Heart failure (HF) is highly prevalent, with an estimated 5.7 million Americans living with the condition, and 670,000 new patients diagnosed each year.1 Despite many advances in pharmacotherapy and device therapy, the mortality of HF still exceeds that of common cancers. It is anticipated that 80% of men and 70% of women <65 years of age who have HF die within 8 years.1 Several aspects of the pathophysiology of HF are gainfully evaluated by radionuclide imaging. The ubiquitous presence of myocardial single photon emission computed tomography (SPECT) imaging in the academic hospital and community settings makes it potentially well suited for application to this highly prevalent condition. This chapter will discuss the established applications of radionuclide cardiac imaging in HF, and also highlight some of its evolving applications in this area.
ASSESSMENT OF LV FUNCTION
The use of scintigraphic techniques for the assessment of ventricular function is discussed in Chaps. 7 and 10. In the context of the HF patient, several management decisions including invasive device therapy with implantable defibrillators and biventricular pacing are predicated by accurate and absolute measurements of ejection fraction (EF). Since reproducibility is high, assessment of LV function over time can be used to determine success of therapies, and potential necessity for devices. However, some clinically important concepts of ventricular function assessment have received insufficient emphasis in the literature. With multiple imaging modalities available for EF assessment, it is important to recognize that the lower limit of normality is modality-specific (Table 18-1).2 Furthermore, the intermodality variability is exaggerated in patients with LV systolic dysfunction.3 Thus, in the commonly encountered situation where patients have had EF assessed by gated SPECT and echocardiography, the absolute numbers are likely to be different, with SPECT-derived EF generally higher than echocardiography-derived EF. It is noteworthy that this intermodality variability in EF assessment was not taken into account even in the design of large multicenter trials with specific EF requirements for inclusion criteria, such as the implantable cardioverter defibrillator (ICD) trials in HF. A powerful advantage of gated SPECT over echocardiography is that automated quantification reduces the variability and error involved in subjective reader interpretation and eliminates the need for manual border tracing that is time consuming, and greatly influenced by the patient's body habitus.4 The two standard deviation limit of variability in the serial assessment of EF by high-dose, rest-gated Tc-99m SPECT studies is estimated to be approximately ±5%.5,6 The variability in EF by different modalities suggests that serial imaging should be confined to the same imaging modality.
Table 18-1Normal Ranges for LVEF by Imaging Modality |Favorite Table|Download (.pdf) Table 18-1 Normal Ranges for LVEF by Imaging Modality
|Method ||Mean LVEF ± SD (%) ||Lower Limit of Normal (%) |
|Gated SPECT ||63 ± 10 ||44 |
|Echocardiography ||60 ± 5 ||48 |
|MRI ||65 ± 5 ||57 |
|Angiography ||67 ± 8 ||51 |