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Background— The effects of varying the wavefront of activation on ventricular scar characterization has not been systematically assessed. Methods and Results— Patients referred for ablation of scar-related ventricular tachycardia underwent voltage maps during a minimum of 2 wavefronts of activation. The bipolar and unipolar low-voltage areas were compared, and direct electrogram analysis was performed in regions where discrepancies were seen. Concordance between wavefronts was measured by calculating percentage of overlap between maps. Sixty endocardial voltage maps (360±147 points) were performed in 29 patients during 2 distinct wavefronts, with 3 wavefronts in 7 patients. With median bipolar and unipolar low-voltage areas of 37 and 116 cm 2 , respectively, 22% and 14% variability in median scar area was observed with a different activation wavefront. Concordance between wavefronts was lower in patients with mixed scar compared to those with dense scar (52% [interquartile range, 29%–70%] versus 84% [interquartile range, 71%–87%]), with septal scars exhibiting the lowest concordance [(27% (interquartile range, 21%–56%)]. Among 16 critical sites for ventricular tachycardia, 3 (18%) were in a discordant region of scar, with one of the wavefronts showing voltage >1.5 mV. Conclusions— Significant differences in bipolar and unipolar low-voltage characterization of scar were observed with different ventricular activation wavefronts, particularly in septal locations and in patients without dense scar. In patients with a paucity of dense, low-voltage regions identified during substrate mapping, an alternate activation wavefront may increase the sensitivity to detect arrhythmogenic substrate and critical sites for ventricular tachycardia.

Aims Complex ablation procedures are supported by accurate representation of an increasing variety of electrophysiological and imaging data within electroanatomic mapping systems (EMS). This study aims to develop a novel method for representing multiple complementary datasets on a single cardiac chamber model. Validation of the system and its application to both atrial and ventricular arrhythmias is examined. Methods and results Dot mapping was conceived to display multiple datasets by utilizing quantitative surface shading to represent one dataset and finely spaced dots to represent others. Dot positions are randomized within triangular (surface meshes) or tetrahedral (volumetric meshes) simplices making the approach directly transferrable to contemporary EMS. Test data representing uniform electrical activation (n = 10) and focal scarring (n = 10) were used to test dot mapping data perception accuracy. User experience of dot mapping with atrial and ventricular clinical data is evaluated. Dot mapping ensured constant screen dot density for regions of uniform dataset values, regardless of user manipulation of the cardiac chamber. Perception accuracy of dot mapping was equivalent to colour mapping for both propagation direction (1.5 ± 1.8 vs. 4.8 ± 5.3°, P = 0.24) and focal source localization (1.1 ± 0.7 vs. 1.4 ± 0.5 mm, P = 0.88). User acceptance testing revealed equivalent diagnostic accuracy and display fidelity when compared with colour mapping. Conclusion Dot mapping provides the unique ability to display multiple datasets from multiple sources on a single cardiac chamber model. The visual combination of multiple datasets may facilitate interpretation of complex electrophysiological and imaging data.

Introduction: Cases of ventricular tachycardia (TV) with hemodynamic compromise present a challenge in achieving non-inducibility by radiofrequency catheter ablation (RFCA). We report our experience of VT RFCA facilitated by elective mechanical circulatory support. Methods and results: Five patients with hemodynamically unstable, recurrent ventricular arrhythmias that were unresponsive to medical therapy underwent extracorporeal membrane oxygenation (ECMO) assisted RFCA of scar related VT. All underwent RFCA under general anesthesia and were connected to an ECMO circuit maintained at minimum flow of 1.5 L /min. In case of VT or VF the blood flow of the ECMO circuit was increased to 4 L/min to allow hemodynamic stability and adequate systemic organ perfusion. A total of 8 VTs were observed. In 4 cases, we mapped during VT the critical isthmus was found and ablated. Four VTs were targeted by substrate mapping only. Complete success, defined as non-inducibility with aggressive program stimulation of any VT, was achieved in 4 patients. In a single patient, a non-clinical VT was still inducible. He died of septic shock 24 hour after the procedure. The remaining 4 were free of ventricular arrhythmia as proven by implanted defibrillator interrogation, over a median follow up of 16 months. Conclusion: ECMO implantation for VTRFCA is safe and assists in reaching the desired endpoint of noninducibility. This approach should be considered in high risk patients who may not otherwise tolerate such procedures.

Traditionally, catheter ablation of ventricular tachycardia (VT) consists of mapping the circuit during VT, and using pacing maneuvers to localize critical isthmus of the circuit. However, substrate-guided ablation of VT is a relatively new technique and involves identifying potentially arrhythmogenic regions of myocardium in sinus rhythm and avoids the need for mapping during VT. In this short editorial article, we aimed to discuss substrate mapping of VT.

Characterization of the Critical Isthmus in VT in TOF.The complexity of postoperative ventricular reentrant tachycardias may limit success of catheter ablation. The objective of this analysis was to compare the usefulness of dynamic substrate mapping (DSM) versus color-coded isopotential mapping of the noncontact mapping system for the identification of the critical diastolic pathway of postoperative ventricular reentrant tachycardias (VT) after surgical repair of tetralogy of Fallot (TOF).Postoperative VT had been studied applying isopotential maps with the noncontact mapping system EnSite in 7 patients, and radiofrequency current lesion lines had been applied across the shortest isthmus to target during sinus rhythm. Data of the noncontact mapping system were reanalyzed applying the DSM algorithm. For DSM, a 2-Hz filter and color settings between 0 mV and 50% of peak negative voltage (PNV) with autofocus turned off were used. DSM was initially applied over the QRS complex duration during sinus rhythm. Abnormal myocardium was defined as35-40% of PNV. DSM was subsequently applied to ventricular diastole during the final 33% of VT cycle length. Areas with70% of PNV within this time frame were to identify the critical diastolic pathway.Applying DSM, the critical diastolic pathway of the VT was identified in all 7 patients that corresponded to the regions targeted for ablation.By focusing the time reference to electrical diastole, when the VT wavefront is moving through the low-voltage area, the region of greatest relative voltage could be highlighted, which corresponded to the diastolic pathway. (J Cardiovasc Electrophysiol, Vol. 23, pp. 930-937, September 2012).

