Differential regional gene expression from cardiac dyssynchrony induced by chronic right ventricular free wall pacing in the mouse

Adeno-associated virus 2 infection in children with non-A-E hepatitis

An outbreak of acute hepatitis of unknown aetiology in children was reported in Scotland1 in April 2022 and has now been identified in 35 countries2. Several recent studies have suggested an association with human adenovirus with this outbreak, a virus not commonly associated with hepatitis. Here we report a detailed case-control investigation and find an association between adeno-associated virus 2 (AAV2) infection and host genetics in disease susceptibility. Using next-generation sequencing, PCR with reverse transcription, serology and in situ hybridization, we detected recent infection with AAV2 in plasma and liver samples in 26 out of 32 (81%) cases of hepatitis compared with 5 out of 74 (7%) of samples from unaffected individuals. Furthermore, AAV2 was detected within ballooned hepatocytes alongside a prominent T cell infiltrate in liver biopsy samples. In keeping with a CD4+ T-cell-mediated immune pathology, the human leukocyte antigen (HLA) class II HLA-DRB1*04:01 allele was identified in 25 out of 27 cases (93%) compared with a background frequency of 10 out of 64 (16%; P = 5.49 × 10-12). In summary, we report an outbreak of acute paediatric hepatitis associated with AAV2 infection (most likely acquired as a co-infection with human adenovirus that is usually required as a 'helper virus' to support AAV2 replication) and disease susceptibility related to HLA class II status.

Cardiogenic control of affective behavioural state

Emotional states influence bodily physiology, as exemplified in the top-down process by which anxiety causes faster beating of the heart1-3. However, whether an increased heart rate might itself induce anxiety or fear responses is unclear3-8. Physiological theories of emotion, proposed over a century ago, have considered that in general, there could be an important and even dominant flow of information from the body to the brain9. Here, to formally test this idea, we developed a noninvasive optogenetic pacemaker for precise, cell-type-specific control of cardiac rhythms of up to 900 beats per minute in freely moving mice, enabled by a wearable micro-LED harness and the systemic viral delivery of a potent pump-like channelrhodopsin. We found that optically evoked tachycardia potently enhanced anxiety-like behaviour, but crucially only in risky contexts, indicating that both central (brain) and peripheral (body) processes may be involved in the development of emotional states. To identify potential mechanisms, we used whole-brain activity screening and electrophysiology to find brain regions that were activated by imposed cardiac rhythms. We identified the posterior insular cortex as a potential mediator of bottom-up cardiac interoceptive processing, and found that optogenetic inhibition of this brain region attenuated the anxiety-like behaviour that was induced by optical cardiac pacing. Together, these findings reveal that cells of both the body and the brain must be considered together to understand the origins of emotional or affective states. More broadly, our results define a generalizable approach for noninvasive, temporally precise functional investigations of joint organism-wide interactions among targeted cells during behaviour.

Open thoracic surgical implantation of cardiac pacemakers in rats

Genetic engineering and implantable bioelectronics have transformed investigations of cardiovascular physiology and disease. However, the two approaches have been difficult to combine in the same species: genetic engineering is applied primarily in rodents, and implantable devices generally require larger animal models. We recently developed several miniature cardiac bioelectronic devices suitable for mice and rats to enable the advantages of molecular tools and implantable devices to be combined. Successful implementation of these device-enabled studies requires microsurgery approaches that reliably interface bioelectronics to the beating heart with minimal disruption to native physiology. Here we describe how to perform an open thoracic surgical technique for epicardial implantation of wireless cardiac pacemakers in adult rats that has lower mortality than transvenous implantation approaches. In addition, we provide the methodology for a full biocompatibility assessment of the physiological response to the implanted device. The surgical implantation procedure takes ~40 min for operators experienced in microsurgery to complete, and six to eight surgeries can be completed in 1 d. Implanted pacemakers provide programmed electrical stimulation for over 1 month. This protocol has broad applications to harness implantable bioelectronics to enable fully conscious in vivo studies of cardiovascular physiology in transgenic rodent disease models.

