Myocardial Substrate Research Articles

Strain-based characterization of electromechanical tissue properties using patient-specific simulation of dyssynchronous hearts: a pilot study

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation (ERA-CVD JTC2018 grant 2018T094; Dr. Dekker Program grant 2015T082 to J.L.) and the Netherlands Organisation for Scientific Research (NWO- ZonMw, VIDI grant 016.176.340 to J.L.) Background/Introduction Interpretation of regional strain patterns in patients with failing hearts is often challenging due to presence of different underlying tissue abnormalities, including electrical conduction delay and myocardial infarction (MI). Purpose To test whether an automatic strain-based computer simulation algorithm can differentiate between electrical and ischemic contractile dysfunction in patients with mechanical dyssynchrony. Methods Three heart failure patients with reduced left ventricular ejection fraction (33 ± 3%) and wide QRS (160 ± 7ms, LBBB morphology) were retrospectively included, two with and one without MI. Longitudinal strain patterns obtained in 18 myocardial segments using speckle tracking echocardiography (STE) and left ventricular (LV) volume measurements were used as an input to the patient-specific simulation algorithm, which automatically optimizes a set of global and regional myocardial tissue parameters such that the regional strain patterns and global volumes simulated by the CircAdapt model of the human heart and circulation were similar to the strains and volumes measured in the patients. As output, the patient-specific simulations revealed onset time of mechanical activation (relative to first activated segment) and relative severity of contractile dysfunction in all 18 segments. We compared predicted mechanical activation delays and segmental contractile dysfunction values with independent measurements of QRS width and transmurality of late gadolinium enhancement (LGE), respectively. Results The model was able to reproduce the dyssynchronous regional strain patterns as measured in the patients (Figure 1: representative example). In all patients, significant septal—to-lateral wall mechanical activation delays (33-55ms) were predicted (Figure 2: blue bullseye plot of same patient used for figure 1), matching the presence of electrical activation delays on the patient’s ECGs (i.e. wide QRS and LBBB morphology). Furthermore, all simulations predicted a global loss of contractile dysfunction, matching the low ejection fractions reported in those patients. The simulations of the two patients with MI predicted more severe contractile dysfunction (>60%) in the regions with transmural LGE (Figure 2: red bullseye plot versus gold standard LGE-MRI image of same patient used for figure 1). Conclusion This pilot study demonstrated the ability of an automatic patient-specific simulation algorithm to differentiate between electrical and ischemic myocardial disease substrates in heart failure patients with electrical conduction abnormalities with and without MI. Future studies will investigate whether this computer algorithm can improve diagnosis of patients with mechanical dyssynchrony. Abstract Figure 1 Abstract Figure 2

Combined assessment of septal scar and septal flash by cardiac magnetic resonance identifies responders to cardiac resynchronization therapy

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): South-Eastern Norway Regional Health Authority. Research grants of the University of Leuven. Background Left ventricular (LV) scar, particularly in the lateral wall and septum, reduces response rate to cardiac resynchronization therapy (CRT), whereas a dyssynchronous LV contraction pattern (septal flash) suggests good response. Lateral wall scar abolishes septal flash. Therefore, a combined approach of septal scar and septal flash may characterize the myocardial substrate responsive to CRT. Cardiac magnetic resonance (CMR) may assess both scar and contraction pattern. Purpose The present study aimed to determine if combined assessment of septal scar and septal flash by CMR as single image modality identifies responders to CRT. Methods We investigated all CRT recipients with available CMR from a prospective, multicenter study (n = 136), with both ischemic and non-ischemic heart failure. Septal scar was assessed by late gadolinium enhancement (LGE) from a stack of short axis slices (n = 128) and septal flash determined visually on ordinary cine sequences (n = 136). CRT response was defined as ≥15% reduction in LV end-systolic volume by echocardiography at 6 months follow-up. We also assessed heart transplantation or death of any cause 39 ± 13 months after device implantation. Results In multivariate analysis including percentage septal scar (LGE), septal flash, QRS-duration and QRS-morphology, septal LGE and septal flash were the only independent predictors of CRT response (both p < 0.001). A combined approach of septal LGE and septal flash predicted CRT response with area under the curve 0.86 (95% confidence interval (CI): 0.78-0.94) and long-term survival without heart transplantation with hazard ratio 0.18 (95% CI: 0.05-0.61). A practical approach to selection of CRT candidates by septal LGE and septal flash is illustrated in the present figure. As shown, absence of septal LGE indicated excellent response rate (93%) to CRT independent of other parameters. When septal LGE was present, however, overall response rate was substantially lower (58%), but presence or absence of septal flash separated responders from non-responders with high accuracy. This sequential approach correctly classified 86% of patients. Importantly, the approach was equally accurate in patients with intermediate QRS duration (130-150ms), where 93% of patients were correctly classified. Conclusions Combined assessment of septal LGE and septal flash by CMR as single image modality identifies CRT responders with high accuracy and predicts long-term survival. Abstract Figure.

