Nassir F. Marrouche

Detection and quantification of left atrial structural remodeling with delayed-enhancement magnetic resonance imaging in patients with atrial fibrillation.

Background— Atrial fibrillation (AF) is associated with diffuse left atrial fibrosis and a reduction in endocardial voltage. These changes are indicators of AF severity and appear to be predictors of treatment outcome. In this study, we report the utility of delayed-enhancement magnetic resonance imaging (DE-MRI) in detecting abnormal atrial tissue before radiofrequency ablation and in predicting procedural outcome. Methods and Results— Eighty-one patients presenting for pulmonary vein antrum isolation for treatment of AF underwent 3-dimensional DE-MRI of the left atrium before the ablation. Six healthy volunteers also were scanned. DE-MRI images were manually segmented to isolate the left atrium, and custom software was implemented to quantify the spatial extent of delayed enhancement, which was then compared with the regions of low voltage from electroanatomic maps from the pulmonary vein antrum isolation procedure. Patients were assessed for AF recurrence at least 6 months after pulmonary vein antrum isolation, with an average follow-up of 9.6±3.7 months (range, 6 to 19 months). On the basis of the extent of preablation enhancement, 43 patients were classified as having minimal enhancement (average enhancement, 8.0±4.2%), 30 as having moderate enhancement (21.3±5.8%), and 8 as having extensive enhancement (50.1±15.4%). The rate of AF recurrence was 6 patients (14.0%) with minimal enhancement, 13 (43.3%) with moderate enhancement, and 6 (75%) with extensive enhancement (P<0.001). Conclusions— DE-MRI provides a noninvasive means of assessing left atrial myocardial tissue in patients suffering from AF and might provide insight into the progress of the disease. Preablation DE-MRI holds promise for predicting responders to AF ablation and may provide a metric of overall disease progression.

Phased-array intracardiac echocardiography monitoring during pulmonary vein isolation in patients with atrial fibrillation: impact on outcome and complications.

Background—The objective of this study was to assess the impact of intracardiac echocardiography (ICE) on the long-term success and complications in patients undergoing pulmonary vein isolation (PVI) for treatment of atrial fibrillation (AF). Methods and Results—Three hundred fifteen patients underwent PVI for treatment of AF. Each patient underwent ostial isolation of all PVs using a cooled-tip ablation catheter. PVI was performed using circular mapping (CM) alone (group 1, 56 patients), CM and ICE (group 2, 107 patients), and CM and ICE with titration of radiofrequency energy based on visualization of microbubbles by ICE (group 3, 152 patients). After a mean follow-up time of 417±145 days, 19.6% (11 of 56), 16.8% (18 of 107), and 9.8% (15 of 152) of patients in groups 1, 2, and 3 experienced recurrence of AF, respectively. Moreover, whereas no group 3 patient experienced severe (>70%) PV stenosis, severe PV stenosis was documented in 3 (3.5%) of 56 patients in group 1 and in 2 (1.8%) of 107 patients in group 2 (P <0.05). No embolic events were detected in group 3 patients. Conclusions—Intracardiac echocardiography improves the outcome of cooled-tip PVI. Power adjustment guided by direct visualization of microbubble formation reduces the risk of PV stenosis and improves long-term cure.

Association of Atrial Tissue Fibrosis Identified by Delayed Enhancement MRI and Atrial Fibrillation Catheter Ablation: The DECAAF Study

