Border Zone Regions Research Articles

Multiscale Fiber Remodeling in the Infarcted Left Ventricle using a Stress-Based Reorientation Law

The organization of myofibers and extra cellular matrix within the myocardium plays a significant role in defining cardiac function. When pathological events occur, such as myocardial infarction (MI), this organization can become disrupted, leading to degraded pumping performance. The current study proposes a multiscale finite element (FE) framework to determine realistic fiber distributions in the left ventricle (LV). This is achieved by implementing a stress-based fiber reorientation law, which seeks to align the fibers with local traction vectors, such that contractile force and load bearing capabilities are maximized. By utilizing the total stress (passive and active), both myofibers and collagen fibers are reoriented. Simulations are conducted to predict the baseline fiber configuration in a normal LV as well as the adverse fiber reorientation that occurs due to different size MIs. The baseline model successfully captures the transmural variation of helical fiber angles within the LV wall, as well as the transverse fiber angle variation from base to apex. In the models of MI, the patterns of fiber reorientation in the infarct, border zone, and remote regions closely align with previous experimental findings, with a significant increase in fibers oriented in a left-handed helical configuration and increased dispersion in the infarct region. Furthermore, the severity of fiber reorientation and impairment of pumping performance both showed a correlation with the size of the infarct. The proposed multiscale modeling framework allows for the effective prediction of adverse remodeling and offers the potential for assessing the effectiveness of therapeutic interventions in the future. Statement of SignificanceThe organization of muscle and collagen fibers within the heart plays a significant role in defining cardiac function. This organization can become disrupted after a heart attack, leading to degraded pumping performance. In the current study, we implemented a stress-based fiber reorientation law into a computer model of the heart, which seeks to realign the fibers such that contractile force and load bearing capabilities are maximized. The primary goal was to evaluate the effects of different sized heart attacks. We observed substantial fiber remodeling in the heart, which matched experimental observations. The proposed computational framework allows for the effective prediction of adverse remodeling and offers the potential for assessing the effectiveness of therapeutic interventions in the future.

Detectability of white matter cerebral blood flow using arterial spin labeling MRI in patients with sickle cell disease: Relevance of flow territory, bolus arrival time, and hematocrit.

Sickle cell disease (SCD) is the most common genetic blood disorder, characterized by red cell hemolysis, anemia, and corresponding increased compensatory cerebral blood flow (CBF). SCD patients are at high risk for cerebral infarcts and CBF quantification is likely critical to assess infarct risk. Infarcts primarily localize to white matter (WM), yet arterial spin labeling (ASL) MRI, the most common non-invasive CBF approach, has poor WM CBF sensitivity owing to low WM CBF and long WM bolus arrival time (BAT). We hypothesize that anemia, and associated cerebral hyperemia, in SCD leads to improved WM detection with ASL. We performed 3-Tesla multi-delay pulsed ASL in SCD (n = 35; age = 30.5 ± 8.3 years) and control (n = 15; age = 28.7 ± 4.5 years) participants and applied t-tests at each inversion time within different flow territories, and determined which regions were significantly above noise floor (criteria: one-sided p < 0.05). Total WM CBF-weighted signal was primarily detectable outside of borderzone regions in SCD (CBF = 17.7 [range = 12.9-25.0] mL/100 g/min), but was largely unphysiological in control (CBF = 8.1 [range = 7.6-9.9)] mL/100 g/min) participants. WM BAT was reduced in SCD versus control participants (ΔBAT = 37 [range = 46-70] ms) and BAT directly correlated with hematocrit (Spearman's-ρ = 0.62; p < 0.001). Findings support the feasibility of WM CBF quantification using ASL in SCD participants for appropriately parameterized protocols.

Antiarrhythmic Mechanisms of Epidural Blockade After Myocardial Infarction.

Thoracic epidural anesthesia (TEA) has been shown to reduce the burden of ventricular tachycardia in small case series of patients with refractory ventricular tachyarrhythmias and cardiomyopathy. However, its electrophysiological and autonomic effects in diseased hearts remain unclear, and its use after myocardial infarction is limited by concerns for potential right ventricular dysfunction. Myocardial infarction was created in Yorkshire pigs (N=22) by left anterior descending coronary artery occlusion. Approximately, six weeks after myocardial infarction, an epidural catheter was placed at the C7-T1 vertebral level for injection of 2% lidocaine. Right and left ventricular hemodynamics were recorded using Millar pressure-conductance catheters, and ventricular activation recovery intervals (ARIs), a surrogate of action potential durations, by a 56-electrode sock and 64-electrode basket catheter. Hemodynamics and ARIs, baroreflex sensitivity and intrinsic cardiac neural activity, and ventricular effective refractory periods and slope of restitution (Smax) were assessed before and after TEA. Ventricular tachyarrhythmia inducibility was assessed by programmed electrical stimulation. TEA reduced inducibility of ventricular tachyarrhythmias by 70%. TEA did not affect right ventricular-systolic pressure or contractility, although left ventricular-systolic pressure and contractility decreased modestly. Global and regional ventricular ARIs increased, including in scar and border zone regions post-TEA. TEA reduced ARI dispersion specifically in border zone regions. Ventricular effective refractory periods prolonged significantly at critical sites of arrhythmogenesis, and Smax was reduced. Interestingly, TEA significantly improved cardiac vagal function, as measured by both baroreflex sensitivity and intrinsic cardiac neural activity. TEA does not compromise right ventricular function in infarcted hearts. Its antiarrhythmic mechanisms are mediated by increases in ventricular effective refractory period and ARIs, decreases in Smax, and reductions in border zone electrophysiological heterogeneities. TEA improves parasympathetic function, which may independently underlie some of its observed antiarrhythmic mechanisms. This study provides novel insights into the antiarrhythmic mechanisms of TEA while highlighting its applicability to the clinical setting.

