Left atrial eccentricity in chronic mitral regurgitation: relation to left atrial function

The Role of the Left Atrium: From Multimodality Imaging to Clinical Practice: A Review

In recent years, new interest is growing in the left atrium (LA). LA functional analysis and measurement have an essential role in cardiac function evaluation. Left atrial size and function are key elements during the noninvasive analysis of diastolic function in several heart diseases. The LA represents a “neuroendocrine organ” with high sensitivity to the nervous, endocrine, and immune systems. New insights highlight the importance of left atrial structural, contractile, and/or electrophysiological changes, introducing the concept of “atrial cardiomyopathy”, which is closely linked to underlying heart disease, arrhythmias, and conditions such as aging. The diagnostic algorithm for atrial cardiomyopathy should follow a stepwise approach, combining risk factors, clinical characteristics, and imaging. Constant advances in imaging techniques offer superb opportunities for a comprehensive evaluation of LA function, underlying specific mechanisms, and patterns of progression. In this literature review, we aim to suggest a practical, stepwise algorithm with integrative multimodality imaging and a clinical approach for LA geometry and functional analysis. This integrates diastolic flow analysis with LA remodelling by the application of traditional and new diagnostic imaging techniques in several clinical settings such as heart failure (HF), atrial fibrillation (AF), coronary artery disease (CAD), and mitral regurgitation (MR).

Left atrial remodeling in heart failure: the role of sphericity index (the SPHERICAT-HF study)

Left atrial sphericity index (LASI) is an echocardiographic index easily obtained; its use in patients with heart failure (HF) has never been investigated so far. This single-centre study aimed to investigate the usefulness of LASI in an unselected cohort of patients hospitalized for acute HF, and its potential correlation with the amino-terminal portion of pro-B-type natriuretic peptide (NT-proBNP) levels and with New York Heart Association (NYHA) functional class. Ninety-four consecutive HF patients underwent a transthoracic echocardiogram with a detailed study of the left atrium (LA) including LASI (calculated from the apical four-chamber view as the ratio between the transverse and longitudinal diameters), and blood tests (including NT-proBNP) on the same day. Median age was 75.5 (interquartile range-IQR 62-82) years and 55% were males, 58.5% had a NYHA class III-IV, and median NT-proBNP was 3284 (IQR 1215-7055) pg/ml. The LA was dilated in 94%, and median biplane LA volume index was 62 ml/m2. Patients with advanced NYHA class showed more advanced LA remodeling. Mean LASI was 0.78 ± 0.09 and did not correlate with NT-proBNP levels (r 0.03; p 0.75) or with patient NYHA class (R2 0.011; p 0.287). None of the echocardiographic indices of LA structural and functional remodeling proved to be independently associated with a high NYHA class on multivariate regression analysis. In conclusion, LA remodeling is almost invariably present in patients with HF. LASI does not correlate with NT-proBNP levels or with NYHA functional class. Further studies are needed to describe the complex patterns of atrial remodeling in HF.

Left Atrial Remodeling and Dysfunction in Swine Models of Mitral Regurgitation

BACKGROUND

Left atrial (LA) dysfunction is one of the predictive factors of worse outcomes after mitral valve surgery for mitral regurgitation (MR). We aimed to investigate the effect of MR etiology on progression of LA remodeling in swine MR models.

METHODS

MR was induced in 14 Yorkshire pigs using catheter-based procedures. Seven pigs underwent simultaneous occlusions of the left circumflex artery and the diagonal branch, which resulted in ischemic MR (IMR group). The other seven pigs underwent chordal severing to induce leaflet prolapse simulating degenerative MR (DMR group). Changes in LA volume and function were assessed at baseline, 1 and 3 months using echocardiography and hemodynamic evaluations. Histopathological assessments were conducted to evaluate LA hypertrophy and fibrosis.

RESULTS

At 3 months, quantitative MR severity was comparable and severe in both groups. Despite the similar degree of MR, minimum LA volume index increased significantly more in the IMR group (IMR: 11.9±6.4 to 73.2±6.4, DMR: 10.7±6.4 to 29.5±6.4 ml/m², p_interaction=0.004). Meanwhile, increase in maximum LA volume index was similar between the groups, resulting in lower LA emptying function in the IMR group (IMR: 60.1±3.1 to 29.4±3.1, DMR: 62.4±3.1 to 58.2±3.1%, p_interaction=0.0003). LA reservoir strain assessed by echocardiography was also significantly lower in the IMR group. Histological analyses revealed increased LA cellular hypertrophy and fibrosis in the IMR group.

CONCLUSIONS

Ischemic MR is associated with aggressive remodeling and reduced emptying function compared to MR due to leaflet prolapse. Earlier intervention might be necessary for ischemic MR to prevent LA remodeling.

Echocardiographic Measurement of Left Atrial Strain - A Key Requirement in Clinical Practice

Unlike the left ventricle (LV), the left atrium (LA) has a thin-walled structure and has been regarded as a simple conduit chamber. However, the unique function of the LA to modulate LV filling has recently drawn much attention. Because LA structure and function are directly influenced by the LV filling pressure, LA assessment is an essential step in the diagnosis of diastolic dysfunction that can help predict new-onset atrial fibrillation, assess the risk of further embolic events, and identify high-risk patients for adverse cardiovascular events. Even in the recent era of multimodality imaging, 2-dimensional (2D) echocardiography is the most common imaging method and the central modality for evaluation of LA function. LA strain derived from 2D echocardiography can help assess LA function objectively and demonstrates the 3 distinct phasic motions of the LA cycle. Further, LA strain provides invaluable pathophysiologic information and helps to predict clinical prognosis in various cardiovascular diseases. In this review article, we focus on LA strain: basic concepts, advantages over conventional parameters, and some unresolved issues. Additionally, we present a brief history of the clinical evidence for LA strain. Through this review, we suggest echocardiography for LA strain assessment in clinical practice.