IMPORTANCE Left atrial fibrosis is prominent in patients with atrial fibrillation (AF). Extensive atrial tissue fibrosis identified by delayed enhancement magnetic resonance imaging (MRI) has been associated with poor outcomes of AF catheter ablation. OBJECTIVE To characterize the feasibility of atrial tissue fibrosis estimation by delayed enhancement MRI and its association with subsequent AF ablation outcome. DESIGN, SETTING, AND PARTICIPANTS Multicenter, prospective, observational cohort study of patients diagnosed with paroxysmal and persistent AF (undergoing their first catheter ablation) conducted between August 2010 and August 2011 at 15 centers in the United States, Europe, and Australia. Delayed enhancement MRI images were obtained up to 30 days before ablation. MAIN OUTCOMES AND MEASURES Fibrosis quantification was performed at a core laboratory blinded to the participating center, ablation approach, and procedure outcome. Fibrosis blinded to the treating physicians was categorized as stage 1 (<10% of the atrial wall), 2 (≥10%-<20%), 3 (≥20%-<30%), and 4 (≥30%). Patients were followed up for recurrent arrhythmia per current guidelines using electrocardiography or ambulatory monitor recording and results were analyzed at a core laboratory. Cumulative incidence of recurrence was estimated by stage at days 325 and 475 after a 90-day blanking period (standard time allowed for arrhythmias related to ablation-induced inflammation to subside) and the risk of recurrence was estimated (adjusting for 10 demographic and clinical covariates). RESULTS Atrial tissue fibrosis estimation by delayed enhancement MRI was successfully quantified in 272 of 329 enrolled patients (57 patients [17%] were excluded due to poor MRI quality). There were 260 patients who were followed up after the blanking period (mean [SD] age of 59.1 [10.7] years, 31.5% female, 64.6% with paroxysmal AF). For recurrent arrhythmia, the unadjusted overall hazard ratio per 1% increase in left atrial fibrosis was 1.06 (95% CI, 1.03-1.08; P < .001). Estimated unadjusted cumulative incidence of recurrent arrhythmia by day 325 for stage 1 fibrosis was 15.3% (95% CI, 7.6%-29.6%); stage 2, 32.6% (95% CI, 24.3%-42.9%); stage 3, 45.9% (95% CI, 35.5%-57.5%); and stage 4, 51.1% (95% CI, 32.8%-72.2%) and by day 475 was 15.3% (95% CI, 7.6%-29.6%), 35.8% (95% CI, 26.2%-47.6%), 45.9% (95% CI, 35.6%-57.5%), and 69.4% (95% CI, 48.6%-87.7%), respectively. Similar results were obtained after covariate adjustment. The addition of fibrosis to a recurrence prediction model that includes traditional clinical covariates resulted in an improved predictive accuracy with the C statistic increasing from 0.65 to 0.69 (risk difference of 0.05; 95% CI, 0.01-0.09). CONCLUSIONS AND RELEVANCE Among patients with AF undergoing catheter ablation, atrial tissue fibrosis estimated by delayed enhancement MRI was independently associated with likelihood of recurrent arrhythmia. The clinical implications of this association warrant further investigation.

Circular Mapping and Ablation of the Pulmonary Vein for Treatment of Atrial Fibrillation Impact of Different Catheter Technologies

OBJECTIVES We conducted this study to compare the efficacy and safety of different catheter ablation technologies and of distal versus ostial pulmonary veins (PV) isolation using the circular mapping technique. BACKGROUND Electrical isolation of the PVs in patients with atrial fibrillation (AF) remains a technical challenge. METHODS Two hundred eleven patients (163 men; mean age 53 +/- 11 years) with symptomatic AF were included in this study. In the first 21 patients (group 1), distal isolation (> or = 5 mm from the ostium) was achieved targeting veins triggering AF. In the remaining 190 patients (group 2), ostial isolation of all PVs was performed using 4-mm tip (47 patients), 8-mm tip (21 patients), or cooled-tip (122 patients) ablation catheters. RESULTS Distal isolation was able to eliminate premature atrial contractions (PACs) and AF in six of 21 patients (29%) and 10 of 34 PVs. After a mean follow-up time of 6 +/- 4 months, no patients treated with the 8-mm tip catheter experienced recurrence of AF, whereas 21% (10 of 47 patients) and 15% (18 of 122 patients) of the patients ablated with the 4-mm tip and the cooled-tip ablation catheters experienced recurrence of AF after a mean follow-up of 10 +/- 3 and 4 +/- 2 months, respectively. Significant complications including stroke, tamponade, and severe stenosis occurred in 3.5% (8/211) of patients. CONCLUSIONS Catheter technologies designed to achieve better lesion size appeared to have a positive impact on procedure time, fluoroscopy time, number of lesions, and overall efficacy. Although distal isolation can be achieved with fewer lesions, ostial isolation is required in the majority of patients to eliminate arrhythmogenic PACs and AF.