Distribution of Silent Cerebral Infarcts in Adults With Sickle Cell Disease.

Previously we demonstrated that 90% of infarcts in children with sickle cell anemia occur in the border zone regions of cerebral blood flow (CBF). We tested the hypothesis that adults with sickle cell disease (SCD) have silent cerebral infarcts (SCIs) in the border zone regions, with a secondary hypothesis that older age and traditional stroke risk factors would be associated with infarct occurrence in regions outside the border zones. Adults with SCD 18-50 years of age were enrolled in a cross-sectional study at 2 centers and completed a 3T brain MRI. Participants with a history of overt stroke were excluded. Infarct masks were manually delineated on T2-fluid-attenuated inversion-recovery MRI and registered to the Montreal Neurological Institute 152 brain atlas to generate an infarct heatmap. Border zone regions between anterior, middle, and posterior cerebral arteries (ACA, MCA, and PCA) were quantified using the Digital 3D Brain MRI Arterial Territories Atlas, and logistic regression was applied to identify relationships between infarct distribution, demographics, and stroke risk factors. Of 113 participants with SCD (median age 26.1 years, interquartile range [IQR] 21.6-31.4 years, 51% male), 56 (49.6%) had SCIs. Participants had a median of 5.5 infarcts (IQR 3.2-13.8). Analysis of infarct distribution showed that 350 of 644 infarcts (54.3%) were in 4 border zones of CBF and 294 (45.6%) were in non-border zone territories. More than 90% of infarcts were in 3 regions: the non-border zone ACA and MCA territories and the ACA-MCA border zone. Logistic regression showed that older participants have an increased chance of infarcts in the MCA territory (odds ratio [OR] 1.08; 95% CI 1.03-1.13; p = 0.001) and a decreased chance of infarcts in the ACA-MCA border zone (OR 0.94; 95% CI 0.90-0.97; p < 0.001). The presence of at least 1 stroke risk factor did not predict SCI location in any model. When compared with children with SCD, in adults with SCD, older age is associated with expanded zones of tissue infarction that stretch beyond the traditional border zones of CBF, with more than 45% of infarcts in non-border zone regions.

Cardiac radiotherapy transiently alters left ventricular electrical properties and induces cardiomyocyte-specific ventricular substrate changes in heart failure.

Ongoing clinical trials investigate the therapeutic value of stereotactic cardiac radioablation (cRA) in heart failure patients with ventricular tachycardia. Animal data indicate an effect on local cardiac conduction properties. However, the exact mechanism of cRA in patients remains elusive. Aim of the current study was to investigate in vivo and in vitro myocardial properties in heart failure and ventricular tachycardia upon cRA. High-density 3D electroanatomic mapping in sinus rhythm was performed in a patient with a left ventricular assist device and repeated ventricular tachycardia episodes upon several catheter-based endocardial radio-frequency ablation attempts. Subsequent to electroanatomic mapping and cRA of the left ventricular septum, two additional high-density electroanatomic maps were obtained at 2- and 4-month post-cRA. Myocardial tissue samples were collected from the left ventricular septum during 4-month post-cRA from the irradiated and borderzone regions. In addition, we performed molecular biology and mitochondrial density measurements of tissue and isolated cardiomyocytes. Local voltage was altered in the irradiated region of the left ventricular septum during follow-up. No change of local voltage was observed in the control (i.e. borderzone) region upon irradiation. Interestingly, local activation time was significantly shortened upon irradiation (2-month post-cRA), a process that was reversible (4-month post-cRA). Molecular biology unveiled an increased expression of voltage-dependent sodium channels in the irradiated region as compared with the borderzone, while Connexin43 and transforming growth factor beta were unchanged (4-month post-cRA). Moreover, mitochondrial density was decreased in the irradiated region as compared with the borderzone. Our study supports the notion of transiently altered cardiac conduction potentially related to structural and functional cellular changes as an underlying mechanism of cRA in patients with ventricular tachycardia.

Pirfenidone increases transverse tubule length in the infarcted rat myocardium.

Transverse (t)-tubule remodelling is a prominent feature of heart failure with reduced ejection fraction (HFrEF). In our previous research, we identified an increased amount of collagen within the t-tubules of HFrEF patients, suggesting fibrosis could contribute to the remodelling of t-tubules. In this research, we tested this hypothesis in a rodent model of myocardial infarction induced heart failure that was treated with the anti-fibrotic pirfenidone. Confocal microscopy demonstrated loss of t-tubules within the border zone region of the infarct. This was documented as a reduction in t-tubule frequency, area, length, and transverse elements. Eight weeks of pirfenidone treatment was able to significantly increase the area and length of the t-tubules within the border zone. Echocardiography showed no improvement with pirfenidone treatment. Surprisingly, pirfenidone significantly increased the thickness of the t-tubules in the remote left ventricle of heart failure animals. Dilation of t-tubules is a common feature in heart failure suggesting this may negatively impact function but there was no functional loss associated with pirfenidone treatment. However, due to the relatively short duration of treatment compared to that used clinically, the impact of long-term treatment on t-tubule structure should be investigated in future studies.

