Key points
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I-123 mIBG can be used to image adrenergic receptors in the heart using conventional planar or SPECT imaging.
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I-123 mIBG H/M measured from planar or SPECT images can provide important information on prognosis in HF patients. It is a more powerful predictor for SCD than LVEF.
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I-123 mIBG H/M measured from planar or SPECT images has been shown to be related to appropriate ICD discharges and the effect of CRT in HF patients, suggesting that mIBG imaging may aid in selection of HF patients who could benefit from ICD and/or CRT therapies.
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Viable but denervated myocardium is very sensitive to sympathetic stimulation and has been suggested to play a role in arrhythmogenesis in IHD.
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Mismatch between mIBG and SPECT perfusion imaging has been shown to be related to ventricular arrhythmias, suggesting that mIBG and MPI SPECT may aid in selection of IHD patients who could benefit from ICD therapy.
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Phase analysis has been developed and validated for measuring LV systolic dyssynchrony from gated SPECT MPI.
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Systolic dyssynchrony measured by phase analysis of gated SPECT MPI has been shown to correlate with systolic dyssynchrony measured by tissue Doppler imaging, and predicts response to CRT in HF patients.
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Phase analysis of gated SPECT MPI has been shown to assess regional activation and localize the site of latest mechanical activation.
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It has been shown that HF patients who undergo CRT with concordant LV pacing lead positioning (leads positioned at the site of latest mechanical activation as assessed by phase analysis) are more likely to have improved response to CRT than HF patients with discordant LV pacing lead positions.
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Phase analysis with multi-harmonic approximation has been shown to measure LV diastolic dyssynchrony from gated SPECT MPI. It has been shown that diastolic dyssynchrony is significantly more prevalent than systolic dyssynchrony and is related to cardiac risk factors and diastolic dysfunction in patients with ESRD and normal LVEF.
Background
Two major tools of nuclear cardiac imaging have recently been developed for assessment of patients with HF. One is I-123 mIBG that can be used to image adrenergic receptors in the heart using conventional planar or SPECT imaging. I-123 mIBG imaging produces a quantitative index, heart-to-mediastinum ratio (H/M), which can evaluate receptor density and sympathetic tone. It has been shown that an abnormal H/M is an independent and more powerful predictor than LVEF for SCD in HF patients. Furthermore, H/M has been shown to be related to appropriate ICD discharges and the effectiveness of CRT in HF patients, suggesting that mIBG imaging may aid in selection of HF patients who could benefit from ICD and/or CRT therapies. In addition, mIBG defect score and mIBG-perfusion mismatch score have been shown to relate to ventricular arrhythmias in IHD patients, further suggesting that mIBG and MPI SPECT may aid in selection of IHD patients who could benefit from ICD therapy.
Another major tool in the assessment of HF is phase analysis of gated SPECT MPI that can measure LV systolic and diastolic dyssynchrony. LV systolic dyssynchrony, measured by phase analysis of gated SPECT MPI, has been shown to correlate with that measured by tissue Doppler imaging. In addition, phase analysis has been shown to identify optimal LV pacing lead position for CRT and to predict response to CRT in HF patients. Recently, phase analysis with multi-harmonic approximation has been shown to assess LV diastolic dyssynchrony—a new LV parameter detected by MPI. In this chapter, both cutting-edge tools of nuclear cardiac imaging for assessment of HF are demonstrated using patient examples.
Case 17-1
Patients With Normal and Abnormal mIBG Uptake Measured by I-123 mIBG Planar Imaging ( Figure 17-1 )
The patient in Figure 17-1, A , is a 68-year-old man with NYHA class II, ischemic cardiomyopathy, and LVEF of 35%. The H/M by mIBG imaging was 1.69. He was under optimal medical therapy, but without ICD. He had no cardiac event during a 2-year follow-up. The patient in Figure 17-1, B , is a 51-year-old man with NYHA class II, ischemic cardiomyopathy, and LVEF of 33%. The H/M was 1.38. He was also under optimal medical therapy, but without ICD. He experienced cardiac death 8 months after the mIBG scan.
Comments
H/M measured from I-123 mIBG planar imaging has been shown to predict adverse cardiac events in HF patients with an optimal cutoff value of 1.60. The two patients had similar baseline characteristics, but one with H/M > 1.60 and the other with H/M < 1.60. The two cases demonstrate that H/M measured from I-123 mIBG planar imaging can provide independent and incremental prognostic value in HF patients over baseline characteristics, such as NYHA class, HF etiology, and LVEF.
Case 17-2
Patients With Normal and Abnormal mIBG Uptake Measured by I-123 mIBG SPECT Imaging ( Figure 17-2 )
Control subject in a multicenter trial of mIBG ( Figure 17-2, A ). This subject had normal mIBG uptake. The H/M measured by I-123 mIBG SPECT was 3.56. An HF patient in the same multicenter trial, but with an abnormal mIBG uptake ( Figure 17-2, B ). The H/M measured by I-123 mIBG SPECT was 0.93.
Comments
H/M measured from I-123 mIBG SPECT has shown to distinguish between abnormal and normal cardiac mIBG uptake. The optimal cutoff value of H/M for distinguishing normal from abnormal cardiac mIBG uptake depends on the image reconstruction method. For FBP, OSEM, and OSEM with DSP, the optimal cutoff values are 2.7, 2.6 and 4.0, respectively. The DSP H/M is larger than the FBP and OSEM H/M because DSP reduces background count level due to septal penetration, resulting in lower mediastinum VOI counts with DSP than with the other two reconstruction methods. H/M measured from I-123 mIBG SPECT, regardless of the reconstruction method used, has been shown to distinguish between normal and abnormal mIBG uptake with comparable sensitivity and specificity to the established H/M measured from I-123 mIBG planar imaging. This case demonstrates I-123 mIBG SPECT images with different mIBG uptakes in a normal subject and a HF patient and the effect of reconstruction method on the absolute values.
Case 17-3
Patients With Mismatched and Matched Defects on mIBG and MPI SPECT Images ( Figure 17-3 )
A patient with IHD who had mismatched defects when comparing images from mIBG and perfusion ( Figure 17-3, A ). This patient had a large defect on the mIBG SPECT polar map. The mIBG defect region was well perfused, as shown on the MPI SPECT polar map. A second patient with IHD who had matched mIBG and perfusion defects ( Figure 17-3, B ). This patient had a large defect at approximately the same location with approximately the same extent on both mIBG and MPI SPECT polar maps.
