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In certain cardiac conduction system pathologies, like bundle branch block, block may be proximal, allowing for electrical stimulation of the more distal His bundle to most effectively restore activation. While selective stimulation of the His bundle is sought, surrounding myocardium may also be excited, resulting in nonselective pacing. The myocardium and His bundle have distinct capture thresholds, but the factors affecting whether His bundle pacing is selective or nonselective remain unelucidated. Objective: We investigated the properties which affect the capture thresholds in order to improve selective pacing. Methods: We performed biophysically detailed, computer simulations of a His fibre running through a septal wedge preparation to compute capture thresholds under various configurations of electrode polarity and orientation. Results: The myocardial capture threshold was close to that of the His bundle. The His fibre needed to intersect with the electrode tip to favor its activation. Inserting the electrode fully within the septum increased the myocardial capture threshold. Reversing polarity, to rely on anode break excitation, also increased the ease of selective pacing. Conclusion: Model results were consistent with clinical observations. For selective pacing, the tip needs to be in contact with the His fibre and anodal stimulation is preferable. Significance: This study provides insight into helping establish electrode and stimulation parameters for selective His bundle pacing in patients.

AIMS Electrocardiographic imaging (ECGi) and the ECG belt are body surface potential mapping systems which can assess electrical dyssynchrony in patients undergoing cardiac resynchronization therapy (CRT). ECGi-derived dyssynchrony metrics are calculated from reconstructed epicardial potentials based on body surface potentials combined with a thoracic CT scan, while the ECG belt relies on body surface potentials alone. The relationship between dyssynchrony metrics from these two systems is unknown. In this study we aim to compare intra-ventricular and inter-ventricular dyssynchrony metrics between ECGi and the ECG belt. METHODS Seventeen patients underwent ECGi after CRT. A subsample of 40 body surface potentials was used to simulate the ECG belt. ECGi dyssynchrony metrics, calculated from reconstructed epicardial potentials, and ECG belt dyssynchrony metrics, calculated from the sampled body surface potentials were compared. RESULTS There was a strong positive correlation between ECGi left ventricular activation time (LVAT) and ECG belt left thorax activation time (LTAT) (R = 0.88 ; P < 0.001) and between ECGi standard deviation of activation times (SDAT) and ECG belt-SDAT (R = 0.76; P < 0.001) during intrinsic rhythm. The correlation for both pairs was also strong during biventricular pacing. Ventricular electrical uncoupling, a well validated ECGi inter-ventricular dyssynchrony metric, correlated strongly with ECG belt-SDAT during intrinsic rhythm (R = 0.76; P < 0.001) but not biventricular pacing (R = 0.29; P = 0.26). Cranial or caudal displacement of the simulated ECG belt did not affect LTAT or SDAT. CONCLUSION ECGi- and ECG belt-derived intra-ventricular and inter-ventricular dyssynchrony metrics were strongly correlated. The ECG belt may offer comparable dyssynchrony assessment to ECGi, with associated practical and cost advantages.

Background The extravascular ICD (EV ICD) is a novel defibrillator that couples a substernal lead to a device under the left axilla. The electrode locations for best defibrillation performance are unknown. In this study we use data from a 21 patient pilot study to address this question. Objective To create computational torso models to study the effect of device and lead position on defibrillation threshold (DFT). Methods Finite element models were developed from CT and intraoperative imaging of the 21 patients enrolled in the EV ICD Pilot Study. Between 150 and 200 combinations of electrode locations were created for each patient, including the actual implant locations as determined from post-implant CT. The shock amplitudes from DFT testing and multiple vector impedance measurements from a large subset of patients and their as-implanted models were used to calibrate global model parameters. In total, 3330 implant models were automatically meshed, simulated and analyzed to compute predicted DFT values. For each patient an acceptable implant zone was calculated in which it is predicted that they would pass implant DFT testing. The zones for all patients were aligned and combined using common anatomical landmarks so that a common zone for acceptable DFT performance could be calculated for the cohort. Results Two patients were omitted due to incomplete CT data and 16 models were used during the calibration phase. Final analysis was performed using 19 patient models. The model results recommend positioning the lead slightly left of the sternal midline with the most proximal electrode 10 mm above the xiphisternal junction. Similarly, the device should be positioned so that its upper margin is at the height of the leftmost projection of the heart as seen in the AP view, and its posterior margin aligned with the posterior margin of the ventricles. The figure illustrates these positions. The model predicts that using these locations will result in acceptable DFT performance for all 19 patients - including one who failed testing at implant. Conclusion Modeling showed that DFT is dependent on both lead and device location. Furthermore, the predicted DFT and impedance values are consistent with clinical measurements. Specific lead and device locations were determined that are both clinically identifiable and provide acceptable DFTs in all patients. Implant positioning Funding Acknowledgement Type of funding source: Private company. Main funding source(s): Medtronic PLC