Cardiomyocyte proliferation is suppressed by ARID1A-mediated YAP inhibition during cardiac maturation

The inability of adult human cardiomyocytes to proliferate is an obstacle to efficient cardiac regeneration after injury. Understanding the mechanisms that drive postnatal cardiomyocytes to switch to a non-regenerative state is therefore of great significance. Here we show that Arid1a, a subunit of the switching defective/sucrose non-fermenting (SWI/SNF) chromatin remodeling complex, suppresses postnatal cardiomyocyte proliferation while enhancing maturation. Genome-wide transcriptome and epigenome analyses revealed that Arid1a is required for the activation of a cardiomyocyte maturation gene program by promoting DNA access to transcription factors that drive cardiomyocyte maturation. Furthermore, we show that ARID1A directly binds and inhibits the proliferation-promoting transcriptional coactivators YAP and TAZ, indicating ARID1A sequesters YAP/TAZ from their DNA-binding partner TEAD. In ischemic heart disease, Arid1a expression is enhanced in cardiomyocytes of the border zone region. Inactivation of Arid1a after ischemic injury enhanced proliferation of border zone cardiomyocytes. Our study illuminates the pivotal role of Arid1a in cardiomyocyte maturation, and uncovers Arid1a as a crucial suppressor of cardiomyocyte proliferation.

Microelectrode voltage mapping for substrate assessment in catheter ablation of ventricular tachycardia: a dual-center experience

Abstract Funding Acknowledgements Type of funding sources: None. Background The assessment of the ventricular myocardial substrate critically depends on the size of mapping electrodes, their orientation with respect to wavefront propagation, and interelectrode distance. Objective we conducted a dual-center study to evaluate the impact of microelectrode mapping in patients undergoing catheter ablation (CA) of ventricular tachycardia (VT). Methods We included 21 consecutive patients (median age, 68 [12], 95% male) with structural heart disease undergoing CA for electrical storm (n=14) or recurrent VT (n=7) using the QDOT Micro catheter and a multipolar catheter (PentaRay, n=9). The associations of peak-to-peak maximum standard bipolar (BVc) and minibipolar (PentaRay, BVp) with microbipolar (BVμMax) voltages were respectively tested in sinus rhythm with mixed effect models. Furthermore, we compared the features of standard bipolar (BE) and microbipolar (μBE) electrograms in sinus rhythm at sites of termination with radiofrequency energy. Results BVμMax was moderately associated with both BVc (β=0.85, p&amp;lt;0.01) and BVp (β=0.56, p&amp;lt;0.01). BVμMax was 0.98 (95% CI, 0.93-1.04, p&amp;lt;0.01) mV larger than corresponding BVc, and 0.27 (95% CI, 0.16-0.37, p&amp;lt;0.01) mV larger than matching BVp in sinus rhythm, with higher percentage differences in low voltage regions, leading to smaller endocardial dense scar (2.3 [2.7] vs. 12.1 [17] cm2, p&amp;lt;0.01) and border zone (3.2 [7.4] vs. 4.8 [20.1] cm2, p=0.03) regions in microbipolar maps compared to standard bipolar maps. At sites of VT termination (n=14), μBE were of higher amplitude (0.9 [0.8] mV versus 0.4 [0.2] mV, p&amp;lt;0.01), longer duration (117 [66] ms versus 74 [38] ms, p&amp;lt;0.01), and with greater number of peaks (4 [2] versus 2 [1], p&amp;lt;0.01) in sinus rhythm compared to BE. Conclusions Microelectrode mapping is more sensitive than standard bipolar mapping in the identification of viable myocytes in SR, and may facilitate recognition of targets for catheter ablation.

Heterogeneity of Repolarization and Cell-Cell Variability of Cardiomyocyte Remodeling Within the Myocardial Infarction Border Zone Contribute to Arrhythmia Susceptibility.

After myocardial infarction, the infarct border zone (BZ) is the dominant source of life-threatening arrhythmias, where fibrosis and abnormal repolarization create a substrate for reentry. We examined whether repolarization abnormalities are heterogeneous within the BZ in vivo and could be related to heterogeneous cardiomyocyte remodeling. Myocardial infarction was induced in domestic pigs by 120-minute ischemia followed by reperfusion. After 1 month, remodeling was assessed by magnetic resonance imaging, and electroanatomical mapping was performed to determine the spatial distribution of activation-recovery intervals. Cardiomyocytes were isolated and tissue samples collected from the BZ and remote regions. Optical recording allowed assessment of action potential duration (di-8-ANEPPS, stimulation at 1 Hz, 37 °C) of large cardiomyocyte populations while gene expression in cardiomyocytes was determined by single nuclear RNA sequencing. In vivo, activation-recovery intervals in the BZ tended to be longer than in remote with increased spatial heterogeneity evidenced by a greater local SD (3.5±1.3 ms versus remote: 2.0±0.5 ms, P=0.036, npigs=5). Increased activation-recovery interval heterogeneity correlated with enhanced arrhythmia susceptibility. Cellular population studies (ncells=635-862 cells per region) demonstrated greater heterogeneity of action potential duration in the BZ (SD, 105.9±17.0 ms versus remote: 73.9±8.6 ms; P=0.001; npigs=6), which correlated with heterogeneity of activation-recovery interval in vivo. Cell-cell gene expression heterogeneity in the BZ was evidenced by increased Euclidean distances between nuclei of the BZ (12.1 [9.2-15.0] versus 10.6 [7.5-11.6] in remote; P<0.0001). Differentially expressed genes characterizing BZ cardiomyocyte remodeling included hypertrophy-related and ion channel-related genes with high cell-cell variability of expression. These gene expression changes were driven by stress-responsive TFs (transcription factors). In addition, heterogeneity of left ventricular wall thickness was greater in the BZ than in remote. Heterogeneous cardiomyocyte remodeling in the BZ is driven by uniquely altered gene expression, related to heterogeneity in the local microenvironment, and translates to heterogeneous repolarization and arrhythmia vulnerability in vivo.

