bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics of Multiple‐Shock Defibrillation
Authors: SWEENEY ROBERT J. , GILL ROBERT M. , REID PHILIP R. 
Published: May 2007

Multiple‐Shock Defibrillation. Introduction: A new method for defibrillation allows two shocks to be combined to defibrillate with reduced current by adjusting their separation according to the cycle length of the fibrillation event. We investigated various aspects of this new method to better understand its characteristics and applicability to defibrillation. Methods and Results: In 48 pentobarbital‐anesthetized dogs, we measured the current for 50% defibrillation success using the new method with sequences of rectangular shocks. Group 1 studied the role of shock total duration and found that two‐shock sequences followed a strength‐duration curve similar to, but below, that for single shocks. Group 2 studied the role of amplitude and duration balance between shocks and found that two‐shock sequences with equal shocks performed best. Group 3 studied whether the new method could be used with either biphasic waveforms or sequential shock pathways. Current reduction for the combined methods equaled the product of current reduction by each method, demonstrating that these methods can be effectively combined. Group 4 extended the method to include three‐shock and four‐shock sequences and found that a fourth shock did not further improve defibrillation. The optimum three‐shock sequence required 33% lower current (P < 0.002) and 34% greater energy (P < 0.095 = NS) than a single shock. Conclusions: The new method allows defibrillation to be distributed over several fibrillatory cycles and has an improved strength‐duration relationship. Two‐ or three‐shock sequences using equal shocks permit a substantial reduction of defibrillation current that can be combined with the reduction for biphasic and sequential methods. Thus, the method may have application in low‐current defibrillation devices.
Unique Properties of Cardiac Action Potentials Recorded with Voltage‐Sensitive Dyes
Authors: GIROUARD STEVEN D. , Ph.D. KENNETH R. LAURITA. , ROSENBAUM DAVID S. 
Published: May 2007

Unique Properties of Optical Action Potentials. Introduction: Optical mapping with voltage‐sensitive dyes has made it possible to record cardiac action potentials with high spatial resolution that is unattainable by conventional techniques. Optically recorded signals possess distinct properties that differ importantly from electrograms recorded with extracellular electrodes or action potentials recorded with microelectrode techniques. Despite the growing application of optical mapping to cardiac electrophysiology, relatively little quantitative information is available regarding the characteristics of optical action potentials recorded from cardiac tissue. Methods and Results: A high‐resolution optical mapping system and microelectrode techniques were used to determine the characteristics of guinea pig ventricular action potentials recorded with the voltage‐sensitive dye di‐4‐ANEPPS. The effects of optical magnification, tissue‐light interaction, sampling rate, voltage resolution, spatial resolution, and cardiac motion on action potential signal characteristics were determined. The optical action potential signal represents the relative change in transmembrance potential arising from a volume of cells, where the area of a recording site is determined by optical magnification and detector area, and the depth of recording is determined by system optics and the visible light transmission characteristics of cardiac muscle. Using photographic lenses, the depth of tissue contributing to the signal is < 250 μm. The action potential plateau and final repolarization can be accurately reconstructed from data digitized at modest sampling rates (450 to 750 Hz), since the frequency content of optical action potentials is band‐limited to approximately 150 Hz. However, faster sampling rates are needed to depict the subtle details of the action potential upstroke. In addition to temporal resolution, it is essential to achieve sufficient dynamic range and voltage resolution to accurately represent the time course of membrane potential change. Voltage resolution is inversely related to the square of spatial resolution, hence, there exists an inherent trade‐off between increased spatial resolution and diminished voltage resolution. Cardiac motion, which can otherwise limit spatial resolution as well as signal fidelity, can be effectively reduced using mechanical stabilization of the heart without distorting action potential characteristics. Conclusions: Optical mapping with voltage‐sensitive dyes provides high‐fidelity multisite action potential recording with flexible spatial resolution. When recording cardiac action potentials with voltage‐sensitive dyes, the Interdependence of temporal, spatial, and voltage resolutions must be carefully considered.
Radiofrequency Catheter Ablation of Atrial Flutter After Orthotopic Heart Transplantation
Authors: LI YI‐GANG , GRÖNEFELD GERIAN , HOHNLOSER STEFAN. H. 
Published: May 2007

