bluuebunny/crossref_metadata_2025_split huggingface dataset:
Postshock Sensing Performance in Transvenous Defibrillation Lead Systems: Analysis of Detection and Redetection of Ventricular Fibrillation
Authors: CALLANS DAVID J. , SWARNA UDAYA S. , SCHWARTZMAN DAVID , GOTTLIEB CHARLES D. , MARCHLINSKI FRANCIS E. 
Published: May 2007

Postshock Sensing in Transvenous Lead Systems. Introduction: The sensing performance of transvenous lead systems may be adversely affected by the delivery of high‐energy shocks. This may be due to the proximity of the sensing and energy‐delivery electrodes on transvenous leads. Methods and Results: The time required for detection of ventricular fibrillation and redetection after a failed first shock was compared in 93 patients with five different lead system‐pulse generator combinations: CadenceTM ‐ EndotakTM 60 series, Ventak PTM ‐ EndotakTM 60 series, JewelTM ‐ TransveneTM, CadenceTM ‐ TVLTM, and CadenceTM ‐ TransveneTM. A total of 418 successful and 204 failed first shocks were delivered during induced ventricular fibrillation. Redetection times (RED) were consistently shorter than detection times (DET) in the Jewel‐Transvene (RED minus DET: 1.9 ± 0.8 sec, P < 0.0001), the Cadence‐TVL (‐1.6 ± l.0sec, P < 0.0001), and the Cadence‐Transvene combinations (‐2.0 ± 0.9 sec, P < 0.0004). Redetection times were not significantly different than detection times in the Cadence‐Endotak combination (‐0.9 ± 3.1 sec; P = 0.09). Redetection times were significantly longer than detection times in the Ventak‐Endotak combination (1.2 ± 2.3 sec; P = 0.034). Prolonged individual redetection episodes (> 8.2 sec) were observed in the Cadence‐Endotak (7 [10%] of 73 episodes) and the Ventak‐Endotak (4 [10%] of 39 episodes), but not in the Jewel‐Transvene, the Cadence‐TVL, and the Cadence‐Transvene combinations. Conclusions: Redetection of ventricular fibrillation may be delayed in some transvenous lead‐pulse generator combinations. Successful redetection of ventricular fibrillation following a failed first shock should be demonstrated prior to hospital discharge of patients with implantable defibrillators.
The Effect of Radiofrequency Catheter Ablation on Myocardial Creatine Kinase Activity
Authors: HAINES DAVID E. , WHAYNE JAMES G. , WALKER JEFFERY , NATH SUNIL , BRUNS DAVID E. 
Published: May 2007

RF Ablation and Creatine Kinase. Introduction: The primary mechanism of myocardial injury during radiofrequency (RF) catheter ablation in the heart is presumed to be thermal. Creatine Kinase has been measured in serum to assess the volume of myocardial injury after ablation. However, its thermal inactivation by RF ablation could lead to underestimation of the true volume of injury. Methods and Results: Serial RF lesions were created in 10 canine left ventricles in vivo, and serial serum Creatine Kinase activities were measured and compared to lesion volume. To assess the stability of myocardial Creatine Kinase during RF catheter ablation, 29 RF ablations were made on the epicardial surface of porcine left ventricle in vivo and a 2‐mm core biopsy was rapidly removed. The cores were rapidly frozen, sectioned longitudinally in 1‐mm slices, and homogenized in 0.3 M Tris buffer solution containing EDTA and dithiothreitol for subsequent analysis of Creatine Kinase activity. An additional 19 tissue cores from RF lesions were stained and used to determine mean lesion depth. Normal tissue biopsies were exposed to 60 seconds of hyperthermia (37° to 85°C, n = 190), or high‐density RF current at 50X (0 to 100 mA/mm2, n = 50), and tissue Creatine Kinase activity was measured. There was no evidence of Creatine Kinase washout within the first 2 hours, and peak values were measured 5 to 7 hours postablation. Tissue Creatine Kinase activity in the first mm depth of RF lesions averaged 10% of control values and increased over the first 5 mm of lesion depth. The mean Creatine Kinase activity within the hemisphere of ablated myocardium was calculated to be 31% of control. Creatine Kinase activity declined significantly at temperatures above 65°C, but no difference in tissue Creatine Kinase activity was observed among differing levels of RF current exposure in the absence of significant heating. Conclusions: Creatine Kinase activity in myocardial tissue is significantly diminished within the RF lesion. Creatine Kinase activity is not stable at temperatures above 65°C, which are routinely achieved within the central zone of RF ablation, and is unaffected by RF current in the absence of hyperthermia. Measurements of serum Creatine Kinase activity after RF catheter ablation may significantly underestimate the volume of myocardial injury.
Modeling the Interaction Between Propagating Cardiac Waves and Monophasic and Biphasic Field Stimuli:
Authors: FISHLER MATTHEW G. , SOBIE ERIC A. , TUNG LESLIE , THAKOR NITISH V. 
Published: May 2007

