Generation Of Arrhythmias Research Articles

Heart rate regulation in diving sea lions: the vagus nerve rules.

Recent publications have emphasized the potential generation of morbid cardiac arrhythmias secondary to autonomic conflict in diving marine mammals. Such conflict, as typified by cardiovascular responses to cold water immersion in humans, has been proposed to result from exercise-related activation of cardiac sympathetic fibers to increase heart rate, combined with depth-related changes in parasympathetic tone to decrease heart rate. After reviewing the marine mammal literature and evaluating heart rate profiles of diving California sea lions (Zalophus californianus), we present an alternative interpretation of heart rate regulation that de-emphasizes the concept of autonomic conflict and the risk of morbid arrhythmias in marine mammals. We hypothesize that: (1) both the sympathetic cardiac accelerator fibers and the peripheral sympathetic vasomotor fibers are activated during dives even without exercise, and their activities are elevated at the lowest heart rates in a dive when vasoconstriction is maximal, (2) in diving animals, parasympathetic cardiac tone via the vagus nerve dominates over sympathetic cardiac tone during all phases of the dive, thus producing the bradycardia, (3) adjustment in vagal activity, which may be affected by many inputs, including exercise, is the primary regulator of heart rate and heart rate fluctuations during diving, and (4) heart beat fluctuations (benign arrhythmias) are common in marine mammals. Consistent with the literature and with these hypotheses, we believe that the generation of morbid arrhythmias because of exercise or stress during dives is unlikely in marine mammals.

Antagonistic and Synergistic Activation of Cardiovascular Vagal and Sympathetic Motor Outflows in Trigeminal Reflexes.

The trigeminal nerve and heart are strongly related through somato-autonomic nervous reflexes that induce rapid changes in cardiovascular function. Several trigeminal reflexes have been described, but the diving and trigeminocardiac reflexes are the most studied. The heart is a target organ dually innervated by the sympathetic and parasympathetic systems. Thus, how cardiac function is regulated during the trigeminal reflexes is the result of the combination of an increased parasympathetic response and increased, decreased, or unaltered sympathetic activity. Various hemodynamic changes occur as a consequence of these alterations in autonomic tone. Often in the oxygen-conserving physiological reflexes such as the diving reflex, sympathetic/parasympathetic co-activation reduces the heart rate and either maintains or increases blood pressure. Conversely, in the trigeminocardiac reflex, bradycardia and hypotension due to parasympathetic activation and sympathetic inactivation tend to be observed. These sudden cardiac innervation disturbances may promote the generation of arrhythmias or myocardial ischemia during surgeries in the trigeminal territory. However, the function and mechanisms involved in the trigeminal reflexes remain to be fully elucidated. The current review provides a brief update and analysis of the features of these reflexes, with special focus on how the autonomic nervous system interacts with cardiovascular function.

Proarrhythmic remodelling of the right ventricle in a porcine model of repaired tetralogy of Fallot

ObjectiveThe growing adult population with surgically corrected tetralogy of Fallot (TOF) is at risk of arrhythmias and sudden cardiac death. We sought to investigate the contribution of right ventricular (RV)...

Cardiac sympatho-vagal balance and ventricular arrhythmia.

A hallmark of cardiovascular disease is cardiac autonomic dysregulation. The phenotype of impaired parasympathetic responsiveness and sympathetic hyperactivity in experimental animal models is also well documented in large scale human studies in the setting of heart failure and myocardial infarction, and is predictive of morbidity and mortality. Despite advances in emergency revascularisation strategies for myocardial infarction, device therapy for heart failure and secondary prevention pharmacotherapies, mortality from malignant ventricular arrhythmia remains high. Patients at highest risk or those with haemodynamically significant ventricular arrhythmia can be treated with catheter ablation and implantable cardioverter defibrillators, but the morbidity and reduction in quality of life due to the burden of ventricular arrhythmia and shock therapy persists. Therefore, future therapies must aim to target the underlying pathophysiology that contributes to the generation of ventricular arrhythmia. This review explores recent advances in mechanistic research in both limbs of the autonomic nervous system and potential avenues for translation into clinical therapy. In addition, we also discuss the relationship of these findings in the context of the reported efficacy of current neuromodulatory strategies in the management of ventricular arrhythmia.