Background Antitachycardia pacing (ATP) for monomorphic VT (MVT) reduces painful defibrillation shocks. Most ICD-treated ventricular arrhythmias are MVT, suggesting an opportunity for improved ATP to decrease shocks. We report on a new algorithm (Yee, Circ AE 2017) that uses electrophysiologic (EP) first-principles to design ATP sequences in real-time. Heart-rate history is used to design the first ATP sequence, and failed ATP post-pacing interval is used to design later sequences. Purpose The purpose of this modeling study was to understand how this new ATP algorithm would perform in a head-to-head comparison with traditional burst ATP. Modeling allows direct comparison of the two algorithms in identical, realistic, patient-derived cardiac arrythmias. Methods Patient-specific late gadolinium enhanced MRI and EP data were used to build an adjudicated cohort of realistic numerical heart models with varied EP, infarct, border zone. Publicly available EP modeling software CARPentry was used to calculate sustained reentrant VT initiated with the programmed electrical stimulation used to induce VT clinically. The VTs were physician-adjudicated to validate models. Burst ATP was 3 sequences of 8 pulses at 88% of VT cycle length, each decremented by 10ms. The new ATP was limited to 3 automatically designed sequences. Results Three hundred unique VT scenarios were generated from 6 human hearts with multiple VT circuits, 5 electrophysiologic states, and 10 pacing locations. Burst ATP terminated 168/300 VTs (56%) and accelerated 2.7%. The new ATP terminated 234/300 VTs (78%) with the same acceleration. The two dominant ATP failure mechanisms were identified as 1) insufficient prematurity to close the excitable gap, and 2) failure to reach the critical isthmus of the VT circuit. For these mechanisms, the new ATP algorithm reduce failures from 64 to 28 (44% reduction) without increasing acceleration. Conclusion The new automated ATP algorithm successfully adapted ATP sequences for VT episodes that burst ATP failed to terminate. The new ATP was successful even with complex scar geometries and electrophysiology heterogeneity as seen in the real world.

Ventricular tachycardia (VT), which can lead to sudden cardiac death, occurs frequently in patients with myocardial infarction. Catheter-based radiofrequency ablation of cardiac tissue has achieved only modest efficacy, owing to the inaccurate identification of ablation targets by current electrical mapping techniques, which can lead to extensive lesions and to a prolonged, poorly tolerated procedure. Here we show that personalized virtual-heart technology based on cardiac imaging and computational modelling can identify optimal infarct-related VT ablation targets in retrospective animal (5 swine) and human studies (21 patients) and in a prospective feasibility study (5 patients). We first assessed in retrospective studies (one of which included a proportion of clinical images with artifacts) the capability of the technology to determine the minimum-size ablation targets for eradicating all VTs. In the prospective study, VT sites predicted by the technology were targeted directly, without relying on prior electrical mapping. The approach could improve infarct-related VT ablation guidance, where accurate identification of patient-specific optimal targets could be achieved on a personalized virtual heart prior to the clinical procedure.

