An improved reporter identifies ruxolitinib as a potent and cardioprotective CaMKII inhibitor.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) hyperactivity causes cardiac arrhythmias, a major source of morbidity and mortality worldwide. Despite proven benefits of CaMKII inhibition in numerous preclinical models of heart disease, translation of CaMKII antagonists into humans has been stymied by low potency, toxicity, and an enduring concern for adverse effects on cognition due to an established role of CaMKII in learning and memory. To address these challenges, we asked whether any clinically approved drugs, developed for other purposes, were potent CaMKII inhibitors. For this, we engineered an improved fluorescent reporter, CaMKAR (CaMKII activity reporter), which features superior sensitivity, kinetics, and tractability for high-throughput screening. Using this tool, we carried out a drug repurposing screen (4475 compounds in clinical use) in human cells expressing constitutively active CaMKII. This yielded five previously unrecognized CaMKII inhibitors with clinically relevant potency: ruxolitinib, baricitinib, silmitasertib, crenolanib, and abemaciclib. We found that ruxolitinib, an orally bioavailable and U.S. Food and Drug Administration-approved medication, inhibited CaMKII in cultured cardiomyocytes and in mice. Ruxolitinib abolished arrhythmogenesis in mouse and patient-derived models of CaMKII-driven arrhythmias. A 10-min pretreatment in vivo was sufficient to prevent catecholaminergic polymorphic ventricular tachycardia, a congenital source of pediatric cardiac arrest, and rescue atrial fibrillation, the most common clinical arrhythmia. At cardioprotective doses, ruxolitinib-treated mice did not show any adverse effects in established cognitive assays. Our results support further clinical investigation of ruxolitinib as a potential treatment for cardiac indications.

CaMKII as a Therapeutic Target in Cardiovascular Disease.

CaMKII (the multifunctional Ca2+ and calmodulin-dependent protein kinase II) is a highly validated signal for promoting a variety of common diseases, particularly in the cardiovascular system. Despite substantial amounts of convincing preclinical data, CaMKII inhibitors have yet to emerge in clinical practice. Therapeutic inhibition is challenged by the diversity of CaMKII isoforms and splice variants and by physiological CaMKII activity that contributes to learning and memory. Thus, uncoupling the harmful and beneficial aspects of CaMKII will be paramount to developing effective therapies. In the last decade, several targeting strategies have emerged, including small molecules, peptides, and nucleotides, which hold promise in discriminating pathological from physiological CaMKII activity. Here we review the cellular and molecular biology of CaMKII, discuss its role in physiological and pathological signaling, and consider new findings and approaches for developing CaMKII therapeutics.

The response to cardiac resynchronization therapy in LMNA cardiomyopathy.

AIMS: Cardiac implantable electronic device (CIED) therapy is fundamental to the management of LMNA cardiomyopathy due to the high frequency of atrioventricular block and ventricular tachyarrhythmias. We aimed to define the role of cardiac resynchronization therapy (CRT) in impacting heart failure in LMNA cardiomyopathy. METHODS AND RESULTS: From nine referral centres, LMNA cardiomyopathy patients who underwent CRT with available pre- and post-echocardiograms were identified retrospectively. Factors associated with CRT response were identified (defined as improvement in left ventricular ejection fraction [LVEF] ≥5% 6 months post-implant) and the associated impact on the primary outcome of death, implantation of a left ventricular assist device or cardiac transplantation was assessed. We identified 105 patients (mean age 51 ± 10 years) undergoing CRT, including 70 (67%) who underwent CRT as a CIED upgrade. The mean change in LVEF ∼6 months post-CRT was +4 ± 9%. A CRT response occurred in 40 (38%) patients and was associated with lower baseline LVEF or a high percentage of right ventricular pacing prior to CRT in patients with pre-existing CIED. In patients with a European Society of Cardiology class I guideline indication for CRT, response rates were 61%. A CRT response was evident at thresholds of LVEF ≤45% or percent pacing ≥50%. There was a 1.3 year estimated median difference in event-free survival in those who responded to CRT (p = 0.04). CONCLUSION: Systolic function improves in patients with LMNA cardiomyopathy who undergo CRT, especially with strong guideline indications for implantation. Post-CRT improvements in LVEF are associated with survival benefits in this population with otherwise limited options.

Metabolic heterogeneous zone assessed by 18 FDG-PET is predictive of postablation mortality in patients with ventricular tachycardia.

