Intramyocardial Adiposity After Myocardial Infarction

Evaluation of a deep learning-enabled automated computational heart modelling workflow for personalized assessment of ventricular arrhythmias

Personalized, image-based computational heart modelling is a powerful technology that can be used to improve patient-specific arrhythmia risk stratification and ventricular tachycardia (VT) ablation targeting. However, most state-of-the-art methods still require manual interactions by expert users. The goal of this study is to evaluate the feasibility of an automated, deep learning-based workflow for reconstructing personalized computational electrophysiological heart models to guide patient-specific treatment of VT. Contrast-enhanced computed tomography (CE-CT) images with expert ventricular myocardium segmentations were acquired from 111 patients across five cohorts from three different institutions. A deep convolutional neural network (CNN) for segmenting left ventricular myocardium from CE-CT was developed, trained and evaluated. From both CNN-based and expert segmentations in a subset of patients, personalized electrophysiological heart models were reconstructed and rapid pacing was used to induce VTs. CNN-based and expert segmentations were more concordant in the middle myocardium than in the heart's base or apex. Wavefront propagation during pacing was similar between CNN-based and original heart models. Between most sets of heart models, VT inducibility was the same, the number of induced VTs was strongly correlated, and VT circuits co-localized. Our results demonstrate that personalized computational heart models reconstructed from deep learning-based segmentations even with a small training set size can predict similar VT inducibility and circuit locations as those from expertly-derived heart models. Hence, a user-independent, automated framework for simulating arrhythmias in personalized heart models could feasibly be used in clinical settings to aid VT risk stratification and guide VT ablation therapy. KEY POINTS: Personalized electrophysiological heart modelling can aid in patient-specific ventricular tachycardia (VT) risk stratification and VT ablation targeting. Current state-of-the-art, image-based heart models for VT prediction require expert-dependent, manual interactions that may not be accessible across clinical settings. In this study, we develop an automated, deep learning-based workflow for reconstructing personalized heart models capable of simulating arrhythmias and compare its predictions with that of expert-generated heart models. The number and location of VTs was similar between heart models generated from the deep learning-based workflow and expert-generated heart models. These results demonstrate the feasibility of using an automated computational heart modelling workflow to aid in VT therapeutics and has implications for generalizing personalized computational heart technology to a broad range of clinical centres.

Whole-Heart Histological and Electroanatomic Assessment of Postinfarction Cardiac Magnetic Resonance Imaging Scar and Conducting Channels

BACKGROUND

Cardiac magnetic resonance imaging (CMR)-defined ventricular scar and anatomic conduction channels (CMR-CCs) offer promise in delineating ventricular tachycardia substrate. No studies have validated channels with coregistered histology, nor have they ascertained the histological characteristics of deceleration zones (DZs) within these channels. We aimed to validate CMR scar and CMR-CCs with whole-heart histology and electroanatomic mapping in a postinfarction model.

METHODS

Five sheep underwent anteroseptal infarction. CMR (116±20 days post infarct) was postprocessed using ADAS-3D, varying pixel intensity thresholds (5545, 6040, 6535, and 7030). DZs were identified by electroanatomic mapping (129±12 days post infarct). Explanted hearts were sectioned and stained with Picrosirius red, and whole-heart histopathologic shells were generated. Scar topography as well as percentage fibrosis, adiposity, and remaining viable myocardium within 3 mm histological biopsies and within CMR-CCs were determined.

RESULTS

Using the standard 6040 thresholding, CMR had 83.8% accuracy for identifying histological scar in the endocardium (κ, 0.666) and 61.4% in the epicardium (κ, 0.276). Thirty-seven CMR-CCs were identified by varying thresholding; 23 (62%) were unique. DZs colocalized to 19 of 23 (83%) CMR-CCs. Twenty (87%) CMR-CCs were histologically confirmed. Within-channel histological fibrosis did not differ by the presence of DZs (P=0.242). Within-channel histological adiposity was significantly higher at sites with versus without DZs (24.1% versus 8.3%; P<0.001).

CONCLUSIONS

Postprocessed CMR-derived scars and channels were validated by histology and electroanatomic mapping. Regions of CMR-CCs at sites of DZs had higher adiposity but similar fibrosis than regions without DZs, suggesting that lipomatous metaplasia may contribute to arrhythmogenicity of postinfarction scar.

Epicardial fat in heart failure-Friend, foe, or bystander

Epicardial adipose tissue (EAT) is a fat depot covering the heart. No physical barrier separates EAT from the myocardium, so EAT can easily affect the underlying cardiac muscle. EAT can participate in the development and progression of heart failure with preserved (HFpEF) and reduced ejection fraction (HFrEF). In healthy humans, excess EAT is associated with impaired cardiac function and worse outcomes. In HFpEF, this trend continues: EAT amount is usually increased, and excess EAT correlates with worse function/outcomes. However, in HFrEF, the opposite is true: reduced EAT amount correlates with worse cardiac function/outcomes. Surprisingly, although EAT has beneficial effects on cardiac function, it aggravates ventricular arrhythmias. Here, we dissect these phenomena, trying to explain these paradoxical findings to find a target for novel heart failure therapies aimed at EAT rather than the myocardium itself. However, the success of this approach depends on a thorough understanding of interactions between EAT and the myocardium.

Computational modeling of cardiac electrophysiology and arrhythmogenesis: toward clinical translation

The complexity of cardiac electrophysiology, involving dynamic changes in numerous components across multiple spatial (from ion channel to organ) and temporal (from milliseconds to days) scales, makes an intuitive or empirical analysis of cardiac arrhythmogenesis challenging. Multiscale mechanistic computational models of cardiac electrophysiology provide precise control over individual parameters, and their reproducibility enables a thorough assessment of arrhythmia mechanisms. This review provides a comprehensive analysis of models of cardiac electrophysiology and arrhythmias, from the single cell to the organ level, and how they can be leveraged to better understand rhythm disorders in cardiac disease and to improve heart patient care. Key issues related to model development based on experimental data are discussed, and major families of human cardiomyocyte models and their applications are highlighted. An overview of organ-level computational modeling of cardiac electrophysiology and its clinical applications in personalized arrhythmia risk assessment and patient-specific therapy of atrial and ventricular arrhythmias is provided. The advancements presented here highlight how patient-specific computational models of the heart reconstructed from patient data have achieved success in predicting risk of sudden cardiac death and guiding optimal treatments of heart rhythm disorders. Finally, an outlook toward potential future advances, including the combination of mechanistic modeling and machine learning/artificial intelligence, is provided. As the field of cardiology is embarking on a journey toward precision medicine, personalized modeling of the heart is expected to become a key technology to guide pharmaceutical therapy, deployment of devices, and surgical interventions.

Lipomatous Metaplasia Is Associated With Ventricular Tachycardia Recurrence Following Ablation in Patients With Nonischemic Cardiomyopathy

BACKGROUND

Ventricular tachycardia (VT) recurrence rates remain high following ablation among patients with nonischemic cardiomyopathy (NICM).

OBJECTIVES

This study sought to define the prevalence of lipomatous metaplasia (LM) in patients with NICM and VT and its association with postablation VT recurrence.

METHODS

From patients who had ablation of left ventricular VT, we retrospectively identified 113 consecutive NICM patients with preprocedural contrast-enhanced cardiac computed tomography (CECT), from which LM was segmented. Nested within this cohort were 62 patients that prospectively underwent CECT and cardiac magnetic resonance from which myocardial border zone and dense late gadolinium enhancement (LGE) were segmented. A control arm of 30 NICM patients without VT with CECT was identified.

RESULTS

LM was identified among 57% of control patients without VT vs 83% of patients without VT recurrence and 100% of patients with VT recurrence following ablation. In multivariable analyses, LM extent was the only independent predictor of VT recurrence, with an adjusted HR per 1-g LM increase of 1.1 (P < 0.001). Patients with LM extent ≥2.5 g had 4.9-fold higher hazard of VT recurrence than those with LM <2.5 g (P < 0.001). In the nested cohort with 32 VT recurrences, LM extent was independently associated with VT recurrence after adjustment for border zone and LGE extent (HR per 1 g increase: 1.1; P = 0.036).

CONCLUSIONS

Myocardial LM is prevalent in patients with NICM of a variety of etiologies, and its extent is associated with postablation VT recurrence independent of the degree of fibrosis.

