Mechanisms of sudden cardiac death in myocardial infarction survivors: insights from the randomized trials of implantable cardioverter-defibrillators

Characteristics and prognosis of patients with elevated triglycerides in acute myocardial infarction: observational data from a large database over a 17-year period: High triglycerides in acute myocardial infarction

From a large regional registry, we aimed to address the characteristics and prognosis of patients with elevated triglycerides (TG) among patients hospitalized for an acute myocardial infarction (MI). From the multicenter database of the RICO survey, all consecutive patients hospitalized for an acute MI (2001-2017) and alive at discharge were included. Among the 10,667 patients included, 17.7% had elevated TG. When compared with patients with TG ≤ 200 mg/dL, patients with high TG (>200 mg/dL) were 10 years younger, had a higher BMI, were more frequently men, diabetic, and smokers. At 1-year follow-up, recurrent ischemic events were more frequent in elevated TG patients. In multivariate logistic regression analysis, high TG (OR (95%CI): 1.356 (1.095-1.679)) remained an independent estimate for recurrent ischemic events, even after adjustment for confounding factors. In our large population-based cohort, elevated TG are common in acute MI, and associated with residual risk of recurrent ischemic events, beyond traditional prognostic markers.

AIEgen-Based Covalent Organic Frameworks for Preventing Malignant Ventricular Arrhythmias Via Local Hyperthermia Therapy

The engineering of aggregation-induced emission luminogens (AIEgen) based covalent organic frameworks (COFs), TDTA-COF, BTDTA-COF, and BTDBETA-COF are reported, as hyperthermia agents for inhibiting the occurrence of malignant ventricular arrhythmias (VAs). These AIE COFs exhibit dual functionality, as they not only directly modulate the function and neural activity of stellate ganglion (SG) through local hyperthermia therapy (LHT) but also induce the browning of white fat and improve the neuroinflammation peri-SG microenvironment, which is favorable for inhibiting ischemia-induced VAs. In vivo studies have confirmed that BTDBETA-COF-mediated LHT enhances thermogenesis and browning-related gene expression, thereby serving a synergistic role in combating VAs. Transcriptome analysis of peri-SG adipose tissue reveals a substantial downregulation of inflammatory cytokines, highlighting the potency of BTDBETA-COF-mediated LHT in ameliorating the neuroinflammation peri-SG microenvironment and offering myocardial and arrhythmia protection. The work on AIE COF-based hyperthermia agent for VAs inhibition provides a new avenue for mitigating cardiac sympathetic nerve hyperactivity.

Sudden Cardiac Arrest in Basketball and Soccer Stadiums, the Role of Automated External Defibrillators: A Review. For the BELTRAN Study (BaskEtbaLl and soccer sTadiums: Registry on Automatic exterNal defibrillators)

Sudden cardiac arrest (SCA) during sports events has a dramatic impact on stadium-goers and the public and is often associated with poor outcomes unless treated with an automated external defibrillator (AED). Despite this, stadiums vary in AED use. This review aims to identify the risks and incidences of SCA, and the use of AEDs in soccer and basketball stadiums. A narrative review of all relevant papers was conducted. Athletes across all sports face an SCA risk of 1:50,000 athlete-years, with the greatest risk of SCA in young male athletes (1:35,000 person-years) and black male athletes (1:18,000 person-years). Africa and South America have the poorest soccer SCA outcomes at 3% and 4% survival. AED use on-site improves survival greater than defibrillation by emergency services. Many stadiums do not have AEDs implemented into medical plans and the AEDs are often unrecognisable or are obstructed. Therefore, AEDs should be used on-site, use clear signalling, have certified trained personnel, and be incorporated into stadiums' medical plans.

Clinical valuation of ST changes in a group of patients with ventricular arrhythmias: The inSighT Study

Background

The inSighT study was designed to determine the prevalence of ischemic changes as recorded by implantable cardioverter–defibrillator (ICD) ST deviations in intracardiac electrocardiograms (EGM) over the 24 h preceding malignant ventricular arrhythmias (VT/VF).

Methods

The study enrolled patients with known coronary artery disease (CAD) or high risk of future development of CAD implanted with an ICD equipped with an ST monitoring feature (Ellipse™/Fortify Assura™, St. Jude Medical). Device session records were collected at each in‐clinic follow‐up. EGM ST levels of the beats over the 15 minutes prior to VT/VF events were compared using a t test with those from a baseline period of 23–24 h prior to the VT/VF event. All events with p < .05 were visually inspected to confirm they were evaluable; additional criteria for exclusion from further analysis included inappropriate therapy, aberrant conduction, and occurrence of VT/VF within 24h prior to the current event.

Results

The study enrolled 481 ICD patients (64 ± 11 years, 83% male) in 14 countries and followed them for 15±5 months. A total of 165 confirmed VT/VF episodes were observed, of which 71 events (in 56 patients, 34% of all patients with VT/VF) were preceded by significant (p < .05) ST‐segment changes unrelated to known non‐ischemic causes. None of the analyzed demographic and clinical factors proved to be associated with greater odds of presenting with ST‐segment changes prior to VT/VF episode.

Conclusion

In this exploratory study, characteristic ST‐segment changes, likely representative of ischemic events, were observed in 34% of all patients with VT/VF episodes.

Therapeutic Acellular Scaffolds for Limiting Left Ventricular Remodelling-Current Status and Future Directions

Myocardial infarction (MI) is one of the leading causes of heart-related deaths worldwide. Following MI, the hypoxic microenvironment triggers apoptosis, disrupts the extracellular matrix and forms a non-functional scar that leads towards adverse left ventricular (LV) remodelling. If left untreated this eventually leads to heart failure. Besides extensive advancement in medical therapy, complete functional recovery is never accomplished, as the heart possesses limited regenerative ability. In recent decades, the focus has shifted towards tissue engineering and regenerative strategies that provide an attractive option to improve cardiac regeneration, limit adverse LV remodelling and restore function in an infarcted heart. Acellular scaffolds possess attractive features that have made them a promising therapeutic candidate. Their application in infarcted areas has been shown to improve LV remodelling and enhance functional recovery in post-MI hearts. This review will summarise the updates on acellular scaffolds developed and tested in pre-clinical and clinical scenarios in the past five years with a focus on their ability to overcome damage caused by MI. It will also describe how acellular scaffolds alone or in combination with biomolecules have been employed for MI treatment. A better understanding of acellular scaffolds potentialities may guide the development of customised and optimised therapeutic strategies for MI treatment.

Predictors of Sudden Cardiac Arrest Among Patients With Post-Myocardial Infarction Ejection Fraction Greater Than 35

Background

Sudden cardiac arrest (SCA) risk increases after myocardial infarction (MI) in patients with a reduced ejection fraction (EF). However, the risk factors for SCA among patients with a post‐MI EF >35% remain poorly understood.