Geometric Factors in Voltage Mapping Background Voltage mapping is an important tool for characterizing proarrhythmic electrophysiological substrate, yet it is subject to geometric factors that influence bipolar amplitudes and thus compromise performance. The aim of this study was to characterize the impact of catheter orientation on the ability of bipolar amplitudes to accurately discriminate between healthy and diseased tissues. Methods and Results We constructed a 3-dimensional, in silico, bidomain model of cardiac tissue containing transmural lesions of varying diameter. A planar excitation wave was stimulated and electrograms were sampled with a realistic catheter model at multiple positions and orientations. We carried out validation studies in animal experiments of acute ablation lesions mapped with a clinical mapping system. Bipolar electrograms sampled at higher inclination angles of the catheter with respect to the tissue demonstrated improvements in both sensitivity and specificity of lesion detection. Removing low-voltage electrograms with concurrent activation of both electrodes, suggesting false attenuation of the bipolar electrogram due to alignment with the excitation wavefront, had little effect on the accuracy of voltage mapping. Conclusions Our results demonstrate possible mechanisms for the impact of catheter orientation on voltage mapping accuracy. Moreover, results from our simulations suggest that mapping accuracy may be improved by selectively controlling the inclination of the catheter to record at higher angles with respect to the tissue.

Background: 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). Methods: We investigated 60 patients who underwent pulmonary vein antrum (PVA) isolation along with LA posterior wall and septal debulking for AF. FPs around the LA surface in well-known GP areas (whichwereconsidered asthesubstitutionofGPareasaroundtheLA)weresegmentedfromthedark-blood MRI. Then the FP and the ablation scar image visualized by late gadolinium enhancement (LGE)-MRI on the LA were merged together. Overlapping areas of FP and the ablation scar image were considered as the ablated FP areas containing GP. Patients underwent 24-hour Holter monitoring after ablation for the analysis of heart rate variability. Results: Ablated FP area was significantly wider in patients without AF recurrence than those in patients with recurrence (5.6 ± 3.1 cm 2 vs 4.2 ± 2.7 cm 2 ,P = 0.03). The mean values of both percentage of differences greater than 50 ms in the RR intervals (pRR > 50) and standard deviation of RR intervals over the entire analyzed period (SDNN), which were obtained from 24-hour Holter monitoring 1-day post-AF ablation, were significantly lower in patients without recurrence than those in patients with recurrence (5.8 ± 6.0% vs 14.0 ± 10.1%; P = 0.0005, 78.7 ± 32.4 ms vs 109.2 ± 43.5 ms; P = 0.005). There was a significant negative correlation between SDNN and the percentage of ablated FP area (Y =− 1.3168X + 118.96, R 2 = 0.1576, P = 0.003). Conclusion: Extensively ablating LA covering GP areas along with PVA isolation enhanced the denervation of autonomic nerve system and seemed to improve procedural outcome in patients with AF. (PACE 2013; 00:1‐10)

Background— Radiofrequency ablation is routinely used to treat cardiac arrhythmias, but gaps remain in ablation lesion sets because there is no direct visualization of ablation-related changes. In this study, we acutely identify and target gaps using a real-time magnetic resonance imaging (RT-MRI) system, leading to a complete and transmural ablation in the atrium. Methods and Results— A swine model was used for these studies (n=12). Ablation lesions with a gap were created in the atrium using fluoroscopy and an electroanatomic system in the first group (n=5). The animal was then moved to a 3-tesla MRI system where high-resolution late gadolinium enhancement MRI was used to identify the gap. Using an RT-MRI catheter navigation and visualization system, the gap area was ablated in the MR scanner. In a second group (n=7), ablation lesions with varying gaps in between were created under RT-MRI guidance, and gap lengths determined using late gadolinium enhancement MR images were correlated with gap length measured from gross pathology. Gaps up to 1.0 mm were identified using gross pathology, and gaps up to 1.4 mm were identified using late gadolinium enhancement MRI. Using an RT-MRI system with active catheter navigation gaps can be targeted acutely, leading to lesion sets with no gaps. The correlation coefficient ( R 2 ) between the gap length was identified using MRI, and the gross pathology was 0.95. Conclusions— RT-MRI system can be used to identify and acutely target gaps in atrial ablation lesion sets. Acute targeting of gaps in ablation lesion sets can potentially lead to significant improvement in clinical outcomes.