Microelectrode voltage mapping for substrate assessment in catheter ablation of ventricular tachycardia: A dual-center experience.

The assessment of the ventricular myocardial substrate critically depends on the size of mapping electrodes, their orientation with respect to wavefront propagation, and interelectrode distance. We conducted a dual-center study to evaluate the impact of microelectrode mapping in patients undergoing catheter ablation (CA) of ventricular tachycardia (VT). We included 21 consecutive patients (median age, 68 [12], 95% male) with structural heart disease undergoing CA for electrical storm (n = 14) or recurrent VT (n = 7) using the QDOT Micro catheter and a multipolar catheter (PentaRay, n = 9). The associations of peak-to-peak maximum standard bipolar (BVc ) and minibipolar (PentaRay, BVp ) with microbipolar (BVμMax ) voltages were respectively tested in sinus rhythm with mixed effect models. Furthermore, we compared the features of standard bipolar (BE) and microbipolar (μBE) electrograms in sinus rhythm at sites of termination with radiofrequency energy. BVμMax was moderately associated with both BVc (β = .85, p < .01) and BVp (β = .56, p < .01). BVμMax was 0.98 (95% CI: 0.93-1.04, p < .01) mV larger than corresponding BVc , and 0.27 (95% CI: 0.16-0.37, p < .01) mV larger than matching BVp in sinus rhythm, with higher percentage differences in low voltage regions, leading to smaller endocardial dense scar (2.3 [2.7] vs. 12.1 [17] cm2 , p < .01) and border zone (3.2 [7.4] vs. 4.8 [20.1] cm2 , p = .03) regions in microbipolar maps compared to standard bipolar maps. Late potentials areas were nonsignificantly greater in microelectrode maps, compared to standard electrode maps. At sites of VT termination (n = 14), μBE were of higher amplitude (0.9 [0.8] vs. 0.4 [0.2] mV, p < .01), longer duration (117 [66] vs. 74 [38] ms, p < .01), and with greater number of peaks (4 [2] vs. 2 [1], p < .01) in sinus rhythm compared to BE. microelectrode mapping is more sensitive than standard bipolar mapping in the identification of viable myocytes in SR, and may facilitate recognition of targets for CA.

Abstract Number ‐ 215: Distinct presentation of RCVS and PRES co‐existence and overlap of their pathophysiology

Introduction Reversible cerebral vasoconstriction syndrome (RCVS), is characterized by reversible segmental and multifocal vasoconstrictionof cerebral arteries leading to infarcts and cytotoxic edema. Posterior reversible encephalopathy syndrome (PRES) is characterized by vasogenic edema predominantly in the parieto‐occipital regions associated with acute onset encephalopathy, seizures, headache, and visual disturbances.Whether PRES and RCVS are independent syndromes and sometimes overlapped or part of a continuum process, these theories are still debated. We report a case of a patient with distinct overlapping of RCVS and PRES. Methods Case Report Results 52‐year‐old woman with past medical Hx of Hypertension, Diabetes, Migraines and cocaine use, initially presented with hypertensive emergency andsubacute headaches with worsening confusion. Initial CT head was negative for bleed but showed evolving subcortical hypodensities in the right parietal and left frontal lobes. CTA head and neck showed multifocal intracranial irregularities of bilateral ACAs and MCAs with paucity of left anterior M2 branch, left V3/V4 steno‐occlusion. This vasculopathy and clinical presentation is very consistent with RCVS.MRI of brain showed multiple acute / subacute punctate infarcts in the left corona radiata, bilateral basal ganglia, right greater than left thalami, right dorsal pons, right mesial temporal lobe, bilateral occipital regions. Vasogenic edema was noted in the bilateral border zone regions, right parietal being most prominent with some contrast enhancement. The MRI showed vasogenic edema and cytotoxic edema with multiple infarcts which is consistent with PRES and RCVS vasculopathy. CSF analysis was negative for pleocytosis and showed mildly elevated protein. The patient was started on Verapamil and Aspirin and Atorvastatin for secondary stroke prevention. With improvement in mental status was discharged to Rehab. Conclusions The pathophysiological mechanisms of PRES and RCVS are still unknown. Theories whether RCVS and PRES are independent syndromes and sometimes overlap or part of spectrum, are still debated. However, some common characteristics make conceivable a common origin linked with impaired cerebral autoregulation, endothelial dysfunction, and BBB breakdown. Increased clinical awareness of their co‐existence may help in quickerdiagnosis and treatment.

Automatic development of 3D anatomical models of border zone and core scar regions in the left ventricle.

