Atrial fibrillation (AF) is the most common cardiac arrythmia encountered in clinical practice. It is estimated that greater than 2.2 million people in the United States are affected by AF with a prevalence reaching 0.4–1% of the general population.  AF also remains a major cause for cardiovascular morbidity and mortality. AF is treated traditionally by rate control or rhythm control strategy with pharmacologic agents. More recently radiofrequency catheter ablation (RFCA) has been offered as an alternative or in conjunction with medical therapy in patients either with refractory AF or with intolerance to antiarrhythmic medications. AF ablation success has been reported between 68% and 86% at 1 year. There have been a variety of factors that have been implicated in ablation success ranging from clinical and historical patient data to anatomic features. Left atrial (LA) size has been closely linked with success of RFCA. The most common measure of LA size has been LA diameter (LAD) measured in a linear dimension by transthoracic echocardiography (TTE). The purpose of this study was to assess the predictive capability of LA diameter (LAD) and LA volume (LAV) by echocardiography and computed tomography (CT) to determine success in patients undergoing RFCA of AF.

483 consecutive patients with recurrent paroxysmal or persistent AF who underwent RFCA of AF were screened. Of this initial population, 88 patients (age 30-78 years, 65 males) met criteria of having a TTE, TEE, and CT measuring the LAV and these patients were subsequently analyzed. TTE LADs and LV ejection fraction as well as TEE LADs and LAVs in three views were recorded. CT LAVs were also recorded. Clinical parameters prior to ablation as well as at 1-year follow-up were assessed.

A total of 40 (45%) patients with paroxysmal AF and 48 (55%) patients with persistent AF were analyzed. Paroxysmal AF patients had a RFCA success rate of 88% at 1 year with persistent AF patients having a 52% success rate (P < 0.001).  A CT-derived LAV ≥ 117 cc was associated with an odds ratio (OR) for recurrence of 4.8 (95% confidence interval [CI] = [1.4–16.4], P = 0.01) while a LAV ≥130 cc was associated with an OR for recurrence of 22.0 (95% CI = [2.5–191.0], P = 0.005) after adjustment for persistent AF. The study also tested the difference between the most commonly used parameter of LA size, the LAD obtained from the parasternal window by TTE, and LAV measured by CT. The correlation between the two parameters was poor (r = 0.55). The correlation increased markedly when LAD was measured using TEE (r = 0.75).

This study is the first to evaluate LA dimensions by multiple modalities in patients undergoing AF ablation. LAD by TEE had an incremental benefit over LAD by TTE (P = 0.053). LAV by CT had a significant benefit over traditional TTE LAD (P = 0.015).

The study has some limitations. It is a single center study. The TEE and CT measurements were performed at a single institution and reanalyzed by the authors, the TTE LAD measurements were obtained from the initial referral echocardiogram performed by the patient's primary cardiologist.  Therefore interobserver variability could be there. The search for AF in follow-up included ECGs at every 3-month visit along with Holter/Event monitoring for any patient with symptoms. It is possible that certain asymptomatic patients with short paroxysms of AF post ablation were missed.

In conclusion, LA dimensions and AF type are highly predictive of AF recurrence following RFCA. LAV by CT has significant predictive benefit over standard LADs in severely enlarged atria even after adjustment for AF type.


Reference:

Parikh SS, Jons C, McNitt S, Daubert JP, Schwarz KQ, Hall B. Predictive capability of left atrial size measured by CT, TEE, and TTE for recurrence of atrial fibrillation following radiofrequency catheter ablation. Pacing Clin Electrophysiol. 2010 May;33(5):532-40.