The aim of this study was to assess acute ablation injuries seen on late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) immediately post-ablation (IPA) and the association with permanent scar 3 months post-ablation (3moPA).Success rates for atrial fibrillation catheter ablation vary significantly, in part because of limited information about the location, extent, and permanence of ablation injury at the time of procedure. Although the amount of scar on LGE MRI months after ablation correlates with procedure outcomes, early imaging predictors of scar remain elusive.Thirty-seven patients presenting for atrial fibrillation ablation underwent high-resolution MRI with a 3-dimensional LGE sequence before ablation, IPA, and 3moPA using a 3-T scanner. The acute left atrial wall injuries on IPA scans were categorized as hyperenhancing (HE) or nonenhancing (NE) and compared with scar 3moPA.Heterogeneous injuries with HE and NE regions were identified in all patients. Dark NE regions in the left atrial wall on LGE MRI demonstrate findings similar to the "no-reflow" phenomenon. Although the left atrial wall showed similar amounts of HE, NE, and normal tissue IPA (37.7 ± 13%, 34.3 ± 14%, and 28.0 ± 11%, respectively; p = NS), registration of IPA injuries with 3moPA scarring demonstrated that 59.0 ± 19% of scar resulted from NE tissue, 30.6 ± 15% from HE tissue, and 10.4 ± 5% from tissue identified as normal. Paired t-test comparisons were all statistically significant among NE, HE, and normal tissue types (p0.001). Arrhythmia recurrence at 1-year follow-up correlated with the degree of wall enhancement 3moPA (p = 0.02).Radiofrequency ablation results in heterogeneous injury on LGE MRI with both HE and NE wall lesions. The NE lesions demonstrate no-reflow characteristics and reveal a better predictor of final scar at 3 months. Scar correlates with procedure outcomes, further highlighting the importance of early scar prediction.

Background Magnetic resonance imaging (MRI) allows visualization of location and extent of radiofrequency (RF) ablation lesion, myocardial scar formation, and real-time (RT) assessment of lesion formation. In this study, we report a novel 3-Tesla RT -RI based porcine RF ablation model and visualization of lesion formation in the atrium during RF energy delivery. Objective The purpose of this study was to develop a 3-Tesla RT MRI-based catheter ablation and lesion visualization system. Methods RF energy was delivered to six pigs under RT MRI guidance. A novel MRI-compatible mapping and ablation catheter was used. Under RT MRI, this catheter was safely guided and positioned within either the left or right atrium. Unipolar and bipolar electrograms were recorded. The catheter tip–tissue interface was visualized with a T1-weighted gradient echo sequence. RF energy was then delivered in a power-controlled fashion. Myocardial changes and lesion formation were visualized with a T2-weighted (T2W) half Fourier acquisition with single-shot turbo spin echo (HASTE) sequence during ablation. Results RT visualization of lesion formation was achieved in 30% of the ablations performed. In the other cases, either the lesion was formed outside the imaged region (25%) or the lesion was not created (45%) presumably due to poor tissue–catheter tip contact. The presence of lesions was confirmed by late gadolinium enhancement MRI and macroscopic tissue examination. Conclusion MRI-compatible catheters can be navigated and RF energy safely delivered under 3-Tesla RT MRI guidance. Recording electrograms during RT imaging also is feasible. RT visualization of lesion as it forms during RF energy delivery is possible and was demonstrated using T2W HASTE imaging.

