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Cardiac Rhythm (cardiac + rhythm)
Selected AbstractsValidation of Three-Dimensional Cardiac Image Integration: Use of Integrated CT Image into Electroanatomic Mapping System to Perform Catheter Ablation of Atrial FibrillationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2006PETER M. KISTLER M.B.B.S., Ph.D. Introduction: Accurate visualization of the complex left atrial (LA) anatomy and the location of an ablation catheter within the chamber is important in the success and safety of ablation for atrial fibrillation (AF). We describe the integration of CT into an electroanatomic mapping (EAM) system and its validation in patients undergoing catheter ablation for AF. Methods and Results: Thirty patients (59.2 ± 8 years, 25 M) with paroxysmal (12) and persistent (18) AF underwent ablation using CT image integration into an electroanatomic mapping system. CT registration using the pulmonary veins as markers (landmark) was achieved with an error of 6.4 ± 2.8 mm with repeat registration required in two patients. Registration of the CT by best fit to a electroanatomic geometry (surface) was achieved with an error of 2.3 ± 0.4 mm. There was no significant difference in the regional LA registration error at superior (1.7 ± 0.7 mm), inferior (2.2 ± 1.4 mm), septal (1.7 ± 0.8 mm), and lateral (1.7 ± 0.7 mm, P = 0.13) sites. Cardiac rhythm at the time of CT did not have a significant effect on total or regional surface registration accuracy (mean total 2.5 ± 0.3 in AF patients vs 2.3 ± 0.5 in SR patients, P = 0.22). The integrated CT was used to guide the encirclement of the pulmonary veins (PV) in pairs with electrical isolation achieved by maintaining ablation along the ablation line in 58 of 60 PV pairs. Postprocedural PV angiography did not demonstrate significant stenosis. Conclusion: CT image integration into an EAM system was successfully performed in patients undergoing catheter ablation for AF. With a greater appreciation of the complex and variable nature of the PV and LA anatomy this new technology may improve the efficacy and safety of the procedure. [source] Gap junction remodeling and cardiac arrhythmogenesis: cause or coincidence?JOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 4 2001Nicholas J. Severs Abstract Gap junctions, clusters of transmembrane channels that link adjoining cells, mediate myocyte-to-myocyte electrical coupling and communication. The component proteins of gap junction channels are termed connexins and, in in vitro expression systems, gap-junctional channels composed of different connexin types exhibit different biophysical properties. In common with other tissues, the heart expresses multiple connexin isoforms. Spatially defined patterns of expression of three connexin isoforms - connexin43, connexin40 and connexin45 - form the cell-to-cell conduction pathways responsible for the orderly spread of current flow that governs the normal cardiac rhythm. Remodeling of gap junction organization and connexin expression is a common feature of human heart disease conditions in which there is an arrhythmic tendency. This remodeling may take the form of disturbances in the distribution of gap junctions and/or quantitative alterations in connexin expression, notably reduced ventricular connexin43 levels. The idea that such changes may contribute to the development of a pro-arrhythmic substrate in the diseased heart has gained ground over the last decade. Recent studies using transgenic mice models have raised new opportunities to explore the significance of gap junction remodeling in the diseased heart. [source] The use of vasopressin for treating vasodilatory shock and cardiopulmonary arrestJOURNAL OF VETERINARY EMERGENCY AND CRITICAL CARE, Issue 2 2009DACVIM, Richard D. Scroggin Jr. Abstract Objective , To discuss 3 potential mechanisms for loss of peripheral vasomotor tone during vasodilatory shock; review vasopressin physiology; review the available animal experimental and human clinical studies of vasopressin in vasodilatory shock and cardiopulmonary arrest; and make recommendations based on review of the data for the use of vasopressin in vasodilatory shock and cardiopulmonary arrest. Data Sources , Human clinical studies, veterinary experimental studies, forum proceedings, book chapters, and American Heart Association guidelines. Human and Veterinary Data Synthesis , Septic shock is the most common form of vasodilatory shock. The exogenous administration of vasopressin in animal models of fluid-resuscitated septic and hemorrhagic shock significantly increases