Ablation of Atrial Flutter After Heart Transplantation. Introduction: Antiarrhythmic drug refractory recurrent atrial flutter occurred in a 39‐year‐old man who had undergone successful orthotopic heart transplantation 3 months ago. Methods and Results: At electrophysiologic study, the transplanted right atrium showed type I atrial flutter. The recipient right atrium was in sinus rhythm with complete atrioatrial dissociation of electrical activity. Mapping demonstrated double‐spike electrograms in the low posterior region of the donor right atrium. During radiofrequency current application near this site, the double potentials were dissociated progressively and atrial flutter was terminated immediately. Thereafter, both the recipient and the transplanted atria were in sinus rhythm of different cycle lengths with continued electrical dissociation. Conclusion: This is the first report of successful radiofrequency catheter ablation of atrial flutter in a transplanted heart. Although mapping of the arrhythmia is more difficult due to the large circumference of the right atrium, which consists of parts of the recipient right atrium and the transplanted atrium, ablation should be considered in those patients with drug refractory supraventricular tachyarrhythmias.
Arrhythmias Caused by Platelet Activating Factor
Authors: HOFFMAN BRIAN F. , GUO SHI‐DUO , FEINMARK STEVEN J. 
Published: May 2007

Platelet Activating Factor and Arrhythmias. Introduction: Both ischemia and reperfusion are associated with ventricular arrhythmias. In both instances, neutrophils migrate into the ischemic zone, are activated by locally released factors, and hind to myocytes. The activated neutrophils liberate platelet activating factor (PAF). We have studied the arrhythmogenic actions of PAF on transmembrane potentials of isolated canine cardiac myocytes. Methods and Results: Cardiac myocytes were prepared from normal canine hearts by standard methods and studied in vitro by recording transmembrane potentials under control conditions and during exposure to graded doses of PAF, usually 0.25 to 1.25 μg (0.25 to 1.2 μM). Myocytes were superfused with Tyrode's solution (2.0 mL/min), paced at a cycle length of 1000 msec, and maintained at a temperature between 36° and 38°C. PAF caused a consistent and dose‐dependent set of alterations in the transmembrane potential, including increased action potential duration, runs of early afterdepolarizations (EADs), and transient arrest of repolarization (PA). In addition, in some myocytes PAF caused intermittent small depolarizations both at the plateau voltage and resting potential. The effects of PAF were transient: only some residual action potential prolongation was noted after Tyrode's washout for 5 minutes. Effects of PAF were blocked in a dose‐dependent manner by the PAF receptor antagonist, CV‐6209. Both tetrodotoxin (1.2× 10‐6 M)and xylocaine (5 × 10‐5 M) antagonized the ability of PAF to cause EADs and PA. Conclusions: PAF consistently exerts arrhythmogenic effects on the membrane of ventricular myocytes. Since PAF is liberated by activated neutrophils and since activated neutrophils migrate into ischemic myocardium on reperfusion, we judge that PAF liberated by such neutrophils is an important arrhythmogenic factor for reperfusion arrhythmias. The same mechanism may be a cause of arrhythmias during the evolution of infarction.
Effects of High and Low Shock Energies on Sinus Electrograms Recorded via Integrated and True Bipolar Nonthoracotomy Lead Systems
Authors: GOTTLIEB CHARLES D. , SCHWARTZMAN DAVID S. , CALLANS DAVID J. , DILLON STEPHEN M. , MARCHLINSKI FRANCIS E. 
Published: May 2007

