The cAMP/PKA signaling pathway conditions cardiac performance in experimental animals with metabolic syndrome.

Metabolic syndrome (MetS) increases the risk of coronary artery disease, but effects of this condition on the working myocardium remain to be fully elucidated. In the present study we evaluated the consequences of diet-induced metabolic disorders on cardiac function and myocyte performance using female mice fed with Western diet. Animals maintained on regular chow were used as control (Ctrl). Mice on the Western diet (WesD) had increased body weight, impaired glucose metabolism, preserved diastolic and systolic function, but increased left ventricular (LV) mass, with respect to Ctrl animals. Moreover, WesD mice had reduced heart rate variability (HRV), indicative of altered cardiac sympathovagal balance. Myocytes from WesD mice had increased volume, enhanced cell mechanics, and faster kinetics of contraction and relaxation. Moreover, levels of cAMP and protein kinase A (PKA) activity were enhanced in WesD myocytes, and interventions aimed at stabilizing cAMP/PKA abrogated functional differences between Ctrl and WesD cells. Interestingly, in vivo ß-adrenergic receptor (ß-AR) blockade normalized the mechanical properties of WesD myocytes and revealed defective cardiac function in WesD mice, with respect to Ctrl. Collectively, these results indicate that metabolic disorders induced by Western diet enhance the cAMP/PKA signaling pathway, a possible adaptation required to maintain cardiac function.

Phosphorylation of cardiac sodium channel at Ser571 anticipates manifestations of the aging myopathy.

Diastolic dysfunction and delayed ventricular repolarization are typically observed in the elderly, but whether these defects are intimately associated with the progressive manifestation of the aging myopathy remains to be determined. In this regard, aging in experimental animals is coupled with increased late Na+ current (INa,L) in cardiomyocytes, raising the possibility that INa,L conditions the modality of electrical recovery and myocardial relaxation of the aged heart. For this purpose, aging male and female wild-type (WT) C57Bl/6 mice were studied together with genetically engineered mice with phosphomimetic (gain of function, GoF) or ablated (loss of function, LoF) mutations of the sodium channel Nav1.5 at Ser571 associated with, respectively, increased and stabilized INa,L. At ∼18 mo of age, WT mice developed prolonged duration of the QT interval of the electrocardiogram and impaired diastolic left ventricular (LV) filling, defects that were reversed by INa,L inhibition. Prolonged repolarization and impaired LV filling occurred prematurely in adult (∼5 mo) GoF mutant mice, whereas these alterations were largely attenuated in aging LoF mutant animals. Ca2+ transient decay and kinetics of myocyte shortening/relengthening were delayed in aged (∼24 mo) WT myocytes, with respect to adult cells. In contrast, delayed Ca2+ transients and contractile dynamics occurred at adult stage in GoF myocytes and further deteriorated in old age. Conversely, myocyte mechanics were minimally affected in aging LoF cells. Collectively, these results document that Nav1.5 phosphorylation at Ser571 and the late Na+ current modulate the modality of myocyte relaxation, constituting the mechanism linking delayed ventricular repolarization and diastolic dysfunction.NEW & NOTEWORTHY We have investigated the impact of the late Na current (INa,L) on cardiac and myocyte function with aging by using genetically engineered animals with enhanced or stabilized INa,L, due to phosphomimetic or phosphoablated mutations of Nav1.5. Our findings support the notion that phosphorylation of Nav1.5 at Ser571 prolongs myocardial repolarization and impairs diastolic function, contributing to the manifestations of the aging myopathy.

Elucidation of Complex Atrial Tachycardia Activation in a Patient with Tetralogy of Fallot Using Omnipolar Mapping Technology: A Case Report.

In this case report, omnipolar mapping, a unique technology, was used to analyze complex atrial arrhythmias in an adult with congenital heart disease. Our patient had surgically corrected tetralogy of Fallot and presented with highly symptomatic atrial arrhythmias. A successful ablation was performed with standard bipolar mapping techniques. However, due to the complex nature of the substrate and arrhythmias in this patient, bipolar arrhythmia maps were difficult to interpret, and ablation lesions were delivered based on inference and "educated guesses." An offline re-analysis with omnipolar technology (OT) research software, days after the procedure was performed, revealed details not seen with traditional mapping and explained why the delivered lesions were effective. The findings of this retrospective analysis are provocative, suggesting that OT may increase the accuracy and efficiency of mapping and ablation of complex arrhythmias. Further investigation using commercially released OT in real time is needed.