PURPOSE: We sought to study the predictive value of the metabolic heterogeneous zone (HZ) as determined by 18 Fluorodeoxyglucose (18 FDG) positron emission tomography (PET) viability studies in ventricular tachycardia (VT) patients. METHODS: PET studies utilizing 82 Rubidium (82 Rb) tracer for perfusion and 18 FDG tracer for viability were analyzed using PMOD (PMOD Technologies) and further analyzed using 684-segment plots. 18 FDG uptake was normalized to the area with maximal perfusion on the rest 82 Rb study. Metabolic scar, HZ, and healthy segments were defined with perfusion-normalized 18 FDG uptake between 0%-50%, 50%-70%, and >70%, respectively. RESULTS: Thirty-four VT patients (age, 63 ± 12 years) were evaluated with 18 FDG-PET viability study. Most (n = 31) patients underwent VT ablation. Patients were categorized to HZ < median versus HZ ≥ median based on a median HZ area size of 21.0 cm2 . HZ size was significantly larger in the deceased group than the alive group (35.2 cm2 vs. 18.1 cm2 , p = .01). Deaths were significantly higher in HZ ≥ 21 cm2 group than HZ < 21 cm2 group (58.8% vs. 11.8%, p = .005). Survival analysis showed significantly higher mortality in the HZ ≥ 21 cm2 group than the HZ < 21 cm2 group (HR = 4.1, 95% CI: 1.3-12.6, p = .016). In a multivariable analysis, HZ was found to be an independent predictor for all-cause mortality (HR = 1.07, 95% CI: 1.02-1.12, p = .01) CONCLUSIONS: Increased HZ size of myocardium was associated with increased mortality. Metabolic HZ quantification may be of value in risk stratification and management of ischemic and nonischemic patients with VT.

Excessive O-GlcNAcylation Causes Heart Failure and Sudden Death.

BACKGROUND: Heart failure is a leading cause of death worldwide and is associated with the rising prevalence of obesity, hypertension, and diabetes. O-GlcNAcylation (the attachment of O-linked ß-N-acetylglucosamine [O-GlcNAc] moieties to cytoplasmic, nuclear, and mitochondrial proteins) is a posttranslational modification of intracellular proteins and serves as a metabolic rheostat for cellular stress. Total levels of O-GlcNAcylation are determined by nutrient and metabolic flux, in addition to the net activity of 2 enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Failing myocardium is marked by increased O-GlcNAcylation, but whether excessive O-GlcNAcylation contributes to cardiomyopathy and heart failure is unknown. METHODS: We developed 2 new transgenic mouse models with myocardial overexpression of OGT and OGA to control O-GlcNAcylation independent of pathologic stress. RESULTS: We found that OGT transgenic hearts showed increased O-GlcNAcylation and developed severe dilated cardiomyopathy, ventricular arrhythmias, and premature death. In contrast, OGA transgenic hearts had lower O-GlcNAcylation but identical cardiac function to wild-type littermate controls. OGA transgenic hearts were resistant to pathologic stress induced by pressure overload with attenuated myocardial O-GlcNAcylation levels after stress and decreased pathologic hypertrophy compared with wild-type controls. Interbreeding OGT with OGA transgenic mice rescued cardiomyopathy and premature death, despite persistent elevation of myocardial OGT. Transcriptomic and functional studies revealed disrupted mitochondrial energetics with impairment of complex I activity in hearts from OGT transgenic mice. Complex I activity was rescued by OGA transgenic interbreeding, suggesting an important role for mitochondrial complex I in O-GlcNAc-mediated cardiac pathology. CONCLUSIONS: Our data provide evidence that excessive O-GlcNAcylation causes cardiomyopathy, at least in part, attributable to defective energetics. Enhanced OGA activity is well tolerated and attenuation of O-GlcNAcylation is beneficial against pressure overload-induced pathologic remodeling and heart failure. These findings suggest that attenuation of excessive O-GlcNAcylation may represent a novel therapeutic approach for cardiomyopathy.

Oxidized CaMKII and O-GlcNAcylation cause increased atrial fibrillation in diabetic mice by distinct mechanisms.

