Metabolic syndrome and long-term cardiovascular outcomes in NSTEMI with unstable angina

BACKGROUND AND AIM

Metabolic syndrome (MS) is associated with cardiovascular mortality and morbidity in patients with acute coronary syndrome. The purpose of this study was to evaluate the impact of MS on long-term clinical outcomes in patients with pure non-ST segment myocardial infarction (NSTEMI) or unstable angina pectoris (USAP).

METHODS AND RESULTS

We prospectively enrolled 310 consecutive NSTEMI/USAP patients (74 females; mean age, 59.3 ± 11.9 years). The study population was divided into two groups: MS(+) and MS(-). The clinical outcomes of the patients were followed for up to 3 years. Increased 3-year cardiovascular mortality and reinfarction were observed in the MS(+) group, as compared to the MS(-) group (15 vs. 3.4%, p = 0.001, and 22.2 vs. 8.3%, p = 0.001, respectively). Hospitalization rates for heart failure and stroke were not significantly different between the two groups on follow-up. By a Cox multivariate analysis, a significant association was noted between MS and the adjusted risk of 3-year cardiovascular mortality (odds ratio 3.4, 95% confidence interval, 1.24-9.1, p = 0.02).

CONCLUSION

These results suggest that MS is associated with an increased risk of 3-year cardiovascular mortality and reinfarction in patients with NSTEMI/USAP.

A study of early afterdepolarizations in a model for human ventricular tissue

Sudden cardiac death is often caused by cardiac arrhythmias. Recently, special attention has been given to a certain arrhythmogenic condition, the long-QT syndrome, which occurs as a result of genetic mutations or drug toxicity. The underlying mechanisms of arrhythmias, caused by the long-QT syndrome, are not fully understood. However, arrhythmias are often connected to special excitations of cardiac cells, called early afterdepolarizations (EADs), which are depolarizations during the repolarizing phase of the action potential. So far, EADs have been studied mainly in isolated cardiac cells. However, the question on how EADs at the single-cell level can result in fibrillation at the tissue level, especially in human cell models, has not been widely studied yet. In this paper, we study wave patterns that result from single-cell EAD dynamics in a mathematical model for human ventricular cardiac tissue. We induce EADs by modeling experimental conditions which have been shown to evoke EADs at a single-cell level: by an increase of L-type Ca currents and a decrease of the delayed rectifier potassium currents. We show that, at the tissue level and depending on these parameters, three types of abnormal wave patterns emerge. We classify them into two types of spiral fibrillation and one type of oscillatory dynamics. Moreover, we find that the emergent wave patterns can be driven by calcium or sodium currents and we find phase waves in the oscillatory excitation regime. From our simulations we predict that arrhythmias caused by EADs can occur during normal wave propagation and do not require tissue heterogeneities. Experimental verification of our results is possible for experiments at the cell-culture level, where EADs can be induced by an increase of the L-type calcium conductance and by the application of I blockers, and the properties of the emergent patterns can be studied by optical mapping of the voltage and calcium.

Comparison of cardiac stem cells and mesenchymal stem cells transplantation on the cardiac electrophysiology in rats with myocardial infarction

INTRODUCTION

Whether transplanted cardiac stem cells (CSCs) and mesenchymal stem cells (MSCs) improved ventricular fibrillation threshold (VFT) similarly is still unclear. We sought to compare the effects of the CSC and MSC transplantation on the electrophysiological characteristics and VFT in rats with myocardial infarction (MI).

METHODS

MI was induced in 30 male Sprague-Dawley rats. Two weeks later, animals were randomized to receive 5 × 10(6) CSCs labeled with PKH26 in PBS or 5 × 10(6) MSCs labeled with PKH26 in phosphate buffer solution(PBS) or PBS alone injection into the infarcted anterior ventricular free wall. Six weeks after the injection, electrophysiological characteristics and VFT were measured. Labeled CSCs and MSCs were observed in 5 μm cryostat sections from each heart.

RESULTS

Malignant ventricular arrhythmias were significantly (P = 0.0055) less inducible in the CSC group than the MSC group. The VFTs were improved in the CSC group compared with the MSC group. Labeled CSCs and MSCs were identified in the infarct zone and infarct marginal zone. Labeled CSCs expressed Connexin-43, von Willebrand factor, α-smooth muscle actin and α-sarcomeric actin,while the Labeled MSCs expressed von Willebrand factor, α-smooth muscle actin and α-sarcomeric actin in vivo.