Assessment of left ventricular dyssynchrony by speckle tracking echocardiography in children with duchenne muscular dystrophy

Prognosis of Duchenne muscular dystrophy (DMD) is related to cardiac dysfunction. Two dimensional-speckle tracking echocardiography (2D-STE) has recently emerged as a non-invasive functional biomarker for early detection of DMD-related cardiomyopathy. This study aimed to determine, in DMD children, the existence of left ventricle (LV) dyssynchrony using 2D-STE analysis. This prospective controlled study enrolled 25 boys with DMD (mean age 11.0 ± 3.5 years) with normal LV ejection fraction and 50 age-matched controls. Three measures were performed to assess LV mechanical dyssynchrony: the opposing-wall delays (longitudinal and radial analyses), the modified Yu index, and the time-to-peak delays of each segment. Feasibility and reproducibility of 2D-STE dyssynchrony were evaluated. All three mechanical dyssynchrony criteria were significantly higher in the DMD group than in healthy subjects: (1) opposing-wall delays in basal inferoseptal to basal anterolateral segments (61.4 ± 45.3 ms vs. 18.3 ± 50.4 ms, P < 0.001, respectively) and in mid inferoseptal to mid anterolateral segments (58.6 ± 35.3 ms vs. 42.4 ± 36.4 ms, P < 0.05, respectively), (2) modified Yu index (33.3 ± 10.1 ms vs. 28.5 ± 8.1 ms, P < 0.05, respectively), and (3) most of time-to-peak values, especially in basal and mid anterolateral segments. Feasibility was excellent and reliability was moderate to excellent, with ICC values ranging from 0.49 to 0.97. Detection of LV mechanical dyssynchrony using 2D-STE analysis is an easily and reproducible method in paediatric DMD. The existence of an early LV mechanical dyssynchrony visualized using 2D-STE analysis in children with DMD before the onset of cardiomyopathy represents a perspective for future paediatric drug trials in the DMD-related cardiomyopathy prevention.Clinical Trial Registration Clinicaltrials.gov NCT02418338. Post-hoc study, registered on April 16, 2015.

Cardiac resynchronization therapy reduces expression of inflammation-promoting genes related to interleukin-1β in heart failure

AIMS

In light of recent data regarding inflammatory signalling pathways in cardiovascular disease and the recently demonstrated impact of pharmacologic inhibition of interleukin-1β (IL-1β) in heart failure, the primary aim was to assess the physiologic effects of cardiac resynchronization therapy (CRT) on the expression of systemic inflammatory, immune-modulatory, metabolic, and apoptotic genes in peripheral blood mononuclear cells (PBMCs) of patients with heart failure.

METHODS AND RESULTS

We used RNA sequencing (RNA-Seq) and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) to identify gene expression changes in PBMCs in response to CRT. In total, 27 patients were analysed: 12 with heart failure undergoing CRT, 6 with heart failure undergoing standard implanted cardioverter defibrillators, and 9 with coronary artery disease but not heart failure. In CRT patients (median age 65.5 years, interquartile range 63.0-66.8 years, 33% female), RNA-Seq analysis identified 40 genes, including multiple genes associated with the IL-1β pathway, with significant correlations (false discovery rate < 0.05) with four key CRT response measures. CRT was associated with suppression of PBMC expression of IL-1β (1.80-fold decrease, P = 0.047), FOS proto-oncogene (FOS) (3.25-fold decrease, P = 0.01), dual specificity phosphatase 1 (DUSP1) (2.05-fold decrease, P = 0.001), and early growth response 1 (EGR1) (7.38-fold decrease, P = 0.03), and suppression was greater in responders vs. non-responders (P = 0.03 for IL-1β, P = 0.02 for FOS, P = 0.02 for DUSP1, and P = 0.11 for EGR1). Baseline FOS and DUSP-1 levels were greater in responders vs. non-responders (6.15-fold higher, FOS, P = 0.002; 2.60-fold higher, DUSP1, P = 0.0001). CRT responders but not non-responders showed higher baseline gene expression of FOS (P = 0.04) and DUSP1 (P = 0.06) compared with control patients without heart failure. Baseline serum high-sensitivity C-reactive protein levels were 3.47-fold higher in CRT responders vs. non-responders (P = 0.008).