Pulmonary Vein Stenosis After Radiofrequency Ablation of Atrial Fibrillation Functional Characterization, Evolution, and Influence of the Ablation Strategy

Background—Pulmonary vein (PV) stenosis is a complication of ablation for atrial fibrillation. The impact of different ablation strategies on the incidence of PV stenosis and its functional characterization has not been described. Methods and Results—PV isolation was performed in 608 patients. An electroanatomic approach was used in 71 and circular mapping in 537 (distal isolation, 25; ostial isolation based on PV angiography, 102; guided by intracardiac echocardiography, 140; with energy delivery based on visualization of microbubbles, 270). Severe (≥70%) narrowing was detected in 21 patients (3.4%), and moderate (50% to 69%) and mild (<50%) narrowing occurred in 27 (4.4%) and 47 (7.7%), respectively. Severe stenosis occurred in 15.5%, 20%, 2.9%, 1.4%, and 0%, respectively. Development of symptoms was correlated with involvement of >1 PV with severe narrowing (P =0.01), whereas all patients with mild and moderate narrowing were asymptomatic. In the latter group, lung perfusion (V/Q) scans were normal in all but 4 patients. All patients with severe stenosis had abnormal perfusion scans. Conclusions—V/Q scans are useful to assess the functional significance of PV stenosis. Mild and moderate degrees of PV narrowing are not associated with development of symptoms and seem to have no or minimal detrimental effect on pulmonary flow. The incidence of severe PV stenosis seems to be declining with better imaging techniques to ensure ostial isolation and to guide power titration. Mild narrowing 3 months after ablation does not preclude future development of severe stenosis and should be assessed with repeat imaging studies.

Response of Atrial Fibrillation to Pulmonary Vein Antrum Isolation Is Directly Related to Resumption and Delay of Pulmonary Vein Conduction

Background—The role of pulmonary vein (PV) isolation in ablative treatment of atrial fibrillation (AF) has been debated in conflicting reports. We sought to compare PV conduction in patients who had no AF recurrence (group I), patients who could maintain sinus rhythm on antiarrhythmic medication (group II), and patients who had recurrent AF despite antiarrhythmic medication (group III) after PV antrum isolation (PVAI). Methods and Results—PV conduction was examined in consecutive patients undergoing second PVAI for AF recurrence. We also recruited some patients cured of AF to undergo a repeat, limited electrophysiological study at >3 months after PVAI. All patients underwent PVAI with an intracardiac echocardiography (ICE)–guided approach with complete isolation of all 4 PV antra (PVA). The number of PVs with recurrent conduction and the shortest atrial to PV (A-PV) conduction delay was measured with the use of consistent Lasso positions defined by ICE. Late AF recurrence was defined as AF >2 months after PVAI with the patient off medications. Patients in groups I (n=26), II (n=37), and III (n=44) did not differ at baseline (38% permanent AF; ejection fraction 53±6%). Recurrence of PV–left atrial (LA) conduction was seen in 1.7±0.8 and 2.2±0.8 PVAs for groups II and III but only in 0.2±0.4 for group I (P=0.02). In patients with recurrent PV-LA conduction, the A-PV delay increased from the first to second procedure by 69±47% for group III, 267±110% for group II, and 473±71% for group I (P<0.001). When pacing was at a faster rate, A-PV block developed in all 5 of the group I patients with recurrent PV-LA conduction. Conclusions—The majority of patients with drug-free cure show no PV-LA conduction recurrence. Substantial A-PV delay is seen in patients able to maintain sinus rhythm on antiarrhythmic medication or cured of AF compared with patients who fail PVAI.

Left atrial strain and strain rate in patients with paroxysmal and persistent atrial fibrillation: relationship to left atrial structural remodeling detected by delayed-enhancement MRI.

Background—Atrial fibrillation (AF) is a progressive condition that begins with hemodynamic and/or structural changes in the left atrium (LA) and evolves through paroxysmal and persistent stages. Because of limitations with current noninvasive imaging techniques, the relationship between LA structure and function is not well understood. Methods and Results—Sixty-five patients (age, 61.2±14.2 years; 67% men) with paroxysmal (44%) or persistent (56%) AF underwent 3D delayed-enhancement MRI. Segmentation of the LA wall was performed and degree of enhancement (fibrosis) was determined using a semiautomated quantification algorithm. Two-dimensional echocardiography and longitudinal LA strain and strain rate during ventricular systole with velocity vector imaging were obtained. Mean fibrosis was 17.8±14.5%. Log-transformed fibrosis values correlated inversely with LA midlateral strain (r=−0.5, P=0.003) and strain rate (r=−0.4, P<0.005). Patients with persistent AF as compared with paroxysmal AF had more fibrosis (22±17% versus 14±9%, P=0.04) and lower midseptal (27±14% versus 38±16%, P=0.01) and midlateral (35±16% versus 45±14% P=0.03) strains. Multivariable stepwise regression showed that midlateral strain (r=−0.5, P=0.006) and strain rate (r=−0.4, P=0.01) inversely predicted the extent of fibrosis independent of other echocardiographic parameters and the rhythm during imaging. Conclusions—LA wall fibrosis by delayed-enhancement MRI is inversely related to LA strain and strain rate, and these are related to the AF burden. Echocardiographic assessment of LA structural and functional remodeling is quick and feasible and may be helpful in predicting outcomes in AF.

