Discussion
The main findings in the current study were as follows: (a) LA strain parameters were significantly reduced in both AL-CA and HHD group; (b) Patients with AL-CA had reduced LASr and LASct compared with those with HHD, and (c) LAScd and SD-TPS were similar between AL-CA and HHD group.
In the current study, we showed lower IVS and LVPW thickness than that in previous studies9,10,19. It suggests that patients enrolled in the current study had less severe disease progression than those in previous studies. Similar to the previous study, all LA strain parameters were severely impaired in AL-CA and HHD group9. LA strain has recently emerged as a powerful assessment in evaluation of left ventricular diastolic dysfunction20.Our previous study showed that LASr was an independent predictor of elevated left ventricular end-diastolic pressure21. In the current study, higher E/e′ values correlated with decreased LASr in AL-CA group and HHD group, which suggesting a decreased diastolic function. Gan et al. demonstrated that LA remodeling reflected by larger LAVI had an incremental negative association with LASr in patients without prior cardiac disease22. In the current study, LA stain parameters negatively correlated with LAVI in patients with AL-CA and patients with HHD, which was consistent with prior study22.
Compared with those with HHD, patients with AL-CA had significantly lower LASr and LASct in the current study. Karen et al. also showed a significant reduction of LASr and LASct in patients with AL-CA compared with those with HHD 9. In AL-CA group, amyloid infiltration into the LA wall may lead to a marked functional deterioration of this thin-walled and very vulnerable structure, and that these alterations may lead to a significant decrease in LA reservoir and pump function. In the current study, higher LA strain values consisted with lower left ventricular thickness than that in previous studies9,10,19.
Notably, the difference in LAScd between AL-CA group and HHD group was not significant in the current study. Kotaro et al. also showed that conduit function of LA was not impaired in all the three aetiologies of CA10. A possible mechanism is that LA volume changes (conduit function) may be a compensatory mechanism when LA reservoir and pump function are impaired.
LA structural and functional remodeling are associated with AF23,24. Kawakami et al. showed that SD-TPS is an independent predictor of new-onset atrial fibrillation (AF) and correlated with LASr18. In order to assess LA strain parameters properly, we excluded patients with AF. Both AL-CA group and HHD group had increased SD-TPS. However, the difference was not significant between the two groups. We hypothesized that the risk of AF was no increased in the early stage of amyloid infiltration, although reservoir and pump function of LA were severely impaired.
Study limitations
There are several limitations to the current study. First, patients with AF were excluded. Typical of AF is LA remodeling. Reactive deposition of collagen fibers in the interstitium causes massive fibrosis, and an inverse relationship exists between the grade of fibrosis and LA strain25,26. As a case-control study, the duration of AF was not available. As a result, LA strain in CA patients with AF should be investigated separately. Second, a specific software for evaluating LA strain by speckle-tracking is not yet available. Therefore, we analyzed LA strain using software for evaluating the left ventricle. Third, this is a single-centered study enrolling AL-CA and HHD patients. Therefore, our findings warrant further confirmation from different centers and in different cardiac amyloidosis populations.