Heart Rate Variability Reveals Altered Autonomic Regulation in Response to Myocardial Infarction in Experimental Animals.

The analysis of beating rate provides information on the modulatory action of the autonomic nervous system on the heart, which mediates adjustments of cardiac function to meet hemodynamic requirements. In patients with myocardial infarction, alterations of heart rate variability (HRV) have been correlated to the occurrence of arrhythmic events and all-cause mortality. In the current study, we tested whether experimental rodent models of myocardial infarction recapitulate dynamics of heart rate variability observed in humans, and constitute valid platforms for understanding mechanisms linking autonomic function to the development and manifestation of cardiovascular conditions. For this purpose, HRV was evaluated in two engineered mouse lines using electrocardiograms collected in the conscious, restrained state, using a tunnel device. Measurements were obtained in naïve mice and animals at 3-∼28 days following myocardial infarction, induced by permanent coronary artery ligation. Two mouse lines with inbred and hybrid genetic background and, respectively, homozygous (Homo) and heterozygous (Het) for the MerCreMer transgene, were employed. In the naïve state, Het female and male mice presented prolonged RR interval duration (∼9%) and a ∼4-fold increased short- and long-term RR interval variability, with respect to sex-matched Homo mice. These differences were abrogated by pharmacological interventions inhibiting the sympathetic and parasympathetic axes. At 3-∼14 days after myocardial infarction, RR interval duration increased in Homo mice, but was not affected in Het animals. In contrast, Homo mice had minor modifications in HRV parameters, whereas substantial (> 50%) reduction of short- and long-term RR interval variation occurred in Het mice. Interestingly, ex vivo studies in isolated organs documented that intrinsic RR interval duration increased in infarcted vs. non-infarcted Homo and Het hearts, whereas RR interval variation was not affected. In conclusion, our study documents that, as observed in humans, myocardial infarction in rodents is associated with alterations in heart rhythm dynamics consistent with sympathoexcitation and parasympathetic withdrawal. Moreover, we report that mouse strain is an important variable when evaluating autonomic function via the analysis of HRV.

Scn1b expression in the adult mouse heart modulates Na+ influx in myocytes and reveals a mechanistic link between Na+ entry and diastolic function.

Voltage-gated sodium channels (VGSCs) are macromolecular assemblies composed of a number of proteins regulating channel conductance and properties. VGSCs generate Na+ current (INa) in myocytes and play fundamental roles in excitability and impulse conduction in the heart. Moreover, VGSCs condition mechanical properties of the myocardium, a process that appears to involve the late component of INa. Variants in the gene SCN1B, encoding the VGSC ß1- and ß1B-subunits, result in inherited neurological disorders and cardiac arrhythmias. But the precise contributions of ß1/ß1B-subunits and VGSC integrity to the overall function of the adult heart remain to be clarified. For this purpose, adult mice with cardiac-restricted, inducible deletion of Scn1b (conditional knockout, cKO) were studied. Myocytes from cKO mice had increased densities of fast (+20%)- and slow (+140%)-inactivating components of INa, with respect to control cells. By echocardiography and invasive hemodynamics, systolic function was preserved in cKO mice, but diastolic properties and ventricular compliance were compromised, with respect to control animals. Importantly, inhibition of late INa with GS967 normalized left ventricular filling pattern and isovolumic relaxation time in cKO mice. At the cellular level, cKO myocytes presented delayed kinetics of Ca2+ transients and cell mechanics, defects that were corrected by inhibition of INa. Collectively, these results document that VGSC ß1/ß1B-subunits modulate electrical and mechanical function of the heart by regulating, at least in part, Na+ influx in cardiomyocytes.NEW & NOTEWORTHY We have investigated the consequences of deletion of Scn1b, the gene encoding voltage-gated sodium channel ß1-subunits, on myocyte and cardiac function. Our findings support the notion that Scn1b expression controls properties of Na+ influx and Ca2+ cycling in cardiomyocytes affecting the modality of cell contraction and relaxation. These effects at the cellular level condition electrical recovery and diastolic function in vivo, substantiating the multifunctional role of ß1-subunits in the physiology of the heart.