Role of Cardiac Magnetic Resonance Imaging in the Evaluation of Athletes with Premature Ventricular Beats.

Premature ventricular beats (PVBs) in athletes are not rare. The risk of PVBs depends on the presence of an underlying pathological myocardial substrate predisposing the subject to sudden cardiac death. The standard diagnostic work-up of athletes with PVBs includes an examination of family and personal history, resting electrocardiogram (ECG), 24 h ambulatory ECG (possibly with a 12-lead configuration and including a training session), maximal exercise testing and echocardiography. Despite its fundamental role in the diagnostic assessment of athletes with PVBs, echocardiography has very limited sensitivity in detecting the presence of non-ischemic left ventricular scars, which can be revealed only through more in-depth studies, particularly with the use of contrast-enhanced cardiac magnetic resonance (CMR) imaging. The morphology, complexity and exercise inducibility of PVBs can help estimate the probability of an underlying heart disease. Based on these features, CMR imaging may be indicated even when echocardiography is normal. This review focuses on interpreting PVBs, and on the indication and role of CMR imaging in the diagnostic evaluation of athletes, with a special focus on non-ischemic left ventricular scars that are an emerging substrate of cardiac arrest during sport.

Overexpression of NOX2 Exacerbates AngII-Mediated Cardiac Dysfunction and Metabolic Remodelling.

The present study aimed to examine the effects of low doses of angiotensin II (AngII) on cardiac function, myocardial substrate utilization, energetics, and mitochondrial function in C57Bl/6J mice and in a transgenic mouse model with cardiomyocyte specific upregulation of NOX2 (csNOX2 TG). Mice were treated with saline (sham), 50 or 400 ng/kg/min of AngII (AngII50 and AngII400) for two weeks. In vivo blood pressure and cardiac function were measured using plethysmography and echocardiography, respectively. Ex vivo cardiac function, mechanical efficiency, and myocardial substrate utilization were assessed in isolated perfused working hearts, and mitochondrial function was measured in left ventricular homogenates. AngII50 caused reduced mechanical efficiency despite having no effect on cardiac hypertrophy, function, or substrate utilization. AngII400 slightly increased systemic blood pressure and induced cardiac hypertrophy with no effect on cardiac function, efficiency, or substrate utilization. In csNOX2 TG mice, AngII400 induced cardiac hypertrophy and in vivo cardiac dysfunction. This was associated with a switch towards increased myocardial glucose oxidation and impaired mitochondrial oxygen consumption rates. Low doses of AngII may transiently impair cardiac efficiency, preceding the development of hypertrophy induced at higher doses. NOX2 overexpression exacerbates the AngII -induced pathology, with cardiac dysfunction and myocardial metabolic remodelling.

Acute Effects of Dapagliflozin on Myocardial Work in Type 2 Diabetics With Heart Failure With Reduced Ejection Fraction: A Crossover Trial

Recent studies have demonstrated benefits of sodium-glucose co-transporter 2 inhibitors (SGLT2i) in the management of heart failure with reduced ejection fraction (HFrEF). Although current literature postulates several salient effects, the primary mechanism is unclear. Intriguingly, benefit is seen rapidly. Improved myocardial energetics and substrate efficiency through Na+/H+ exchanger inhibition and increased β-hydroxybutyrate metabolism may rapidly reduce myocardial work.

