A conceptual paradox of MIBG uptake in heart failure: retention with incontinence!

[123 I-MIBG scintigraphy in the assessment of heart failure prognosis and effectiveness of cardiac resynchronization therapy]

Cardiac resynchronization therapy (CRT) is one of the methods of treating patients with chronic heart failure, which can reduce the mortality rate of this group. Scintigraphic assessment of sympathetic myocardial innervation allows us to evaluate the heart failure prognosis and the effectiveness of interventional treatment. The method is based on use of the radiopharmaceutical 123 I-methiodiobenzylguanidine (123 I-MIBG), which is a structural analogue of norepinephrine and is able to selectively accumulate in the sympathetic nerve endings. This review includes a brief description of norepinephrine metabolism and pharmacokinetics of 123 I-MIBG in the sympathetic nerve ending, a brief description of the study methodology and the clinical significance of this method in patients with heart failure. Particular attention is paid to the possibilities of using this method in patients with severe chronic heart failure before and after CRT.

Regional Cardiac Sympathetic Nervous System Evaluation Using 123I-mIBG SPECT in Patients with Heart Failure

BACKGROUND

Heart failure (HF) involves both mechanical and autonomic nervous system dysfunction that can lead to sudden cardiac death. In the failing human heart, there is increased release of norepinephrine from neurons and reduced uptake. Iodine-123-labeled metaiodobenzylguanidine (123I-mIBG) demonstrates reduced global uptake and increased washout associated with increased mortality in HF. This research examined the potential benefits of single-photon emission computed tomography (SPECT) regional quantitation in risk stratification of HF patients and its role in prediction of cardiac morbidity and mortality.

METHODS

Twenty-two clinically diagnosed HF patients were recruited into this study. The subjects underwent myocardial perfusion SPECT and cardiac sympathetic imaging with 123I-mIBG. Early (at 15 min after injection) and delayed (four hours after injection) planar and SPECT were performed. Visual and semiquantitative analysis was conducted, and global (from planar imaging) and regional (from SPECT imaging) uptake and washout indices determined. The patients were clinically followed for up to two years, and the cardiac events (CEs) in these patients were recorded and correlated with the various parameters.

RESULTS

The occurrence of a CE in HF was independent of the patients' demographics or the cause of HF. Genetic biomarkers were unable to reliably predict CEs. Global or regional uptake had limited ability to predict a CE, whereas regional washout from the inferior wall (P = .005) was a statistically significant predictor of CEs. Similarly, a high washout of 40% or more from the peri-infarcted and noninfarcted segments on myocardial perfusion scintigraphy was also a significant predictor of CEs (P = .035).

CONCLUSION

HF is a complex, multifactorial, progressive disease that appears to begin regionally. 123I-mIBG provides a valuable tool in imaging the global and regional sympathetic nervous system innervation of the heart. This may allow early identification and stratification of patients at risk of sudden cardiac death.

Myocardial innervation and perfusion imaging during LVAD implantation: a nuclear imaging approach

In recent years, heart failure has been recognized as a major and increasing public health issue. In the context of the shortage of heart donors and increasing waiting time on the transplantation list, nonpulsatile left ventricular assist devices (LVAD) have shown their efficiency in reducing mortality and improving quality of life in patients with end-stage heart failure. Among LVAD recipients, a minority of patients will recover a normal cardiac function, allowing pump weaning. However, the evaluation of intrinsic cardiac function is particularly challenging and still a matter of debate in LVAD recipients.

Extension of myocardial necrosis differently affects MIBG retention in heart failure caused by ischaemic heart disease or by dilated cardiomyopathy

PURPOSE

This study aims to investigate the relationship between cardiac sympathetic nervous function (CSNF) and myocardial perfusion/function in patients with heart failure (HF) due to dilated cardiomyopathy (DCM) or ischaemic heart disease (CAD).

METHODS

Twenty patients (10 DCM, 10 CAD, 17 males, age 69+/-5 years) with NYHA class IIIb HF were studied. CSNF was evaluated by early/delayed (123)I-metaiodobenzylguanidine (MIBG) uptake and regional washout (WO). Myocardial perfusion and function were evaluated by (99m)Tc-tetrofosmin gated single-photon emission tomography (G-SPECT) using a 20-segment model for 400 segments. In each segment, regional MIBG WO was computed as (count density in early images-count density in delayed images/count density in early images)x100.

RESULTS

DCM and CAD showed similar summed rest perfusion score (6.7+/-5 vs 9.5+/-5, p=NS) and mean ejection fraction values (29+/-7% vs 30+/-9%, p=NS). By contrast, the summed thickening score was higher in DCM than in CAD patients (26+/-7 vs 17+/-6, p<0.05). QGS analysis identified akinesis/dyskinesis in 129/137 (94%) severely hypoperfused segments which were considered as damaged. According to the underlying aetiology of HF, marked differences in regional MIBG WO were observed. In fact, within the CAD group, regional MIBG WO was lower in reference than in damaged segments (38+/-21% vs 46+/-19%, p<0.05). By contrast, in DCM patients, regional MIBG WO was faster in reference than in damaged segments (49+/-18% vs 41+/-30%, p<0.05). When the two groups were directly compared, regional MIBG WO from damaged areas was similar irrespective of the underlying disease, while it was faster in DCM than in CAD patients from reference segments.

CONCLUSION

These data confirm the hypothesis that the presence of myocardial necrosis in HF due to CAD and the consequent loss of neuronal endings cause alterations in regional MIBG WO different from those observed in DCM.