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- ↵⁎Address for correspondence:
Dr. Henry Gewirtz, Cardiac Unit/Yawkey 5E, Massachusetts General Hospital, 55 Fruit Street, Boston, Massachusetts 02114
quantitative positron emission tomography (pet) imaging to assess absolute myocardial blood flow (mbf) is superior to standard stress/rest tracer uptake images for functional assessment of the coronary circulation (1) and in selected patients (e.g., renal insufficiency, low prior probability of coronary artery disease [CAD]) may provide an attractive alternative to coronary angiography to assess for CAD. PET measurements of absolute MBF provide detailed information concerning: 1) extent and functional severity of CAD (Fig. 1); 2) presence of uniform marked reduction in hyperemic response to adenosine (Fig. 2); and 3) evidence of coronary steal (Fig. 3), which is often associated with impaired regional contractile function (2). Moreover, electrocardiography gated images of the left ventricular (LV) myocardium can provide absolute measurements of LV volumes (Fig. 4) from which physiological parameters such as stroke work and power are derived. These indexes are essential to assessment of absolute values of MBF and provide important clinical information such as response to therapy in patients with dilated cardiomyopathy (DCM).
The studies presented below demonstrate the importance of PET measurements of absolute MBF and LV contractile function in improving the evaluation of patients with DCM. Absolute MBF measurements make it possible to detect regional asymmetries in response to vasodilator stimuli (Fig. 1), including coronary steal (Fig. 3), which are not detectable by standard uptake images (Fig. 1) and thereby considerably enhance recognition of the extent and severity of CAD. Similarly, absolute MBF measurements make possible the recognition of globally impaired responsiveness to vasodilator challenge (Fig. 2) and suggest the presence of a nonischemic etiology for DCM. Since severe triple vessel disease with dilated LV in theory may result in relatively uniform reduction in responsiveness to vasodilator stimulus and so be indistinguishable from DCM due to diffuse microvascular disease (e.g., DCM associated with combination of obesity, hypertension, and type 2 diabetes mellitus, without significant epicardial CAD), additional clinical studies will be needed to better define the extent of asymmetries which can be seen in each. In selected cases it also may be necessary to make measurements of rest MBF in patients being evaluated for etiology of DCM, since coronary steal, an important sign of DCM related to epicardial CAD as opposed to diffuse microvascular disease, cannot be recognized without them.
The author thanks Mr. Steve Weise for his technical assistance. Dr. Gewirtz has reported that he has no relationships to disclose.
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