Cardiac sodium channel palmitoylation regulates channel availability and myocyte excitability with implications for arrhythmia generation.

Cardiac voltage-gated sodium channels (Nav1.5) play an essential role in regulating cardiac electric activity by initiating and propagating action potentials in the heart. Altered Nav1.5 function is associated with multiple cardiac diseases including long-QT3 and Brugada syndrome. Here, we show that Nav1.5 is subject to palmitoylation, a reversible post-translational lipid modification. Palmitoylation increases channel availability and late sodium current activity, leading to enhanced cardiac excitability and prolonged action potential duration. In contrast, blocking palmitoylation increases closed-state channel inactivation and reduces myocyte excitability. We identify four cysteines as possible Nav1.5 palmitoylation substrates. A mutation of one of these is associated with cardiac arrhythmia (C981F), induces a significant enhancement of channel closed-state inactivation and ablates sensitivity to depalmitoylation. Our data indicate that alterations in palmitoylation can substantially control Nav1.5 function and cardiac excitability and this form of post-translational modification is likely an important contributor to acquired and congenital arrhythmias.

Electrophysiological properties of iPS cell-derived cardiomyocytes from a patient with long QT syndrome type 1 harboring the novel mutation M437V of KCNQ1.

IntroductionLong QT syndrome type 1 (LQT1) is caused by mutations in KCNQ1 coding slowly-activating delayed-rectifier K+ channels. We identified the novel missense mutation M437V of KCNQ1 in a LQT1 patient. Here, we employed iPS cell (iPSC)-derived cardiomyocytes to investigate electrophysiological properties of the mutant channel and LQT1 cardiomyocytes.MethodsTo generate iPSCs from the patient and a healthy subject, peripheral blood T cells were reprogrammed by Sendai virus vector encoding human OCT3/4, SOX2, KLF4, and c-MYC. Cardiomyocytes were prepared from iPSCs and human embryonic stem cells using a cytokine-based two-step differentiation method and were subjected to patch clamp experiments.ResultsLQT1 iPSC-derived cardiomyocytes exhibited prolongation of action potential duration (APD), which was due to a reduction of the KCNQ1-mediated current IKs; Na+, Ca2+ and other K+ channel currents were comparable. When expressed in HEK293 and COS7 cells, the mutant KCNQ1 was normally expressed in the plasma membrane but generated smaller currents than the wild type. Isoproterenol significantly prolonged APDs of LQT1 cardiomyocytes, while shortening those of healthy ones. A mathematical model for IKs-reduced human ventricular myocytes reproduced APD prolongation and generation of early afterdepolarizations (EADs) under β-adrenergic stimulation.ConclusionsQT prolongation of the LQT1 patient with the mutation M437V of KCNQ1 was caused by IKs reduction, which may render the patient vulnerable to generation of EADs and arrhythmias.

Molecular Mechanisms of Sympathetic Remodeling and Arrhythmias.