CONCLUSIONS

After 6 weeks of cell transplantation, CSCs are superior to MSCs in modulating the electrophysiological abnormality and improving the VFT in rats with MI. CSCs and MSCs express markers that suggest muscle, endothelium and vascular smooth muscle phenotypes in vivo, but MSCs rarely express Connexin-43.

Long and short term QT-RR interval co-variability in type 2 diabetes

This paper examines the long and short term co-variability of QT and RR intervals for diabetic patients to explore if the QT-RR co-variability could yield a noble index for the stratification of clinical severity of the disease. Twenty four hour Holter ECG recordings are made for 19 type 2 diabetic (T2DM) patients and 25 normal subjects. RR and QT intervals are extracted from ECG signals sampled at 200 Hz and their co-variability has been examined. To see the long term QT-RR co-variability, correlation coefficients and mutual entropies between QT and RR intervals have been estimated for original beat to beat intervals and smoothed median interval series of successive one hundred beats. Mutual entropy for both beat-to-beat and smoothed median QT and RR interval series showed statistically significant differences between T2DM and control subjects whereas differences in correlation coefficients showed significant difference only for beat-to-beat intervals. Mutual entropy between both beat-to-beat and smoothed median QT-RR interval sequences showed the equally well separation between T2DM patients and control subjects: Mutual entropy and serial correlation coefficients for beat to beat intervals are respectively 1.42 ± 0.33 (bits), 0.856 ± 0.055 for control and 0.752 ± 0.23 (bits), 0.756 ± 0.10 for T2DM patients. Scatter diagram between RR and QT intervals show apparent nonlinearity which validate this result. Short term QT-RR co-variability has been examined by spline smoothed QTc series and sporadic changes have been observed for the control subjects whereas no such changes are found in diabetic patients. This new phenomenon could be a mean for the clinical characterization of diabetes.

Long-term pharmacological therapy of Brugada syndrome: is J-wave attenuation a marker of drug efficacy?

We herein describe two patients with Brugada syndrome in whom J-waves were successfully modified by drugs. Case 1 was a 54-year-old man who presented with repeated ventricular fibrillations (VF) and J-point elevation in the right precordial and lateral leads. After administration of cilostazol (200 mg/d), J-waves disappeared and coved-type ST-segment elevation changed to a saddleback-type for 25 months. Case 2 was a 31-year-old man who presented with a VF storm and J-point elevation in the lateral leads. After administration of quinidine (300 mg/d), J-waves and coved-type ST-segment elevation disappeared for 20 months. J-wave disappearance and coved-type ST-segment elevation were followed by VF suppression, probably due to transient outward potassium current (Ito) suppression.

[Sick sinus syndrome and conduction disorders in women--frequency, treatment]

Conduction disorders in women are often presented as sick sinus syndrome in comparison to men who have more often disturbances of AV conduction diseases and sinus carotid diseases. Nearly every heart disease with prevalence of ischeamic heart disease and idiopathic degenerative fibrotic process, which leads to reduction number of trigger cells, can result in conduction disorders. As a gold standard in treatment is pacemaker implantation with appropriate pacing mode, after exclusion a reversable reason of the disease.

Whole-exome sequencing to identify a novel LMNA gene mutation associated with inherited cardiac conduction disease

Background

Inherited cardiac conduction diseases (CCD) are rare but are caused by mutations in a myriad of genes. Recently, whole-exome sequencing has successfully led to the identification of causal mutations for rare monogenic Mendelian diseases.

Objective

To investigate the genetic background of a family affected by inherited CCD.

Methods and Results

We used whole-exome sequencing to study a Chinese family with multiple family members affected by CCD. Using the pedigree information, we proposed a heterozygous missense mutation (c.G695T, Gly232Val) in the lamin A/C (LMNA) gene as a candidate mutation for susceptibility to CCD in this family. The mutation is novel and is expected to affect the conformation of the coiled-coil rod domain of LMNA according to a structural model prediction. Its pathogenicity in lamina instability was further verified by expressing the mutation in a cellular model.

Conclusions

Our results suggest that whole-exome sequencing is a feasible approach to identifying the candidate genes underlying inherited conduction diseases.

