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    • br Material and methods Patients

    2019-05-18


    Material and methods Patients who underwent a first-ever RF catheter ablation procedure for AF and were evaluated by CMR pre-, up to 48h after, and 3 months post procedure were included in this adenosine receptor antagonist study. Consent for participation was obtained from each patient. Ethics approval was obtained from the Sunnybrook Health Sciences Center Research Ethics Board (Study Number: 357-2006; Initial Approval Date: September 18th 2006; Study Closure Date: October 2013).
    Results Eight patients were imaged at all three time points. The median age was 58 years (range: 48–76) and all patients were male. Six of the patients paroxysmal AF, 3 had hypertension, and none had diabetes. The LA diameter on echocardiography was 41mm (range: 34–53). All patients underwent irrigated RF ablation, and in 4 the procedure was performed with a robotic approach. The median total RF ablation time for each case was 4134s (range: 3040–4786). No patient developed PV stenosis after the procedure. Long-term freedom from recurrent atrial arrhythmia was noted in 5 of the 8 patients. Fig. 3 shows the change in the LAA diameters and area for each of the 8 patients. Compared to pre-ablation values, the respective median differences in the D1 diameter, D2 diameter, and LAA area were +1.8mm, +1.7mm, and +0.6cm2 immediately post ablation (all NS) and −2.7mm, −2.3mm, and −0.5cm2 at 3 months (all NS). Inter-patient variability in the degree and direction of change in the D1 and D2 diameters and the LAA area at the two post-ablation time points was apparent (Fig. 3). The mean absolute differences between the two radiologists for measurements of the LAA diameter (D1 or D2 at all time points) and LAA area (at all time points) were 2.4mm and 0.7cm2, respectively. Delayed enhancement was not present in any patient pre ablation but was present within the LA and pulmonary venous antrum in all patients post ablation (Fig. 4). No patient showed evidence of delayed enhancement within the LAA at any time point. Of note, 1 patient had evidence of delayed enhancement along the pulmonary venous ridge immediately post ablation, but not within the LAA itself (Fig. 4, Panel B).
    Discussion Current techniques for percutaneous endocardial LAA occlusion rely on attempting occlusion by deploying devices within the ostial region of the LAA. While differences exist between commercially available percutaneous devices, common features include their placement generally at or slightly distal to the os of the LAA and the use of stabilizing barbs that aid in anchoring the device to the adjacent tissue [19]. Therefore, it is important to obtain knowledge of any alteration of the LAA ostial size or tissue characteristics of the LAA wall during an AF ablation procedure prior to proceeding with LAA device occlusion at the time of PV isolation. The magnitude of the changes observed at all time points throughout our pilot study is probably not clinically important and is potentially related to inherent inaccuracies in measurement. Furthermore, these changes may not affect device implantation given the practice of “over-sizing,” that is, selecting a percutaneous LAA device with a diameter 10–20% larger than the largest measured LAA dimension [12,19]. However, the variability in the magnitude of change observed between patients in our pilot study coupled with the consequences of inappropriate LAA device sizing highlights the need for further study in a larger patient population. DE-MRI has been shown to identify atrial myocardium changes after ablation procedures [20–22]. Gadolinium diffuses into the extracellular space created by myocardial edema, a reversible form of myocardial injury, as well as into the intracellular space with loss of cell membrane integrity [20,23], which may correspond to varying degrees of coagulation necrosis and intra-lesional hemorrhage [24]. Owing to the inaccuracies associated with catheter localization and stability relating to the presence of cardiac and respiratory motion, RF energy may be unintentionally delivered within the region of the LAA during ablation of the anterior portion of the left PVs. The presence of acute RF tissue injury in this region may be a deterrent to the implantation of an LAA occlusion device, as edematous or necrotic tissue may lead to device instability, resulting in device embolization or LAA perforation secondary to device over-sizing or to the inadvertent positioning of a barb within friable tissue. To the best of our knowledge, our work is the first to evaluate the presence of gadolinium enhancement in the region of the LAA, and suggests that the LAA likely remains free of significant RF injury despite ablation to the adjacent left PV. While this finding may appear intuitive, it is important to confirm this intuition as one would want to be confident that the LAA is free of injury prior to the placement of an LAA occlusion device.