We demonstrated that, in subjects with moderate and severe obesity without known cardiac disease, LAEh2 was associated with an increased risk for LA dysfunction, in contrast to LAEBSA and other traditional parameters of LV diastolic function. Furthermore, we confirmed findings of previous studies, showing that indexation of LAV to height2 resulted in a higher prevalence of LAE compared to indexation of LAV to BSA in these subjects. Considering the limitations of indexation to BSA in obesity, LAEh2 may be of added value in determining increased risk of cardiac dysfunction in patients with obesity.
LAE in obesity
Obesity is an important risk factor for developing LAE [
18], which is an essential parameter in identifying diastolic dysfunction and HFpEF [
1,
2]. In addition, both obesity and LAE are associated with an increased risk for developing atrial fibrillation (AF) [
19‐
22]. There are several mechanisms by which obesity can lead to LAE. For example, obesity can induce hemodynamic changes that can alter cardiac structures, it can cause atrial myopathy related to systemic inflammation, and promote paracrine effects from epicardial adipose tissue [
23‐
25].
Normalization of heart chamber sizes is common and necessary, as it reduces the effect of dissimilarities in patients’ proportions. Additionally, normalization allows inter- and intragroup comparisons of cardiac dimensions [
26]. Normal values enable the possibility to define normal ranges, that can be used to predict, diagnose, and monitor disease. The use of BSA as indexation method in LA scaling dates back to the 1980s [
27], and is still recommended in the current guidelines [
2]. However, indexation of LAV to BSA is inaccurate for patients with obesity [
6]. The reasons for this are several fold. First of all, indexing LAV to BSA assumes a linear relationship. However, data on the growth patterns of the human heart indicate that the growth relationship is exponential rather than linear [
26,
28,
29]. This can be overcome by choosing allometric scaling instead, as allometric scaling assumes an exponential relationship [
6]. A few previous studies have assessed different indexation methods in patients with obesity. First, Zong et al. found that allometric scaling was superior to conventional isometric indexation in a population of 717 patients with obesity with a mean BMI of 42.2 kg/m2 [
30]. Second, in a paper by Carnavelini et al., a similar conclusion was drawn in 63 patients with mild, and 26 patients with moderate obesity [
31]. Although both studies demonstrated that allometric scaling was superior to isometric scaling, potential supportive data regarding the relation of alternative indexing methods with LA function was not available.
The second concern with indexing LAV to BSA in obesity, is that cardiac size is driven by fat free mass (FFM) [
26]. In normal weight subjects, BSA is a suitable surrogate for FFM and thus a suitable scaler to index LAV [
32]. However, in patients with obesity, BSA is disproportional to FFM and therefore possibly overcorrects LAV [
6]. Height appears to be a better estimate for FFM [
6]. Our results are consistent with this notion, as can be seen in Fig.
1 where LAV indexed to height
2 was related to increasing BMI as expected, in contrast to LAV indexed to BSA. In addition, we found that indexing LAV to height
2 resulted in a higher prevalence of LAE compared to BSA. A recent study showed similar results, where as many as 55.4% of the severely obese patients were reclassified as having LAE when height
2 was used for indexation instead of BSA [
7]. Additionally, recent studies have demonstrated that indexation of LAV to height
2 has better predictive value concerning clinical outcomes in patients with obesity [
7,
8]. However, both studies did not investigate the relation between LAV
h2 and LA function.
Relation between LAVh2 and LA function in obesity
In order to investigate whether LAV
h2 may also better identify LA dysfunction in patients with obesity as compared to LAV
BSA, this study was the first to relate LAV
h2 and LAV
BSA to LA strain. Recently, LA strain has emerged as a parameter that has potential added value in identifying diastolic dysfunction. LASr and LASct are both associated with LV filling pressures [
33‐
35]. Patients with obesity with LAE
h2 had significantly lower LASct compared to patients without LAE
h2. Also, more patients with abnormal LASct were identified by LAE
h2 as compared to LAE
BSA. In addition, LAE
h2 was associated with an increased risk (OR 2.64) for an abnormal LASct, in contrast to LAE
BSA and other traditional diastolic parameters. Our novel findings underscore the notion that LAV
h2 is not only a more sensitive measure of LAE in patients with obesity, but indeed more sensitive for identification of LA dysfunction as well. As LAE and LA dysfunction are important parameters of LV diastolic dysfunction, use of LAV
h2 may improve the utility of a diastolic function qualification algorithm. However, we have not investigated that in our study. Further studies confirming improved prognostic value of LAV
h2 as compared to LAV
BSA are mandatory first.
Study limitations
This study has some limitations that should be noted. First of all, LA strain analysis requires good image quality and not all our subjects (26%) had analyzable LA images, which may have affected the identified proportion of LA dysfunction. Second, a considerable proportion of the subjects had comorbidities, such as hypertension and diabetes, that can also affect LA function. Third, our cohort mostly consisted of females which could have biased the results. Around 80% of patients who undergo bariatric surgery are female, which explains the high percentage of females in our study. Fourth, only LASct and not LASr and LAScd were different between patients with and without LAE
h2. Although most of the previous research has focused on LASr, added value of LASct has already been proven as well [
16] and is therefore also considered to be an important measure of LA function. Finally, diagnostic value of other echocardiographic parameters in subjects with moderate to severe obesity may also improve when indexed to height
2 instead of BSA. However, this fell beyond the scope of the current study.