Field‐Induced Excitatory Responses Across Propagating Waves. Introduction: Biphasic (BP) defibrillation waveforms have been shown to be significantly more efficacious than equivalent monophasic (MP) waveforms. However, when defibrillation falls, it tends to do so first in distal regions of the heart where induced field gradient magnitudes are lowest. We tested the hypothesis that the improved efficacy of BP waveforms results from their enhanced ability to prevent the initiation of new postshock activation fronts behind preexisting; wavetails, rather than from any significantly improved ability to terminate preexisting wavefronts. Methods and Results: An idealized computer model of a one‐dimensional cardiac strand was used to investigate the spatial and temporal interactions between an underlying propagation front (or tail) and uniform MP or BP field stimuli of various intensities. Axial discontinuities from intercellular junctions induced sawtooth patterns of polarization during such field stimuli, enabling the shocks to interact directly with all cells. MP and BP diastolic thresholds were essentially equal. All suprathreshold MP and BP field stimuli successfully terminated preexisting wavefronts by directly depolarizing tissue ahead of those fronts, thus blocking their continued progression. However, the postshock response at the wavetail was significantly dependent on the shape and strength of the administered field. Low‐strength MP stimuli induced an all‐or‐none excitation response across the wavetail, producing a sharp spatial transmembrane voltage gradient from which a new sustained anterogradely propagating wavefront was initiated. In contrast, low‐strength BP field stimuli induced a spatially graded excitatory response whose voltage gradient was insufficient to initiate such a wavefront. Higher‐strength MP and BP stimuli both produced graded excitatory responses with no subsequent propagation. Conclusions: Shock‐induced spatial “all‐or‐none” excitatory responses facilitate, and graded excitatory responses prevent, the postshock initiation of new propagating wavefronts. Moreover, BP field stimuli can induce such graded excitatory responses at significantly lower stimulus strengths than otherwise equivalent MP stimuli. Therefore, these results support an alternative “graded excitatory response” mechanism for the improved efficacy of BP over MP field stimuli in low gradient regions.
Antiarrhythmic and Electrophysiologic Effects of Intravenous Ibutilide and Sotaloi in the Canine Sterile Pericarditis Model
Authors: BUCHANAN LEWIS V. , Le May RICHELLE J. , WALTERS RODNEY R. , HSU CHANG‐YUAN L. , BRUNDEN MARSHAL N. , GIBSON JOHN K. 
Published: May 2007

Ibutilide, Sotalol, and Atrial Flutter. Introduction: Atrial arrhythmias are a frequent clinical complication following open heart surgery. We compared the Class III agents d,I‐sotalol and ibutilide fumarate in an intravenous cross‐over study using the canine atrial sterile pericarditis model. Methods and Results: We studied pacing‐induced sustained atrial flutter over a 7‐day post‐surgical period in conscious dogs, alternating analysis of ibutilide (1.0 to 30.0 μg/kg) and d,I‐sotalol (0.1 to 3.0 mg/kg). Ibutilide significantly increased atrial flutter cycle length (AFL CL) II ± 2 msec and atrial effective refractory period (AERP) 13 ± 2 msec, and terminated atrial flutter in all cases (n = 12) following a mean dose of 6 ± 2 μg/kg. Plasma concentrations of ibutilide were 53 ± 13 ng/mL. Ventricular effective refractory period (VERP) was not signiflcantly affected (4 ± 2 msec). Following termination with ibutilide, atrial flutter could he reinitiated in 1 of 12 trials, and was nonsustained (40‐sec duration). Sotalol significantly increased AFL CL 23 ± 3 msec and terminated atrial flutter in 8 of 12 trials following a mean dose of 1.5 ± 0.4 mg/kg. AERP and VERP were significantly increased 20 ± 6 and 12 ± 2 msec, respectively. The incidence of reinduced atrial flutter was 9 of 12 trials (P ≥ 0.05 vs ibutilide) (7 nonsustained 57 ± 7 sec duration, and 2 sustained). Sotalol failed to terminate atrial flutter in two dogs on days 1 and 5, despite increases in AFL CL (21 ± 8 msec) and AERP (16 ± 9 msec), whereas on day 3, ibutilide (20 ± 7 μg/kg) terminated atrial flutter in those two dogs while increasing AFL CL and AERP 18 ± 6 and 15 ± 0 msec, respectively. Conclusion: Both sotalol and ibutilide terminate atrial flutter in this model. Ibutilide converted atrial flutter in dogs in which sotalol was not successful. Following atrial flutter termination, ibutilide had a lower incidence of reinduced arrhythmias compared to sotalol. Ibutilide produced atrial antiarrhythmic effects while having no significant electrophysiologic effects on the ventricle.
Cardiac Output Is Not Affected During Intraoperative Testing of the Automatic Implantable Cardioverter Defibrillator
Authors: MEYER JÖRG , MÖLLHOFF THOMAS , SEIFERT THOMAS , BRUNN JÜREN , RÖTKER JÜRGEN , BLOCK MICHAEL , PRIEN THOMAS 
Published: May 2007