Objectives This study investigated the impact on recurrences of 2 different substrate approaches for the treatment of these arrhythmias. Background Catheter ablation of electrical storms (ES) for ventricular arrhythmias (VAs) has shown moderate long-term efficacy in patients with ischemic cardiomyopathy. Methods Ninety-two consecutive patients (81% male, age 62 ± 13 years) with ischemic cardiomyopathy and ES underwent catheter ablation. Patients were treated either by confining the radiofrequency lesions to the endocardial surface with limited substrate ablation (Group 1, n = 49) or underwent endocardial and epicardial ablation of abnormal potentials within the scar (homogenization of the scar, Group 2, n = 43). Epicardial access was obtained in all Group 2 patients, whereas epicardial ablation was performed in 33% (14) of these patients. Results Mean ejection fraction was 27 ± 5. During a mean follow-up of 25 ± 10 months, the VAs recurrence rate of any ventricular tachycardia (VTs) was 47% (23 of 49 patients) in Group 1 and 19% (8 of 43 patients) in Group 2 (log-rank p = 0.006). One patient in Group 1 and 1 patient in Group 2 died at follow-up for noncardiac reasons. Conclusions Our study demonstrates that ablation using endo-epicardial homogenization of the scar significantly increases freedom from VAs in ischemic cardiomyopathy patients.

Introduction: Substrate mapping is evolving as a potential strategy for atrial fibrillation ablation. Defining scar borders and functional boundaries is typically under taken with bipolar electrodes. Catheter orientation affects electrogram (EGM) signal amplitude due to an orientation dependence of bipoles. We developed orientation independent Omnipolar Technology (OT) and compared OT EGM amplitude with traditional bipolar (Bi) methods. Methods: Four anesthetized swine were studied in 6 sessions with a 3D mapping system and a multielectrode OT ablation catheter placed in RA and LA locations in 4 rhythms. With the OT catheter in a stable location, 30 successive atrial beats were acquired. OT electrodes provided bipole (Bi) as well as OT signals along both activation (OTa) and surface normal (OTn) directions. Peak to peak amplitudes (Vpp) of OT and Bi signals were compared for magnitude and consistency. Results: As shown in the table, OT signal amplitudes over all atrial locations and rhythms were greater than traditional bipole amplitudes. The coefficients of variation for signal amplitude over successive cardiac beats were substantially less for OTa and OTn (*p < 0.01 with respect to Bi) than for Bi, reflecting electrode pair orientation effects. Conclusions: Distinct electrogram signals were resolved by OT along physiologic (activation) and anatomic (surface normal) directions. Catheter orientation independent OT signal amplitudes were more self-consistent and reliable than those from orientation dependent bipolar electrode pairs. Omnipolar technology approaches may permit more accurate and specific definition of substrate and thus catheter ablation of arrhythmias.

Introduction: Bipolar voltage mapping detects areas of scar and guides ablation of VT. The role of endocardial unipolar voltage mapping is not well defined. We examined the endo-epicardial substrate in a mixed cohort of patients with structural heard disease (SHD) to determine whether an endocardial unipolar low voltage area predicts the presence and location of an epicardial scar. Results: Data from 24 consecutive patients with SHD (11 ICM, 6 NICM, 3 HCM, 2 ARVC, 1 myocarditis, 1 Brugada) with a detailed (mean points per map 200) combined endocardial-epicardial substrate mapping were retrospectively reviewed. Maps were obtained using a 3D mapping system (CARTO 3) and normal thresholds used were ≤1.5 mV for bipolar voltage, and ≤5.5 (RV) or ≤8.3 mV (LV) for unipolar voltage. Mapping was performed in the LV in 17 patients, in the RV in 6 patients, in both in 1 patient. An endocardial unipolar low voltage area was found in 21/25 maps. In 12/21 maps there was no corresponding epicardial scar, while in 3/4 cases an epicardial scar was detected despite a negative unipolar map (PPV=43%, NPV=25%, P=NS; Fig. 1). In the 9 cases with both positive endocardial unipolar and epicardial bipolar maps, the epicardial scar was found in the corresponding ventricular region of the endocardial low-voltage area, although unipolar area had a tendency to overestimate the area of the scar (115 vs 95 cm 2 ). Conclusion: In this series of patients with SHD, analysis of unipolar voltage maps could not reliably predict the epicardial arrhythmogenic substrate. There is a modest correlation between areas of endocardial unipolar low voltage and epicardial scars (57% of patients with an abnormal unipolar map had a normal epicardial substrate). Moreover, an epicardial substrate cannot be safely excluded based on a normal unipolar endocardial map. Fig. 1 Abnormal bipolar epicardial map (left) with corresponding normal unipolar endocardial map (right) in a patient with ARVC. Pink dots represent area of defragmentation.

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.

We report a patient with non-ischemic dilated cardiomyopathy presenting with an electrical storm because of a poorly tolerated monomorphic ventricular tachycardia. Electroanatomical mapping revealed a scar restricted to the epicardium, whereas the endocardial voltage map was completely normal. Epicardial catheter ablation based on substrate mapping and limited pace and entrainment mapping eliminated the tachycardia.

A 72-year-old man with ischemic cardiomyopathy was admitted for the treatment of ventricular tachycardia (VT). Because his VT was poorly tolerated hemodynamically, substrate mapping was performed. The map revealed the presence of low-voltage areas in the inferolateral wall of the LV. Late potentials (LPs) were recorded during sinus rhythm, and pacing at the site revealed a good pacemap for targeting the VT. Delivery of radiofrequency (RF) current to the area where LPs were recorded rendered the targeted VT noninducible. After RF delivery, dissociation of the LPs with an interval of 3140ms was documented during sinus rhythm.

