Diminished cardiac fibrosis in heart failure is associated with altered ventricular arrhythmia phenotype

Protective effects of Dapagliflozin on the vulnerability of ventricular arrhythmia in rats with pulmonary artery hypertension induced by monocrotaline

Monocrotaline (MCT)-induced pulmonary artery hypertension (PAH) has been reported to cause right heart failure (RHF). Moreover, Right heart diseases have been determined to cause ventricular arrhythmia (VA). So we can conclude that MCT-induced PAH increases the incidence of VA. In addition, Previous studies have determined the benefits of Dapagliflozin (DA) on the cardiac system, but the responses of MCT-induced RHF to DA are not fully reported. So the present study sought to evaluate the effects of DA on the MCT-induced PAH. A dose intraperitoneal injection of MCT (60 mg/kg) was carried out to induce a rat model with PAH. DA (60 mg/l) was administered for 4 weeks following MCT injection. Echocardiography, body weight, blood pressure, blood glucose, electrophysiological study, and Western blot were performed. Four weeks after the MCT injection, MCT-treated rats decreased body weight, blood glucose and blood pressure. In addition, MCT caused the formation of PAH and RHF. Moreover, MCT-induced PAH rats increased the incidence of VA, prolonged action potential duration (APD), and shortened effective refractory period (ERP). Additionally, PAH rats significantly prevented the activated expressions of Ion channel proteins such as potassium channel (Kv1.5, Kv2.1, Kv4.2, Kv4.3) and L-type Ca channel (Cav1.2). As we expected, these changes above in PAH rats were reversed when DA was administered. Mechanistically, DA significantly reduced the levels of toll-like receptor (TLR4), the nuclear factor kappa B (NF-κB) in MCT-treated rats. In conclusion, these findings determine that DA reduces the vulnerability of VA in PAH rats through the TLR4/NF-κB signaling pathway.

Aggressive beta-blocker titration in stabilized acute heart failure patients with low left ventricular ejection fraction

Objectives

A beta-blocker should be initiated in patients with stable acute heart failure (AHF). Beta-blocker titration should be conducted after a two-week interval. The benefits of aggressive beta-blocker titration are still unclear. This study aimed to investigate the aggressive beta-blocker titration outcomes in stabilized AHF patients with low left ventricular ejection fraction (LVEF).

Methods

In this retrospective cohort study, we analysed clinical data from the heart failure (HF) registry. AHF Patients with LVEF <40% were divided into aggressive and guideline-directed beta-blocker titration groups. The composite of worsening HF, ventricular arrhythmia, and mortality during hospitalization were defined as the primary outcomes. We considered secondary outcomes as the components of primary outcomes and also the outcomes during a 90-day follow-up after hospital discharge, including HF readmission and mortality.

Results

The primary outcomes between both groups were not significantly different (12.3% vs 24.4%; relative risk [RR] 0.51; 95% confidence interval [CI] 0.25–1.01; p = 0.055). However, the aggressive beta-blocker titration reduced ventricular arrhythmia events (5.7% vs 17.8%; RR 0.32; 95% CI 0.12–0.84; p = 0.016). The 90-day HF readmission rate (2.6% vs 7.5%; RR 0.35; 95% CI 0.07–1.66; p = 0.179) and mortality rate (4.3% vs 5%; RR 0.87; 95% CI 0.18–4.31; p = 1.000) between both groups were not found to be significantly different.

Conclusion

Compared to the guideline-directed beta-blocker titration, the aggressive beta-blocker titration was safe in low LVEF AHF patients who have been previously stabilized. Additionally, aggressive beta-blocker titration effectively reduced ventricular arrhythmia events.

Kanglexin protects against cardiac fibrosis and dysfunction in mice by TGF-β1/ERK1/2 noncanonical pathway

Cardiac fibrosis is a common pathological manifestation accompanied by various heart diseases, and antifibrotic therapy is an effective strategy to prevent diverse pathological processes of the cardiovascular system. We currently report the pharmacological evaluation of a novel anthraquinone compound (1,8-dihydroxy-6-methyl-9,10-anthraquinone-3-oxy ethyl succinate) named Kanglexin (KLX), as a potent cardioprotective agent with antifibrosis activity. Our results demonstrated that the administration of KLX by intragastric gavage alleviated cardiac dysfunction, hypertrophy, and fibrosis induced by transverse aortic constriction (TAC) surgical operation. Meanwhile, KLX administration relieved endothelial to mesenchymal transition of TAC mice. In TGF β1-treated primary cultured adult mouse cardiac fibroblasts (CFs) and human umbilical vein endothelial cells (HUVECs), KLX inhibited cell proliferation and collagen secretion. Also, KLX suppressed the transformation of fibroblasts to myofibroblasts in CFs. Further studies revealed that KLX-mediated cardiac protection was due to the inhibitory role of TGF-β1/ERK1/2 noncanonical pathway. In summary, our study indicates that KLX attenuated cardiac fibrosis and dysfunction of TAC mice, providing a potentially effective therapeutic strategy for heart pathological remodeling.