Adipose tissue as a linchpin of organismal ageing

Ageing is a conserved biological process, modulated by intrinsic and extrinsic factors, that leads to changes in life expectancy. In humans, ageing is characterized by greatly increased prevalence of cardiometabolic disease, type 2 diabetes and disorders associated with impaired immune surveillance. Adipose tissue displays species-conserved, temporal changes with ageing, including redistribution from peripheral to central depots, loss of thermogenic capacity and expansion within the bone marrow. Adipose tissue is localized to discrete depots, and also diffusely distributed within multiple organs and tissues in direct proximity to specialized cells. Thus, through their potent endocrine properties, adipocytes are capable of modulating tissue and organ function throughout the body. In addition to adipocytes, multipotent progenitor/stem cells in adipose tissue play a crucial role in maintenance and repair of tissues throughout the lifetime. Adipose tissue may therefore be a central driver for organismal ageing and age-associated diseases. Here we review the features of adipose tissue during ageing, and discuss potential mechanisms by which these changes affect whole-body metabolism, immunity and longevity. We also explore the potential of adipose tissue-targeted therapies to ameliorate age-associated disease burdens.

Epicardial fat and ventricular arrhythmias

The arrhythmogenic role of epicardial adipose tissue (EAT) in atrial arrhythmias is well established, but its effect on ventricular arrhythmias has been significantly less investigated. Since ventricular arrhythmias are thought to cause 75%-80% of cases of sudden cardiac death, this is not a trivial issue. We provide an overview of clinical data as well as experimental and molecular data linking EAT to ventricular arrhythmias, attempting to dissect possible mechanisms and indicate future directions of research and possible clinical implications. However, despite a wealth of data indicating the role of epicardial and intramyocardial fat in the induction and propagation of ventricular arrhythmias, unfortunately there is currently no direct evidence that indeed EAT triggers arrhythmia or can be a target for antiarrhythmic strategies.

Mechanistic insight into the functional role of human sinoatrial node conduction pathways and pacemaker compartments heterogeneity: A computer model analysis

The sinoatrial node (SAN), the primary pacemaker of the heart, is responsible for the initiation and robust regulation of sinus rhythm. 3D mapping studies of the ex-vivo human heart suggested that the robust regulation of sinus rhythm relies on specialized fibrotically-insulated pacemaker compartments (head, center and tail) with heterogeneous expressions of key ion channels and receptors. They also revealed up to five sinoatrial conduction pathways (SACPs), which electrically connect the SAN with neighboring right atrium (RA). To elucidate the role of these structural-molecular factors in the functional robustness of human SAN, we developed comprehensive biophysical computer models of the SAN based on 3D structural, functional and molecular mapping of ex-vivo human hearts. Our key finding is that the electrical insulation of the SAN except SACPs, the heterogeneous expression of If, INa currents and adenosine A1 receptors (A1R) across SAN pacemaker-conduction compartments are required to experimentally reproduce observed SAN activation patterns and important phenomena such as shifts of the leading pacemaker and preferential SACP. In particular, we found that the insulating border between the SAN and RA, is required for robust SAN function and protection from SAN arrest during adenosine challenge. The heterogeneity in the expression of A1R within the human SAN compartments underlies the direction of pacemaker shift and preferential SACPs in the presence of adenosine. Alterations of INa current and fibrotic remodelling in SACPs can significantly modulate SAN conduction and shift the preferential SACP/exit from SAN. Finally, we show that disease-induced fibrotic remodeling, INa suppression or increased adenosine make the human SAN vulnerable to pacing-induced exit blocks and reentrant arrhythmia. In summary, our computer model recapitulates the structural and functional features of the human SAN and can be a valuable tool for investigating mechanisms of SAN automaticity and conduction as well as SAN arrhythmia mechanisms under different pathophysiological conditions.

Association of epicardial and intramyocardial fat with ventricular arrhythmias

BACKGROUND

Among patients with ischemic cardiomyopathy (ICM) and nonischemic cardiomyopathy (NICM), myocardial fibrosis is associated with an increased risk for ventricular arrhythmia (VA). Growing evidence suggests that myocardial fat contributes to ventricular arrhythmogenesis. However, little is known about the volume and distribution of epicardial adipose tissue and intramyocardial fat and their relationship with VAs.

OBJECTIVE

The purpose of this study was to assess the association of contrast-enhanced computed tomography (CE-CT)-derived left ventricular (LV) tissue heterogeneity, epicardial adipose tissue volume, and intramyocardial fat volume with the risk of VA in ICM and NICM patients.

METHODS

Patients enrolled in the PROSE-ICD registry who underwent CE-CT were included. Intramyocardial fat volume (voxels between -180 and -5 Hounsfield units [HU]), epicardial adipose tissue volume (between -200 and -50 HU), and LV tissue heterogeneity were calculated. The primary endpoint was appropriate ICD shocks or sudden arrhythmic death.

RESULTS

Among 98 patients (47 ICM, 51 NICM), LV tissue heterogeneity was associated with VA (odds ratio [OR] 1.10; P = .01), particularly in the ICM cohort. In the NICM subgroup, epicardial adipose tissue and intramyocardial fat volume were associated with VA (OR 1.11, P = .01; and OR = 1.21, P = .01, respectively) but not in the ICM patients (OR 0.92, P =.22; and OR = 0.96, P =.19, respectively).

CONCLUSION

In ICM patients, increased fat distribution heterogeneity is associated with VA. In NICM patients, an increased volume of intramyocardial fat and epicardial adipose tissue is associated with a higher risk for VA. Our findings suggest that fat's contribution to VAs depends on the underlying substrate.

Nonmyocytes as electrophysiological contributors to cardiac excitation and conduction

Although cardiac action potential (AP) generation and propagation have traditionally been attributed exclusively to cardiomyocytes (CM), other cell types in the heart are also capable of forming electrically conducting junctions. Interactions between CM and nonmyocytes (NM) enable and modulate each other's activity. This review provides an overview of the current understanding of heterocellular electrical communication in the heart. Although cardiac fibroblasts were initially thought to be electrical insulators, recent studies have demonstrated that they form functional electrical connections with CM in situ. Other NM, such as macrophages, have also been recognized as contributing to cardiac electrophysiology and arrhythmogenesis. Novel experimental tools have enabled the investigation of cell-specific activity patterns in native cardiac tissue, which is expected to yield exciting new insights into the development of novel or improved diagnostic and therapeutic strategies.

Lipomatous Metaplasia Facilitates Slow Conduction in Critical Ventricular Tachycardia Corridors Within Postinfarct Myocardium

BACKGROUND

Myocardial lipomatous metaplasia (LM) has been reported to be associated with post-infarct ventricular tachycardia (VT) circuitry.

OBJECTIVES

This study examined the association of scar versus LM composition with impulse conduction velocity (CV) in putative VT corridors that traverse the infarct zone in post-infarct patients.

METHODS

The cohort included 31 post-infarct patients from the prospective INFINITY (Intra-Myocardial Fat Deposition and Ventricular Tachycardia in Cardiomyopathy) study. Myocardial scar, border zone, and potential viable corridors were defined by late gadolinium enhancement cardiac magnetic resonance (LGE-CMR), and LM was defined by computed tomography. Images were registered to electroanatomic maps, and the CV at each electroanatomic map point was calculated as the mean CV between that point and 5 adjacent points along the activation wave front.

RESULTS

Regions with LM exhibited lower CV than scar (median = 11.9 vs 13.5 cm/s; P < 0.001). Of 94 corridors computed from LGE-CMR and electrophysiologically confirmed to participate in VT circuitry, 93 traversed through or near LM. These critical corridors displayed slower CV (median 8.8 [IQR: 5.9-15.7] cm/s vs 39.2 [IQR: 28.1-58.5]) cm/s; P < 0.001) than 115 noncritical corridors distant from LM. Additionally, critical corridors demonstrated low-peripheral, high-center (mountain shaped, 23.3%) or mean low-level (46.7%) CV patterns compared with 115 noncritical corridors distant from LM that displayed high-peripheral, low-center (valley shaped, 19.1%) or mean high-level (60.9%) CV patterns.

CONCLUSIONS

The association of myocardial LM with VT circuitry is at least partially mediated by slowing nearby corridor CV thus facilitating an excitable gap that enables circuit re-entry.