Increased persistent sodium current due to decreased PI3K signaling contributes to QT prolongation in the diabetic heart

Diabetes is an independent risk factor for sudden cardiac death and ventricular arrhythmia complications of acute coronary syndrome. Prolongation of the QT interval on the electrocardiogram is also a risk factor for arrhythmias and sudden death, and the increased prevalence of QT prolongation is an independent risk factor for cardiovascular death in diabetic patients. The pathophysiological mechanisms responsible for this lethal complication are poorly understood. Diabetes is associated with a reduction in phosphoinositide 3-kinase (PI3K) signaling, which regulates the action potential duration (APD) of individual myocytes and thus the QT interval by altering multiple ion currents, including the persistent sodium current INaP. Here, we report a mechanism for diabetes-induced QT prolongation that involves an increase in INaP caused by defective PI3K signaling. Cardiac myocytes of mice with type 1 or type 2 diabetes exhibited an increase in APD that was reversed by expression of constitutively active PI3K or intracellular infusion of phosphatidylinositol 3,4,5-trisphosphate (PIP3), the second messenger produced by PI3K. The diabetic myocytes also showed an increase in INaP that was reversed by activated PI3K or PIP3. The increases in APD and INaP in myocytes translated into QT interval prolongation for both types of diabetic mice. The long QT interval of type 1 diabetic hearts was shortened by insulin treatment ex vivo, and this effect was blocked by a PI3K inhibitor. Treatment of both types of diabetic mouse hearts with an INaP blocker also shortened the QT interval. These results indicate that downregulation of cardiac PI3K signaling in diabetes prolongs the QT interval at least in part by causing an increase in INaP. This mechanism may explain why the diabetic population has an increased risk of life-threatening arrhythmias.

Spanish pacemaker registry. 10th official report of the Spanish Society of Cardiology Working Group on Cardiac Pacing (2012)

INTRODUCTION AND OBJECTIVES

Our aim was to analyze the pacemaker implantations and replacements reported to the Spanish Pacemaker Registry in 2012 with special reference to the selection of pacing modes.

METHOD

The analysis was based on information provided by the European Pacemaker Patient Identification Card.

RESULTS

Data were received from 115 hospitals, with a total of 12 856 cards. An estimated 745.8 pacemaker generators and 53.1 resynchronization devices were implanted per million population. Active fixation leads were implanted in more than 70% of the patients; of these leads, more than 20% were safe for use with magnetic resonance. The most common electrocardiographic indication for pacemaker implantation was atrioventricular block (56%). In all, 28% of the patients with sick sinus syndrome were paced in VVIR mode.

CONCLUSIONS

The use of conventional pacemakers remained stable, whereas the implantation of resynchronization devices increased. Active fixation leads are now employed in most patients. The findings of this study confirm the higher incidence of implantation in men and at an earlier age due to the higher rate of conduction disorders. Age is a factor that influences the choice of the appropriate pacing mode.

Electrocardiographic signs of acute myocardial infarction in left bundle branch block

INTRODUCTION

Acute myocardial infarction is characterized by typical chest pain, electrocardiographic changes in terms of lesion and/or myocardial ischemia and increased cardiac enzymes. It is often difficult to make diagnosis in the presence of non-specific chest pain, the short duration of symptoms and electrocardiographic signs of a complete left bundle branch block.

LITERATURE REVIEW

Many authors have tried to set the electrocardiographic criteria that can increase the possibility of correct diagnosis of acute myocardial infarction in such situations. The most widely used and recognized criterion is Sgarbossa scoring system that includes concordant ST segment elevation > 1 mm ST segment, disconcordant denivelation of ST segment > 1 mm in the leads V1-V3 and disconcordant ST segment elevation > 5 mm with acceptable sensitivity and specificity. In subsequent studies, the sensitivity and specificity increased by replacing the third criterion with ST/S ratio < -0.25.

CONCLUSION

The knowledge of certain electrocardiographic signs in patients with acute coronary syndrome and left bundle branch block increases the chances of early diagnosis and the possibility of better and timely treatment.