mean arterial pressure and improves survival. The effect of vasopressin on return to spontaneous circulation, initial cardiac rhythm, and survival compared with epinephrine is mixed. Improved survival in human patients with ventricular fibrillation, pulseless ventricular tachycardia, and nonspecific cardiopulmonary arrest has been observed in 4 small studies of vasopressin versus epinephrine. Three large studies, though, did not find a significant difference between vasopressin and epinephrine in patients with cardiopulmonary arrest regardless of initial cardiac rhythm. No veterinary clinical trials have been performed using vasopressin in cardiopulmonary arrest. Conclusion , Vasopressin (0.01,0.04 U/min, IV) should be considered in small animal veterinary patients with vasodilatory shock that is unresponsive to fluid resuscitation and catecholamine (dobutamine, dopamine, and norepinephrine) administration. Vasopressin (0.2,0.8 U/kg, IV once) administration during cardiopulmonary resuscitation in small animal veterinary patients with pulseless electrical activity or ventricular asystole may be beneficial for myocardial and cerebral blood flow. [source] In vitro characterization of HCN channel kinetics and frequency dependence in myocytes predicts biological pacemaker functionalityTHE JOURNAL OF PHYSIOLOGY, Issue 7 2009Xin Zhao The pacemaker current, mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, contributes to the initiation and regulation of cardiac rhythm. Previous experiments creating HCN-based biological pacemakers in vivo found that an engineered HCN2/HCN1 chimeric channel (HCN212) resulted in significantly faster rates than HCN2, interrupted by 1,5 s pauses. To elucidate the mechanisms underlying the differences in HCN212 and HCN2 in vivo functionality as biological pacemakers, we studied newborn rat ventricular myocytes over-expressing either HCN2 or HCN212 channels. The HCN2- and HCN212-over-expressing myocytes manifest similar voltage dependence, current density and sensitivity to saturating cAMP concentrations, but HCN212 has faster activation/deactivation kinetics. Compared with HCN2, myocytes expressing HCN212 exhibit a faster spontaneous rate and greater incidence of irregular rhythms (i.e. periods of rapid spontaneous rate followed by pauses). To explore these rhythm differences further, we imposed consecutive pacing and found that activation kinetics of the two channels are slower at faster pacing frequencies. As a result, time-dependent HCN current flowing during diastole decreases for both constructs during a train of stimuli at a rapid frequency, with the effect more pronounced for HCN2. In addition, the slower deactivation kinetics of HCN2 contributes to more pronounced instantaneous current at a slower frequency. As a result of the frequency dependence of both instantaneous and time-dependent current, HCN2 exhibits more robust negative feedback than HCN212, contributing to the maintenance of a stable pacing rhythm. These results illustrate the benefit of screening HCN constructs in spontaneously active myocyte cultures and may provide the basis for future optimization of HCN-based biological pacemakers. [source] TASER X26 Discharges in Swine Produce Potentially Fatal Ventricular ArrhythmiasACADEMIC EMERGENCY MEDICINE, Issue 1 2008Robert J. Walter PhD Abstract Objectives:, Data from the authors and others suggest that TASER X26 stun devices can acutely alter cardiac function in swine. The authors hypothesized that TASER discharges degrade cardiac performance through a mechanism not involving concurrent acidosis. Methods:, Using an Institutional Animal Care and Use Committee (IACUC)-approved protocol, Yorkshire pigs (25,71 kg) were anesthetized, paralyzed with succinylcholine (SCh; 2 mg/kg), and then exposed to two 40-second discharges from a TASER X26 with a transcardiac vector. Vital signs, blood chemistry, and electrolyte levels were obtained before exposure and periodically for 48 hours postdischarge. Electrocardiograms and echocardiography (echo) were performed before, during, and after the discharges. p-Values < 0.05 were considered significant. Results:, Electrocardiograms were unreadable during the discharges due to electrical interference, but echo images showed unmistakably that cardiac rhythm was captured immediately at a rate of 301 ± 18 beats/min (n = 8) in all animals tested. Capture continued for the duration of the discharge and in one animal degenerated into fatal ventricular fibrillation (VF). In the remaining animals, ventricular tachycardia (VT) occurred postdischarge for 1,17 seconds, whereupon