Differential echocardiographic profiles in immunoglobulin light chain and transthyretin amyloid cardiomyopathy: insights from speckle tracking analysis

Amyloid cardiomyopathy is mainly caused by two main subtypes of amyloidosis; immunoglobulin light chains cardiomyopathy (AL-CM) and transthyretin cardiomyopathy (TTR-CM).

The aim of the present study was to elucidate the differences in echocardiographic findings between AL-CM and TTR-CM using speckle tracking echocardiography.

The study included patients with a confirmed diagnosis of cardiac amyloidosis through cardiac biopsy and who underwent transthoracic echocardiography between March 2013 and October 2022. The relative apical sparing index (RASI) was calculated using speckle tracking echocardiography: mean apical strain value/(mean basal strain value + mean mid strain value).

The final study population consisted of 50 patients with a confirmed diagnosis of cardiac amyloidosis diagnosed pathologically (AL-CM: 21 patients, TTR-CM: 29 patients). Mean age was 72 ± 11 years, 70% being male. AL-CM exhibited a lower left ventricular mass index compared to TTR-CM (124.5 ± 48.9 vs. 152.2 ± 39.2 g/m2, P = 0.001). In 35 patients available with longitudinal strain analysis, no significant difference was observed in left ventricular global longitudinal strain between the two subgroups (-9.9 ± 4.8 vs. -9.3 ± 2.4% , P = 0.63). However, RASI was significantly lower in AL-CM compared to TTR-CM as shown in Figure (0.92 ± 0.29 vs. 1.46 ± 0.53, P = 0.001). Receiver operating characteristic curve analysis shows a RASI cut-off value of <1.0 proved useful in differentiating the diagnosis of AL-CM from TTR-CM (sensitivity: 81%, specificity: 70%, AUC:0.82), and RASI <1.0 remained a significant association with the diagnosis of AL-CM, even after adjusted by conventional echocardiographic variables.

Apical sparing phenomenon was more remarkable in TTR-CM compared with AL-CM, although global longitudinal strain was comparable between the two groups. RASI was useful for the discrimination of cardiac amyloidosis subtypes.