T1 Mapping Tissue Heterogeneity Provides Improved Risk Stratification for ICDs Without Needing Gadolinium in Patients With Dilated Cardiomyopathy

OBJECTIVES

This study sought to determine whether myocardial tissue heterogeneity scanned by native T₁ mapping could improve risk stratification in patients with nonischemic dilated cardiomyopathy (NICM) evaluated for primary prevention by ICD.

BACKGROUND

The benefit of insertable cardiac-defibrillator (ICD) as primary prevention ICD in patients with NICM remains to be fully clarified.

METHODS

A total of 115 NICM candidates for primary prevention and 55 healthy controls with similar distributions of age and sex were prospectively enrolled. Imaging was performed at 1.5-T using a protocol that included cine magnetic resonance for left ventricular function, late gadolinium enhancement (LGE) for focal scarring, and 5-slice native T₁ mapping for diffuse fibrosis and heterogeneity. The last method was assessed by mean absolute deviation of the segmental pixel-SD from the average pixel-SD (Mad-SD). The primary endpoint was a composite of appropriate ICD therapy and sudden cardiac death.

RESULTS

During a median follow-up of 24 months, 13 patients (11%) experienced the primary endpoint. Dichotomized Mad-SD >0.24 provided a comparable outcome to the presence of LGE for the primary endpoint (annual event rate: 9.8% vs. 10.9%). The integration of Mad-SD to global native T₁ showed excellent arrhythmic event-free survival (annual event rate: 0%), and high sensitivity of 85% (95% confidence interval [CI]: 55% to 98%) and moderate specificity of 72% (95% CI: 62% to 80%), with a C-statistic of 0.76 (95% CI: 0.64 to 0.87), which was comparable to the presence, location, or extent of LGE in its ability to predict arrhythmic events.

CONCLUSIONS

Combined myocardium tissue heterogeneity and interstitial fibrosis assessment by native T₁ mapping is an important predictor of ventricular tachycardia and ventricular fibrillation and provides additive risk stratification for primary prevention ICD in NICM patients without the need for gadolinium contrast.

Development of endomyocardial fibrosis model using a cell patterning technique: In vitro interaction of cell coculture of 3T3 fibroblasts and RL-14 cardiomyocytes

Cardiac functions can be altered by changes in the microstructure of the heart, i.e., remodeling of the cardiac tissue, which may activate pathologies such as hypertrophy, dilation, or cardiac fibrosis. Cardiac fibrosis can develop due to an excessive deposition of extracellular matrix proteins, which are products of the activation of fibroblasts. In this context, the anatomical-histological change may interfere with the functioning of the cardiac tissue, which requires specialized cells for its operation. The purpose of the present study was to determine the cellular interactions and morphological changes in cocultures of 3T3 fibroblasts and RL-14 cardiomyocytes via the generation of a platform an in vitro model. For this purpose, a platform emulating the biological characteristics of endomyocardial fibrosis was generated using a cell patterning technique to study morphological cellular changes in compact and irregular patterns of fibrosis. It was found that cellular patterns emulating the geometrical distributions of endomyocardial fibrosis generated morphological changes after interaction of the RL-14 cardiomyocytes with the 3T3 fibroblasts. Through this study, it was possible to evaluate biological characteristics such as cell proliferation, adhesion, and spatial distribution, which are directly related to the type of emulated endomyocardial fibrosis. This research concluded that fibroblasts inhibited the proliferation of cardiomyocytes via their interaction with specific microarchitectures. This behavior is consistent with the histopathological distribution of cardiac fibrosis; therefore, the platform developed in this research could be useful for the in vitro assessment of cellular microdomains. This would allow for the experimental determination of interactions with drugs, substrates, or biomaterials within the engineering of cardiac tissues.

Assessment of Remote Myocardium Heterogeneity in Patients with Ventricular Tachycardia Using Texture Analysis of Late Iodine Enhancement (LIE) Cardiac Computed Tomography (cCT) Images

Purpose

Diffuse remodeling of myocardial extra-cellular matrix is largely responsible for left ventricle (LV) dysfunction and arrhythmias. Our hypothesis is that the texture analysis of late iodine enhancement (LIE) cardiac computed tomography (cCT) images may improve characterization of the diffuse extra-cellular matrix changes. Our aim was to extract volumetric extracellular volume (ECV) and LIE texture features of non-scarred (remote) myocardium from cCT of patients with recurrent ventricular tachycardia (rVT), and to compare these radiomic features with LV-function, LV-remodeling, and underlying cardiac disease.