Conduction Velocity Dispersion Predicts Postinfarct Ventricular Tachycardia Circuit Sites and Associates With Lipomatous Metaplasia

BACKGROUND

Regional myocardial conduction velocity (CV) dispersion has not been studied in postinfarct patients with ventricular tachycardia (VT).

OBJECTIVES

This study sought to compare the following: 1) the association of CV dispersion vs repolarization dispersion with VT circuit sites; and 2) myocardial lipomatous metaplasia (LM) vs fibrosis as the anatomic substrate for CV dispersion.

METHODS

Among 33 postinfarct patients with VT, we characterized dense and border zone infarct tissue by late gadolinium enhancement cardiac magnetic resonance, and LM by computed tomography, with both images registered with electroanatomic maps. Activation recovery interval (ARI) was the time interval from the minimum derivative within the QRS complex to the maximum derivative within the T-wave on unipolar electrograms. CV at each EAM point was the mean CV between that point and 5 adjacent points along the activation wave front. CV and ARI dispersion were the coefficient of variation (CoV) of CV and ARI per American Heart Association (AHA) segment, respectively.

RESULTS

Regional CV dispersion exhibited a much larger range than ARI dispersion, with median 0.65 vs 0.24; P < 0.001. CV dispersion was a more robust predictor of the number of critical VT sites per AHA segment than ARI dispersion. Regional LM area was more strongly associated with CV dispersion than fibrosis area. LM area was larger (median 0.44 vs 0.20 cm2; P < 0.001) in AHA segments with mean CV <36 cm/s and CoV_CV >0.65 than those with mean CV <36 cm/s and CoV_CV <0.65.

CONCLUSIONS

Regional CV dispersion more strongly predicts VT circuit sites than repolarization dispersion, and LM is a critical substrate for CV dispersion.

Noninvasive Assessment of Lipomatous Metaplasia as a Substrate for Ventricular Tachycardia in Chronic Infarct

Myocardial lipomatous metaplasia (LM) has been increasingly reported in patients with prior myocardial infarction. Cardiac magnetic resonance and cardiac contrast-enhanced computed tomography have been used to noninvasively detect and quantify myocardial LM in postinfarct patients, and may provide useful information for understanding cardiac mechanics, arrhythmia susceptibility, and prognosis. This review aims to summarize the advantages and disadvantages, clinical applications, and imaging features of different cardiac magnetic resonance sequences and cardiac contrast-enhanced computed tomography for LM detection and quantification. We also briefly summarize LM prevalence in different cohorts of postinfarct patients and review the clinical utility of cardiac imaging in exploring myocardial LM as an arrhythmogenic substrate in patients with prior myocardial infarction.

Utility of cardiac imaging in patients with ventricular tachycardia

Ventricular tachycardia (VT) is a life-threatening arrhythmia that may be idiopathic or result from structural heart disease. Cardiac imaging is critical in the diagnostic workup and risk stratification of patients with VT. Data gained from cardiac imaging provides information on likely mechanisms and sites of origin, as well as risk of intervention. Pre-procedural imaging can be used to plan access route(s) and identify patients where post-procedural intensive care may be required. Integration of cardiac imaging into electroanatomical mapping systems during catheter ablation procedures can facilitate the optimal approach, reduce radiation dose, and may improve clinical outcomes. Intraprocedural imaging helps guide catheter position, target substrate, and identify complications early. This review summarises the contemporary imaging modalities used in patients with VT, and their uses both pre-procedurally and intra-procedurally.

Lipomatous metaplasia prolongs repolarization and increases repolarization dispersion within post-infarct ventricular tachycardia circuit cites

AIMS

Post-infarct myocardium contains viable corridors traversing scar or lipomatous metaplasia (LM). Ventricular tachycardia (VT) circuitry has been separately reported to associate with corridors that traverse LM and with repolarization heterogeneity. We examined the association of corridor activation recovery interval (ARI) and ARI dispersion with surrounding tissue type.

METHODS AND RESULTS

The cohort included 33 post-infarct patients from the prospective Intra-Myocardial Fat Deposition and Ventricular Tachycardia in Cardiomyopathy (INFINITY) study. We co-registered scar and corridors from late gadolinium enhanced magnetic resonance, and LM from computed tomography with intracardiac electrogram locations. Activation recovery interval was calculated during sinus or ventricular pacing, as the time interval from the minimum derivative within the QRS to the maximum derivative within the T-wave on unipolar electrograms. Regional ARI dispersion was defined as the standard deviation (SD) of ARI per AHA segment (ARISD). Lipomatous metaplasia exhibited higher ARI than scar [325 (interquartile range 270-392) vs. 313 (255-374), P < 0.001]. Corridors critical to VT re-entry were more likely to traverse through or near LM and displayed prolonged ARI compared with non-critical corridors [355 (319-397) vs. 302 (279-333) ms, P < 0.001]. ARISD was more closely associated with LM than with scar (likelihood ratio χ2 50 vs. 12, and 4.2-unit vs. 0.9-unit increase in 0.01*Log(ARISD) per 1 cm2 increase per AHA segment). Additionally, LM and scar exhibited interaction (P < 0.001) in their association with ARISD.

CONCLUSION

Lipomatous metaplasia is closely associated with prolonged local action potential duration of corridors and ARI dispersion, which may facilitate the propensity of VT circuit re-entry.

Genetic lineage tracing identifies cardiac mesenchymal-to-adipose transition in an arrhythmogenic cardiomyopathy model

Arrhythmogenic cardiomyopathy (ACM) is one of the most common inherited cardiomyopathies, characterized by progressive fibrofatty replacement in the myocardium. However, the cellular origin of cardiac adipocytes in ACM remains largely unknown. Unraveling the cellular source of cardiac adipocytes in ACM would elucidate the underlying pathological process and provide a potential target for therapy. Herein, we generated an ACM mouse model by inactivating desmosomal gene desmoplakin in cardiomyocytes; and examined the adipogenic fates of several cell types in the disease model. The results showed that SOX9⁺, PDGFRa⁺, and PDGFRb⁺ mesenchymal cells, but not cardiomyocytes or smooth muscle cells, contribute to the intramyocardial adipocytes in the ACM model. Mechanistically, Bmp4 was highly expressed in the ACM mouse heart and functionally promoted cardiac mesenchymal-to-adipose transition in vitro.

The scar: the wind in the perfect storm-insights into the mysterious living tissue originating ventricular arrhythmias

BACKGROUND

Arrhythmic death is very common among patients with structural heart disease, and it is estimated that in European countries, 1 per 1000 inhabitants yearly dies for sudden cardiac death (SCD), mainly as a result of ventricular arrhythmias (VA). The scar is the result of cardiac remodelling process that occurs in several cardiomyopathies, both ischemic and non-ischemic, and is considered the perfect substrate for re-entrant and non-re-entrant arrhythmias.

METHODS

Our aim was to review published evidence on the histological and electrophysiological properties of myocardial scar and to review the central role of cardiac magnetic resonance (CMR) in assessing ventricular arrhythmias substrate and its potential implication in risk stratification of SCD.

RESULTS

Scarring process affects both structural and electrical myocardial properties and paves the background for enhanced arrhythmogenicity. Non-uniform anisotropic conduction, gap junctions remodelling, source to sink mismatch and refractoriness dispersion are some of the underlining mechanisms contributing to arrhythmic potential of the scar. All these mechanisms lead to the initiation and maintenance of VA. CMR has a crucial role in the evaluation of patients suffering from VA, as it is considered the gold standard imaging test for scar characterization. Mounting evidences support the use of CMR not only for the definition of gross scar features, as size, localization and transmurality, but also for the identification of possible conducting channels suitable of discrete ablation. Moreover, several studies call out the CMR-based scar characterization as a stratification tool useful in selecting patients at risk of SCD and amenable to implantable cardioverter-defibrillator (ICD) implantation.

CONCLUSIONS

Scar represents the substrate of ventricular arrhythmias. CMR, defining scar presence and its features, may be a useful tool for guiding ablation procedures and for identifying patients at risk of SCD amenable to ICD therapy.