New magnetic resonance imaging-based method for defining the extent of left atrial wall injury after the ablation of atrial fibrillation.

OBJECTIVES We describe a noninvasive method of detecting and quantifying left atrial (LA) wall injury after pulmonary vein antrum isolation (PVAI) in patients with atrial fibrillation (AF). Using a 3-dimensional (3D) delayed-enhancement magnetic resonance imaging (MRI) sequence and novel processing methods, LA wall scarring is visualized at high resolution after radiofrequency ablation (RFA). BACKGROUND Radiofrequency ablation to achieve PVAI is a promising approach to curing AF. Controlled lesion delivery and scar formation within the LA are indicators of procedural success, but the assessment of these factors is limited to invasive methods. Noninvasive evaluation of LA wall injury to assess permanent tissue injury may be an important step in improving procedural success. METHODS Imaging of the LA wall with a 3D delayed-enhanced cardiac MRI sequence was performed before and 3 months after ablation in 46 patients undergoing PVAI for AF. Our 3D respiratory-navigated MRI sequence using parallel imaging resulted in 1.25 x 1.25 x 2.5 mm (reconstructed to 0.6 x 0.6 x 1.25 mm) spatial resolution with imaging times ranging 8 to 12 min. RESULTS Radiofrequency ablation resulted in hyperenhancement of the LA wall in all patients post-PVAI and may represent tissue scarring. New methods of reconstructing the LA in 3D allowed quantification of LA scarring using automated methods. Arrhythmia recurrence at 3 months correlated with the degree of wall enhancement with >13% injury predicting freedom from AF (odds ratio: 18.5, 95% confidence interval: 1.27 to 268, p = 0.032). CONCLUSIONS We define noninvasive MRI methods that allow for the detection and quantification of LA wall scarring after RF ablation in patients with AF. Moreover, there seems to be a correlation between the extent of LA wall injury and short-term procedural outcome.

Pulmonary Vein Stenosis after Catheter Ablation of Atrial Fibrillation: Emergence of a New Clinical Syndrome

