Koji Higuchi

Higher Degree of Left Atrial Structural Remodeling in Patients with Atrial Fibrillation and Left Ventricular Systolic Dysfunction

Catheter ablation significantly improves the left ventricular (LV) function in patients with atrial fibrillation (AF) and LV systolic dysfunction. In this study, we compared the degree of left atrial structural remodeling (LA‐SRM) in patients with normal versus reduced LV ejection fraction (LVEF). We also studied the impact of LA‐SRM on LVEF improvement in patients undergoing ablation of AF.

Relationship between left atrial tissue structural remodelling detected using late gadolinium enhancement MRI and left ventricular hypertrophy in patients with atrial fibrillation

AIMS Therapeutic effectiveness of ablation of atrial fibrillation (AF) is related to cardiovascular comorbidities. We studied the relationship between left ventricular hypertrophy (LVH) and left atrial tissue structural remodelling (LA-SRM), in patients presenting for AF ablation. METHODS AND RESULTS We identified 404 AF patients who received a late gadolinium enhancement magnetic resonance imaging (LGE-MRI) prior to catheter ablation. Left ventricular hypertrophy was defined as LV mass index >116 g/m(2) in men and >104 g/m(2) in women. One hundred and twenty-two patients were classified as the LVH group and 282 as the non-LVH group. We stratified patients into four stages based on their degree of LA-SRM (minimal, <5% fibrosis; mild, >5-20%; moderate, >20-35%; and extensive, >35%). All patients underwent catheter ablation with pulmonary vein isolation and posterior wall and septal debulking. The procedural outcome was monitored over a 1-year follow-up period. The mean LA-SRM was significantly higher in patients with LVH (19.4 ± 13.2%) than in non-LVH patients (15.3 ± 9.8%; P< 0.01). Patients with LVH generally had extensive LA-SRM (moderate and extensive stages; 38.5% of LVH group) as compared with non-LVH patients (23.1% of non-LVH group; P < 0.01). A Cox regression analysis showed that patients with LVH also had significantly higher AF recurrence rates than non-LVH patients (43.2 vs. 28%; P = 0.008) during the 1-year follow-up period post-ablation. CONCLUSION Patients with LVH tend to have a significantly greater degree of LA-SRM, when compared with patients without LVH. Moreover, LA-SRM is a predictor for procedural success in patients undergoing AF ablation procedure.

Chronic atrial fibrillation causes left ventricular dysfunction in dogs but not goats: experience with dogs, goats, and pigs

Structural remodeling in chronic atrial fibrillation (AF) occurs over weeks to months. To study the electrophysiological, structural, and functional changes that occur in chronic AF, the selection of the best animal model is critical. AF was induced by rapid atrial pacing (50-Hz stimulation every other second) in pigs (n = 4), dogs (n = 8), and goats (n = 9). Animals underwent MRIs at baseline and 6 mo to evaluate left ventricular (LV) ejection fraction (EF). Dogs were given metoprolol (50-100 mg po bid) and digoxin (0.0625-0.125 mg po bid) to limit the ventricular response rate to <180 beats/min and to mitigate the effects of heart failure. The pacing leads in pigs became entirely encapsulated and lost the ability to excite the heart, often before the onset of sustained AF. LV EF in dogs dropped from 54 ± 11% at baseline to 33 ± 7% at 6 mo (P < 0.05), whereas LV EF in goats did not drop significantly (69 ± 8% at baseline vs. 60 ± 9% at 6 mo, P = not significant). After 6 mo of AF, fibrosis levels in dog atria and ventricles increased, whereas only atrial fibrosis levels increased in goats compared with control animals. In our experience, the pig model is not appropriate for chronic rapid atrial pacing-induced AF studies. Rate-controlled chronic AF in the dog model developed HF and LV fibrosis, whereas the goat model developed only atrial fibrosis without ventricular dysfunction and fibrosis. Both the dog and goat models are representative of segments of the patient population with chronic AF.

The effect of fat pad modification during ablation of atrial fibrillation: late gadolinium enhancement MRI analysis.

Magnetic resonance imaging (MRI) can visualize locations of both the ablation scar on the left atrium (LA) after atrial fibrillation (AF) ablation and epicardial fat pads (FPs) containing ganglionated plexi (GP).

The degree of left atrial structural remodeling impacts left ventricular ejection fraction in patients with atrial fibrillation