Catheter ablation of hemodynamically unstable ventricular tachycardia (VT) relies on substrate mapping of sites critical for reentry. Late potentials (LP), commonly seen in post-infarction scars, reflect areas of myocardium where conduction is slowed and interrupted by fibrosis (1,2). Although LPs are not specific for critical isthmuses, they are highly sensitive as a guide for targeting ablation in patients with ischemic cardiomyopathy (ICM) (3–5). The prevalence and value of LPs as ablation targets in patients with nonischemic cardiomyopathy (NICM) remains unknown. Analysis of human explanted hearts with dilated cardiomyopathy has revealed fibrosis, myocyte disarray, and membrane abnormalities.(6,7) Fractionated electrograms in patients with NICM have been attributed to lines of activation block from fibrosis, resulting in nonuniform conduction.(8) However, scar in NICM differs from infarct scar with less confluence, a basal predilection, and less endocardial involvement.(9–11) The purpose of this study was to compare the characteristics and prevalence of LPs within scar tissue in patients with NICM and ICM and to assess their value as ablation targets.

The ablation of ventricular tachycardia (VT) can be achieved using anatomically guided approaches using differentiated mapping and ablation techniques. The aim of this study was to evaluate the efficacy of limited linear ablation in the VT exit region identified during sinus rhythm mapping alone. One hundred fifteen consecutive patients presenting for ablation of post-myocardial infarction VT were included. After induction of the target VT during invasive electrophysiology, left ventricular substrate mapping during sinus rhythm to identify scar and border zone on the basis of endocardial bipolar voltage was performed. The exit site of the target VT was regionalized by a simplified vector pace mapping approach and targeted using limited linear ablation within the scar border zone. Seventy-seven percent of all inducible VT was successfully ablated. In 71 patients (62%), no sustained VT was inducible at the end of ablation procedure (complete success). During a median follow-up period of 16 + or - 10 months, 89 patients (77%) had no documented sustained ventricular arrhythmia. Seven patients (2%) had recurrences of the initially ablated VT, and 16 (14%) had new-onset VT. Patients with complete success had a significantly lower number of ventricular arrhythmia reoccurrences than patients with incomplete ablation success (11% vs 37%, p = 0.002). In conclusion, postinfarct VT was effectively ablated in 97% of patients without mapping during ongoing VT using a simplified regional linear ablation approach targeting the scar border zone. Freedom from any ventricular arrhythmia was achieved in 77% of patients during midterm follow-up.

An inexpensive and rapid technique for mapping instream habitat of navigable rivers is needed by natural resource professionals. Unlike more expensive side scan sonar devices, the Humminbird® Side Imaging system employs a boat-mounted transducer enabling the survey of shallow, rocky streams. This device can be used to obtain high resolution, georeferenced images of underwater habitat. We developed a technique employing geographic information systems (GIS) to transform raw sonar images to fit the configuration of a stream channel. The end product is a GIS layer that can be interpreted to map instream habitat. We demonstrated this approach by mapping substrate and large woody debris in a southwest Georgia stream, and evaluated the technique through a comprehensive accuracy assessment. An overall classification accuracy of 77% was observed for substrate mapping and sonar estimates of large woody debris were correlated (r2 = 0.79) with actual wood abundance. Sonar mapping generated estimates of reach and subs...

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— Two principal mechanisms are thought to be responsible for Brugada syndrome (BS): (1) right ventricular (RV) conduction delay and (2) RV subepicardial action potential shortening. This in vivo high-density mapping study evaluated the conduction and repolarization properties of the RV in BS subjects. Methods and Results— A noncontact mapping array was positioned in the RV of 18 BS patients and 20 controls. Using a standard S 1 -S 2 protocol, restitution curves of local activation time and activation recovery interval were constructed to determine local maximal restitution slopes. Significant regional conduction delays in the anterolateral free wall of the RV outflow tract of BS patients were identified. The mean increase in delay was 3-fold greater in this region than in control ( P =0P r 2 , was greater in BS patients versus controls (0.94±0.04 versus 0.89±0.09 [mean±SD]; P 1 was 3.86 versus controls. Five episodes of provoked ventricular tachycardia arose from wave breaks originating from RV outflow tract slow-conduction zones in 5 BS patients. Conclusions— Marked regional endocardial conduction delay and heterogeneities in repolarization exist in BS. Wave break in areas of maximal conduction delay appears to be critical in the initiation and maintenance of ventricular tachycardia. These data indicate that further studies of mapping BS to identify slow-conduction zones should be considered to determine their role in spontaneous ventricular arrhythmias.

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.

Background: We investigated the efficacy and safety of strict voltage-based substrate mapping and radiofrequency catheter ablation (SV-substrate-map ablation) in patients with electrical storm. Methods and Results: SV-substrate-map ablation was performed in 15 patients suffering from multiple appropriate shocks (6.0 ± 3.8/day) from implantable cardioverter defibrillators (ICDs). Strict voltage criteria were defined as: non-arrhythmogenic areas, >0.6mV; low voltage areas, >0.1 to ≤0.6 mV; and scar, ≤0.1 mV. Using an electroanatomic mapping system, catheter ablation was performed at every possible arrhythmogenic region inside the low voltage areas. Further, we presented a review of the literature and investigated the published data on substrate-mapping guided ablation for electrical storm. After repeat endocardial ablation procedures in 4 patients and an epicardial approach in one, the targeted ventricular tachycardias (VTs) were successfully ablated, and the electrical storms were completely controlled in all. During a mean follow-up period of 801 ± 409 days, only one VT followed by an appropriate ICD shock was observed. No potential complications occurred during the procedure or follow-up. Our results were comparable or better than that of previous substrate-mapping guided ablation studies. Conclusion: SV-substrate-mapping ablation may be effective and safe for resolving serious clinical situations and prolonging the longevity of ICD devices in patients with electrical storms.

