Left Atrial Dysfunction in Cardiac Amyloidosis and Hypertrophic Cardiomyopathy

This study aims to explore the changes of left atrial function in patients with cardiac amyloidosis (CA) by speckle tracking echocardiography (STE) and identify the difference of left atrial properties between patients with CA and those with hypertrophic cardiomyopathy (HCM). In this study, 16 patients with CA, 16 patients with HCM, and 16 age-matched healthy controls were enrolled. The time-dependent strain parameters (LASr, LAScd, and LASdt) and strain rate parameters (m-SRs, m-SRe, and m-SRa) of left atrial function were measured by STE in patients with CA, then were compared with that in patients with HCM. Compared with the control group, CA group showed significantly reduced LVEDV/BSA, LVESV/BSA, A, and GLS of the left ventricle, and significantly increased heart rate, IVSd, IVPWd, E, E/A, E/e', LAd and LAV/BSA. The left atrial reserve (LASr and m-SRs), conduit (LAScd and m-SRe) and pump (LASdt and mSRa) functions of CA group were significantly reduced compared with that of controls (P<0.05). The left atrial reserve and pump functions of CA group were significantly reduced compared with that of HCM group. In the CA group, the left atrial reserve function (LASr and m-SRs), conduit function (LAScd and m-SRe) and pump function (LASct and m-SRa) were all related to left ventricular GLS and E/e'. The reserve function, conduit function and pump function of left atrial in the CA group decreased significantly than that in the health control group. When comparing with HCM group, CA group showed reduced reserve function and pump function of left atrial. STE is a qualified technique for the diagnosis of CA.


Introduction
Cardiac amyloidosis (CA) is a rare cardiomyopathy, characterized by the accumulation of the abnormal folded protein amyloid in cardiomyocytes and extracellular matrix [1] . The deposits of fibrillary protein can result in thickening of different sections of the heart, leading to disrupted cardiac architecture and function [2] .
CA is a substantially progressive and underdiagnosed cause of heart failure [3] . If untreated, CA is rapidly fatal, with a median survival ranging from <6 months for light chain amyloidosis [4] . Early detection and therapeutic intervention is critical for the prognosis of patients with CA.
The diagnosis of CA is challenging and mainly relies on an endomyocardial biopsy and a combination of imaging techniques [5,6] . Vague symptoms in the early disease course and the diversity of ultrasonic manifestations of CA often leads to a delay in diagnosis. Whereas, current evidence identifies higher incidence than previously thought. A recent study revealed a significantly increased prevalence rate (8 to 17 per 100 000 person-years) from 2000 to 2012 in the United States [7] , with improved amyloidosis awareness and advancements of noninvasive technologies. Specifically, as a promising new imaging modality, speckle-tracking echocardiography (STE) shows significant effect in differentiating CA from hypertrophic cardiomyopathy (HCM). It permits offline calculation of deformation parameters, such as strain and strain rate (SR). Given the various influence factors of global strain parameters, however, the potential clinical utility of STE still needs to be investigated.
In addition, previous studies mainly explored the effect of amyloid infiltration on the left ventricle [2,8] , and few studies focused on the specific changes of left atrial function in CA and the difference with HCM-induced myocardial hypertrophy. In this study, we performed a single-center, case-control imaging study to evaluate left atrial morphology and function in patients with CA, and compared findings with normal controls and patients with primary HCM. This study might provide important reference for the echocardiographic diagnosis of CA.

Subjects
From January 2018 to January 2020, 16 patients with CA and 16 patients with HCM admitted to our hospital were enrolled in this study. The diagnosis of CA was in line with the consensus recommendations for multimodality imaging in cardiac amyloidosis 2019 [9] and was confirmed by pathological biopsy or cardiac MRI. The diagnosis of HCM was in accordance with current ACCF/AHA guideline [10] . In addition, 16 gender-and age-matched healthy subjects were enrolled as a control group in the study. The exclusion criteria were as follows: systemic hypertension, ischemic heart disease or stroke, previous myocardial infarction, dilated or end-stage cardiomyopathy, severe mitral or aortic regurgitation, permanent/persistent atrial fibrillation, aortic stenosis, chronic lung disease, severe renal or liver dysfunction, and obstructive hypertrophic cardiomyopathy.
This was a single-center, case-control imaging study. All subjects underwent conventional 2D echocardiography and 2D-STE in the same examination. Clinical data of all subjects were collected at the time of examination. The study protocol was approved by local ethics review committee, and written informed consent was obtained from all subjects.