Diabetes mellitus (DM) and atrial fibrillation (AF) are major unsolved public health problems, and diabetes is an independent risk factor for AF. However, the mechanism(s) underlying this clinical association is unknown. ROS and protein O-GlcNAcylation (OGN) are increased in diabetic hearts, and calmodulin kinase II (CaMKII) is a proarrhythmic signal that may be activated by ROS (oxidized CaMKII, ox-CaMKII) and OGN (OGN-CaMKII). We induced type 1 (T1D) and type 2 DM (T2D) in a portfolio of genetic mouse models capable of dissecting the role of ROS and OGN at CaMKII and global OGN in diabetic AF. Here, we showed that T1D and T2D significantly increased AF, and this increase required CaMKII and OGN. T1D and T2D both required ox-CaMKII to increase AF; however, we did not detect OGN-CaMKII or a role for OGN-CaMKII in diabetic AF. Collectively, our data affirm CaMKII as a critical proarrhythmic signal in diabetic AF and suggest ROS primarily promotes AF by ox-CaMKII, while OGN promotes AF by a CaMKII-independent mechanism(s). These results provide insights into the mechanisms for increased AF in DM and suggest potential benefits for future CaMKII and OGN targeted therapies.

Location, variations, and predictors of epicardial fat mapping using multidetector computed tomography to assist epicardial ventricular tachycardia ablation.

BACKGROUND: A significant number of ventricular tachycardia circuits are located close to the epicardial surface and are amendable to epicardial ablation. Epicardial fat often interferes with substrate mapping and ablation, though little is known regarding the distribution of fat and its fluctuation with the cardiac cycle. METHODS: We studied 40 patients who underwent a 64-slice multidetector computed tomography in order to describe patterns of epicardial fat distribution, variation during cardiac cycle, and clinical predictors of epicardial fat. Multiplanar reconstructions were analyzed during systole and diastole in six cross-sections. Epicardial fat thickness was measured across multiple wall segments in each view. RESULTS: Epicardial fat was found to be thicker in areas overlying coronary vasculature (7.8 ± 2.6 mm vs 3.5 ± 0.9 mm, P = 0.001), along with the right ventricular wall (3.9 ± 0.8 mm vs 2.6 ± 0.6 mm, P = 0.001) and the ventricular base (6.1 ± 1.7 mm vs 4.6 ± 1.6 mm, P < 0.01). Epicardial fat thickness increased 27% during systole as compared to diastole (4.9 ± 2.7 mm vs 6.2 ± 3.0 mm, P = 0.04). Variation with cardiac cycle was most evident along the right ventricular wall (3.9 ± 0.8 mm vs 5.0 ± 1.3 mm, P = 0.001) and nonvascular areas (P = 0.001), especially at the ventricular base (3.7 ± 1.1 mm vs 5.3 ± 1.5 mm, P = 0.001). In multivariate logistic regression, we found that age >50 years (P = 0.031) and coronary artery disease (P = 0.023) were statistically correlated with epicardial fat >5-mm thickness and body mass index > 33 (P = 0.052) nearly so. CONCLUSIONS: Baseline epicardial fat thickness >5 mm is common in areas typically targeted during epicardial ablation and further increases during the cardiac cycle. Simple clinical characteristics can identify patients with >5 mm epicardial fat in which preprocedural computed tomography imaging and three-dimensional fat map reconstruction may facilitate epicardial ablation.

Atrial remodelling in atrial fibrillation: CaMKII as a nodal proarrhythmic signal.

CaMKII is a serine-threonine protein kinase that is abundant in myocardium. Emergent evidence suggests that CaMKII may play an important role in promoting atrial fibrillation (AF) by targeting a diverse array of proteins involved in membrane excitability, cell survival, calcium homeostasis, matrix remodelling, inflammation, and metabolism. Furthermore, CaMKII inhibition appears to protect against AF in animal models and correct proarrhythmic, defective intracellular Ca(2+) homeostasis in fibrillating human atrial cells. This review considers current concepts and evidence from animal and human studies on the role of CaMKII in AF.

Meta-Analysis of the Relation of Ventricular Arrhythmias to All-Cause Mortality After Implantation of a Left Ventricular Assist Device.