Brugada syndrome clinical update.

Brugada syndrome (BrS) was initially described in southeast Asians with a structurally normal heart presenting with polymorphic ventricular tachycardia and fibrillation. This condition is marked by J-point elevation ≥ 2 mm with coved-type ST segment elevation followed by negative T wave inversions in at least one precordial lead (V1 or V2) when other etiologies have been excluded. These changes on electrocardiogram (EKG) can either be spontaneous or manifest after sodium channel blockade. The worldwide prevalence of BrS is about 0.4%; however, it is higher in the Asian population at 0.9%. This article will review the current hypotheses regarding the pathophysiology, spectrum of clinical presentation, strategies for prevention of sudden cardiac death and the treatment for recurrent arrhythmias in BrS.

Unique technique to relieve left ventricular assist device electromagnetic interference with an implantable cardioverter defibrillator.

We introduced a simple technique to eliminate electromagnetic interference between a left ventricular assist device (LVAD) and an implantable cardioverter defibrillator (ICD). A 43-year-old male with heart failure and a reduced ejection fraction who had an ICD presented with decompensated heart failure and received an LVAD as a bridge to transplant. Remote monitoring showed persistent atrial fibrillation causing an inappropriate ICD shock leading to a decision to disable shock therapies. However, an in-office interrogation was unsuccessful due to electromagnetic interference. Patient was instructed to extend his arm above his head on the ipsilateral side of the ICD, thus increasing the distance between LVAD and ICD, eliminating the interaction to allow reprogramming of the device.

Noninvasive Radioablation of Ventricular Tachycardia.

Ventricular tachycardia (VT) occurs most commonly in the presence of structural heart disease or myocardial scarring from prior infarction. It is associated with increased mortality, especially when it results in cardiac arrest outside of a hospital. When not due to reversible causes (such as acute ischemia/infarction), placement of an implantable cardioverter-defibrillator for prevention of future sudden death is indicated. The current standard of care for recurrent VT is medical management with antiarrhythmic agents followed by invasive catheter ablation for VT that persists despite appropriate medical therapy. Stereotactic arrhythmia radioablation (STAR) is a novel, noninvasive method of treating VT that has been shown to reduce VT burden for patients who are refractory to medical therapy and/or catheter ablation, or who are unable to tolerate catheter ablation. STAR is the term applied to the use of stereotactic body radiation therapy for the treatment of arrhythmogenic cardiac tissue and requires collaboration between an electrophysiologist and a radiation oncologist. The process involves identification of VT substrate through a combination of electroanatomic mapping and diagnostic imaging (computed tomography, magnetic resonance imaging, positron emission tomography) followed by carefully guided radiation therapy. In this article, we review currently available literature describing the utilization, efficacy, safety profile, and potential future applications of STAR for the management of VT.

Rhythm dynamics of the aging heart: an experimental study using conscious, restrained mice.

Heart rate variability (HRV) is a measure of variation in time interval between heartbeats and reflects the influence of autonomic nervous system and circulating/locally released factors on sinoatrial node discharge. Here, we tested whether electrocardiograms (ECGs) obtained in conscious, restrained mice, a condition that affects sympathovagal balance, reveal alterations of heart rhythm dynamics with aging. Moreover, based on emergence of sodium channels as modulators of pacemaker activity, we addressed consequences of altered sodium channels on heart rhythm. C57Bl/6 mice and mice with enhanced late sodium current due to Nav1.5 mutation at Ser571 (S571E) at ~4 to ~24 mo of age, were studied. HRV was assessed using time- and frequency-domain and nonlinear parameters. For C57Bl/6 and S571E mice, standard deviation of RR intervals (SDRR), total power of RR interval variation, and nonlinear standard deviation 2 (SD2) were maximal at ~4 mo and decreased at ~18 and ~24 mo, together with attenuation of indexes of sympathovagal balance. Modulation of sympathetic and/or parasympathetic divisions revealed attenuation of autonomic tone at ~24 mo. At ~4 mo, S571E mice presented lower heart rate and higher SDRR, total power, and SD2 with respect to C57Bl/6, properties reversed by late sodium current inhibition. At ~24 mo, heart rate decreased in C57Bl/6 but increased in S571E, a condition preserved after autonomic blockade. Collectively, our data indicate that aging is associated with reduced HRV. Moreover, sodium channel function conditions heart rate and its age-related adaptations, but does not interfere with HRV decline occurring with age.NEW & NOTEWORTHY We have investigated age-associated alterations of heart rate properties in mice using conscious electrocardiographic recordings. Our findings support the notion that aging is coupled with altered sympathovagal balance with consequences on heart rate variability. Moreover, by using a genetically engineered mouse line, we provide evidence that sodium channels modulate heart rate and its age-related adaptations.