Methods and Results

Using the Optum de‐identified electronic health record data set from 2008 to 2017, we identified patients with an incident MI diagnosis and troponin elevation who had a post‐MI EF >35% and underwent coronary angiography. Primary outcome was SCA within 1 year post‐MI. The database was divided into derivation (70%) and validation (30%) cohorts by random selection. Cox proportional hazard regression was used to generate and validate a risk prediction model. Among 31 286 patients with an MI (median age 64.1; 39% female; 87% White), 499 experienced SCA within 1 year post‐MI (estimated probability 1.8%). Lack of revascularization at MI, post‐MI EF <50%, Black race, renal failure, chronic obstructive pulmonary disease, antiarrhythmic therapy, and absence of beta blocker therapy were independent predictors of SCA. A multivariable model consisting of these variables predicted SCA risk (C‐statistic 0.73). Based on this model, the estimated annual probability of SCA was 4.4% (95% CI, 3.9–4.9) in the highest quartile of risk versus 0.6% (95% CI, 0.4–0.8) in the lowest quartile.

Conclusions

Patients with a post‐MI EF >35% have a substantial annual risk of SCA. A risk model consisting of acute coronary revascularization, EF, race, renal failure, chronic obstructive pulmonary disease, antiarrhythmic therapy, and beta blocker therapy can identify patients with higher risk of SCA, who may benefit from further risk stratification and closer monitoring.

Cardiac Fibrosis: Key Role of Integrins in Cardiac Homeostasis and Remodeling

Cardiac fibrosis is a common finding that is associated with the progression of heart failure (HF) and impacts all chambers of the heart. Despite intense research, the treatment of HF has primarily focused upon strategies to prevent cardiomyocyte remodeling, and there are no targeted antifibrotic strategies available to reverse cardiac fibrosis. Cardiac fibrosis is defined as an accumulation of extracellular matrix (ECM) proteins which stiffen the myocardium resulting in the deterioration cardiac function. This occurs in response to a wide range of mechanical and biochemical signals. Integrins are transmembrane cell adhesion receptors, that integrate signaling between cardiac fibroblasts and cardiomyocytes with the ECM by the communication of mechanical stress signals. Integrins play an important role in the development of pathological ECM deposition. This review will discuss the role of integrins in mechano-transduced cardiac fibrosis in response to disease throughout the myocardium. This review will also demonstrate the important role of integrins as both initiators of the fibrotic response, and modulators of fibrosis through their effect on cardiac fibroblast physiology across the various heart chambers.

Platelet-derived growth factor-AB improves scar mechanics and vascularity after myocardial infarction

Therapies that target scar formation after myocardial infarction (MI) could prevent ensuing heart failure or death from ventricular arrhythmias. We have previously shown that recombinant human platelet-derived growth factor-AB (rhPDGF-AB) improves cardiac function in a rodent model of MI. To progress clinical translation, we evaluated rhPDGF-AB treatment in a clinically relevant porcine model of myocardial ischemia-reperfusion. Thirty-six pigs were randomized to sham procedure or balloon occlusion of the proximal left anterior descending coronary artery with 7-day intravenous infusion of rhPDGF-AB or vehicle. One month after MI, rhPDGF-AB improved survival by 40% compared with vehicle, and cardiac magnetic resonance imaging showed left ventricular (LV) ejection fraction improved by 11.5%, driven by reduced LV end-systolic volumes. Pressure volume loop analyses revealed improved myocardial contractility and energetics after rhPDGF-AB treatment with minimal effect on ventricular compliance. rhPDGF-AB enhanced angiogenesis and increased scar anisotropy (high fiber alignment) without affecting overall scar size or stiffness. rhPDGF-AB reduced inducible ventricular tachycardia by decreasing heterogeneity of the ventricular scar that provides a substrate for reentrant circuits. In summary, we demonstrated that rhPDGF-AB promotes post-MI cardiac wound repair by altering the mechanics of the infarct scar, resulting in robust cardiac functional improvement, decreased ventricular arrhythmias, and improved survival. Our findings suggest a strong translational potential for rhPDGF-AB as an adjunct to current MI treatment and possibly to modulate scar in other organs.

Death and Myocardial Infarction Following Initial Revascularization Versus Optimal Medical Therapy in Chronic Coronary Syndromes With Myocardial Ischemia: A Systematic Review and Meta-Analysis of Contemporary Randomized Controlled Trials

Background

In chronic coronary syndromes, myocardial ischemia is associated with a greater risk of death and nonfatal myocardial infarction (MI). We sought to compare the effect of initial revascularization with percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) plus optimal medical therapy (OMT) with OMT alone in patients with chronic coronary syndrome and myocardial ischemia on long‐term death and nonfatal MI.

Methods and Results

Ovid Medline, Embase, Scopus, and Cochrane Library databases were searched for randomized controlled trials of PCI or CABG plus OMT versus OMT alone for patients with chronic coronary syndromes. Studies were screened and data were extracted independently by 2 authors. Random‐effects models were used to generate pooled treatment effects. The search yielded 7 randomized controlled trials that randomized 10 797 patients. Median follow‐up was 5 years. Death occurred in 640 of the 5413 patients (11.8%) randomized to revascularization and in 647 of the 5384 patients (12%) randomized to OMT (odds ratio [OR], 0.97; 95% CI, 0.86–1.09; P=0.60). Nonfatal MI was reported in 554 of 5413 patients (10.2%) in the revascularization arms compared with 627 of 5384 patients (11.6%) in the OMT arms (OR, 0.75; 95% CI, 0.57–0.99; P=0.04). In subgroup analysis, nonfatal MI was significantly reduced by CABG (OR, 0.35; 95% CI, 0.21–0.59; P<0.001) but was not reduced by PCI (OR, 0.92; 95% CI, 0.75–1.13; P=0.43) (P‐interaction <0.001).

Conclusions

In patients with chronic coronary syndromes and myocardial ischemia, initial revascularization with PCI or CABG plus OMT did not reduce long‐term mortality compared with OMT alone. CABG plus OMT reduced nonfatal MI compared with OMT alone, whereas PCI did not.

The microRNA in ventricular remodeling: the miR-30 family

Ventricular remodeling (VR) is a complex pathological process of cardiomyocyte apoptosis, cardiac hypertrophy, and myocardial fibrosis, which is often caused by various cardiovascular diseases (CVDs) such as hypertension, acute myocardial infarction, heart failure (HF), etc. It is also an independent risk factor for a variety of CVDs, which will eventually to damage the heart function, promote cardiovascular events, and lead to an increase in mortality. MicroRNAs (miRNAs) can participate in a variety of CVDs through post-transcriptional regulation of target gene proteins. Among them, microRNA-30 (miR-30) is one of the most abundant miRNAs in the heart. In recent years, the study found that the miR-30 family can participate in VR through a variety of mechanisms, including autophagy, apoptosis, oxidative stress, and inflammation. VR is commonly found in ischemic heart disease (IHD), hypertensive heart disease (HHD), diabetic cardiomyopathy (DCM), antineoplastic drug cardiotoxicity (CTX), and other CVDs. Therefore, we will review the relevant mechanisms of the miR-30 in VR induced by various diseases.