Procedures

Forty-eight patients suffering from rVT were prospectively enrolled: 5/48 with idiopathic VT (IVT), 23/48 with post-ischemic dilated cardiomyopathy (ICM), 9/48 with idiopathic dilated cardiomyopathy (IDCM), and 11/48 with scars from a previous healed myocarditis (MYO). All patients underwent echocardiography to assess LV systolic and diastolic function and cCT with pre-contrast, angiographic, and LIE scan to obtain end-diastolic volume (EDV), ECV, and first-order texture parameters of Hounsfield Unit (HU) of remote myocardium in LIE [energy, entropy, HU-mean, HU-median, standard deviation (SD), and mean absolute deviation (MAD)].

Results

Energy, HU mean, and HU median by cCT texture analysis correlated with ECV (rho = 0.5650, rho = 0.5741, rho = 0.5068; p < 0.0005). cCT-derived ECV, HU-mean, HU-median, SD, and MAD correlated directly to EDV by cCT and inversely to ejection fraction by echocardiography (p < 0.05). SD and MAD correlated with diastolic function by echocardiography (rho = 0.3837, p = 0.0071; rho = 0.3330, p = 0.0208). MYO and IVT patients were characterized by significantly lower values of SD and MAD when compared with ICM and IDCM patients, independently of LV-volume systolic and diastolic function.

Conclusions

Texture analysis of LIE may expand cCT capability of myocardial characterization. Myocardial heterogeneity (SD and MAD) was associated with LV dilatation, systolic and diastolic function, and is able to potentially identify the different patterns of structural remodeling characterizing patients with rVT of different etiology.

Increased myocardial native T1 relaxation time in patients with nonischemic dilated cardiomyopathy with complex ventricular arrhythmia

PURPOSE

To study the relationship between diffuse myocardial fibrosis and complex ventricular arrhythmias (ComVA) in patients with nonischemic dilated cardiomyopathy (NICM). We hypothesized that NICM patients with ComVA would have a higher native myocardial T1 time, suggesting more extensive myocardial diffuse fibrosis.

MATERIALS AND METHODS

We prospectively enrolled NICM patients with a history of ComVA (n = 50) and age-matched NICM patients without ComVA (n = 57). Imaging was performed at 1.5T with a protocol that included cine magnetic resonance imaging (MRI) for left ventricular (LV) function, late gadolinium enhancement (LGE) for focal scar, and native T1 mapping for diffuse fibrosis assessment.

RESULTS

Global native T1 time was significantly higher in patients with NICM with ComVA when compared to patients with NICM without ComVA (1131 ± 42 vs. 1107 ± 45 msec, P = 0.006), and this finding remained after excluding segments with scar on LGE (1124 ± 36 vs. 1102 ± 44 msec, P = 0.006). Native T1 was similar in NICM patients with and without the presence of LGE (1121 ± 39 vs. 1117 ± 48 msec, P = 0.68) and mildly correlated with LV end-diastolic volume index (r = 0.27, P = 0.005), LV end-systolic volume index (r = 0.24, P = 0.01), and LV ejection fraction (r = -0.28, P = 0.003). Native T1 value for each 10-msec increment was an independent predictor of ComVA (odds ratio 1.14, 95% confidence interval 1.03-1.25; P = 0.008) beyond LV function and LGE.

CONCLUSION

NICM patients with ComVA have higher native T1 compared to NICM without any documented ComVA. Native myocardial T1 is independently associated with ComVA, after adjusting for LV function and LGE.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:779-786. In memoriam: The authors are grateful for Dr. Josephson's inspiring guidance and contributions to this study.

[Myocardial fibrosis: Current aspects of the problem]

Fibrosis is one of the main components in the progression of most cardiovascular diseases, including coronary heart disease, by causing structural changes in the myocardium and vascular wall. The quantitative and qualitative characteristics of fibrosis of the myocardium are responsible for decreasing its elastic properties, developing diastolic dysfunction, impairing myocardial contractility, developing systolic dysfunction and cardiac arrhythmias, and worsening coronary blood flow in patients with heart failure of different etiologies. The important aspect of studying fibrosis is not only its interpretation as a model of the typical pathological process, but also its consideration as a systemic lesion of various organs and tissues. At the same time, the identification of myocardial fibrosis biomarkers that are available for their determination in circulating blood is of particular interest. Since there was evidence for the role of fibrosis in developing dysfunction of various organs and ensuring the systematicity of most diseases, especially at their development stages, the process of fibrosis came to be regarded as a promising therapeutic target. It is relevant to further investigate myocardial fibrosis, which is aimed at increasing the efficiency of its diagnosis and predicting its course and pathogenetically sound therapy.

