The role of nuclear imaging in the failing heart: myocardial blood flow, sympathetic innervation, and future applications.

Heart failure represents a common disease affecting approximately 5 million patients in the United States. Several conditions play an important role in the development and progression of heart failure, including abnormalities in myocardial blood flow and sympathetic innervation. Nuclear imaging represents the only imaging modality with sufficient sensitivity to assess myocardial blood flow and sympathetic innervation of the failing heart. Although nuclear imaging with single-photon emission computed tomography (SPECT) is most commonly used for the evaluation of myocardial perfusion, positron emission tomography (PET) allows absolute quantification of myocardial blood flow beyond the assessment of relative myocardial perfusion. Both techniques can be used for evaluation of diagnosis, treatment options, and prognosis in heart failure patients. Besides myocardial blood flow, cardiac sympathetic innervation represents another important parameter in patients with heart failure. Currently, sympathetic nerve imaging with 123-iodine metaiodobenzylguanidine (123-I MIBG) is often used for the assessment of cardiac innervation. A large number of studies have shown that an abnormal myocardial sympathetic innervation, as assessed with 123-I MIBG imaging, is associated with increased mortality and morbidity rates in patients with heart failure. Also, cardiac 123-I MIBG imaging can be used to risk stratify patients for ventricular arrhythmias or sudden cardiac death. Furthermore, novel nuclear imaging techniques are being developed that may provide more detailed information for the detection of heart failure in an early phase as well as for monitoring the effects of new therapeutic interventions in patients with heart failure.