A variety of pathological conditions can increase risk for development of ventricular arrhythmias in humans including diabetes mellitus, obesity, myocardial infarction (MI), and heart failure. Many of these diseases involve global disruption of the autonomic nervous system, including increased sympathetic drive and parasympathetic withdrawal, but another common factor among these disorders is sympathetic dysfunction within the heart. Treatments that target cardiac sympathetic transmission, including β-blockers and ganglionectomy, prolong life and decrease arrhythmias.1–5 Sympathetic control of the heart under normal conditions occurs primarily via norepinephrine acting on β adrenergic receptors (β-AR) to stimulate increases in heart rate (chronotropy), conduction velocity (dromotropy), and contractility (inotropy). These positive effects of sympathetic stimulation allow myocytes to meet increased cardiac demands during stress or exercise, serving to maintain homeostasis. The nervous system adapts to changing conditions, however, and sympathetic neurons undergo structural and functional alterations in response to injury and disease. There are at least 4 types of sympathetic remodeling that occur during conditions of increased arrhythmia susceptibility: hyperinnervation (increased nerve density), denervation (decreased nerve density), altered neurotransmitter or neuropeptide production and increased neuronal excitability. Rubart and Zipes6 proposed a model to explain how these diverse changes in sympathetic transmission might contribute to arrhythmia generation, suggesting that inappropriate heterogeneity of norepinephrine release within the heart leads to differential electric remodeling of cardiac myocytes and predisposes the heart to electric instability. Many studies now support the hypothesis that heterogeneity of noradrenergic transmission increases the risk of arrhythmia and have identified some of the mechanisms that underlie neuronal remodeling. This review will examine the mechanisms of sympathetic remodeling and will connect neural changes to increased arrhythmia susceptibility. We will focus on ventricular arrhythmias because atrial arrhythmias were reviewed recently.7 Regional hyperinnervation was the first type of neural remodeling linked to arrhythmia generation …

Cisplatin-related Atrial Fibrillation during PEB Chemotherapy for Testicular Seminoma: A Case Report

Introduction: Cisplatin-related arrhythmias are not routinely described in the literature and their cardiac complications can lead to relevant hemodynamic events that could compromise the administration of chemotherapy and, above all, they could cause life threatening consequences. Methods: A 37-year-old man with stage II B testicular seminoma was admitted to our department. The patient had a negative cardiologic history, blood count and chemistry were within normal limits except for hypomagnesaemia, and hence PEB chemotherapy was started. During cisplatin infusion, the patient experienced pulse arrhythmia with EKG diagnosis of atrial fibrillation. Results: Despite the finding of atrial fibrillation, thanks to digoxin infusion and magnesium supplementation, chemotherapy was completed and on the next morning the heartbeat was rhythmical again. Conclusion: One of the most important causes of arrhythmia is electrolytic imbalance and, for this reason, sodium, potassium, calcium, chlorine and magnesium plasmatic levels should be accurately checked before, during and after chemotherapy. In particular, magnesium seems to have a dominant role in the generation of arrhythmias during cisplatin-based chemotherapy because this antineoplastic compound increases ionic renal waste due to tubular damage. This case gives strength to the role of oral and intravenous electrolytes supplementation during platinumbased chemotherapy.

Ryanodine receptor cluster fragmentation and redistribution in persistent atrial fibrillation enhance calcium release.

AimsIn atrial fibrillation (AF), abnormalities in Ca2+ release contribute to arrhythmia generation and contractile dysfunction. We explore whether ryanodine receptor (RyR) cluster ultrastructure is altered and is associated with functional abnormalities in AF.Methods and resultsUsing high-resolution confocal microscopy (STED), we examined RyR cluster morphology in fixed atrial myocytes from sheep with persistent AF (N = 6) and control (Ctrl; N = 6) animals. RyR clusters on average contained 15 contiguous RyRs; this did not differ between AF and Ctrl. However, the distance between clusters was significantly reduced in AF (288 ± 12 vs. 376 ± 17 nm). When RyR clusters were grouped into Ca2+ release units (CRUs), i.e. clusters separated by <150 nm, CRUs in AF had more clusters (3.43 ± 0.10 vs. 2.95 ± 0.02 in Ctrl), which were more dispersed. Furthermore, in AF cells, more RyR clusters were found between Z lines. In parallel experiments, Ca2+ sparks were monitored in live permeabilized myocytes. In AF, myocytes had >50% higher spark frequency with increased spark time to peak (TTP) and duration, and a higher incidence of macrosparks. A computational model of the CRU was used to simulate the morphological alterations observed in AF cells. Increasing cluster fragmentation to the level observed in AF cells caused the observed changes, i.e. higher spark frequency, increased TTP and duration; RyR clusters dispersed between Z-lines increased the occurrence of macrosparks.ConclusionIn persistent AF, ultrastructural reorganization of RyR clusters within CRUs is associated with overactive Ca2+ release, increasing the likelihood of propagating Ca2+ release.