Background— Esophageal wall thermal injury after atrial fibrillation ablation is a potentially serious complication. However, no noninvasive modality has been used to describe and screen patients to examine whether esophageal wall injury has occurred. We describe a noninvasive method of using delayed-enhancement MRI to detect esophageal wall injury and subsequent recovery after atrial fibrillation ablation. Methods and Results— We analyzed the delayed-enhancement MRI scans of 41 patients before ablation and at 24 hours and 3 months after ablation to determine whether there was evidence of contrast enhancement in the esophagus after atrial fibrillation ablation. In patients with contrast enhancement, 3D segmentation of the esophagus was performed using a novel image processing method. Upper gastrointestinal endoscopy was then performed. Repeat delayed-enhancement MRI and upper gastrointestinal endoscopy was performed 1 week later to track changes in lesions. The wall thickness of the anterior and posterior wall of the esophagus was measured at 3 time points: before ablation, 24 hours after ablation, and 3 months after ablation. Evaluation of preablation MRI scans demonstrated no cases of esophageal enhancement. At 24 hours, 5 patients showed contrast enhancement. Three of these patients underwent upper gastrointestinal endoscopy, which demonstrated esophageal lesions. Repeat upper gastrointestinal endoscopy and MRI 1 week later demonstrated resolution of the lesions. All 5 patients had confirmed resolution of enhancement at 3 months. All patients with esophageal tissue enhancement demonstrated left atrial wall enhancement directly adjacent to the regions of anterior wall esophageal enhancement. Conclusions— Our preliminary results indicate delayed-enhancement MRI can assess the extent and follow progression of esophageal wall injury after catheter ablation of atrial fibrillation. It appears that acute esophageal injury recovers within 1 week of the procedure.

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 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.

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 × 1.25 × 2.5 mm (reconstructed to 0.6 × 0.6 × 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.

The caption descriptions for Figs ​Figs44 and ​and55 are switched. The authors have provided a corrected version here. Fig 4 Maps of APD distribution for atrial models Utah III (left) and Utah IV (right). Fig 5 Transmembrane potential maps at four time instants in substrates Utah III (top row) and Utah IV (bottom row) following pacing from a “prime” region outside the PVs (pacing sites marked by red arrows).

Personalized computational cardiac models are emerging as an important tool for studying cardiac arrhythmia mechanisms, and have the potential to become powerful instruments for guiding clinical anti-arrhythmia therapy. In this article, we present the methodology for constructing a patient-specific model of atrial fibrosis as a substrate for atrial fibrillation. The model is constructed from high-resolution late gadolinium-enhanced magnetic resonance imaging (LGE-MRI) images acquired in vivo from a patient suffering from persistent atrial fibrillation, accurately capturing both the patient's atrial geometry and the distribution of the fibrotic regions in the atria. Atrial fiber orientation is estimated using a novel image-based method, and fibrosis is represented in the patient-specific fibrotic regions as incorporating collagenous septa, gap junction remodeling, and myofibroblast proliferation. A proof-of-concept simulation result of reentrant circuits underlying atrial fibrillation in the model of the patient's fibrotic atrium is presented to demonstrate the completion of methodology development.

Method: These studies were carried out in a pig model (n=5). Access to the right atrium was obtained through the femoral vein. A MRI compatible catheter was advanced (MRI Interventions, Irvine, CA) to the right atrium and discrete ablation lesions were made using 30 to 40 W for 30 60 secs. Ablation was carried out using real time catheter visualization provided by the Interactive Front End (IFE) software (Siemens, Princeton, NJ). After ablation, gadolinium was infused and delayed enhancement images were acquired with a 1 x 1 x 1.5 mm resolution. The gap between ablation lesions in MRI was measured using Osirix Imaging Software. The cardiac tissue was stained with 2,3,5-Triphenyl-2H-tetrazolium chloride (TTC) to delineate the ablation lesions. The gap length measured in the gross pathology specimen was correlated with the gap determined by MRI.