Cardiac Fibrosis and Arrhythmogenesis

Myocardial injury, mechanical stress, neurohormonal activation, inflammation, and/or aging all lead to cardiac remodeling, which is responsible for cardiac dysfunction and arrhythmogenesis. Of the key histological components of cardiac remodeling, fibrosis either in the form of interstitial, patchy, or dense scars, constitutes a key histological substrate of arrhythmias. Here we discuss current research findings focusing on the role of fibrosis, in arrhythmogenesis. Numerous studies have convincingly shown that patchy or interstitial fibrosis interferes with myocardial electrophysiology by slowing down action potential propagation, initiating reentry, promoting after-depolarizations, and increasing ectopic automaticity. Meanwhile, there has been increasing appreciation of direct involvement of myofibroblasts, the activated form of fibroblasts, in arrhythmogenesis. Myofibroblasts undergo phenotypic changes with expression of gap-junctions and ion channels thereby forming direct electrical coupling with cardiomyocytes, which potentially results in profound disturbances of electrophysiology. There is strong evidence that systemic and regional inflammatory processes contribute to fibrogenesis (i.e., structural remodeling) and dysfunction of ion channels and Ca2+ homeostasis (i.e., electrical remodeling). Recognizing the pivotal role of fibrosis in the arrhythmogenesis has promoted clinical research on characterizing fibrosis by means of cardiac imaging or fibrosis biomarkers for clinical stratification of patients at higher risk of lethal arrhythmia, as well as preclinical research on the development of antifibrotic therapies. At the end of this review, we discuss remaining key questions in this area and propose new research approaches. © 2017 American Physiological Society. Compr Physiol 7:1009-1049, 2017.

The Prognostic Role of Tissue Characterisation using Cardiovascular Magnetic Resonance in Heart Failure

Despite significant advances in heart failure diagnostics and therapy, the prognosis remains poor, with one in three dying within a year of hospital admission. This is at least in part due to the difficulties in risk stratification and personalisation of therapy. The use of left ventricular systolic function as the main arbiter for entrance into clinical trials for drugs and advanced therapy, such as implantable defibrillators, grossly simplifies the complex heterogeneous nature of the syndrome. Cardiovascular magnetic resonance offers a wealth of data to aid in diagnosis and prognostication. The advent of novel cardiovascular magnetic resonance mapping techniques allows us to glimpse some of the pathophysiological mechanisms underpinning heart failure. We review the growing prognostic evidence base using these techniques.

Differential Regulatory Role of Soluble Klothos on Cardiac Fibrogenesis in Hypertension

BACKGROUND

Soluble Klotho functions as an endocrine factor that plays important roles in a variety of pathophysiological processes. Soluble Klotho contains 130 KDa and 65 KDa isoforms. However, their distinct individual functional heterogeneity remains uncertain. Herein, we investigated the regulatory role of two soluble Klothos on cardiac fibrogenic responses.

METHODS AND RESULTS

The effect of soluble Klothos on myofibroblast differentiation, proliferation, and collagen synthesis/degradation were examined in cultured mouse cardiac myofibroblasts. The role of 130 KDa Klotho on fibrosis in hypertensive heart disease were examined in wild type (WT) and Klotho transgenic (Tg/+) mice receiving chronic angiotensin (Ang)II infusion. Our in vitro studies revealed that addition of 130 KDa soluble Klotho isoform increased collagen synthesis in a dose dependent manner. Furthermore, 130 KDa Klotho significantly stimulated myofibroblast differentiation, proliferation, and ERK phosphorylation, which were abolished by fibroblast growth factor (FGF) receptor antagonist (SU5402). In contrast, 65 KDa soluble Klotho treatment significantly suppressed myofibroblast proliferation and collagen synthesis. In vivo study further demonstrated that chronic AngII infusion lead to cardiac fibrosis in both WT and Tg/+ mice. However, cardiac collagen, TGF-β1, TIMP-2, and α-smooth muscle actin (SMA) levels were markedly upregulated in Tg/+ mice compared to WT cohort.

CONCLUSION

Taken together, these findings implicate that 130 KDa soluble Klotho plays a stimulatory role in cardiac myofibroblast growth and activity through FGF pathway, whereas 65 KDa soluble Klotho exerts an anti-fibrotic effect in cardiac myofibroblasts. Thus, two distinct isoforms of soluble Klotho appear to play the counter-regulatory roles in cardiac fibrogenic responses.

