Heart failure (HF) strikes an estimated 300,000 patients annually in the U.S. While treatment strategies for this patient population have gained traction in the recent years, configuring the optimum diagnosis and management strategies for the disease still needs work. Studies published in recent years have shown that nuclear imaging, using both PET and SPECT, may have the potential to provide clinically useful data to enable better stratification and most favorable treatments for HF patients.
Myocardium: Dead or alive?
Practices have begun using FDG-PET to evaluate myocardial viability in patients with ischemic heart disease and impaired left ventricular (LV) function. The technique helps to identify patients at a heightened risk for developing cardiac events and can determine whether cardiac function can be improved with revascularization. This modality uniquely classifies heart tissue as either dead or viable.
"FDG-PET can detect cell integrity and is very sensitive for viability," Rob S.B. Beanlands, MD, chief of cardiac imaging and director of the National Cardiac PET Centre at the University of Ottawa Heart Institute in Canada. "This strategy helps define cell metabolism and hibernation."
To understand whether FDG-PET in HF can help inform decisions with ischemic cardiomyopathy, Beanlands and colleagues evaluated the benefits of PET-guided management in patients with LV dysfunction and coronary artery disease (CAD), (J Nucl Med 2010;51:567-574). In the Ottawa-FIVE trial, researchers randomized 111 patients who had reduced LV dysfunction from the PARR 2 study to receive FDG-PET (56 patients) or standard care (55 patients). Cardiac events were significantly reduced for patients who underwent FDG-PET-assisted management, 19 percent versus 41 percent. The authors concluded that FDG-PET helped to point physicians toward revascularization or not. When followed, patients saw improved outcomes.
"We are confident that FDG-PET viability can be used to direct therapy," Beanlands notes. "If surgeons are on the fence about whether to perform revascularization in this sick HF population, PET can help decide which road to take."
Determining myocardial viability via FDG-PET can improve functional prediction and survival, says Andrew Van Tosh, MD, director of nuclear cardiology at St. Francis Hospital in Roslyn, N.Y.
Myocardial viability studies are performed by reviewing myocardial perfusion, and its relationship to cardiac glucose metabolism as measured with FDG-PET. In these cases, FDG-PET can help recognize whether myocardium, which would be classified as "dead" (or scarred) with other modalities, is actually in hibernation. If it is characterized as in hibernation, the blood flow can be restored and function will improve.
However, the results of the STICH substudy presented at ACC.11, were contradictory, finding that utilizing nuclear imaging modalities for myocardial viability may not be reliable. Bonow et al found that the presence of viable myocardium was associated with a greater chance of survival in CAD and LV dysfunction patients—but it was not statistically significant.
Yet, Beanlands attributes these negative findings to the fact that SPECT was used rather than PET; the definition of tissue viability may have overestimated the presence of myocardial viability; incorrect assignment of patients in the viability positive cohort; and selection bias was introduced in the non-randomized substudy (N Engl J Med 2011;364:1617-1625).
"Based on these results, some may think that viability imaging may not be useful but quite the opposite is true," says Beanlands. "In fact, viability assessment is particularly helpful in the sickest patients."
Improving HF management
Nuclear imaging also is being assessed for other HF indications, such as a risk prediction tool and markers for treatment responses.
Marcelo F. Di Carli, MD, chief of nuclear medicine and molecular imaging and director of cardiovascular imaging at Brigham and Women's Hospital in Boston, and colleagues are currently evaluating the use of PET and SPECT for the following applications in HF patients:
- To detect CAD in patients presenting with HF; and
- PET detection and monitoring of treatment for cardiac sarcoidosis, an inflammatory disease of the heart muscle.
"PET can separate patients who have HF symptoms with a marked ischemic component from those whose HF is predominantly due to resting myocardial fibrosis and irreversible dysfunction," Van Tosh offers.