[A comparative study of antiarrhythmic and antihypoxic effects of magnesium sulfate, its prolonged form and blockers of calcium channels]

The aim of the study is the comparative study of treatment of heart and brain damages during the hypoxia with magnesium sulfate, verapamil, diltiazem. As a result of the experiment carried out on rats it was proved that magnesium sulfate and its prolonged form are not less active than the blockers of calcium channels, such as verapamil and diltiazem. It is possible to avoid lethal fibrillations caused by calcium chloride with the help of 25% magnesium sulfate solution (after intraperitoneal administration with the dose of 1000 mg/kg) in case we make arrythmogenic injection 5 minutes after inputting magnesium sulfate solution. During the arrhythmia induced by calcium chloride prolonged form of magnesium sulfate is also effective only if we inject the drug subcutaneous 30 minutes before the arrythmogenic injection. If the interval is 5 minutes lethal fibrillations cant be avoided as the release of magnesium ions from the drug form is slowed down. The drugs containing magnesium ions also displayed cytoprotective activity on the model of normobaric hypoxia. This was resulted in the increase of protective index. Neuroprotective action of magnesium ions (in the condition of hypoxia) is caused by maintaining homeostasis of calcium ions and by inhibition of exocytosis of neuromediators in the synaptic cleft. Thus, magnesium sulfate and its prolonged form can be used with the purpose of pharmacocorrection of heart and brain injuries during hypoxic conditions.

Genetic mutation in Korean patients of sudden cardiac arrest as a surrogating marker of idiopathic ventricular arrhythmia

Mutation or common intronic variants in cardiac ion channel genes have been suggested to be associated with sudden cardiac death caused by idiopathic ventricular tachyarrhythmia. This study aimed to find mutations in cardiac ion channel genes of Korean sudden cardiac arrest patients with structurally normal heart and to verify association between common genetic variation in cardiac ion channel and sudden cardiac arrest by idiopathic ventricular tachyarrhythmia in Koreans. Study participants were Korean survivors of sudden cardiac arrest caused by idiopathic ventricular tachycardia or fibrillation. All coding exons of the SCN5A, KCNQ1, and KCNH2 genes were analyzed by Sanger sequencing. Fifteen survivors of sudden cardiac arrest were included. Three male patients had mutations in SCN5A gene and none in KCNQ1 and KCNH2 genes. Intronic variant (rs2283222) in KCNQ1 gene showed significant association with sudden cardiac arrest (OR 4.05). Four male sudden cardiac arrest survivors had intronic variant (rs11720524) in SCN5A gene. None of female survivors of sudden cardiac arrest had SCN5A gene mutations despite similar frequencies of intronic variants between males and females in 55 normal controls. Common intronic variant in KCNQ1 gene is associated with sudden cardiac arrest caused by idiopathic ventricular tachyarrhythmia in Koreans.

A heterozygous deletion mutation in the cardiac sodium channel gene SCN5A with loss- and gain-of-function characteristics manifests as isolated conduction disease, without signs of Brugada or long QT syndrome

BACKGROUND

The SCN5A gene encodes for the α-subunit of the cardiac sodium channel NaV1.5, which is responsible for the rapid upstroke of the cardiac action potential. Mutations in this gene may lead to multiple life-threatening disorders of cardiac rhythm or are linked to structural cardiac defects. Here, we characterized a large family with a mutation in SCN5A presenting with an atrioventricular conduction disease and absence of Brugada syndrome.

METHOD AND RESULTS

In a large family with a high incidence of sudden cardiac deaths, a heterozygous SCN5A mutation (p.1493delK) with an autosomal dominant inheritance has been identified. Mutation carriers were devoid of any cardiac structural changes. Typical ECG findings were an increased P-wave duration, an AV-block I° and a prolonged QRS duration with an intraventricular conduction delay and no signs for Brugada syndrome. HEK293 cells transfected with 1493delK showed strongly (5-fold) reduced Na(+) currents with altered inactivation kinetics compared to wild-type channels. Immunocytochemical staining demonstrated strongly decreased expression of SCN5A 1493delK in the sarcolemma consistent with an intracellular trafficking defect and thereby a loss-of-function. In addition, SCN5A 1493delK channels that reached cell membrane showed gain-of-function aspects (slowing of the fast inactivation, reduction in the relative fraction of channels that fast inactivate, hastening of the recovery from inactivation).

CONCLUSION

In a large family, congregation of a heterozygous SCN5A gene mutation (p.1493delK) predisposes for conduction slowing without evidence for Brugada syndrome due to a predominantly trafficking defect that reduces Na(+) current and depolarization force.

