changes only, the value of a positive troponin T is
vital in risk stratification. All patients who are troponin T
positive should be considered as high risk, whilst in contrast, a
negative troponin T 12 hours or more after the onset of
symptoms puts the individual in a low risk group. If the result
of a negative troponin T test taken 12 hours or more after the
onset of chest pain is taken in conjunction with a pre-discharge
exercise test, this further reduces the chance of an inappropriate
discharge.^4 Figure 20.1 illustrates one possible management
algorithm.
