Impact of Tc-99m Pyrophosphate Scan on Workflow When Diagnosing Cardiac Amyloidosis

The diagnostic environment has changed significantly since the advent of technetium 99m pyrophosphate (PYP) scanning, which has improved the diagnosis of transthyretin cardiac amyloidosis (ATTR-CM) with a remarkably high rate of accuracy.

To assess the impact of this technology and identify potential areas of improvement and its impact on workflow, Mariam Saleem, MD, and colleagues from the Henry Ford Health System in Detroit, MI, conducted a single-center analysis of PYP scans, specifically looking at the impact on diagnostic workup for cardiac amyloidosis after intermediate PYP scans and to perform a quality control re-review PYP scans to identify areas of improvement.

In a retrospective study, data from 69 patients who underwent PYP scanning for the diagnosis of ATTR-CM in the previous 3 years were analyzed in an independent re-review by a Level 111 nuclear reader. The researchers identified 3 cohorts: PYP low uptake (N = 25; heart-to-contralateral [H/CL] ratio <1.2 + visual grade 1/0), PYP intermediate uptake (N = 20, H/CL ratio 1.2-1.49+ visual grade 2/3), and PYP high uptake (N = 24, H/CL ratio >1.5 + visual grade 2/3).

The researchers examined patient demographics and history, laboratory and imaging diagnostic testing, biopsy results and echo parameters. The female-to-male ratio of patients was 4:1, with African American patients representing 55% of all patients in the study. The mean age of patients in the study was approximately 73 years.

All groups were similar in terms of cardiac biomarkers (B-type natriuretic peptide and troponin), ejection fraction, and cardiovascular comorbidities. Researchers reported statistically significant differences in terms of mean interventricular septal thickness between the PYP low uptake (1.44) and the PYP high uptake (1.72) groups (P = .005). They also reported differences in mean posterior wall thickness between the groups (1.33 PYP low vs 1.58 PYP high; P = .009).

The PYP low group had no patients diagnosed with ATTR-CM, compared with 5 patients (25%) in the PYP intermediate group. A substantial majority of patients (22/24; 92%) in the PYP high group had ATTR-CM.

Diagnostic testing methods used with the PYP intermediate group included urine protein electrophoresis (70% of patients received), free light chain serum (85%), serum protein electrophoresis (95%), cardiovascular magnetic resonance imaging (35%), tissue biopsy (25%), and bone marrow biopsy (20%; all P = not significant between the PYP low and PYP high groups).

Five (25%) patients in the PYP intermediate group had a diagnosis of ATTR-CM ascertained with adjunctive testing (P = .001 compared with other groups). Re-review of the PYP scans resulted in “identification of wrong region of interest in 2 cases and reclassification to [PYP low] as no [ATTR-CM] based on blood pool misinterpretation of planar data,” the researchers wrote in their summary of these results. In total, 5 cases in the PYP low and PYP intermediate groups had their visual PYP grade changed.

This study adds to the body of evidence suggesting that PYP scanning is an accurate noninvasive test for ATTR-CM. To further improve outcomes and avoid misdiagnosis, improvements in internal quality control measures and enhanced continuing education for PYP scan readers and technologists is critically important.

Reference

Saleem M, Sadat B, Van Harn M, et al. Towards a diagnosis of cardiac amyloidosis: single center experience with Tc-99m pyrophosphate scan in the workflow. Presented at: American Society of Nuclear Cardiology 2020 Virtual Scientific Session. Abstract 308-03.

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