Obesity and sudden cardiac death: Prevalence, pathogenesis, prevention and intervention

Obesity and sudden cardiac death (SCD) share common risk factors. Obesity, in and of itself, can result in the development of SCD. Numerous epidemiologic and clinical studies have demonstrated the close relationships between obesity and SCD, however, the underlying mechanisms remain incompletely understood. Various evidences support the significance of excess adiposity in determining the risk of SCD, including anatomical remodeling, electrical remodeling, metabolic dysfunction, autonomic imbalance. Weight reduction has improved obesity related comorbidities, and reversed abnormal cardiac remodeling. Indeed, it is still unknown whether weight loss contributes to decreased risk of SCD. Further high-quality, prospective trials are needed to strengthen our understanding on weight management and SCD.

Native T1 Mapping for the Diagnosis of Myocardial Fibrosis in Patients With Chronic Myocardial Infarction

BACKGROUND

Myocardial fibrosis is a fundamental process in cardiac injury. Cardiac magnetic resonance native T1 mapping has been proposed for diagnosing myocardial fibrosis without the need for gadolinium contrast. However, recent studies suggest that T1 measurements can be erroneous in the presence of intramyocardial fat.

OBJECTIVES

The purpose of this study was to investigate whether the presence of fatty metaplasia affects the accuracy of native T1 maps for the diagnosis of myocardial replacement fibrosis in patients with chronic myocardial infarction (MI).

METHODS

Consecutive patients (n = 312) with documented chronic MI (>6 months old) and controls without MI (n = 50) were prospectively enrolled. Presence and size of regions with elevated native T1 and infarction were quantitatively determined (mean + 5SD) on modified look-locker inversion-recovery and delayed-enhancement images, respectively, at 3.0-T. The presence of fatty metaplasia was determined using an out-of-phase steady-state free-precession cine technique and further verified with standard fat-water Dixon methods.

RESULTS

Native T1 mapping detected chronic MI with markedly higher sensitivity in patients with fatty metaplasia than those without fatty metaplasia (85.6% vs 13.3%) with similar specificity (100% vs 98.9%). In patients with fatty metaplasia, the size of regions with elevated T1 significantly underestimated infarct size and there was a better correlation with fatty metaplasia size than infarct size (r = 0.76 vs r = 0.49). In patients without fatty metaplasia, most of the modest elevation in T1 appeared to be secondary to subchronic infarcts that were 6 to 12 months old; the T1 of infarcts >12 months old was not different from noninfarcted myocardium.

CONCLUSIONS

Native T1 mapping is poor at detecting replacement fibrosis but may indirectly detect chronic MI if there is associated fatty metaplasia. Native T1 mapping for the diagnosis and characterization of myocardial fibrosis is unreliable.

Arrhythmic Sudden Cardiac Death in Heart Failure With Preserved Ejection Fraction: Mechanisms, Genetics, and Future Directions

Heart failure with preserved ejection fraction (HFpEF) is an increasingly recognized disorder. Many clinical trials have failed to demonstrate benefit in patients with HFpEF but have recognized alarming rates of sudden cardiac death (SCD). Genetic testing has become standard in the workup of patients with otherwise unexplained cardiac arrest, but the genetic architecture of HFpEF, and the overlap of a genetic predisposition to HFpEF and arrhythmias, is poorly understood. An understanding of the genetics of HFpEF and related SCD has the potential to redefine and generate novel diagnostic, prognostic, and therapeutic tools. In this review, we examine recent pathophysiological and clinical advancements in our understanding of HFpEF, which reinforce the heterogeneity of the condition. We also discuss data describing SCD events in patients with HFpEF and review the current literature on genetic underpinnings of HFpEF. Mechanisms of arrhythmogenesis which may lead to SCD in this population are also explored. Lastly, we outline several areas of promise for experimentation and clinical trials that have the potential to further advance our understanding of and contribute to improved clinical care of this patient population.

Intramyocardial hemorrhage drives fatty degeneration of infarcted myocardium

Sudden blockage of arteries supplying the heart muscle contributes to millions of heart attacks (myocardial infarction, MI) around the world. Although re-opening these arteries (reperfusion) saves MI patients from immediate death, approximately 50% of these patients go on to develop chronic heart failure (CHF) and die within a 5-year period; however, why some patients accelerate towards CHF while others do not remains unclear. Here we show, using large animal models of reperfused MI, that intramyocardial hemorrhage - the most damaging form of reperfusion injury (evident in nearly 40% of reperfused ST-elevation MI patients) - drives delayed infarct healing and is centrally responsible for continuous fatty degeneration of the infarcted myocardium contributing to adverse remodeling of the heart. Specifically, we show that the fatty degeneration of the hemorrhagic MI zone stems from iron-induced macrophage activation, lipid peroxidation, foam cell formation, ceroid production, foam cell apoptosis and iron recycling. We also demonstrate that timely reduction of iron within the hemorrhagic MI zone reduces fatty infiltration and directs the heart towards favorable remodeling. Collectively, our findings elucidate why some, but not all, MIs are destined to CHF and help define a potential therapeutic strategy to mitigate post-MI CHF independent of MI size.

Lipomatous Metaplasia Enables Ventricular Tachycardia by Reducing Current Loss Within the Protected Corridor

BACKGROUND

Post-myocardial infarction ventricular tachycardia (VT) is due to re-entry through surviving conductive myocardial corridors across infarcted tissue. However, not all conductive corridors participate in re-entry.

OBJECTIVES

This study sought to test the hypothesis that critical VT corridors are more likely to traverse near lipomatous metaplasia (LM) and that current loss is reduced during impulse propagation through such corridors.

METHODS

Among 30 patients in the Prospective 2-center INFINITY (Intra-Myocardial Fat Deposition and Ventricular Tachycardia in Cardiomyopathy) study, potential VT-viable corridors within myocardial scar or LM were computed from late gadolinium enhancement cardiac magnetic resonance images. Because late gadolinium enhancement highlights both scar and LM, LM was distinguished from scar by using computed tomography. The SD of the current along each corridor was measured.

RESULTS

Scar exhibited lower impedance than LM (median Z-score -0.22 [IQR: -0.84 to 0.35] vs -0.07 [IQR: -0.67 to 0.54]; P < 0.001). Among all 381 corridors, 84 were proven to participate in VT re-entry circuits, 83 (99%) of which traversed or were adjacent to LM. In comparison, only 13 (4%) non-VT corridors were adjacent to LM. Critical corridors adjacent to LM displayed lower SD of current compared with noncritical corridors through scar but distant from LM (2.0 [IQR: 1.0 to 3.4] μA vs 8.4 [IQR: 5.5 to 12.8] μA; P < 0.001).

CONCLUSIONS

Corridors critical to VT circuitry traverse infarcted tissue through or near LM. This association is likely mediated by increased regional resistance and reduced current loss as impulses traverse corridors adjacent to LM.

Fat infiltration in the infarcted heart as a paradigm for ventricular arrhythmias

Infiltrating adipose tissue (inFAT) has been recently found to co-localize with scar in infarcted hearts and may contribute to ventricular arrhythmias (VAs), a life-threatening heart rhythm disorder. However, the contribution of inFAT to VA has not been well-established. We investigated the role of inFAT versus scar in VA through a combined prospective clinical and mechanistic computational study. Using personalized computational heart models and comparing the results from simulations of VA dynamics with measured electrophysiological abnormalities during the clinical procedure, we demonstrate that inFAT, rather than scar, is a primary driver of arrhythmogenic propensity and is frequently present in critical regions of the VA circuit. We determined that, within the VA circuitry, inFAT, as opposed to scar, is primarily responsible for conduction slowing in critical sites, mechanistically promoting VA. Our findings implicate inFAT as a dominant player in infarct-related VA, challenging existing paradigms and opening the door for unexplored anti-arrhythmic strategies.

Cardio-respiratory motion-corrected 3D cardiac water-fat MRI using model-based image reconstruction

PURPOSE

Myocardial fat infiltrations are associated with a range of cardiomyopathies. The purpose of this study was to perform cardio-respiratory motion-correction for model-based water-fat separation to image fatty infiltrations of the heart in a free-breathing, non-cardiac-triggered high-resolution 3D MRI acquisition.

METHODS

Data were acquired in nine patients using a free-breathing, non-cardiac-triggered high-resolution 3D Dixon gradient-echo sequence and radial phase encoding trajectory. Motion correction was combined with a model-based water-fat reconstruction approach. Respiratory and cardiac motion models were estimated using a dual-mode registration algorithm incorporating both motion-resolved water and fat information. Qualitative comparisons of fat structures were made between 2D clinical routine reference scans and reformatted 3D motion-corrected images. To evaluate the effect of motion correction the local sharpness of epicardial fat structures was analyzed for motion-averaged and motion-corrected fat images.

