Kristina Lemola

Computed Tomographic Analysis of the Anatomy of the Left Atrium and the Esophagus. Implications for Left Atrial Catheter Ablation

Background—During left atrial (LA) catheter ablation, an atrioesophageal fistula can develop as a result of thermal injury of the esophagus during ablation along the posterior LA. No in vivo studies have examined the relationship of the esophagus to the LA. The purpose of this study was to describe the topographic anatomy of the esophagus and the posterior LA by use of CT. Methods and Results—A helical CT scan of the chest with 3D reconstruction was performed in 50 patients (mean age, 54±11 years) with atrial fibrillation before an ablation procedure. Consecutive axial and sagittal sections of the CT scan were examined to determine the relationship, size, and thickness of the tissue layers between the LA and the esophagus. The mean length and width of the esophagus in contact with the posterior LA were 58±14 and 13±6 mm, respectively. The esophagus had a variable course along the posterior LA. The esophagus was close (10±6 mm from the ostia) and parallel to the left-sided pulmonary veins (PVs) in 56% of patients and had an oblique course from the left superior PV to the right inferior PV in 36% of patients. The mean thicknesses of the posterior LA and anterior esophageal walls were 2.2±0.9 and 3.6±1.7 mm, respectively. In 98% of patients, there was a fat layer between the esophagus and the posterior LA. However, this layer was often discontinuous. Conclusions—The esophagus and posterior LA wall are in close contact over a large area that may often lie within the atrial fibrillation ablation zone, and there is marked variation in the anatomic relationship of the esophagus and the posterior LA. Both the esophageal and atrial walls are quite thin. However, a layer of adipose tissue may serve to insulate the esophagus from thermal injury, explaining why atrioesophageal fistulas are rare.

Noninducibility of Atrial Fibrillation as an End Point of Left Atrial Circumferential Ablation for Paroxysmal Atrial Fibrillation A Randomized Study

Background—An anatomic approach of left atrial radiofrequency circumferential ablation (LACA) to encircle the pulmonary veins is often effective in eliminating paroxysmal atrial fibrillation (AF). However, no electrophysiological end points other than voltage abatement and/or conduction slowing or block across ablation lines have been used. It has been unclear whether noninducibility of AF is a clinically useful end point. Methods and Results—In 100 patients with paroxysmal AF (mean age, 55±10 years), LACA to encircle the left- and right-sided pulmonary veins was performed during AF, with additional ablation lines in the posterior left atrium and mitral isthmus, with an 8-mm-tip catheter. After completion of this lesion set, sinus rhythm was present, and AF lasting >60 seconds was not inducible in 40 patients (40%; group 1). The 60 patients in whom AF was still present or who still had inducible AF were randomly assigned to no further ablation (group 2; 30 patients) or to additional ablation lines along the left atrial septum, roof, and/or anterior wall where there were fractionated electrograms (group 3; 30 patients). In group 3, AF was rendered noninducible in 27 of 30 patients (90%). At a 6-month follow-up, 67% of patients in group 2 were free of AF without drug therapy compared with 86% of patients in group 3. (P=0.05, log-rank test). Left atrial flutter occurred in 17% and 27% of patients in each group, respectively (P=0.3). Conclusions—After LACA in patients with paroxysmal AF, AF usually can be rendered noninducible by additional ablation at sites of fractionated electrograms. Noninducibility of AF attained by additional electrogram-guided left atrial ablation may be associated with a better midterm clinical outcome than when AF is still inducible after LACA alone.

A Tailored Approach to Catheter Ablation of Paroxysmal Atrial Fibrillation

Background— Because the genesis of atrial fibrillation (AF) is multifactorial and variable, an ablation strategy that involves pulmonary vein isolation and/or a particular set of ablation lines may not be equally effective or efficient in all patients with AF. A tailored strategy that targets initiators and drivers of AF is a possible alternative to a standardized lesion set. Methods and Results— Catheter ablation was performed in 153 consecutive patients (mean age, 56±11 years) with symptomatic paroxysmal AF with the use of an 8-mm tip radiofrequency ablation catheter. The esophagus was visualized with barium. The pulmonary veins and left atrium were mapped during spontaneous or induced AF. Arrhythmogenic pulmonary veins were isolated or encircled. If AF was still present or inducible, complex electrograms in the left atrium, coronary sinus, and superior vena cava were targeted for ablation. The end point of ablation was absence of frequent atrial ectopy and spontaneous AF during isoproterenol infusion and noninducibility of AF. Routine energy applications near the esophagus were avoided. During follow-up, left atrial flutter developed in 19% of patients and was still present in 10% at >12 weeks of follow-up. A repeat ablation procedure was performed in 18% of patients. During a mean follow-up of 11±4 months, 77% of patients were free from AF and/or atrial flutter without antiarrhythmic drug therapy. Pericardial tamponade or transient neurological events occurred in 2% of procedures. Conclusions— A tailored ablation strategy that only targets triggers and drivers of AF is feasible and eliminates paroxysmal AF in ≈80% of patients.