Background— Recurrent ventricular tachycardia (VT) is an important cause of mortality and morbidity late after myocardial infarction. With frequent use of implantable cardioverter-defibrillators, these VTs are often poorly defined and not tolerated for mapping, factors previously viewed as relative contraindications to ablation. This observational multicenter study assessed the outcome of VT ablation with a saline-irrigated catheter combined with an electroanatomic mapping system. Methods and Results— Two hundred thirty-one patients (median LV ejection fraction, 0.25; heart failure in 62%) with recurrent episodes of monomorphic VT (median, 11 in the preceding 6 months) caused by prior myocardial infarction were enrolled. All inducible monomorphic VTs with a rate approximating or slower than any spontaneous VTs were targeted for ablation guided by electroanatomic mapping during sinus rhythm and/or VT. Patients were not excluded for multiple VTs (median, 3 per patient) or unmappable VT (present in 69% of patients). Ablation abolished all inducible VTs in 49% of patients. The primary end point of freedom from recurrent incessant VT or intermittent VT after 6 months of follow-up was achieved for 123 patients (53%). In 142 patients with implantable cardioverter-defibrillators before and after ablation for intermittent VT who survived 6 months, VT episodes were reduced from a median of 11.5 to 0 ( P Conclusions— Catheter ablation is a reasonable option to reduce episodes of recurrent VT in patients with prior myocardial infarction, even when multiple and/or unmappable VTs are present. This population remains at high risk for death, warranting surveillance and further study.

Background— X-ray fluoroscopy constitutes the fundamental imaging modality for catheter visualization during interventional electrophysiology procedures. The minimal tissue discriminative capability of fluoroscopy is mitigated in part by the use of electroanatomic mapping systems and enhanced by the integration of preacquired 3-dimensional imaging of the heart with computed tomographic or magnetic resonance (MR) imaging. A more ideal paradigm might be to use intraprocedural MR imaging to directly image and guide catheter mapping procedures. Methods and Results— An MR imaging–based electroanatomic mapping system was designed to assess the feasibility of navigating catheters to the left ventricle in vivo using MR tracking of microcoils incorporated into the catheters, measuring intracardiac ventricular electrograms, and integrating this information with 3-dimensional MR angiography and myocardial delayed enhancement images to allow ventricular substrate mapping. In all animals (4 normal, and 10 chronically infarcted swine), after transseptal puncture under fluoroscopic guidance, catheters were successfully navigated to the left ventricle with MR tracking (13 to 15 frames per second) by both transseptal and retrograde aortic approaches. Electrogram artifacts related to the MR imaging gradient pulses were successfully removed with analog and digital signal processing. In all animals, it was possible to map the entire left ventricle and to project electrogram voltage amplitude maps to identify the scarred myocardium. Conclusions— It is possible to use MR tracking to navigate catheters to the left ventricle, to measure electrogram activity, and to render accurate 3-dimensional voltage maps in a porcine model of chronic myocardial infarction, completely in the MR imaging environment. Myocardial delayed enhancement guidance provided dense sampling of the proximity of the infarct and accurate localization of complex infarcts.

In routine substrate mapping of the left ventricle, an abnormal area is defined as having an amplitude1.5 mV. However, that is usually too large for catheter ablation in post-infarction ventricular tachycardia (VT) and the use of strict voltage criteria may produce better outcomes.Twenty patients with post-infarction VT underwent substrate mapping using an electroanatomic mapping system. Strict voltage criteria were defined as: non-arrhythmogenic area,0.6 mV; low-voltage area (LVA),0.1 toor=0.6 mV; scar,or=0.1 mV. Radiofrequency applications targeted the LVA only, which was 48+/-26 cm(2), 55% smaller than that of the generally targeted area with an amplitudeor=1.5 mV. The prevalence of delayed electrograms (durationor=150 ms) was significantly higher in the LVAs than in the border areas with an amplitude of0.6 toor=1.5 mV (33.2% vs 3.7%, p0.001). With the exception of 2 instances of peri-mitral VT, all VT isthmuses resided within the LVA. During follow-up of 24+/-13 months, 16 patients (80%) have been free of any VT episodes.Catheter ablation targeting LVAs with an amplitudeor=0.6 mV appears to be useful for efficient and effective treatment of post-infarction VT.

Aims To use monophasic action potentials (MAPs) to better assess the rate and the presence of fractionated electrograms during the mapping of atrial fibrillation (AF). Substrate mapping is increasingly central to AF ablation. However, traditional bipolar signals poorly represent waveform shape, making it unclear whether fractionation reflects local waveform variations, true electrogram fragmentation, or noise, and raising issues on whether their spectral dominant frequencies (DFs) accurately estimate AF rate. Methods and results In 28 patients with paroxysmal or persistent AF (left atrial diameters 44 ± 8 mm), we studied 49 epochs of right atrial MAPs during AF. We compared fractionation, spectral and time-domain AF rate estimates using MAPs and bipolar electrograms obtained by filtering the MAPs. Fractionation was overestimated in bipolar rather than MAP electrograms ( P = 0.005) and often reflected artefacts on the MAPs. Conversely, local waveform variability in the MAPs, including alternans or fractionation, was often uniform in the bipolar electrograms. The measured AF cycle length (CL) was accurately represented by the DF of the MAPs ( r = 0.73, P < 0.001) but, due to double counting, not by the DF of bipolar signals ( r = 0.29, P = 0.07). Spectral CL estimates were therefore accurate (≤20 ms from measured CL) for 77% of MAPs but for 45% of bipolar signals only. A novel autocorrelation method better estimated CL in MAPs ( r = 0.92; P < 0.001) and bipoles ( r = 0.82; P < 0.001), with 89 and 77% accuracy, respectively ( P < 0.01). Conclusion Atrial fibrillation organization and rate are better represented by MAPs, which portray fibrillatory waveform shape, than by bipolar recordings. This approach may more reliably portray electrogram variability, fragmentation, and rate for the mapping of AF substrates.

