Computer Simulation Methods of Cardiac Electrophysiology

The Luo Rudy models of mammalian ventricular cell were chosen in studying cardiac electrophysiology. Rush and Larsen’s algorithm and adaptive time step methods were used to solve the ordinary differential equations (ODE’s). The operator splitting (or time splitting) and adaptive time step methods were used to solve the partial differential equations (PDE’s) in cardiac tissue conduction models. The alternating direction implicit (ADI) method was used to integrate the PDE. Using these methods we accomplished the simulation programs of single cardiomyocyte model, one dimensional cable model(1 D) and two dimensional(2 D) tissue model. The methods of initiating spiral waves were studied with these software. The data getting from 2 D simulation can be used for further study on isopotential contour lines, spiral wave tip trajectories, and pseudo ECG. The software for computer simulation have been successfully used in simulation studying of electrophysiology properties of single cardiomyocyte, conduction in one dimensional cable model(1 D) and two dimensional(2 D) tissue model.

Femoral Access with Ultrasound-Guided Puncture and Z-Stitch Hemostasis for Adults with Congenital Heart Diseases Undergoing Electrophysiological Procedures

Aims:Although the application of ultrasound-guided vascular puncture and Z-stitch hemostasis to manage femoral access has been widely utilized,there is limited data on this combined application in adult congenital heart disease(ACHD)patients undergoing electrophysiological(EP)procedures.We sought to evaluate the safety and efficacy of ultrasound-guided puncture and postprocedural Z-stitch hemostasis for ACHD patients under-going EP procedures.Methods and Results:The population of ACHD patients undergoing transfemoral EP pro-cedures at the University of Zurich Heart Center between January 2019 and December 2022 was observed and analyzed.During the study period,femoral access(left/right,arterial/venous)was performed under real-time ultrasound guidance.At the end of the procedure,a single Z-stitch was performed at the puncture site.We eval-uated the incidence of in-hospital complications associated with femoral access puncture in this population.Among 101 patients who had a total of 147 previous ipsilateral vascular punctures(mean 1.5 per person),100 patients underwent successful femoral vascular access for EP procedures.The median age of the patients was 47±15 years and 34(34%)were male.Z-stitches were performed after the procedure in 100 patients with 303 femoral vascular accesses(mean 3 punctures per person).No patient developed vascular puncture relevant inguinal hematoma,pseudo aneurysm,arteriovenousfistula,venous or arterial thrombosis.Conclusion:In ACHD patients undergoing EP procedures,optimal femoral access management can be achieved with ultra-sound-guided puncture and postprocedural Z-stitch hemostasis.

Cardiac evaluation of liver transplant candidates

Physicians previously thought that heart disease was rare in patients with end stage liver disease. However, recent evidence shows that the prevalence of ischemic heart disease and cardiomyopathy is increased in transplant candidates compared to most other surgical candidates. Investigators estimate that up to 26% of all liver transplant candidates have at least one critical coronary artery stenosis and that at least half of these patients will die perioperatively of cardiac complications. Cardiomyopathy also occurs in greater frequency. While all patients with advanced cardiac disease have defects in cardiac performance, a larger than expected number of patients have classical findings of dilated, restrictive and hypertropic cardiomyopathy. This may explain why up to 56% of patients suffer from hypoxemia due to pulmonary edema following transplant surgery. There is considerable controversy on how to screen transplant candidates for the presence of heart disease. Questions focus upon, which patients should be screened and what tests should be used. This review examines screening strategies for transplant candidates and details the prognostic value of common tests used to identify ischemic heart disease. We also review the physiological consequences of cardiomyopathy in transplant candidates and explore the specific syndrome of "cirrhotic cardiomyopathy".