[The implantable cardiac defibrillator: indications and complications]

The implantation of an implantable cardiac defibrillator (ICD) is indicated as a secondary prevention measure for sudden cardiac death in patients surviving a life-threatening ventricular arrhythmia that had no reversible or treatable cause. An ICD is indicated as a primary prevention measure for sudden cardiac death in patients with a left-ventricular ejection fraction (LVEF) ≤ 35%. A biventricular ICD is indicated in patients with heart failure class ≥ II according to the New York Heart Association classification, a widened QRS complex and an LVEF ≤ 35%. Guidelines do not differentiate between men and women or according to age, but there is no evidence in the literature for decreased mortality from applying ICD therapy in women and in patients older than 70-75 years. This is relevant in discussions over the cost-effectiveness of the treatment. Sudden cardiac death occurs most frequently in patients with an LVEF ≥ 35%; the effect of ICDs as a primary prevention measure in this patient group has, however, never been investigated. The most important complications following ICD implantation are inappropriate ICD shocks and lead dysfunction. Automated home-monitoring enables early detection of technical defects.

Detection of myocardial ischemia episode using morphological features

In this study, we propose to use morphological features that are easy to identify to differentiate myocardial ischemic beats from normal beats. In general, myocardial ischemia causes alterations in electrocardiographic (ECG) signal such as deviation in the ST segment. When the ST segment level deviates from a certain voltage, the beat would be diagnosing as myocardial ischemia. To emphasize on ST variations, the QRS complex of the ECG signal was first subtracted and replaced with a straight line. Five-level discrete wavelet transform (DWT) followed to decompose the waveform into subband components and the A5 subband, which is most sensitive to the changes in the ST segment, was reconstructed for the calculation of 12 morphological features. The support vector machine (SVM) and the 10-fold cross-validation method were employed to evaluate the performance of the method. The results show high values of 95.20%, 93.29%, and, 93.63% in sensitivity, specificity, and accuracy, respectively, that were demonstrated to outperform the other methods in the literature.

[12-lead ECG teletransmission in emergency medicine teams' actions]

INTRODUCTION

Sudden health-threatening conditions with cardiovascular aetiology constitute a great number of all interventions of emergency medicine teams. Diagnostic and therapeutic abilities of modern cardiology lead to the necessity of introducing diagnostic methods which enable effective pre-hospital diagnostics in patients with circulatory system diseases also in emergency medicine. The ECG teletransmissions performed by emergency medicine teams prior to hospitalization increase the accuracy of the diagnosis and thus improve the organization of medical transport of patients to the medical centres appropriate to their medical condition.

MATERIAL AND METHODS

A 12-lead ECG teletransmission system and a system of teleconsultations was set up in September 2009 at the Voivodship Emergency Service and Medical Transport Station (WSPRiTS) "Meditrans" in Warsaw. The system consists of: emergency medicine teams and the Teletransmission Centre located in the Cardiac Department of WSPRiTS "Meditrans. The WSPRiTS "Meditrans" emergency medicine teams and helicopter emergency medicine teams performed standard ECGs at the place of the incident, sending them then via telephone to the Teletransmission Centre. Performing an ECG is recommended in the following cases: a pain in the chest, collapse and syncope, perceptible cardiac arrhythmia, dyspnoea and in any case when the head of the emergency medicine team (ZRM) took the decision to perform an ECG. The ECG record as well as the information about the patient supplied by the head of the team were analyzed by a consulting doctor on 24-hour duty at the receiving station. On basis of the received information the doctor from the Teletransmission Centre instructed the ZRM as to further procedure with the patient. There were 20117 ECG teletransmissions performed within the analyzed period.

RESULTS

In the period between September 2009 and September 30th, 2012 there were 20 117 12-lead ECG teletransmissions performed, where 18139 (90.2%) were successful. 1978 (9.8%) were unsuccessful. 19 997 ECG transmissions were sent from WSPRiTS "Meditrans"ambulances and 120 by helicopter emergency teams. Women constituted 55% and men 45% of the investigated population of patients. The average age was 61 years. The average ECG transmission time was 7 minutes 10 seconds and did not extend the time of emergency medicine actions. The analysis of collected data revealed that ZRMs applied the teletransmission system particularly in cases others than acute coronary syndromes - 16 998 (93.7%) cases. The most frequent reasons to perform an ECG and consultation were pains in the chest - 23% cases, cardiac arrhythmias (18%) and collapses and syncope (13%). Among cardiac arrhythmias, arterial fibrillations (11%) were most often stated and in this group 79% cases were paroxysmal arrhythmias. During the 3 years 1141 cases of acute coronary syndromes were diagnosed in the pre-hospital period, what constituted only 6.3% of all teletransmissions. During a 9-month period 389 transports were carried out to primary health care centres from where the ECG records were then transferred to the Teletransmission Centre. In 117 cases (30%) the consultant changed the initial decision and patients were transported to other medical centres withour interventional cardiology departments.