BoNT/F7, one of the seven subtypes of botulinum neurotoxin type F (F1 to F7), is the second-most divergent subtype of this group. Despite sharing >60% identity with BoNT/F1 at both holotoxin and enzymatic domain levels, it requires an N-terminal extended peptide substrate for efficient substrate cleavage, suggesting its unique substrate recognition and specificity mechanism. Substrate mapping and saturation mutagenesis analysis revealed that VAMP2 (20-65) was likely a minimally effective substrate for LC/F7 (light chain of BoNT/F7), and in addition, LC/F7 recognized VAMP2 in a unique way, which differed significantly from that of LC/F1, although both of them share similar substrate binding and hydrolysis mode. LC/F7 utilizes distinct pockets for specific substrate binding and recognition in particular for the B1, B2 and S2 sites recognitions. Our findings provide insights into the distinct substrate recognition features of BoNT subtypes and useful information for therapy development for BoNT/F.

Most patients with structural heart disease referred for ventricular tachycardia ablation have unstable tachycardias not suitable for conventional mapping (ie, entrainment mapping). Substrate-guided mapping and ablation during sinus rhythm are intended to overcome the limitations of conventional mapping and ablation. Substrate ablation permits elimination of multiple ventricular tachycardias irrespective of their inducibility during the procedure or their hemodynamic tolerability. Moreover, the elimination/isolation of the arrhythmogenic substrate identified during sinus rhythm has been associated with better outcomes. There is currently no standardized approach for substrate-guided ablation. This article discusses the main aspects of the proposed techniques and substrate ablation targets.

Article history: Received 15 July 2015 Accepted 1 August 2015 Available online 3 August 2015 3.5 mm irrigated-tip catheter (NaviStar or SmartTouch Thermocool, BiosenseWebster) was used for mapping and ablation. The electroanatomic mapping of the left ventricle was performed using a threedimensional non-fluoroscopic mapping system (CARTO XP and CARTO 3, BiosenseWebster) via a retrograde transaortic approach. Intravenous heparin was administered throughout the procedure, targeting an activated clotting time around 300 s. A detailed substrate mapping during

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.

Catheter ablation is an established therapeutic approach for ventricular tachycardia (VT), especially in patients with drug-refractory VT. Despite advances in modern state-of-the-art ablation techniques and greater operator experience, the VT recurrence rate after ablation still approaches 50% at 6 months in a large series.1 The majority of current VT ablation strategies rely heavily on targeting anatomic and scar-based substrate and include activation and substrate mapping; the latter particularly helpful for patients with hemodynamically unstable or noninducible VT. However, these techniques are limited by multiple technical and nontechnical factors, including challenges posed by the complex 3-dimensional morphology of scar, particularly in an intramyocardial location, possible artifacts because of poor catheter contact, low spatial resolution, and the time-consuming nature of the techniques themselves. Furthermore, VT substrate not only is anatomic and scar-based but also has physiological components, including ischemia, inflammation, metabolism, and autonomic innervation, which are generally not considered when delineating potential targets for VT ablation. These factors may, in part, explain the high rate of VT recurrence after ablation and highlight the need to consider incorporating functional targets such as those available with several noninvasive imaging modalities into electroanatomic mapping to refine targets for catheter ablation of VT.2–4 Article see p 583 In this issue of Circulation: Arrhythmia and Electrophysiology , Klein et al5 present a single-center experience demonstrating the feasibility of integrating iodine-123-labeled- meta -iodobenzylguanidine (123I- m IBG) scintigraphy with voltage mapping for postinfarction VT ablation in 15 patients. Areas defined as denervated by 123I- m IBG were 2.5× larger than scar identified by bipolar voltage mapping. On the contrary, the voltage-defined border zone tended to be larger than the 123I- m IBG transition zone, but this difference was not statistically significant. By bipolar voltage mapping, 36% of VT ablation …

Background The clinical characteristics and prognostic value of early repolarization (ER) in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) and symptomatic ventricular arrhythmias remain unclear. We investigated the prevalence, clinical features, and cardiovascular outcomes of patients with symptomatic ARVD/C and ER. Methods A total of 59 consecutive ARVD/C patients hospitalized for catheter ablation, presenting with and without J-point elevations of ≥0.1mV in at least 2 inferior leads or lateral leads were enrolled. Clinical characteristics, electrophysiological study, substrate mapping, catheter ablation, and future clinical outcomes in a prospective patient registry were investigated. Results ER was observed in 38 patients (64.4%). Among these patients, ER was found in the inferior leads in 18 patients (47.4%), in the lateral leads in 2 patients (5.3%), and in both inferior and lateral leads in 18 patients (47.4%). Patients exhibiting ER were commonly men, had lower right ventricular ejection fraction, had higher incidence of clinical ventricular fibrillation or aborted sudden cardiac death, had more defibrillator implantations, had higher the need of epicardial ablation, and had more major criteria according to the task force criteria. Significant higher incidence of induced ventricular fibrillation and shorter tachycardia cycle length of induced ventricular tachycardia were found during procedure. The recurrence rate of ventricular arrhythmias did not differ between patients with and without ER after catheter ablation. Conclusions A high prevalence of electrocardiographic ER was found among symptomatic ARVD/C patients undergoing catheter ablation. ER in 12-lead ECG is associated with an increased risk of clinical fatal ventricular arrhythmias.