RESULTS

The reformatted 3D motion-corrected reconstructions yielded qualitatively comparable fat structures and fat structure sharpness in the heart as the standard 2D breath-hold. Respiratory motion correction improved the local sharpness on average by 32% ± 24% with maximum improvements of 81% and cardiac motion correction increased the sharpness further by another 15% ± 11% with maximum increases of 31%. One patient showed a fat infiltration in the myocardium and cardio-respiratory motion correction was able to improve its visualization in 3D.

CONCLUSION

The 3D water-fat separated cardiac images were acquired during free-breathing and in a clinically feasible and predictable scan time. Compared to a motion-averaged reconstruction an increase in sharpness of fat structures by 51% ± 27% using the presented motion correction approach was observed for nine patients.

A novel mRNA decay inhibitor abolishes pathophysiological cellular transition

In cells, mRNA synthesis and decay are influenced by each other, and their balance is altered by either external or internal cues, resulting in changes in cell dynamics. We previously reported that it is important that an array of mRNAs that shape a phenotype are degraded before cellular transitions, such as cellular reprogramming and differentiation. In adipogenesis, the interaction between DDX6 and 4E-T had a definitive impact on the pathway in the processing body (PB). We screened a library of α-helix analogs with an alkaloid-like backbone to identify compounds that inhibit the binding between DDX6 and 4E-T proteins, which occurs between the α-helix of structured and internally disordered proteins. IAMC-00192 was identified as a lead compound. This compound directly inhibited the interaction between DDX6 and 4E-T. IAMC-00192 inhibited the temporal increase in PB formation that occurs during adipogenesis and epithelial-mesenchymal transition (EMT) and significantly suppressed these cellular transitions. In the EMT model, the half-life of preexisting mRNAs in PBs was extended twofold by the compound. The novel inhibitor of RNA decay not only represents a potentially useful tool to analyze in detail the pathological conditions affected by RNA decay and how it regulates the pathological state. The identification of this inhibitor may lead to the discovery of a first-in-class RNA decay inhibitor drug.

Influence of respiration and tissue contact on ventricular substrate identification during high density mapping: results from an ovine infarct model

INTRODUCTION

Multi-electrode mapping (MEM) and automated point collection are important enhancements to substrate mapping in ventricular tachycardia ablation. The effects of tissue contact and respiration on electrogram voltage with differing depolarisation wavefronts with MEM catheters are unclear.

METHODS

Bipolar and unipolar voltages were collected from control (n=5) and infarcted (n=7) animals with a multi-spline MEM catheter. Electro-anatomic maps were created in sinus rhythm, and right and left ventricular pacing. Analysis was performed across three collection settings: standard (SS), respiratory-phase gating (RG), and electrode-tissue proximity (TP). Comparison was made to scar detected by cardiac MRI (cMRI).

RESULTS

Compared to SS and RG acquisition, median bipolar and unipolar voltages were higher using TP, regardless of the depolarization wavefront. In infarct animals, bipolar voltages were 30.7-50.5% higher for bipolar and 8.7-13.8% higher on unipolar voltages with TP, compared to SS. The effect of RG on bipolar and unipolar voltages was minimal. Percentage of local abnormal ventricular activities was not impacted by acquisition settings or wavefront direction in infarct animals. Compared with cMRI defined scar, all three acquisition settings overestimated scar area using standard voltage-based cutoffs. RG improved the low voltage area concordance with MRI by 1.6-5.1% whereas TP improved by 5.9-8.4%.

CONCLUSIONS

High density voltage mapping with a MEM catheter is influenced by point collection settings. Tissue contact filters reduced low voltage areas and improved agreement with cMRI fibrosis in infarcted ovine hearts. These findings have critical implications for optimising filter settings for high density substrate mapping in the left ventricle. This article is protected by copyright. All rights reserved.

Interconnection between Cardiac Cachexia and Heart Failure—Protective Role of Cardiac Obesity

Cachexia may be caused by congestive heart failure, and it is then called cardiac cachexia, which leads to increased morbidity and mortality. Cardiac cachexia also worsens skeletal muscle degradation. Cardiac cachexia is the loss of edema-free muscle mass with or without affecting fat tissue. It is mainly caused by a loss of balance between protein synthesis and degradation, or it may result from intestinal malabsorption. The loss of balance in protein synthesis and degradation may be the consequence of altered endocrine mediators such as insulin, insulin-like growth factor 1, leptin, ghrelin, melanocortin, growth hormone and neuropeptide Y. In contrast to many other health problems, fat accumulation in the heart is protective in this condition. Fat in the heart can be divided into epicardial, myocardial and cardiac steatosis. In this review, we describe and discuss these topics, pointing out the interconnection between heart failure and cardiac cachexia and the protective role of cardiac obesity. We also set the basis for possible screening methods that may allow for a timely diagnosis of cardiac cachexia, since there is still no cure for this condition. Several therapeutic procedures are discussed including exercise, nutritional proposals, myostatin antibodies, ghrelin, anabolic steroids, anti-inflammatory substances, beta-adrenergic agonists, medroxyprogesterone acetate, megestrol acetate, cannabinoids, statins, thalidomide, proteasome inhibitors and pentoxifylline. However, to this date, there is no cure for cachexia.

Functions and origins of cardiac fat

Triglyceride droplets can be stored within cardiac adipocytes (CAs) and cardiomyocytes in the heart. Cardiac adipocytes reside in three distinct regions: pericardial, epicardial, and intramyocardial adipose tissues. In healthy individuals, cardiac adipose tissues modulate cardiovascular functions and energy partitioning, which are, thus, protective. However, ectopic deposition of cardiac adipose tissues turns them into adverse lipotoxic, prothrombotic, and pro-inflammatory tissues with local and systemic contribution to the development of cardiovascular disorders. Accumulation of triglyceride droplets in cardiomyocytes may lead to lipotoxic injury of cardiomyocytes and contribute to the development of cardiac hypertrophy and dysfunction. Here, we summarize the roles of CAs and myocardial triglyceride droplets under physiological and pathological conditions and review the cellular sources of CAs in heart development and diseases. Understanding the functions and cellular origins of cardiac fat will provide clues for future studies on pathophysiological processes and treatment of cardiovascular diseases.

Epicardial adipose tissue is associated with left atrial volume and fibrosis in patients with atrial fibrillation

Background

Obesity is a risk factor for atrial fibrillation (AF) and strongly influences the response to treatment. Atrial fibrosis shows similar associations. Epicardial adipose tissue (EAT) may be a link between these associations. We sought to assess whether EAT is associated with body mass index (BMI), left atrial (LA) fibrosis and volume.

Methods

LA fibrosis and EAT were assessed using late gadolinium enhancement, and Dixon MRI sequences, respectively. We derived 3D models incorporating fibrosis and EAT, then measured the distance of fibrotic and non-fibrotic areas to the nearest EAT to assess spatial colocalization.

Results

One hundred and three AF patients (64% paroxysmal, 27% female) were analyzed. LA volume index was 54.9 (41.2, 69.7) mL/m², LA EAT index was 17.4 (12.7, 22.9) mL/m², and LA fibrosis was 17.1 (12.4, 23.1)%. LA EAT was significantly correlated with BMI (R = 0.557, p < 0.001); as well as with LA volume and LA fibrosis after BSA adjustment (R = 0.579 and R = 0.432, respectively, p < 0.001 for both). Multivariable analysis showed LA EAT to be independently associated with LA volume and fibrosis. 3D registration of fat and fibrosis around the LA showed no clear spatial overlap between EAT and fibrotic LA regions.

Conclusion

LA EAT is associated with obesity (BMI) as well as LA volume and fibrosis. Regions of LA EAT did not colocalize with fibrotic areas, suggesting a systemic or paracrine mechanism rather than EAT infiltration of fibrotic areas.