Cardiac Output and ICD Implantation. Introduction: Perioperative mortality of patients undergoing implantation of automatic implantable cardioverter defibrillators (ICDs) has been reduced dramatically following the availibility of trans venous‐subcutaneous defibrillation leads. However, patients with severely reduced left ventricular function show a substantial rate of nonsudden cardiac mortality within the first year. Whether repeated intraoperative inductions of ventricular tachycardia/fibrillation (VT/VF) during implantation lead to hemodynamic deterioration and thus might contribute to development of end‐stage heart failure in these patients is unknown. The purpose of the present study was to determine cardiac output and hemodynamic performance during transvenous‐subcutaneous ICD implantation in patients with severe left ventricular dysfunction. Methods and Results: In 11 patients with a left ventricular ejection fraction (EF) ≤ 0.35, cardiac output was measured automatically with a combined continuous cardiac output/mixed venous oxygen saturation pulmonary artery catheter system. ICD implantation was performed during standardized general anesthesia. In the 11 patients (EF = 27 ± 2% [mean ± SEM]) a total of 95 episodes of VT/VF followed by defibrillation were induced (epsiodes per patient = 9 ± 1; range 6 to 11). Cardiac index was 2.2 ± 0.2 L·min‐1·min‐2 after induction of anesthesia (before start of surgery), and 1.9 ± 0.1 L·min‐1·m‐2 immediately before first induction of VT/VF. After the last episode of VT/VF, cardiac index was 2.1 ± 0.2 L·min‐1·m‐2. Cardiac index measured 1, 2, and 3 minutes after induction of VT/VF was not significantly different when compared to the preinduction value during any episode of VT/VF induction. Similarly, stroke volume index was 39 ± 5 mL·m‐2 immediately before first induction of VT/VF and 36 ± 3 mL·m‐2 after the last episode of VT/VF (NS). At the end of surgery, hemodynamic parameters did not exhibit any significant difference when compared to the data obtained before start of ICD implantation and testing. Conclusion: Extensive defibrillation tests during transvenous‐subcutaneous ICD implantation in patients with severe left ventricular dysfunction are not associated with acute deterioration of cardiac performance.
Radiofrequency Catheter Ablation of the Left Bundle Branch in a Canine Model
Authors: HELGUERA MARCELO E. , TROHMAN RICHARD G. , TCHOU PATRICK J. 
Published: May 2007

Left Bundle Branch Ablation. Introduction: Transcatheter ablation of the left bundle branch may be considered for management of selected macroreentrant ventricular tachycardias. Left bundle ablation can also change the sequence of left ventricular contraction and may simulate pacing in hypertrophic obstructive cardiomyopathy. The purpose of this study was to determine electrophysiologic and anatomic parameters for successful selective transcatheter left bundle ablation in a canine model. Methods and Results: A catheter was advanced to the left ventricular apex and the tip deflected toward the septum, until a discrete left bundle potential (LBP) was found. Radiofrequency (RF) energy was then applied until left bundle branch block or complete AV block occurred. In 29 (85%) dogs, an LBP (mean LBP‐V 16 ± 3 msec; range 10 to 20 msec) was identified resulting in successful left bundle ablation. In 5 (15%) dogs, a similar potential (mean potential‐V 28 ± 4 msec; P = 0.001 vs LBP‐V) was identified, but RF energy application produced complete AV block. The A:V electrogram ratio at the successful LBP ablation site was < 1:10 in all 29 dogs successfully ablated, but only 2 (40%) of 5 dogs in the unsuccessful group (P = 0.0017). In 4 successfully ablated dogs, the right bundle potential was mapped and complete AV block was created by RF energy application, confirming that the left bundle was completely ablated. In 9 dogs, the left bundle and AV junction were sequentially ablated with 1 lesion at each site. Postmortem examination showed 2 discrete lesions 1.2 ± 0.7 cm apart. Conclusions: Selective transcatheter left bundle ablation was successfully guided by the LBP. The distance between the AV junction and the main left bundle was 1.2 cm in this canine model. An A:V ratio < 1:10 and an LBP‐V time < 20 msec appear to minimize the risk of AV block. Prudent use of similar techniques may cure macroreentrant ventricular tachycardias and reduce the need for permanent pacing in hypertrophic obstructive cardiomyopathy.
Activation and Repolarization Patterns are Governed by Different Structural Characteristics of Ventricular Myocardium:
Authors: EFIMOV IGOR R. , ERMENTROUT BARD , HUANG DAVID T. , SALAMA GUY 
Published: May 2007