Ventricular arrhythmias (VAs) are commonly reported after implantation of left ventricular assist devices (LVADs). Their relation to all-cause mortality and potential risk factors remains unclear. We conducted a meta-analysis of observational studies with the primary objective of evaluating the association of post-LVAD VAs with all-cause mortality at 60, 120, and 180 days. The secondary end point was the association of potential risk factors (cause of cardiomyopathy, indication for LVAD, and history of VA) with mortality in patients with post-LVAD VAs. We searched MEDLINE, Embase, and Cochrane Central from 2001 to 2015. Two reviewers independently searched, selected, and assessed quality of included studies with differences resolved by consensus. Data were collected and analyzed using random- and fixed-effect model, as appropriate, with inverse-variance weighting. Of 2,393 studies identified, 9 observational studies were eligible including 1,179 patients with a mean follow-up of 220 days. Post-LVAD VAs were associated with increased risk of all-cause mortality after adjusting for competing risk factors at 60 days (adjusted odds ratio [OR] 1.91, 95% confidence interval [CI] 1.18 to 3.11, p = 0.001), 120 days (adjusted OR 1.97, 95% CI 1.01 to 3.85, p = 0.05), and 180 days (adjusted OR 2.04, 95% CI 1.01 to 4.15, p = 0.05). Using meta-regression analysis, it was found that only history of VA was a risk factor for mortality after LVAD implantation. In conclusion, post-LVAD VA is associated with an increased risk of all-cause mortality with pre-LVAD VAs acting as a risk factor. This meta-analysis, despite being only hypothesis generating, sets the stage for prospective collection of VA information in a prospective device trial or in the Interagency Registry for Mechanically Assisted Circulatory Support.

Three-dimensional 123I-meta-iodobenzylguanidine cardiac innervation maps to assess substrate and successful ablation sites for ventricular tachycardia: feasibility study for a novel paradigm of innervation imaging.

BACKGROUND: Innervation is a critical component of arrhythmogenesis and may present an important trigger/substrate modifier not used in current ventricular tachycardia (VT) ablation strategies. METHODS AND RESULTS: Fifteen patients referred for ischemic VT ablation underwent preprocedural cardiac (123)I- meta-iodobenzylguanidine ((123)I-mIBG) imaging, which was used to create 3-dimensional (3D) innervation models and registered to high-density voltage maps. 3D (123)I-mIBG innervation maps demonstrated areas of complete denervation and (123)I-mIBG transition zone in all patients, which corresponded to 0% to 31% and 32% to 52% uptake. (123)I-mIBG denervated areas were ≈2.5-fold larger than bipolar voltage-defined scar (median, 24.6% [Q1-Q3, 18.3%-34.4%] versus 10.6% [Q1-Q3, 3.9%-16.4%]; P<0.001) and included the inferior wall in all patients, with no difference in the transition/border zone (11.4% [Q1-Q3, 9.5%-13.2%] versus 16.6% [Q1-Q3, 12.0%-18.8%]; P=0.07). Bipolar/unipolar voltages varied widely within areas of denervation (0.8 mV [Q1-Q3, 0.3-1.7 mV] and 4.0 mV [Q1-Q3, 2.9-5.6 mV]) and (123)I-mIBG transition zones (0.8 mV [Q1-Q3, 0.4-1.8 mV] and 4.6 mV [Q1-Q3, 3.2-6.3 mV]). Bipolar voltages in denervated areas and (123)I-mIBG transition zones were <0.5 mV, 0.5 to 1.5 mV, and >1.5 mV in 35%, 36%, and 29%, as well as 35%, 35%, and 30%, respectively (P>0.05). Successful ablation sites were within bipolar voltage-defined scar (7%), border zone (57%), and areas of normal voltage (36%), but all ablation sites were abnormally innervated (denervation/(123)I-mIBG transition zone in 50% each). CONCLUSIONS: (123)I-mIBG innervation defects are larger than bipolar voltage-defined scar and cannot be detected with standard voltage criteria. Thirty-six percent of successful VT ablation sites demonstrated normal voltages (>1.5 mV), but all ablation sites were within the areas of abnormal innervation. (123)I-mIBG innervation maps may provide critical information about triggers/substrate modifiers and could improve understanding of VT substrate and facilitate VT ablation. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique Identifier: NCT01250912.

Differences in quantitative assessment of myocardial scar and gray zone by LGE-CMR imaging using established gray zone protocols.