Patients with myocardial infarction are at elevated risk of sudden cardiac death, and scar tissue arising from infarction is known to play a role. The accurate identification of scars therefore is crucial for risk assessment, quantification and guiding interventions. Typically, core scars and grey peripheral zones are identified by radiologists and clinicians based on cardiac late gadolinium enhancement magnetic resonance images (LGE-MRI). Scar regions from LGE-MRI vary in size, shape, heterogeneity, artifacts, and image resolution. Thus, manual segmentation is time consuming, and influenced by the observer's experience (bias effect). We propose a fully automatic framework that develops 3D anatomical models of the left ventricle with border zone and core scar regions that are free from bias effect. Our myocardium (SOCRATIS), border scar and core scar (BZ-SOCRATIS) segmentation pipelines were evaluated using internal and external validation datasets. The automatic myocardium segmentation framework performed a Dice score of 81.9% and 70.0% in the internal and external validation dataset. The automatic scar segmentation pipeline achieved a Dice score of 60.9% for the core scar segmentation and 43.7% for the border zone scar segmentation in the internal dataset and in the external dataset a Dice score of 44.2% for the core scar segmentation and 54.8% for the border scar segmentation respectively. To the best of our knowledge, this is the first study outlining a fully automatic framework to develop 3D anatomical models of the left ventricle with border zone and core scar regions. Our method exhibits high performance without the need for training or tuning in an unseen cohort (unsupervised).

Role of collateral flow in infarct border zone extent and contractile function in patients with chronic coronary total occlusion

PurposeThere is a paucity of data regarding the border zone parameters in patients with chronic coronary total occlusion (CTO). We investigated the border zone extent and contractile function and their associations with collateral flow. MethodsCTO patients (n = 47) and sex- and age-matched volunteers (n = 15) were prospectively enrolled and underwent cardiac MRI examinations to acquire cine and late-gadolinium enhancement (LGE) images. Myocardial peak strain (PS) and the time to PS were determined at the segmental level and global level. Infarct, border zone, adjacent, and remote regions were defined according to the transmural extent of infarction (TEI) by LGE at each segment. Angiographic collateral flow was evaluated using the Rentrop grading system. ResultsCTO patients with well-developed collateral flow had a higher TEI in border zone regions compared to patients with poorly developed collateral flow (p = 0.02). Conversely, CTO patients with poorly developed collaterals showed a higher TEI in infarct regions (p < 0.01). Enhanced border function, characterized by greater PS and earlier time to PS, was noted in well-developed collaterals (all p < 0.05). In the multivariate linear analyses, the level of collateral flow was an independent predictor of the border zone extent (β = 0.40, p = 0.02) and contractile function (radial: β = -0.42, p = 0.02; circumferential: β = 0.39, p = 0.02; and longitudinal: β = 0.47, p < 0.01). ConclusionsIn CTO patients, the presence of well-developed collateral flow was closely linked to a greater extent of LGE and contractile function in border zone regions. Our findings shed light on the cardiac MRI-based pathophysiological underpinning in border zone regions, which could offer complementary and prognostic information in clinical practice.

Acute afterload leads to increased electrophysiological heterogeneity after myocardial infarction

Abstract Background Myocardial infarction (MI) results in altered mechanical loading and changes in the cardiac electrical properties. The infarct border zone is pro-arrhythmic but the exact role of mechano-electrical coupling remains unclear. Objective We studied spatial electrical heterogeneity in MI animals during acute afterload increase using a novel E-field methodology for high resolution mapping of local activation-repolarization intervals (ARI) in vivo. Methods Anterior-septal MI was induced in five domestic pigs by 120-minute occlusion of the left anterior descending artery followed by reperfusion. This led to an infarct size of 17.7±2.1% of the left ventricle. After 1 month, electro-anatomical mapping was performed before and during an acute afterload challenge induced by partially inflating a balloon in the descending aorta. A non-contact recording of a 64-electrode array was translated to 2048 non-contact electrograms distributed over the left ventricle. The non-contact electrograms were processed to determine the ARIs using a custom-made algorithm, previously validated against monophasic action potential recordings. Based on the contact map we defined border zone (BZ, voltage 0.5 to 1.5 mV) and remote (&amp;gt;1.5mV) regions. Heterogeneity was defined as the interquartile range (IQR) of ARIs in fixed neighborhoods of 1cm radius (figure 1A) and analyzed in 10 segments (5 BZ and 5 remote) of a modified version of the AHA model (49 segments by dividing the 16 non-apical segments). Other segments were discarded due to artefacts mainly caused by the array touching the septal and apical wall. Results Acute afterload challenge resulted in an increase of the systolic left ventricular pressure of 41.7±5.4% and increased left ventricular repolarization heterogeneity (IQR 4.03±1.23ms baseline to 4.85±1.38ms during inflation, p=0.004). There was a significant increase in heterogeneity in both BZ (4.78±1.60ms to 5.64±1.66ms, p=0.020) and remote (2.24±0.17ms to 3.00±0.86ms, p=0.034) regions (figure 1B). The IQR in the infarct BZ was higher compared to the remote zone at rest (4.78±1.60ms vs 2.24±0.17ms, p=0.010) as well as during inflation (5.64±1.66ms vs 3.00±0.86ms, p=0.008) (figure 1B). Both BZ and remote regions responded equally to acute afterload (p for interaction = 0.803). Conclusion Increased afterload leads to increased repolarization heterogeneity. This heterogeneity is higher in the infarct BZ. These alterations could provide a functional substrate for reentry. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): KU Leuven - C1 funding