Non-arrhythmic causes of sudden death: A comprehensive review

Sudden cardiac death (SCD) is a major public health issue in the United States and worldwide. It is estimated to affect between 1 and 1.5 million patients worldwide annually, with the global burden expected to rise due to the concomitant rise in coronary artery disease in the developing world. Although arrhythmic causes of SCD such as ventricular tachycardia and ventricular fibrillation are common and well-studied, non-arrhythmic causes are also important, with diverse etiologies from ischemia-related structural heart disease to non-ischemic heart diseases, non-atherosclerotic coronary pathologies, and inflammatory states. Recent research has also found that risk factors and/or demographics predispose certain individuals to a higher risk of non-arrhythmia-related SCD. This review discusses the epidemiology, mechanisms, etiologies, and management of non-arrhythmic SCD.

Autonomic Neuromodulation for Preventing and Treating Ventricular Arrhythmias

The cardiac autonomic nervous system (CANS) is associated with modulation of cardiac electrophysiology and arrhythmogenesis. In this mini review, we will briefly introduce cardiac autonomic anatomy and autonomic activity in ventricular arrhythmias (VAs) and discuss novel approaches of CANS modulation for treating VAs. Studies over the decades have provided a better understanding of cardiac autonomic innervation and revealed overwhelming evidence of the relationship between autonomic tone and VAs. A high sympathetic tone and low parasympathetic (vagal) tone are considered as the major triggers of VAs in patients with myocardial ischemia, which can cause sudden cardiac death. In recent years, novel methods of autonomic neuromodulation have been investigated to prevent VAs, and they have been verified as being beneficial for malignant VAs in animal models and humans. The clinical outcome of autonomic neuromodulation depends on the level of cardiac neuraxis, stimulation parameters, and patient's pathological status. Since autonomic modulation for VA treatment is still in the early stage of clinical application, more basic and clinical studies should be performed to clarify these mechanisms and optimize autonomic neuromodulation therapies for patients with VAs in the future.

Downregulation of VEGFR3 signaling alters cardiac lymphatic vessel organization and leads to a higher mortality after acute myocardial infarction

Heart has a wide lymphatic network but the importance of cardiac lymphatic system in heart diseases has remained unclear. Vascular Endothelial Growth Factor Receptor 3 (VEGFR3) is a key molecule in the development and maintenance of cardiac lymphatic vessels. Here we characterized the role of VEGFR3 in healthy hearts and after myocardial infarction (MI) by using sVEGFR3 transgenic mice expressing a soluble decoy VEGFR3 under K14 promoter and Chy mice which have an inactivating mutation in the VEGFR3 gene. Cardiac lymphatic vessels were significantly dilated in the healthy hearts of sVEGFR3 mice when compared to controls. Lymphatic vessels formed large sheet-like structures in Chy mice. Attenuated VEGFR3 signaling led to a more severe MI predisposing to a significantly higher mortality in sVEGFR3 mice than in control mice. sVEGFR3 mice displayed intramyocardial hemorrhages in the infarcted area indicating hyperpermeability of the vasculature. Furthermore, novel MRI methods TRAFF2 and TRAFF4 and histological analysis revealed a modified structure of the fibrotic infarcted area in sVEGFR3 mice. In conclusion, the downregulation of VEGFR3 signaling modifies the structure of cardiac lymphatic network and causes vascular leakiness and increased mortality after MI.

Arrhythmia care in Africa

Data on cardiovascular disease, including arrhythmias, in Africa is limited. However, the burden of cardiovascular disease appears to be on the rise. Recent global data suggests an increase in atrial fibrillation rates despite declining rates of rheumatic heart disease. Atrial fibrillation is also associated with increased mortality in Africa. Current management with medical therapy is sub-optimal and ablation procedures, inaccessible. Atrial fibrillation is also an independent risk factor for death in patients with rheumatic heart disease. Sudden cardiac deaths from ventricular arrhythmias are under-recognized and inadequately treated with very high rates out of hospital cardiac arrest due to poor education of the general public on cardiopulmonary resuscitation skills and lack of essential healthcare infrastructure. Use of cardiac devices such as implantable defibrillators and pacemakers is low with significant regional variations and is almost non-existent in sub-Saharan Africa. There is a great unmet need for arrhythmia diagnosis and management in Africa. Governments and healthcare stakeholders need to include cardiovascular disease as a healthcare priority given the rising burden of disease and associated mortality.

Role of Non-Myocyte Gap Junctions and Connexin Hemichannels in Cardiovascular Health and Disease: Novel Therapeutic Targets?

The heart is a complex organ composed of multiple cell types, including cardiomyocytes and different non-myocyte populations, all working closely together to determine the hearts properties and maintain normal cardiac function. Connexins are abundantly expressed proteins that form plasma membrane hemichannels and gap junctions between cells. Gap junctions are intracellular channels that allow for communication between cells, and in the heart they play a crucial role in cardiac conduction by coupling adjacent cardiomyocytes. Connexins are expressed in both cardiomyocytes and non-myocytes, including cardiac fibroblasts, endothelial cells, and macrophages. Non-myocytes are the largest population of cells in the heart, and therefore it is important to consider what roles connexins, hemichannels, and gap junctions play in these cell types. The aim of this review is to provide insight into connexin-based signalling in non-myocytes during health and disease, and highlight how targeting these proteins could lead to the development of novel therapies. We conclude that connexins in non-myocytes contribute to arrhythmias and adverse ventricular remodelling following myocardial infarction, and are associated with the initiation and development of atherosclerosis. Therefore, therapeutic interventions targeting these connexins represent an exciting new research avenue with great potential.

Sudden cardiac death in patients with rheumatoid arthritis

An increased cardiovascular morbidity and mortality, including the risk of sudden cardiac death (SCD), has been shown in patients with rheumatoid arthritis (RA). Abnormalities in autonomic markers such as heart rate variability and ventricular repolarization parameters, such as QTc interval and QT dispersion, have been associated with sudden death in patients with RA. The interplay between these parameters and inflammation that is known to exist with RA is of growing interest. In this article, we review the prevalence and predictors of SCD in patients with RA and describe the potential underlying mechanisms, which may contribute to this. We also review the impact of biologic agents on arrhythmic risk as well as cardiovascular morbidity and mortality.

Macrophages Facilitate Electrical Conduction in the Heart

Organ-specific functions of tissue-resident macrophages in the steady-state heart are unknown. Here, we show that cardiac macrophages facilitate electrical conduction through the distal atrioventricular node, where conducting cells densely intersperse with elongated macrophages expressing connexin 43. When coupled to spontaneously beating cardiomyocytes via connexin-43-containing gap junctions, cardiac macrophages have a negative resting membrane potential and depolarize in synchrony with cardiomyocytes. Conversely, macrophages render the resting membrane potential of cardiomyocytes more positive and, according to computational modeling, accelerate their repolarization. Photostimulation of channelrhodopsin-2-expressing macrophages improves atrioventricular conduction, whereas conditional deletion of connexin 43 in macrophages and congenital lack of macrophages delay atrioventricular conduction. In the Cd11b^DTR mouse, macrophage ablation induces progressive atrioventricular block. These observations implicate macrophages in normal and aberrant cardiac conduction.

