Nontransmural Scar Research Articles

Assessing the field of view of multisize electrodes in ischemic cardiomyopathy by validating against ex-vivo high resolution cardiac magnetic resonance

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Leiden University Medical Centre Background Substrate identification after myocardial infarction (MI) relies on voltage mapping. Early reperfusion results in non-transmural scar (NTS). Narrow-spaced microelectrodes (ME) are thought to have a limited field of view (FOV). The role of ME for delineation of NTS is unclear. Purpose To evaluate mapping with multi-size electrodes for identifying NTS, validated against high-resolution ex-vivo cardiac magnetic resonance imaging (HR-LGE-CMR). Methods Nine swine with early reperfusion MI underwent endocardial electroanatomical voltage mapping (EAVM) with the QDOT catheter which incorporates three ME in the 3.5mm tip electrode. HR-LGE-CMR (0.3mm slices) were obtained and merged with EAVM. At each EAVM point a transmural cylinder (5mm radius) was projected on the CMR and the volume of viable myocardium (VM) in the cylinder quantified (Otsu method). Unipolar (UV) and bipolar (BV) voltages from conventional (c) and microelectrodes (µ) were related to VM. Cut-off values for normal myocardium were based on 5th percentiles of areas without fibrosis. Results In each swine 220 (IQR 216-260) mapping points were collected (total 2322 points). Cut-off for normal myocardium were 3.18 mV, 0.85 mV, 3.28mV and 1.93 mV for UVc, BVc, UVµ and BVµ, respectively. Wall thickness (WT) was reduced in areas with fibrosis vs. no fibrosis (5.4mm, IQR 3.2- 6.9 vs. 7.4mm, IQR 5.3 - 9.6). All voltages were reduced at sites with fibrosis vs. no fibrosis (UVs 4.4mV vs. 6.8mV; BVc 1.2mV vs. 2.1mV; UVµ 2.5mV vs. 5.5mV, and BVµ 2.9mV vs. 5.4mV, all p<0.001). For areas with any fibrosis, all voltages increased with increasing WT up to the maximal WT of 13mm (fig. 1). Similarly, all voltages increased with an increase in VM volumes from >200mm3 to >600 mm3 (equivalent to a cylinder with h=7.64mm) (fig. 2) with the strongest correlation for UVµ (r=0.47). Below a volume of 200mm3 VM voltages did not correlate significantly with VM. Conclusion In NTS, UVc, BVc, and, notably, BVµ and UVµ increase with increasing WT and increasing transmural volume of VM, with the biggest role perhaps laid out for UVµ to estimate transmural VM. EAVM cannot accurately delineate areas with the lowest amount of VM, potentially due to insufficient far field cancellation in NTS. Both these findings argue against a limited FOV of ME.

PO-679-08 ASSESSING THE FIELD OF VIEW OF MULTISIZE ELECTRODES IN ISCHEMIC CARDIOMYOPATHY BY VALIDATING AGAINST EX-VIVO HIGH RESOLUTION CARDIAC MAGNETIC RESONANCE

Substrate identification after myocardial infarction (MI) relies on voltage mapping. Early reperfusion results in non-transmural scar (NTS). Narrow-spaced microelectrodes (ME) are thought to have a limited field of view (FOV). The role of ME for delineation of NTS is unclear.

Can nuclear imaging accurately detect scar in ischemic cardiac resynchronization therapy candidates?

Accurate scar assessment is crucial in cardiac resynchronization therapy (CRT) candidates, since its presence is a negative predictor for CRT response. Therefore, we assessed the performance of different PET parameters to detect scar in CRT candidates. Twenty-nine CRT candidates underwent 18F-fluorodeoxyglucose (18F-FDG)-PET/computed tomography (CT), resting 13N-NH3-PET/CT and cardiac magnetic resonance (CMR) prior to CRT implantation. Segmental 18F-FDG uptake, late 13N-NH3 uptake and absolute myocardial blood flow (MBF) were evaluated for scar detection using late gadolinium enhancement (LGE) CMR as reference. A receiver operator characteristic (ROC) area under the curve (AUC) ≥0.8 indicated a good accuracy of the methods evaluated. Scar was present in 111 of 464 segments. None of the approaches could reliably identify segments with nontransmural scar, except for 18F-FDG uptake in the lateral wall (AUC 0.83). Segmental transmural scars could be detected with all methods (AUC ≥ 0.8), except for septal 18F-FDG uptake and MBF in the inferior wall (AUC < 0.8). Late 13N-NH3 uptake was the best parameter for transmural scar detection, independent of its location, with a sensitivity of 80% and specificity of 92% using a cutoff of 66% of the maximum tracer activity. Late 13N-NH3 uptake is superior to 13N-NH3 MBF and 18F-FDG in detecting transmural scar, independently of its location. However, none of the tested PET parameters was able to accurately detect nontransmural scar.