Two-dimensional echocardiography
Standard transthoracic echocardiographic examinations were performed using commercial ultrasound systems (GE vividE9 and GE vividE95, GE Medical Systems, Milwaukee, Wisconsin), equipped with a M5S two-dimensional transducer.
High-resolution ultrasound images were acquired via parasternal long axis view, parasternal short axis views at mitral valve and apical levels, and apical 4-chamber and 5-chamber views. Echocardiographic measurements of left ventricular (LV) dimensions, volumes and ejection fraction was obtained in accordance with the recommendations of the American Society of Echocardiography [11] .

Speckle-tracking echocardiography
The strain measurements were performed off-line using a dedicated software package (EchoPAC Advanced Analysis Technologies; GE Medical Systems). The echocardiographic images were obtained in 3 standard apical views (4-chamber, 3-chamber and 2-chamber) using 3 to 5 cardiac cycle. Images with good quality were acquired using a frame rate of 40-80 fps. AFI technology was employed to measure LV strain, and global longitudinal strain (GLS) was calculated as the average LV longitudinal strain using apical 2-, 3-and 4-chamber views [12] . The collected indexes included GLS and left atrial reserve function, conduit function, and pump function.
The specific parameters included left atrial peak strain (LASr) and strain rate (m-SRs), left atrial early peak strain (LAScd) and strain rate (m-SRe), and left atrial late peak strain (LASct) and strain rate (m-SRa) (Figure 1 and 2).

Statistical analysis
Continuous data are summarized as mean ± standard deviation, and categorical data as frequency (percentage). Variables were compared using Student's t test, chi-square test, Kruskal-Wallis test as appropriate. Statistical analyses were performed using SPSS version 25.0 (SPSS, Chicago, IL, USA). P<0.05 was considered statistically significant.

Results
Demographic and baseline clinical characteristics of the subjects are listed in Table 1.
There was no significant difference in age, gender and body surface area among controls, CA and HCM groups (P ＞ 0.05). Specifically, we compared the baseline characteristics of two-dimensional ultrasound between CA group and normal controls ( Table 2). Compared with normal controls, the LVEDV/BSA, LVESV/BSA, A peak, GLS, LAD and LAV/BSV of CA group were significantly lower (P<0.05). Whereas, heart rate, IVS, IVPW, E peak, E/A, and E/e' of CA group were significantly higher than those of normal controls (P<0.05). The left atrial function parameters measured by speckle-tracking echocardiography are listed in Table 3. The left atrial reserve function (LASr, m-SRs), conduit function (LAScd, m-SRe), and pump function (LASct, m-SRa) of both HCM and CA groups were significantly lower than those of normal controls (P<0.05). However, compared with HCM group, the left atrial reserve function and pump function in CA Group were significantly reduced (Table 3 and Figure 3).

