Valoración anatómica y eléctrica del sustrato de la fibrilación auricular persistente

Resumen

Background: atrial fibrosis is the anatomical substrate largely responsible for the genesis and maintenance of atrial fibrillation (AF), especially in persistent AF. In addition, its presence and extent influences the efficacy of current AF ablation procedures. One of the subrogate markers of fibrosis is atrial low-voltage areas (LVA) determined by electroanatomical mapping. We studied fibrosis from different points of view. We hypothesized that LVA extent varied according to the heart rhythm at which electroanatomic mapping was performed and that fibrosis identified by magnetic resonance imaging (MRI) could correspond to LVA on electroanatomic maps. To perform this study, we divided the research into three different sections. 1. In the first section, we worked on the assessment of the extension and location of LVA by electroanatomical mapping in patients with persistent AF undergoing pulmonary vein isolation, comparing the results of the sinus rhythm (SR) maps and the AF maps in each patient. 2. In the second section, we worked on the study of fibrosis distribution in the left atrium in patients with persistent AF by cardio-MRI and the anatomical correlation between the areas of fibrosis on the MRI and the LVA on the electroanatomical mapping. 3. In the third and final section, a more functional approach was proposed, focusing on the secondary objectives of the study and trying to locate the possible sources of the arrhythmia using a surface vest. We tried to verify whether these electrophysiological sources had or not an anatomical relationship with the LVA. Methods: prospective single-center study which included patients with persistent AF undergoing pulmonary vein isolation. 1) Comparison of maps in SR and AF: We recorded bipolar signals, first in AF and later in sinus rhythm (SR). Two thresholds delimited low-voltage areas (LVA): 0.5 and 0.3 mV. We compared LVA extension between maps in SR and AF in each patient. 2) MRI Fibrosis and LVA: MRI and atrial fibrosis identification were performed prior to ablation. Subsequently, we compared the fibrosis location by MRI to LVA <0.5 mV in the electroanatomical maps. 3) Rotors and LVA: we used a vest with 252 surface electrodes to obtain the rotors. Five bipolar intracavitary electrograms (EGMs) were recorded. The EGMs were rectified and subsequently filtered The largest peak of the spectrum was identified and defined as the dominant frequency (DF). To measure the periodicity and organization of the signals, the regularity (RI) and organization (OI) indexes were implemented. The rotors location was qualitatively compared with the LVA (<0.5 mV) location of the electroanatomical maps. We performed first conventional ablation and subsequently rotors ablation. Results: 1) Comparison of maps in SR and AF: A total of 23 patients were included in the study, mean age 59.2 years, 74% male . LVA were significantly larger in maps in AF (0.5 mV threshold, mean area in AF 41.3 ± 42.5 cm2 vs. 11.7 ± 17.9 cm2 in SR, p < 0.001; 0.3 mV threshold, mean area in AF 15.6 ± 22.1 cm2 vs. 6.2 ± 11.5 cm2 in SR, p < 0.001). 2) MRI fibrosis and LVA: 7 patients were included, mean age 54.6 years, 100% male. In 6 of the 7 patients (85.7% of the included patients) an area compatible with fibrosis was identified on MRI. Of these 6 patients, only 3 presented LVA in the SR maps, of which two included the areas identified as fibrosis in the MRI, while in the third case, the area of fibrosis and the LVA differed in its location. The only patient without fibrosis on MRI did not present LVA. Therefore, overall, in 3 of the 7 patients (42.8% of the patients included), there was adequate correspondence in the fibrosis location and LVA location in the SR maps. Because of the small sample size and the variability of the results, we were unable to verify that the fibrosis location by MRI and LVA coincided. 3) Rotors and LVA: 8 patients (75% men), mean age 63 years, were included. Although only 12.5% of patients returned to SR during ablation, a decrease in DF and an increase in both OI and RI were observed in 6 of 8 patients (75%) between baseline and the end of the ablation. Out of a total of 42 rotors, 85.7% were located in areas corresponding to LVA. Conclusions 1) Significant differences can be seen in the areas that could be considered fibrosis in the maps in AF and in SR. AF maps could overestimate fibrosis or SR maps could underestimate it. The voltage that defines fibrosis could be different depending on whether the map is performed in AF or SR. 2) Rotors largely correspond to LVA. Despite the fact that most patients required cardioversion to return to SR, we saw an improvement (reduction) in DF and EGMs with higher rates of regularity and organization after ablation.