Modulation of Cardiac Arrhythmogenesis by Epicardial Adipose Tissue: JACC State-of-the-Art Review

Obesity is a significant risk factor for arrhythmic cardiovascular death. Interactions between epicardial adipose tissue (EAT) and myocytes are thought to play a key role in the development of arrhythmias. In this review, the authors investigate the influence of EAT on arrhythmogenesis. First, they summarize electrocardiographic evidence showing the association between increased EAT volume and atrial and ventricular conduction delay. Second, they detail the structural cross talk between EAT and the heart and its arrhythmogenicity. Adipose tissue infiltration within the myocardium constitutes an anatomical obstacle to cardiac excitation. It causes activation delay and increases the risk of arrhythmias. Intercellular electrical coupling between cardiomyocytes and EAT can further slow conduction and increase the risk of block, favoring re-entry and arrhythmias. Finally, EAT secretes multiple substances that influence cardiomyocyte electrophysiology either by modulating ion currents and electrical coupling or by stimulating fibrosis. Thus, structural and paracrine cross talk between EAT and cardiomyocytes facilitates arrhythmias.

Right Heart Morphology and Its Association With Excessive and Deficient Cardiac Visceral Adipose Tissue

Visceral adipose tissue is an independent risk factor for the development of atherosclerotic coronary disease, arterial hypertension, diabetes and metabolic syndrome. Right heart morphology often involves the presence of adipose tissue, which can be quantified by non-invasive imaging methods. The last decade brought a wealth of new insights into the function and morphology of adipose tissue, with great emphasis on its role in the pathogenesis of heart disease. Cardiac adipose tissue is involved in thermogenesis, mechanical protection of the heart and energy storage. However, it can also be an endocrine organ that synthesises numerous pro-inflammatory and anti-inflammatory cytokines, the effect of which is accomplished by paracrine and vasocrine mechanisms. Visceral adipose tissue has several compartments that differ in their embryological origin and vascularisation. Deficiency of cardiac adipose tissue, often due to chronic pathological conditions such as oncological diseases or chronic infectious diseases, predicts increased mortality and morbidity. To date, knowledge about the influence of visceral adipose tissue on cardiac morphology is limited, especially the effect on the morphology of the right heart in a state of excess or deficient visceral adipose tissue.

Epicardial adipose tissue modulates arrhythmogenesis in right ventricle outflow tract cardiomyocytes

AIMS

Ventricular arrhythmia (VA) frequently occurs in fatty infiltrative cardiomyopathy or epicardial adipose tissue (EAT) abundant hearts. Right ventricular outflow tract (RVOT), commonly covered with EAT, is vital for VA genesis. This study explored whether EAT contributes to RVOT arrhythmogenesis.

METHODS AND RESULTS

Conventional microelectrodes and whole-cell patch clamp were used to record electrical activity and ionic currents in rabbit RVOT tissue preparation or isolated single cardiomyocytes with or without (control) connected EAT. Epicardial adipose tissue-connected (N = 6) RVOT had more portions of fibrosis than did control (N = 5) RVOT (160.3 ± 23.2 vs. 91.9 ± 13.4 μm2/mm2, P < 0.05). Epicardial adipose tissue-connected RVOT cardiomyocytes (n = 18) had lower negative resting membrane potential (-68 ± 1 vs. -73 ± 2 mV, P < 0.05); smaller action potential (AP) amplitude (108 ± 4 vs. 135 ± 6 mV, P < 0.005); and longer 90%, 50%, and 20% of AP duration repolarization (361 ± 18 vs. 309 ± 9 ms, P < 0.05; 310 ± 17 vs. 256 ± 13 ms, P < 0.05; and 182 ± 19 vs. 114 ± 24 ms, P < 0.05, respectively) than did control (n = 13) RVOT cardiomyocytes. Moreover, compared with control RVOT cardiomyocytes, EAT-connected RVOT cardiomyocytes had larger transient outward potassium currents, similar delayed rectifier potassium currents, smaller L-type calcium currents, and inward rectifier potassium currents. After ajmaline (10 μM, a sodium channel blocker) superfusion, high VA inducibility was observed through rapid pacing in EAT-connected RVOT but not in control RVOT.

CONCLUSIONS

Epicardial adipose tissue exerts distinctive electrophysiological effects on RVOT with a propensity towards VA induction, which might play a role in lipotoxicity pathogenesis-related ventricular arrhythmogenesis.

Obesity and Cardiovascular Disease: A Scientific Statement From the American Heart Association

The global obesity epidemic is well established, with increases in obesity prevalence for most countries since the 1980s. Obesity contributes directly to incident cardiovascular risk factors, including dyslipidemia, type 2 diabetes, hypertension, and sleep disorders. Obesity also leads to the development of cardiovascular disease and cardiovascular disease mortality independently of other cardiovascular risk factors. More recent data highlight abdominal obesity, as determined by waist circumference, as a cardiovascular disease risk marker that is independent of body mass index. There have also been significant advances in imaging modalities for characterizing body composition, including visceral adiposity. Studies that quantify fat depots, including ectopic fat, support excess visceral adiposity as an independent indicator of poor cardiovascular outcomes. Lifestyle modification and subsequent weight loss improve both metabolic syndrome and associated systemic inflammation and endothelial dysfunction. However, clinical trials of medical weight loss have not demonstrated a reduction in coronary artery disease rates. In contrast, prospective studies comparing patients undergoing bariatric surgery with nonsurgical patients with obesity have shown reduced coronary artery disease risk with surgery. In this statement, we summarize the impact of obesity on the diagnosis, clinical management, and outcomes of atherosclerotic cardiovascular disease, heart failure, and arrhythmias, especially sudden cardiac death and atrial fibrillation. In particular, we examine the influence of obesity on noninvasive and invasive diagnostic procedures for coronary artery disease. Moreover, we review the impact of obesity on cardiac function and outcomes related to heart failure with reduced and preserved ejection fraction. Finally, we describe the effects of lifestyle and surgical weight loss interventions on outcomes related to coronary artery disease, heart failure, and atrial fibrillation.

Recurrent ventricular tachycardia associated with lipomatous metaplasia of a myocardial scar

Lipomatous metaplasia in chronic postmyocardial infarction scars is a common and underappreciated finding seen in histopathology and cardiac MRI. Evidence suggests that lipomatous metaplasia is capable of altering the electroconductivity of the myocardium leading to re-entry pathways that are implicated in the pathogenesis of postmyocardial infarction arrhythmogenesis. We report a case of a patient who presented with non-sustained ventricular tachycardia and was found to have lipomatous metaplasia of a prior myocardial infarct-related scar.

RNA decay in processing bodies is indispensable for adipogenesis

The RNA decay pathway plays key regulatory roles in cell identities and differentiation processes. Although adipogenesis is transcriptionally and epigenetically regulated and has been thoroughly investigated, how RNA metabolism that contributes to the stability of phenotype-shaping transcriptomes participates in differentiation remains elusive. In this study, we investigated Ddx6, an essential component of processing bodies (PBs) that executes RNA decay and translational repression in the cytoplasm and participates in the cellular transition of reprogramming. Upon adipogenic induction, Ddx6 dynamically accumulated to form PBs with a binding partner, 4E-T, at the early phase prior to emergence of intracellular lipid droplets. In contrast, preadipocytes with Ddx6 knockout (KO) or 4E-T knockdown (KD) failed to generate PBs, resulting in significant suppression of adipogenesis. Transcription factors related to preadipocytes and negative regulators of adipogenesis that were not expressed under adipogenic stimulation were maintained in Ddx6-KO and 4E-T-KD preadipocytes under adipogenic induction. Elimination of Dlk1, a major negative regulator of adipogenesis, in 3T3L1 Ddx6-KO cells did not restore adipogenic differentiation capacity to any extent. Similar to murine cells, human primary mesenchymal stem cells, which can differentiate into adipocytes upon stimulation with adipogenic cocktails, required DDX6 to maturate into adipocytes. Therefore, RNA decay of the entire parental transcriptome, rather than removal of a strong negative regulator, could be indispensable for adipogenesis.

Cardiac Adiposity and Arrhythmias: The Role of Imaging

Increased cardiac fat depots are metabolically active tissues that have a pronounced pro-inflammatory nature. Increasing evidence supports a potential role of cardiac adiposity as a determinant of the substrate of atrial fibrillation and ventricular arrhythmias. The underlying mechanism appears to be multifactorial with local inflammation, fibrosis, adipocyte infiltration, electrical remodeling, autonomic nervous system modulation, oxidative stress and gene expression playing interrelating roles. Current imaging modalities, such as echocardiography, computed tomography and cardiac magnetic resonance, have provided valuable insight into the relationship between cardiac adiposity and arrhythmogenesis, in order to better understand the pathophysiology and improve risk prediction of the patients, over the presence of obesity and traditional risk factors. However, at present, given the insufficient data for the additive value of imaging biomarkers on commonly used risk algorithms, the use of different screening modalities currently is indicated for personalized risk stratification and prognostication in this setting.

