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Background Right bundle branch block (RBBB) ventricular tachycardia (VT) morphology is a criterion for left ventricular (LV) involvement in arrhythmogenic right ventricular cardiomyopathy (ARVC). Objective The purpose of this study was to determine the frequency and chamber of origin of RBBB VT in patients with ARVC and VT. Methods We studied 110 consecutive patients with VT who met the diagnostic International Task Force criteria for ARVC and underwent VT mapping/ablation. Patients with ≥1 RBBB VT were identified. Right ventricular (RV) origin of the RBBB VT was determined based on standard mapping criteria and elimination with ablation. Results Nineteen patients (17%) had 26 RBBB VTs. Eleven of these 19 patients (58%) had 16 RBBB VTs from the RV, and 9 patients (47%) had 10 RBBB VTs originating from the LV, with 1 patient demonstrating both. RBBB VT from RV most commonly (13/16 RBBB VTs) had an early precordial QRS transition (V2 or V3), with superiorly and typically leftward directed frontal plane axis, consistent with exit from dilated RV adjacent to inferior LV septum, whereas all 10 VTs from LV had RBBB morphology with positive R waves to V5 or V6 and rightward axis in 6 VTs characteristic of basal lateral origin. Conclusion In patients with ARVC and VT presenting for VT ablation, RBBB VT occurs in 17% of cases, with most RBBB VTs (62%) originating from the RV and not indicative of LV origin. Precordial R-wave transition and frontal plane axis can be used to identify the anticipated chamber of origin of RBBB VT.

Ventricular bipolar voltage values0.5 and1.0/1.5 mV (epi- and endocardium) correlating with dense scar and border zone, respectively, were established using a 3.5-mm tip catheter. Novel microelectrode catheters promise improved mapping resolution; however, whether standard voltage criteria apply to catheters with smaller electrode size and interelectrode distance remains unclear.The purpose of this study was to determine whether traditional bipolar voltage criteria for scar apply during substrate mapping with a microelectrode catheter.Paired bipolar and microbipolar voltage values were acquired from control swine (n = 2) using the microelectrode catheter and assessed for systemic differences. In a postinfarction swine model (n = 6), scar characteristics were compared between the bipolar maps and microbipolar maps using both standard and adjusted voltage criteria derived from the control animals.In control swine, although 5th percentile values for bipolar and microbipolar voltage were similar (1.12 vs 1.22 mV [left ventricular (LV) endo]; 0.88 mV vs 0.98 mV [epi]), median values were significantly greater when acquired by microbipolar electrodes (3.60 vs 6.76 mV, P = .002 [LV endo]; 2.61 vs 2.72 mV, P = .02 [epi]). Microbipolar values were systematically larger by 2.0× and 1.4× in the LV endocardium and epicardium, respectively. Application of standard voltage values to microbipolar maps in postinfarct swine underestimated scar area by approximately 41% in the LV endocardium (13.7 vs 33.4 cmBipolar voltage values acquired from microelectrodes are systemically larger than those acquired from standard catheters. New reference values should be established for these novel catheters.

Catheter ablation of postinfarction reentrant ventricular tachycardia (VT) has received renewed interest owing to the increased availability of high-resolution electroanatomic mapping systems that can describe the VT circuits in greater detail, and the emergence and need to target noninvasive external beam radioablation. These recent advancements provide optimism for improving the clinical outcome of VT ablation in patients with postinfarction and potentially other scar-related VTs. The combination of analyses gleaned from studies in swine and canine models of postinfarction reentrant VT, and in human studies, suggests the existence of common electroanatomic properties for reentrant VT circuits. Characterizing these properties may be useful for increasing the specificity of substrate mapping techniques and for noninvasive identification to guide ablation. Herein, we describe properties of reentrant VT circuits that may assist in elucidating the mechanisms of onset and maintenance, as well as a means to localize and delineate optimal catheter ablation targets.