Activation and Repolarization Patterns. Introduction: Substantial progress has been made in our understanding of transmural activation across ventricular muscle through studies of excitation patterns and potential distributions. In contrast, repolarization sequences are poorly understood because of experimental difficulties in mapping action potential durations (APDs) using extracellular electrodes. Methods and Results: Langendorff‐perfused guinea pig hearts and isolated coronaryperfused left ventricular sheet preparations were stained with the voltage‐sensitive dye RH‐421 and optical APs were recorded with a photodiode array. Epicardial maps were constructed using a triangulation method applied to matrices of activation and repolarization times determined from (dF/dt)max and (d2F/dt2)max′ respectively. Numerical simulations were carried out based on: (1) a modified Luo‐Rudy model; (2) the three‐dimensional architecture of ventricular fibers; and (3) the intrinsic spatial distribution of APDs. In ventricular sheets, epicardial stimulation elicited elliptical activation patterns with the major axis aligned with the longitudinal axis of epicardial fibers. When the pacing electrode was progressively inserted from epicardium to endocardium, the major axes rotated gradually, clockwise by 45°, and the eccentricity decreased from 2 to 1.14. Repolarization showed a relatively uniform pattern, independent of pacing site, beginning at the apex and spreading to the base. Conclusion: In experiments and simulations, the helical rotation of epicardial excitation isochrones caused by pacing at increasing depth in the myocardium correlated with the helical three‐dimensional architecture of ventricular fibers. In contrast, repolarization was independent of the activation sequence and was mainly guided by spatial differences in APDs between apex and base.
Serial Defibrillation Lead Impedance in Patients with Epicardial and Nonthoracotomy Lead Systems
Authors: SCHWARTZMAN DAVID , HULL MICHAEL L. , CALLANS DAVID J. , GOTTLIEB CHARLES D. , MARCHLINSKI ERANCIS E. 
Published: May 2007

Lead Impedance in ICDs. Introduction: The stability of implantable cardiac defibrillation lead impedance subsequent to implantation has not been reported and may have important clinical implications. The objective was to characterize the incidence and degree of impedance changes occurring after implantation of defibrillation lead systems. Methods and Results: The study cohort consisted of patients who received epicardial or nonthoracotomy lead systems. Defibrillation impedance was recorded at implantation, prior to hospital discharge (predischarge), and during follow‐up. For each individual the magnitude of the impedance change relative to implantation was characterized. Among patients with an epicardial system, a significant decrease in impedance was observed at predischarge (mean 9.3 Ω). The magnitude of the decrease was large in 39% and moderate in 31% of individuals. Subsequently, a gradual rise in mean impedance was apparent. At 18–21 months postimplantation, impedance was significantly increased relative to implantation (mean 6.8 ω). At this time, the magnitude of the increase was large in 46% and moderate in 23% of patients. Among patients with a nonthoracotomy lead system including a subcutaneous patch, a significant decrease in mean impedance was observed at predischarge (mean 3.5 ω). The magnitude of the decrease was large in 8% and moderate in 50% of individuals. Subsequently, a gradual rise in impedance was apparent. At 5–6 months, it was significantly increased relative to implantation (mean 2.3 ω). The magnitude of the increase was large in 10% and moderate in 33% of patients. Among the group of patients whose nonthoracotomy lead system did not include a subcutaneous patch, there was no significant change in mean impedance at predischarge relative to implantation. In subsequent intervals, a gradual rise was apparent. At 5–6 months, impedance was significantly increased relative to implantation (mean 4.3 ω). The magnitude of the increase was large in 16% and moderate in 47% of individuals. Conclusion: Significant changes in defibrillation lead impedance occur after implantation of epicardial and nonthoracotomy defibrillation lead systems. These data may serve as a standard for identifying the anticipated maximum change in lead impedance and thus may be useful as a tool for recognizing problems with defibrillation lead integrity.
Mechanisms of Recurrent Atrial Fibrillation: Comparisons Between Segmental Ostial Versus Circumferential Pulmonary Vein Isolation
Authors: LO LI‐WEI , TAI CHING‐TAI , LIN YENN‐JIANG , CHANG SHIH‐LIN , WONGCHAROEN WANWARANG , HSIEH MING‐HSIUNG , TUAN TA‐CHUAN , UDYAVAR AMEYA R. , HU YU‐FENG , CHEN YI‐JEN , TSAO HSUAN‐MING , CHEN SHIH‐ANN 
Published: May 2007

