17 Who should have a thallium scan? How does it
compare with standard exercise tests in
determining risk?
Liz Prvulovich
Exercise electrocardiography (ECG) is often the initial test in
patients with chest pain being investigated for coronary artery
disease (CAD). When this is unhelpful or leaves doubt then
myocardial perfusion imaging (MPI) is recommended. This may
occur when equivocal ST segment changes occur with exercise,
the exercise ECG is abnormal in a patient at low risk for CAD or
normal in a patient at high risk. MPI should be used instead of
exercise ECG when a patient has restricted exercise tolerance and
when the resting ECG is abnormal.^1 Importantly, recent data
confirm that investigative strategies for chest pain which include
MPI are cost effective.^2
The prognostic value of MPI arises from the relationship
between the depth and extent of perfusion abnormalities and the
likelihood of future cardiac events. A normal MPI scan after
adequate stress predicts a favourable prognosis (cardiac event rate
below 1% annually).^3 Conversely, severe and extensive inducible
perfusion defects imply a poor prognosis, as do stress-induced
left ventricular dilatation and increased lung uptake of tracer.
Several studies have shown that MPI is the most powerful single
prognostic test and that it provides independent and incremental
information to the exercise ECG in nearly all settings.3,4 A
prognostic strategy including MPI is also cost effective.^5
RReeffeerreenncceess
1 Underwood SR, Godman B, Salyani S et al.Economics of myocardial
perfusion imaging in Europe – The Empire Study. Eur Heart J1999; 2200 :
157–66.
2 De Bono D, for the joint working party of the British Cardiac Society and
Royal College of Physicians of London. Investigation and management
of stable angina: revised guidelines. Heart1999; 8811 : 546–55.
3 Brown KA. Prognostic value of myocardial perfusion imaging: state of
the art and new developments. J Nucl Cardiol1996; 33 : 516–38.
4 Ladenheim ML, Kotler TS, Pollock BH et al. Incremental prognostic
power of clinical history, exercise electrocardiography and myocardial
perfusion scintigraphy in patients with suspected coronary disease.
Am J Cardiol1987; 5599 : 270–7.