Background Recurrences of atrial fibrillation (AF) after ablation have been attributed to conduction gaps and nontransmural ablation lesions. Objective The purpose of this study was to assess the feasibility of adjunctive percutaneous mapping of the epicardial regions of the left atrium to characterize the transmural extent of substrate and ablation lesions. Methods Between 2014 and 2018, combined epicardial and endocardial mapping of AF was performed in 18 patients via an inferior subxiphoid percutaneous approach (16 with previously failed ablation procedures and 2 patients with long-standing persistent AF) at 2 centers. Epicardial substrate mapping was compared with endocardial mapping to assess transmural uniformity. Results Of 18 patients, 4 (22%) demonstrated nontransmural atrial low-voltage regions with relative epicardial sparing in the left atrial posterior wall. Transmural isolation of the posterior wall was achieved after an endocardial "box" lesion set in 6/9 (67%), guided by epicardial voltage data, while epicardial and endocardial dissociation during AF was observed in 1 patient. In 3 patients, epicardial capture along the endocardial pulmonary vein lesion set despite endocardial capture loss and bidirectional block was observed. Two cases of mitral flutter were terminated from the epicardium. A balloon was positioned in the pericardial space in 6 patients for esophageal protection during ablation. Conclusion A percutaneous epicardial approach for mapping and ablation of the left atrium is feasible in the electrophysiology laboratory during endocardial catheter ablation for AF and may be useful as an adjunctive approach in refractory cases. High-density epicardial mapping can provide direct evidence of nonuniform lesion and substrate transmurality of the human left atrium before and after ablation.

Background Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) provides tissue characterization of ventricular myocardium and scar that can be depicted as pixel signal intensity (PSI) maps. Objective To assess the possible benefit of guiding the ventricular tachycardia (VT) substrate mapping by integrating these PSI maps into the navigation system. Methods In total, 159 consecutive patients (66 ± 11 years old, 151 men [95%]) with scar-related left ventricular (LV) VT were included. VT substrate ablation used the scar dechanneling technique. A CMR-aided ablation using the PSI maps was performed in 54 patients (34%). Procedural data as well as acute and long-term outcomes were compared with those of the remaining 105 patients (66%). Results Mean procedure duration and fluoroscopy time were 229 ± 67 minutes and 20 ± 9 minutes, respectively, without significant differences between groups. Both the number of radiofrequency (RF) applications and RF delivery time were lower in the CMR-aided group (28 ± 18 applications vs 36 ± 18 applications, P = .037, and 19 ± 12 minutes vs 27 ± 16 minutes, P = .009, respectively). After substrate ablation, monomorphic VT inducibility was lower in the CMR-aided than in the control group (17 [32%] vs 53 [51%] patients, P = .022). After a mean follow-up period of 20 ± 19 months, patients from the CMR-aided group had a lower recurrence rate than those in the control group (10 patients [18.5%] vs 46 patients [43.8%], respectively, P = .002; log-rank P = .017). Multivariate analysis found that CMR-aided ablation (hazard ratio, 0.48 [95% Confirdence Interval (CI) 0.24–0.96], P = .037) was an independent predictor of recurrences. Conclusion CMR-aided scar dechanneling is associated with a lower need for RF delivery, higher noninducibility rates after substrate ablation, and a higher VT-recurrence-free survival.

Background Catheter ablation of ventricular tachycardia (VT) can be technically challenging due to difficulty with catheter positioning in the left ventricle (LV) and achieving stable contact. The Hansen Sensei Robotic system (HRS) has been used in atrial fibrillation but its utility in VT is unclear. Objective The purpose of this study was to test the technical feasibility of robotic catheter ablation of LV ventricular tachycardia (VT) using the HRS. Methods Twenty-three patients underwent LV VT mapping and ablation with the HRS via a transseptal, transmitral valve approach. Nineteen patients underwent substrate mapping and ablation (18 had ischemic cardiomyopathy, 1 had an apical variant of hypertrophic cardiomyopathy). Four patients had focal VT requiring LV VT mapping and ablation. Procedural endpoints included substrate modification by endocardial scar border ablation and elimination of late potentials, or elimination of inducible focal VT. Results Mapping and ablation were entirely robotic without requiring manual catheter manipulation in all patients and reaching all LV regions with stable contact. Fluoroscopy time of the LV procedure was 22.2 ± 11.2 minutes. Radiofrequency time was 33 ± 21 minutes. Total procedural times were 231 ± 76 minutes. Complications included a left groin hematoma (opposite to the HRS sheath), 1 pericardial effusion without tamponade that was drained successfully, and transient right ventricular failure in a patient with previous left ventricular assist device. At 13.4 ± 6.7 months of follow-up (range 1–19 months), recurrence of VT occurred in 3 of 23 patients. Conclusion Our initial experience suggests that the HRS allows successful mapping and ablation of LV VT.