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) imaging is the gold standard for myocardial scar evaluation. Heterogeneous areas of scar ('gray zone'), may serve as arrhythmogenic substrate. Various gray zone protocols have been correlated to clinical outcomes and ventricular tachycardia channels. This study assessed the quantitative differences in gray zone and scar core sizes as defined by previously validated signal intensity (SI) threshold algorithms. High quality LGE-CMR images performed in 41 cardiomyopathy patients [ischemic (33) or non-ischemic (8)] were analyzed using previously validated SI threshold methods [Full Width at Half Maximum (FWHM), n-standard deviation (NSD) and modified-FWHM]. Myocardial scar was defined as scar core and gray zone using SI thresholds based on these methods. Scar core, gray zone and total scar sizes were then computed and compared among these models. The median gray zone mass was 2-3 times larger with FWHM (15 g, IQR: 8-26 g) compared to NSD or modified-FWHM (5 g, IQR: 3-9 g; and 8 g. IQR: 6-12 g respectively, p < 0.001). Conversely, infarct core mass was 2.3 times larger with NSD (30 g, IQR: 17-53 g) versus FWHM and modified-FWHM (13 g, IQR: 7-23 g, p < 0.001). The gray zone extent (percentage of total scar that was gray zone) also varied significantly among the three methods, 51 % (IQR: 42-61 %), 17 % (IQR: 11-21 %) versus 38 % (IQR: 33-43 %) for FWHM, NSD and modified-FWHM respectively (p < 0.001). Considerable variability exists among the current methods for MRI defined gray zone and scar core. Infarct core and total myocardial scar mass also differ using these methods. Further evaluation of the most accurate quantification method is needed.

Improved conduction and increased cell retention in healed MI using mesenchymal stem cells suspended in alginate hydrogel.

INTRODUCTION: Mesenchymal stem cells (MSCs) have been associated with reduced arrhythmias; however, the mechanism of this action is unknown. In addition, limited retention and survival of MSCs can significantly reduce efficacy. We hypothesized that MSCs can improve impulse conduction and that alginate hydrogel will enhance retention of MSCs in a model of healed myocardial infarction (MI). METHODS AND RESULTS: Four weeks after temporary occlusion of the left anterior descending artery (LAD), pigs (n = 13) underwent a sternotomy to access the infarct and then were divided into two studies. In study 1, designed to investigate impulse conduction, animals were administered, by border zone injection, 9-15 million MSCs (n = 7) or phosphate-buffered saline (PBS) (control MI, n = 5). Electrogram width measured in the border zone 2 weeks after injections was significantly decreased with MSCs (-30 ± 8 ms, p < 0.008) but not in shams (4 ± 10 ms, p = NS). Optical mapping from border zone tissue demonstrated that conduction velocity was higher in regions with MSCs (0.49 ± 0.03 m/s) compared to regions without MSCs (0.39 ± 0.03 m/s, p < 0.03). In study 2, designed to investigate MSC retention, animals were administered an equal number of MSCs suspended in either alginate (2 or 1 % w/v) or PBS (n = 6/group) by border zone injection. Greater MSC retention and survival were observed with 2% alginate compared to PBS or 1% alginate. Confocal immunofluorescence demonstrated that MSCs survive and are associated with expression of connexin-43 (Cx43) for either PBS (control), 1%, or 2% alginate. CONCLUSIONS: For the first time, we are able to directly associate MSCs with improved impulse conduction and increased retention and survival using an alginate scaffold in a clinically relevant model of healed MI.

Impact of ICD artifact burden on late gadolinium enhancement cardiac MR imaging in patients undergoing ventricular tachycardia ablation.

BACKGROUND: Cardiac magnetic resonance imaging (CMRI) is the gold standard for myocardial scar evaluation. Although ideal for substrate assessment in ventricular tachycardia (VT), most patients have an implantable cardioverter-defibrillator (ICD) at presentation for ablation. This study evaluates the ICD artifact burden during standard late gadolinium enhancement CMRI (LGE-CMRI) evaluation of myocardial scar in VT patients with ICDs. METHODS: Thirty-one patients with ICD and cardiomyopathy underwent LGE-CMRI using 1.5-T magnetic resonance scanner before VT ablation. Using the American Heart Association (AHA) 17-segment model, short-axis LGE series were analyzed for artifact burden localization and assessment. RESULTS: Preablation CMRI was performed in 31 patients with single chamber (n = 13), dual chamber (n = 11), and biventricular (n = 7) ICDs. Pre- and post-MRI ICD parameters were unchanged. All patients had susceptibility artifact and 51.6% (256 of 496) of segments were affected by artifact. The artifact area (178 ± 136 cm(2) ) resulted in an artifact burden of 54 ± 21% of the LV myocardial area (327 ± 15 cm(2) ). The anterior wall was most affected by artifact (89%) compared with 52%, 49%, and 23% in the lateral, septal, and inferior walls, respectively (P < 0.0001). The apical segments had more artifact burden (66%) than the mid (49%) and basal (44%) segments (P = 0.0005). Artifact area correlated with ICD-heart distance on anteroposterior chest radiograph (r = 0.42, P = 0.021) and body mass index (r = -0.48, P = 0.008). CONCLUSIONS: Current clinical LGE-CMRI scar imaging protocols produce ICD artifacts that affect >50% of the LV myocardium and correlate with the ICD-heart distance. This significantly limits the application of CMRI for image-guided VT ablation.