Non-invasive Stereotactic Body Radiation Therapy for Refractory Ventricular Arrhythmias: Venturing into the Unknown.

Stereotactic body radiation therapy (SBRT) is a promising new method for non-invasive management of life-threatening ventricular arrhythmias. Numerous case reports and case series have provided encouraging short-term results suggesting good efficacy and safety, but randomized data and long-term outcomes are not yet available. The primary hypothesis as to the mechanism of action for SBRT relates to the development of cardiac fibrosis in arrhythmogenic myocardial substrate; however, limited animal model data offer conflicting insights into this theory. The use of SBRT for patients with refractory ventricular arrhythmias is rapidly increasing, but ongoing translational science work and randomized clinical trials will be critical to address many outstanding questions regarding this novel therapy.

Effects of Short Term Adiponectin Receptor Agonism on Cardiac Function and Energetics in Diabetic db/db Mice.

ObjectiveImpaired cardiac efficiency is a hallmark of diabetic cardiomyopathy in models of type 2 diabetes. Adiponectin receptor 1 (AdipoR1) deficiency impairs cardiac efficiency in non-diabetic mice, suggesting that hypoadiponectinemia in type 2 diabetes may contribute to impaired cardiac efficiency due to compromised AdipoR1 signaling. Thus, we investigated whether targeting cardiac adiponectin receptors may improve cardiac function and energetics, and attenuate diabetic cardiomyopathy in type 2 diabetic mice.MethodsA non-selective adiponectin receptor agonist, AdipoRon, and vehicle were injected intraperitoneally into Eight-week-old db/db or C57BLKS/J mice for 10 days. Cardiac morphology and function were evaluated by echocardiography and working heart perfusions.ResultsBased on echocardiography, AdipoRon treatment did not alter ejection fraction, left ventricular diameters or left ventricular wall thickness in db/db mice compared to vehicle-treated mice. In isolated working hearts, an impairment in cardiac output and efficiency in db/db mice was not improved by AdipoRon. Mitochondrial respiratory capacity, respiration in the presence of oligomycin, and 4-hydroxynonenal levels were similar among all groups. However, AdipoRon induced a marked shift in the substrate oxidation pattern in db/db mice towards increased reliance on glucose utilization. In parallel, the diabetes-associated increase in serum triglyceride levels in vehicle-treated db/db mice was blunted by AdipoRon treatment, while an increase in myocardial triglycerides in vehicle-treated db/db mice was not altered by AdipoRon treatment.ConclusionAdipoRon treatment shifts myocardial substrate preference towards increased glucose utilization, likely by decreasing fatty acid delivery to the heart, but was not sufficient to improve cardiac output and efficiency in db/db mice.

Local impedance for the optimization of radiofrequency lesion delivery: A review of bench and clinical data.

Radiofrequency catheter ablation is a cornerstone of treatment for many cardiac arrhythmias. Progression in three-dimensional mapping and contact-force sensing technologies have improved our capability to achieve success, but challenges still remain. In this article, we discuss the importance of overall circuit impedance in radiofrequency lesion formation. This is followed by a review of the literature regarding recently developed "local impedance" technology and its current and future potential applications and limitations, in the context of established surrogate markers currently used to infer effective ablation. We discuss the role of local impedance in assessing myocardial substrate, as well as its role in clinical studies of ablation. We also discuss safety considerations, limitations and ongoing research. Local impedance is a novel tool which has the potential to tailor ablation in a manner distinct from other established metrics.

671 First-in-man mapping and ablation of ventricular tachycardia using a novel ablation catheter with microelectrodes and thermocouples

