Dr. Pasquale Perrone-Filardi
Non-invasive imaging is playing an emerging role in patients with chronic heart failure, especially for selecting appropriate candidates for different therapeutic strategies and for evaluating therapeutic effects. As new imaging modalities and new imaging techniques are being proposed for clinical use, there is a strong need for balanced and critical information about the advantages and limitations of different available imaging modalities.
The role of non-invasive imaging is consolidated for selecting appropriate candidates for surgical revascularization among patients with ischemic left ventricular dysfunction. In fact, presence of a substantial amount of residual viable myocardium is strongly and independently associated with adverse prognosis in patients treated with medical therapy, whereas these patients benefit most from myocardial revascularization. Echocardiography, PET, SPECT, MRI using the late enhancement approach, and, more recently and still investigational, CT have all been evaluated for myocardial viability assessment in patients. Using as gold standard the recovery of resting contractile function after revascularization, perfusion and metabolic assessment of viability using nuclear techniques has been proven to be more sensitive although less specific than evaluation of contractile function using dobutamine administration in conjunction with MR or echocardiographic imaging. More recently, direct visualization of necrotic myocardium using the late enhancement technique with MRI (and in the near future with cardiac CT) provided another powerful approach to evaluate viability, perfusion, geometry and function within a single study. However, insofar as the accuracy is tested against the recovery of contractile function, there is at the moment no one perfect technique, especially in situations of myocardial dysfunctional territories consisting of an admixture of necrotic and viable myocardium. In these common cases, integration of different imaging modalities looking at different aspects of viable myocardium (e.g. metabolic imaging with contractile reserve, late enhancement imaging with contractile reserve, etc) maybe superior and more useful than a single modality approach for selecting appropriate candidates for surgical therapy.
Another relevant consolidated use of imaging in heart failure patients is in selection of candidate patients for resynchronization therapy. It is well recognized that current guidelines indications are relatively broad and a relevant proportion (up to 30%) of implanted patients are non responders. Evaluation of asynchrony, especially with TDI echocardiography, has been repeatedly proven to identify inter- and intra-ventricular asynchrony, and, therefore, is helpful in selecting patients, especially among those without substantial QRS elongation. However, recent MRI studies, aiming at evaluating the pathophysiological substrate of asynchrony, have reported that asynchrony may be non reversible, and, therefore, patients can be non responders, when a substantial amount of scar is present, especially at the site of lead stimulation.
Future potentially relevant applications of non-invasive imaging may come from evaluation of stem cell therapy in patients with heart failure. Using SPECT, PET or MR techniques, stem cells can be appropriately labelled and imaged in the hosting myocardium. Alternatively, indirect imaging using injected reported genes can also be used to permanently track the localization and proliferation of injected stem cells.
Finally, the role of non-invasive imaging, especially with emerging MRI applications, is under investigation in patients with non ischemic cardyomyopathies and in patients with myocarditis in whom MRI provides relevant etiologic and pathophysiological information together with independent and clinically valuable prognostic information.
There is no doubt that non-invasive cardiac imaging plays a crucial role in the evaluation of patients with heart failure. This role is mostly consolidated for the evaluation of patients with ischemic cardiomyopathies in order to select most appropriate therapeutic options. As long as new techniques and new imaging modalities rapidly emerge from technical progress, there is an urgent need for clinicians to acquire sufficient competence for selection of the most useful and cost-beneficial imaging sequence in the individual patient.
Imaging to guide therapy in heart failure Symposium
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