Clueless with fewer cues from endothelin. Commentary: Venous endothelin guides sympathetic innervation of the developing mouse heart.

Clueless with fewer cues from endothelin. Commentary: Venous endothelin guides sympathetic innervation of the developing mouse heart.

Analysis of 90 compounds using human induced pluripotent stem cell-derived cardiomyocytes to detect compound effects on cardiac repolarization and generation of arrhythmia

Analysis of 90 compounds using human induced pluripotent stem cell-derived cardiomyocytes to detect compound effects on cardiac repolarization and generation of arrhythmia

Drug-induced proarrhythmia: risk factors and electrophysiological mechanisms.

Drug-induced ventricular tachyarrhythmias can be caused by cardiovascular drugs, noncardiovascular drugs, and even nonprescription agents. They can result in arrhythmic emergencies and sudden cardiac death. If a new arrhythmia or aggravation of an existing arrhythmia develops during therapy with a drug at a concentration usually considered not to be toxic, the situation can be defined as proarrhythmia. Various cardiovascular and noncardiovascular drugs can increase the occurrence of polymorphic ventricular tachycardia of the 'torsade de pointes' type. Antiarrhythmic drugs, antimicrobial agents, and antipsychotic and antidepressant drugs are the most important groups. Age, female sex, and structural heart disease are important risk factors for the occurrence of torsade de pointes. Genetic predisposition and individual pharmacodynamic and pharmacokinetic sensitivity also have important roles in the generation of arrhythmias. An increase in spatial or temporal dispersion of repolarization and a triangular action-potential configuration have been identified as crucial predictors of proarrhythmia in experimental models. These studies emphasized that sole consideration of the QT interval is not sufficient to assess the proarrhythmic risk. In this Review, we focus on important triggers of proarrhythmia and the underlying electrophysiological mechanisms that can enhance or prevent the development of torsade de pointes.

Oxidative shift in tissue redox potential increases beat-to-beat variability of action potential duration.

Profound changes in tissue redox potential occur in the heart under conditions of oxidative stress frequently associated with cardiac arrhythmias. Since beat-to-beat variability (short term variability, SV) of action potential duration (APD) is a good indicator of arrhythmia incidence, the aim of this work was to study the influence of redox changes on SV in isolated canine ventricular cardiomyocytes using a conventional microelectrode technique. The redox potential was shifted toward a reduced state using a reductive cocktail (containing dithiothreitol, glutathione, and ascorbic acid) while oxidative changes were initiated by superfusion with H2O2. Redox effects were evaluated as changes in "relative SV" determined by comparing SV changes with the concomitant APD changes. Exposure of myocytes to the reductive cocktail decreased SV significantly without any detectable effect on APD. Application of H2O2 increased both SV and APD, but the enhancement of SV was the greater, so relative SV increased. Longer exposure to H2O2 resulted in the development of early afterdepolarizations accompanied by tremendously increased SV. Pretreatment with the reductive cocktail prevented both elevation in relative SV and the development of afterdepolarizations. The results suggest that the increased beat-to-beat variability during an oxidative stress contributes to the generation of cardiac arrhythmias.