Defibrillators: Selecting the Right Device for the Right Patient

Advances in the field of defibrillation have brought to practice different types of devices that include the transvenous implantable cardioverter-defibrillator (ICD) with or without cardiac resynchronization therapy, the subcutaneous ICD (S-ICD), and the wearable cardioverter-defibrillator. To ensure optimal use of these devices and to achieve best patient outcomes, clinicians need to understand how these devices work, learn the characteristics of patients who qualify them for one type of device versus another, and recognize the remaining gaps in knowledge surrounding these devices. The transvenous ICD has been shown in several randomized clinical trials to improve the survival of patients resuscitated from near-fatal ventricular fibrillation and those with sustained ventricular tachycardia with syncope or systolic heart failure as a result of ischemic or nonischemic cardiomyopathy despite receiving guideline-directed medical therapy. Important gaps in knowledge regarding the transvenous ICD involve the role of the ICD in patient subgroups not included, or not well represented, in clinical trials and the need to refine the selection criteria for the ICD in patients who are indicated for it. S-ICDs were recently introduced into the clinical arena as another option for many patients who have an approved indication for a transvenous ICD. The main advantage of the S-ICD is a lower risk of infection and lead-related complications; however, the S-ICD does not offer bradycardia or antitachycardia pacing. The S-ICD may be ideal for patients with limited vascular access, high infection risk, or some congenital heart diseases. However, more data are needed regarding the efficacy and effectiveness of the S-ICD in comparison to transvenous ICDs, the extent of defibrillation testing required, and the use of the S-ICD with other novel technologies, including leadless pacemakers. Cardiac resynchronization therapy-defibrillators are indicated in patients with a left ventricular ejection fraction ≤35%, QRS width ≥130 ms, and New York Heart Association class II, III, or ambulatory IV symptoms despite treatment with guideline-directed medical therapy. Multiple randomized controlled trials have shown that the cardiac resynchronization therapy-defibrillator improves survival, quality of life, and several echocardiographic measures. One main challenge related to cardiac resynchronization therapy-defibrillators is the 30% nonresponse rate. Many initiatives are underway to address this challenge including improved cardiac resynchronization therapy and imaging technologies and enhanced selection of patients and device programming.

Retracted Article: Vitexin mitigates myocardial ischemia reperfusion-induced damage by inhibiting excessive autophagy to suppress apoptosis via the PI3K/Akt/mTOR signaling cascade

Myocardial ischemia reperfusion (MI/R) injury is reported to induce apoptosis and autophagy of myocardial cells and contribute to adverse cardiovascular outcomes.

Ventricular Arrhythmia after Acute Myocardial Infarction: 'The Perfect Storm'

Ventricular tachyarrhythmias (VAs) commonly occur early in ischaemia, and remain a common cause of sudden death in acute MI. The thrombolysis and primary percutaneous coronary intervention era has resulted in the modification of the natural history of an infarct and subsequent VA. Presence of VA could independently influence mortality in patients recovering from MI. Appropriate risk assessment and subsequent treatment is warranted in these patients. The prevention and treatment of haemodynamically significant VA in the post-infarct period and of sudden cardiac death remote from the event remain areas of ongoing study.

Cardiac sympathetic innervation via middle cervical and stellate ganglia and antiarrhythmic mechanism of bilateral stellectomy

Cardiac sympathetic denervation (CSD) is reported to reduce the burden of ventricular tachyarrhythmias [ventricular tachycardia (VT)/ventricular fibrillation (VF)] in cardiomyopathy patients, but the mechanisms behind this benefit are unknown. In addition, the relative contribution to cardiac innervation of the middle cervical ganglion (MCG), which may contain cardiac neurons and is not removed during this procedure, is unclear. The purpose of this study was to compare sympathetic innervation of the heart via the MCG vs. stellate ganglia, assess effects of bilateral CSD on cardiac function and VT/VF, and determine changes in cardiac sympathetic innervation after CSD to elucidate mechanisms of benefit in 6 normal and 18 infarcted pigs. Electrophysiological and hemodynamic parameters were evaluated at baseline, during bilateral stellate stimulation, and during bilateral MCG stimulation in 6 normal and 12 infarcted animals. Bilateral CSD (removal of bilateral stellates and T₂ ganglia) was then performed and MCG stimulation repeated. In addition, in 18 infarcted animals VT/VF inducibility was assessed before and after CSD. In infarcted hearts, MCG stimulation resulted in greater chronotropic and inotropic response than stellate ganglion stimulation. Bilateral CSD acutely reduced VT/VF inducibility by 50% in infarcted hearts and prolonged global activation recovery interval. CSD mitigated effects of MCG stimulation on dispersion of repolarization and T-peak to T-end interval in infarcted hearts, without causing hemodynamic compromise. These data demonstrate that the MCG provides significant cardiac sympathetic innervation before CSD and adequate sympathetic innervation after CSD, maintaining hemodynamic stability. Bilateral CSD reduces VT/VF inducibility by improving electrical stability in infarcted hearts in the setting of sympathetic activation.NEW & NOTEWORTHY Sympathetic activation in myocardial infarction leads to arrhythmias and worsens heart failure. Bilateral cardiac sympathetic denervation reduces ventricular tachycardia/ventricular fibrillation inducibility and mitigates effects of sympathetic activation on dispersion of repolarization and T-peak to T-end interval in infarcted hearts. Hemodynamic stability is maintained, as innervation via the middle cervical ganglion is not interrupted.

U0126 attenuates ischemia/reperfusion-induced apoptosis and autophagy in myocardium through MEK/ERK/EGR-1 pathway

Myocardial ischemia is one of the main causes of sudden cardiac death worldwide. Depending on the cell type and stimulus, ERK activity mediates different anti-proliferative events, such as apoptosis, autophagy, and senescence. The aim of this study was to determine the protective effect of 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio] butadiene (U0126), an ERK kinase inhibitor, on myocardial ischemia/reperfusion (I/R) injury and the mechanisms involved. An I/R model was established in vivo in C57BL/6 mice and in vitro using mouse cardiomyocytes, respectively. To evaluate the protective effects of U0126 on I/R injury, we measured the myocardial infarct area, apoptosis, and autophagy. Our data indicated that pretreatment with U0126 significantly reduced the infarct area caused by I/R. Moreover, U0126 reduced the caspase-3 activity and the number of TUNEL-positive cardiomyocytes, which together indicate decreased apoptosis. Additionally, U0126 remarkable reduced the level of Beclin-1 and LC3 and increased p62 expression, which indicates that U0126 suppressed H/R-induced autophagy. Furthermore, the relationship between U0126 and MEK/ERK pathway activation in H/R-induced cardiomyocytes was also investigated. U0126 ameliorated H/R injury through inhibition of the MEK/ERK pathway and by suppressing in the downstream EGR-1 expression. Together, our research suggests that U0126 may protect against H/R injury by preventing H/R-induced myocardium apoptosis and autophagy via the MEK/ERK/EGR-1 pathway, and may be a potential therapeutic approach for attenuating myocardial I/R injury.