Abstract Aims Catheter ablation (CA) is an important therapeutic option for patients with recurrent ventricular tachycardia (VT). Recently, a novel contact-force sensing catheter (QDOT, Biosense Webster) allowing radiofrequency ablation in a temperature-controlled fashion, equipped with microelectrodes and thermocouples has been developed and tested in very-high power short duration CA of atrial fibrillation. As of today, this catheter has never been used for VT ablation. To describe the safety and short-term clinical performance of the novel QDOT catheter for the ablation of recurrent VT/electrical storm. Methods and results Case 1: a 43-year-old male patient with prior anterior myocardial infarction (MI), left ventricular (LV) dysfunction with an apical aneurysm, and recurrent VT episodes was admitted to our hospital for CA of VT. The patient underwent high-density electroanatomical mapping of the left ventricle using a multipolar catheter (PentaRay, Biosense Webster), which showed an extensive apical dense scar region, corresponding to the ventricular aneurysm. When the QDOT catheter was advanced in that region, late/fragmented potentials were detected by microelectrodes as well as by conventional electrodes. During the procedure, a sustained VT with right bundle branch block (RBBB)-inferior axis morphology and transition in V2 could be induced. We recorder diastolic fragmented potentials inside the aneurysm, where the novel catheter previously showed late/fragmented potentials; radiofrequency energy delivery with conventional settings (40 W) in that area led to rapid arrhythmia termination (Figure A). At the end of the procedure, VTs were no more inducible. Case 2: a 79-year-old male patient with prior inferior MI, mild LV dysfunction with a 5 cm × 5 cm × 3 cm aneurysm of the basal-mid inferior wall, and two previous CAs for recurrent VT presented to our hospital for electrical storm due to multiple episodes of slow VT (cycle, 470 ms, RBBB morphology, inferior axis, transition in V6), which were refractory to antiarrhythmic drug treatment. We decided to perform redo CA using the QDOT catheter, which revealed long and fragmented low-amplitude diastolic potentials inside the LV aneurysm (Figure B). VT was rapidly terminated by means of radiofrequency energy delivery with usual settings (40 W) in this region, and was no more inducible afterwards. Conclusions The novel ablation catheter showed favourable manoeuverability in the ventricle, while also allowing a precise characterization of the tachycardia circuitry and of the arrhythmogenic myocardial substrate, which was enhanced by the availability of microelectrodes. We believe that this preliminary experience may pave the way for further assessments of this new technology in the so far unexplored ventricular milieu.

Machine learning based deconvolution of microarray atrial samples from atrial fibrillation patients reveals increased fractions of follicular CD4+ T lymphocytes and gamma-delta T cells.

A potential relationship between T cell immunity and development of atrial fibrillation (AF) has been proposed. Historically in AF patients it has been reported that peripheral blood had elevated CD4+ T cells. However few studies have explored whether there is a direct increase of CD4+ T cells in atrial tissues with AF. In this study, public domain micro-array dataset of cardiac surgery patients with atrial tissue biopsies in AF and non-AF patients have been used to explore immune cell subsets. Machine learning based deconvolution of permanent atrial fibrillation microarray atrial samples was applied using Cibersort to enumerate the relative fractions of twenty-two different leukocyte sub-populations. Cibersort enumerated significantly increased fractions of follicular CD4+ T lymphocytes and gamma-delta T cells in the atria of permanent AF subjects. Gene expression analysis of permanent AF microarray tissue samples with elevated follicular CD4+ T cell fractions with gene pathways associated with myocardial substrate remodelling. That is both integrin and non-integrin mediated gene interactions between inflammatory cells and the extra cellular matrix, including infiltrating follicular CD4+ T cells that trafficked to the atria by virtue of the repertoire of cell surfaced expressed adhesion molecules. Additionally, IL-17 and other interleukin inflammatory gene heat maps were associated with enhanced CD4+ follicular T cell expression in our profiled atrial tissues with AF. These observations suggest that atrial structural remodelling was associated with the presence of pathogenic T cell mediated inflammation, present in AF atria but not in non-AF atria.

Understanding Circadian Mechanisms of Sudden Cardiac Death: A Report From the National Heart, Lung, and Blood Institute Workshop, Part 1: Basic and Translational Aspects.