201 Age-Associated Decline in Nav1.4 and Nav1.5 Isoforms of the Sodium Channel in Rat Heart

Voltage-gated sodium channels (VGSCs) generate the Na + current (I Na ) responsible for the cardiac action potential upstroke largely due to the ‘cardiac’ isoform Na v 1.5, but other isoforms are responsible for ˜20% of the upstroke and a component of a sustained sodium current. This sustained component has been attributed with an increasing arrhythmia risk, particularly within the elderly and has been the target of development for new anti-arrhythmic drugs. Our study has investigated the age-associated changes in protein density and localisation of the VGSC alpha-subunits Na v 1.5 and Na v 1.4 in the rat heart. Rats at 6, 12 and 28 months of age were sacrificed, their hearts dissected into the regions of left and right ventricle, left and right atria, epicardium and endocardium (n = 5). These regions were analysed by western blot to determine the protein expression of Na v 1.5 and Na v 1.4 (Alomone, Israel), normalised to the expression of desmin (Dako, UK). Immunocytochemistry of single cardiac myocytes was used to observe the protein distribution and location of Na v 1.5 and Na v 1.4 conjugated to Alexa 488 (Molecular probes, UK), and cellular membranes were labelled by wheat germ agglutinin conjugated to rhodamine (Vector, UK), viewed by confocal microscopy (Zeiss 710, Germany). Ethical approval was given by the University of Hull. Mean±SEM. Na v 1.5 protein was expressed at the lateral membrane, intercalated disk and t-tubular membrane in single myocytes. When examining the tissues, the relative expression of Na v 1.5 was significantly reduced with age (ANOVA, p = 0.01). It was determined Na v 1.5 protein expression in the right atria was at 6 months (100 ± 12.3%) and similar at 12 months, however at 24 months there was a significant decline to 50 ± 8.65% (Student T-test, Bonferroni adjustment v 1.4, and a similar significant decline in right atrial protein expression observed at 24 months (ANOVA, p = 0.05). We conclude that there is an age-dependent decline in both Na v 1.5 and Na v 1.4 within the right atria, possibly contributing towards arrhythmia generation in the elderly, however the underlying mechanisms remain unclear.

0298 : Action potential shortening in the pig right ventricular outflow tract epicardium

The right ventricular outflow tract (RVOT) has a distinct embryological origin from the rest of the right ventricle (RV) and is a frequent origin for idiopathic and disease-related arrhythmias. We hypothesised that heterogeneous action potential duration (APD) across the right ventricle (RV) may contribute to RVOT arrhythmia generation. Pigs were anesthetized and monophasic action potentials (MAPs) recorded in sinus rhythm from the epicardium of the RV free wall and RVOT. The RV was isolated and perfused via both right and left anterior coronary arteries. The preparation was paced (1-5Hz) and the electrical activity optically mapped (di-4-ANEPPS, 10μM) on both epicardial (EPI) and endocardial (ENDO) surfaces. The expression of potassium channels was assessed by RT-PCR. In vivo, MAP durations measured at 20% and 80% repolarization were both significantly shorter in the RVOT than in the RV free wall EPI (P<0.05). Similar APD variations were observed ex vivo as RVOT APD20 and APD80 were decreased by 29% and 15% respectively compared to free wall (P<0.01). Interestingly, no APD difference was observed on the ENDO resulting in a larger transmural APD difference in the RVOT than in the RV free wall. The RVOT EPI APD80 shortening was preserved over a range of stimulation frequencies leading to a downward shift of the restitution curve and a significant decrease of its slope (P<0.05). In accordance with these results, expression level of mRNA coding for Kv4.3 (Ito) and Kv11.1 (IKr) were upregulated in the RVOT compared to the RV free wall epicardium (P<0.01) while no difference was found for Kv7.1 (IKs) or Kv4.2 (Ito). Moreover, no variation in K+ channel expression was observed across the RV endocardium. Action potentials are shorter in the RVOT than elsewhere in the RV EPI. This electrophysiological signature was mirrored by regional variations in specific K+ channels. The resulting APD dispersion may facilitate RV re-entrant arrhythmias in the context of a RVOT ectopy.