Late Gadolinium Enhancement Cardiovascular Magnetic Resonance Assessment of Substrate for Ventricular Tachycardia With Hemodynamic Compromise.

Background: The majority of data regarding tissue substrate for post myocardial infarction (MI) VT has been collected during hemodynamically tolerated VT, which may be distinct from the substrate responsible for VT with hemodynamic compromise (VT-HC). This study aimed to characterize tissue at diastolic locations of VT-HC in a porcine model.Methods: Late Gadolinium Enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging was performed in eight pigs with healed antero-septal infarcts. Seven pigs underwent electrophysiology study with venous arterial-extra corporeal membrane oxygenation (VA-ECMO) support. Tissue thickness, scar and heterogeneous tissue (HT) transmurality were calculated at the location of the diastolic electrograms of mapped VT-HC.Results: Diastolic locations had median scar transmurality of 33.1% and a median HT transmurality 7.6%. Diastolic activation was found within areas of non-transmural scar in 80.1% of cases. Tissue activated during the diastolic component of VT circuits was thinner than healthy tissue (median thickness: 5.5 mm vs. 8.2 mm healthy tissue, p < 0.0001) and closer to HT (median distance diastolic tissue: 2.8 mm vs. 11.4 mm healthy tissue, p < 0.0001). Non-scarred regions with diastolic activation were closer to steep gradients in thickness than non-scarred locations with normal EGMs (diastolic locations distance = 1.19 mm vs. 9.67 mm for non-diastolic locations, p < 0.0001). Sites activated late in diastole were closest to steep gradients in tissue thickness.Conclusions: Non-transmural scar, mildly decreased tissue thickness, and steep gradients in tissue thickness represent the structural characteristics of the diastolic component of reentrant circuits in VT-HC in this porcine model and could form the basis for imaging criteria to define ablation targets in future trials.

ST-segment resolution as a marker for severe myocardial fibrosis in ST-segment elevation myocardial infarction

ObjectiveTo investigate the relationship between ST-segment resolution (STR) and myocardial scar thickness after percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI).MethodsForty-two STEMI patients with single-branch coronary artery stenosis or occlusion were enrolled. ST-segment elevations were measured at emergency admission and at 24 h after PCI. Late gadolinium-enhanced cardiac magnetic resonance imaging (CMR-LGE) was performed 7 days after PCI to evaluate myocardial scars. Statistical analyses were performed to assess the utility of STR to predict the development of transmural (> 75%) or non-transmural (< 75%) myocardial scars, according to previous study.ResultsThe sensitivity and specificity of STR for predicting transmural scars were 96% and 88%, respectively, at an STR cut-off value of 40.15%. The area under the curve was 0.925. Multivariate logistic proportional hazards regression analysis disclosed that patients with STR < 40.15% had a 170.90-fold higher probability of developing transmural scars compared with patients with STR ≥ 40.15%. Pearson correlation and linear regression analyses showed STR percentage was significantly associated with myocardial scar thickness and size.ConclusionSTR < 40.15% at 24 h after PCI may provide meaningful diagnostic information regarding the extent of myocardial scarification in STEMI patients.

Assessing the ability of substrate mapping techniques to guide ventricular tachycardia ablation using computational modelling

BackgroundIdentification of targets for ablation of post-infarction ventricular tachycardias (VTs) remains challenging, often requiring arrhythmia induction to delineate the reentrant circuit. This carries a risk for the patient and may not be feasible. Substrate mapping has emerged as a safer strategy to uncover arrhythmogenic regions. However, VT recurrence remains common. GoalTo use computer simulations to assess the ability of different substrate mapping approaches to identify VT exit sites. MethodsA 3D computational model of the porcine post-infarction heart was constructed to simulate VT and paced rhythm. Electroanatomical maps were constructed based on endocardial electrogram features and the reentry vulnerability index (RVI - a metric combining activation (AT) and repolarization timings to identify tissue susceptibility to reentry). Since scar transmurality in our model was not homogeneous, parameters derived from all signals (including dense scar regions) were used in the analysis. Potential ablation targets obtained from each electroanatomical map during pacing were compared to the exit site detected during VT mapping. ResultsSimulation data showed that voltage cut-offs applied to bipolar electrograms could delineate the scar, but not the VT circuit. Electrogram fractionation had the highest correlation with scar transmurality. The RVI identified regions closest to VT exit site but was outperformed by AT gradients combined with voltage cut-offs. The performance of all metrics was affected by pacing location. ConclusionsSubstrate mapping could provide information about the infarct, but the directional dependency on activation should be considered. Activation-repolarization metrics have utility in safely identifying VT targets, even with non-transmural scars.

