This is the first report on the assessment of LAVF utilizing 4D flow MRI in individuals with CHD. We investigated the correlation between LAVF and left atrial function among postoperative patients with CHD and discovered two findings. First, compared with healthy participants, a greater number of postoperative patients with CHD exhibited a lack of LAVF. Second, patients with a loss of LAVF demonstrated lower left atrial ejection fraction, reservoir, and conduit function.

A significant number of postoperative patients with CHD had no LAVF. Suwa et al. conducted 4D flow MRI and transthoracic echocardiography in 32 participants and disclosed that patients devoid of LAVF had significantly more heart disease [3]. Although the patients in that study had heart diseases that were different from those in the present study, such as myocardial infarction, takotsubo cardiomyopathy, aortic regurgitation, and hypertensive heart disease, the results were similar in that LAVF vanished in individuals with heart disease. Although the clinical significance of LAVF remains unclear, Park et al. reported that it may serve to avert intra-atrial blood stasis [9]. Postoperative patients with CHD are more likely to develop arrhythmias, which are caused by congenital abnormalities of the conduction system, acquired hemodynamic abnormalities due to pressure and volume loading, conduction system abnormalities, and myocardial damage complicated by hypoxia, surgery, and aging [1]. A loss of LAVF may increase the risk of intra-atrial thrombus formation due to stasis of blood flow and arrhythmias, such as atrial fibrillation.

The present study observed that patients with a loss of LAVF exhibited a decline in left atrial ejection fraction, reservoir, and conduit function. Considering that LAVF typically manifests during the late phase of ventricular systole, also known as late atrial diastole, it was hypothesized that the decline in reservoir function was closely linked to the loss of vortex flow. Patients with CHD may display augmented left atrial stiffness as a result of fibrosis and remodeling due to pressure and volume loading, as well as surgical intervention [10,11,12]. Consequently, the left atrial reservoir function was reduced, and the LAVF vanished (Fig. 3) [13]. Left atrial reservoir function is an important determinant of cardiac output and is among the prognostic factors for diastolic dysfunction [14, 15]. In this current investigation, LAVF was absent in patients with a left atrial reservoir function of ≤ 25%. Nonetheless, some patients with a left atrial reservoir function of > 25% also showed a loss of LAVF, implying that the absence of LAVF may be an early sign of left atrial dysfunction. If the absence of LAVF results from left atrial remodeling, it may also serve as a valuable predictor of future arrhythmias. Therefore, patients with absent LAVF may be closely monitored for potential thrombus formation and arrhythmias.

The mechanics underlying left atrial vortex flow in patients with postoperative congenital heart disease (CHD) are demonstrated. In such individuals, surgical intervention leads to the development of fibrosis and remodeling, which subsequently results in augmented left atrial stiffness, pressure, and volume loading. It is hypothesized that this heightened stiffness diminishes left atrial reservoir function, ultimately leading to the disappearance of left atrial vortex flow

The limitations of this study are as follows. First, this was a single-center study, which restricted the number of evaluators who measured LAVF and function. Second, the sample size was significantly small. To generalize these findings, a large number of cases must be included in a large-scale prospective study. Third, there was no direct comparison between left atrial fibrosis or stiffness and vortex flow. Cardiac MRI is often inconclusive in diagnosing left atrial fibrosis while being challenging to quantify this condition. However, left atrial stiffness can be approximated using the results of cardiac catheterization, and we are considering conducting future studies.