CONCLUSION

Treatment of heart failure with CRT resulted in decreased PBMC expression of genes linked to inflammation. Moreover, CRT responders had higher expression of these inflammatory genes prior to CRT and greater suppression of these genes after CRT compared with non-responders.

MiniVStimA: A miniaturized easy to use implantable electrical stimulator for small laboratory animals

According to PubMed, roughly 10% of the annually added publications are describing findings from the small animal model (mice and rats), including investigations in the field of muscle physiology and training. A subset of this research requires neural stimulation with flexible adjustments of stimulation parameters, highlighting the need for reliable implantable electrical stimulators, small enough (~1 cm³), that even mice can tolerate them without impairing their movement. The MiniVStimA is a battery-powered implant for nerve stimulation with an outer diameter of 15 mm and an encapsulated volume of 1.2 cm³ in its smallest variation. It can be pre-programmed according to the experimental protocol and controlled after implantation with a magnet. It delivers constant current charge-balanced monophasic rectangular pulses up to 2 mA and 1 ms phase width (1 kΩ load). The circuitry is optimized for small volume and energy efficiency. Due to the variation of the internal oscillator (31 kHz ± 10%), calibration measures must be implemented during the manufacturing process, which can reduce the deviation of the frequency related parameters down to ± 1%. The expected lifetime of the smaller (larger) version is 100 (480) days for stimulation with 7 Hz all day and 10 (48) days for stimulation with 100 Hz. Devices with complex stimulation patterns for nerve stimulation have been successfully used in two in-vivo studies, lasting up to nine weeks. The implant worked fully self-contained while the animal stayed in its familiar environment. External components are not required during the entire time.

Chronic Atrial and Ventricular Pacing in the Mouse

BACKGROUND

The mouse is the most widely used mammal in experimental biology. Although many clinically relevant in vivo cardiac stressors are used, one that has eluded translation is long-term cardiac pacing. Here, we present the first method to chronically simulate and simultaneously record cardiac electrical activity in conscious mobile mice. We then apply it to study right ventricular pacing induced electromechanical dyssynchrony and its reversal (resynchronization).

METHODS AND RESULTS

The method includes a custom implantable bipolar stimulation and recording lead and flexible external conduit and electrical micro-commutator linked to a pulse generator/recorder. This achieved continuous pacing for at least 1 month in 77% of implants. Mice were then subjected to cardiac ischemia/reperfusion injury to depress heart function, followed by 4 weeks pacing at the right ventricle (dyssynchrony), right atrium (synchrony), or for 2 weeks right ventricle and then 2 weeks normal sinus (resynchronization). Right ventricular pacing-induced dyssynchrony substantially reduced heart and myocyte function compared with the other groups, increased gene expression heterogeneity (>10 fold) comparing septum to lateral walls, and enhanced growth and metabolic kinase activity in the late-contracting lateral wall. This was ameliorated by restoring contractile synchronization.

CONCLUSIONS

The new method to chronically pace conscious mice yields stable atrial and ventricular capture and a means to dissect basic mechanisms of electromechanical physiology and therapy. The data on dyssynchrony and resynchronization in ischemia/reperfusion hearts is the most comprehensive to date in ischemic heart disease, and its similarities to nonischemic canine results support the translational utility of the mouse.

A Miniaturized, Programmable Pacemaker for Long-Term Studies in the Mouse

RATIONALE

Cardiac pacing is a critical technology for the treatment of arrhythmia and heart failure. The impact of specific pacing strategies on myocardial function is an area of intense research and high clinical significance. Mouse models have proven extremely useful for probing mechanisms of heart disease, but there is currently no reliable technology for long-term pacing in the mouse.

OBJECTIVE

We sought to develop a device for long-term pacing studies in mice. We evaluated the device for (1) treating third-degree atrioventricular block after macrophage depletion, (2) ventricular pacing-induced cardiomyopathy, and (3) high-rate atrial pacing.