Background The biatrial substrate properties in patients with paroxysmal atrial fibrillation (AF) originating from the pulmonary veins (PVs) and superior vena cava (SVC) are not available. Objective The purpose of this study is to characterize the differences of biatrial substrate properties in patients with different types of AF. Methods A total of 36 patients with paroxysmal AF originating from the PV (PV-AF) and 9 patients with paroxysmal AF initiating from the SVC (SVC-AF) were included. Regional electrogram voltage, conduction velocity (CV), and spectral analysis to identify the AF nest were performed to characterize the biatrial, PVs, and SVC substrate. Results In the left atrial (LA) body, the bipolar voltage, total activation time, CV, and dominant frequency (DF) were similar between the PV-AF and SVC-AF. However, in the PV regions, the electrogram voltage, CV, and DF were decreased in the PV-AF. The proportions of AF nest in the LA body (72.2% vs. 22.2%, P = .008) and PV regions (100% vs. 22.2%, P .001) were higher in PV-AF compared with SVC-AF, respectively. On the other hand, lower bipolar voltage, longer total activation time, and slower CV of RA body were recognized in the SVC-AF as compared with the PV-AF. In the SVC, lower bipolar voltage, slower CV, higher DF, and higher proportions of AF nest in SVC (16.7% vs. 66.7%, P = .002) were identified in SVC-AF. Conclusion These most-remodeled substrates in different types of paroxysmal AF indicated the importance of the atrial substrate in the vicinity of the arrhythmogenic thoracic veins.

Contact point-to-point electroanatomic mapping (Pt-Map) is a validated tool to evaluate right ventricular (RV) substrate. When using the EnSite NavX system (St. Jude Medical, St Paul, Minnesota), geometry reconstruction by dragging the mapping catheter (Geo-Map) allows for quicker acquisition of a large number of points and better definition of anatomy, but it is not validated for substrate mapping.This study evaluates the feasibility and accuracy of Geo-Map.Thirteen patients (mean age 38 +/- 12 years) with RV arrhythmias and an apparently normal heart underwent cardiac magnetic resonance imaging (MRI), Pt-Map, and Geo-Map. The 2 maps were compared in terms of mapping procedural time, radiation time, and total number of points acquired. We finally compared the number and characteristics of low-potential areas on each patient's Pt-Map, Geo-Map, and cardiac MRI.Geo-Map required significantly shorter mapping and radiation times in comparison to Pt-Map (12.4 +/- 4.6 vs. 31.9 +/- 10.1 and 5.8 +/- 2.1 vs. 12.1 +/- 3.9, P.001). Furthermore, Geo-Map was based on a significantly higher density of points in comparison to Pt-Map (802 +/- 205 vs. 194 +/- 38, P.001). Taking into consideration the total number of RV regions analyzed, the Pt-Map and Geo-Map disagreed in 2 of 65 (3%) regions (P = NS), which only Geo-Map identified as low-potential areas and indeed corresponded to wall motion abnormalities on MRI.Voltage maps obtained through RV geometry acquisition have accuracy comparable to that of conventional point-by-point mapping in detecting low-voltage areas, have a good correlation with MRI wall motion abnormalities, and allow a significant reduction in procedural time and x-ray exposure.

Background Complex fractionated atrial electrograms are used as potential targets for catheter ablation therapy of atrial fibrillation. Although fibrosis has been associated with the presence of fractionated electrograms, characterizing the substrate through the inspection of electrograms is challenging. Objective This study sought to determine how progression of microfibrosis and slow conduction affect electrogram morphology. Methods A microstructure computer model representing a monolayer of cardiac cells was developed. Slow conduction was induced by: (1) sodium channel blockade, (2) uniform reduction in cell-to-cell coupling, and (3) microfibrosis incorporated as a set of collagenous septa disconnecting transverse coupling. The density (0 to 30%) and length (30 to 945 μm) of these collagenous septa were varied. Unipolar and bipolar electrograms were computed during paced rhythm for a set of electrodes with different tip sizes. Results The analysis of unipolar electrograms with realistic temporal and spatial filtering showed that increasing the density and length of collagenous septa decreased conduction velocity by up to 75% and increased the amount of fractionation (up to 14 deflections) and asymmetry of the electrograms. In contrast, slow conduction induced by sodium channel blockade or uniformly reduced coupling did not result in electrogram fractionation. When a larger electrode was used, electrogram amplitude was smaller and fractionation increased in a substrate-dependent way. Conclusion Microscale obstacles cause significant changes to electrogram waveforms. Conduction velocity and electrogram amplitude and degree of fractionation can be used to discriminate the nature of the substrate and characteristics of fibrosis, giving rise to slow conduction.