Effect of angiotensin-converting enzyme inhibitors and receptor blockers on appropriate implantable cardiac defibrillator shock in patients with severe systolic heart failure (from the GRADE Multicenter Study)

Sudden cardiac death (SCD) is a leading cause of mortality in patients with cardiomyopathy. Although angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARBs) decrease cardiac mortality in these cohorts, their role in preventing SCD has not been well established. We sought to determine whether the use of ACEi or ARB in patients with cardiomyopathy is associated with a lower incidence of appropriate implantable cardiac defibrillator (ICD) shocks in the Genetic Risk Assessment of Defibrillator Events study that included subjects with an ejection fraction of ≤30% and ICDs. Treatment with ACEi/ARB versus no-ACEi/ARB was physician dependent. There were 1,509 patients (mean age [SD] 63 [12] years, 80% men, mean [SD] EF 21% [6%]) with 1,213 (80%) on ACEi/ARB and 296 (20%) not on ACEi/ARB. We identified 574 propensity-matched patients (287 in each group). After a mean (SD) of 2.5 (1.9) years, there were 334 (22%) appropriate shocks in the entire cohort. The use of ACEi/ARB was associated with lower incidence of shocks at 1, 3, and 5 years in the matched cohort (7.7%, 16.7%, and 18.5% vs 13.2%, 27.5%, and 32.0%; RR = 0.61 [0.43 to 0.86]; p = 0.005). Among patients with glomerular filtration rate (GFR) >60 and 30 to 60 ml/min/1.73 m(2), those on no-ACEi/ARB were at 45% and 77% increased risk of ICD shock compared with those on ACEi/ARB, respectively. ACEi/ARB were associated with significant lower incidence of appropriate ICD shock in patients with cardiomyopathy and GFR ≥30 ml/min/1.73 m(2) and with neutral effect in those with GFR <30 ml/min/1.73 m(2).

Myocardial tissue characterization by cardiac magnetic resonance imaging using T1 mapping predicts ventricular arrhythmia in ischemic and non-ischemic cardiomyopathy patients with implantable cardioverter-defibrillators

BACKGROUND

Diffuse myocardial fibrosis may provide a substrate for the initiation and maintenance of ventricular arrhythmia. T1 mapping overcomes the limitations of the conventional delayed contrast-enhanced cardiac magnetic resonance (CE-CMR) imaging technique by allowing quantification of diffuse fibrosis.

OBJECTIVE

The purpose of this study was to assess whether myocardial tissue characterization using T1 mapping would predict ventricular arrhythmia in ischemic and non-ischemic cardiomyopathies.

METHODS

This was a prospective longitudinal study of consecutive patients receiving implantable cardioverter-defibrillators in a tertiary cardiac center. Participants underwent CMR myocardial tissue characterization using T1 mapping and conventional CE-CMR scar assessment before device implantation. The primary end point was an appropriate implantable cardioverter-defibrillator therapy or documented sustained ventricular arrhythmia.

RESULTS

One hundred thirty patients (71 ischemic and 59 non-ischemic) were included with a mean follow-up period of 430 ± 185 days (median 425 days; interquartile range 293 days). At follow-up, 23 patients (18%) experienced the primary end point. In multivariable-adjusted analyses, the following factors showed a significant association with the primary end point: secondary prevention (hazard ratio [HR] 1.70; 95% confidence interval [95% CI] 1.01-1.91), noncontrast T1(_native) for every 10-ms increment in value (HR 1.10; CI 1.04-1.16; 90-ms difference between the end point-positive and end point-negative groups), and Grayzone(_2sd-3sd) for every 1% left ventricular increment in value (HR 1.36; CI 1.15-1.61; 4% difference between the end point-positive and end point-negative groups). Other CE-CMR indices including Scar(_2sd), Scar(_FWHM), and Grayzone(_2sd-FWHM) were also significantly, even though less strongly, associated with the primary end point as compared with Grayzone(_2sd-3sd).

CONCLUSION

Quantitative myocardial tissue assessment using T1 mapping is an independent predictor of ventricular arrhythmia in both ischemic and non-ischemic cardiomyopathies.

The C-terminus of the long AKAP13 isoform (AKAP-Lbc) is critical for development of compensatory cardiac hypertrophy