Effects of Shock Energies on Electrograms. Introduction: The purpose of this investigation was to prospectively evaluate the voltage‐ and time‐dependent characteristics of a biphasic defibrillator discharge on the amplitude of the rate sensing electrogram recorded from two “integrated” and one true bipolar nonthoracotomy lead system. Prolongation of redetection time has been noted after a failed first shock with nonthoracotomy lead systems. However, prospective evaluation of the time‐ and voltage‐dependent effects of biphasic shocks on electrogram amplitude with clinically utilized lead systems has not been systematically performed. Methods and Results: Five‐ then 30‐J R wave synchronous biphasic discharges were delivered during the supraventricular rhythm through three nonthoracotomy lead systems (Medtronic Transvene, Ventritex TVL, and CPI Endotak C 60 Series). The R wave amplitude was measured immediately postshock and for up to 1 minute. Amplitude changes were compared with reshock baseline value. A 5‐J discharge had minimal effect on the R wave amplitude recorded from the three lead systems; however. 30 J resulted in significant diminution in R wave amplitude recorded from the integrated bipolar leads (in the Endotak lead to a greater extent than the TVL lead) with minimal effects on the Transvene lead. Following a 30‐J discharge, the time constant for R wave recovery was 4.2, 14.9, and 15.3 seconds for Transvene. TVL, and Endotak 60 leads, respectively. Conclusion: There are voltage‐ and time‐dependent reductions in postshock R wave amplitude. Integrated bipolar systems appear more affected than the “true” bipolar lead evaluated. This may he due in part, to lead design, distance of distal defibrillating surface from rate sensing cathode, and the incorporation of the defibrillating surface as the rate sensing anode. The influence of postshock R wave diminution on subsequent redetection remains speculative but may have implications for subsequent lead development.
Management of Ventricular Fibrillation with Transvenous Defibrillators Without Baseline Electrophysiologic Testing or Antiarrhythmic Drugs
Authors: LEE DOLACK G. , POOLE JEANNE E. , KUDENCHUK PETER J. , RAITT MERRITT H. , GLEVA MARYE J. , ANDERSON JILL , TROUTMAN CHARLES , BARDY GUST H. 
Published: May 2007

Tranvenous Defibrillators Without EP Testing. Introduction: Baseline electrophysiologic study (EPS) is routinely performed in patients resuscitated from ventricular fibrillation (VF) to risk stratify and select patients for chronic antiarrhythmic drug therapy. The role of EP testing prior to insertion of a multiprogrammable implantable cardioverter defibrillator (ICD), however, is unclear. Methods and Results: This study was a retrospective review of outcome in 66 survivors of an initial episode of out‐of‐hospital VF not associated with a Q wave myocardial infarction or reversible causes, treated with transvenous ICDs as first‐line therapy. Patients were excluded from the study if they had a previous history of monomorphic ventricular tachycardia (VT), a clinical history suggestive of supraventricular tachycardia, or had undergone preoperative EP testing. Fifty‐two of the patients (79%) were male with an average age of 58 ± 11 years. Coronary artery disease was present in 43 patients (66%), cardiomyopathy in 15 patients (23%), and valvular heart disease in 1 patient (1.5%). Seven patients (11%) had no detectable structural heart disease. The mean left ventricular ejection fraction was 0.40 ± 0.16. With an average follow‐up of 25 ± 12 months, survival free of death from any cause was 100%. Twenty‐three patients (35%) experienced 48 episodes of recurrent rapid VT or VF (average cycle length: 236 ± 47 msec) treated by their device. The mean time to first therapy was 223 ± 200 days. Only one of these patients also received antitachycardia pacing for two episodes of VT. One patient (1. 5%) temporarily received amiodarone after removal of an infected device that was subsequently replaced. No other patient received antiarrhythmic drug therapy. Conclusion: After a cardiac arrest due to primary VF, select patients treated with multiprogrammable ICDs can be managed successfully without baseline EPS or antiarrhythmic drug therapy.
Functional Bundle Branch Block as a Delayed Manifestation of Retrograde Concealment in the His‐Purkinje System
Authors: GONZALEZ‐ZUELGARAY JORGE , SHEIKH SHABBIR , AKHTAR MASOOD , JAZAYERI MOHAMMAD R. 
Published: May 2007

Delayed Manifestation of Retrograde HPS Concealment. Introduction: The mechanism of functional bundle branch block induced at the onset of supraventricular tachycardia (SVT) is well established. However, no data exist to address the underlying mechanism of functional bundle branch block occurring in the second beat of SVT, when the first beat is conducted with a narrow QRS morphology and preceded by ventricular stimulation. Methods and Results: Two patients showing such a phenomenon form the basis of this report. Patient 1 with AV nodal reentrant tachycardia of the common variety persistently demonstrated functional right bundle branch block in the second SVT complex when a short train of ventricular pacing was introduced during SVT. This occurred without any discernible change in the SVT cycle length. Patient 2 bad a manifest posteroseptal accessory pathway and inducible orthodromic reentrant tachycardia. Functional bundle branch block during propagation of the second SVT complex invariably occurred either in the left bundle when SVT was induced by a bundle branch reentrant complex during premature ventricular stimulation, or in the right bundle when SVT was induced with a short train of ventricular pacing. The development of functional bundle branch block was preceded by minimal or no cycle length variations in the His‐bundle inputs. Conclusion: These observations suggest that the type of functional bundle branch block occurring in the second SVT complex as a de novo phenomenon may be related to the relative timing of the retrograde penetration of the right versus left bundle during ventricular pacing or bundle branch reentrant complex. Therefore, due to its longest cycle length of activation and refractoriness, the earliest site of retrograde penetration is the most likely site of functional block during propagation of the second SVT complex. This delayed manifestation of retrograde concealment may provide new information regarding the electrophysiologic behavior of the His‐Purkinje system.
Temperature and Impedance Monitoring During Slow Pathway Ablation in Patients with AV Nodal Reentrant Tachycardia
Authors: STRICKBERGER S. ADAM , ZIVIN ADAM , DAOUD EMILE G. , BOGUN FRANK , HARVEY MARK , GOYAL RAJIVA , NIEBAUER MARK , MAN K. CHIN , MORADY FRED 
Published: May 2007