Atrial fibrillation, a cardiac arrhythmia characterized by unsynchronized electrical activity in the atrial chambers of the heart, is a rapidly growing problem in modern societies. One treatment, referred to as catheter ablation, targets specific parts of the left atrium for radio frequency ablation using an intracardiac catheter. Magnetic resonance imaging has been used for both pre- and and post-ablation assessment of the atrial wall. Magnetic resonance imaging can aid in selecting the right candidate for the ablation procedure and assessing post-ablation scar formations. Image processing techniques can be used for automatic segmentation of the atrial wall, which facilitates an accurate statistical assessment of the region. As a first step towards the general solution to the computer-assisted segmentation of the left atrial wall, in this paper we use shape learning and shape-based image segmentation to identify the endocardial wall of the left atrium in the delayed-enhancement magnetic resonance images.

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 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.

Background Atrial fibrillation (AF) ablation uses radiofrequency (RF) energy to induce thermal damage to the left atrium (LA) in an attempt to isolate AF circuits. This injury can be seen using delayed enhancement magnetic resonance imaging (DE-MRI). Objective The purpose of this study was to describe DE-MRI findings of the LA in the acute and chronic stages postablation. Methods Twenty-five patients were scanned at two time points postablation. The first group (n = 10) underwent DE-MRI at 24 hours and at 3 months. The second group (n = 16) was scanned at 3 months and at 6 or 9 months. One patient had three scans (24 hours, 3 months, 9 months) and was included in both groups. The location and extent of enhancement were then analyzed between both groups. Results The median change in LA wall injury between 24 hours and 3 months was −6.38% (range −11.7% to 12.58%). The median change in LA wall injury between 3 months and later follow-up was +2.0% (range −4.0% to 6.58%). There appears to be little relationship between the enhancement at 24 hours and 3 months (R 2 = 0.004). In contrast, a strong correlation is seen at 3 months and later follow-up (R 2 = 0.966). Qualitative comparison revealed a stronger qualitative relationship between MRI findings at 3 months and later follow-up than at 24 hours and 3 months. Conclusion RF-induced scar appears to have formed by 3 months postablation. At 24 hours postablation, DE-MRI enhancement appears consistent with a transient inflammatory response rather than stable LA scar formation.

Background Late gadolinium enhanced (LGE) MRI is the gold standard test for non-invasive detection of myocardial scar. Many VT ablation candidates who would derive benefit from LGE MRI do not undergo cardiac MRI largely due to image artifacts generated by cardiac devices. A recent study reported improved LGE MRI for patients with implantable cardiac devices using a custom-made wideband adiabatic inversion-recovery (IR) pulse [1]. The purpose of this study was to implement off-resonanceinsensitive LGE MRI based on commercially available IR pulse for imaging ventricular scar without image artifacts induced by cardiac devices. Methods We implemented cardiac-device-insensitive LGE MRI by modifying a commercially available adiabatic IR pulse (Siemens_external_RF_file:IR10240H180.IR180_36B1_2) with the following parameters:b = 750radians/s, μ =1 0 (dimensionless), pulse duration = 6.1 ms. We designed the IR pulse to achieve B1 +o f 1050 Hz and 779 Hz at 1.5T and 3T, respectively, in order to achieve adiabaticity within the RF amplifier and SAR limits. Standard and wideband LGE MRI pulse sequences were evaluated in phantoms and seven canines (with ICD placed 10 cm away from the heart) with myocardial lesions created by radio-frequency ablation at 3T, as well as in one patient with ICD at 1.5T. Both LGE MRI pulse sequences used the same standard imaging parameters, except for the IR pulse. Two readers independently evaluated the image quality(1-5;worst-best) and artifact level(1-5;least-most) using a 5-point Likert scale. After administration of TTC, animals were euthanized for heart removal and gross pathology.

Catheter ablation is effective in symptomatic, drug refractory atrial fibrillation and can result in cure but success rates vary significantly with recurrences ranging from 40-86%. In the months following ablation, LA wall scarring on late gadolinium enhancement (LGE) is useful for determining the location and extent of injury and has been used to guide follow up ablation to 'close the gaps' after unsuccessful PVAI. More recently, imaging acute ablation injury using double inversion recovery (DIR) sequences has been shown feasible and has generated interest for its potential clinical value in guiding ablations.