Diagnostic Utility of Relative Apical Sparing Index in Cardiac Amyloidosis Subtypes: A Comparative Study of Immunoglobulin Light Chain and Transthyretin Amyloid Cardiomyopathy

Abstract

Background

Speckles tracking echocardiography imaging enables clinicians to detect subtle systolic dysfunction. The aim of the present study was to elucidate the differences in speckle tracking echocardiographic findings between immunoglobulin light chain amyloid cardiomyopathy (AL-CM) and transthyretin amyloid cardiomyopathy (TTR-CM).

Methods

The patients with a confirmed diagnosis of cardiac amyloidosis through cardiac biopsy from March 2013 to October 2022 were included. The relative apical sparing index (RASI) was calculated using speckle tracking echocardiography by the following equation; average apical strain/(average basal strain + mid strain).

Results

The final study population consisted of 35 patients with cardiac amyloidosis (AL-CM: 10 patients, TTR-CM: 25 patients). The mean age was 74 ± 12 years. Although both subgroups had a gradual change of strain values from basal to apical segments, RASI was significantly lower in AL-CM compared to TTR-CM (0.92 ± 0.29 vs. 1.46 ± 0.53, p = 0.001). A RASI cutoff value of <1.0 proved useful in differentiating the diagnosis of AL-CM from TTR-CM (sensitivity: 81%, specificity: 70%, AUC: 0.82). A significant positive correlation with left ventricular mass index and RASI was found in AL-CM, but not in TTR-CM.

Conclusion

The apical sparing phenomenon was more remarkable in TTR-CM compared with AL-CM. RASI might be useful for the discrimination of cardiac amyloidosis subtypes. There was a difference in the relationship of RASI with left ventricular wall thickness between the cardiac amyloidosis subtypes.