221Evaluating the ability of different substrate mapping techniques to identify scar-related ventricular tachycardia circuits using computational modelling

Abstract Funding Acknowledgements National Institute for Health Research; British Heart Foundation; and The Wellcome Trust and Engineering and Physical Sciences Research Council. Background Accurate identification of targets for catheter ablation therapy of ventricular tachycardias (VTs) in the postinfarction heart remains a significant challenge. Identification of such targets often requires VT-induction to delineate the entry/exit points of the reentrant circuit sustaining the VT. However, inducibility may not be possible due to hemodynamic instability. In this scenario, substrate ablation strategies can still be performed to uncover the arrhythmogenic substrate during sinus or paced rhythm. However, substrate mapping may fail to accurately delineate the reentrant circuit resulting in VT recurrence after the procedure. Purpose To use computer simulations to compare the ability of different electroanatomical maps constructed following typical substrate ablation strategies to identify the VT exit site. Methods An image-based computational model of the porcine post-infarction left ventricle was constructed to simulate VT and paced rhythm. Electroanatomical maps were constructed based on the following features extracted from electrograms computed on the endocardial surface: activation time (AT), bipolar electrogram amplitude, signal fractionation and the reentry vulnerability index (RVI - a metric combining activation and repolarization timings to identify tissue susceptibility to reentry). Potential ablation targets during substrate mapping were compared for: highest 5% AT gradient; lowest 5% bipolar signal amplitudes; areas with fragmented signals (more than one peak); and lowest 5% RVI. The minimum distance, d, between the manually identified VT exit site and the targets was measured. Results The RVI performed better than the other metrics at detecting the VT exit site (see Figure). The minimum distance between sites of lowest RVI and the exit site was 3.2mm compared to 13.1mm and 15.9mm in traditional AT and voltage maps, respectively. As the scar was not transmural, parameters derived from all electrograms (including those located on dense scar regions) were used to construct the electroanatomical maps. This improved the performance of the RVI significantly, making it more specific than the other metrics as can be seen in the Figure. Conclusions Among all metrics investigated here, the RVI identified the vulnerable region closest to VT exit site. This finding suggests that activation-repolarization metrics may improve the detection of pro-arrhythmic regions without having to induce VT. Moreover, the RVI may be particularly well suited for detecting vulnerable regions within non-transmural scars. Abstract Figure. VT and Substrate Mapping

Multisize Electrodes for SubstrateIdentification in IschemicCardiomyopathy: Validation by Integration of Whole Heart Histology.

This study sought to evaluate the value of combined electrogram (EGM) information provided by simultaneous mapping using micro- and conventional electrodes in the identification of post-myocardial infarction ventricular tachycardia substrate. Ventricular tachycardias after myocardial infarction are related to scars with complex geometry. Scar delineation and ventricular tachycardia substrate identification relies on bipolar voltages (BV) and EGM characteristics. Early reperfusion therapy results in small, nontransmural scars, the details of which may not be delineated using 3.5 mm tip catheters. Nine swine with early reperfusion myocardial infarction were mapped using Biosense Webster's QDOT Micro catheter, incorporating 3 microelectrodes at the tip of the standard 3.5 mm electrode. Analysis of EGM during sinus rhythm, right ventricular pacing, and short-coupled right ventricular extrastimuli was performed. The swine were sacrificed and mapping data were projected onto the heart. Transmural biopsies (n=196) corresponding to mapping points were obtained, allowing a head-to-head comparison of EGM recorded by micro- and conventional electrodes with histology. To identify scar areas using standard electrodes, unique cutoff values of unipolar voltage<5.44mV, BV<1.27mV (conventional), and BV<2.84mV (microelectrode) were identified. Combining the information provided by unipolar voltage and BV mapping, the sensitivity of scar identification was increased to 93%. Micro-EGM were better able to distinguish small near-fields corresponding to a layer of viable subendocardium than conventional EGM were. The combined information provided by multisize electrode mapping increases the sensitivity with which areas of scar are identified. EGM from microelectrodes, with narrower spacing, allow identification of near-fields arising from thin subendocardial layer and layers activated with short delay obscured in EGM from conventional mapping catheter.