sinus rhythm was regained spontaneously. Blood chemistry values and vital signs were minimally altered postdischarge and no significant acidosis was seen. Conclusions:, Extreme acid,base disturbances usually seen after lengthy TASER discharges were absent with SCh, but TASER X26 discharges immediately and invariably produced myocardial capture. This usually reverted spontaneously to sinus rhythm postdischarge, but fatal VF was seen in one animal. Thus, in the absence of systemic acidosis, lengthy transcardiac TASER X26 discharges (2 × 40 seconds) captured myocardial rhythm, potentially resulting in VT or VF in swine. [source] The GH,IGF-I axis and the cardiovascular system: clinical implicationsCLINICAL ENDOCRINOLOGY, Issue 3 2008Annamaria Colao Summary Background, GH and IGF-I affect cardiac structure and performance. In the general population, low IGF-I has been associated with higher prevalence of ischaemic heart disease and mortality. Both in GH deficiency (GHD) and excess life expectancy has been reported to be reduced because of cardiovascular disease. Objective, To review the role of the GH,IGF-I system on the cardiovascular system. Results, Recent epidemiological evidence suggests that serum IGF-I levels in the low-normal range are associated with increased risk of acute myocardial infarction, ischaemic heart disease, coronary and carotid artery atherosclerosis and stroke. This confirms previous findings in patients with acromegaly or with GH-deficiency showing cardiovascular impairment. Patients with either childhood- or adulthood-onset GHD have cardiovascular abnormalities such as reduced cardiac mass, diastolic filling and left ventricular response at peak exercise, increased intima-media thickness and endothelial dysfunction. These abnormalities can be reversed, at least partially, after GH replacement therapy. In contrast, in acromegaly chronic GH and IGF-I excess causes a specific cardiomyopathy: concentric cardiac hypertrophy (in more than two-thirds of the patients at diagnosis) associated to diastolic dysfunction is the most common finding. In later stages, impaired systolic function ending in heart failure can occur, if GH/IGF-I excess is not controlled. Abnormalities of cardiac rhythm and of cardiac valves can also occur. Successful control of acromegaly is accompanied by decrease of the left ventricular mass and improvement of cardiac function. Conclusion, The cardiovascular system is a target organ for GH and IGF-I. Subtle dysfunction in the GH,IGF-I axis are correlated with increased prevalence of ischaemic heart disease. Acromegaly and GHD are associated with several abnormalities of the cardiovascular system and control of GH/IGF-I secretion reverses (or at least stops) cardiovascular abnormalities. [source] Disparities in the Emergency Department Evaluation of Chest Pain PatientsACADEMIC EMERGENCY MEDICINE, Issue 2 2007Liliana E. Pezzin PhD Background The existence of race and gender differences in the provision of cardiovascular health care has been increasingly recognized. However, few studies have examined whether these differences exist in the emergency department (ED) setting. Objectives To evaluate race, gender, and insurance differences in the receipt of early, noninvasive diagnostic tests among persons presenting to an ED with a complaint of chest pain. Methods Data were drawn from the U.S. National Hospital Ambulatory Health Care Survey of EDs. Visits made during 1995,2000 by persons aged 30 years or older with chest pain as a reason for the visit were included. Factors affecting the likelihood of ordering electrocardiography, cardiac monitoring, oxygen saturation measurement using pulse oximetry, and chest radiography were analyzed using multivariate probit analysis. Results A total of 7,068 persons aged 30 years or older presented to an ED with a primary complaint of chest pain during the six-year period, corresponding to more than 32 million such visits nationally. The adjusted probability of ordering a test was highest for non,African American patients for all tests considered. African American men had the lowest probabilities (74.3% and 62% for electrocardiography and chest radiography, respectively), compared with 81.1% and 70.3%, respectively, among non,African American men. Only 37.5% of African American women received cardiac monitoring, compared with 54.5% of non,African American men. Similarly, African American women were significantly less likely than non,African American men to have their oxygen saturation measured. Patients who were uninsured or self-pay, as well as patients with "other" insurance, also had a lower probability than insured persons of having these tests ordered. Conclusions This study documents race, gender, and insurance differences in the provision of electrocardiography and chest radiography testing as well as cardiac rhythm and oxygen saturation monitoring in patients presenting with chest pain. These observed differences should catalyze further study into the underlying causes of disparities in cardiac care at an earlier point of patient contact with the health care system. [source] Induction Ovens and Electromagnetic Interference:PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 7p1 2003What is the Risk for Patients with Implanted Pacemakers? Electromagnetic fields may interfere with normal pacemaker function. Despite the introduction of modern pacemakers and bipolar lead systems, electromagnetic interference (EMI) still remains to be a concern during daily lives when patients are exposed to cellular phones, electronic security systems, and several household appliances. The aim of this study was to evaluate potential EMI risk of induction ovens, which are increasingly used in private households. The study included 40 consecutive patients (22 men, 18 women; age73 ± 11 years) with implanted DDD, VVI, VDD, and AAI pacemaker systems. The pacemakers were programmed to unipolar sensing and pacing. Sensitivity remained unchanged, if the measured sensing threshold was more than twice the programmed value; otherwise, it was set at half of the measured sensing threshold. Patients were placed in a sitting position at the closest possible distance of about 20 cm between two cooking pots and pacemaker bending the upper part of the body slightly over the induction oven. The energy was increased stepwise to the maximum. One pot was removed and placed again at the highest oven level. Potential interference was monitored continuously. The study showed no incidence of pacemaker malfunction during the entire test while the patients with intrinsic cardiac rhythms were exposed to the induction oven at varying energy strengths. Likewise, there was no external interference when the patients were paced at heart rates of 10,15 beats/min above their heart rates. The programmed parameters remained unchanged after the study. In conclusion, this study shows no EMI risk of an induction oven in patients with bipolar or right-sided unipolar pacemakers. (PACE 2003; 26[Pt. I]:1494,1497) [source] Echocardiographic Evaluation of a TASER-X26 Application in the Ideal Human Cardiac AxisACADEMIC EMERGENCY MEDICINE, Issue 9 2008Jeffrey D. Ho MD Abstract Objectives:, TASER electronic control devices (ECDs) are used by law enforcement to subdue aggressive persons. Some deaths temporally proximate to their use have occurred. There is speculation that these devices can cause dangerous cardiac rhythms. Swine research supports this hypothesis and has reported significant tachyarrhythmias. It is not known if this occurs in humans. The objective of this study was to determine the occurrence of tachyarrhythmias in human subjects subjected to an ECD application. Methods:, This was a prospective, nonblinded study. Human volunteers underwent limited echocardiography before, during, and after a 10-second TASER X26 ECD application with preplaced thoracic electrodes positioned in the upper right sternal border and the cardiac apex. Images were analyzed using M-mode through the anterior leaflet of the mitral valve for evidence of arrhythmia. Heart rate (HR) and the presence of sinus rhythm were determined. Data were analyzed using descriptive statistics. Results:, A total of 34 subjects were enrolled. There were no adverse events reported. The mean HR prior to starting the event was 108.7 beats/min (range 65 to 146 beats/min, 95% CI = 101.0 to 116.4 beats/min). During the ECD exposure, the mean HR was 120.1 beats/min (range 70 to 158 beats/min, 95% CI = 112.2 to 128.0 beats/min) and a mean of 94.1 beats/min (range 55 to 121 beats/min, 95% CI = 88.4 to 99.7 beats/min) at 1 minute after ECD exposure. Sinus rhythm was clearly demonstrated in 21 (61.7%) subjects during ECD exposure (mean HR 121.4 beats/min; range 75 to 158 beats/min, 95% CI = 111.5 to 131.4). Sinus rhythm was not clearly demonstrated in 12 subjects due to movement artifact (mean HR 117.8 beats/min, range 70 to 152 beats/min, 95% CI = 102.8 to 132.8 beats/min). Conclusions:, A 10-second ECD exposure in an ideal cardiac axis application did not demonstrate concerning tachyarrhythmias using human models. The swine model may have limitations when evaluating ECD technology. [source] | ||||||||||