Discussion
This work confirms potential value of STE in evaluating left atrial morphology and function in patients with CA, which is significant for the early detection and differential diagnosis.
For patients with CA, myocardial longitudinal systolic dysfunction may precede heart failure. This characteristic of CA can be easily detected by strain imaging. Previous studies have focused on this characteristic of CA through various strain imaging techniques, especially in left ventricular strain parameters [13,14] . STE can overcome the angle dependence of conventional strain Doppler imaging, and accurately measure the strain and strain rate of each segment and the whole heart [15,16] . Under STE examination, the left ventricular GLS in patients with CA was significantly reduced, and the longitudinal strain in the basal segment was significantly lower than that in the apical segment, which could be used to differentiate with HCM.  [17] .
Moreover, hypertension-caused left ventricular wall hypertrophy can affect the left ventricular diastolic function, and then cause the left atrial function damage. In CA, extracellular amyloid protein deposition in heart leads to mechanical damage of ventricular diastolic filling, and shows progressive diastolic dysfunction. Diastolic pressure filling disorders usually result in increased left ventricular, atrial, and pulmonary vascular pressure [17] . The left atrial function is particularly affected by the severity of left ventricular diastolic function, especially in the case of chronic increase of left ventricular filling pressure, and the left atrial function can reflect the change of left ventricular diastolic function to a great extent [18] . In normal condition, left ventricular diastolic filling mainly occurs in the early diastolic period. In patients with CA, the ventricular compliance decreased. When the diastolic function decreased, the left ventricular early suction function decreased, and the late diastolic filling mediated by the atrial assist pump function increased. Therefore, left atrial function plays an important role in the diagnosis of CA. It is showed that left atrial enlargement and dysfunction are also independent predictors of poor prognosis of CA [19] .
STE is an objective quantitative evaluation of the overall and local myocardial function technology. Its strain and strain rate are obtained by automatically measuring the distance change between any "spots" of interest selected frame by frame on the basis of two-dimensional echocardiography. It is a direct method to measure intrinsic myocardial deformation, which is relatively independent of load conditions and geometric assumptions of atrium, without angle dependence, and has high feasibility and repeatability [20] . STE can well detect the longitudinal myocardial strain and strain rate of left atrium, and effectively evaluate the local and overall myocardial function of left atrium [21,22] .
Previous studies have indicated that the left atrial function of patients with CA is damaged [17] , and this study confirmed this viewpoint. In our study, compared with normal controls, left atrial conduit function parameters (mSRe and LAScd) in the CA group were significantly reduced, which may be due to the deposition of amyloid, This indicates that the decrease of left atrial tension during systolic period, which is related to the increase of left ventricular end-diastolic pressure, the decrease of left ventricular systolic function, and the decrease of left atrial compliance [22,24] . When  [25,26] .
Kwongry et al. [27] found a relatively high incidence of late gadolinium enhancement on the left atrial wall in CA patients. Therefore, it is reasonable to consider that the infiltration of amyloid directly leads to the decrease of compliance of left atrial walls, which is also a factor of the decrease of left atrial reserve function. Thus, our results showed that the direct deposition of amyloid played an indispensable role in the atrial dysfunction of patients with CA. Modesto et al. [17] compared the left atrial function of CA patients with left ventricular enlargement and diastolic function decline, but without amyloid infiltration in the control group, and found that the left atrial systolic function was significantly reduced in the CA group. Kwong et al. [27] reported that CMR strongly suggested the characteristics of left atrial infiltration, and left atrial infiltration was closely related to the impairment of left atrial emptying function. In addition, the difference of left atrium between CA and HCM provides a new perspective for us to distinguish CA from HCM.
In this study, the correlation between left atrial function and left ventricular related function were also examined. Our results indicated that left atrial storage function, catheter function, and accessory pump function were related to the indexes of left ventricular systolic function (GLS) and left ventricular diastolic function (E/e', E, and A). That is to say, the worse the systolic and diastolic function of the left ventricle is, the more serious the left atrial dysfunction will be. The association shows that left atrial function is affected by the increase of left ventricular filling pressure.

Limitations
The major limitation of this study is that this is a single center study with small sample size, which may limit the persuasiveness of the experimental results.
Meanwhile, it is unable to propose a clear cut-off value of left atrial index between CA and HCM groups due to small sample size. In addition, the strain parameters measured by STE are limited by the differences of various machine manufacturers and analysis software, making the clinical utilization still difficult.  Availability of data and materials

Conclusions
As described in the methods section.

Competing interests
The authors declare that they have no competing interests.

Funding
Not applicable.
Contributions SC conceived and designed the experients,YW,HB give some advices on the design ; SC recruited subjects, collected clinical data ,analyze the data and wrote the manuscript.YW help to translate and polish the article.All authors read and approved the final manuscript.

Acknowledgements
The author would like to thank other colleagues whom were not listed in the authorship of The Second Hospital of Hebei Medical University for their helpful comments on the manuscript. Figure 1 Left atrial strain.

Figure 2
Left atrial strain rate.