METHODS AND RESULTS

We developed a mouse pacemaker by refashioning a 26 mm×6.7 mm clinical device powered by a miniaturized, highly efficient battery. The electrode was fitted with a single flexible lead, and custom software extended the pacing rate to up to 1200 bpm. The wirelessly programmable device was implanted in the dorsal subcutaneous space of 39 mice. The tunneled lead was passed through a left thoracotomy incision and attached to the epicardial surface of the apex (for ventricular pacing) or the left atrium (for atrial pacing). Mice tolerated the implantation and both long-term atrial and ventricular pacing over weeks. We then validated the pacemaker's suitability for the treatment of atrioventricular block after macrophage depletion in Cd11b ^DTR mice. Ventricular pacing increased the heart rate from 313±59 to 550 bpm ( P<0.05). In addition, we characterized tachypacing-induced cardiomyopathy in mice. Four weeks of ventricular pacing resulted in reduced left ventricular function, fibrosis, and an increased number of cardiac leukocytes and endothelial activation. Finally, we demonstrated the feasibility of chronic atrial pacing at 1200 bpm.

CONCLUSIONS

Long-term pacing with a fully implantable, programmable, and battery-powered device enables previously impossible investigations of arrhythmia and heart failure in the mouse.

Prominent differences in left ventricular performance and myocardial properties between right ventricular and left ventricular-based pacing modes in rats

Biventricular pacing is an important modality to improve left ventricular (LV) synchronization and long-term function. However, the biological effects of this treatment are far from being elucidated and existing animal models are limited and demanding. Recently, we introduced an implanted device for double-site epicardial pacing in rats and echocardiographically demonstrated favorable effects of LV and biventricular (LV-based) pacing modes typically observed in humans. Here, this new animal model was further characterized. Electrodes were implanted either on the right atria (RA) and right ventricle (RV) or on the RV and LV. Following recovery, rats were either used for invasive hemodynamic measurements (pressure-volume analysis) or exposed to sustained RV vs. biventricular tachypacing for 3 days. RV pacing compromised, while LV-based pacing modes markedly enhanced cardiac performance. Changes in LV performance were associated with prominent compensatory changes in arterial resistance. Sustained RV tachypacing increased the electrocardiogram QTc interval by 7.9 ± 3.1 ms (n = 6, p < 0.05), dispersed refractoriness between the right and left pacing sites and induced important molecular changes mainly in the early-activated septal tissue. These effects were not observed during biventricular tachypacing (n = 6). Our results demonstrate that the rat is an attractive new model to study the biological consequences of LV dyssynchrony and resynchronization.

Cellular and Molecular Aspects of Dyssynchrony and Resynchronization

Dyssynchronous contraction of the ventricle significantly worsens morbidity and mortality in patients with heart failure (HF). Approximately one-third of patients with HF have cardiac dyssynchrony and are candidates for cardiac resynchronization therapy (CRT). The initial understanding of dyssynchrony and CRT was in terms of global mechanics and hemodynamics, but lack of clinical benefit in a sizable subgroup of recipients who appear otherwise appropriate has challenged this paradigm. This article reviews current understanding of these cellular and subcellular mechanisms, arguing that these aspects are key to improving CRT use, as well as translating its benefits to a wider HF population.

Cardiac disease and arrhythmogenesis: Mechanistic insights from mouse models

The mouse is the second mammalian species, after the human, in which substantial amount of the genomic information has been analyzed. With advances in transgenic technology, mutagenesis is now much easier to carry out in mice. Consequently, an increasing number of transgenic mouse systems have been generated for the study of cardiac arrhythmias in ion channelopathies and cardiomyopathies. Mouse hearts are also amenable to physical manipulation such as coronary artery ligation and transverse aortic constriction to induce heart failure, radiofrequency ablation of the AV node to model complete AV block and even implantation of a miniature pacemaker to induce cardiac dyssynchrony. Last but not least, pharmacological models, despite being simplistic, have enabled us to understand the physiological mechanisms of arrhythmias and evaluate the anti-arrhythmic properties of experimental agents, such as gap junction modulators, that may be exert therapeutic effects in other cardiac diseases. In this article, we examine these in turn, demonstrating that primary inherited arrhythmic syndromes are now recognized to be more complex than abnormality in a particular ion channel, involving alterations in gene expression and structural remodelling. Conversely, in cardiomyopathies and heart failure, mutations in ion channels and proteins have been identified as underlying causes, and electrophysiological remodelling are recognized pathological features. Transgenic techniques causing mutagenesis in mice are extremely powerful in dissecting the relative contributions of different genes play in producing disease phenotypes. Mouse models can serve as useful systems in which to explore how protein defects contribute to arrhythmias and direct future therapy.

