Application of cardiac magnetic resonance feature tracking (CMR-FT) for quantitative assessment of left atrial function in nonobstructive hypertrophic cardiomyopathy.

Background: Magnetic resonance imaging (MRI) is used to measure the diameter and volume of the left atrium in patients with nonobstructive hypertrophic cardiomyopathy (NOHCM). However, these morphological data cannot explain the complexity of left atrial (LA) function. The study aimed to evaluate LA function by applying cardiac magnetic resonance feature tracking (CMR-FT) for LA strain analysis in patients with NOHCM, and to examine the impact of NOHCM on LA and left ventricular (LV) structure and function.

Methods: We collected retrospectively clinical and MRI data from 58 patients with NOHCM (NOHCM group) and 30 healthy controls (HC group) and measured the LA volume index (LAVI) and overall LA functional parameters, which included myocardial reservoir parameters [total strain (εs), peak positive strain rate (SRs), and LA total ejection fraction (LATEF)], conduit parameters [passive strain (εe), peak early negative strain rate (SRe), and LA passive ejection fraction (LAPEF)], and booster pump parameters [active strain (εa), peak late negative strain rate (SRa), and LA active ejection fraction (LAAEF)]. Additionally, LV functional parameters [LV ejection fraction (LVEF), LV cardiac output (LVCO), and LV cardiac index (LVCI)] and structural parameters [LV maximal wall thickness (LVWT), LV mass (LVM), LV mass index (LVMI), LV end-diastolic volume index (LVEDVi), and LV end-systolic volume index (LVESVi)] were also measured. Statistical methods, including the two-sample -test and Mann-Whitney test, were used to compare the differences in quantitative parameters between the two groups. The diagnostic efficacy of LA parameters was assessed using receiver operating characteristic (ROC) curves. Pearson or Spearman correlation coefficients were applied to analyze the relationships between the structural and functional parameters of the left atrium and ventricle.

Results: The NOHCM group had significantly higher values of LVWT, LVM, LVMI, and LAVI compared to the HC group (P<0.05). LA functional parameters, including LATEF, LAPEF, LAAEF, εs, εe, εa, SRs, SRe, and SRa, were significantly lower in the NOHCM group than in the HC group (P<0.05). The differences in LVWT at the hypertrophied regions of the LV myocardium were statistically significant (P<0.05). In NOHCM patients with normal LA size, LATEF (53.57%±8.56% 61.20%±7.59%, P=0.001), LAPEF (22.36%±6.26% 30.80%±6.71%, P<0.001), εs (29.97%±9.57% 42.60%±10.88%, P<0.001), εe (15.48%±6.44% 25.30%±7.95%, P<0.001), SRs (1.57±0.52 2.02±0.53 s, P=0.001), and SRe [-1.48 (-1.88, -0.79) -2.08 (-2.96, -1.70) s, P<0.001] values were significantly lower compared to the HC group (P<0.05). The combined index test showed the highest diagnostic efficacy for LA impairment in NOHCM patients with normal LAVI (AUC =0.838). Strong correlations were observed between LATEF and εs (r=0.811, P<0.01), LAPEF and εe (r=0.758, P<0.01), and LAAEF and εa (r=0.827, P<0.01) across all cases.

Conclusions: The measurement of LA strain by CMR-FT is a feasible and reliable method for assessing LA function. Myocardial reservoir and conduit function of the LA decline prior to LA enlargement, and strain parameters enable early detection of LA dysfunction. The combination of LA strain parameters with ejection fraction provides added value in diagnosing LA dysfunction. LA ejection fraction (LAEF) across all phases of the LA cycle shows a strong correlation with strain parameters.