The objective of this study was to determine the role of A-Kinase Anchoring Protein (AKAP)-Lbc in the development of heart failure, by investigating AKAP-Lbc-protein kinase D1 (PKD1) signaling in vivo in cardiac hypertrophy. Using a gene-trap mouse expressing a truncated version of AKAP-Lbc (due to disruption of the endogenous AKAP-Lbc gene), that abolishes PKD1 interaction with AKAP-Lbc (AKAP-Lbc-ΔPKD), we studied two mouse models of pathological hypertrophy: i) angiotensin (AT-II) and phenylephrine (PE) infusion and ii) transverse aortic constriction (TAC)-induced pressure overload. Our results indicate that AKAP-Lbc-ΔPKD mice exhibit an accelerated progression to cardiac dysfunction in response to AT-II/PE treatment and TAC. AKAP-Lbc-ΔPKD mice display attenuated compensatory cardiac hypertrophy, increased collagen deposition and apoptosis, compared to wild-type (WT) control littermates. Mechanistically, reduced levels of PKD1 activation are observed in AKAP-Lbc-ΔPKD mice compared to WT mice, resulting in diminished phosphorylation of histone deacetylase 5 (HDAC5) and decreased hypertrophic gene expression. This is consistent with a reduced compensatory hypertrophy phenotype leading to progression of heart failure in AKAP-Lbc-ΔPKD mice. Overall, our data demonstrates a critical in vivo role for AKAP-Lbc-PKD1 signaling in the development of compensatory hypertrophy to enhance cardiac performance in response to TAC-induced pressure overload and neurohumoral stimulation by AT-II/PE treatment.

Histone deacetylases in cardiac fibrosis: current perspectives for therapy

Cardiac fibrosis is an important pathological feature of cardiac remodeling in heart diseases. The molecular mechanisms of cardiac fibrosis are unknown. Histone deacetylases (HDACs) are enzymes that balance the acetylation activities of histone acetyltransferases on chromatin remodeling and play essential roles in regulating gene transcription. In recent years, the role of HDACs in cardiac fibrosis initiation and progression, as well as the therapeutic effects of HDAC inhibitors, has been well studied. Moreover, numerous studies indicated that HDAC activity is associated with the development and progression of cardiac fibrosis. In this review, the innovative aspects of HDACs are discussed, with respect to biogenesis, their role in cardiac fibrosis. Furthermore, the potential applications of HDAC inhibitors in the treatment of cardiac fibrosis associated with fibroblast activation and proliferation.

Pathological ventricular remodeling: mechanisms: part 1 of 2

Despite declines in heart failure morbidity and mortality with current therapies, rehospitalization rates remain distressingly high, substantially affecting individuals, society, and the economy. As a result, the need for new therapeutic advances and novel medical devices is urgent. Disease-related left ventricular remodeling is a complex process involving cardiac myocyte growth and death, vascular rarefaction, fibrosis, inflammation, and electrophysiological remodeling. Because these events are highly interrelated, targeting a single molecule or process may not be sufficient. Here, we review molecular and cellular mechanisms governing pathological ventricular remodeling.

Diffuse ventricular fibrosis is a late outcome of tachycardia-mediated cardiomyopathy after successful ablation

BACKGROUND

Successful arrhythmia ablation normalizes ejection fraction (EF) in tachycardia-mediated cardiomyopathy, but recurrent heart failure and late sudden death have been reported. The aim of this study was to characterize the left ventricle (LV) of tachycardia-mediated cardiomyopathy patients long after definitive arrhythmia cure.

METHODS AND RESULTS

Thirty-three patients with a history of successfully ablated incessant focal atrial tachycardia 64±36 months prior, and 20 healthy controls were recruited. At ablation, 18 patients had EF<50% (AT-low EF) that recovered within 3 months from 37±12 to 56±4% (P<0.001), whereas 15 patients had EF>55% (AT-normal EF). No subjects had EF of 50% to 55%. Subjects underwent echocardiography with speckle tracking and contrast-enhanced cardiac MRI with ventricular T1 mapping as an index of diffuse fibrosis. Contrast-enhanced cardiac MRI was performed using a clinical 1.5-T scanner and 0.2 mmol/kg gadolinium-diethylene triamine penta-acetic acid for contrast. Subject characteristics were similar across the 3 groups. Compared with AT-normal EF patients and controls, AT-low EF patients had lower EF (60±6 versus 64±4 and 65±4%; P<0.05), greater indexed LV end-diastolic volume (102±34 versus 84±14 and 85±16 mL/m(2); P<0.05), and greater indexed LV end-systolic volume (41±11 versus 31±7 and 30±8 mL/m(2); P<0.01) on contrast-enhanced cardiac MRI. Compared with controls, AT-low EF patients had reduced global LV corrected T1 time (442±53 versus 529±61; P<0.05) consistent with diffuse fibrosis.

CONCLUSIONS

Tachycardia-mediated cardiomyopathy patients exhibit differences in LV structure and function including diffuse fibrosis long after arrhythmia cure, indicating that recovery is incomplete.

Urokinase plasminogen activator induces pro-fibrotic/m2 phenotype in murine cardiac macrophages

Objective

Inflammation and fibrosis are intertwined in multiple disease processes. We have previously found that over-expression of urokinase plasminogen activator in macrophages induces spontaneous macrophage accumulation and fibrosis specific to the heart in mice. Understanding the relationship between inflammation and fibrosis in the heart is critical to developing therapies for diverse myocardial diseases. Therefore, we sought to determine if uPA induces changes in macrophage function that promote cardiac collagen accumulation.