Pathophysiology of dyssynchrony: of squirrels and broken bones

The genesis of cardiac resynchronisation therapy (CRT) consists of 'bedside' research and 'bench' studies that are performed in series with each other. In this field, the bench studies are crucial for understanding the pathophysiology of dyssynchrony and resynchronisation. In a way, CRT started with the insight that abnormal ventricular conduction, as caused by right ventricular pacing, has adverse effects. Out of this research came the ground-breaking insight that 'simple' disturbances in impulse conduction, which were initially considered innocent, proved to result in a host of molecular and cellular derangements that lead to a vicious circle of remodelling processes that facilitate the development of heart failure. As a consequence, CRT does not only correct conduction abnormalities, but also improves myocardial properties at many levels. Interestingly, corrections by CRT do not exactly reverse the derangements, induced by dyssynchrony, but also activate novel pathways, a property that may open new avenues for the treatment of heart failure.

Cellular and Molecular Aspects of Dyssynchrony and Resynchronization

Dyssynchronous contraction of the ventricle significantly worsens morbidity and mortality in patients with heart failure (HF). Approximately one-third of patients with HF have cardiac dyssynchrony and are candidates for cardiac resynchronization therapy (CRT). The initial understanding of dyssynchrony and CRT was in terms of global mechanics and hemodynamics, but lack of clinical benefit in a sizable subgroup of recipients who appear otherwise appropriate has challenged this paradigm. This article reviews current understanding of these cellular and subcellular mechanisms, arguing that these aspects are key to improving CRT use, as well as translating its benefits to a wider HF population.

Speckle-tracking echocardiography elucidates the effect of pacing site on left ventricular synchronization in the normal and infarcted rat myocardium

Background

Right ventricular (RV) pacing generates regional disparities in electrical activation and mechanical function (ventricular dyssynchrony). In contrast, left ventricular (LV) or biventricular (BIV) pacing can improve cardiac efficiency in the setting of ventricular dyssynchrony, constituting the rationale for cardiac resynchronization therapy (CRT). Animal models of ventricular dyssynchrony and CRT currently relay on large mammals which are expensive and not readily available to most researchers. We developed a methodology for double-site epicardial pacing in conscious rats. Here, following post-operative recovery, we compared the effects of various pacing modes on LV dyssynchrony in normal rats and in rats with ischemic cardiomyopathy.

Methods

Two bipolar electrodes were implanted in rats as follows: Group A (n = 6) right atrial (RA) and RV sites; Group B (n = 7) RV and LV sites; Group C (n = 8) as in group B in combination with left coronary artery ligation. Electrodes were exteriorized through the back. Following post-operative recovery, two-dimensional transthoracic echocardiography was performed during pacing through the different electrodes. Segmental systolic circumferential strain (Ecc) was used to evaluate LV dyssynchrony.

Results

In normal rats, RV pacing induced marked LV dyssynchrony compared to RA pacing or sinus rhythm, as measured by the standard deviation (SD) of segmental time to peak Ecc, SD of peak Ecc, and the average delay between opposing ventricular segments. LV pacing and, to a greater extend BIV pacing diminished the LV dyssynchrony compared to RV pacing. In rats with extensive MI, the effects of LV and BIV pacing were markedly attenuated, and the response of individual animals was variable.

Conclusions

Rodent cardiac pacing mimics important features seen in humans. This model may be developed as a simple new tool to study the pathophysiology of ventricular dyssynchrony and CRT.