Cardiac Electrophysiological Differences Between Kunming and C57BL6/J Mice

Objective To investigate the alterations of cardiac electrophysiological properties and substantial mechanism and find the stable arrhythmia mouse model in Kunming （KM） and C57BL6/J （C57） mice. Methods Electrocardiogram recordings were used to analyze the QT interval in vivo, and mono- phasic action potential of right and left ventricular epicardium was recorded to elicit changes of action potential duration （APD） in conventional and programmed electrical stimulation （PES）. Transient outward potassium current （Its,） was recorded via whole-cell patch-clamp technique in single right and left epicardial myocytes. Results QT interval was prolonged in KM mice relative to C57 mice （62.51±4.47 ms vs. 52.59±4.85 ms, P〈0.05）. The APD at 50% repolarization of the left ventricular epicardium （18.60±0.91 ms vs. 12.90±0.35 ms）, and APDs at 50% （17.31±6.05 ms vs. 12.00±3.24 ms） and 70% repolarization （36.13±5.32 ms vs. 2 1.95±8.06 ms） of the right ventricular epicardium in KM mice were significantly pro- longed compared with C57 mice, respectively （all P〈0.05）. KM mice were more sensitive to PES-induced ventricular tachycardia （25%, 3 of 12 hearts）, and especially to Burst-induced ventricular tachycardia （50%, 6 of 12 hearts） compared with C57 mice, which were 20% （2 of 10 hearts） and 30% （3 of 10 hearts） respec- tively. It,, densities both in the left and right ventricular epicardial myocytes from KM mice were significantly decreased compared with C57 mice, respectively （all P〈0.01）. Conclusion Our data showed that KM mice with tile prolonged QT interval and APD are ruiner- abilities to ventricular arrhythmia, which are attributed to lower Ito densities in ventricular myocytes ob- tained from KM mice than that from C57 mice.

Use of antiarrhythmic drugs in elderly patients

Human aging is a global issue with important implications for current and future incidence and prevalence of health conditions and disability. Cardiac arrhythmias, including atrial fibrillation, sudden cardiac death, and bradycardia requiring pacemaker placement, all increase exponentially after the age of 60. It is important to distinguish between the normal, physiological consequences of aging on cardiac electrophysiology and the abnormal, pathological alterations. The age-related cardiac changes include ventricular hypertrophy, senile amyloidosis, cardiac valvular degenerative changes and annular calcification, fibrous infiltration of the conduction system, and loss of natural pacemaker cells and these changes could have a profound effect on the development of arrhythmias. The age-related cardiac electrophysiological changes include up- and down-regulation of specific ion channel expression and intmcellular Ca2＋ overload which promote the development of cardiac arrhythmias. As ion channels are the substrates of antiarrhythmic drugs, it follows that the pharmacokinetics and pharmacodynamics of these drugs will also change with age. Aging alters the absorption, distribution, metabolism, and elimination of antiarrhythmic drugs, so liver and kidney function must be monitored to avoid potential adverse drug effects, and antiarrhythmic dosing may need to be adjusted for age. Elderly patients are also more susceptible to the side effects of many antiarrhytbanics, including bradycardia, orthostatic hypotension, urinary retention, and falls. Moreover, the choice of antiarrhythmic drugs in the elderly patient is frequently complicated by the presence of co-morbid conditions and by polypharmacy, and the astute physician must pay careful attention to potential drug-drug interactions. Finally, it is important to remember that the use of antiarrhythmic drugs in elderly patients must be individualized and tailored to each patient＇s physiology, disease processes, and medication regimen.

Cardiac differentiation and electrophysiology characteristics of bone marrow mesenchymal stem cells

Objective To review the progress of cardiac differentiation and electrophysiological characteristics of bone marrow mesenchymal stem cells. Data sources The databases of PubMed, Springer Link, Science Direct and CNKI were retrieved for papers published from January 2000 to January 2012 with the key words of ＂bone marrow mesenchymal stem cells, cardiac or heart, electrophysiology or electrophysiological characteristics＂. Study selection The articles concerned cardiac differentiation and electrophysiological characteristics of bone marrow mesenchymal stem cells were collected. After excluding papers that study purposes are not coincident with this review or contents duplicated, 56 papers were internalized at last. Results For the treatment of myocardial infarction and myocardiac disease, the therapeutic effects of transplantation of bone marrow mesenchymal stem cells which have the ability to develop into functional myocardial cells by lots of methods have been proved by many researches. But the arrhythmogenic effect on ventricles after transplantation of bone marrow mesenchymal stem cells derived myocardial cells is still controversial in animal models. Certainly, the low differentiation efficiency and heterogeneous development of electricial function could be the most important risk for proarrhythmia. Conclusion Many studies of cardiac differentiation of bone marrow mesenchymal stem cells have paid attention to improve the cardiac differentiation rate, and the electrophysiology characteristics of the differentiated cells should be concerned for the risk for proarrhythmia as well.