Methods and Results

We analyzed the effect of the uPA transgene on expression of pro-inflammatory (M1) and pro-fibrotic (M2) genes and proteins in hearts and isolated macrophages of uPA overexpressing mice. We found that although there was elevation of the pro-inflammatory cytokine IL-6 in hearts of transgenic mice, IL-6 is not a major effector of uPA induced cardiac fibrosis. However, uPA expressing bone marrow-derived macrophages are polarized to express M2 genes in response to IL-4 stimulation, and these M2 genes are upregulated in uPA expressing macrophages following migration to the heart. In addition, while uPA expressing macrophages express a transcriptional profile that is seen in tumor–associated macrophages, these macrophages promote collagen expression in cardiac but not embryonic fibroblasts.

Conclusions

Urokinase plasminogen activator induces an M2/profibrotic phenotype in macrophages that is fully expressed after migration of macrophages into the heart. Understanding the mechanisms by which uPA modulates macrophage function may reveal insights into diverse pathologic processes.

Oxidative stress, fibrosis, and early afterdepolarization-mediated cardiac arrhythmias

Animal and clinical studies have demonstrated that oxidative stress, a common pathophysiological factor in cardiac disease, reduces repolarization reserve by enhancing the L-type calcium current, the late Na, and the Na-Ca exchanger, promoting early afterdepolarizations (EADs) that can initiate ventricular tachycardia and ventricular fibrillation (VT/VF) in structurally remodeled hearts. Increased ventricular fibrosis plays a key facilitatory role in allowing oxidative-stress induced EADs to manifest as triggered activity and VT/VF, since normal non-fibrotic hearts are resistant to arrhythmias when challenged with similar or higher levels of oxidative stress. The findings imply that antifibrotic therapy, in addition to therapies designed to suppress EAD formation at the cellular level, may be synergistic in reducing the risk of sudden cardiac death.

The biology and therapeutic implications of HDACs in the heart

The heart responds to stresses such as chronic hypertension and myocardial infarction by undergoing a remodeling process that is associated with myocyte hypertrophy, myocyte death, inflammation and fibrosis, often resulting in impaired cardiac function and heart failure. Recent studies have revealed key roles for histone deacetylases (HDACs) as both positive and negative regulators of pathological cardiac remodeling, and small molecule HDAC inhibitors have demonstrated efficacy in animal models of heart failure. This chapter reviews the functions of individual HDAC isoforms in the heart and highlights issues that need to be addressed to enable development of novel HDAC-directed therapies for cardiovascular indications.

Reversibility of adverse, calcineurin-dependent cardiac remodeling

RATIONALE

Studies to dissect the role of calcineurin in pathological cardiac remodeling have relied heavily on murine models, in which genetic gain- and loss-of-function manipulations are initiated at or before birth. However, the great majority of clinical cardiac pathology occurs in adults. Yet nothing is known about the effects of calcineurin when its activation commences in adulthood. Furthermore, despite the fact that ventricular hypertrophy is a well-established risk factor for heart failure, the relative pace and progression of these 2 major phenotypic features of heart disease are unknown. Finally, even though therapeutic interventions in adults are designed to slow, arrest, or reverse disease pathogenesis, little is known about the capacity for spontaneous reversibility of calcineurin-dependent pathological remodeling.

OBJECTIVE

We set out to address these 3 questions by studying mice engineered to harbor in cardiomyocytes a constitutively active calcineurin transgene driven by a tetracycline-responsive promoter element.

METHODS AND RESULTS

Expression of the mutant calcineurin transgene was initiated for variable lengths of time to determine the natural history of disease pathogenesis, and to determine when, if ever, these events are reversible. Activation of the calcineurin transgene in adult mice triggered rapid and robust cardiac growth with features characteristic of pathological hypertrophy. Concentric hypertrophy preceded the development of systolic dysfunction, fetal gene activation, fibrosis, and clinical heart failure. Furthermore, cardiac hypertrophy reversed spontaneously when calcineurin activity was turned off, and expression of fetal genes reverted to baseline. Fibrosis, a prominent feature of pathological cardiac remodeling, manifested partial reversibility.

CONCLUSIONS

Together, these data establish and define the deleterious effects of calcineurin signaling in the adult heart and reveal that calcineurin-dependent hypertrophy with concentric geometry precedes systolic dysfunction and heart failure. Furthermore, these findings demonstrate that during much of the disease process, calcineurin-dependent remodeling remains reversible.

