Non-invasive cardiac imaging in patients with systemic amyloidosis: a practical approach with emphasis on clinical contribution of bone-seeking radiotracers

Diagnosis of cardiac amyloid transthyretin (ATTR) amyloidosis by early (soft tissue) phase [99mTc]Tc-DPD whole body scan: comparison with late (bone) phase imaging

OBJECTIVES

Although expert consensus recommendations suggest 2-3 h as the time interval between bone-seeking radiotracers injection and acquisition, it has been reported that images obtained early after [^99mTc]Tc-HMDP administration are sufficient to diagnose cardiac amyloidosis. We evaluated the diagnostic performance of [^99mTc]Tc-DPD early phase whole body scan with respect to late phase imaging.

METHODS

We qualitatively and semiquantitatively reviewed [^99mTc]Tc-DPD imaging of 53 patients referred for suspect cardiac amyloidosis. Findings of early and late phase images were compared with SPECT results (considered the standard-of-reference) determining sensitivity and specificity for visual analysis of each phase imaging and for each semiquantitative index.

RESULTS

SPECT imaging was negative for cardiac accumulation in 25 patients and positive in 28. Visual analysis of early phase whole body scan had an extremely significant capability to predict SPECT results; nevertheless, complete agreement was not reached. Visual analysis of late phase imaging showed slightly better results. Semiquantitative analysis of early phase images, namely heart to mediastinum ratio, performed better than semiquantitative analysis of late phase images.

CONCLUSION

Visual analysis of [^99mTc]Tc-DPD early phase whole body scan is promising in diagnosing cardiac amyloidosis; further studies are needed to confirm our results in different clinical scenarios.

KEY POINTS

• Visual analysis of early phase planar imaging using [^99mTc]Tc-DPD is accurate to diagnose cardiac amyloidosis and may be satisfactory at least in frail patients with high cardiac burden of amyloid fibrils.

Serial scanning with 99mTc-3, 3-diphosphono-1, 2-propanodicarboxylic acid (99mTc-DPD) for early detection of cardiac amyloid deposition and prediction of clinical worsening in subjects carrying a transthyretin gene mutation

BACKGROUND

To determine the capability of 99mTc-DPD scintigraphy to detect early cardiac involvement and predict clinical worsening in transthyretin (TTR) gene mutation patients.

METHODS

Eleven mutated subjects with normal interventricular septum (IVS) thickness, NT-proBNP level and no cardiac symptoms underwent three seriate 99mTc-DPD scans (visually and semiquantitatively analyzed), and was followed-up for 5-8-years.

RESULTS

Six patients showed no myocardial accumulation in all scans. Increased IVS thickness occurring in one patient 4 years after the last scan was the only abnormal finding in these patients; no cardiac symptoms developed during the follow-up. In three patients, cardiac radiotracer uptake was found at enrollment; other laboratory/instrumental abnormal findings occurred later and cardiac symptoms developed during the follow-up period. Two patients had a negative 99mTc-DPD scan at enrollment and showed cardiac uptake in the following scans. Increased mean left-ventricular (LV) wall thickness was found 3 years after positive scintigraphy; NT-proBNP increased later in one patient. These patients developed cardiac symptoms during the follow-up period.

CONCLUSIONS

99mTc-DPD scan detects cardiac involvement in subjects with TTR gene mutation earlier than ECG, echocardiography and biochemical markers, occurring some years before the fulfillment of current diagnostic criteria for cardiac amyloidosis. A positive 99mTc-DPD scan predicts cardiac symptoms onset.