PDGFRb+ mesenchymal cells, but not NG2+ mural cells, contribute to cardiac fat

Understanding cellular origins of cardiac adipocytes (CAs) can offer important implications for the treatment of fat-associated cardiovascular diseases. Here, we perform lineage tracing studies by using various genetic models and find that cardiac mesenchymal cells (MCs) contribute to CAs in postnatal development and adult homeostasis. Although PDGFRa⁺ and PDGFRb⁺ MCs both give rise to intramyocardial adipocytes, PDGFRb⁺ MCs are demonstrated to be the major source of intramyocardial adipocytes. Moreover, we find that PDGFRb⁺ cells are heterogenous, as PDGFRb is expressed not only in pericytes and smooth muscle cells (SMCs) but also in some subendocardial, pericapillary, or adventitial PDGFRa⁺ fibroblasts. Dual-recombinase-mediated intersectional genetic lineage tracing reveals that PDGFRa⁺PDGFRb⁺ double-positive periendothelial fibroblasts contribute to intramyocardial adipocytes. In contrast, SMCs and NG2⁺ pericytes do not contribute to CAs. These in vivo findings demonstrate that PDGFRb⁺ MCs, but not NG2⁺ coronary vascular mural cells, are the major source of intramyocardial adipocytes.

Personalized Digital-Heart Technology for Ventricular Tachycardia Ablation Targeting in Hearts With Infiltrating Adiposity

BACKGROUND

Infiltrating adipose tissue (inFAT) is a newly recognized proarrhythmic substrate for postinfarct ventricular tachycardias (VT) identifiable on contrast-enhanced computed tomography. This study presents novel digital-heart technology that incorporates inFAT from contrast-enhanced computed tomography to noninvasively predict VT ablation targets and assesses the capability of the technology by comparing its predictions with VT ablation procedure data from patients with ischemic cardiomyopathy.

METHODS

Digital-heart models reflecting patient-specific inFAT distributions were reconstructed from contrast-enhanced computed tomography. The digital-heart identification of fat-based ablation targeting (DIFAT) technology evaluated the rapid-pacing-induced VTs in each personalized inFAT-based substrate. DIFAT targets that render the inFAT substrate noninducible to VT, including VTs that arise postablation, were determined. DIFAT predictions were compared with corresponding clinical ablations to assess the capabilities of the technology.

RESULTS

DIFAT was developed and applied retrospectively to 29 ischemic cardiomyopathy patients with contrast-enhanced computed tomography. DIFAT ablation volumes were significantly less than the estimated clinical ablation volumes (1.87±0.35 versus 7.05±0.88 cm³, P<0.0005). DIFAT targets overlapped with clinical ablations in 79% of patients, mostly in the apex (72%) and inferior/inferolateral (74%). In 3 patients, DIFAT targets colocalized with redo ablations delivered years after the index procedure.

CONCLUSIONS

DIFAT is a novel digital-heart technology for individualized VT ablation guidance designed to eliminate VT inducibility following initial ablation. DIFAT predictions colocalized well with clinical ablation locations but provided significantly smaller lesions. DIFAT also predicted VTs targeted in redo procedures years later. As DIFAT uses widely accessible computed tomography, its integration into clinical workflows may augment therapeutic precision and reduce redo procedures.

Atglistatin Pretreatment Preserves Remote Myocardium Function Following Myocardial Infarction

The pathological role of adipose derived fatty acids following myocardial infarction has long been hypothesized. However, most methods for reducing adipocyte lipolysis have significant non-adipose effects. Atglistatin, a direct inhibitor of the initial lipase in the lipolysis cascade, has been recently shown to inhibit adipose tissue lipolysis after oral administration. To explore the ability of Atglistatin to impact the pathophysiology of cardiac ischemia we performed prophylactic treatment of mice with Atglistatin for 2 days before 1-hour cardiac ischemia. After 7 days of reperfusion, hearts of Atglistatin treated mice showed significantly improved systolic pump function while infarct and scar size were unaffected. Strain analysis of echocardiographic data revealed an enhanced performance of the remote myocardium as cause for overall improved systolic function. The present study provides evidence that inhibition of adipocyte adipose triglyceride lipase (ATGL) using Atglistatin is able to improve cardiac function after MI by targeting the remote myocardium.

Variations in native T1 values in patients with Duchenne muscular dystrophy with and without late gadolinium enhancement

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder leading to progressive skeletal and cardiac myopathy. Elevated myocardial T1 values correlate with fibrosis in most disease processes, but DMD skeletal and cardiac histopathology is defined by fibrofatty replacement that may result in a decrease in T1 values, due to the low T1 of fat. The study goal was to assess myocardial T1 values in DMD patients with and without late gadolinium enhancement (LGE). A retrospective analysis was performed on all patients with DMD referred for CMR at our institution from 7/5/2017 to 10/24/2018. T1 measurements were performed using breath-held modified Look Locker inversion recovery (MOLLI) sequences at the basal and mid-ventricular levels. The cohort was separated into patients without the presence of LGE (LGE-) and patients with current or previous LGE (LGE+). A total of 207 CMR studies were analyzed. The LGE- group comprised 88 patients while 119 patients were in the LGE+ group. The LGE+ group was older, had larger indexed LV end-diastolic volume and lower LV ejection fraction (LVEF) compared to the LGE- group. T1 values in the LGE+ group were lower compared to the LGE- group (mid T1 1012 ms vs. 1035 ms; p = 0.002), with 5 CMR studies demonstrating mid T1 values < 900 ms. There was no correlation between mid T1 and LVEF in the LGE- group. In the LGE+ cohort, lower T1 values correlated with worse LVEF (r = 0.34, p = 0.0002). The association between mid T1 values and LVEF remained statistically significant on multivariable analysis when accounting for number of LGE segments, LVEDVi, and age (p = 0.009). This is the largest study assessing native T1 values in patients with DMD. The results demonstrate that patients with LGE had lower T1 values than patients without LGE. In the LGE+ group, lower T1 values correlated with worse LV systolic function. These results are consistent with the evolving recognition of fibrofatty replacement in advanced stages of DMD myopathy. Furthermore, our study supports that there is not a simple linear relationship between increasing T1 values and advancing disease progression reported in most other cardiomyopathies.

Arrhythmic risk stratification by cardiac magnetic resonance tissue characterization: disclosing the arrhythmic substrate within the heart muscle

Sudden cardiac death (SCD) is a pivotal health problem worldwide. The identification of subjects at increased risk of SCD is crucial for the accurate selection of candidates for implantable cardioverter defibrillator (ICD) therapy. Current strategies for arrhythmic stratification largely rely on left ventricular (LV) ejection fraction (EF), mostly measured by echocardiography, and New York Heart Association functional status for heart failure with reduced EF. For specific diseases, such as hypertrophic and arrhythmogenic cardiomyopathy, some risk scores have been proposed; however, these scores take into account some parameters that are a partial reflection of the global arrhythmic risk and show a suboptimal accuracy. Thanks to a more comprehensive evaluation, cardiac magnetic resonance (CMR) provides insights into the heart muscle (the so-called tissue characterization) identifying cardiac fibrosis as an arrhythmic substrate. Combining sequences before and after administration of contrast media and mapping techniques, CMR is able to characterize the myocardial tissue composition, shedding light on both intracellular and extracellular alterations. Over time, late gadolinium enhancement (LGE) emerged as solid prognostic marker, strongly associated with major arrhythmic events regardless of LVEF, adding incremental value over current strategy in ischemic heart disease and non-ischemic cardiomyopathies. The evidence on a potential prognostic role of mapping imaging is promising. However, mapping techniques require further investigation and standardization. Disclosing the arrhythmic substrate within the myocardium, CMR should be considered as part of a multiparametric approach to personalized arrhythmic stratification.

