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Since the initial description of the pivotal role of the pulmonary veins (PVs) in the initiation of atrial fibrillation (AF), significant strides have been made in the ablative treatment of AF.1 Recently, 5-year follow-up data on the outcome following PV isolation for the treatment of AF were reported.2 3 In patients with paroxysmal AF, arrhythmia recurrence was common following initial PV isolation but decreased to about 20% after a median of one (one to three) procedure.2 In a second study, success rate was lower in patients with long-standing persistent AF.3 In a systematic review, non-paroxysmal AF was an independent risk predictor for arrhythmia recurrence following first-time PV isolation.4
Several other factors have demonstrated predictive value in patients undergoing AF ablation. Left atrial (LA) size commonly serves as a surrogate marker for atrial remodelling and is easily and reproducibly measured using preprocedural echocardiography. LA diameter predicts first-time occurrence of AF as well as AF recurrence in patients undergoing catheter ablation.5 6 In a study by Berruezo et al, the presence of hypertension exerted cumulative prognostic value in addition to LA diameter in predicting recurrent AF after PV isolation.7 However, it is important to note that true LA size poorly correlates with M-mode-derived anteroposterior LA diameter.8 Assessment of LA volume is significantly more accurate, demonstrating superiority over LA diameter in predicting clinical outcome.8 9 Furthermore, since LA remodelling will affect atrial mechanical function, strain rate imaging for assessment of atrial deformation has shown to predict outcome after catheter ablation of AF.10
Structural remodelling will result in atrial fibrosis, which in turn changes the functional and tissue characteristics of the left atrium. Significant atrial interstitial fibrosis may be seen in the setting of near-normal LA size.11 Hence, detection of LA fibrosis in patients with AF may provide additional insight into prognosis and procedural outcome. In a study by Verma et al, the presence of LA scarring detected by electroanatomical bipolar voltage mapping at time of ablation served as a predictor of procedural failure.12 Recently, preprocedural delayed-enhanced magnetic resonance imaging (DE-MRI) has evolved as a new method to quantify the degree of LA fibrosis in patients with AF.13 In an observational study, the extent of atrial fibrosis visualised on DE-MRI was predictive of successful outcome after AF ablation.14 Additional studies are needed to define the exact role of DE-MRI in the assessment of atrial fibrosis and how it relates to clinical outcome, while its routine clinical use is currently limited by cost and lack of accessibility in many centres.
Integrated backscatter (IBS) analysis describes the qualitative assessment of reflected signals before postprocessing into a real-time, two-dimensional echocardiographic image. Atrial fibrosis will result in a change in signal intensity compared to normal myocardial tissue and can be measured from standard grayscale images in a parasternal view. Kubota et al demonstrated a correlation between the degree of atrial fibrosis assessed by histological examination and calibrated IBS in LA autopsy specimens. Of note, in patients with paroxysmal AF, the presence of LA fibrosis preceded the onset of atrial enlargement.11
In their paper published in Heart, den Uijl et al report on the use of calibrated IBS analysis for assessment of atrial fibrosis in 170 patients with paroxysmal or persistent AF undergoing circumferential PV isolation.15 The authors found that 39% of patients experienced recurrent AF over a 1-year follow-up period. LA volume indexed to body surface area, type of AF and LA fibrosis were predictors of AF recurrence. Importantly, LA fibrosis demonstrated incremental value over LA volume index and type of AF. Patients with a high degree of atrial fibrosis but small LA size exhibited worse outcome than patients with large LA volume index and low degree of fibrosis.
Characterising the extent of LA fibrosis in patients with AF may facilitate staging of the disease process and aid in the development of an individualised treatment strategy. However, IBS analysis has not seen ubiquitous use in the clinical setting. Its application is technically challenging, and to date, it serves mainly as a research tool.16 One criticism relates to interobserver and intraobserver variability analysing IBS recordings. In their study, den Uijl et al report excellent agreement in interpreting results. However, in comparison to a centre experienced in advanced echocardiography, calibrated IBS analysis will have to be tested in routine clinical practice in order to prove its widespread utility. Until then, one has to rely on more conventional risk predictors, while imaging techniques for the assessment of LA fibrosis in patients with AF will invariably undergo further refinement.
Competing interests None.
Provenance and peer review Commissioned; not externally peer reviewed.
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