A fully implantable pacemaker for the mouse: from battery to wireless power

Animal models have become a popular platform for the investigation of the molecular and systemic mechanisms of pathological cardiovascular physiology. Chronic pacing studies with implantable pacemakers in large animals have led to useful models of heart failure and atrial fibrillation. Unfortunately, molecular and genetic studies in these large animal models are often prohibitively expensive or not available. Conversely, the mouse is an excellent species for studying molecular mechanisms of cardiovascular disease through genetic engineering. However, the large size of available pacemakers does not lend itself to chronic pacing in mice. Here, we present the design for a novel, fully implantable wireless-powered pacemaker for mice capable of long-term (>30 days) pacing. This design is compared to a traditional battery-powered pacemaker to demonstrate critical advantages achieved through wireless inductive power transfer and control. Battery-powered and wireless-powered pacemakers were fabricated from standard electronic components in our laboratory. Mice (n = 24) were implanted with endocardial, battery-powered devices (n = 14) and epicardial, wireless-powered devices (n = 10). Wireless-powered devices were associated with reduced implant mortality and more reliable device function compared to battery-powered devices. Eight of 14 (57.1%) mice implanted with battery-powered pacemakers died following device implantation compared to 1 of 10 (10%) mice implanted with wireless-powered pacemakers. Moreover, device function was achieved for 30 days with the wireless-powered device compared to 6 days with the battery-powered device. The wireless-powered pacemaker system presented herein will allow electrophysiology studies in numerous genetically engineered mouse models as well as rapid pacing-induced heart failure and atrial arrhythmia in mice.

LTBP-2 acts as a novel marker in human heart failure - a preliminary study

BACKGROUND

We have observed increased expression of latent TGF-β binding protein (LTBP)-2 mRNA in human failing hearts. This study was aimed to further confirm LTBP-2 act as a novel marker in human acute heart failure.

METHODS AND RESULTS

We demonstrated that median level of LTBP-2 in myocardial samples from heart failure patients was significantly elevated, and TGF-β1 significantly promoted LTBP-2 expression in neonatal rat cardiomyocytes. To investigate the potential of LTBP-2 as a biomarker to diagnose heart failure with reduced ejection fraction (HFREF), another cohort of 133 consecutive patients with dyspnea were enrolled. In receiver operating characteristic (ROC) curve analyses to detect HFREF, LTBP-2 achieved an area under curve (AUC) of 0.67 (95% confidence intervals (CI) 0.58-0.75), comparable to the diagnostic ability of NT-proBNP 0.68 (95% CI 0.59-0.77).

CONCLUSION

The serum LTBP-2 levels might act as a promising biomarker in HFREF.

Cell adhesion molecule mediation of myocardial inflammatory responses associated with ventricular pacing

Poorly synchronized activation of the ventricles can lead to impairment of normal cardiac structure/function. We reported previously that short term (4 h) left ventricular (LV) pacing-induced ventricular dyskinesis led to an inflammatory response localized to the epicardium. Results from this study demonstrated that neutrophils may play a major role in this inflammatory process. Neutrophil recruitment to a site of injury is a process that is highly dependent on an upregulation of cell adhesion molecules (CAM). The dependence of ventricular dysynchrony-induced inflammatory responses on CAM upregulation has not been explored. To gain further insight, we used a mouse model of LV pacing to evaluate the role of CAM in mediating the inflammatory response associated with ventricular dyskinesis. We first examined the effects of LV pacing in wild-type mice. Results demonstrate that 40 min of LV pacing increases ICAM-1 immunostaining as well as myeloperoxidase activity and tissue oxidative stress by twofold in early-activated myocardium. Matrix metalloproteinase-9 activity also increased in the same region by ∼3.5-fold. To determine the role of CAM, mice null for ICAM-1 or p-selectin were subjected to 40 min LV pacing. Results demonstrate that the inflammatory response seen in the wild-type mice was significantly mitigated in the ICAM-1 and p-selectin null mice. In conclusion, results demonstrate that CAM expression plays a critical role in the triggering of LV pacing-induced inflammation, thus providing evidence of a vascular mechanism underlying this response. The mechanisms that trigger an upregulation of myocardial CAM expression and, therefore, inflammation await further investigation since they suggest a specific involvement of vascular events.