Survival of a Patient with an Esophagopericardial Fistula After Catheter Ablation for Atrial Fibrillation: A Case Report and Literature Review.

Esophageal injury leading to esophagopericardial fistula (EPF) or atrioesophageal fistula is a very rare and dreaded complication of catheter ablation for atrial fibrillation that carries a high mortality rate. We present a case of EPF following radiofrequency catheter ablation for atrial fibrillation and an extensive review of the literature regarding catheter ablation-related esophageal injury.

Arrhythmogenic Right Ventricular Cardiomyopathy Diagnosis.

Arrhythmogenic right ventricular cardiomyopathy, formerly called "arrhythmogenic right ventricular dysplasia," is an under-recognized clinical entity characterized by ventricular arrhythmias and a characteristic ventricular pathology. Diagnosis is often difficult due to the nonspecific nature of the disease and the broad spectrum of phenotypic variations. Therefore, consensus diagnostic criteria have been developed which combine electrocardiographic, echocardiographic, cardiac magnetic resonance imaging and histologic criteria. In 1994, an international task force first proposed the major and minor diagnostic criteria of arrhythmogenic right ventricular cardiomyopathy based on family history, arrhythmias, electrocardiographic abnormalities, tissue characterization, and structural and functional right ventricular abnormalities. In 2010, the task force criteria were revised to include quantitative abnormalities. These diagnostic modalities and the most recent task force criteria are discussed in this review.

Left Atrial Appendage Occlusion in the Management of Stroke in Patients With Atrial Fibrillation.

Atrial fibrillation (AF) is associated with a substantially higher risk of thromboembolism, particularly stroke events, resulting in significant morbidity and mortality. Oral anticoagulation (OAC), while effective in reducing embolic events in AF patients, is associated with an increased bleeding risk. Thus, not all patients with AF are candidates for OAC and some are only candidates for OAC in the short term. Of the available nonpharmacologic strategies for the management of AF, left atrial appendage occlusion (LAAO) has emerged as a potential approach for reducing the risk of systemic thromboembolism in AF patients eligible for OAC. LAAO can be achieved either surgically or percutaneously using an epicardial, endocardial, or a combined approach. Although available data are limited, currently available LAAO devices, and those being developed, have shown promise in reducing bleeding risk in AF patients because of the reduced overall need for anticoagulation, while maintaining efficacy in preventing thromboembolism. The optimal device will reduce both embolic and hemorrhagic strokes, and other bleeds, with a high implant success rate and a low complication rate. Until that time, anticoagulation remains the gold standard that these devices strive to surpass, and thus LAAO devices are currently indicated in patients with relative contraindication to OAC therapy.

Role of Imaging in the Management of Ventricular Arrhythmias.

The management of ventricular arrhythmias (VA) has evolved over time to an advanced discipline, incorporating many technologies in the diagnosis and treatment of the myriad types of VA. The first application of imaging is in the assessment for structural heart disease, as this has the greatest impact on prognosis. Advanced imaging has its greatest utility in the planning and execution of ablation for VA. The following review outlines the application of different imaging modalities, such as ultrasonography, magnetic resonance imaging, computed tomography, and positron emission tomography, for the treatment of VA.

Arrhythmia Evaluation and Management.

Patients with hypertrophic cardiomyopathy may present with a number of arrhythmias. Although not unique, arrhythmias in hypertrophic cardiomyopathy require management approaches that may differ from other populations. Standard permanent pacemaker indications can be seen, but unique applications and implantation considerations pertain to this population. Ventricular and supraventricular tachyarrhythmias may be experienced by patients with hypertrophic cardiomyopathy, treatment for which must be tailored to the hypertrophic cardiomyopathy substrate. In this article, permanent pacemaker indications, techniques and special considerations, and specific management issues of ventricular and supraventricular tachyarrhythmias in hypertrophic cardiomyopathy, are discussed.