Slow Pathway Ablation. Introduction: Successful radiofrequency ablation of an accessory pathway has been demonstrated to be associated with an electrode‐tissue interface temperature of approximately 60°C or an impedance change of −5 to −10 Ω. However, the temperature and impedance changes associated with ablation of AV nodal reentrant tachycardia (AVNRT) using the slow pathway approach have not been reported. Therefore, the purpose of this study was to define the temperature and impedance changes achieved during ablation of AVNRT. Methods and Results: The study included 35 consecutive patients with AVNRT undergoing radiofrequency ablation of the slow pathway with a fixed power output of 32 W, and using a catheter with a thermistor bead embedded in the distal 4‐mm electrode. The procedure was successful in each patient. The steady‐state electrode‐tissue interface temperature during successful applications of energy was 48.5 ± 3.3°C (range 42° to 56°C), and the steady‐state temperature during ineffective applications was 46.8°± 5.5°C (P = 0.03). The mean impedance change during all applications of energy was −1.4 ± 2.8 ω, and did not differ significantly during effective and ineffective applications. Coagulum formation resulted during five applications (2.7%) in two patients (5.7%). There were no recurrences during 114 ± 21 days of follow‐up. Conclusions: Successful ablation of AVNRT using fixed power output is achieved at an electrode‐tissue interface temperature of approximately 48°C and is associated with a drop in impedance of 1 to 2 ω. These findings suggest that slow pathway ablation requires less heating at the electrode‐tissue interface than does accessory pathway or AV junction ablation.
Temperature Dependence of Macroscopic L‐Type Calcium Channel Currents in Single Guinea Pig Ventricular Myocytes
Authors: ALLEN T. JEFFREY A. 
Published: May 2007

Calcium Channels and Temperature. Introduction: Lowering temperature greatly reduces calcium influx through calcium channels. Studies on a number of tissues demonstrate that the peak inward current, ICa exhibits Q10 values ranging from 1.8 to 3.5; however, it remains unclear which component(s) of calcium channel gating may give rise to this large temperature sensitivity. Components of gating that may affect channel availability include phosphorylation and changes in [Ca2+)i, processes that vary in pertinence depending on the channel examined. This study addresses this problem by examining the temperature sensitivity (from 34° to 14°C) of cardiac ICa under control conditions, during attenuation or activation of protein kinase A (PKA) activity, and when intracellular [Ca2+] has been elevated. Methods and Results: ICa was studied using the whole cell configuration of the patch clamp technique. In control, lowering temperature from 34° to 24°C resulted in a shift in the potential for maximum slope (Va and the peak current (Ymax) toward more positive membrane potentials. The Q10, values for the decrease in Ymax and the macroscopic slope conductance (Gmax), which reflects the number of available channels, were 3.15 ± 0.19 and 2.57 ± 0.13, respectively. At 0 mV the Ca2+ current decayed biexponentially, and the two time constants (T1 and T2) showed Q10 values of 1.79 ± 0.21 and 2.06 ± 038, while their contribution to the total current (I1 and I2) showed a Q10 of 5.99 ± 0.83 and 1.61 ± 0.22. In myocytes loaded with inhibitors of the PKA cycle sufficient to inhibit the increase of ICa to 1 μM isoprenaline, the Q10 values for some of the kinetic parameters were increased with the Q10 for I1 increasing to 17.06 ± 3.48. Stimulation of ICa by exposing myocytes to 1 μM isoprenaline reduced the temperature sensitivity of Ymax, Gmax, and I1, yielding respective values of 2.00 ± 0.18, 1.85 ± 0.07, and 2.04 ± 0.15. Raising [Ca2+], to enhance Ca2+i‐dependent inactivation, while affecting inactivation and activation kinetics, affected temperature sensitivity little compared to control. The Q10 for time to peak changed little under experimental conditions (2.3 to 2.4) Conclusions: Increasing the phosphorylated states of calcium channels, but not Ca2+i‐dependent inactivation, reduces temperature sensitivity of certain gating parameters. The data suggest that the rate of the transitions between the unavailable and also between the various closed states are changed in the opposite direction to that induced by PKA‐dependent phosphorylation. Processes, e.g., inhibitory mechanisms, may be involved to maintain channels in unavailable or “unphosphorylated” states, and it may he these that contribute to the high Q10 of macroscopic channel currents.
Early Postoperative Rise in Defibrillation Threshold in Patients with Nonthoracotomy Defibrillation Lead Systems:
Authors: SCHWARTZMAN DAVID , CALLANS DAVID J. , GOTTLIEB CHARLES D. , HEO JAEKYEONG , MARCHLINSKI FRANCIS E. 
Published: May 2007

