Bipolar disorder (BD) is a severe mental illness typically characterized by multifaceted manifestations that emerge during adolescence and young adulthood (McIntyre et al., 2020). In addition to shouldering the burden imposed by mood symptoms, patients with BD are at a high risk of medical morbidity and mortality across multiple organ systems (Chen et al., 2021, Chen et al., 2022a; Crump et al., 2013; Forty et al., 2014). Congestive heart failure is a leading cause of natural death and causes excessive cardiovascular mortality in individuals with BD who are older than 50 years (Chen et al., 2020; Correll et al., 2017). Moreover, individuals with BD often exhibit cardiac dysfunction at a younger age (Chen et al., 2022b).

Multiple factors contribute to the high cardiovascular burden in individuals with BD (Goldstein et al., 2020). Specifically, psychotropic medications engender adverse cardiometabolic effects (Correll et al., 2015, Correll et al., 2017), and lifestyle (Bly et al., 2014; Jackson et al., 2015) and bipolar affective symptoms (Chen et al., 2017; Fiedorowicz et al., 2009; Kennedy et al., 2023) also raise cardiovascular risk in individuals with BD. The putative biological mechanisms linked BD and cardiovascular disease may involve systemic inflammation (Marshe et al., 2017), oxidative stress (Bøgh et al., 2022; Hatch et al., 2015), and endothelial dysfunction (Fiedorowicz et al., 2012; Schmitz et al., 2018). Although cardiac structure has a critical influence on cardiac function, few studies have evaluated factors that aggravate cardiac structural abnormalities among individuals with BD.

In cardiovascular medicine, cardiac remodeling refers to molecular, cellular, and interstitial changes in the myocardium that adversely affect cardiac geometry after heart injury (Burchfield et al., 2013). In general, cardiac remodeling leads to left ventricular (LV) hypertrophy, which is a critical determinant of disease progression to heart failure (Stewart et al., 2018). The LV mass index (LVMI) and LV relative wall thickness (RWT) are the standard indices used to classify the geometric patterns of LV hypertrophy. While LVMI describes the growth of myocardial mass in patients with LV hypertrophy, LV RWT indicates the relationship between LV wall thickness and cavity size. Kennedy et al. (2024) recently conducted magnetic resonance imaging and reported the absence of an increased LV mass in youth with BD. However, our previous study demonstrated that the LVMI was elevated in adults with BD and was associated with obesity and an increase in interleukin-8 levels (Tsai et al., 2023). Jointly, these findings suggest that the LVMI starts to increase in patients with BD during adulthood. Nevertheless, data regarding whether LV RWT increases in adults with BD are limited. The literature has provided strong evidence that increased LV RWT is a risk marker for heart failure (Lavie et al., 2014; Stewart et al., 2018). Accordingly, the present study compared LV hypertrophy indices, specifically LV RWT, between individuals with BD and age-matched and sex-matched healthy controls by using standard echocardiographic protocols recommended from the American Society of Echocardiography, and investigated risk factors associated with LV hypertrophy indices within the BD group. Furthermore, we conducted secondary analysis stratified by sex given data from UK Biobank indicating a sex-specific association between BD and cardiovascular disease (Ortiz et al., 2022). Identifying such factors may facilitate the development of strategies that are useful to alleviate heart failure in individuals with BD.