Sudden cardiac death (SCD), the unexpected death due to acquired or genetic cardiovascular disease, follows distinct 24-hour patterns in occurrence. These 24-hour patterns likely reflect daily changes in arrhythmogenic triggers and the myocardial substrate caused by day/night rhythms in behavior, the environment, and endogenous circadian mechanisms. To better address fundamental questions regarding the circadian mechanisms, the National Heart, Lung, and Blood Institute convened a workshop, Understanding Circadian Mechanisms of Sudden Cardiac Death. We present a 2-part report of findings from this workshop. Part 1 summarizes the workshop and serves to identify research gaps and opportunities in the areas of basic and translational research. Among the gaps was the lack of standardization in animal studies for reporting environmental conditions (eg, timing of experiments relative to the light dark cycle or animal housing temperatures) that can impair rigor and reproducibility. Workshop participants also pointed to uncertainty regarding the importance of maintaining normal circadian rhythmic synchrony and the potential pathological impact of desynchrony on SCD risk. One related question raised was whether circadian mechanisms can be targeted to reduce SCD risk. Finally, the experts underscored the need for studies aimed at determining the physiological importance of circadian clocks in the many different cell types important to normal heart function and SCD. Addressing these gaps could lead to new therapeutic approaches/molecular targets that can mitigate the risk of SCD not only at certain times but over the entire 24-hour period.

Effect of elevated plasma ketones on cardiac efficiency

BackgroundThe mechanism(s) responsible for the cardiac benefits of SGLT2 inhibitors remain unknown. Specific AimTo examine the effect of increased plasma ketone concentration (with infusion of beta-hydroxybutyrate [BOHB]) on LV function and myocardial glucose uptake. MethodsTwo groups (6 per group) of T2DM with HFrEF (<45%) were studied. Group I (Age=59; BMI=31 kg/m2; A1c = 7.2%; EF=41%) received in random order a 6-hour BOHB infusion (Prime =1.5 mg/kg.min, then 0.75 mg/kg.min) or 6-hour HCO3 infusion with matching volume (control). Group II (Age=56; BMI=34 kg/m2; A1c=7.2%; EF=38%) received a 3-hour BOHB infusion at a higher rate (Prime=4.0 mg/kg.min, then 2.0 mg/kg.min). A cardiac MRI was performed before and after each infusion. Additionally, Group I underwent a PET study with 18F-2-DOG and 15O. ResultsGroups I and II achieved plasma ketone levels of 1.4 and 2.5 mmol/L, respectively. In Group II, BOHB infusion significantly (P<0.01) increased CO and EF, whereas in Group I the increase in CO and EF tend toward significance (p=0.06), suggesting a dose-dependent response to the increase in plasma ketone concentration. NaHCO3 infusion had no effect on any cardiac indices (Fig.1). Myocardial blood flow increased significantly (P<0.01) in both Group I and II. Myocardial glucose uptake was not altered by BOHB infusion. ConclusionIn patients with T2DM and HFrEF, a physiologic increase in plasma ketone concentration significantly increased LV function and myocardial blood flow without affecting cardiac glucose metabolism. These results suggest that altered myocardial substrate metabolism can be employed therapeutically to improve cardiac function in HFrEF.

Myocardial Aldosterone Receptor and Aquaporin 1 Up-Regulation Is Associated with Cardiomyocyte Remodeling in Human Heart Failure.

Background: Abnormal aldosterone signaling is a recognized source of cardiovascular damage. Its influence on cardiomyocyte structure, function, and hormonal receptors when associated with heart failure is still unreported. Methods: Twenty-six consecutive patients with heart failure (LVEF < 40%) and normal coronaries and valves underwent left ventricular endomyocardial biopsy (EMB) for evaluation of myocardial substrate. Biopsy samples were processed for histology, electron microscopy, immunohistochemistry, and Western blot analysis of myocardial aldosterone receptor and aquaporin-1 correlated with plasma aldosterone (AD) and renin activity (PRA). Eight patients with virus-negative inflammatory cardiomyopathy (ICM) had a control EMB after 6 months of immunosuppressive therapy and recovery of cardiac function with re-evaluation of cardiomyocyte structure and receptor expression. Results: EMB in addition to the diagnosis of myocarditis (15 cases), dilated cardiomyopathy CM (6), alcohol CM (2), and diabetic CM (3) showed vacuolar degeneration and cloudy swelling of cardiomyocytes corresponding at electron microscopy to ions and water accumulation into cytosol, membrane-bound vesicles, nucleus, and other organelles, and was associated with an increased AD, PRA, and myocardial expression of aldosterone receptor (2.6 fold) and aquaporin 1 (2.7 fold). In the 8 patients recovered from ICM, cardiomyocyte diameter reduced with disappearance of intracellular vacuoles and normalization of cytosol, nucleus, and cell organelles’ electron-density, along with down-regulation of aldosterone receptor and aquaporin-1. Conclusion: Human heart failure is associated with overexpression of myocardial aldosterone receptor and aquaporin-1. These molecular changes are paralleled by intracellular water overloading and cardiomyocyte swelling and dysfunction. Cardiac recovery is accompanied by down-regulation of hormonal receptors and normalization of cell structure and composition.