Relationship of myocardial hibernation, scar, and angiographic collateral flow in ischemic cardiomyopathy with coronary chronic total occlusion

BackgroundThe relationship between myocardial viability and angiographic collateral flow is not fully elucidated in ischemic cardiomyopathy (ICM) with coronary artery chronic total occlusion (CTO). We aimed to clarify the relationship between myocardial hibernation, myocardial scar, and angiographic collateral flow in these patients. Methods and ResultsSeventy-one consecutive ICM patients with 122 CTOs and 652 dysfunctional segments within CTO territories were retrospectively analyzed. Myocardial hibernation (perfusion-metabolism mismatch) and the extent of 18F-fluorodeoxyglucose (FDG) abnormalities were assessed using 99mTc-sestamibi and 18F–FDG imaging. Myocardial scar was evaluated by late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) imaging. Collateral flow observed on coronary angiography was assessed using Rentrop classification. In these patients, neither the extent nor frequency of myocardial hibernation or scar was related to the status of collateral flow. Moreover, the matching rate in determining myocardial viability was poor between any 2 imaging indices. The extent of 18F-FDG abnormalities was linearly related to the extent of LGE rather than myocardial hibernation. Of note, nearly one-third (30.4%) of segments with transmural scar still had hibernating tissue. Hibernation and non-transmural scar had higher sensitivity (63.0% and 66.7%) than collateral flow (37.0%) in predicting global functional improvement. ConclusionsAngiographic collateral cannot accurately predict myocardial viability, and has lower sensitivity in prediction of functional improvement in CTO territories in ICM patients. Hence, assessment of myocardial viability with non-invasive imaging modalities is of importance. Moreover, due to the lack of correlation between myocardial hibernation and scar, these two indices are complementary but not interchangeable.

Targeting the Hidden Substrate Unmasked by Right Ventricular Extrastimulation Improves Ventricular Tachycardia Ablation Outcome After Myocardial Infarction.

This study sought to determine whether ablation of hidden substrate unmasked by right ventricular extrastimulation (RVE) improves ablation outcome of post-myocardial infarction (MI) ventricular tachycardia (VT). In patients with small or nontransmural scars after MI, part of the VT substrate may be functional and,in addition, masked by high-voltage far-field signals arising from adjacent normal myocardium. In 60 consecutive patients, systematic analysis of electrograms recorded from the presumed infarct area was performed during sinus rhythm, RV pacing at 500 ms, and during a short-coupled RV extrastimulus. Sites showing low-voltage, near-field potentials with evoked conduction delay in response to RVE were targeted. In 37 (62%) patients, ablation target sites located in areas with normal voltage during sinus rhythm were unmasked by RVE (hidden substrate group). These patients had better left ventricular function (36 ± 11% vs. 26 ± 12%; p= 0.003), smaller electroanatomical scars (<1.5 mV), and smaller dense scars (<0.5 mV) (median 59 and 14 cm2 vs. 82 and 44 cm2; p= 0.044 and p= 0.003) than did those in whom no hidden substrate was identified (overt substrate group). During a median follow-up of 16 months, 13 (22%) patients had VT recurrence. Patients with hidden substrate had a lower incidence of VT recurrence (12-month VT-free survival 89% vs. 50% in patients with overt substrate; p=0.005). Compared with a historical cohort of 90 post-MI patients matched for left ventricular function and electroanatomical scar area, in whom no RVE was performed, patients in the hidden substrate group had a higher 1-year VT-free survival (89% vs. 73%; p= 0.039). Hidden substrate ablation unmasked by RVE improves ablation outcome in post-MI patientswithsmall or nontransmural scars.

Association of mean platelet volume with presence of non-viable myocardium in ischaemic cardiomyopathy.