CONCLUSIONS

The system of ECG teletransmissions and consultations was appreciated by ZRMs and significantly supported their actions. The system should be supervised and coordinated by emergency medicine centres such as the Teletransmission Centre, Emergency Departments or Emergency Rooms. ECG teletransmissions make it possible to extend the paramedics and nurses' competences as regards emergency medical actions with patients with circulatory system diseases. The introduction of ECG teletransmissions from the place of the incident and the doctor's consultation have led to the optimization of transport of patients to appropriate in respect to their condition medical centres.

[The bionic heart patient: care about aftercare]

During the last few decades, care for heart patients has significantly improved. The enormous increase in the number of diagnostic and therapeutic options has resulted in a much better prognosis for many patients with cardiovascular disorders. Implantable cardioverter defibrillators (ICDs) and resynchronization therapy combined with ICDs decrease the risk of sudden death due to ventricular arrhythmias and improve symptoms related to cardiovascular failure. Percutaneous valve implants and percutaneous techniques to repair valve leakages have improved the prognosis of patients deemed inoperable. As well as positive effects, all these interventions are associated with a risk of sometimes severe complications. Infections, perforations and even death can occur related to the procedure. Long term complications caused by infections in or failure of technically complicated devices and electrodes are still a threat for many patients. Careful multi-disciplinary patient selection prior to the procedure and extensive follow-up are therefore mandatory to achieve the best results for these procedures.

Dissection of a quantitative trait locus for PR interval duration identifies Tnni3k as a novel modulator of cardiac conduction

Atrio-ventricular conduction disease is a common feature in Mendelian rhythm disorders associated with sudden cardiac death and is characterized by prolongation of the PR interval on the surface electrocardiogram (ECG). Prolongation of the PR interval is also a strong predictor of atrial fibrillation, the most prevalent sustained cardiac arrhythmia. Despite the significant genetic component in PR duration variability, the genes regulating PR interval duration remain largely elusive. We here aimed to dissect the quantitative trait locus (QTL) for PR interval duration that we previously mapped in murine F2 progeny of a sensitized 129P2 and FVBN/J cross. To determine the underlying gene responsible for this QTL, genome-wide transcriptional profiling was carried out on myocardial tissue from 109 F2 mice. Expression QTLs (eQTLs) were mapped and the PR interval QTL was inspected for the co-incidence of eQTLs. We further determined the correlation of each of these transcripts to the PR interval. Tnni3k was the only eQTL, mapping to the PR-QTL, with an established abundant cardiac-specific expression pattern and a significant correlation to PR interval duration. Genotype inspection in various inbred mouse strains revealed the presence of at least three independent haplotypes at the Tnni3k locus. Measurement of PR interval duration and Tnni3k mRNA expression levels in six inbred lines identified a positive correlation between the level of Tnni3k mRNA and PR interval duration. Furthermore, in DBA/2J mice overexpressing hTNNI3K, and in DBA.AKR.hrtfm2 congenic mice, which harbor the AKR/J “high-Tnni3k expression” haplotype in the DBA/2J genetic background, PR interval duration was prolonged as compared to DBA/2J wild-type mice (“low-Tnni3k expression” haplotype). Our data provide the first evidence for a role of Tnni3k in controlling the electrocardiographic PR interval indicating a function of Tnni3k in atrio-ventricular conduction.

