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.

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. A prognostic strategy including MPI is also cost effective.

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