Abstract P1116: Genetic Mapping Of Cardiomyocyte Ploidy Phenotypes To Identify Genetic Determinants Of Outcomes After Infarction

Outcomes following cardiac injury are influenced by lifestyle and environment, as well as genetic background. Our interest lies in the latter, where very few genes have successfully been linked to heart failure. Contributors to this low success rate include high genetic diversity of patient populations, inability to control for non-genetic factors, and cellular complexities that contribute to outcomes. We propose utilizing the Hybrid Rat Diversity Panel (HRDP) to assess high throughput surrogate phenotypes, which can be predictive of outcomes after injury when measured in the basal state. This approach can offer a solution to the limitations of association studies for complex diseases like heart failure. Our surrogate phenotype of interest is cardiomyocyte ploidy, where high frequency of diploid cardiomyocytes is predictive of ability to regenerate and functional recovery. Conversely, an increased proportion of polyploid (≥8N) cardiomyocytes is associated with adverse ventricular remodeling and dilated cardiomyopathy. Having analyzed 50 of the 96 strains, we see that frequency of the MNDCMs varies from 1.3-20.3% across strains, while frequency of the highly polyploid CMs (≥8N) varies from 0.8-20.9%. Four strains have been selected for myocardial infarction (MI) studies, including M520 (17.4%) and F344 (20.3%) with high MNDCM content and GK (2.8%) and HXB23 (1.8%) with low MNDCM content. Following MI, both M520 and F344 rats exhibit a higher percentage of BrdU+ cardiomyocytes in the border zone region compared to HXB23 rats, supporting the hypothesis that strains with high MNDCM frequency would be better at mounting a proliferative response. This also translated to a greater functional improvement and smaller scars in M520 rats, but not in F344. Additionally, we looked at the size of cardiomyocytes following MI and found that HXB23 rats (20.9% ≥8N CMs) have an increased cross-sectional area in comparison to the other strains, which may be indicative of concentric hypertrophy in response to injury. The HRDP could serve as a powerful tool for mapping traits related to outcomes following MI, allowing us to identify potential gene candidates that may be interrogated further for future use in precision medicine-based therapies. Mapping studies are ongoing.

Adrenergic stimulation amplifies the difference in beat-to-beat variability between the scar border zone and remote region

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): KU Leuven BOF-C1 “Blood pressure induced premature ventricular beats as triggers for ventricular arrhythmia in ischemic cardiomyopathy” Background Myocardial infarction (MI) results in a dense scar region surrounded by a heterogeneous region of fibrosis and remodeled myocytes called the border zone (BZ). Beta-adrenergic stimulation results in increased beat-to-beat variability of repolarization (BVR) which could increase spatial heterogeneity and arrhythmia vulnerability. Objective To examine the effect of adrenergic stimulation on the beat-to-beat variability in the BZ, compared to the remote region, using novel methodology for determining spatially dense activation-repolarization intervals. Methods Anterior-septal myocardial infarction (MI) was induced in 10 domestic pigs by 120-minute occlusion of the left anterior descending artery followed by reperfusion. Electro-anatomical mapping was performed after one month. The BZ was defined using contact mapping as the region with bipolar voltage between 0.5 and1.5mV. A non-contact recording of a 64-electrode array was translated to 2048 non-contact electrograms distributed over the LV (EnSite PrecisionTM, St. Jude/Abbott Medical). Electrophysiological recordings were made during baseline and during an isoproterenol (ISO) infusion (incremental doses of 0.01µg/kg until 0.04µg/kg). In each of the 2048 points non-contact electrograms over 25 consecutive beats were processed to determine the BVR using a custom-made algorithm, validated against monophasic action potential recordings. Results During baseline conditions the maximal BVR was increased in the BZ compared to the remote region (BZ: 3.28±0.90 ms vs remote: 2.61±0.67 ms, P=0.002). During ISO infusion the maximal BVR was also increased in the BZ (BZ: 3.55±0.74 ms vs remote: 2.21±0.60 ms, P&amp;lt;0.001). During baseline the BZ exhibited a larger spatial variance of BVR than the remote region (BZ: 0.20±0.11 ms2 vs remote: 0.087±0.055 ms2, P=0.002). During ISO infusion the spatial variance of BVR was larger in the BZ (BZ: 0.23±0.12 ms2 vs remote: 0.083±0.056 ms2, P=0.001). The maximal BVR was not significantly different during baseline and ISO in the BZ, nor the remote region (P&amp;gt;0.05). However, the difference of the maximal BVR between BZ and remote regions was significantly increased during ISO (baseline: 0.67±0.48 ms vs ISO: 1.34±0.49ms, P=0.001). Conclusion The MI BZ showed increased temporal heterogeneity in repolarization that could serve as functional substrate for re-entry. Adrenergic stimulation amplified this vulnerability by increasing the difference in maximal BVR between BZ and remote regions.