Connexin43 contributes to electrotonic conduction across scar tissue in the intact heart

Studies have demonstrated non-myocytes, including fibroblasts, can electrically couple to myocytes in culture. However, evidence demonstrating current can passively spread across scar tissue in the intact heart remains elusive. We hypothesize electrotonic conduction occurs across non-myocyte gaps in the heart and is partly mediated by Connexin43 (Cx43). We investigated whether non-myocytes in ventricular scar tissue are electrically connected to surrounding myocardial tissue in wild type and fibroblast-specific protein-1 driven conditional Cx43 knock-out mice (Cx43fsp1KO). Electrical coupling between the scar and uninjured myocardium was demonstrated by injecting current into the myocardium and recording depolarization in the scar through optical mapping. Coupling was significantly reduced in Cx43fsp1KO hearts. Voltage signals were recorded using microelectrodes from control scars but no signals were obtained from Cx43fsp1KO hearts. Recordings showed significantly decreased amplitude, depolarized resting membrane potential, increased duration and reduced upstroke velocity compared to surrounding myocytes, suggesting that the non-excitable cells in the scar closely follow myocyte action potentials. These results were further validated by mathematical simulations. Optical mapping demonstrated that current delivered within the scar could induce activation of the surrounding myocardium. These data demonstrate non-myocytes in the scar are electrically coupled to myocytes, and coupling depends on Cx43 expression.

Life-threatening ventricular tachyarrhythmias in the cardiology department: Implications for appropriate prescription of telemetry monitoring

BACKGROUND

in-hospital life-threatening ventricular arrhythmias (LT-VA) may complicate the course of cardiovascular patients. We aimed to assess the incidence, circumstances, determinants, and outcome of in-hospital LT-VA in order to help clinicians in prescribing appropriate levels of monitoring.

METHODS

the study population consisted of all 10,741 consecutive patients (65 ± 15 years, 67.7% males) admitted to a cardiology department in 2009-2014. Terminally ill patients and those with primary arrhythmia diagnosis were excluded. The composite end-point included sudden arrhythmic death, ventricular fibrillation, unstable ventricular tachycardia and appropriate ICD shock unrelated to invasive interventions.

RESULTS

the incidence of LT-VA was 0.6%, with no differences regarding age, gender and primary diagnosis of coronary artery disease between patients with and without LT-VA. The incidence of LT-VA was significantly higher (1.2% versus 0.1%, p<0.001) among urgent compared with elective admissions and among patients with left ventricular ejection fraction (LV-EF) <45% (1.7% versus 0.2%, p<0.001). At multivariable analysis, urgent admission and LV-EF <45%, but not primary diagnosis of coronary artery disease, remained independent predictors of LT-VA. At the time of the event, 97.1% fulfilled either class I or class II indications for telemetry monitoring according to the American Heart Association guidelines. Survival to discharge with good neurological status was 70.6%.

CONCLUSIONS

acutely ill patients with heart failure and LV systolic dysfunction showed the highest rate of LT-VAs, regardless of the underlying cardiac disease (ischemic or non-ischemic). Current guidelines demonstrated high sensitivity in identifying patients at risk. These findings may favor proper utilization of telemetry monitoring resources.

Functional Impact of Ryanodine Receptor Oxidation on Intracellular Calcium Regulation in the Heart

Type 2 ryanodine receptor (RyR2) serves as the major intracellular Ca²⁺ release channel that drives heart contraction. RyR2 is activated by cytosolic Ca²⁺ via the process of Ca²⁺-induced Ca²⁺ release (CICR). To ensure stability of Ca²⁺ dynamics, the self-reinforcing CICR must be tightly controlled. Defects in this control cause sarcoplasmic reticulum (SR) Ca²⁺ mishandling, which manifests in a variety of cardiac pathologies that include myocardial infarction and heart failure. These pathologies are also associated with oxidative stress. Given that RyR2 contains a large number of cysteine residues, it is no surprise that RyR2 plays a key role in the cellular response to oxidative stress. RyR's many cysteine residues pose an experimental limitation in defining a specific target or mechanism of action for oxidative stress. As a result, the current understanding of redox-mediated RyR2 dysfunction remains incomplete. Several oxidative modifications, including S-glutathionylation and S-nitrosylation, have been suggested playing an important role in the regulation of RyR2 activity. Moreover, oxidative stress can increase RyR2 activity by forming disulfide bonds between two neighboring subunits (intersubunit cross-linking). Since intersubunit interactions within the RyR2 homotetramer complex dictate the channel gating, such posttranslational modification of RyR2 would have a significant impact on RyR2 function and Ca²⁺ regulation. This review summarizes recent findings on oxidative modifications of RyR2 and discusses contributions of these RyR2 modifications to SR Ca²⁺ mishandling during cardiac pathologies.

The Impact of Hospital-Based Cardiac Rehabilitation on Signal Average ECG Parameters of the Heart After Myocardial Infarction

Background:

Cardiac rehabilitation is a combination of integrated programs aimed at improving outcomes in patients recovering from heart events.

Objectives:

The present study aimed to evaluate the early benefits of supervised exercise training on electrophysiological function of post-ischemic myocardium. In this regard, signal-averaged electrocardiogram (SAECG) was used.

Patients and Methods:

Between May and September 2012, all patients (n = 100) admitted to our center, with the diagnosis of acute Myocardial Infarction (MI), were enrolled in this study. Every other patient was assigned to two groups receiving either inpatient cardiac rehabilitation plus standard post-MI care (cases) or only standard post-MI care (controls). Electrophysiological function was assessed by SAECG in all the patients at baseline and on the day 5. The patients were considered as having late potential if they had abnormalities in at least two SAECG indices.

Results:

Cardiac rehabilitation led to significant improvements in QRS duration (P < 0.001), square root of amplitude in the last 40 ms (P < 0.001) and duration of terminal signal with low amplitude (P < 0.001). Cardiac rehabilitation also resulted in amelioration of SAECG parameters; frequency of patients with late potential significantly decreased from 64% to 20% after five days (P < 0.001).

Conclusions:

Supervised in-hospital exercise training was associated with improvements in SAECG-measured electrical activity post-MI.

