Viability assessment by delayed enhancement cardiovascular magnetic resonance: will low-dose dobutamine dull the shine?

Since mechanical revascularization methods such as coronary artery bypass graft surgery (CABG) and percutaneous coronary intervention became available, the issue of identifying dysfunctional yet viable myocardium has been of crucial clinical importance. Among patients with ischemic cardiomyopathy and viable myocardium, mechanical revascularization is associated with improved systolic function, symptoms, and survival,1–3 yet the best method to identify viable myocardium remains disputed. Current options include positron-emission tomography (PET) to assess myocardial metabolic activity, single-photon emission computed tomography (SPECT) with technetium-99m sestamibi or thallium-201 to assess myocardial perfusion and membrane integrity, and dobutamine echocardiography or cine cardiovascular magnetic resonance (CMR) to assess myocardial contractile reserve. Each approach, however, has limitations. For example, the index measured may not reflect the quantity of viable myocytes but rather a physiological parameter, such as perfusion or contractile reserve, that has only an indirect relation to viability. Other limitations include partial volume effects due to poor spatial resolution (SPECT, PET), attenuation and scatter artifacts (SPECT), and the occasional inability to visualize all parts of the left ventricle (dobutamine echocardiography).