BACKGROUNDThe presence of a cardiovascular implantable electronic device has long been a contraindication for the performance of magnetic resonance imaging (MRI). We established a prospective registry to determine the risks associated with MRI at a magnetic field strength of 1.5 tesla for patients who had a pacemaker or implantable cardioverterdefibrillator (ICD) that was "non-MRI-conditional" (i.e., not approved by the Food and Drug Administration for MRI scanning). METHODSPatients in the registry were referred for clinically indicated nonthoracic MRI at a field strength of 1.5 tesla. Devices were interrogated before and after MRI with the use of a standardized protocol and were appropriately reprogrammed before the scanning. The primary end points were death, generator or lead failure, induced arrhythmia, loss of capture, or electrical reset during the scanning. The secondary end points were changes in device settings. RESULTSMRI was performed in 1000 cases in which patients had a pacemaker and in 500 cases in which patients had an ICD. No deaths, lead failures, losses of capture, or ventricular arrhythmias occurred during MRI. One ICD generator could not be interrogated after MRI and required immediate replacement; the device had not been appropriately programmed per protocol before the MRI. We observed six cases of self-terminating atrial fibrillation or flutter and six cases of partial electrical reset. Changes in lead impedance, pacing threshold, battery voltage, and P-wave and R-wave amplitude exceeded prespecified thresholds in a small number of cases. Repeat MRI was not associated with an increase in adverse events. CONCLUSIONSIn this study, device or lead failure did not occur in any patient with a non-MRIconditional pacemaker or ICD who underwent clinically indicated nonthoracic MRI at 1.5 tesla, was appropriately screened, and had the device reprogrammed in accordance with the prespecified protocol. (Funded by St. Jude Medical and others; MagnaSafe ClinicalTrials.gov number, NCT00907361.)

The majority of SVTs in stable OHT patients can be attributed to macro-reentrant tachycardias (flutter and scar reentry). Catheter ablation is effective in management of these SVTs. Atrial fibrillation was never encountered in stable patients in our series, and its occurrence should prompt an evaluation for acute rejection and/or vasculopathy.

Background-Reducing sympathetic output to the heart from the neuraxis can protect against ventricular arrhythmias. The purpose of this study was to assess the value of thoracic epidural anesthesia (TEA) and left cardiac sympathetic denervation (LCSD) in the management of ventricular arrhythmias in patients with structural heart disease. Methods and Results-Clinical data of 14 patients (25 to 75 years old, meanϮSD of 54.2Ϯ16.6 years; 13 men) who underwent TEA, LCSD, or both to control ventricular tachycardia (VT) refractory to medical therapy and catheter ablation were reviewed. Twelve patients were in VT storm, and 2 experienced recurrent VT despite maximal medical therapy and catheter ablation procedures. The total number of therapies per patient before either procedure ranged from 5 to 202 (median of 24; 25th and 75th percentile, 5 and 56). Eight patients underwent TEA, and 9 underwent LCSD (3 patients had both procedures). No major procedural complications occurred. After initiation of TEA, 6 patients had a large (Ն80%) decrease in VT burden. After LCSD, 3 patients had no further VT, 2 had recurrent VT that either resolved within 24 hours or responded to catheter ablation, and 4 continued to have recurrent VT. Nine of 14 patients survived to hospital discharge (2 TEA alone, 3 TEA/LCSD combined, and 4 LCSD alone), 1 of the TEA alone patients underwent an urgent cardiac transplantation. Conclusions-Initiation of TEA and LCSD in patients with refractory VT was associated with a subsequent decrease in arrhythmia burden in 6 (75%) of 8 patients (68% confidence interval 51% to 91%) and 5 (56%) of 9 patients (68% confidence interval 34% to 75%), respectively. These data suggest that TEA and LCSD may be effective additions to the management of refractory ventricular arrhythmias in structural heart disease when other treatment modalities have failed or may serve as a bridge to more definitive therapy. (Circulation. 2010;121:2255-2262.)

Background It is not known if the most delayed late potentials are functionally most specific for scar-related ventricular tachycardia (VT) circuits. Methods and Results Isochronal late activation maps (ILAM) were constructed to display ventricular activation during sinus rhythm over eight isochrones. Analysis was performed at successful VT termination sites and prospectively tested. 33 patients with 47 scar-related VTs where a critical site was demonstrated by termination of VT during ablation were retrospectively analyzed. In those that underwent mapping of multiple surfaces, 90% of critical sites were on the surface that contained the latest late potential. However, only 11% of critical sites were localized to the latest isochrone (87.5–100%) of ventricular activation. The median percentage of latest activation at critical sites was 78% at a distance from the latest isochrone of 18 mm. Sites critical to reentry were harbored in regions with slow conduction velocity, where 3 isochrones were present within a 1 cm radius. 10 consecutive patients underwent ablation prospectively guided by ILAM, targeting concentric isochrones outside of the latest isochrone. Elimination of the targeted VT was achieved in 90%. Termination of VT was achieved in 6 patients at a mean ventricular activation percentage of 78%, with only 1 requiring ablation in the latest isochrone. Conclusions Late potentials identified in the latest isochrone of activation during sinus rhythm are infrequently correlated with successful ablation sites for VT. The targeting of slow conduction regions propagating into the latest zone of activation may be a novel and promising strategy for substrate modification.

The utilization of the NIOBE™ magnetic navigation system (MNS, Stereotaxis, St. Louis, MO, USA) has increased significantly since the first published report in 2002. There has been much enthusiasm for this technology as a means to reduce radiation exposure to the patient and physician alike, and potentially decrease risks associated with catheter manipulation by less experienced operators. However, there are limited data regarding the acute, intermediate, and long-term results and procedural characteristics from ablation procedures utilizing this system. We present a review of the outcomes and procedural data available to date.

Parasympathetic activation during AF ablation is associated with the presence of pre-ablation high-amplitude fractionated EGMs in sinus rhythm. Local acetylcholine release could potentially explain this phenomenon.

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The major coronary arteries lie in close proximity of the RVOT, and their anatomic course should be taken into consideration during ablation of ventricular tachycardias arising from the RV outflow tract.