Cardiac rest and stress metabolism in type 2 diabetes (T2D): can the diabetic heart flex under stress?

Abstract Background Efficient matching of energy supply to demand is essential for maintaining normal cardiac function. Altered cardiac metabolism may contribute to the development of cardiac dysfunction by impairing metabolic flexibility in type 2 diabetes (T2D). Purpose We aimed to evaluate the effect of T2D on myocardial substrate preferences in response to acute increases in cardiac workload and the effects on contractile function utilising simultaneous coronary sinus (CS) and aorta blood sampling and cardiac magnetic resonance (CMR) imaging Methods Eligible participants without obstructive coronary artery disease (&amp;gt;50% luminal coronary artery stenosis on coronary angiography) underwent transmyocardial arteriovenous blood sampling. Metabolites in paired coronary sinus and arterial samples were quantified to determine myocardial fuel selection at rest and during a stress protocol with intravenous dobutamine. Free fatty acid (FFA), glucose, 3-hydroxybutyric acid (3HBA) and lactate utilisation at rest and haemodynamic stress was calculated as an extraction fraction % (EF). Participants underwent dobutamine stress multiparametric CMR imaging at 3.0 Tesla (Skyra, Siemens, Germany) on a separate visit within 21 days to quantify cardiac volumes, function and perfusion. Results Two thousand and sixty-one participants were screened and due to stringent inclusion and exclusion criteria for this mechanistic study, three T2D patients and five matching controls were enrolled. Baseline demographics and metabolic and CMR results are documented in Table 1. At peak stress levels there was a significant increase in FFA use from rest to stress in controls only (p=0.002). There were no significant differences in FA or glucose uptake between T2D patients and controls at rest or stress. 3HBA EF was significantly increased in T2D during stress (25.04% vs 5.31%, p=0.007). Mean FFA and 3-HBA changes calculated as extraction fraction at stress and rest are illustrated in Figure 1. Conclusions We demonstrate for the first time in vivo that the diabetic heart switches to ketone bodies during increased workloads as a significant fuel source. At present, it is unknown whether enhanced ketone body metabolism in T2D is beneficial, maladaptive, or a bystander. As the energetic properties of ketones are favourable, increased myocardial ketone oxidation could be an adaptive change designed to compensate for defects in myocardial energy metabolism in diabetes. Further, larger studies are warranted. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): British Heart Foundation - Clinical Research Training FellowshipWellcome Trust Seed Grant Table 1Figure 1

Time-efficient three-dimensional transmural scar assessment provides relevant substrate characterization for ventricular tachycardia features and long-term recurrences in ischemic cardiomyopathy

Delayed gadolinium-enhanced cardiac magnetic resonance (LGE-CMR) imaging requires novel and time-efficient approaches to characterize the myocardial substrate associated with ventricular arrhythmia in patients with ischemic cardiomyopathy. Using a translational approach in pigs and patients with established myocardial infarction, we tested and validated a novel 3D methodology to assess ventricular scar using custom transmural criteria and a semiautomatic approach to obtain transmural scar maps in ventricular models reconstructed from both 3D-acquired and 3D-upsampled-2D-acquired LGE-CMR images. The results showed that 3D-upsampled models from 2D LGE-CMR images provided a time-efficient alternative to 3D-acquired sequences to assess the myocardial substrate associated with ischemic cardiomyopathy. Scar assessment from 2D-LGE-CMR sequences using 3D-upsampled models was superior to conventional 2D assessment to identify scar sizes associated with the cycle length of spontaneous ventricular tachycardia episodes and long-term ventricular tachycardia recurrences after catheter ablation. This novel methodology may represent an efficient approach in clinical practice after manual or automatic segmentation of myocardial borders in a small number of conventional 2D LGE-CMR slices and automatic scar detection.