Impact of fluoroscopy unit on the accuracy of a magnet-based electroanatomic mapping and navigation system: an in vitro and in vivo validation study.

INTRODUCTION: During mapping and ablation procedures, the movement of large ferromagnetic items (i.e., fluoroscopic equipment) introduce heterogeneities in the electromagnetic field, which may affect the accuracy of electromagnet-based navigation. We aimed to assess the impact of common periprocedural fluoroscopic equipment movement on the accuracy of an electromagnet-based navigation system. METHODS AND RESULTS: The impact of fluoroscopic equipment movement on the accuracy of the Carto® 3 System (Biosense Webster, Inc., Diamond Bar, CA, USA) was assessed both in vitro (n = 20 patients, phantom model) and in vivo (n = 18 patients). Location recordings were obtained with unchanged catheter position for fluoroscopic equipment rotational movements (RMs) and maximal to closest distance (MD to CD) to phantom/patient. The effects of both single- and biplane fluoroscopy were assessed. In vitro, the movement of fluoroscopic equipment resulted in an average catheter location estimation error of 0.8 mm (interquartile range 0.3-1.3). The maximal location estimation errors with MD to CD movement and RM were 2.3 mm and 1.3 mm, respectively. Changing from single-plane to biplane setup resulted in an average location estimation change of 1.5 mm (maximum 2.1). Larger location changes were observed in vivo (2.9 mm vs 0.8 mm, P < 0.0001) with 28.7% of these exceeded 4 mm versus none of the in vitro measurements (P < 0.0001). CONCLUSION: Although fluoroscopy manipulation affected the accuracy of the Carto® 3 System, the in vitro data suggest that these inaccuracies are likely of limited clinical consequences. The larger in vivo inaccuracies are most likely due to nonferromagnetic interferences, such as respiratory or cardiac movements.

Assessment of ventricular tachycardia scar substrate by intracardiac echocardiography.

BACKGROUND: Intracardiac echocardiography (ICE) is increasingly used to guide complex ablation procedures. This study aimed to assess the scar substrate of ventricular tachycardia (VT) by ICE in patients undergoing VT ablation. METHODS: In 22 patients undergoing VT ablation (10 ischemic, 12 nonischemic), the Biosense CARTOSOUND module (Biosense Webster, Diamond Bar, CA, USA) was used for three-dimensional reconstruction of the ventricles. The characteristics and appearance with ICE imaging of voltage-defined scar zones (bipolar voltage <0.5 mV), border zones (0.5-1.5 mV), and normal myocardium (>1.5 mV) on electroanatomic maps were evaluated. The standard image analysis software Image J (National Institutes of Health, Bethesda, MD, USA) was used to analyze signal intensity (mean pixel signal intensity unit [SIU]) and heterogeneity (standard deviation of signal intensity in analyzed area) on ICE images. RESULTS: A total of 83 myocardial areas were analyzed from two-dimensional ICE images (15 scars, 31 border zones, and 37 normal). Voltage-defined scar zones had increased signal intensities compared to border zones (149 SIU vs 104 SIU, P < 0.0001) and normal myocardium (88 SIU, P < 0.0001). Border zones were more likely to have heterogeneous densities compared to normal myocardium (standard deviation of signal intensity 20 SIU vs 12 SIU, P < 0.0001). In receiver-operator characteristic analyses, signal intensity ≥ 137 SIU differentiated scar from nonscar zones (area under curve 0.91, P < 0.0001). Software-based color enhancement of areas with signal intensity ≥ 137 SIU allowed identification of the VT substrate in all 15 patients with voltage-defined scar zones. CONCLUSIONS: ICE provides important information about the VT anatomical substrate and may have potential to identify areas of scarred myocardium.