Quantitation vs visual assessment of 99mTc-DPD cardiac uptake in patients with suspected cardiac amyloidosis

Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Universitary Clinic Hospital of Valencia Aim Cardiac uptake of 99mTc-DPD has proved its diagnostic efficacy in transthyretin cardiac amyloidosis(ATTR). We compared the usual visual assessment with two quantitative methods to evaluate cardiac activity and its possible relation with clinical follow-up. Methods We have studied 37 successive patients(p):32 men, 52-90 y/o (79.6 ± 9.3), submitted by suspected cardiac amyloidosis TTR by echo/cardiac MRI. After IV administration of 21.5 ± 3.4mCi of 99mTc-DPD, we obtained early (at 5min) and late (at 3h) whole body(WB) planar images and late SPECT. We assessed cardiac uptake in planar images by visual score (0-absent, 1-cardiac uptake lower than bone uptake, 2-equal, 3- higher than bone uptake), considering 2-3 score compatible with ATTR in absence of abnormal light chains on serum-urine. We obtained quantitative evaluation by heart/contralateral thoracic activity ratio (H/CL) in late images and from early and late WB images the heart retention(HR) ratio and heart/whole body(HWB) activity ratio. Clinical follow-up (12.4 ± 8.3 months) considering as cardiac events(CE): cardiac death and heart failure(HF) admissions. Results Visual score 0(11p), 1(2p), 2(4p) and 3(20p), considering group1(0-1) not suggestive of ATTR and group2(2-3) compatible with ATTR. SPECT showed biventricular uptake with septal predominance in group2. H/CL index was 2.23 ± 0.54(group2) vs 1.05 ± 0.10(group1) p < 0.001), according to published(≥1.5 compatible with ATTR). HR and HWB ratios were also significantly higher in group2 vs group1, respectively 6 ± 3.14vs2.17 ± 0.4(p < 0.001) and 6.51 ± 1.97vs2.65 ± 0.49(p < 0.001). There were a trend to higher values in p with visual score3 than 2, not reaching statistically significant(only 4p with visual score2). There were significant correlation between H/CL-HR(r:0.66,p < 0.01), H/CL-HWB(r:0.85,p < 0.001) and HR-HWB(r:0.85,p < 0.001). After follow-up we detected 6 CE(3p with HF admission, 3p cardiac death): 5p with visual score3 and one with 2, all 6p with high mean values of H/CL: 2.28 ± 0.76, HR: 6.02 ± 3.4 and HWB:5.97 ± 1.69. Conclusion We have found excellent correlation between visual score and the evaluated methods of quantitation of 99mTc-DPD cardiac uptake in our patients referred by suspected cardiac amyloidosis. These quantitative methods could be a helpful tool to correctly identify some patients with doubtful activity and could be useful in the follow-up evaluation, although it is necessary to study a greater number of patients.