OBJECTIVES The extent of left atrial (LA) wall structural remodeling (fibrosis) detected by late gadolinium enhancement-magnetic resonance imaging (LGE-MRI) is correlated with advanced atrial fibrillation (AF). The concomitant occurrence of AF and left ventricular (LV) dysfunction is not uncommon. We studied the effect of LA fibrosis, a confounder of both AF and LV dysfunction, on LV ejection fraction (EF). STUDY DESIGN For the analysis, we identified and included 384 patients from our retrospective AF database who underwent LGE-MRI and transthoracic echocardiography prior to AF ablation. Based on the degree of LA fibrosis, patients were categorized into four stages as: Utah 1 (<5% LA fibrosis), Utah 2 (5-20% fibrosis), Utah 3 (20-35% fibrosis), and Utah 4 (>35% fibrosis). RESULTS The average pre-ablation LVEF was 60.5%±8.5% (n=24) in Utah stage 1 patients, 55.7%±10.3% (n=240) in Utah stage 2 patients, 51.7±11.5% (n=90) in Utah stage 3 patients, and 48.9%±11.6% (n=30) in Utah stage 4 patients (p<0.001, one-way ANOVA). The percentage of LA fibrosis was significantly negatively correlated to LVEF pre-ablation in a univariate analysis (p<0.001). In a multivariate model accounting for age, gender, AF type, and comorbidities such as diabetes and hypertension, Utah stage remained a significant predictor of pre-ablation EF (p<0.001). CONCLUSION Patients with extensive LA fibrosis appear to have depressed LV function pre-ablation, suggesting that structural remodeling in the LA may also be triggering and promoting remodeling within the ventricular myocardium.

A point-correspondence approach to describing the distribution of image features on anatomical surfaces, with application to atrial fibrillation

This paper describes a framework for summarizing and comparing the distributions of image features on anatomical shape surfaces in populations. The approach uses a point-based correspondence model to establish a mapping among surface positions and may be useful for anatomy that exhibits a relatively high degree of shape variability, such as cardiac anatomy. The approach is motivated by the MRI-based study of diseased, or fibrotic, tissue in the left atrium of atrial fibrillation (AF) patients, which has been difficult to measure quantitatively using more established image and surface registration techniques. The proposed method is to establish a set of point correspondences across a population of shape surfaces that provides a mapping from any surface to a common coordinate frame, where local features like fibrosis can be directly compared. To establish correspondence, we use a previously-described statistical optimization of particle-based shape representations. For our atrial fibrillation population, the proposed method provides evidence that more intense and widely distributed fibrosis patterns exist in patients that do not respond well to radiofrequency ablation therapy.

The importance of superior vena cava isolation in ablation strategy for atrial fibrillation.

Purpose of review Superior vena cava (SVC) is one of the most important nonpulmonary vein origins of atrial fibrillation, and SVC should be carefully treated in order to decrease the recurrence of atrial fibrillation after ablation. Despite the fact that pulmonary vein isolation (PVI) should be performed prophylactically for all pulmonary veins, prophylactic SVC isolation (SVCI) is still controversial. This review describes recent data on treatments for SVC focus during atrial fibrillation ablation. Recent findings There are two different major approaches to treat SVC focus during atrial fibrillation ablation. One is the conventional approach, in which SVCI is performed only if atrial fibrillation from SVC origin is recognized using pacing maneuvers and/or isoproterenol infusions. Another approach is performing SVCI in all cases prophylactically in addition to PVI. The rate of atrial fibrillation freedom 1 year after initial atrial fibrillation ablation by prophylactic PVI along with SVCI was almost the same as with the conventional method (85–90% atrial fibrillation freedom). In addition, the conventional method also had a good result even 5 years after ablation (73.3%). Summary Because of the good result after using the conventional approach and possible complications during SVCI, SVCI should be performed only if SVC focus is recognized, not prophylactically.

Still looking for the right mechanism as a target during ablation of atrial fibrillation.

Atrial fibrillation (AF) is the most commonly encountered cardiac arrhythmia in the clinical practice. The electrophysiological mechanisms underlying AF have been extensively investigated in the past and have revealed evidence for both focal electrical activity triggering AF1 and reentrant activity (multiple wavelet reentry) maintaining AF.2 The predominant site of focal electrical activity triggering AF is the pulmonary vein (PV).1,3 The abnormal automaticity, triggered activity, and microreentry have been proposed as the model of underlying mechanism of electrical activity in the PV. Recent studies have shown that catheter ablation is one of the most effective treatments for AF. Without doubt, pulmonary vein isolation (PVI) to isolate electrically arrhythmogenic foci located in the PVs from the LA4,5 is the cornerstone of catheter ablation for AF. Moreover, several techniques other than PVI have been proposed for AF ablation. Among alternative or additional methods to PVI, ablation targeting complex-fractionated atrial electrograms (CFAE) and ganglionated plexi (GP) would be 2 main approaches. Nademanee et al.6 first proposed in 2004 that CFAEs would represent “nests” of AF and would be ideal target sites for ablation to eliminate AF. They presumed that CFAEs correlate with areas of slow conduction zone and pivot points of small reentrant wavelets to maintain AF. They reported the unique method of AF ablation using CFAE guidance, the result of which was comparable or even superior to PVI. However, Oral et al.7 reported that ablation for AF only targeting CFAEs had modest short-term efficacy and patients required repeat procedures. Recently, some investigators demonstrated favorable effect when combining CFAEs as an adjunctive therapy with PVI.8-10 The involvement of the autonomic nervous system (ANS) in ventricular arrhythmia has been well recognized from a long time ago. For example, a study over 100 years ago by Eidenbroudt11 demonstrated that direct cervical vagus nerve stimulation increased the threshold for ventricular fibrillation (VF) induction. Schwartz et al.12 also showed the strong evidence of relationship between impaired cardiac autonomic control and lethal ventricular arrhythmias, especially VF. As