Abstract P445: A Combinatorial Approach Comprehensively Improves The Maturation Of Human Induced Pluripotent Stem Cell Derived Atrial Cardiomyocytes

Introduction: The limited success of pharmacological approaches to atrial fibrillation ( AF ) is due to limitations of in vitro and in vivo models and inaccessibility of human atrial tissue. Patient-specific induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-aCMs) are a robust platform to model the heterogeneous myocardial substrate of AF, but their immaturity limits their fidelity. Objective: We hypothesized that a combinatorial approach of biochemical (triiodothyronine [ T3 ], insulin-like growth factor-1 [ IGF-1 ], and dexamethasone; collectively TID ), bioenergetic (fatty acids [ FA ]), and electrical stimulation ( ES ) will enhance electrophysiological ( EP ), structural, and metabolic maturity of iPSC- a CMs. Methods: We assessed maturation with whole cell patch clamping, calcium transients, immunofluorescence (IF), Seahorse Analyzer, contractility assay, RT-PCR, Western Blotting, and RNA sequencing (RNAseq). Using a time series with RNAseq we identified signaling pathways and transcriptional regulation that drive EP, structural, and metabolic atrial development and compared iPSC-aCM maturity with human aCMs (haCMs) obtained from the same patient. Results: TID+FA+ES significantly improved structural organization and cell morphology ( Fig. 1a ), enhanced membrane potential stability and improved depolarization ( Fig. 1b ), improved Ca 2+ kinetics with faster and increased Ca 2+ release from sarcoplasmic reticulum ( Fig. 1c ), and increased expression of Na + , Ca 2+ , and K + channels, markers of structural maturity, FA metabolism, and oxidative phosphorylation ( Fig. 1d ). There was no difference in each parameter between TID+FA+ES iPSC-aCMs and haCMs from the same patient. Conclusion: Our optimized, combinatorial TID+FA+ES approach markedly enhanced EP, structural, and metabolic maturity of human iPSC-aCMs, which will be useful for elucidating the genetic basis of AF developing precision drug therapies.

Post-translational Acetylation Control of Cardiac Energy Metabolism.

Perturbations in myocardial energy substrate metabolism are key contributors to the pathogenesis of heart diseases. However, the underlying causes of these metabolic alterations remain poorly understood. Recently, post-translational acetylation-mediated modification of metabolic enzymes has emerged as one of the important regulatory mechanisms for these metabolic changes. Nevertheless, despite the growing reports of a large number of acetylated cardiac mitochondrial proteins involved in energy metabolism, the functional consequences of these acetylation changes and how they correlate to metabolic alterations and myocardial dysfunction are not clearly defined. This review summarizes the evidence for a role of cardiac mitochondrial protein acetylation in altering the function of major metabolic enzymes and myocardial energy metabolism in various cardiovascular disease conditions.

B-PO05-175 CONDUCTION VELOCITY MAPPING: VALIDATING TIME ANNOTATION AGNOSTIC METHOD FROM AN OPTICAL MAPPING REFERENCE STANDARD