Context Because electrical signals initiating atrial fibrillation originate in the pulmonary veins, radiofrequency catheter ablation has been highly successful in curing the arrhythmia. Pulmonary vein stenosis is a recognized complication of this procedure, but past research has not established its frequency or clinical characteristics. Contribution Of 335 patients who received catheter ablation, 18 developed severe pulmonary vein stenosis. Only 44% were symptomatic. Failure to recognize the problem often led to inappropriate work-up and treatment. After pulmonary vein dilatation and stenting, 57% of patients improved. Implications Pulmonary vein stenosis following catheter ablation of atrial fibrillation is relatively common and clinically recognizable. Mechanical relief of venous obstruction can alleviate symptoms. The Editors Atrial fibrillation is one of the most common cardiac rhythm disorders and is associated with significant morbidity and mortality. Recent advances in the pathophysiologic understanding of this disorder have pointed to a focal origin that is mainly localized in the pulmonary veins and is thus amenable to ablative catheter procedures (1-6). Pulmonary vein stenosis is a recognized potential complication of radiofrequency ablation. Its incidence has been reported to range from 3% to 42%, depending on the ablative technique used and the method of assessment (6-11). Recognition of pulmonary vein stenosis is important to avoid unnecessary work-up and to allow initiation of appropriate treatment. However, reports on the constellation of signs and symptoms characterizing pulmonary vein stenosis are lacking. In this study, we describe our experience with patients who developed pulmonary vein stenosis as a complication of radiofrequency ablation of atrial fibrillation. Methods Study Sample Three hundred thirty-five patients (272 men; mean age, 54.0 years [range, 18 to 79 years]) with symptomatic, drug-refractory atrial fibrillation (mean duration [SD], 5.4 3.6 years) were referred to our laboratory for electrophysiologic study and catheter ablation. Therapy with antiarrhythmic drugs and use of oral anticoagulants were discontinued 5 half-lives and 5 days, respectively, before ablation. In all but three patients, amiodarone was withdrawn 1 month before the procedure. Informed consent was obtained from all patients before the procedure, and the institutional review board approved the collection and analysis of the data. In 71 patients, we used a three-dimensional nonfluoroscopic electroanatomic system (CARTO, Biosense Webster, Diamond Bar, California) to map and ablate arrhythmogenic pulmonary veins, as described elsewhere (3). Briefly, this system uses a low-level magnetic field to continuously record the mapping catheter location and create a catalog of electrical activity. The acquired information is then color-coded and displayed on a three-dimensional chamber geometry model of the heart chamber of interest. In 264 additional patients, we instead performed circumferential mapping and electrical isolation of all pulmonary veins, regardless of demonstration of ectopic activity. Procedure Description Patients came to the electrophysiology laboratory while fasting. Immediately before the procedure, transesophageal echocardiography was performed in all patients to exclude left atrial thrombus. A custom-made catheter (Cardiac Assist Device, Inc., Cleveland, Ohio) was placed in the coronary sinus. The proximal eight electrodes were positioned between the superior vena cava and the high crista terminalis, whereas the distal eight electrodes were placed in the coronary sinus. A transesophageal recording lead was used to record activation of the left atrial posterior wall. Mapping of left atrium and pulmonary veins was completed after the left atrium was accessed through the transseptal approach. A circular catheter (LASSO, Biosense Webster) and a steerable quadripolar catheter were placed in the pulmonary veins for mapping and ablation, respectively, through separate transseptal access points. Quadripolar 4-mmtip, 8-mmtip (Biosense Webster), and cooled-tip (Chilli, EPT, Sunnyvale, California) catheters were used for ablation. The procedure end point was the demonstration of electrical isolation of all pulmonary veins from the left atrium by evidence of entrance block. Initially, radiofrequency lesions were delivered inside the veins. For most patients, however, proximal isolation was obtained by energy delivery at the pulmonary veinleft atrium junction, which was defined by a phase-array intracardiac echocardiographic probe or by pulmonary vein angiography. The latter was performed during adenosine-induced asystole for better resolution. In patients in whom the electroanatomic system was used, only the superior pulmonary veins were targeted, unless firing from other veins was noted. The pulmonary vein profiles were reconstructed by using the electroanatomic system and by angiography. The procedure end point was pulmonary vein isolation, elimination of ectopic activity capable of initiating atrial fibrillation, or both. Follow-up Patients were given aspirin immediately after the procedure, and warfarin was restarted on the same evening. Antiarrhythmic medications were used for 6 weeks in patients who had permanent atrial fibrillation before the procedure. An arrhythmia transmitter was given to all patients before hospital discharge for detection of recurrent atrial fibrillation. Routine follow-up visits took place 3, 6, and 12 months after the procedure. Spiral computed tomography (CT) of the pulmonary veins, with three-dimensional reconstruction, was performed 3 months after ablation in all patients, regardless of the development of symptoms, to screen for pulmonary vein stenosis. Computed tomography was considered earlier if symptoms suggestive of stenosis developed; it was repeated at 6 and 12 months if any degree of pulmonary vein narrowing was observed. Pulmonary vein stenosis was judged by digital measurements of luminal diameters on adjacent segments as well as by comparison with previous films, when available. Stenosis was considered mild if luminal narrowing was less than 50%, moderate if luminal narrowing was 50% to 70%, or severe if luminal narrowing was more than 70%. Statistical Analysis We used the paired t-test to compare perfusion scan data and the Fisher exact test to evaluate the relation between the number of stenosed pulmonary veins and symptoms. StatXact software, version 3.0 (Cytel Corp., Cambridge, Massachusetts), was used for these analyses. Results Demographic characteristics of the study sample are presented in Table 1. At the 6-month follow-up visit, pulmonary vein isolation guided by the circular mapping technique had cured atrial fibrillation without use of medications in 80% of patients (212 of 264). Thirty-five patients underwent a second procedure, which resulted in an overall success rate of 92% (243 of 264 patients). This represented a significant improvement when compared with the electroanatomically guided technique, in which only 30% patients (21 of 71) were free of arrhythmia while not taking medications. Table 1. Demographic Characteristics of the Study Sample at Baseline Eighteen of 335 patients (5% [95% CI, 3% to 8%]) developed severe pulmonary vein stenosis, detected by spiral CT, a mean (SD) of 5.2 2.6 months after ablation. The mean age of these patients was 50.6 years (range, 26 to 71 years), and 78% were men. Five of these 18 patients (28%) had structural heart disease. The mean number of pulmonary veins ablated was three per patient (range, two to four per patient). Twelve patients had ablation guided by the circular mapping technique, and 6 patients had ablation guided by the CARTO system. Shortness of breath, the only respiratory symptom detected before the ablation procedure, was present in 5 patients and was attributed to atrial fibrillation. One patient had underlying pulmonary disease (asthma). Eight patients with severe pulmonary vein stenosis (44%) were asymptomatic. Among patients who had symptoms, shortness of breath was the most prevalent (8 patients [44%]), followed by cough (7 patients [39%]) and hemoptysis (5 patients [28%]). Pleuritic pain was observed in 4 patients (22%) and was usually associated with hemoptysis and cough. The presence of severe stenosis in more than one pulmonary vein was associated with a higher risk for symptoms (relative risk, 12.5 [CI, 1.2 to 391]; P = 0.04). Radiographic findings were abnormal in 9 of the 18 patients with severe stenosis (50%). The most common abnormal finding was lung consolidation (observed in 78% of patients), followed by left pleural effusions (observed in 56% of patients). Of note, in 7 of the 9 patients with radiologic abnormalities of the lungs (78%), symptoms were initially attributed to other diseases: pneumonia (4 patients), lung cancer (1 patient), and pulmonary embolism (2 patients). It is important to note that pulmonary vein stenosis was not initially considered in any of the patients who had the disorder. Misdiagnoses led to improper diagnostic and therapeutic procedures, such as prolonged antibiotic treatment (5 patients), treatment for possible asthmatic syndrome and bronchitis (3 patients), placement of a vena cava filter (1 patient), and lung resection surgery (1 patient). Table 2 summarizes the clinical and radiologic findings and pulmonary vein interventions performed. Of interest, in 5 patients who initially presented with symptomatic pulmonary vein stenosis (50%), symptoms spontaneously resolved before interventional procedures were undertaken. Table 2. Summary of Clinical and Radiologic Findings and Pulmonary Vein Interventions in 18 Patients Lung perfusion scans were obtained before and after pulmonary vein dilatation and showed a significant improvement in perfusion after the intervention. Average pulmonary flow to the affected lung increased from 15% (CI, 2% to 33%) to 23% (

