Background: Heightened activity of the sympathetic nervous system in heart failure patients is a major contributor to disease progression and death. I-123 metaiodobenzylguanidine (MIBG) provides an accurate, noninvasive method to assess cardiac sympathetic nerve activity.
Methods: Thirty-seven patients with New York Heart Association class II, III, or IV heart failure underwent baseline measurement of I-123 MIBG heart-to-mediastinum ratios, maximum oxygen consumption, radionuclide left ventricular ejection fraction, and plasma norepinephrine levels. Patients were followed 48.8+/-8.6 months to endpoints of cardiac death or transplantation. The heart-to-mediastinum ratio of I-123 MIBG activity measured 15 minutes after injection was the only independent predictor of transplant-free survival (P<.0001). I-123 MIBG imaging at 15 minutes identified patients with subsequent cardiac transplantation or death with a sensitivity of 92% and specificity of 72%, whereas the corresponding values for maximum oxygen consumption were 75% and 56%. By Kaplan-Meier survival analysis, the time to a cardiac endpoint was significantly shorter in patients with a 15-minute I-123 MIBG heart-to-mediastinum ratio below the group mean ratio of 1.536, compared with patients with a preserved I-123 MIBG ratio. Maximum oxygen consumption was not predictive of time to cardiac transplant or death.
Conclusions: In this study of patients with congestive heart failure resulting from dilated cardiomyopathy, a 15-minute heart-to-mediastinum ratio of I-123 MIBG activity provided more accurate prediction of cardiac transplantation or death than other standard clinical tests.