Parameters derived from complete blood count, such as mean platelet volume (MPV), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR), have recently been proposed as measures of inflammation in addition to C-reactive protein (CRP), a classical inflammatory marker. Significant association of these parameters with atherosclerosis and complications have increasingly been reported. The aim of the study is to evaluate the relationship between these parameters and the presence of myocardial viability assessed with positron emission tomography (PET) in patients with ischaemic cardiomyopathy (ICM). A total of 122 ICM patients who had undergone PET were enrolled in this study. The patients were dichotomised depending on the presence of transmural scar. Group 1 consisted of 21 patients who had transmural scar tissue only, who were accepted as the group having non-viable myocardium. Group 2 consisted of 101 patients who had hibernation and/or non-transmural scar, who were accepted as the group having viable myocardium. Haematological parameters within 30 days of PET imaging were retrospectively analysed. There were no significant differences between the two groups regarding values of white blood cell, neutrophil, lymphocyte, platelet, haemoglobin, red cell distribution width, CRP, PLR, and NLR. Patients with non-viable myocardium have significantly higher levels of MPV (p = 0.002). In multiple logistic regression analysis, MPV (odds ratio [OR] = 0.373, 95% confidence interval [CI] 0.20-0.69, p = 0.002), was identified as an independent predictor of non-viable myocardium. In receiver-operator characteristic (ROC) analysis, a cut-point of 8.19 identified patients with non-viable myocardium (area under curve: 0.72, 95% CI 0.60-0.84). An MPV value greater than 8.19 demonstrated a sensitivity of 76% and a specificity of 55%. \ CONCLUSIONS: The present study showed that MPV is an inexpensive, clinical, and routinely measurable parameter that is associated with the presence of viable myocardium in ICM.

Scar voltage threshold determination using ex vivo magnetic resonance imaging integration in a porcine infarct model: Influence of interelectrode distances and three-dimensional spatial effects of scar

Studies analyzing optimal voltage thresholds for scar detection with electroanatomic mapping frequently lack a gold standard for comparison. The purpose of this study was to use a porcine infarct model with ex vivo magnetic resonance imaging (MRI) integration to characterize the relationship between interelectrode spacing and bipolar voltage thresholds and examine the influence of 3-dimensional scar on unipolar voltages. Thirty-two combined endocardial-epicardial electroanatomic maps were created in 8 postinfarct porcine subjects (bipolar 2-mm, 5-mm, and 8-mm interelectrode spacing and unipolar) for comparison with ex vivo MRI. Two thresholds were compared: (1) 95% normal distribution and (2) best fit to MRI. Direct electrogram analysis was performed in regions across from MRI-defined scar and adjacent to scar border zone. A linear increase in optimal thresholds was observed with wider bipole spacing. The 95% thresholds for scar were lower than MRI-matched thresholds with moderate sensitivity for nontransmural scar (54% endo, 63% epi). Unipolar endocardial scar area exceeded MRI-defined scar, resulting in mismatched false scar in 5 of 8 (63%). Endocardial and epicardial unipolar voltages were lower than normal in regions adjacent and across from scar. Variations in interelectrode spacing necessitate tailored bipolar voltage thresholds to optimize scar detection. Statistical 95% thresholds appear to be conservative and not fully sensitive for the detection of scar defined by high-resolution ex vivo MRI. In the presence of endocardial scar, unipolar mapping to quantitatively characterize epicardial scar may be overly sensitive due to 3-dimensional spatial averaging.

Relation of Functional Echocardiographic Parameters to Infarct Scar Transmurality by Magnetic Resonance Imaging

Identification of viable but dysfunctional myocardium after myocardial infarction is important for management, including the decision for revascularization. Assessment of infarct transmurality (TRM) by late contrast enhancement on magnetic resonance imaging (MRI) is frequently used for this task but has several limitations, particularly its availability. The goal of this study was to compare the value of several simple echocardiographic parameters measured at rest at the bedside for the identification of three degrees of infarct TRM, with contrast-enhanced MRI as the gold standard. In a prospective, single-center study, 41 patients (33 men; mean age, 62 ± 10 years; 32 with ST-segment elevation infarctions) underwent resting echocardiography and contrast-enhanced MRI <5 days after infarction. Wall motion score, preejection velocity by tissue Doppler, and longitudinal, circumferential, and radial peak systolic strain by speckle-tracking-based strain imaging were assessed, and the findings were compared with infarct TRM stratified by contrast-enhanced MRI (no scar, 0% TRM; nontransmural scar, 1%-50% TRM; and transmural scar, 51%-100% TRM). Four hundred segments showed no scar, 125 showed nontransmural scar, and 213 showed transmural scar on contrast-enhanced MRI. The sensitivity and specificity of visual wall motion scoring to detect any scar versus no scar were 71% and 81%, respectively, similar to values for circumferential strain (sensitivity and specificity both 81% with a cutoff of -14.5%). Longitudinal and radial strain performed less well, and the presence of preejection velocity performed distinctly worse (45% and 90%, respectively). The sensitivity and specificity for identifying nontransmural versus transmural infarction was better for circumferential strain (78% and 75%, respectively, with a cutoff of -10.5%) than for the other strain types, preejection velocity (52% and 67%, respectively), or visual wall motion scoring (50% and 81%, respectively, for a score > 2). Visual wall motion analysis alone is able to detect infarcted myocardium but cannot differentiate sufficiently between transmural and nontransmural infarction. This is best achieved at the bedside using speckle-tracking-based circumferential strain.