Atrio-ventricular (AV) conduction disease (delay), characterized by prolongation of the PR interval on the surface electrocardiogram (ECG), is a common feature in Mendelian rhythm disorders and is associated with sudden cardiac death. Prolongation of the PR interval is also a strong predictor of atrial fibrillation (AF), the most common sustained cardiac arrhythmia. Although there is a substantial heritable component to the variability of the PR interval, the causative genes remain largely elusive. The identification of these genetic factors in the human population has been difficult owing to wide genetic heterogeneity and an uncontainable environment. We here exploited the homogeneous genetic background and controlled environment of inbred laboratory mouse strains to detect a genetic modifier of the PR interval. We identify Tnni3k as prime candidate for the modulation of the PR interval duration and suggest a new role for this gene, in the modulation of atrio-ventricular conduction.

Cardiac sodium channel Nav1.5 mutations and cardiac arrhythmia

As a major cardiac voltage-gated sodium channel isoform in the heart, the Nav1.5 channel is essential for cardiac action potential initiation and subsequent propagation throughout the heart. Mutations of Nav1.5 have been linked to a variety of cardiac diseases such as long QT syndrome (LQTs), Brugada syndrome, cardiac conduction defect, atrial fibrillation, and dilated cardiomyopathy. The mutagenesis approach and heterologous expression systems are most frequently used to study the function of this channel. This review focuses primarily on recent findings of Nav1.5 mutations associated with type 3 long QT syndrome (LQT3) in particular. Understanding the functional changes of the Nav1.5 mutation may offer critical insight into the mechanism of long QT3 syndrome. In addition, this review provides the updated information on the current progress of using various experimental model systems to study primarily the long QT3 syndrome.

A connexin40 mutation associated with a malignant variant of progressive familial heart block type I

BACKGROUND

Progressive familial heart block type I (PFHBI) is a hereditary arrhythmia characterized by progressive conduction disturbances in the His-Purkinje system. PFHBI has been linked to genes such as SCN5A that influence cardiac excitability but not to genes that influence cell-to-cell communication. Our goal was to explore whether nucleotide substitutions in genes coding for connexin proteins would associate with clinical cases of PFHBI and if so, to establish a genotype-cell phenotype correlation for that mutation.

METHODS AND RESULTS

We screened 156 probands with PFHBI. In addition to 12 sodium channel mutations, we found a germ line GJA5 (connexin40 [Cx40]) mutation (Q58L) in 1 family. Heterologous expression of Cx40-Q58L in connexin-deficient neuroblastoma cells resulted in marked reduction of junctional conductance (Cx40-wild type [WT], 22.2±1.7 nS, n=14; Cx40-Q58L, 0.56±0.34 nS, n=14; P<0.001) and diffuse localization of immunoreactive proteins in the vicinity of the plasma membrane without formation of gap junctions. Heteromeric cotransfection of Cx40-WT and Cx40-Q58L resulted in homogenous distribution of proteins in the plasma membrane rather than in membrane plaques in ≈50% of cells; well-defined gap junctions were observed in other cells. Junctional conductance values correlated with the distribution of gap junction plaques.

CONCLUSIONS

Mutation Cx40-Q58L impairs gap junction formation at cell-cell interfaces. This is the first demonstration of a germ line mutation in a connexin gene that associates with inherited ventricular arrhythmias and emphasizes the importance of Cx40 in normal propagation in the specialized conduction system.

The incidence and prognostic significance of cardiac arrhythmias and conduction abnormalities in patients with acute coronary syndromes and renal dysfunction

BACKGROUND

The incidence of cardiac arrhythmias, including atrial fibrillation (AF) in chronic kidney disease, is unknown, although AF is several times more common in patients with end-stage kidney disease than in the general population.

AIM

To assess the incidence, types and management of cardiac arrhythmias and conduction abnormalities in patients with acute coronary syndromes (ACS) and renal dysfunction. We also evaluated the prognostic significance of arrhythmias in this patient group.

METHODS

We analysed 86 patients with renal dysfunction (GFR < 60 mL/min) out of 1005 patients hospitalised in our department between 2008 and 2009 for unstable angina and ST-elevation and non-ST-elevation myocardial infarction.

RESULTS

Cardiac arrhythmias were observed in 44 (51.1%) patients with AF being the most common (27 patients, 31.4%), predominantly in the paroxysmal form (21.4%). A total of 14 (16.3%) patients had cardiac arrhythmias requiring temporary or permanent pacing. Only 4 (4.6%) patients showed transient conduction abnormalities due to hyperkalaemia in the course of renal failure, while the remaining 10 (11.6%) patients demonstrated conduction abnormalities due to ACS. A total of 3 (3.5%) patients had other arrhythmias (atrial tachycardia, ventricular arrhythmias). During the follow-up period (mean duration: 14.3 months) 7 out of 44 patients (15.9%) with renal dysfunction and arrhythmia and 2 out of 42 patients (4.7%) without arrhythmia died (p < 0.05).

