Left atrial size as a predictor of successful radiofrequency catheter ablation for atrial fibrillation

Radiofrequency catheter ablation (RFCA) is a curative treatment option for patients with atrial fibrillation (AF). However, this treatment modality is associated with a considerable recurrence rate and a small risk for serious complications. 1 To improve the success rate and to avoid unnecessary procedure-related risks in patients with a high likelihood of AF recurrence, proper patient selection is mandatory. According to the Heart Rhythm Society/European Heart Rhythm Association/European Cardiac Arrhythmia Society expert consensus statement, considerations in the selection of patient for AF ablation should include: severity of symptoms, age, duration of AF, and left atrial (LA) diameter. 2 However, as an alternative to LA diameter, a more comprehensive evaluation of the ‘true’ LA size may improve the identification of patients with a high likelihood of maintaining sinus rhythm after RFCA. Abecasis et al.3 prospectively investigated the use of LA volume assessed by multi-slice computed tomography (MSCT) as a predictor of successful ablation for AF. Ninety-nine consecutive patients undergoing circumferential pulmonary vein ablation were studied. A pre-procedural MSCT examination was performed in all patients and LA volume was measured using semi-automatic software to detect the endocardial borders. The authors demonstrated that an increase in the LA volume on MSCT was related to increased risk for AF recurrence after RFCA. Using ROC curve analysis, a cut-off value of 145 mL for LA volume was identified to provide the best predictive value for recurrent AF after RFCA. LA enlargement is considered an important risk factor for AF. In the Framingham Heart Study, LA enlargement was found to be an independent predictor of new onset AF in the general population. 4 Moreover, LA enlargement has been identified as a risk factor for AF recurrence after RFCA. In a group of 148 patients, Berruezo et al.5 demonstrated that the anterior–posterior LA diameter was an independent predictor of AF recurrence after RFCA. This finding was confirmed by Shin et al.6 who demonstrated the predictive value of LA volume for AF recurrence after RFCA in a group of 68 patients. Significantly dilated atria are generally thought to be associated with a high degree of atrial remodelling which limits the efficacy of RFCA. As a consequence, many clinical trials on RFCA for AF have restricted their enrolment to patients with an LA anterior–posterior diameter of <50–55 mm. However, when using LA enlargement as a patient selection criterion, it should be noted that the LA anterior–posterior diameter is not the most accurate representation of the ‘true’ LA size. 7 Owing to constraints of the thoracic cavity, LA enlargement is often asymmetric and oriented predominantly in superior–inferior and medial–lateral direction. Therefore, the application of the anterior–posterior diameter to select patients eligible for RFCA may be limited. This was demonstrated by Abecasis et al. who showed that LA volume on MSCT was related to the outcome of RFCA, whereas the LA anterior–posterior diameter on transthoracic echocardiography was not. 3 The most likely explanation for this finding is that three-dimensional imaging modalities like MSCT provide a more accurate estimation of the ‘true’ LA size than two-dimensional echocardiography and therefore have a higher prognostic value for the outcome after RFCA. 7 Accordingly, a similar prognostic value is expected when using other three-dimensional imaging modalities to assess the LA size such as three-dimensional echocardiography. Importantly, MSCT is associated with a considerable amount of radiation exposure which limits its applicability as a patient selection tool. Alternatively, three-dimensional echocardiography allows the accurate assessment of cardiac volumes without radiation exposure and can also be used to monitor functional improvement or reverse remodelling of the atria after RFCA. 8 , 9 In contrast to MSCT, three-dimensional echocardiography does not provide information about the pulmonary vein anatomy, which is essential for safety of RFCA. Magnetic resonance imaging provides information about the pulmonary vein anatomy and allows the accurate assessment of LA volume without radiation exposure. 10 However, the use of magnetic resonance imaging is limited by its limited availability and high costs. In conclusion, as demonstrated by Abecasis et al. , 3 accurate assessment of LA volume using a three-dimensional imaging modality is essential for improvement of patient selection for RFCA of AF. Three-dimensional imaging provides a more accurate representation of the ‘true’ LA size than two-dimensional imaging and has a higher prognostic value for outcome after RFCA. The available three-dimensional imaging modalities include MSCT, magnetic resonance imaging, and three-dimensional echocardiography. Importantly, each of these imaging modalities has its own advantages and limitations. Nevertheless, all can be used to accurately assess LA size, which may significantly improve prediction of successful RFCA for AF. Conflict of interest: J.J.B. receives research grants from General Electric Healthcare, Bristol-Myers Squibb medical imaging, St Jude, Medtronic, Boston Scientific, Biotronik, and Edwards Lifesciences.