1030Role of cardiac magnetic resonance and echocardiography prior to cardiac resynchronization therapy

Purpose: Cardiac resynchronization therapy is an established method for treatment of patients with heart failure. Optimal left ventricular lead implantation guided by novel imaging techniques appears to be a promising method to increase the response to this therapy. Methods: 29 patients scheduled for cardiac resynchronization therapy underwent detailed ECHO and cardiac magnetic resonance studies prior to CRT device implantation. The aim of the imaging studies was to determine an optimal pacing site for the left ventricular lead placement. The off-line analysis was performed by two experienced readers in a blinded fashion. CMR was performed on 3T system (Siemens). Cine, late gadolinium enhancement and myocardial tagging sequences were acquired. Image software Segment (Sweden) was used for left ventricular segmentation. Left ventricular wall motion and myocardial scar analysis were performed in all 17 segments . Tagging sequences were analysed with inTag (Universite de Lyon) in short axis slices at basal, mid ventricular and apical levels of the left ventricle. The care was taken to ensure correct alignment of these slices to achieve the same segmentation as with echocardiography. Standard echocardiographic parasternal and apical views were stored and analysed off-line. Left ventricular radial, longitudinal and circumferential strains were assessed using commercially available software (EchoPac 6.1). The cut-off value for regional longitudinal strain was – 4.5% to discriminate between transmural (>50%) and nontransmural (<50%) myocardial scar (Roes S.D., Mollema S.A., Bax J.J., Am J Cardiol 2009;104;312-317). Results: Wall motion analysis was possible in all 493 segments in CMR and in 472 (96%) in echocardiography studies. Mean ejection fraction of the left ventricle was 29 ± 5 % when assessed by echocardiography and 23 ± 9 % in CMR studies (P = 0.0005). The average LV EDVi was 99 ± 21 ml/m2 (ECHO) and 115 ± 32 ml/m2 (CMR) (P = 0.003). Scar transmurality was significantly overestimated by ECHO using the longitudinal strain cut-off -4.5% for discrimination between transmural and nontransmural scar – 2.8 times. The dyssynchrony analysis targeted to define the latest activated LV segment showed significant agreement between the two methods. The exact segments agreement was detected in 19 cases (66%). In 6 cases (21%) targeted segment was ± 1 neighbour segment. Discordance between the latest activated segment was detected in 4 patiens (14 %). Conclusions: We have demonstrated that CMR has a potential to improve diagnostic preoperative assessment in patients with severe heart failure and might be a useful tool for LV dyssynchrony assessment. CMR is an excellent method for scar assessment and is a useful tool for LV strain analysis.

Temporal changes of strain parameters in the progress of chronic ischemia: with comparison to transmural infarction

The aim of this study was to reveal the temporal and spatial changes of strain parameters during the progression of chronic coronary ischemia. Fourteen pigs received occluder implantation to create gradual ischemia (CI), while six pigs underwent a sham surgery (Control). Six pigs after myocardial infarction were also studied (MI). Strain analysis was performed using a speckle-tracking algorithm. Eleven of the 14 animals with occluder implantation had total occlusion of the left anterior descending artery with collaterals at 1 month (early occlusion group), whereas three pigs had occlusion at 3 months (late occlusion group). Both radial strain (RS) and circumferential strain (CS) of ischemic area deteriorated at 1 month in the early occlusion group and remained at the same level throughout the remaining 2 months of the experiment. In the late occlusion group, RS gradually declined, while CS took the same course as Control until the 2 month time point. Thereafter, both metrics reached the same level as the early occlusion group at the time of occlusion. Interestingly, RS in the remote area decreased moderately, whereas CS remained normal in CI pigs. The comparison between CI and MI revealed preserved CS at the ischemic area in CI pigs. Both RS and CS deteriorate by the time total coronary occlusion was established and remain at the same level thereafter. Altered RS in the remote area may be an indicator of remodeling in the non-ischemic area, whereas CS may be useful for distinguishing between transmural and non-transmural scar.