Variability in electrophysiological properties and conducting obstacles controls re-entry risk in heterogeneous ischaemic tissue

Ischaemia, in which inadequate blood supply compromises and eventually kills regions of cardiac tissue, can cause many types of arrhythmia, some life-threatening. A significant component of this is the effects of the resulting hypoxia, and concomitant hyperklaemia and acidosis, on the electrophysiological properties of myocytes. Clinical and experimental data have also shown that regions of structural heterogeneity (fibrosis, necrosis, fibro-fatty infiltration) can act as triggers for arrhythmias under acute ischaemic conditions. Mechanistic models have successfully captured these effects in silico. However, the relative significance of these separate facets of the condition, and how sensitive arrhythmic risk is to the extents of each, is far less explored. In this work, we use partitioned Gaussian process emulation and new metrics for source-sink mismatch that rely on simulations of bifurcating cardiac fibres to interrogate a model of heterogeneous ischaemic tissue. Re-entries were most sensitive to the level of hypoxia and the fraction of non-excitable tissue. In addition, our results reveal both protective and pro-arrhythmic effects of hyperklaemia, and present the levels of hyperklaemia, hypoxia and percentage of non-excitable tissue that pose the highest arrhythmic risks. This article is part of the theme issue 'Uncertainty quantification in cardiac and cardiovascular modelling and simulation'.

Atrial Fibrillation: Development Mechanisms, Approaches and Prospects of Therapy

Atrial fibrillation (AF) is the most common arrhythmia. It is diagnosed in more than 33 million people worldwide and is the leading cause of hospitalization for arrhythmias. AF is characterized by fast and irregular atrial activation without discrete P-waves at a surface electrocardiography. AF pathophysiological mechanisms are very complex and include the dynamic interaction between arrhythmia substrate and triggers. Consequently, the clinical search for effective therapeutic targets should include the entire process of the onset and progression of the disease: from the first paroxysms to the development of a stable permanent form of AF.

Characterization of the human myocardium by optical coherence tomography

Imaging of cardiac tissue structure plays a critical role in the treatment and understanding of cardiovascular disease. Optical coherence tomography (OCT) offers the potential to provide valuable, high-resolution imaging of cardiac tissue. However, there is a lack of comprehensive OCT imaging data of the human heart, which could improve identification of structural substrates underlying cardiac abnormalities. The objective of this study was to provide qualitative and quantitative analysis of OCT image features throughout the human heart. Fifty human hearts were acquired, and tissues from all chambers were imaged with OCT. Histology was obtained to verify tissue composition. Statistical differences between OCT image features corresponding to different tissue types and chambers were estimated using analysis of variance. OCT imaging provided features that were able to distinguish structures such as thickened collagen, as well as adipose tissue and fibrotic myocardium. Statistically significant differences were found between atria and ventricles in attenuation coefficient, and between adipose and all other tissue types. This study provides an overview of OCT image features throughout the human heart, which can be used for guiding future applications such as OCT-integrated catheter-based treatments or ex vivo investigation of structural substrates.

Cardiac intramural electrical mapping reveals focal delays but no conduction velocity slowing in the peri-infarct region

Altered electrical behavior alongside healed myocardial infarcts (MIs) is associated with increased risk of sudden cardiac death. However, the multidimensional mechanisms are poorly understood and described. This study characterizes, for the first time, the intramural spread of electrical activation in the peri-infarct region of chronic reperfusion MIs. Four sheep were studied 13 wk after antero-apical reperfusion infarction. Extracellular potentials (ECPs) were recorded in a ~20 × 20-mm² region adjacent to the infarct boundary (25 plunge needles <0.5-mm diameter with 15 electrodes at 1-mm centers) during multisite stimulation. Infarct geometry and electrode locations were reconstructed from magnetic resonance images. Three-dimensional activation spread was characterized by local activation times and interpolated ECP fields (n = 191 records). Control data were acquired in 4 non-infarcted sheep (n = 96 records). Electrodes were distributed uniformly around 15 ± 5% of the intramural infarct boundary. There were marked changes in pacing success and ECP morphology across a functional border zone (BZ) ±2 mm from the boundary. Stimulation adjacent to the infarct boundary was associated with low-amplitude electrical activity within the BZ and delayed activation of surrounding myocardium. Bulk tissue depolarization occurred 3.5-14.6 mm from the pacing site for 39% of stimuli with delays of 4-37 ms, both significantly greater than control (P < 0.0001). Conduction velocity (CV) adjacent to the infarct was not reduced compared with control, consistent with structure-only computer model results. Insignificant CV slowing, irregular stimulus-site specific activation delays, and obvious indirect activation pathways strongly suggest that the substrate for conduction abnormalities in chronic MI is predominantly structural in nature.NEW & NOTEWORTHY Intramural in vivo measurements of peri-infarct electrical activity were not available before this study. We use pace-mapping in a three-dimensional electrode array to show that a subset of stimuli in the peri-infarct region initiates coordinated myocardial activation some distance from the stimulus site with substantial associated time delays. This is site dependent and heterogeneous and occurs for <50% of ectopic stimuli in the border zone. Furthermore, once coordinated activation is initiated, conduction velocity adjacent to the infarct boundary is not significantly different from control. These results give new insights to peri-infarct electrical activity and do not support the widespread view of uniform electrical remodeling in the border zone of chronic myocardial infarcts, with depressed conduction velocity throughout.

Sphingolipid Synthesis Inhibition by Myriocin Administration Enhances Lipid Consumption and Ameliorates Lipid Response to Myocardial Ischemia Reperfusion Injury

Myocardial infarct requires prompt thrombolytic therapy or primary percutaneous coronary intervention to limit the extent of necrosis, but reperfusion creates additional damage. Along with reperfusion, a maladaptive remodeling phase might occur and it is often associated with inflammation, oxidative stress, as well as a reduced ability to recover metabolism homeostasis. Infarcted individuals can exhibit reduced lipid turnover and their accumulation in cardiomyocytes, which is linked to a deregulation of peroxisome proliferator activated receptors (PPARs), controlling fatty acids metabolism, energy production, and the anti-inflammatory response. We previously demonstrated that Myriocin can be effectively used as post-conditioning therapeutic to limit ischemia/reperfusion-induced inflammation, oxidative stress, and infarct size, in a murine model. In this follow-up study, we demonstrate that Myriocin has a critical regulatory role in cardiac remodeling and energy production, by up-regulating the transcriptional factor EB, PPARs nuclear receptors and genes involved in fatty acids metabolism, such as VLDL receptor, Fatp1, CD36, Fabp3, Cpts, and mitochondrial FA dehydrogenases. The overall effects are represented by an increased β–oxidation, together with an improved electron transport chain and energy production. The potent immunomodulatory and metabolism regulatory effects of Myriocin elicit the molecule as a promising pharmacological tool for post-conditioning therapy of myocardial ischemia/reperfusion injury.

Post-Myocardial Infarction Scar With Fat Deposition Shows Specific Electrophysiological Properties and Worse Outcome After Ventricular Tachycardia Ablation

Background Fat deposition (FD) is part of the healing process after myocardial infarction. The characteristics of FD and its impact on the outcome in patients undergoing ventricular tachycardia (VT) ablation have not been thoroughly studied. Methods and Results We studied consecutive patients undergoing post-myocardial infarction VT ablation with pre-procedural cardiac computed tomography. FD was defined as intra-myocardial attenuation ≤ -30 HU on computed tomography. Clinical, anatomical, and post-procedural outcome was assessed in the overall population. Electrophysiological characteristics were assessed is a subgroup of patients with high-density electro-anatomical maps. Sixty-nine patients were included (66±12 years). FD was detected in 44 (64%) patients. The presence of FD related to scar age (odds ratio [OR]: 1.14 per year; P=0.001) and scar extent (OR: 1.27 per segment; P=0.02). On electro-anatomical maps, FD was characterized by lower bipolar amplitude (P<0.001) and prolonged electrogram duration (P<0.001). Although the proportion of local abnormal ventricular activation was similar (P=0.22), local abnormal ventricular activation showed lower amplitude (P<0.001) and were more delayed (P<0.001) in scars with FD. After a mean follow-up of 26 months, patients with FD experienced a worse outcome including all-cause mortality and VT recurrence (70% versus 28%, P log rank=0.009). On multivariate analysis, FD (hazard ratio=2.69; 95% CI, 1.12-6.46; P=0.027) and left ventricular systolic dysfunction (hazard ratio=2.57; 95% CI, 1.13-5.85; P=0.024) were independent predictors of adverse outcomes. Conclusions FD in patients with post-myocardial infarction VT undergoing catheter ablation relates to scar age and size and may be a marker of adverse outcomes including all-cause mortality and VT recurrence.