Left Atrial Volumes and Strain: Integrating Approach in Predicting Atrial Fibrillation and Recurrence after Ablation

Atrial fibrillation (AF) is a cardiac arrhythmia that is becoming increasingly common as the population ages, with an estimated prevalence between 2 and 4% worldwide, and is considered a heart disease epidemic of the 21st century [1]. It is classified into paroxysmal AF (PAF) and persistent (persistent, long-standing persistent, permanent) according to the ACC-AHA and ESC guidelines [2, 3] by comprehensively considering symptoms, 12-lead electrocardiogram, 24 h Holter or other data available. To date, the pathogenesis of AF has not been fully elucidated and identifying its underlying causes in individual patients can be challenging. Current studies suggest that it may start with hemodynamic overload and/or atrial remodeling, which mainly includes enlargement and fibrosis of the left atrium (LA) that interferes with normal electrical conduction and causes reentry circuits. On the other hand, the presence of AF leads to LA dilation and impaired function. Mechanical LA remodeling can further damage the active contribution to ventricular filling, resulting in reduced left ventricular (LV) function [2]. LA dysfunction may also be secondary to LV systolic or diastolic dysfunction and occur even before the patient becomes symptomatic.A rhythm control strategy is based on a combination of treatment approaches including anti-arrhythmic medications, synchronized direct current cardioversion, and/or radiofrequency catheter ablation (RFCA). The success rate of RFCA is lower in persistent AF (PerAF) than in paroxysmal AF and, despite significant technological progress, a considerable number of patients (20–30%) experience recurrence [2, 3]. Significantly enlarged LA size, advancing age, long AF duration, arterial hypertension, obesity, diabetes, and high CHA2DS2-VASc score are considered major risk factors of AF recurrence in PerAF. Therefore, the decision whether or not to proceed with RFCA should be based on consideration of risk factors for AF recurrence after the procedure and, in particular, structural atrial remodeling and atrial scar load. The atrial scar can be assessed by various modalities such as cardiovascular magnetic resonance imaging (CMR) and low-voltage area on electroanatomical mapping (EAM). However, CMR complexity and limited accessibility restrict its use in clinical practice and EAM is only available at the time of ablation and is not applicable for RFCA candidate selection. A comprehensive echocardiographic study of left atrial anatomy and function (Fig. 1) may represent an effective, noninvasive and easily accessible alternative approach to assess atrial structural remodeling and predict AF or its recurrence after ablation.LA plays an integral role in cardiac performance by modulating LV filling with its reservoir, conduit and contractile functions and contributes to roughly 30% of the LV stroke volume [4, 5]. The LA maximum volume index (LAVImax) measurement represents a “snapshot” of LA function at a specific point in the cardiac cycle. Since during diastole LA is directly exposed to LV cavity pressure, events during each phase of “LA phasic function” are influenced by factors from both LA and LV. It was shown [6] that LA enlargement (defined as LAVI >36 mL/m2) and LV diastolic dysfunction are independent risk factors associated with AF recurrence after initial successful rhythm control attempt and these findings have implications for timing of either catheter ablation (pulmonary vein isolation) or cardioversion.Theoretical considerations and a growing literature suggest that LA minimum volume index (LAVImin), also known as LA end-diastolic volume index, should also be a parameter of interest [7]. The relationship between LAVImin and diastolic function appears to be more direct, as in end diastole the mitral valve is open and LA is directly exposed to LV end-diastolic pressure. Since left atrial expansion index [LAEI = (LAVImax − LAVImin)/LAVImin × 100] describes the relative LA volume increase during LA reservoir phase and represents a combination of active atrial relaxation and compliance, it is expected to be an early indicator of atrial remodeling caused by elevated LV end-diastolic pressure. A LAEI of less than 62.5% [8] was superior to LA volume and mitral E/e′ as an independent predictor of recurrent stroke of both embolic and non-embolic origin.Measurement of LA phasic volumes using two-dimensional echocardiography (2DE) is time-consuming, and errors can arise from the geometric assumptions of biplane volume calculations even using LA-focused views and from inappropriate timing of various atrial events. Real time three-dimensional echocardiography (3DE) has been introduced to overcome these limitations [9, 10] and has acceptable temporal resolution, which is not easily achieved with cardiac computed tomography. Also, 3DE-derived LA volumes showed higher correlation and less underestimation compared to CMR than 2DE measurements.Speckle-tracking echocardiography has also emerged as an excellent approach to assess biatrial remodeling which is a critical feature of AF [10‒16]. This imaging modality provides a noninvasive assessment of LA strain (Fig. 2), which is inversely related to LA wall fibrosis and AF burden. LA mechanics differ between AF subtypes of PAF and PerAF, and these characteristics affect the clinical interpretation of measures. Although differences in LA remodeling between AF subtypes remain debatable, it was shown [11] that PerAF have more fibrosis and lower midseptal and mid-lateral LA strains than PAF. The noninvasively estimated LA stiffness index, defined as the ratio between the mitral E/e′ and LA strain during the reservoir phase, has been described as a strong independent predictor of recurrence after ablation, suggesting a mechanistic link between fibrosis, reduced atrial wall compliance, and recurrent AF [12, 15]. LA mechanical dispersion (segmental strain dyssynchrony) has also been reported as a useful biomarker to estimate