Heterogeneous myocyte remodelling and spatial heterogeneity of repolarization within the myocardial infarction border zone

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Fund for Scientific Research-Flanders (FWO) Background Sudden cardiac death due to ventricular arrhythmias is a major cause of mortality after myocardial infarction (MI). The border zone (BZ) surrounding the infarct is the dominant source of arrhythmias. Here a substrate of heterogeneous repolarization is implicated, which could be due to heterogeneous myocyte remodelling. Objective To examine myocyte remodelling within the BZ, in comparison to the remote myocardium, and evaluate the local profile of repolarization of these regions in vivo. Methods MI was induced by 120-minute occlusion of the left anterior descending coronary artery followed by reperfusion in 6 domestic pigs. After 4 weeks, magnetic resonance imaging was performed to assess infarct remodelling and local wall thickness. Within 3 days, electro-anatomical mapping was performed. A non-contact recording of a 64-electrode array was translated to 2048 electrograms distributed over the LV and local activation-recovery-interval (ARI) determined by custom software. After recovery (2-4 days), the pigs were sacrificed, and samples collected from the BZ and remote region for RNA analysis and single cardiomyocyte isolation. Cell dimensions were measured and cellular AP duration (APD) was optically recorded using a fluorescent voltage dye, Di-8-Annepps (stimulation at 1Hz, 37°C). Expression and variability of cardiomyocyte hypertrophy biomarkers were extracted from single nuclear RNA sequencing data (10x Genomics). Results Cardiomyocyte APD in large population samples (&amp;gt; 100 cells per region in each pig) revealed higher heterogeneity in the BZ than the remote region, quantified as the standard deviation (SD) (BZ: 105.9 ± 17.0ms vs remote: 73.9 ± 8.6ms, P = 0.001). Cellular APD heterogeneity correlated strongly with in vivo local ARI heterogeneity, which demonstrated increased heterogeneity in the BZ (R2 = 0.67, P = 0.002). BZ myocytes were hypertrophied with greater increase in cell width than length, and cellular hypertrophy was more heterogeneous by SD in the BZ (BZ: 12.9 ± 2.4μm vs remote: 8.3 ± 1.1μm, P &amp;lt; 0.001). NPPB transcripts reporting on hypertrophic remodelling were higher in BZ than remote (mean lognorm gene expression, BZ: 0.431 ± 0.014 vs remote: 0.107 ± 0.004, P &amp;lt; 0.001), and showed greater heterogeneity in expression between cells by proportion of hypertrophic (NPPB +ve) cells (BZ: 30.86% vs remote: 8.37%, P &amp;lt; 0.001). Wall thickness variance was higher in the BZ compared to the remote region (anterior BZ: 0.15 ± 0.02mm, septal BZ: 0.16 ± 0.04mm vs remote: 0.04 ± 0.02mm, P &amp;lt; 0.001), contributing to increased heterogeneity of local wall stress in BZ. Conclusion Cardiomyocyte remodelling in the BZ is heterogeneous, possibly related to differences in local wall stress, which may contribute to heterogeneous repolarization in vivo and underlie arrhythmia vulnerability within the BZ.

Identification of Infarct Border Zone Using Late Gadolinium Enhanced MRI in Rats

BackgroundFollowing acute myocardial infarction (MI), cardiac myocyte death and the formation of a fibrotic scar in the left ventricular free wall (LVFW) alters the biomechanical behavior of the myocardium resulting in changes to organ‐level function. Despite significant advances in understanding LVFW remodeling in the setting of MI, the extent of tissue remodeling in the regions where infarct tissue transitions to healthy tissue, commonly called the border zone (BZ), is not well understood. Additionally, the effect of alterations in biomechanical behavior of the BZ on LV pump function remains understudied. We hypothesize that image‐based cardiac modeling can effectively address this gap. To this end, our objective was to develop an automated method to identify the infarct and BZ regions in rats using ex‐vivo late gadolinium‐enhanced magnetic resonance images (LGE‐MRI) and make use of these delineations to study regional structural remodeling in MI.MethodsAnterobasal MI was induced in Wistar‐Kyoto rats (n=2) by ligating the left anterior descending artery. Prior to sacrifice, subjects in the infarct group were given gadolinium contrast agent for MRI enhancement. Animals were sacrificed at 4 weeks post‐infarct and cardiac MRI scans were performed at an isotropic 100 µm resolution. The mean value of the voxel signal‐intensity (SI) of the posterobasal region of the heart was calculated and is hereafter referred to as the baseline SI (BSI). The image voxels were then segmented in to three regions by using the following SIs as threshold value cutoffs: i) SI of greater than 125% of BSI was considered infarcted myocardium, ii) SI between 115% and 125% of BSI was considered BZ, iii) SI of less than 115% BSI was considered remote myocardium. The geometry and dimensions of the infarct region were confirmed with measurements from the excised heart of the animal.ResultsIncreased SI was noted in the anterobasal region of the infarcted hearts (Fig 1), indicating myocyte necrosis and scar formation. Mean SI of the infarct region defined via this method was 1.6‐fold larger compared to that of the remote region. The infarct region resulting from the automated identification method closely matched the gemometry and dimensions of the infarct scar region of the excised hearts.ConclusionsThe extent of myocardial remodeling in LVFW during the post‐infarct healing process determines the contractile behavior in the LVFW and influences long‐term outcomes. Automated identification of infarct, BZ, and remote myocardium regions using LGE‐MRI is a step towards image‐based characterization of the heterogenous remodeling in the LVFW. Additionally, our algorithm enables the simple definition of a BZ of varied size and could allow us to better understand the influence of distinct regional remodeling events on organ‐level function as MI proceeds from early‐stage scarring to late‐stage remodeling.

