Transthyretin Cardiac Amyloidosis and Novel Therapies to Treat This Not-so-rare Cause of Cardiomyopathy

Validation of [99mTc]Tc-HMDP SPECT/CT myocardium-to-blood ratio for the detection of ATTR cardiomyopathy

BACKGROUND

This study validates the accuracy of 99mTc-hydroxymethylene diphosphonate ([99mTc]Tc-HMDP) single-photon emission tomography/computed tomography (SPECT/CT) in the diagnosis of transthyretin amyloidosis (ATTR) cardiomyopathy using myocardium-to-blood ratio (MBR).

METHODS

The final study population was 80 patients who underwent [99mTc]Tc-HMDP SPECT/CT for suspected ATTR cardiomyopathy at Helsinki University Hospital or Jorvi Central Hospital in Finland. Patients were diagnosed according to the currently accepted European Society of Cardiology criteria as either non-ATTR (n = 48) or ATTR cardiomyopathy patients (n = 32). The left ventricular (LV) MBR was calculated by dividing LV maximal myocardial uptake with maximal left atrial uptake. Right ventricular (RV) uptake was calculated as the maximal uptake ratio on the RV-free wall and right atrium. Data are presented as mean ± standard deviation.

RESULTS

The LV MBR was higher in ATTR patients than in non-ATTR patients (4.6 ± 1.2 vs .9 ± .2, P < .001). The LV MBR of 1.5 identified ATTR cardiomyopathy with 100% accuracy. LV MBR was associated with LV wall thickness on echocardiography in univariable analysis but not with LV ejection fraction or E/e'. The RV MBR was higher in ATTR patients (2.9 ± 1.0 vs .8 ± .2, P < .001). Neither LV nor RV MBR were associated with the clinical severity of ATTR cardiomyopathy in univariable analysis.

CONCLUSIONS

LV myocardium-to-blood ratio (MBR) greater than 1.5 was 100% accurate for detecting ATTR cardiomyopathy using [99mTc]Tc-HMDP SPECT/CT. Left ventricular MBR was associated with wall thickness on echocardiography but not with the clinical severity of ATTR cardiomyopathy.

Cardiac amyloidosis: Innovations in diagnosis and treatment

Cardiac amyloidosis (CA) is a progressive, underdiagnosed condition caused by the deposition of misfolded proteins in the myocardium, forming amyloid fibrils that impair cardiac structure and function. This review highlights recent advances in the diagnosis and treatment of amyloid light-chain (AL) and transthyretin (ATTR) CA, which globally account for most cases of CA. Novel diagnostic tools, including artificial intelligence-enhanced analysis and advanced imaging modalities like positron emission tomography with amyloid-specific tracers, might improve detection rates and diagnostic accuracy to enable non-invasive subtype differentiation. Furthermore, many innovative treatments are being investigated. For AL-CA, anti-fibril therapies are showing promising results, complementing traditional chemotherapy and autologous stem cell transplantation. In ATTR-CA, gene silencing and anti-fibril therapies are being tested in clinical trials and hold promise of halting disease progression and reducing amyloid deposits, respectively.

99mTc-PYP SPECT and SPECT/CT quantitation for diagnosing cardiac transthyretin amyloidosis

BACKGROUND

We investigated quantitative 99mTc-pyrophosphate (PYP) SPECT/CT reproducibility and accuracy for diagnosing cardiac transthyretin amyloidosis (ATTR), and whether SPECT/CT improved visual and quantitative results compared to SPECT-only.

METHODS

Data were reviewed for 318 patients with suspected ATTR who underwent PYP SPECT/CT. Myocardial-to-blood pool count (MBP) ratios were computed and repeated independently > 1 month later. A physician independently scored LV myocardial-to-rib uptake on SPECT/CT as: 0 (negative), 1 < rib (equivocal), 2 = rib (positive) or 3 > rib (positive), and the image quality as: 1 (poor), 2 (adequate), and 3 (good). SPECT-only MBP ratios and visual scores were assessed separately for a subgroup of the first sequential 191 patients.

RESULTS

25% of patients had positive myocardial uptake (myocardial-to-rib uptake score of ≥ 2). SPECT/CT MBP ratios were reproducible (1.35 ± .68 vs 1.33 ± .74, p = .09) and corresponded with visual scores ≥ 2 (ROC AUC = 99 ± 1%) more accurately than SPECT-only MBPs (93 ± 3%, p = .02). SPECT/CT image quality was better than that of SPECT-only (2.7 ± .5 vs 2.1 ± .5, p < .0001) with fewer equivocal results (2.6% vs 22.5%, p < .0001).

CONCLUSION

SPECT/CT produces MBP ratios that are reproducible and accurately identify a positive scan, with better image quality and fewer equivocal cases than SPECT-only.