Percutaneous Pericardial Instrumentation for Endo-Epicardial Mapping of Previously Failed Ablations

Background—The epicardial location of an arrhythmia could be responsible for unsuccessful endocardial catheter ablation. Methods and Results—In 48 patients referred after prior unsuccessful endocardial ablation, we considered percutaneous, subxiphoid instrumentation of the pericardial space for mapping and ablation. Thirty patients had ventricular tachycardia (VT), 6 patients had a right- and 4 had a left-sided accessory pathway (AP), 4 patients had inappropriate sinus tachycardia, and 4 patients had atrial arrhythmias. Of the 30 VTs, 24 (6 with ischemic cardiomyopathy, 3 with idiopathic cardiomyopathy, and 15 with normal hearts) appeared to originate from the epicardium. Seventeen (71%) of these 24 VTs were successfully ablated with epicardial lesions. The other 7 VTs had early epicardial sites that were inaccessible, predominantly because of interference from the left atrial appendage. Six of these were successfully ablated from the left coronary cusp. In 5 of the 10 patients with an AP, the earliest activation was recorded epicardially. Three of these were right atrial appendage–to–right ventricle APs, and epicardial ablation was successful. No significant complications were observed. Conclusions—Failure of endocardial ablation could reflect the presence of an epicardial arrhythmia substrate. Epicardial instrumentation and ablation appeared feasible and safe and provided an alternative strategy for the treatment of patients with a variety of arrhythmias. This was particularly true for VT, including patients without structural heart disease.