The infarct characteristics on magnetic resonance imaging and ventricular tachycardia: do we see what we need to see?

This editorial refers to ‘The heart rate of ventricular tachycardia following an old myocardial infarction is inversely related to the size of scarring’ by L. Woie et al., on page 864. The underlying mechanism of most ventricular tachycardias (VTs) after myocardial infarction (MI) is reentry involving areas of ventricular scar. Dense fibrous scars alone cannot cause arrhythmias; however, when surrounded by bundles of surviving myocytes in the peri-infarction zone, an arrhythmogenic substrate may arise. Areas of dense fibrosis intersperse with surviving myocardial bundles and form regions of conduction block that define reentry circuit borders. The presence of fibrosis between these surviving bundles prolongs the pathway for impulse propagation, creating slow conduction through the scar.1 The complex structure of these scars is likely to determine reentrant circuit characteristics and thereby VT characteristics.2 Late gadolinium-enhancement cardiac magnetic resonance (LGE-CMR) has increasingly been used to visualize the three-dimensional (3D) geometry of myocardial fibrosis and has become the gold standard for detection of non-transmural scars because of its superior spatial resolution.3 Woie et al .4 have addressed an interesting question of whether myocardial scar characteristics as visualized and defined by LGE-CMR correlate with VT characteristics, specifically with the VT cycle length (VTCL). They hypothesized that the rate of spontaneous VTs is related to the size of the post-infarction scar or its border zone. They studied 24 patients with remote MI and indication for implantation of an internal cardioverter-defibrillator for primary or secondary prevention who underwent LGE-CMR for quantification of left ventricular (LV) volumes, function, size of core infarct, and size of the infarct border zone prior to device implantation. Patients were followed every 3 months during the first year after implantation. Twenty out of 24 patients had VTs with a median VTCL of 325 ms (range 239–438 ms). None of …

Transmurality of scar influences the effect of a hybrid-intervention with autologous bone marrow cell injection and aortocoronary bypass surgery (MNC/CABG) in patients after myocardial infarction

BackgroundCell therapy (CTx) is a strategy to support cardiac regeneration after myocardial infarction (MI). Thus far, clinical studies provided mixed results. Here, we investigated whether transmurality of the infarct may play a relevant role. Methods18 patients (63±3years, 15 male) undergoing elective coronary artery bypass graft (CABG) surgery 2.2±0.7months post MI participated. 10 had transmural and 8 non-transmural infarct scars assessed by Tc-99m-MIBI Single-Photon Emission Computed Tomography (SPECT) and F18-FDG-Positron-Emission-Tomography (PET). During surgery, 10ml of sternal bone marrow were obtained, mononuclear cells (MNC) were isolated. At the end of surgery MNC were injected into the infarctions' center and border zones (10 injections, 2ml total, 6.6±1.3×107 MNC). ResultsNo major complications attributable to cell therapy were observed. The sizes of non-transmural scars were reduced at 3 and 24months after treatment (7.7±1.1% and 5.5±1.8 vs. 17.5±4.9%, P=0.05 and P=0.04), while transmural scars remained unchanged (23.5±2.6% and 23.8±3.2 vs. 23.5±2.6%, P>0.99 and P=0.95). A trend towards improved LVEF was seen in patients with non-transmural scars (MRI: 48.8±5.1% vs. 30.6±8.7%, P=0.3; SPECT: 54.1±3.1 vs. 41.0±4.0, P=0.086), but not in patients with transmural scars (MRI: 36.7±3.9 vs. 34.3±5.0, P=0.63, SPECT: 37.8±3.1 vs. 37.9±2.3%, P=0.96). ConclusionsA single hybrid intervention of MNC recovery, purification and injection with CABG-surgery (MNC/CABG) may be an attractive modality for cell therapy. However, no regeneration of avital transmural scar tissue seems to occur, while the contribution of MNC to improved perfusion in non-transmural myocardial infarct scars remains to be determined.