Mapping cardiac conduction velocity may provide assessment of myocardial substrate, fiber anisotropy and zones of myocardium that may be critical to arrhythmia maintenance. However, validating new methodology is limited by the lack of a true reference standard. Optical mapping provides true local assessment of myocardial depolarization and true wave front mapping. To validate Omnipolar mapping technology derived wave speed (OT-WS) and wave direction (OT-DI) from an optical mapping standard. Optical mapping data was acquired from whole heart rabbit Langendorff model. Waves were produced by electrically stimulating the heart at the edge of the mapping field. Conduction velocity (CV) measurements were performed on a 4 x 4 array of virtual electrodes equally spaced by 2.4 mm, located in the middle of the mapping field. Traditional CV measurement methods based on local activation time (LAT, Dubois, Bayly) produced a gold standard of wave speed (LAT-WS) and direction (LAT-DI). These parameters were compared against OT-WS and OT-DI respectively. Beat to beat variability of speed and direction from both methods were also compared. 3 rabbit hearts experiments and 6 pacing locations were studied. Average OT-WS was 45.2 ± 10.6 cm/s, compared to 48.6 ± 14.6 for LAT_WS. OT-WS variability was comparable to LAT-WS (3.8 cm/s vs. 4.0 cm/s, p=0.85) as well as OT-DI variability versus LAT-DI (5.8° vs. 6.6°, p=0.76). OT measurements of speed and direction are comparable to gold standard in an optical mapping model without the need of LAT annotation. Beat-to-beat stability of OT measurements suggests OT might be superior predictor than LAT-based methods.

B-IN02-03 USING PULSED ELECTRIC FIELDS TO CAUSE FOCAL FIBROSIS IN THE INTERVENTRICULAR SEPTUM

Pulse electric fields (PEF) are being investigated as an alternative ablation modality to traditional radiofrequency ablation for modification of myocardial substrate. Assess the extent and time course of myocardial scar formation caused by application of PEF at the interventricular septum. Four-week survival experiments were performed in 8 canines. Energy was delivered using ablation catheters in bipolar configuration to apply PEF to the septum. Two animals were administered pulses at microsecond pulse widths and six received nanosecond pulses for a total 75-189 J delivered per animal. MRI studies were performed in 4 of the 8 animals. Scar formation was assessed by measuring late gadolinium enhancement (LGE) and confirmed by histology. Sites of PEF delivery exhibited myocardial edema on triple inversion recovery and early scar with some LGE visible after 7 days. Lesion volumes were larger for transmural configurations vs. bipolar PEF delivered in a single cardiac chamber (10.7 ± 2.3 cm3 vs. 2.9 ± 1.1 cm3). At 30 days, lesions predominantly exhibited LGE and total lesion volumes were similar for both groups (5.3 ± 2.4 cm3 vs. 4.0 ± 0.2 cm3). Transmural MRI lesions were achieved when bipolar electrodes were placed on either side of the septum, and total lesion volume was dose-dependent. Myocardial fibrosis was identified on histology. Bipolar configurations entirely within a chamber produced superficial lesions, even with delivery of higher energy. Application of PEF to the myocardium can cause substrate modification, including transmural fibrosis. Lesion volume is dose-dependent for transmural electrode configurations.

Myocardial glucose and fatty acid metabolism is altered and associated with lower cardiac function in young adults with Barth syndrome

BackgroundBarth syndrome (BTHS) is a rare X-linked condition resulting in cardiomyopathy, however; the effects of BTHS on myocardial substrate metabolism and its relationships with cardiac high-energy phosphate metabolism and left ventricular (LV) function are unknown. We sought to characterize myocardial glucose, fatty acid (FA), and leucine metabolism in BTHS and unaffected controls and examine their relationships with cardiac high-energy phosphate metabolism and LV function. Methods/ResultsYoung adults with BTHS (n = 14) and unaffected controls (n = 11, Control, total n = 25) underwent bolus injections of 15O-water and 1-11C-glucose, palmitate, and leucine and concurrent positron emission tomography imaging. LV function and cardiac high-energy phosphate metabolism were examined via echocardiography and 31P magnetic resonance spectroscopy, respectively. Myocardial glucose extraction fraction (21 ± 14% vs 10 ± 8%, P = .03) and glucose utilization (828.0 ± 470.0 vs 393.2 ± 361.0 μmol·g−1·min−1, P = .02) were significantly higher in BTHS vs Control. Myocardial FA extraction fraction (31 ± 7% vs 41 ± 6%, P < .002) and uptake (0.25 ± 0.04 vs 0.29 ± 0.03 mL·g−1·min−1, P < .002) were significantly lower in BTHS vs Control. Altered myocardial metabolism was associated with lower cardiac function in BTHS. ConclusionsMyocardial substrate metabolism is altered and may contribute to LV dysfunction in BTHS.Clinical Trials #: NCT01625663.