CONCLUSIONS

Cardiac arrhythmias occur more often in patients with ACS if renal dysfunction is also present and are associated with poor prognosis.

[AAI stimulation and nodal rhythm]

We describe the case of a 77 year-old white woman treated by AAI pacing. Nodal rhythm with ventriculo-atrial conduction and retrograde P wave were observed in ECG Holter monitoring. The retrograde P wave was sensed by the pacemaker, which responded correctly.

A novel mechanism for LQT3 with 2:1 block: a pore-lining mutation in Nav1.5 significantly affects voltage-dependence of activation

BACKGROUND

SCN5A mutations that cause a gain of function in the cardiac voltage-gated sodium channel (Nav1.5) lead to long QT syndrome and a higher risk for sudden cardiac death.

OBJECTIVE

Here we functionally characterize the biophysical properties of the LQT3 variant, V411M, found in a newborn with a QT interval of 640 ms and 2:1 atrioventricular block.

METHODS

Whole cell patch clamp was performed on wild-type and V411M Nav1.5 channels stably expressed in human embryonic kidney cells.

RESULTS

V411M channels showed hyperpolarizing shifts in both the conductance-voltage (V(1/2) = -48.5 ± 2.2 mV vs. -40.4 ± 1.6 mV for wild-type) and inactivation-voltage (-95.6 ± 1.9 mV vs. -87.7 ± 1.7 mV) relationships, and a two-fold increase in late (sustained) sodium current during voltage ramp repolarizations. While neither mexiletine nor lidocaine exhibited potency differences between WT and V411M, or shortened the QTc in vivo, increased mutant block was observed with 10 μM flecainide (71.4 ± 3.0% vs. 60.3 ± 2.8%), in a voltage-dependent manner. Incorporation of V411M kinetics into atrial and ventricular action potential models reproduced prolonged action potential repolarization.

CONCLUSIONS

Our data suggest a novel mechanism for LQT3, a result of a hyperpolarizing shift in the steady state activation relationship and re-activation of Nav1.5 towards a higher open probability during repolarization of the cardiac action potential. This results in an increased number of open-activated sodium channels, and so drugs that bind this state preferentially are expected to shorten the QTc more than those that favour the inactivated state.

[Progress in endogenous cardioprotection induced by ischemic postconditioning]

Restoration of blood flow is the definitive therapy to salvage myocardium following ischemic injury. Sudden restoration of blood flow to the ischemic myocardium may, however, also cause reperfusion injury. Therefore, to prevent such ischemia/reperfusion (I/R) injury, one strategy could be to evoke endogenous myocardial protective mechanisms. Ischemic preconditioning (IPC) and postconditioning (I-postC) are endogenous protective mechanisms capable of protecting the myocardium from myocardial infarction, stunning, and ventricular arrhythmia induced by I/R injury. The mechanisms involve induction of triggers, activation of signaling pathways, and end-effectors, which attenuate generation of free radicals and calcium overload induced by I/R. The fact that I-postC can be applied after a prolonged period of ischemia offers a novel approach to myocardial protection. This article mainly reviews the cardioprotection, mechanisms, and application to clinical cardiology of I-postC.

Peri-infarction block; electrocardiographic abnormality occasionally resembling bundle branch block and local ventricular block of other types

Curves which represent bundle branch block can usually be identified. More important are those which represent peri-infarction block. Multiple unipolar leads enable identification of the latter from the former, which they may closely resemble in the limb leads, and from intraventricular block of other types. Criteria and examples of peri-infarction block are presented and an incidence and explanation are offered.

Certain clinical states and pathologic changes associated with deeply inverted T waves in the precordial electrocardiogram

A correlation of the clinical and electrocardiographic findings was undertaken in 110 cases which had in common the presence of deeply inverted T waves in central terminal leads centered about position 3 on the precordium. The results of this study are reviewed. A summary is presented of changes encountered at the time of necropsy in nine cases in which electrocardiographic changes of similar type had been recorded. These observations are integrated with concepts derived from the dipole theory. The total evidence is viewed in relation to observations reported by other investigators.