LA structural and electrical remodeling regardless of LA enlargement [13]. Moreover, LA reservoir and contraction strain were independent predictors of subclinical AF in elderly at risk of stroke, and this also applied to individuals with normal LA size and diastolic function [14]. LA strain was shown to assess atrial scar burden and predict the recurrence of atrial arrhythmias after RFCA or electrical cardioversion both in patients who were in sinus rhythm at the time of echocardiographic analysis than in patients being in PerAF at the time of analysis [15]. Additionally, the potential additive role of right atrial parameters was evaluated [16].In the present issue of Cardiology [17], authors have shown that assessment of LA structure and function before and after ablation in PAF patients is of great significance for guiding early clinical treatment and prognosis assessment. The novelty of their study lies in the combined use of two-dimensional speckle tracking echocardiography (2DSTE) and 3DE to provide a more comprehensive evaluation of LA structural and functional changes after RFCA. Although previous studies have focused on the value of LA strain in post-RFCA patients, their study uniquely integrates both 2D and 3D echocardiographic techniques to assess LA dimensions, volumes, ejection fraction, and strain rates at multiple time points (1, 3, and 6 months). Authors are to be congratulated for the presentation of their results. Even if these findings should be confirmed using other vendors because of the inter-vendor variability, they were able to delineate specific STE changes attributable to RFCA, thus providing new insights into the usefullness of advanced echocardiography in PAF patients.They suggest these data, despite some technical limitations, have significant clinical implications for the management and prediction of PAF. Preoperative reductions in LA strain and strain rate, especially in the basal and mid segments of LA lateral wall and interatrial septum, indicate impaired atrial reservoir, conduit, and booster pump functions, and this LA functional impairment is associated with PAF development and persistence. Early assessment of LA strain and volume can aid to select patients at higher risk for PAF and allow targeted maneuvers. Furthermore, the study emphasizes the potential benefits of monitoring LA function postoperatively. The improvement in strain parameters and LA function in patients who maintained sinus rhythm at 6 months suggests that successful restoration of rhythm may reverse some of the atrial remodeling associated with PAF. This highlights the importance of effective rhythm control strategies and follow-up assessments in the management of PAF. Although their findings need to be confirmed because they did not use long-term ECG monitoring and may not have been able to detect all asymptomatic AF episodes during follow-up, this study demonstrates that integrating a detailed assessment of left atrial function into clinical practice can improve predictive accuracy and guide treatment strategies.However, some issues deserve further comment. Recent studies suggest a relationship between high signal intensity at late gadolinium enhancement CMR and low-voltage areas at electroanatomic mapping when assessing atrial fibrosis. A correlation between speckle tracking echocardiography, LGE-CMR and extent of fibrosis has been reported [18]. In multivariable analysis, increased LGE was associated with lower LA passive emptying fraction (which represents conduit function), peak global longitudinal LA strain (which represents reservoir function), systolic strain rate, early diastolic strain rate, and late diastolic strain rate (which represent reservoir, conduit and booster pump functions). In the study already cited [17] authors did not perform LGE-CMR and, therefore, could not evaluate whether STE measurements would have a better predictive accuracy for predicting the success of RFCA than this technique. Correlative STE-CMR studies may provide additional insights into procedural outcomes and stroke risk stratification in AF patients.Also, the correlation of STE parameters with EAM should be taken into consideration. It was shown [19] that AF patients with >5% low-voltage zones (LVZs) obtained by 3D-electro-anatomical-mapping have higher recurrence rate post-ablation. LVZs ≥5% had a negative association with LA reservoir strain (reservoir function specifically and not conduit or contraction measurements). Patients with larger atrial scar tissue demonstrated LA strain <12.98% (in <0.1 mV), <16.16% (in <0.2 mV), and <19.55% (in <0.5 mV). Additional studies investigating the relationships between STE and EAM could enhance the use of STE as a noninvasive method to assess significant LA remodeling and fibrosis in AF patients.Finally, the study [17] did not utilize 3D-strain imaging (3DSTE), which could offer more detailed insights into left atrial function. 2DSTE and 3DSTE both have strengths and limitations. 2DSTE enables imaging during sinus rhythm as well as during AF and provides high accuracy and time resolution. 3DSTE allows for a comprehensive assessment of atrial deformation and may provide additional information on the spatial distribution of atrial strain, potentially improving the accuracy of atrial parameters from this perspective [20]. Incorporating 3D-strain data into future research could improve our understanding of atrial remodeling and its implications for AF prediction and management.In conclusion, 2DSTE and 3DE allow quantitative analysis of left atrial structure and function before and after RFCA in PAF patients. Patients with PAF show increased LA diameter and volume, decreased segmental and global strain, and some impairment of reservoir, conduit, and booster pump functions. After RFCA, patients have reverse left atrial remodeling and improved structure and function. Further studies that delve deeper into the topic are recommended.The author has no conflicts of interest to declare.The author did not receive any financial support.A.V. wrote the editorial.