In vitro arrhythmia generation by mild hypothermia: a pitchfork bifurcation type process

The neurological damage after cardiac arrest presents a huge challenge for hospital discharge. Therapeutic hypothermia (34 °C − 32 °C) has shown its benefits in reducing cerebral oxygen demand and improving neurological outcomes after cardiac arrest. However, it can have many adverse effects, among them cardiac arrhythmia generation which represents an important part (up to 34%, according different clinical studies).A monolayer cardiac culture is prepared with cardiomyocytes from a newborn rat, directly on a multi-electrode array, which allows the acquisition of the extracellular potential of the culture. The temperature range is 37 °C − 30 °C–37 °C, representing the cooling and rewarming process of therapeutic hypothermia.Experiments showed that at 35 °C, the acquired signals are characterized by period-doubling phenomenon, compared with signals at other temperatures. Spiral waves, commonly considered to be a sign of cardiac arrhythmia, are observed in the reconstructed activation map. With an approach from nonlinear dynamics, phase space reconstruction, it is shown that at 35 °C, the trajectories of these signals formed a spatial bifurcation, even trifurcation. Another transit point is found between 30 °C–33 °C, which agreed with other clinical studies that induced hypothermia after cardiac arrest should not fall below 32 °C.The process of therapeutic hypothermia after cardiac arrest can be represented by a pitchfork bifurcation type process, which could explain the different ratios of arrhythmia among the adverse effects after this therapy. This nonlinear dynamic suggests that a variable speed of cooling/rewarming, especially when passing 35 °C, would help to decrease the ratio of post-hypothermia arrhythmia and then improve the hospital output.

Optogenetic release of norepinephrine from cardiac sympathetic neurons alters mechanical and electrical function.

Release of norepinephrine (NE) from sympathetic neurons enhances heart rate (HR) and developed force through activation of β-adrenergic receptors, and this sympathoexcitation is a key risk for the generation of cardiac arrhythmias. Studies of β-adrenergic modulation of cardiac function typically involve the administration of exogenous β-adrenergic receptor agonists to directly elicit global β-adrenergic receptor activation by bypassing the involvement of sympathetic nerve terminals. In this work, we use a novel method to activate sympathetic fibres within the myocardium of Langendorff-perfused hearts while measuring changes in electrical and mechanical function. The light-activated optogenetic protein channelrhodopsin-2 (ChR2) was expressed in murine catecholaminergic sympathetic neurons. Sympathetic fibres were then photoactivated to examine changes in contractile force, HR, and cardiac electrical activity. Incidence of arrhythmia was measured with and without exposure to photoactivation of sympathetic fibres, and hearts were optically mapped to detect changes in action potential durations and conduction velocities. Results demonstrate facilitation of both developed force and HR after photostimulated release of NE, with increases in contractile force and HR of 34.5 ± 5.5 and 25.0 ± 9.3%, respectively. Photostimulation of sympathetic fibres also made hearts more susceptible to arrhythmia, with greater incidence and severity. In addition, optically mapped action potentials displayed a small but significant shortening of the plateau phase (-5.5 ± 1.0 ms) after photostimulation. This study characterizes a powerful and clinically relevant new model for studies of cardiac arrhythmias generated by increasing the activity of sympathetic nerve terminals and the resulting activation of myocyte β-adrenergic receptors.

Dantrolene rescues aberrant N-terminus intersubunit interactions in mutant pro-arrhythmic cardiac ryanodine receptors.