Atrial fibrillation (AF) is the most commonly clinically-encountered arrhythmia. Catheter ablation of AF is mainly based on trigger elimination and modification of the AF substrate. Substrate mapping ablation of complex fractionated atrial electrograms (CFAEs) has emerged to be a promising technique. To improve substrate mapping based on CFAE analysis, automatic detection algorithms need to be developed in order to simplify and accelerate the ablation procedures. According to the latest studies, the level of fractionation has been shown to be promisingly well estimated from CFAE measured during radio frequency (RF) ablation of AF. The nature of CFAE is generally nonlinear and nonstationary, so the use of complexity measures is considered to be the appropriate technique for the analysis of AF records. This work proposes the use of sample entropy (SampEn), not only as a way to discern between non-fractionated and fractionated atrial electrograms (A-EGM), but also as a tool for characterizing the degree of A-EGM regularity, which is linked to changes in the AF substrate and to heart tissue damage. The use of SampEn combined with a blind parameter estimation optimization process enables the classification between CFAE and non-CFAE with statistical significance (p < 0:001), 0.89 area under the ROC, 86% specificity and 77% sensitivity over a mixed database of A-EGM combined from two independent CFAE signal databases, recorded during RF ablation of AF in two EU countries (542 signals in total). On the basis of the results obtained in this study, it can be suggested that the use of SampEn is suitable for real-time support during navigation of RF ablation of AF, as only 1.5 seconds of signal segments need to be analyzed., This work has been supported by the Spanish Ministry of Science and Innovation, Research Project TEC 2009-14222, by the Ministry of Education Youth and Sports of the Czech Republic, the Grant Agency of the Czech Technical University in Prague No. SGS13/203/OHK3/3T/13 and by the Czech Science 300 Foundation post-doctoral GACR research project GACR #P103/11/P106.

Background— Mapping to identify scar-related ventricular tachycardia re-entry circuits during sinus rhythm focuses on sites with abnormal electrograms or pace-mapping findings of QRS morphology and long stimulus to QRS intervals. We hypothesized that (1) these methods do not necessarily identify the same sites and (2) some electrograms are far-field potentials that can be recognized by pacing. Methods and Results— From 12 patients with coronary disease and recurrent ventricular tachycardia undergoing catheter ablation, we retrospectively analyzed electrograms and pacing at 546 separate low bipolar voltage (P Conclusions— Far-field potentials are common in scar areas. Combining analysis of electrogram characteristics and assessment of pace capture may refine identification of substrate targets for radiofrequency ablation.

Objective: To study fluctuations in intracardiac atrial fibrillation (AF) cycle length (CL). Background: Sites of short AF CL may be good ablation targets, and cycle lengthening predicts ablation success. However, the optimum method for measuring AF CL, and its stability, are unclear. We hypothesized that autocorrelation better estimates AF CL than spectral dominant frequency (DF), which is susceptible to double counting, using monophasic action potentials (MAPs) to separate atrial activation from artifact. Methods: In 28 patients with paroxysmal or persistent AF, we analyzed 49 AF epochs using MAPs at the high (HRA) and low (LRA) right atrium. We estimated AF CL over 2 seconds, 10 seconds, and 2 minutes using spectral DF and autocorrelation in MAPs and filtered bipoles. Results: In the HRA, manually measured CL was 167 ± 25 ms. Spectral DF poorly estimated AF CL in bipolar signals (R = 0.31; P = NS), due to double counting, but accurately estimated MAP CL (R = 0.73, P < 0.001). Autocorrelation estimated MAP (R = 0.92; P < 0.001) and bipolar (R = 0.83; P < 0.001) CL, with lower errors than spectral DF (P < 0.0001). Over time, changes in DF consistently preceded reciprocal changes in organization (P < 0.001). Finally, excluding inaccurate spectra, DF and AF organization differed between HRA and LRA over 2 seconds, but correlated over 10 seconds and 2 minutes (P < 0.05). Conclusions: AF CL is better estimated by autocorrelation than spectral DF, particularly for bipoles, and stable when measured for >10 seconds. Notably, changes in AF CL preceded reciprocal changes in organization, yet changes in organization did not precede changes in AF CL. These results may help to interpret AF CL fluctuations.

The Plasmodium falciparum cysteine peptidases FP-2 (falcipain-2) and FP-3 (falcipain-3), members of the papain-like CAC1 family, are essential haemoglobinases and are therefore potential anti-malarial drug targets. To facilitate a rational drug discovery programme, in the current study we analysed the synthetic substrate and model inhibitor profiles of FP-2 and FP-3 as well as BP-2 (berghepain-2), an orthologue from the rodent parasite Plasmodium berghei. With respect to substrate catalysis, FP-2 exhibited a promiscuous substrate profile based around a consensus non-primeside motif, FP-3 was somewhat more restricted and BP-2 was comparatively specific. Substrate turnover for FP-2 was driven by a basic or acidic P1 residue, whereas for FP-3 turnover occurred predominately through a basic P1 residue only, and for BP-2, turnover was again mainly through a basic P1 residue for some motifs and surprisingly a glycine in the P1 position for other motifs. Within these P1 binding elements, additional recognition motifs were observed with subtle nuances that switched substrate turnover on or off through specific synergistic combinations. The peptidases were also profiled against reversible and irreversible cysteine peptidase inhibitors. The results re-iterated the contrasting kinetic behaviour of each peptidase as observed through the substrate screens. The results showed that the substrate and inhibitor preferences of BP-2 were markedly different from those of FP-2 and FP-3. When FP-2 and FP-3 were compared to each other they also displayed similarities and some significant differences. In conclusion, the in vitro data highlights the current difficulties faced by a peptidase directed anti-malarial medicinal chemistry programme where compounds need to be identified with potent activity against at least three peptidases, each of which displays distinct biochemical traits.