The primary goal of catheter ablation of scar-related ventricular tachycardia (VT) is the interruption of critical areas of slow conduction responsible for the development and maintenance of the reentrant VT circuit. Most patients with scar-related VT present with unstable arrhythmias that are not amenable to interrogation from multiple sites to define the VT circuit based on the intracardiac activation sequence and the response to entrainment mapping. In order to effectively target unstable VTs, a number of ablation approaches have been described with the aim of targeting the abnormal substrate defined with mapping in sinus or paced rhythm. Some of these strategies (eg, late potential and local abnormal ventricular activity ablation or scar homogenization) target the entire abnormal substrate harboring abnormal electrograms, defined with a variety of different criteria. Scar dechanneling, linear ablation through sites matching VT with pacing, and the core isolation approach focus on more discrete regions within the abnormal substrate that have been proven relevant to the clinical and/or inducible arrhythmias by means of physiologic maneuvers, although this does not necessarily translate to fewer radiofrequency lesions to achieve the procedural end-point. Observational studies evaluating different substrate-based ablation techniques have reported fairly uniform arrhythmia-free survivals at short- and mid-term follow-up, although direct comparisons between different techniques are lacking. In this article, we summarize the different state-of-the-art substrate mapping and ablation approaches for targeting unstable VT, with a particular focus on the relative merits and limitations of the described techniques.

Background Conventional mapping of ventricular tachycardia (VT) after myocardial infarction is limited in patients with hemodynamically untolerated or noninducible VT. Objectives The purpose of this study was to develop a unique strategy using noncontact unipolar mapping to define infarct substrate and VT circuits. Methods Dynamic substrate mapping (DSM) was performed in seven pigs with healed anterior myocardial infarction. This technique defined substrate as the intersection of low-voltage areas identified in sinus rhythm and during pacing around the infarct. Pacing was also performed within the substrate to determine exit sites. Results Anteroapical transmural scar was identified in all animals. A mean of three pacing sites was used for substrate definition. The mean area (± SD) was 18.4 ± 8.8 cm 2 by DSM and 15.4 ± 6.9 cm 2 by pathology ( P >.5). A mean of 4.5 sites was paced within substrate. Ten of 18 paced wavefronts exited substrate adjacent to the pacing area, seven exited at distant areas, and one had two exits. VT was induced in five animals (1.6 morphologies per animal). Except for one VT, circuit exit sites were identified at substrate borders on the endocardium. VT exit sites were at (n = 6) or near (n = 3) a pacing exit site. Electrogram voltages differed significantly between substrate, border, and nonsubstrate areas in infarcted animals and in comparison with control animals. No substrate was identified in two control animals. Conclusion DSM is a reliable method for infarct substrate localization in this model. Pacing within substrate can predict VT exit sites and may prove useful for ablation of unmappable VT after myocardial infarction.

Standard electroanatomic mapping systems use a single catheter to perform left ventricular substrate mapping. A new mapping system uses a 64-electrode mini-basket catheter to perform rapid automated acquisition of chamber geometry, voltage, and activation.The aim of this study was to compare the accuracy of electroanatomic mapping using the basket catheter with that of mapping using a standard linear catheter in a swine model of chronic myocardial infarction.Ten swine underwent left anterior descending coronary artery occlusion to create an anteroseptal myocardial infarction. Animals underwent delayed-enhancement magnetic resonance imaging (MRI) and then detailed left ventricular voltage mapping with both the basket and the linear catheter. Map characteristics and scar area were compared between the basket catheter, linear catheter, and MRI. Induced ventricular tachycardia (VT) was mapped with the basket catheter.More points were acquired with the basket catheter than with the standard catheter (8762 ± 3164 vs 1712 ± 551; P.001). The fifth percentile of normal bipolar voltage distribution with the basket catheter was 1.54 mV. Using a bipolar voltage cutoff of 1.5 mV, the total infarct areas measured using the basket catheter, linear catheter, and MRI were similar (17.8 cm(2) vs 20.9 cm(2) vs 17.5 cm(2); P = .69); however, the correlation between MRI and catheter scar area measurement was best for the basket catheter (basket vs linear: r = .76 vs r = .71). In 3 animals, sustained poorly tolerated VT was initiated and the circuit mapped successfully with the basket catheter in5 minutes.Rapid substrate and activation mapping using a 64-electrode mini-basket catheter allows detailed voltage and activation mapping in postinfarction cardiomyopathy. This system may be useful for substrate and VT mapping in human postinfarction cardiomyopathy.

We describe catheter ablation of recurrent ventricular tachycardia using high-resolution definition of a myocardial infarct scar by contrast-enhanced cardiac computed tomography (CT). Positron emission tomography scanning as well as three-dimensional electroanatomic mapping confirmed the extent of scar prior to ablation. Catheter ablation based on substrate mapping was successful in eliminating the ventricular tachycardia. Detection of scar by cardiac CT has the potential to abbreviate voltage/substrate mapping in the electrophysiology laboratory. To our knowledge, this is the first time myocardial scar was defined by cardiac CT and utilized for defining an ablation strategy for ventricular tachycardia.