Dipeptidyl peptidase-4 inhibitor improves cardiac function by attenuating adverse cardiac remodelling in rats with chronic myocardial infarction

NEW FINDINGS

What is the central question of this study? Although cardioprotective effects of dipeptidyl peptidase-4 (DPP-4) inhibitors have been demonstrated, their cardiac effects in chronic myocardial infarction (MI) are unclear. We determined the effects of a DPP-4 inhibitor on cardiac function and remodelling in rats with chronic MI. What is the main finding and its importance? We demonstrated, for the first time, that DPP-4 inhibitor, but not metformin, exerted similar efficacy in improving cardiac function and attenuating cardiac fibrosis compared with enalapril in rats with chronic MI. These findings reveal benefits additional to the glycaemic control by the DPP-4 inhibitor in chronic MI, and it might become the new drug of choice for MI in patients with diabetes mellitus. Adverse cardiac remodelling after myocardial infarction (MI) leads to progressive heart failure. Dipeptidyl peptidase-4 (DPP-4) inhibitors are new antidiabetic drugs that exert cardioprotection. However, their role in cardiac function and remodelling in chronic MI is unclear. We hypothesized that the DPP-4 inhibitor vildagliptin reduces adverse cardiac remodelling and improves cardiac function in rats with chronic MI. These effects were also compared with enalapril and metformin. Male Wistar rats (n = 36) with chronic MI induced by ligation of the left anterior descending coronary artery were divided into six groups to receive vehicle, vildagliptin (3 mg kg(-1)  day(-1) ), metformin (30 mg kg(-1)  day(-1) ), enalapril (10 mg kg(-1)  day(-1) ), combined metformin and enalapril or combined vildagliptin and enalapril for 8 weeks. At the end of the study, plasma malondialdehyde (MDA), heart rate variability (HRV), left ventricular (LV) function, pathological and biochemical studies of cardiac remodelling were investigated. Our study demonstrated that rats with chronic MI had increased oxidative stress levels, depressed HRV, adverse cardiac remodelling, indicated by cardiac fibrosis, and LV dysfunction. Treatment with vildagliptin or enalapril significantly decreased oxidative stress, attenuated cardiac fibrosis and improved HRV and LV function. We conclude that vildagliptin exerts similar cardioprotective effects to enalapril in attenuating oxidative stress and cardiac fibrosis and improving cardiac function in rats with chronic MI. Metformin does not provide these benefits in this model. Moreover, addition of either metformin or vildagliptin to enalapril does not provide additional benefit in attenuating cardiac remodelling or improving LV function compared with enalapril alone.

The AMPK Agonist PT1 and mTOR Inhibitor 3HOI-BA-01 Protect Cardiomyocytes After Ischemia Through Induction of Autophagy

Myocardial ischemia has become one of the main causes of sudden cardiac death worldwide. Autophagy has been demonstrated to protect cardiomyocytes from ischemia/reperfusion (I/R)-induced damage. A novel small molecule compound 2-Chloro-5-[[5-[[5-(4,5-Dimethyl-2-nitrophenyl)-2-furanyl]methylene]-4,5-dihydro-4-oxo-2-thiazolyl]amino]benzoic acid (PT1) has been previously shown to specifically activate 5'-adenosine monophosphate-activated protein kinase (AMPK). Because AMPK activation effectively induces autophagy, we tested the protective efficacy of PT1 on cardiomyocytes after oxygen glucose deprivation/reoxygenation (OGD/R) in vitro. Mouse neonatal cardiomyocytes were treated with PT1 after OGD/R. 3-[4-(1,3-benzodioxol-5-yl)-2-oxo-3-buten-1-yl]-3-hydroxy-1,3-dihydro-2H-indol-2-one (3HOI-BA-01), a novel small compound showing potent inhibitory effect on mammalian target of rapamycin (mTOR) activation, was also tested for its cardioprotective effect, based on the established relationship between mTOR signaling and autophagy. Cell survival and autophagy-related signal pathways were examined after treatment with these agents. Our data indicate that both PT1 and 3HOI-BA-01 enhance cell survival after OGD/R. As expected, both PT1 and 3HOI-BA-01 induced autophagy in cardiomyocytes through activating AMPK pathway and inhibiting mTOR signaling, respectively. Induction of autophagy by PT1 and 3HOI-BA-01 was responsible for their cardioprotective effect, since inhibition of autophagy abolished the protective efficacy. Furthermore, simultaneous administration of PT1 and 3HOI-BA-01 profoundly upregulated autophagy after OGD/R and significantly promoted survival of cardiomyocytes. In vivo administration of PT1 and 3HOI-BA-01 in a murine myocardial (I/R injury model remarkably reduced infarct size and induced autophagy. Taken together, our research suggests that PT1 and 3HOI-BA-01 could be promising therapeutic agents for myocardial ischemia.

Left renal nerves stimulation facilitates ischemia-induced ventricular arrhythmia by increasing nerve activity of left stellate ganglion

INTRODUCTION

Renal sympathetic nerve (RSN) activity plays a key role in systemic sympathetic hyperactivity. Previous studies have shown that cardiac sympathetic hyperactivity, especially the left stellate ganglion (LSG), contributes to the pathogenesis of ventricular arrhythmias (VAs) after acute myocardial infarction (AMI).

METHODS AND RESULTS

Twenty-eight dogs received 3 hours of continuous left-sided electrical stimulation of RSN (LRS; Group-1, n = 9), sham RSN stimulation (Group-2, n = 9), or LSG ablation plus 3 hours of LRS (Group-3, n = 10) were included. AMI was induced by ligating the proximal left anterior descending coronary artery. LRS was performed using electrical stimulation on the adventitia of left renal artery at the voltage increasing the systolic blood pressure (BP) by 10%. BP, heart rate variability (HRV), serum norepinephrine (NE) level, and LSG function were measured at baseline and the end of each hour of LRS. C-fos and nerve growth factor (NGF) protein expressed in the LSG were examined in Group-1 and Group-2. Compared with baseline, 3 hours of LRS induced a significant increase in BP, sympathetic indices of HRV, serum NE level, and LSG function. The incidence of VAs in Group-1 was significantly higher than other groups. The expression of c-fos and NGF protein in the LSG was significantly higher in Group-1 than Group-2.

CONCLUSION

Three hours of LRS induces both systemic and cardiac sympathetic hyperactivity and increases the incidence of ischemia-induced VAs.

Renal sympathetic denervation modulates ventricular electrophysiology and has a protective effect on ischaemia-induced ventricular arrhythmia

Recently, a beneficial effect of renal sympathetic denervation (RSD) has been seen in patients with ventricular electrical storm. However, the effect of RSD on ventricular electrophysiology remains unclear. Thirty-three mongrel dogs were included in the present study. Renal sympathetic denervation was performed by radiofrequency ablation of the adventitial surface of the renal artery. In group 1 (n = 8), programmed stimulation was performed before and after RSD to determine the ventricular effective refractory period (ERP) and action potential duration (APD) restitution properties. The same parameters were measured in five other animals that underwent sham RSD to serve as controls. In group 2 (n = 10), acute myocardial ischaemia (AMI) was induced by ligating the proximal left anterior descending coronary artery after the performance of RSD, and the incidence of ventricular arrhythmia (VA) was calculated during 1 h of recording. In another 10 dogs (group 3), AMI was induced and VA was measured with sham RSD. In group 1, RSD significantly prolonged ventricular ERP and APD, reduced the maximal slope (Smax) of the restitution curve and suppressed APD alternans at each site. Renal sympathetic denervation also significantly decreased the spatial dispersion of ERP, APD and Smax. In the five control animals, no significant electrophysiological change was detected after sham RSD. The occurrence of spontaneous VA during 1 h of AMI in group 2 was significantly lower than that in group 3. These data suggest that RSD stabilizes ventricular electrophysiological properties in normal hearts and reduces the occurrence of VA in hearts experiencing AMI.