Objectives The purpose of this study was to investigate the relationship between the abnormal substrate and peak negative voltage (PNV) in the right atrium (RA) with atypical flutter. Background The impact of a local abnormally low voltage electrogram on the local activation pattern and velocity of atrial flutter (AFL) remains unclear. Methods Twelve patients with clinically documented AFL were included to undergo noncontact mapping of the RA. The atrial substrate was characterized by the: 1) activation mapping; 2) high-density voltage mapping; and 3) conduction velocity along the flutter re-entrant circuit. The normalized PNV (i.e., the relative ratio to the maximal PNV) in each virtual electrode recording was used to produce the voltage maps of the entire chamber. The protected isthmus was bordered by low voltage zones. Results Atypical AFL of the RA was induced by atrial pacing in 12 patients, including 10 upper loop re-entry and 2 RA free wall re-entry flutter. These protected isthmuses were located near the crista terminalis. The mean width of the protected isthmus was 1.7 ± 0.3 cm and mean voltage at the isthmus was −0.91 ± 0.39 mV. The conduction velocities within these paths were significantly slower than outside the path (0.30 ± 0.18 m/s vs. 1.14 ± 0.41 m/s, respectively; p = 0.004). The ratiometric PNV of 37.6% of the maximal PNV had the best cut-off value to predict slow conduction, with a high sensitivity (92.3%) and specificity (85.7%). Conclusions Characterization of the RA substrate in terms of the unipolar PNV is an effective predictor of the slow conduction path within the critical isthmus of the re-entrant circuit.

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.

The electrical storm (ES) is defined as a state of electrical instability with three or more sustained ventricular arrhythmias (VAs) occurring within twenty-four hours, which needs intravenous antiarrhythmic medications and frequent defibrillation. Recently, radiofrequency catheter ablation evolved as a sole therapy to terminate ES in patients with ICD, and the survival has been reported to be improved with successful ablation during follow-up. In this review, we briefly summarize substrate mapping and substrate ablation strategy in patients with ES, and discuss the reason of recurrence after ablation.

Introduction: Catheter ablation of ventricular tachycardia (VT) in remote myocardial infarction (MI) often requires excessive mapping procedures. Documentation of the electrical substrate via electrogram amplitude may help to identify regions of altered myocardium resembling exit areas of reentrant VTs. Methods and Results: A patient with multiple symptomatic monomorphic VTs (biventricular ICD, remote MI) underwent electroanatomic substrate mapping (CARTO™) for VT ablation. Regions of scar (bipolar electrogram amplitudes ≤0.5 mV), normal myocardium (≥1.5 mV), and “altered” myocardium (0.5–1.5 mV) were identified. Ablation was directed to regions with “altered” myocardium based on pace map correlation. After ablation the clinical VT did not reoccur. The patient died due to worsening of heart failure 7 days afterward. During postmortal evaluation specified sites of electroanatomic mapping were correlated to histopathological findings. Annotated scar areas were documented to consist of areas with massive fibrosis (≥80% of mural composition). Ablations were found to span through regions with intermediate fibrosis (21–79%) mapped as “altered” myocardium. Ablation produced transmural coagulation necrosis of mesh-like fibrotic tissue with interspersed remnants of myocardial cells up to a maximum depth of 7.0 mm. Subendocardial intramural bleedings were universal findings 7 days after ablation. Conclusions: Electroanatomic substrate mapping for VT ablation sufficiently identified regions of scar and normal myocardium. Regions with bipolar electrogram amplitudes between 0.5 and 1.5 mV were found to correlate to areas of “intermediate” fibrosis (21–79%) with only remnant strands of myocardial cells and were identified as target region for ablation. Cooled-tip endocardial radiofrequency ablation lead to transmural coagulation necrosis up to a depth of 7.0 mm.

OBJECTIVES The purpose of this study was to correlate infarct age with characteristics of the endocardial electrograms (EGM) obtained in patients undergoing mapping procedures for postinfarction ventricular tachycardia (VT). BACKGROUND Experimental studies have demonstrated that infarct age influences EGM duration in the subepicardial left ventricle (LV). The relationship between infarct age and endocardial EGM characteristics has not been investigated in patients with postinfarction VT. METHODS In a consecutive series of 23 patients with a history of remote infarction (range 1 to 31 years) and VT, endocardial LV mapping was performed with an electroanatomical mapping system (CARTO, Biosense Webster Inc., Diamond Bar, California) during sinus rhythm. Electrogram morphology and width were analyzed and correlated with infarct age. Isthmus sites of the VT re-entry circuits were identified by entrainment mapping and related to the results of substrate mapping. RESULTS There was a significant correlation between infarct age and width of the bipolar endocardial EGM during baseline rhythm in the peri-infarct zone (r = 0.84; p < 0.0001). Increasing infarct age was associated with progressive activation delays in the scar and with isolated potentials separated by an isoelectric interval, the duration of which also correlated with infarct age (r = 0.77; p < 0.001). Among all endocardial sites, the VT isthmus sites displayed the most delay and broadest EGMs during sinus rhythm. CONCLUSIONS The presence of broad, fractionated EGMs and isolated potentials indicates a healed myocardial infarction; the older the infarction, the broader the EGM width. Remodeling over time alters the electrophysiologic properties of the peri-infarct tissue.