Effect of spironolactone on patients with atrial fibrillation and structural heart disease

BACKGROUND

Several studies have shown that the modulation of fibrotic scar in cardiac diseases has beneficial effects on cardiac arrhythmias. In addition, recent reports suggest a potential role of mineralocorticoid receptor upregulation in atrial fibrillation (AF). The role of spironolactone, a mineralocorticoid receptor blocker and a potent antifibrotic agent, in AF is as yet unexplored. The aim of this study was to determine if spironolactone, a mineralocorticoid receptor blocker with potent antifibrotic properties, has beneficial effects on AF.

HYPOTHESIS

Spironolactone therapy in patients with atrial fibrillation provides additional clinical benefits in addition to the current conventional pharmacological agents.

METHODS

A comprehensive retrospective analysis was performed on 83 patients with AF, including 23 who were treated with spironolactone for ≥3 months. The combined primary outcome of hospitalization for AF or direct current cardioversion (DCCV) was compared between patients treated with spironolactone in addition to the usual care for AF and those receiving conventional medical therapy alone.

RESULTS

Patients receiving spironolactone had significantly fewer primary outcome events (AF-related hospitalizations or DCCV) (22% vs 53%, P = 0.027).

CONCLUSIONS

Spironolactone therapy is associated with a reduction in the burden of AF, as reflected by a combination of hospitalizations for AF and DCCV. Larger randomized controlled studies should be performed to evaluate the efficacy and safety of spironolactone as an adjunctive therapy for patients with AF.

Targeting cardiac fibrosis: a new frontier in antiarrhythmic therapy?

Cardiac fibrosis is known to alter cardiac conduction and promote reentry. Recent evidence indicates that fibrosis characterized by increased interstitial collagen accumulation and increased myofibroblast proliferation also promotes enhanced automaticity and early afterdepolarizations (EADs) causing triggered activity. Fibrosis then becomes an effective therapeutic target for the management of lethal cardiac arrhythmias. While oxidative stress with hydrogen peroxide (H(2)O(2)) is shown to readily promote EADs and triggered activity in isolated rat and rabbit ventricular myocytes however, this same stress fails to cause EADs in well-coupled, non-fibrotic hearts due to source-to-sink mismatches arising from cell-to-cell coupling. The triggered activity in the aged fibrotic hearts causes focal ventricular tachycardia (VT) that degenerates within seconds to ventricular fibrillation (VF) after the emergence of spatially discordant action potential duration alternans leading to wavebreak, reentry and VF. Computer simulations in 2D tissue incorporating variable degrees of fibrosis showed that intermediate (but not mild or very severe) fibrosis promoted EADs and TA. Human studies have shown that myocardial fibrosis was an independent predictor for arrhythmias including sustained VT and VF. A variety of drug classes including, torsemide, a loop diuretic, that inhibits the enzyme involved in the myocardial extracellular generation of collagen type I molecules and the inhibitors of the renin-angiotensin-aldosterone system (RAAS), the mineralocorticoid receptors and endothelin receptors reduce cardiac fibrosis with reduction of myocardial stiffness and improved ventricular function. It is hoped that in the near future effective antifibrotic drug regimen would be developed to reduce the risk of fibrosis related VT and VF.

Spironolactone therapy is associated with reduced ventricular tachycardia rate in patients with cardiomyopathy

INTRODUCTION

Multiple pharmacological therapies currently in prevalent clinical use for cardiac diseases have antifibrotic properties. Spironolactone, a potent antifibrotic agent, is currently used for advanced heart failure. Therapies such as HMG-CoA reductase inhibitors (statins) and angiotensin-converting enzyme inhibitors (ACEi) also have antifibrotic properties. However, the effect of these medications on the ventricular arrhythmia phenotype is currently unknown. Therefore, we set out to define the ventricular arrhythmia rates in patients actively treated with such therapies.

METHODS AND RESULTS

We retrospectively evaluated the ventricular tachycardia (VT) rates in patients with structural heart disease actively treated with therapies with antifibrotic properties. VT rates were significantly diminished in patients treated with spironolactone (158 ± 26 beats per minute [bpm], n = 21) compared to patients on no medications (205 ± 22 bpm, n = 13) or those who were on similar heart-failure therapies but not on spironolactone (186 ± 32 bpm, n = 82). In addition, we observed that VT rates showed a significant trend toward lower rates in patients receiving either statins or ACEi, compared to patients on no medical therapy. In multivariate analysis, spironolactone therapy was identified as the single most significant variable for reduced VT rate.

CONCLUSION

Use of spironolactone in patients with heart failure is associated with reduced VT rate. Similar but less-significant reductions in VT rates were observed with use of other pharmacological agents with antifibrotic properties, such as statins and ACEi. Our findings, at least in part, could account for reduction in sudden cardiac death rates documented with use of these therapies.