Adjuvant antiarrhythmic therapy in patients with implantable cardioverter defibrillators

The risk of sudden cardiac death from ventricular fibrillation or ventricular tachycardia in patients with cardiomyopathy related to structural heart disease has been favorably impacted by the wide adaptation of implantable cardioverter defibrillators (ICDs) for both primary and secondary prevention. Unfortunately, after ICD implantation both appropriate and inappropriate ICD therapies are common. ICD shocks in particular can have significant effects on quality of life and disease-related morbidity and mortality. While not indicated for primary prevention of ICD therapies, beta-blockers and antiarrhythmic drugs are a cornerstone for secondary prevention of them. This review will summarize our current understanding of adjuvant antiarrhythmic drug therapy in ICD patients. The review will also discuss the roles of nonantiarrhythmic drug approaches that are used in isolation and in combination with antiarrhythmic drugs to reduce subsequent risk of ICD shocks.

At-admission risk stratification for in-hospital life-threatening ventricular arrhythmias and death in non-ST elevation myocardial infarction patients

AIMS

Identification of patients with non-ST elevation acute myocardial infarction (NSTEMI) at higher risk of in-hospital life-threatening ventricular arrhythmias (LT-VA) and death is crucial for determining appropriate levels of care/monitoring during hospitalisation. We assessed predictors of in-hospital LT-VA and all-cause mortality in a consecutive series of NSTEMI patients.

METHODS AND RESULTS

We prospectively studied 1325 consecutive patients (69.7% males, median age 70 (61-79) years) presenting with NSTEMI and undergoing continuous electrocardiographic monitoring. The primary study end-point was the occurrence of spontaneous (unrelated to coronary interventions) in-hospital LT-VA, including sustained ventricular tachycardia and ventricular fibrillation; the secondary end-point was in-hospital mortality from all causes. Of 1325 patients, 21 (1.5%) experienced LT-VA and 62 (4.7%) died from either arrhythmias (n=1) or other causes (n=61). Seven of the 20 patients who survived LT-VA subsequently died of heart failure. Independent predictors of in-hospital LT-VA were the Global Registry of Acute Coronary Events (GRACE) score >140 (odds ratio (OR)=7.5; 95% confidence interval (CI) 1.7-33.3; p=0.008) and left ventricular ejection fraction (LV-EF)<35% (OR=4.1; 95% CI 1.7-10.3; p=0.002). GRACE score >140 (OR=14.6; 95% CI 3.4-62) and LV-EF <35% (OR=4.4; 95% CI 1.9-10) also predicted in-hospital all-cause death. The cumulative probability of in-hospital LT-VA and death was respectively 9.2% and 23% in the 98 (7.4%) patients with GRACE score >140 and LV-EF<35%, while it was respectively 0.2% and 0% among the 627 (47.3%) with GRACE score ≤140 and LV-EF ≥35%.

CONCLUSIONS

Simple risk stratification at admission based on GRACE score and echocardiographic LV-EF allows early identification of NSTEMI patients at higher risk of both in-hospital LT-VA and all-cause mortality.

The Israel Nationwide Heart Failure Survey: Sex differences in early and late mortality for hospitalized heart failure patients

BACKGROUND

Current data on the influence of sex on the prognosis of heart failure (HF) are conflicting, possibly owing to the use of different end points and a heterogeneous heart failure population in earlier studies. We sought to evaluate the effect of sex on the risk of early and late mortality outcomes after hospitalization for acute heart failure.

METHODS AND RESULTS

The prospective cohort study population comprised 2,212 hospitalized patients with acute HF enrolled in a multicenter national survey in Israel. Cox proportional-hazards regression modeling was used to evaluate the effect of sex on the risk of early (≤6 months) and late (>6 months to 4 years) mortality after the index hospitalization. Among the study patients, 998 (45%) were women. Women with HF displayed significantly different clinical characteristics compared with men, including older age, higher frequency of HF with preserved ejection fraction and hypertensive heart disease, and lower percentage of coronary artery disease (all P < .001). The fully adjusted multivariable analyses for mortality outcomes showed that women tended toward an increased risk for early (≤6 months) mortality (hazard ratio [HR] 1.16, 95% confidence interval [CI] 0.96-1.41; P = .13), whereas men had significantly increased risk for late (>6 months) mortality (HR 1.25, 95% CI 1.09-1.43; P = .001).

CONCLUSIONS

There are important differences in the clinical characteristics and the short- and long-term outcomes between men and women hospitalized with acute HF after adjusting for multiple confounding variables.

Survival benefit of primary prevention implantable cardioverter-defibrillator therapy after myocardial infarction: does time to implant matter? A meta-analysis using patient-level data from 4 clinical trials

BACKGROUND

Whether there is an optimal time to place an implantable cardioverter-defibrillator (ICD) more than 40 days after myocardial infarction (MI) in guideline-eligible patients is unknown.

OBJECTIVE

To evaluate the effect of time from MI to randomization on mortality, rehospitalizations, and complications.

METHODS

Individual data on patients enrolled in 9 primary prevention ICD trials were provided. Clinical trials were eligible for the current analysis if they enrolled patients with an MI more than 40 days prior to randomization to primary prevention ICD therapy vs usual care: Multicenter Automatic Defibrillator Implantation Trial I, Multicenter UnSustained Tachyardia Trial, Multicenter Automatic Defibrillator Implantation Trial II, and Sudden Cardiac Death in Heart Failure Trial.

RESULTS

ICD recipients died less frequently than nonrecipients at 5 years across all subgroups of time from MI to randomization. In unadjusted Cox proportional hazards regression, a survival benefit was evident in most subgroups. Adjusted Bayesian Weibull survival modeling yielded hazard ratio (HR) 0.50, 95% posterior credible interval (PCI) 0.20-1.25 41-180 days after MI; HR 0.98, 95% PCI 0.37-2.37 181-365 days after MI; HR 0.22, 95% PCI 0.07-0.59>1-2 years after MI; HR 0.42, 95% PCI 0.17-0.90>2-5 years after MI; HR 0.55, 95% PCI 0.25-1.15>5-10 years after MI; and HR 0.48, 95% PCI 0.20-1.02>10 years after MI. There was no evidence of an interaction between time from MI and all-cause mortality, rehospitalizations, or complications.

CONCLUSIONS

In this meta-analysis, there was scant evidence that the efficacy of primary prevention ICD therapy depends on time to implantation more than 40 days after MI. Similarly, there was no evidence that the risks of rehospitalizations or complications depend on time more than 40 days after MI.

