• myocardial viability
• magnetic resonance imaging

• DSE, dobutamine stress echocardiography
• LV, left ventricle
• MRI, magnetic resonance imaging
• PET, positron emission tomography
• SPECT, single photon emission computed tomography

In recent years, it has become evident that myocardial dysfunction in ischaemic heart disease is not always a result of infarction and that contractile function can improve significantly after revascularisation.¹² A number of non-invasive techniques have been developed in an attempt to identify these patients with dysfunctional but viable myocardium, since it is generally agreed that it is this group, as compared to the group with irreversible myocardial damage, that has a favourable clinical risk-to-benefit profile for undergoing coronary revascularisation. The primary aim of these non-invasive techniques is to provide a regional map of the heart in which the amount of viable myocardium is quantified. Unfortunately, currently available techniques, such as single photon emission computed tomography (SPECT), dobutamine stress echocardiography (DSE), and positron emission tomography (PET), have various limitations. For example, what is measured may not be the direct presence and exact quantity of viable myocytes, but a physiologic parameter, such as contractile reserve or perfusion, that has only an indirect relation to viability. Other limitations related to the specific technique include partial volume effects due to poor spatial resolution (SPECT, PET), attenuation and scatter artefacts (SPECT), errors in registration between comparison images (DSE), and the occasional inability to visualise all parts of the left ventricular myocardium (DSE).

In this article we will re-examine some fundamental concepts in the assessment of myocardial viability. We propose that even if a technique were available that could provide direct quantification of regional viability without technical limitations (no artefacts, infinite spatial resolution, etc), there would still be insufficient information to provide a comprehensive assessment of viability and thus insufficient information to provide the highest accuracy in predicting wall motion improvement or clinical benefit after coronary revascularisation. Certainly, there are additional factors that are not related to limitations in non-invasive testing that could …