The main findings of our study were as follows: (1) LA booster pump function defined as PACS and reservoir function defined as total LAEF, decline immediately after AF ablation and partially recovers by 3 months post procedure; (2) impaired LA contractile function on the first day after AF ablation is an independent risk factor associated with arrhythmia recurrence at long-term follow-up.
LA function plays a critical role in overall cardiac function, impacting outcomes in patients with heart failure, hypertrophic cardiomyopathy, hypertension and AF [18–21]. Both impaired LA booster (contractile) and reservoir function have been correlated with occurrence of AF and with LA fibrosis assessed by CMR [22–24]. Previous studies have focused on the importance of preserved LA reservoir function in restoration of SR with cardioversion and maintenance of SR following catheter ablation [23, 25]. However, there has been less emphasis on LA booster function. In this study, we observed that impaired peak LA contraction strain immediately following ablation is a risk factor for long term AF recurrence, irrespective of recovery of LA contraction strain at 3 months. We did not observe that reservoir function measured by LAEF at baseline or at 1 day impacted long term maintenance of SR, but this may reflect differences in characterization of LA reservoir function by strain vs. 2D derived LAEF. Nevertheless, our findings suggest that LA contractile function may also play a significant role in occurrence of AF.
Our observation that temporary decline in LA contractile function post-ablation impacts maintenance of SR may have procedural implications as well as implications for patient selection and post ablation management, for example potentially greater value or benefit of prophylactic antiarrhythmic drug therapy and continuation of anticoagulation therapy. Although catheter ablation eliminates trigger activities and/or modifies electrophysiological substrate for AF initiation and maintenances, the procedure induces LA injury which may have longer term deleterious effects on LA structure and function [26]. First, there are direct effects from LA injury: radio-frequency energy damages the atrial myocardium, as evidenced by elevated troponin and tissue edema on imaging studies immediately post procedure, which may lead to fibrosis. Up to 30–35% of the LA wall may be replaced by scar following ablation depending on the extent of ablation and number of procedures [27]. Ablation may also affect autonomic nerve circuits involved in volume modulation of the LA, impairing LA reservoir function [28]. Second, ablation causes LA stunning in > 70% of patients, resulting in decreased contractile and reservoir function [29–32]. The decreased PACS at 1 day and LAEF in our group is consistent with impaired LA function post ablation, either through direct injury or stunning. If LA dysfunction sustained beyond 3 months as observed in some of our patients, empirically discontinuation of anticoagulant at that the end of blanking period may place the patients at risk of thromboembolism. While our cohort was too small to examine whether differences in ablation techniques (ostial PVI only or more extensive LA linear ablations) impact the severity of LA functional impairment, our findings argue for more thoughtful assessment of the impact of ablation on LA function and methods to identify patients who are most at risk of LA functional impairment and therefore AF recurrence.
Previous studies investigating LA strain for risk of AF recurrence have assessed LA strain during AFas well as during SR [33]. In patients who are in AF, impaired atrial reservoir function may have the most value in predicting AF recurrence, since booster function is absent and peak LA contraction strain can only be measured during SR [33, 34]. Our study was therefore limited to patients with PAF and those with PerAF who could be temporarily converted to SR prior to ablation. We could only include a small number of PerAF patients; those patients had larger BMI, LAVI, and more frequent heart failure, and may have had different anatomical, electrophysiological and neuroendocrine profiles as well as degrees of LA remodeling than the patients with PAF [35]. Therefore peak LA contraction strain following ablation may have different implications for patients with PerAF than PAF. Our observation supports the need for further investigation into the implications of LA booster function for AF recurrence in PerAF as well as PAF.
Our study is unique in that it is one of few studies that investigated temporal changes in LA function following catheter ablation for AF, including changes in LA booster function. While PACS and LAEF recovered in most patients, LA function remained abnormal, both in comparison to normal reference values and to baseline pre-ablation LA function even for patients remaining in SR. Whether further LA recovery or remodeling can occur beyond 3 months post ablation and affect AF recurrence risk remains to be determined [36]. In contrast with previous reports we observed that only LA strain one day after ablation, as opposed to baseline or LA strain at 3 months post ablation, is an independent predictor of AF recurrence [33]. This discrepancy reflects our longer length of follow up and our focus on LA contraction strain rather than LA longitudinal (reservoir) strain. However, our findings are complementary and suggest that both LA contractile and reservoir strain affect the risk of AF recurrence and should be measured when feasible as part of the pre and post ablation echocardiographic assessment.
Study limitations
One study limitation is the small sample size, especially of PerAF patients who presented in SR when the baseline TTE was performed. Because of the technology available at the time these patients were studied, we used a Doppler method for acquiring LA peak contraction strain. This was measured only for the LA inferior wall, due to the need to optimize the Doppler angle. The inferior wall has the highest deformation value in comparison with the septal and superior segments and has a particularly important role in LA function [37]. However, regional heterogeneity of LA strain has been reported. 2D speckle tracking method has recently become available for online assessment of global peak LA contraction strain, which will make it much easier to incorporate this measurement into clinical practice. Total LAEF was chosen as a measure of reservoir function due to limitations of Doppler based strain to assess global reservoir function. Finally, documentation of AF recurrence was not systematic and was driven by patient symptoms and detected by periodic ECG or Holter monitoring. Asymptomatic episodes of atrial arrhythmia may not have been captured, resulting in under-estimation of AF recurrence.