The ryanodine receptor (RyR2) is an intracellular Ca(2+) release channel essential for cardiac excitation-contraction coupling. Abnormal RyR2 channel function results in the generation of arrhythmias and sudden cardiac death. The present study was undertaken to investigate the mechanistic basis of RyR2 dysfunction in inherited arrhythmogenic cardiac disease. We present several lines of complementary evidence, indicating that the arrhythmia-associated L433P mutation disrupts RyR2 N-terminus self-association. A combination of yeast two-hybrid, co-immunoprecipitation, and chemical cross-linking assays collectively demonstrate that a RyR2 N-terminal fragment carrying the L433P mutation displays substantially reduced self-interaction compared with wild type. Moreover, sucrose density gradient centrifugation reveals that the L433P mutation impairs tetramerization of the full-length channel. [(3)H]Ryanodine-binding assays demonstrate that disrupted N-terminal intersubunit interactions within RyR2(L433P) confer an altered sensitivity to Ca(2+) activation. Calcium imaging of RyR2(L433P)-expressing cells reveals substantially prolonged Ca(2+) transients and reduced Ca(2+) store content indicating defective channel closure. Importantly, dantrolene treatment reverses the L433P mutation-induced impairment and restores channel function. The N-terminus domain constitutes an important structural determinant for the functional oligomerization of RyR2. Our findings are consistent with defective N-terminus self-association as a molecular mechanism underlying RyR2 channel deregulation in inherited arrhythmogenic cardiac disease. Significantly, the therapeutic action of dantrolene may occur via the restoration of normal RyR2 N-terminal intersubunit interactions.

Phosphodiesterase-3 inhibitor (cilostazol) attenuates oxidative stress-induced mitochondrial dysfunction in the heart.

BackgroundCilostazol is a type 3 phosphodiesterase inhibitor which has been previously demonstrated to prevent the occurrence of tachyarrhythmia and improve defibrillation efficacy. However, the mechanism for this beneficial effect is still unclear. Since cardiac mitochondria have been shown to play a crucial role in fatal cardiac arrhythmias and that oxidative stress is one of the main contributors to arrhythmia generation, we tested the effects of cilostazol on cardiac mitochondria under severe oxidative stress.MethodsMitochondria were isolated from rat hearts and treated with H2O2 to induce oxidative stress. Cilostazol, at various concentrations, was used to study its protective effects. Pharmacological interventions, including a mitochondrial permeability transition pore (mPTP) blocker, cyclosporine A (CsA), and an inner membrane anion channel (IMAC) blocker, 4′-chlorodiazepam (CDP), were used to investigate the mechanistic role of cilostazol on cardiac mitochondria. Cardiac mitochondrial reactive oxygen species (ROS) production, mitochondrial membrane potential change and mitochondrial swelling were determined as indicators of cardiac mitochondrial function.ResultsCilostazol preserved cardiac mitochondrial function when exposed to oxidative stress by preventing mitochondrial depolarization, mitochondrial swelling, and decreasing ROS production.ConclusionsOur findings suggest that cardioprotective effects of cilostazol reported previously could be due to its prevention of cardiac mitochondrial dysfunction caused by severe oxidative stress.

Quantitative Imaging of Preamyloid Oligomers, a Novel Structural Abnormality, in Human Atrial Samples.

Abnormalities in atrial myocardium increase the likelihood of arrhythmias, including atrial fibrillation (AF). The deposition of misfolded protein, or amyloidosis, plays an important role in the pathophysiology of many diseases, including human cardiomyopathies. We have shown that genes implicated in amyloidosis are activated in a cellular model of AF, with the development of preamyloid oligomers (PAOs). PAOs are intermediates in the formation of amyloid fibrils, and they are now recognized to be the cytotoxic species during amyloidosis. To investigate the presence of PAOs in human atrium, we developed a microscopic imaging-based protocol to enable robust and reproducible quantitative analysis of PAO burden in atrial samples harvested at the time of elective cardiac surgery. Using PAO- and myocardial-specific antibodies, we found that PAO distribution was typically heterogeneous within a myocardial sample. Rigorous imaging and analysis protocols were developed to quantify the relative area of myocardium containing PAOs, termed the Green/Red ratio (G/R), for a given sample. Using these methods, reproducible G/R values were obtained when different sections of a sample were independently processed, imaged, and analyzed by different investigators. This robust technique will enable studies to investigate the role of this novel structural abnormality in the pathophysiology of and arrhythmia generation in human atrial tissue.