SPECT and PET Protocols for Imaging Myocardial Viability

Could myocardial viability be related to left ventricular dyssynchrony? Simultaneous evaluation by gated SPECT-MPI

BACKGROUND

Left ventricular contraction dyssynchrony (LVCD) has been related to induced ischemia and transmural scar but the interplay of myocardial viability and dyssynchrony is unknown. The aim of the present study was to establish the role of dyssynchrony in the context of a viability study performed with nitrate augmentation gated single photon emission computed tomography (GSPECT) myocardial perfusion imaging (MPI).

METHODS

Fifty-four consecutive patients with ischemic dilated cardiomyopathy (IDC) and depressed left ventricular ejection fraction (LVEF) were included. They underwent a two-day rest/nitroglycerine (NTG) study GSPECT MPI to determine the myocardial viability. Patients with a nitrate-induced uptake increase of > 10% vs baseline, in at least, two consecutive dysfunctional segments were considered viable as well as those who showed no improvement in the uptake but the uptake was > 50% on post NTG study. Patients with no nitrate-induced uptake increase of > 10% and the uptake of < 50% were considered non-viable. Perfusion, function and LVCD were compared in 25 viable patients vs 29 non-viable patients at baseline and after NTG administration.

RESULTS

After NTG administration, in the viable group, the LVEF increased (36.44 ± 6.64% vs 39.84 ± 6.39%) and the end-systolic volume decreased significantly (119.28 ± 31.77 mL vs 109.08 ± 33.17 mL) (P < 0.01). These patients also experienced a significant reduction in the LVCD variables: phase standard deviation was reduced in the post NTG study (57.77° ± 19.47° vs 52.02° ± 17.09°) as well as the phase histogram bandwidth (190.20° ± 78.83° vs 178.0° ± 76.14°) (P < 0.05). Functional and LVCD variables remained similar in the non-viable patients (P > 0.05).

CONCLUSION

In patients with IDC and depressed LVEF, the myocardial viability detected by rest/ NTG GSPECT MPI, might determine LVCD improvement.

Radioiodinated hypericin disulfonic acid sodium salts as a DNA-binding probe for early imaging of necrotic myocardium

Necrotic myocardium imaging can provide great indicators of salvaged myocardial areas for clinical guidances to patients with myocardial infarction (MI). One of the key challenges in necrotic myocardium imaging however, is lack of ideal necrotic imaging tracers for exactly and timely depicting the necrotic myocardium. ¹³¹I-hypericin (¹³¹I-Hyp) is a promising tracer in exact necrotic myocardium delineation. However, it can't clearly image necrotic myocardium until 9h post injection (p.i.) for the high background signals in blood and lung due to the strong lipophilicity. Herein, an optimized ¹³¹I-hypericin-2,5-disulfonic acid sodium salts (¹³¹I-Shyp) probe was synthesized for better pharmacokinetic and biodistribution properties to necrosis imaging. And the related mechanisms of necrotic avidity ability of ¹³¹I-Hyp and ¹³¹I-Shyp were also explored. In the results, ¹³¹I-Shyp still showed selectively high accumulation in both necrotic cells and tissues. Biodistribution data revealed the decreased uptake of ¹³¹I-Shyp in normal organs (lung, spleen and heart) and blood (as shown in pharmacokinetics studies). ¹³¹I-Shyp presented quicker and clearer imaging for necrotic myocardium at 4h p.i. compared with ¹³¹I-Hyp, suggesting that improved hydrophilicity of ¹³¹I-Shyp may be conducive to its better pharmacokinetic and biodistribution properties to imaging. Additionally, DNA competitive binding assays and blocking experiments indicated that E-DNA is the possible target of Shyp and Hyp for their necrosis avidity. ¹³¹I-Shyp may serve as a potential E-DNA targeted probe for necrotic myocardium imaging with molecular specificity for clinical use.