Ventricular Tachycardia and the Scar Border Zone. Introduction: It is unknown if identification of scar border zones by electroanatomical mapping correlates with successful ablation sites determined from mapping during ventricular tachycardia (VT) post-myocardial infarction (MI). We sought to assess the relationship between successful ablation sites of hemodynamically stable post-MI VTs determined by mapping during VT with the scar border zone defined in sinus rhythm. Methods and Results: Forty-six patients presenting with hemodynamically stable, mappable monomorphic VT post-MI and who had at least one such VT successfully ablated were prospectively included in the study. In each patient, VT was ablated by targeting regions during VT that exhibited early activation, ′ isolated mid-diastolic potentials, and concealed entrainment suggesting a critical isthmus site. Prior to ablation, a detailed sinus-rhythm CARTO voltage map of the left ventricle was obtained. A voltage

Purpose of review Patients with ventricular tachycardia are subject to frequent recurrences and antiarrhythmic drug therapy has been disappointing. Catheter ablation offers an alternative means of controlling ventricular tachycardia. Recent findings The origin and pathophysiology of ventricular tachycardia are being defined for newly recognized types of ventricular tachycardia as well as scar-related ventricular tachycardias. The approach to mapping and ablation of ventricular tachycardia depends on the nature of the arrhythmia substrate, which is largely determined by the underlying heart disease. Focal origin ventricular tachycardias often occur in patients without structural heart disease. The right ventricular and left ventricular outflow tracts are common locations. Ablation is usually successful unless the focus is epicardial in location or in close proximity to the ostia of a coronary artery. The reentry path for idiopathic left ventricular reentrant ventricular tachycardia is now defined. In patients with heart disease, most ventricular tachycardias are scar related, with areas of fibrous tissue forming the border for reentry paths. Substrate mapping defines areas of scar, abnormal conduction, and reentry circuit exits during sinus rhythm. Ablation of multiple ventricular tachycardias and unstable ventricular tachycardias performed largely during sinus rhythm is often possible. Ablation is usually adjunctive therapy to an ICD in these patients. Epicardial mapping and ablation are needed in some patients. Summary Ablation is a reasonable alternative to antiarrhythmic drug therapy for controlling frequent ventricular tachycardia episodes in many patients. Further technological advances can be anticipated.

Nearshore substrate characteristics such as texture (grain size) and composition, available surface area, pattern, distribution, and relative stability are critical parameters that determine how biological organisms (and communities) utilize those substrates during different life stages. Geo-referenced sidescan-sonar data are used in combination with traditional sampling techniques and Geographic Information System (GIS) technologies to map substrate contacts and aquatic habitat distributions within Great Lakes nearshore areas. New methods are developed that includes area change analysis and centroid analysis to quantitatively assess net change in substrate area and evaluate relative substrate stability. An Area Change Ratio (ACR) can be calculated for individual substrate polygons (patch analysis) or groups of substrate polygons (area analysis) of the same substrate type. Areas of relative stability are represented by ACR values near zero. Areas of moderate stability are represented by values ranging between 0.2 and 0.5 and highly unstable areas are represented by values of 0.5 or greater. Substrate centroids or “centers of mass” are also calculated and can be used to quantitatively integrate change in substrate area and the location of individual substrate polygons or groups of polygons within a survey area. Comparison of centroid movement provides a quantitative measure of the magnitude and direction of change in substrate area through time. These techniques address many of the spatial and temporal limitations associated with more traditional approaches, e.g., shore-normal profiling, detailed bathymetric surveys, and repetitive sampling of bottom materials, and yet can be combined with these traditional approaches to develop a more detailed understanding of nearshore habitat distribution and stability.

Ablation of ventricular tachycardias in arrhythmogenic right ventricular dysplasia (ARVD-VTs) still remains a clinical challenge. We reported the value of abnormal electrophysiological substrate mapping for guiding ablation of ARVD-VTs using a non-contact mapping system.Dynamic substrate mapping was performed in three male ARVD patients during sinus rhythm. The sites of earliest activation, exit point and activation sequence were mapped for each induced VT. Three different patterns of substrates were determined in 3 patients and located in right ventricular outflow tract, anterior right ventricular wall, and anterolateral right ventricular wall, respectively. Five different clinical VTs (mean CL, 348 +/- 65 ms) were induced. Of 5 VTs, three originated from or near the boundary of substrate, and two had a remote origin. One VT conducted through the substrate. Linear ablations were created between the sites of the earliest ventricular activation and the VT exit point, or across the critical isthmus. The five clinical VTs were successfully ablated with a median of 17 radiofrequency applications. One patient was treated with amiodarone for a VT not clinically observed. There were no VT recurrences during 8.6 months of follow-up.Defining the abnormal anatomical VT substrates is useful for understanding the mechanisms of ARVD-VTs and determining an ablation strategy. Linear ablation across a critical isthmus or between the early activation and the exit point can effectively cure these arrhythmias.

Objectives We report on the initiation of ventricular fibrillation (VF) storm in patients with ischemic cardiomyopathy (ICM) and the results of targeted ablation to treat VF storm. Background Monomorphic premature ventricular contractions (PVCs) have been shown to initiate VF in patients without structural heart disease. Methods A total of 29 patients with ICM and documented VF initiation were identified. In 21 patients, VF storm was controlled with antiarrhythmic drugs and/or treatment of heart failure. Eight patients with VF (mean 52 ± 25 episodes) refractory to medical management required ablation. All patients underwent three-dimensional electroanatomical mapping using CARTO (Biosense-Webster Inc., Diamond Bar, California), and PVCs were mapped when present. Scarred areas were identified using voltage mapping. Results Monomorphic PVCs initiated VF in all 29 identified patients. Five of eight patients requiring ablation had frequent PVCs that allowed PVC mapping. The earliest activation site was consistently located in the scar border zone. The PVCs were always preceded by a Purkinje-like potential (PLP). Ablation was successfully performed at these sites. In three patients, infrequent PVCs prevented mapping, but PLPs were recorded around the scar border. Ablation targeting these potentials along the scar border was successfully performed. During follow-up (10 ± 6 months), one patient had a single VF episode and another developed sustained, monomorphic ventricular tachycardia. There was no recurrence of VF storm. Conclusions Ventricular fibrillation in ICM is triggered by monomorphic PVCs originating from the scar border zone with preceding PLPs; targeting these PVCs may prevent VF recurrence. In the absence of PVCs, both substrate mapping and ablation appear to be equally effective.