Pulmonary Vein Region Ablation in Experimental Vagal Atrial Fibrillation Role of Pulmonary Veins Versus Autonomic Ganglia

Background— Pulmonary vein (PV) –encircling radiofrequency ablation frequently is effective in vagal atrial fibrillation (AF), and there is evidence that PVs may be particularly prone to cholinergically induced arrhythmia mechanisms. However, PV ablation procedures also can affect intracardiac autonomic ganglia. The present study examined the relative role of PVs versus peri-PV autonomic ganglia in an experimental vagal AF model. Methods and Results— Cholinergic AF was studied under carbachol infusion in coronary perfused canine left atrial PV preparations in vitro and with cervical vagal stimulation in vivo. Carbachol caused dose-dependent AF promotion in vitro, which was not affected by excision of all PVs. Sustained AF could be induced easily in all dogs during vagal nerve stimulation in vivo both before and after isolation of all PVs with encircling lesions created by a bipolar radiofrequency ablation clamp device. PV elimination had no effect on atrial effective refractory period or its responses to cholinergic stimulation. Autonomic ganglia were identified by bradycardic and/or tachycardic responses to high-frequency subthreshold local stimulation. Ablation of the autonomic ganglia overlying all PV ostia suppressed the effective refractory period–abbreviating and AF-promoting effects of cervical vagal stimulation, whereas ablation of only left- or right-sided PV ostial ganglia failed to suppress AF. Dominant-frequency analysis suggested that the success of ablation in suppressing vagal AF depended on the elimination of high-frequency driver regions. Conclusions— Intact PVs are not needed for maintenance of experimental cholinergic AF. Ablation of the autonomic ganglia at the base of the PVs suppresses vagal responses and may contribute to the effectiveness of PV-directed ablation procedures in vagal AF.

Detection of Inadvertent Catheter Movement into a Pulmonary Vein During Radiofrequency Catheter Ablation by Real-Time Impedance Monitoring

Introduction: During radiofrequency ablation to encircle or isolate the pulmonary veins (PVs), applications of radiofrequency energy within a PV may result in stenosis. The aim of this study was to determine whether monitoring of real‐time impedance facilitates detection of inadvertent catheter movement into a PV.

Effects of eliminating complex electrograms by radiofrequency catheter ablation on spectral characteristics of atrial fibrillation

SESSION 32: CATHETER ABLATION V: New Techniques and Approaches Friday, May 6, 2005 10:45 a.m.–12:15 p.m.

1052-221 Accurate identification of pulmonary vein ostia with real-time impedance measurements

Ca rd ia c Ar rh yt hm ia s PAF episodes were divided into group A (“sudden onset”) and group B (“PAC activity before onset”). The mean PAF episode durations of both groups were then compared. Sudden PAF onset was defined as missing PAC activity in the last 10 beats before PAF initiation. Results: Group A comprised 145 (54.9 %) PAF episodes. A significantly longer mean PAF episode duration was found in group A as compared to group B (6.06 ± 42.36 vs. 1.85 ± 6.72 hours, p < 0.01). Conclusion: 1. In our study group more than half of the PAF episodes were initiated without any PAC activity in the last 10 beats before onset. 2. Arrhythmia episodes with sudden PAF onset were associated with a prolonged PAF episode duration as compared to PAF episodes with prevalent pre-onset PAC activity. 3. The combination of missing PAC activity and long PAF episode duration may reflect a higher atrial “substrate factor” facilitating PAF induction and maintenance. The efficacy of preventive pacing algorithms might therefore be limited in patients with predominantly sudden onset of PAF.

Pulseless atrial fibrillation: a medical mystery?

A 65-year-old man presented to the emergency room with shortness of breath that started 3 hours earlier. He was referred from another clinic with the ECG diagnosis of atrial fibrillation with a slow ventricular response. Shortly after presentation, the patient showed signs of worsening heart failure. The patient had a history of mechanical aortic valve prosthesis and subpectoral implantation of a transvenous biventricular pacemaker system. A DeBakey left ventricular assist device (LVAD) was implanted 7 weeks ago due to end-stage heart failure with severely decreased left ventricular systolic function. The patient remained conscious, but his pulse and blood pressure were not measurable; oxygen saturation was 96%.