The "missing" link between acute hemodynamic effect and clinical response

The hemodynamic, mechanical and electrical effects of cardiac resynchronization therapy (CRT) occur immediate and are lasting as long as CRT is delivered. Therefore, it is reasonable to assume that acute hemodynamic effects should predict long-term outcome. However, in the literature there is more evidence against than in favour of this idea. This raises the question of what factor(s) do relate to the benefit of CRT. There is increasing evidence that dyssynchrony, presumably through the resultant abnormal local mechanical behaviour, induces extensive remodelling, comprising structure, as well as electrophysiological and contractile processes. Resynchronization has been shown to reverse these processes, even in cases of limited hemodynamic improvement. These data may indicate the need for a paradigm shift in order to achieve maximal long-term CRT response.

Prevalence and distribution of regional scar in dysfunctional myocardial segments in Duchenne muscular dystrophy

BACKGROUND

The segmental relationship between cardiovascular magnetic resonance (CMR) peak circumferential strain (Ecc) and myocardial scar has not been well characterized in Duchenne muscular dystrophy (DMD), and it is unknown whether echocardiography accurately measures Ecc in DMD. We assessed segmental Ecc and scar using CMR with myocardial tissue tagging and late gadolinium enhancement (LGE) in patients with DMD, then compared CMR with echocardiographic velocity vector imaging (VVI) for regional Ecc based on independent observer assessments.

RESULTS

Participants enrolled (n = 16; age 8-23) had median left ventricular (LV) ejection fraction of 0.52 (range 0.28-0.69), and 156 basal and mid-cavity myocardial segments from the 13 patients completing the LGE protocol were analyzed for strain and scar. Segmental CMR Ecc in the most negative quartile (quartile 4) ruled out scar in that segment, but scar was present in 46% of segments in the least negative (most dysfunctional) Ecc quartile 1, 33% of Ecc quartile 2 segments, and 15% of Ecc quartile 3 segments. Overall scar prevalence in inferior, inferolateral, and anterolateral segments was eight times higher than in inferoseptal, anteroseptal, and anterior segments (p < 0.001). This increased proportion of scar in lateral versus septal segments was consistent across CMR Ecc quartiles (quartile 1: 76% versus 11%, p = 0.001; quartile 2: 65% versus 9%, p < 0.001; quartile 3: 38% versus 0%, p < 0.001). Echocardiographic analysis could be performed in 12 of 14 patients with CMR exams and had to be limited to mid-cavity slices. Echo segmental Ecc in the most negative quartile made scar by CMR in that segment highly unlikely, but the correlation in segmental Ecc between CMR and echo was limited (r = 0.27; p = 0.02).

CONCLUSIONS

The relationship between scar and Ecc in DMD is complex. Among myocardial segments with depressed Ecc, scar prevalence was much higher in inferior, inferolateral, and anterolateral segments, indicating a regionally dependent association between abnormal Ecc and scar, with free wall segments commonly developing dysfunction with scar and septal segments developing dysfunction without scar. Although normal echocardiographic Ecc predicted absence of scar, regional echocardiographic Ecc by VVI has only a limited association with CMR Ecc in DMD.

Global gene expression profiling in the failing myocardium

Heart failure (HF) is a syndrome that involves multiple cellular mechanisms leading to a common phenotype of reduced ventricular contraction and cardiac chamber dilation. To clarify the mechanisms, a number of microarray analyses of the failing myocardium have been conducted. Gene expression profiles are usually compared between opposing pairs of samples, such as non-failing vs failing hearts, ischemic vs non-ischemic hearts, male vs female failing hearts or atria vs ventricles of failing hearts. Apart from these conventional methods, a different novel approach identified cardiac myosin light chain kinase (MLCK) as a HF-related gene by the comprehensive search for the genes that had an expression level that strongly correlated with the severity of HF; further investigations proved the important role of cardiac MLCK in HF. Moreover, a robust gene expression signature composed of 27 genes was revealed on analysis of 4 independent microarray data sets from the failing myocardium of dilated cardiomyopathy. The authors newly demonstrate 107 HF-related genes that were listed in 2 or more of 7 microarray data sets previously reported. Among these genes, many were observed to be involved in mitochondrial dysfunction and oxidative phosphorylation and 3 extracellular molecules, including periostin, pleiotrophin, and SERPINA3, which might become novel diagnostic and therapeutic targets for HF. These novel strategies warrant the new identification of specific genes that are linked to the pathophysiology of HF.