Head-to-head comparison of contrast-enhanced magnetic resonance imaging and electroanatomical voltage mapping to assess post-infarct scar characteristics in patients with ventricular tachycardias: real-time image integration and reversed registration

Substrate-based ablation of ventricular tachycardia (VT) relies on electroanatomical voltage mapping (EAVM). Integration of scar information from contrast-enhanced magnetic resonance imaging (CE-MRI) with EAVM may provide supplementary information. This study assessed the relation between electrogram voltages and CE-MRI scar characteristics using real-time integration and reversed registration. Fifteen patients without implantable cardiac defibrillator (14 males, 64 ± 9 years) referred for VT ablation after myocardial infarction underwent CE-MRI. Contours of the CE-MRI were used to create three-dimensional surface meshes of the left ventricle (LV), aortic root, and left main stem (LM). Real-time integration of CE-MRI-derived scar meshes with EAVM of the LV and aortic root was performed using the LM and the CARTO surface registration algorithm. Merging of CE-MRI meshes with EAVM was successful with a registration error of 3.8 ± 0.6 mm. After the procedure, voltage amplitudes of each mapping point were superimposed on the corresponding CE-MRI location using the reversed registration matrix. Infarcts on CE-MRI were categorized by transmurality and signal intensity. Local bipolar and unipolar voltages decreased with increasing scar transmurality and were influenced by scar heterogeneity. Ventricular tachycardia reentry circuit isthmus sites were correlated to CE-MRI scar location. In three patients, VT isthmus sites were located in scar areas not identified by EAVM. Integration of MRI-derived scar maps with EAVM during VT ablation is feasible and accurate. Contrast-enhanced magnetic resonance imaging identifies non-transmural scars and infarct grey zones not detected by EAVM according to the currently used voltage criteria and may provide important supplementary substrate information in selected patients.

Nontransmural Scar Detected by Magnetic Resonance Imaging and Origin of Ventricular Tachycardia in Structural Heart Disease

Contrast-enhanced magnetic resonance imaging (CMR) identifies scar tissue as an area of delayed enhancement (DE). The scar region might be the substrate for ventricular tachycardia (VT). However, the relationship between the occurrence of VT and the characteristics of scar tissue has not been fully studied. CMR was performed in 34 patients with monomorphic, sustained VT and dilated cardiomyopathy (DCM, n = 18), ischemic cardiomyopathy (ICM, n = 10), or idiopathic VT (IVT, n = 6). The VT exit site was assessed by a detailed analysis of the QRS morphology, including bundle branch block type, limb lead polarity, and precordial R-wave transition. On CMR imaging, the transmural score of each of the 17 segments was assigned, using a computer-assisted, semiautomatic technique, to measure the DE areas. Segmental scars were classified as nontransmural when DE was 1-75% and transmural when DE was 76-100% of the left ventricular mass in each segment. A scar was detected in all patients with DCM or ICM. Nontransmural scar tissue was often found at the VT exit site, in patients with DCM or ICM. In contrast, no scar was found in patients with IVT. CMR clarified the characteristics and distribution of scar tissue in patients with structural heart disease, and the presence and location of scar tissue might predict the VT exit site in these patients.

The Impact of Myocardial Viability on the Clinical Outcome of Cardiac Resynchronization Therapy

Around 30% of patients do not respond to cardiac resynchronization therapy (CRT). Nonischemic cardiomyopathy has been identified as an independent predictor of response to CRT, probably due to the absence of compact scar. The relationship between cardiac scar, ischemia, and hibernation (both at the left-ventricular pacing site and as a total burden) and response to CRT was studied in patients with ischemic cardiomyopathy using the perfusion-viability positron emission tomography (PET) test. Sixty-six patients with ischemic cardiomyopathy and traditional criteria for CRT were included. All patients underwent PET scan prior to CRT. Using PET, the amount and location of scarred, ischemic, and hibernating myocardium were characterized. No revascularization was indicated. Responders were defined by an improvement of left-ventricular ejection fraction (LVEF) >or= 5% and/or New York Heart Association (NYHA) class >or= 1 degree. During a mean follow-up of 26.2 +/- 22.2 months, there was a significant improvement in NYHA class and reverse remodeling in patients with the LV lead inserted remotely from the scar. However, reverse remodeling of a similar degree was present also in patients with extensive scarring including the lateral wall. The presence of ischemia, hibernation, or nontransmural scar at the pacing-site did not significantly modify the outcome of CRT as compared with viable myocardium. There were only 38% of CRT-nonresponders. Neither the extent of scar, ischemia, hibernation, or viability predicted outcome or mortality. Twenty patients died during the follow-up, one patient underwent heart transplant. At follow-up, response to CRT is observed regardless of the presence of extensive scarring. Left ventricular (LV) pacing at sites with ischemia, hibernation, or nontransmural scar does not appear to modify the effect of CRT as compared to viable tissue.