RATE-DEPENDENT SLOW CONDUCTION VELOCITY IN THE CAVO-TRICUSPID ISTHMUS AND SEPTUM IN PATIENTS WITH ATRIAL FLUTTER

Purpose. To evaluate and compare the effects of heart rate on conduction velocity in the cavotricus-pid isthmus (CTI) and septum in patients with and without typical atrial flutter (AF) using electro-anatomic mapping (EAM) of the right atrium (RA).Methods. Ten patients(age 53+10 yrs,7M/3F)with AF and 13 patients (age 51+11 yrs, 5M/8F) with atrio-ventricular nodal reentrant tachycardia (AVNRT) underwent conventional electrophysionogical study, electro -anatomic mapping and radiofrequency ablation. Using EAMs obtained during coronary sinus pacing at pacing cycle length (PCL) 600 ms, 400 ms, and 300 ms, we evaluated conduction velocities in the CTI and septum of RA in 10 patients with AF and compared EAMs to 13 patients with AVNRT to determine whether the conduction slowing required to maintain AFL was related to changes in volume alone or altered RA electrophysiology.Results. Conduction velocities in CTI and septum were significantly slower at all PCL when AF was compared to AVNRT(P<0.05). Additionally, in the AF group, septal conduction velocities were slower at PCL 600 ms and 400 ms, but not at 300 ms compared to CTI (P<0.05). In AF, during PCL 300. conduction in CTI slowed significantly compared to PCL 600 and 400 ms such that there was no difference between CTI and septum at PCL 300.Conclusions. There is slower conduction in the septum compared to the CTI in all patients. However, in patients with AF, there is significant slowing of conduction in the CTI and septum as well as decremen-tal rate-dependent slowing of conduction in the CTI. These findings indicate that in addition to RA enlargement, changes in atrial electrophysiology distinguish AF patients from patients with AVNRT.

Effect of tetrandrine on cellular electrophysiology and calcium uptake of myocardium in guinea pigs and dogs

Objective To study the effects of tetrandrine, a Chinese herbal medicine, on the action potential (AP),contraction as well as sarcoplasmic reticulum (SR) calcium uptake of myocardium in guinea-pigs and dogs.Methods Changes in AP, dV/dt, peak tension (PT) and dT/dt of myocardial cells were studied using the technique of glass electrode. Changes of the calcium uptake rate by sarcoplasmic reticulum and release of inorganic phosphate from sarcoplasmic reticulum were assessed with biochemical techniques.Results Tetrandrine exerts a concentration-dependent and frequency-dependent negative inotropic effect and shortens action potential duration. Tetrandrine depresses both dT(E)/dt and dT(L)/dt as well as the tension of myocardium, and reduces dV/dt and amplitude only in the slow action potential, thus implying that tetrandrine blocks the slow calcium channel. In addition, compared with thapsigargin, a specific inhibitor of Ca2+-ATPase on SR, tetrandrine more apparently suppresses the contraction of the myocardium.Conclusions Tetrandrine is a wide-range calcium antagonist of plant origin. Not only it blocks the voltageoperated calcium channels as other authors reported, but also may play an important role in affecting the function of Ca2+ -ATPase and calcium release channels on SR. From this study, we also suggest that the calcium channel appears to be more critical than SR for the contraction of my ocardium.

Superaligned carbon nanotubes guide oriented cell growth and promote electrophysiological homogeneity for synthetic cardiac tissues

With the support by the National Natural Science Foundation of China,the research team led by Professor Li Yigang(李毅刚)at Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine and Professor Peng Huisheng(彭慧胜)at Fudan University presented a new type of

Simulation of biatrial conduction via different pathways during sinus rhythm with a detailed human atrial model

In order to better understand biatrial conduction,investigate various conduction pathways,and compare the differences between isotropic and anisotropic conductions in human atria,we present a simulation study of biatrial conduction with known/assumed conduction pathways using a recently developed human atrial model.In addition to known pathways:(1) Bachmann's bundle(BB),(2) limbus of fossa ovalis(LFO),and(3) coronary sinus(CS),we also hypothesize that there exist two fast conduction bundles that connect the crista terminalis(CT),LFO,and CS.Our simulation demonstrates that use of these fast conduction bundles results in a conduction pattern consistent with experimental data.The comparison of isotropic and anisotropoic conductions in the BB case showed that the atrial working muscles had small effect on conduction time and conduction speed,although the conductivities assigned in anisotropic conduction were two to four times higher than the isotropic conduction.In conclusion,we suggest that the hypothesized intercaval bundles play a significant role in the biatrial conduction and that myofiber orientation has larger effects on the conduction system than the atrial working muscles.This study presents readers with new insights into human atrial conduction.