Ventricular Electrophysiological Effects of Vagal Nerve Stimulation in Humans With and Without Structural Heart Disease

Background and ObjectiveClinical trials investigating the benefits of vagus nerve stimulation (VNS) in heart failure have shown mixed results. This variation maybe due to inconsistent stimulation parameters, which may fail to adequately stimulate cardiomotor fibers required for cardio‐protection. However, overstimulation of the vagus nerve may cause adverse off‐target effects. Thus, the aim of this study was to assess the beneficial effects of moderate frequency VNS in patients with structurally normal hearts (SNH) and those with cardiomyopathy (CM).HypothesisModerate frequency VNS (10 Hz) confers ventricular electrophysiological effects.MethodsPatients with SNH and supraventricular tachycardia (n = 5) and cardiomyopathy patients with ventricular tachycardia (CM, n = 5) undergoing electrophysiology procedures were recruited. A multi‐electrode circular electrophysiology catheter was advanced from the femoral to the right internal jugular vein via a long sheath. Bipolar electrode pairs were serially stimulated and capture/stimulation of the vagus nerve identified by a negative chronotropic response. Threshold current was defined as a 10‐15% decrease in heart rate (HR) at 20 Hz and 1 ms pulse‐width. Stimulation was then performed at threshold current for 10 seconds at 10 and 20 Hz. Endocardial unipolar electrograms were continuously recorded using ventricular multielectrode mapping catheters and used to calculate activation recovery intervals (ARI), a validated surrogate of local action potential duration (APD). Electrodes were designated as overlying scar, border zone, or viable myocardium based on standard bipolar voltage mapping criteria in CM patients. ARIs were corrected for HR by the Framingham method.ResultsThe current of stimulation was 13.2 ± 1.7 mA in SNH and 14.4 ± 3.1 mA in CM (p = ns). VNS at 20 Hz significantly decreased HR (p ≤ 0.01) in both SNH and CM patients (12.6 ± 1.4% in SNH vs 12.9 ± 1.7% in CM, p= ns) while significantly prolonging global ventricular ARIs (2.2 ± 0.4% in SNH vs 4.6 ± 1.0% in CM, p= ns). The chronotropic effects of 10 Hz VNS were similar to 20 Hz in SNH (12.0 ± 1.4% at 10 Hz vs 12.6 ± 1.4% at 20 Hz, p = ns) but blunted in CM patients (12.0 ± 1.4% in SNH vs 4.9 ± 2.4% in CM, p≤ 0.05). Surprisingly, despite reduced chronotropic responses, global ARI prolongation persisted (4.0 ± 0.7% at 10 Hz vs 4.6 ± 1.0% at 20 Hz, p= ns) in CM patients. Importantly, ARI prolongation was observed in scar (326 ± 23 to 340 ± 22 ms, p≤ 0.05) and border zone regions (312 ± 18 ms to 323 ± 17 ms, p≤ 0.05). Moreover, after correcting ARI for heart rate (ARIc), 10 Hz VNS in CM patients caused significantly greater prolongation in ARIc than 20 Hz (1.8 ± 0.6% at 10 Hz vs ‐1.0 ± 0.6% at 20 Hz, p≤ 0.05), suggesting that higher frequency VNS may potentially cause a net shortening of ventricular APD.ConclusionsAcute application of moderate frequency VNS (10 Hz) demonstrated ventricular electrophysiological effects, with ARI prolongation observed in scar and border zone regions in diseased hearts. This human data validates previously reported effects of moderate frequency VNS in large animal infarct models. Stimulation at 20 Hz is unnecessary and may have negative ventricular electrophysiological effects. Further clinical trials assessing electrophysiological effects of chronic VNS in humans are required.

Proarrhythmic Effects of Sympathetic Activation Are Mitigated by Vagal Nerve Stimulation in Infarcted Hearts.

The goal of this study was to evaluate whether intermittent VNS reduces electrical heterogeneities and arrhythmia inducibility during sympathoexcitation. Sympathoexcitation increases the risk of ventricular tachyarrhythmias (VT). Vagal nerve stimulation (VNS) has been antiarrhythmic in the setting of ischemia-driven arrhythmias, but it is unclear if it can overcome the electrophysiological effects of sympathoexcitation in the setting of chronic myocardial infarction (MI). In Yorkshire pigs after chronic MI, a sternotomy was performed, a 56-electrode sock was placed over the ventricles (n=17), and a basket catheter was positioned in the left ventricle (n=6). Continuous unipolar electrograms from sock and basket arrays were obtained to analyze activation recovery interval (ARI), a surrogate of action potential duration. Bipolar voltage mapping was performed to define scar, border zone, or viable myocardium. Hemodynamic and electrical parameters and VT inducibility were evaluated during sympathoexcitation with bilateral stellate ganglia stimulation (BSS) and during combined BSS with intermittent VNS. During BSS, global epicardial ARIs shortened from 384 ± 59 milliseconds to 297 ± 63 milliseconds and endocardial ARIs from 359 ± 36 milliseconds to 318 ± 40 milliseconds. Dispersion in ARIs increased in all regions, with the greatest increase observed in scar and border zone regions. VNS mitigated the effects of BSS on border zone ARIs (from-18.3% ± 6.3% to-2.1% ± 14.7%) and ARI dispersion (from 104ms2 [1 to 1,108ms2] to -108ms2 [IQR: -588 to 30ms2]). VNS reduced VT inducibility during sympathoexcitation (from 75%-40%; P< 0.05). After chronic MI, VNS overcomes the detrimental effects of sympathoexcitation by reducing electrophysiological heterogeneities exacerbated by sympathetic stimulation, decreasing VT inducibility.