DFT Rise with Nonthoracotomy Lead Systems. introduction: In patients with nonthoracotomy defibrillation lead (NTL) systems coupled with monophasic shock waveforms, the defibrillation threshold (DFT) rises early after implantation. There is little information regarding features predictive of the DFT rise, or DFT changes early after implantation of NTL systems coupled with biphasic shock waveforms. Methods and Results: DFT measurements were performed serially at implantation, prior to hospital discharge (mean 4 ± 3 days), and at follow‐up (mean 49 ± 22 days) in 146 patients with an NTL system. Factors were assessed for association with a “clinically important” early postimplantation DFT rise, defined as a rise of ≥ 2 energy steps (2 to 4 J per step; ≥ 5 J total). A clinically important early postimplantation DFT rise occurred in 48 patients (33%). Univariate predictors of the rise included the monophasic shock waveform, the Medtronic Transvene lead system, the presence of a subcutaneous defibrillation patch, and the number of shocks delivered during the implantation procedure. However, the only independent predictor of a clinically important DFT rise was the monophasic shock waveform (F = 18, P < 0.001). For the monophasic patient group (n = 79), the incidence of a DFT rise was 53% (n = 42). For the biphasic patient group (n = 67), the incidence of a DFT rise was 9% (n = 6). The clinical characteristics of the monophasic and biphasic groups were not significantly different, nor were their DFTs at implantation. Among a subgroup of 18 consecutive patients who underwent serial DFT testing utilizing both monophasic and biphasic waveforms, the incidence of a clinically important DFT rise with monophasic (n = 9, 50%) was higher than with biphasic shocks (n = 3, 17%; P = 0.05). Conclusion: NTL systems coupled with biphasic shock waveforms have an attenuated incidence of a clinically important DFT rise early after implantation, relative to patients with NTL systems coupled to monophasic waveforms.
A New Technique to Perform Epicardial Mapping in the Electrophysiology Laboratory
Authors: SOSA EDUARDO , SCANAVACCA MAURICIO , D'AVILA ANDRÉ , PILLEGGI EÚLVIO 
Published: May 2007

Epicardial Mapping. Introduction: A possible epicardial site of origin may be the reason for unsuccessful endocardial application of radiofrequency energy to control recurrent ventricular tachycardia. This study tests the feasibility and safety of a new epicardial mapping technique in patients with Chagas’ disease and recurrent ventricular tachycardia. Methods and Results: Epicardial mapping was performed through a pericardial puncture as an epidural introducer needle was advanced into the pericardial space under fluoroscopic guidance. Medium contrast was injected to demonstrate the position of the needle tip, and a guidewire was introduced until its tip lay within the pericardial space. A 8‐French Hemaquet was advanced and 4‐mm deflectable tip catheter introduced into the pericardial sac to map the right and left ventricular epicardium. Transthoracic echocardiographic monitoring was performed on the day of the procedure and on the day of hospital discharge. The pericardial space was reached in all patients with no complications. Electrophysiologic data suggesting the existence of an epicardial circuit was found in one patient. No complications occurred during the hospitalization period. Conclusion: Epicardial mapping can be safely performed through a pericardial puncture in the electrophysiology laboratory.