Diagnostic value of magnetocardiography in coronary artery disease and cardiac arrhythmias: a review of clinical data

Despite the availability of several advanced non-invasive diagnostic tests such as echocardiography and magnetic resonance imaging, electrocardiography (ECG) remains as the most widely used diagnostic technique in clinical cardiology. ECG detects electrical potentials that are generated by cardiac electrical activity. In addition to electrical potentials, the same electrical activity of the heart also induces magnetic fields. These extremely weak cardiac magnetic signals are detected by a non-invasive, contactless technique called magnetocardiography (MCG), which has been evaluated in a number of clinical studies for its usefulness in diagnosing heart diseases. We reviewed the basic principles, history and clinical data on the diagnostic role of MCG in coronary artery disease and cardiac arrhythmias.

ECG marker of adverse electrical remodeling post-myocardial infarction predicts outcomes in MADIT II study

BACKGROUND

Post-myocardial infarction (MI) structural remodeling is characterized by left ventricular dilatation, fibrosis, and hypertrophy of the non-infarcted myocardium.

OBJECTIVE

The goal of our study was to quantify post-MI electrical remodeling by measuring the sum absolute QRST integral (SAI QRST). We hypothesized that adverse electrical remodeling predicts outcomes in MADIT II study participants.

METHODS

Baseline orthogonal ECGs of 750 MADIT II study participants (448 [59.7%] ICD arm) were analyzed. SAI QRST was measured as the arithmetic sum of absolute QRST integrals over all three orthogonal ECG leads. The primary endpoint was defined as sudden cardiac death (SCD) or sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) with appropriate ICD therapies. All-cause mortality served as a secondary endpoint.

RESULTS

Adverse electrical remodeling in post-MI patients was characterized by wide QRS, increased magnitudes of spatial QRS and T vectors, J-point deviation, and QTc prolongation. In multivariable Cox regression analysis after adjustment for age, QRS duration, atrial fibrillation, New York Heart Association heart failure class and blood urea nitrogen, SAI QRST predicted SCD/VT/VF (HR 1.33 per 100 mV*ms (95%CI 1.11-1.59); P = 0.002), and all-cause death (HR 1.27 per 100 mV*ms (95%CI 1.03-1.55), P = 0.022) in both arms. No interaction with therapy arm and bundle branch block (BBB) status was found.

CONCLUSIONS

In MADIT II patients, increased SAI QRST is associated with increased risk of sustained VT/VF with appropriate ICD therapies and all-cause death in both ICD and in conventional medical therapy arms, and in patients with and without BBB. Further studies of SAI QRST are warranted.

Sudden cardiac death in low- and middle-income countries

Cardiovascular disease, and the incidence of sudden cardiac death (SCD), will increase significantly in low- and middle-income countries (LMIC). Thus, SCD threatens to become a global public health problem. We present a summary of the current research that has investigated the epidemiology of SCD in LMIC. Few studies of SCD in LMIC exist, and they are of variable methodological quality. Risk factors for SCD are described, taking into account recent global burden of disease and risk factor statistics. We describe 1 proposal for a community-based, prospective, multiple-source methodology for SCD monitoring and surveillance that can be implemented in LMIC. Further research into the epidemiology of SCD in LMIC, using standardized methodology, would allow investigators and policy makers to determine the regions, communities, and individuals most at need for SCD prevention. Focusing on SCD and its prevention in LMIC should be a priority for the global health community.

Cardiovascular magnetic resonance characterization of peri-infarct zone remodeling following myocardial infarction

BACKGROUND

Clinical studies implementing late gadolinium-enhanced (LGE) cardiovascular magnetic resonance (CMR) studies suggest that the peri-infarct zone (PIZ) contains a mixture of viable and non-viable myocytes, and is associated with greater susceptibility to ventricular tachycardia induction and adverse cardiac outcomes. However, CMR data assessing the temporal formation and functional remodeling characteristics of this complex region are limited. We intended to characterize early temporal changes in scar morphology and regional function in the PIZ.

METHODS AND RESULTS

CMR studies were performed at six time points up to 90 days after induction of myocardial infarction (MI) in eight minipigs with reperfused, anterior-septal infarcts. Custom signal density threshold algorithms, based on the remote myocardium, were applied to define the infarct core and PIZ region for each time point. After the initial post-MI edema subsided, the PIZ decreased by 54% from day 10 to day 90 (p = 0.04). The size of infarct scar expanded by 14% and thinned by 56% from day 3 to 12 weeks (p = 0.004 and p < 0.001, respectively). LVEDV increased from 34.7. ± 2.2 ml to 47.8 ± 3.0 ml (day 3 and week 12, respectively; p < 0.001). At 30 days post-MI, regional circumferential strain was increased between the infarct scar and the PIZ (-2.1 ± 0.6 and -6.8 ± 0.9, respectively;* p < 0.05).

CONCLUSIONS

The PIZ is dynamic and decreases in mass following reperfused MI. Tensile forces in the PIZ undergo changes following MI. Remodeling characteristics of the PIZ may provide mechanistic insights into the development of life-threatening arrhythmias and sudden cardiac death post-MI.

Shortened Ca2+ signaling refractoriness underlies cellular arrhythmogenesis in a postinfarction model of sudden cardiac death

RATIONALE

Diastolic spontaneous Ca(2+) waves (DCWs) are recognized as important contributors to triggered arrhythmias. DCWs are thought to arise when [Ca(2+)] in sarcoplasmic reticulum ([Ca(2+)](SR)) reaches a certain threshold level, which might be reduced in cardiac disease as a consequence of sensitization of ryanodine receptors (RyR2s) to luminal Ca(2+).

OBJECTIVE

We investigated the mechanisms of DCW generation in myocytes from normal and diseased hearts, using a canine model of post-myocardial infarction ventricular fibrillation (VF).

METHODS AND RESULTS

The frequency of DCWs, recorded during periodic pacing in the presence of a β-adrenergic receptor agonist isoproterenol, was significantly higher in VF myocytes than in normal controls. Rather than occurring immediately on reaching a final [Ca(2+)](SR), DCWs arose with a distinct time delay after attaining steady [Ca(2+)](SR) in both experimental groups. Although the rate of [Ca(2+)](SR) recovery after the SR Ca(2+) release was similar between the groups, in VF myocytes the latency to DCWs was shorter, and the [Ca(2+)](SR) at DCW initiation was lower. The restitution of depolarization-induced Ca(2+) transients, assessed by a 2-pulse protocol, was significantly faster in VF myocytes than in controls. The VF-related alterations in myocyte Ca(2+) cycling were mimicked by the RyR2 agonist, caffeine. The reducing agent, mercaptopropionylglycine, or the CaMKII inhibitor, KN93, decreased DCW frequency and normalized restitution of Ca(2+) release in VF myocytes.

CONCLUSIONS

The attainment of a certain threshold [Ca(2+)](SR) is not sufficient for the generation of DCWs. Postrelease Ca(2+) signaling refractoriness critically influences the occurrence of DCWs. Shortened Ca(2+) signaling refractoriness due to RyR2 phosphorylation and oxidation is responsible for the increased rate of DCWs observed in VF myocytes and could provide a substrate for synchronization of arrhythmogenic events at the tissue level in hearts prone to VF.