Complex fractionated electrograms (CFAEs) detected during substrate mapping for atrial fibrillation (AF) reflect etiologies that are difficult to separate. Without knowledge of local refractoriness and activation sequence, CFAEs may represent rapid localized activity, disorganized wave collisions, or far-field electrograms.The purpose of this study was to separate CFAE types in human AF, using monophasic action potentials (MAPs) to map local refractoriness in AF and multipolar catheters to map activation sequence.MAP and adjacent activation sequences at 124 biatrial sites were studied in 18 patients prior to AF ablation (age 57 ± 13 years, left atrial diameter 45 ± 8 mm). AF cycle length, bipolar voltage, and spectral dominant frequency were measured to characterize types of CFAE.CFAE were observed at 91 sites, most of which showed discrete MAPs and (1) pansystolic local activity (8%); (2) CFAE after AF acceleration, often with MAP alternans (8%); or (3) nonlocal (far-field) signals (67%). A fourth CFAE pattern lacked discrete MAPs (17%), consistent with spatial disorganization. CFAE with discrete MAPs and pansystolic activation (consistent with rapid localized AF sites) had shorter cycle length (P.05) and lower voltage (P.05) and trended to have higher dominant frequency than other CFAE sites. Many CFAEs, particularly at the septa and coronary sinus, represented far-field signals.CFAEs in human AF represent distinct functional types that may be separated using MAPs and activation sequence. In a minority of cases, CFAEs indicate localized rapid AF sites. The majority of CFAEs reflect far-field signals, AF acceleration, or disorganization. These results may help to interpret CFAE during AF substrate mapping.

Background Once chamber geometry is determined, the EnSite 3000 noncontact mapping system can create a voltage map during a single cardiac cycle. The EnSite uses an inverse solution to the Laplace equation to process the amplified far-field signals from the noncontact catheter. This process creates a three-dimensional endocardial potential map from a single cardiac cycle. Dynamic substrate mapping (DSM) is an algorithm designed to identify conduction boundaries, such as myocardial scars based on voltage distribution within the corresponding chamber. Objective The purpose of this study was to investigate the correlation between DSM- and magnetic resonance imaging (MRI)-determined scar areas and to identify a suitable DSM voltage threshold. Methods A total of eight dogs were studied. Four healthy foxhounds underwent ligation of the left anterior descending coronary artery. Evidence of myocardial infarction, including ECG changes and elevated cardiac troponin T levels, was noted in all animals. Cardiac MRI scan was performed 29 ± 2 days after ligation of the left anterior descending coronary artery. Subsequently, noncontact mapping of the left ventricle was obtained in each dog, and myocardial infarction size was determined using DSM at different filter settings. As a control group, another four foxhounds underwent sham thoracotomy/pericardiotomy. Results A significant linear correlation of infarction size using DSM compared with MRI measurements was found at the filter setting "peak negative 34%" ( P = .001, r=0.99). Mean relative infarction size was 15.9% ± 4.5% with DSM and 16.0% ± 4.2% with MRI. Compared with the sham group, a significant reduction in left ventricular ejection fraction was found after ligation of the left anterior descending coronary artery (51.0% ± 3.8% vs 69.2% ± 5.9%, P=.002). Pathoanatomic studies were performed to confirm the measured infarct dimensions. No scars were detectable in sham-operated dogs using DSM or MRI. Conclusion Noncontact mapping allows identification of scar tissue within the left ventricle. An excellent correlation was observed between DSM–scar surface and MRI-determined scar size. Identifying and marking these areas can be useful when planning an ablation strategy in the clinical setting of ischemic heart disease.

a mean procedure time of 122 42 min (range 75-246 min). In 5/50 patients common atrial flutter reoccured within one month after cryoablation. Successful reablation using radiofrequency (RF) energy was performed in all of them. In 30/32 recurrence free patients, who gave final consent to invasive control stimulation, persistency of BCB was verified. In 2 patients recovery of isthmus conduction was detectable. Including the relapses 81.1% of the patients (30/37) showed persistency of BCB. Cryo applications were painless in general. No procedural complications were observed. Conclusions: Cryoablation of the CTI using the large tip catheter is feasible and safe in the treatment of common atrial flutter. Acute and short-term success rates are comparable to those reported for RF ablation. Besides short term clinical success the persistency of BCB one month after cryoablation proves efficacy of cryoablation technique.