Ion channel subunit expression changes in cardiac Purkinje fibers: a potential role in conduction abnormalities associated with congestive heart failure

Purkinje fibers (PFs) play key roles in cardiac conduction and arrhythmogenesis. Congestive heart failure (CHF) causes well-characterized atrial and ventricular ion channel subunit expression changes, but effects on PF ion channel subunits are unknown. This study assessed changes in PF ion channel subunit expression (real-time PCR, immunoblot, immunohistochemistry), action potential properties, and conduction in dogs with ventricular tachypacing-induced CHF. CHF downregulated mRNA expression of subunits involved in action potential propagation (Nav1.5, by 56%; connexin [Cx]40, 66%; Cx43, 56%) and repolarization (Kv4.3, 43%, Kv3.4, 46%). No significant changes occurred in KChIP2, KvLQT1, ERG, or Kir3.1/3.4 mRNA. At the protein level, downregulation was seen for Nav1.5 (by 38%), Kv4.3 (42%), Kv3.4 (57%), Kir2.1 (26%), Cx40 (53%), and Cx43 (30%). Cx43 dephosphorylation was indicated by decreased larger molecular mass bands (pan-Cx43 antibody) and a 57% decrease in Ser368-phosphorylated Cx43 (phospho-specific antibody). Immunohistochemistry revealed reduced Cx40, Cx43, and phospho-Cx43 expression at intercalated disks. Action potential changes were consistent with observed decreases in ion channel subunits: CHF decreased phase 1 slope (by 56%), overshoot (by 32%), and phase 0 dV/dt(max) (by 35%). Impulse propagation was slowed in PF false tendons: conduction velocity decreased significantly from 2.2+/-0.1 m/s (control) to 1.5+/-0.1 m/s (CHF). His-Purkinje conduction also slowed in vivo, with HV interval increasing from 35.5+/-1.2 (control) to 49.3+/-3.4 ms (CHF). These results indicate important effects of CHF on PF ion channel subunit expression. Alterations in subunits governing conduction properties may be particularly important, because CHF-induced impairments in Purkinje tissue conduction, which this study is the first to describe, could contribute significantly to dyssynchronous ventricular activation, a major determinant of prognosis in CHF-patients.

Update on the pathophysiological basics of cardiac resynchronization therapy

Cardiac resynchronization therapy is an established treatment for patients with severe heart failure and ventricular conduction disturbance. Cardiac resynchronization therapy improves cardiac pump function and clinical status, and reduces morbidity and mortality. This electrical treatment for heart failure has also contributed enormously to the understanding of the pathophysiology of ventricular conduction disturbance. This article highlights the latest findings about the pathophysiology of ventricular conduction disturbance and pacing as well as that of resynchronization, with emphasis on the role of regional mechanical performance in triggering remodeling processes involved and on the selection of patients using mechanical dyssynchrony.

Physiology of biventricular pacing

Biventricular pacing (cardiac resynchronization therapy ) has been shown to be a very effective therapy for patients with heart failure and dyssynchrony, with improved survival now shown in a recent trial. Electrical dyssynchrony, usually quantified by the duration of the QRS complex, is distinct from mechanical dyssynchrony. Intraventricular mechanical dyssynchrony is most commonly manifest by decreased septal work with concomitant early lateral wall prestretch and subsequent inefficient late contraction. Intraventricular dyssynchrony appears to be more predictive of response to CRT than interventricular dyssynchrony. Mechanical left ventricular dyssynchrony also is associated with regional molecular derangements in connexin-43, stress response kinases, and tumor necrosis factor-alpha. These molecular derangements may lead to abnormalities in conduction velocity and action potential duration, which may predispose to ventricular arrhythmia. Biventricular pacing corrects abnormal regional wall stresses and results in electrical, mechanical, and molecular left ventricular remodeling.