Background: Electrical isolation of pulmonary veins (PVs) is an effective therapy for atrial fibrillation (AF). Both segmental ostial PV ablation and circumferential ablation with PV–left atrial (LA) block have been implicated to eliminate AF. However, the mechanism of the recurrent AF after undergoing either strategy remains unclear. Methods and Results: Of the 73 consecutive patients with symptomatic AF that underwent PV isolation and had recurrences of AF, Group 1 consisted of 46 patients (age 56 ± 13 years old, 35 males) who underwent PV isolation by segmental ostial PV ablation and Group 2 consisted of 27 patients (age 51 ± 11 years old, 24 males) who underwent circumferential ablation with PV–LA block. In Group 1, the earliest ectopic beat or ostial PV potentials were targeted. In Group 2, circumferential ablation with PV–LA block was performed by encircling the extraostial regions around the left and right PVs. During the first procedure, all patients had PV–AF. There was no difference in the non‐PV ectopy between Group 1 and Group 2. During the second procedure, the incidence of an LA posterior wall ectopy initiating AF was significantly lower (20% vs. 0%, P = 0.01) in Group 2. There was no difference in the PV ectopy initiating AF during the second procedure. Conclusion: Circumferential ablation of AF with PV–LA block may eliminate the LA posterior wall ectopy and decrease the incidence of LA posterior wall ectopy initiating AF during the second procedure.
Effects of Certain Metal Ions on Growth of Tetrahymena pyriformis
Authors: HALL R. P. 
Published: May 2007

Growth of Tetrahymena pyriformis in a peptone medium is inhibited slightly to extensively by comparable concentrations of oxalate, citrate, and ethylenediaminetetraacetic acid (in ascending order). Single additions of Ca, Cu, Zn, and Mg, in increasing order of effectiveness, reversed citrate inhibition. EDTA inhibition was completely reversed by single additions of Ca or of certain other metals (Al, Co, Cu, Fe, Mn, Ni, Zn) forming more stable EDTA complexes. Reversal by added Mg was slight. The data suggest physiological importance of Ca for T. pyriformis.Pre‐treatment of peptone solution with a cation exchanger (Natrinil) resulted in little or no growth; growth was restored almost to normal by the addition of Mg. The growth‐response showed a linear relationship to quantity of Mg.
The Effects of Ethanol on Conjugation and Division in Paramecium caudatum*
Authors: PACE DONALD M. , HOAGLAND ROBERT A. 
Published: May 2007

The effects of ethanol on conjugation and division in Paramecium caudatum were studied in six concentrations ranging from 0.001M to 0.5M, over a period of 72 hours.A marked increase in the number of conjugants was noted in concentrations between 0.001M and 0.05M alcohol, especially during the first 48 hours of exposure. The optimum concentration for conjugation was 0.005M at which there were 439% more conjugants than in the control.Division also increased in the same alcohol concentrations that caused increase in conjugation. The optimum concentration for division was 0.005M. This stimulating effect of alcohol on division reached its peak within the first 24 hours.
Further Studies in the Chemotherapy of Plasmodium hexamerium Infections in Ducks
Authors: MANWELL REGINALD D. , KHABIR PARVIZ A. 
Published: May 2007

Five standard antimalarial drugs have been tested, in the present study, against trophozoite‐induced Plasmodium hexamerium infections in ducks; namely, chloroquine, proguanil (paludrine), pyrimethamine (daraprim), pentaquine and isopentaquine. (Four others were used previously.) Two doses daily were given for a treatment period of 7 days. The effectiveness of treatment was measured in terms of its ability to suppress parasitemia and to completely prevent relapse (i.e. to achieve sterilization). Of the five drugs, the two pentaquines were about equally effective. They rapidly cleared the blood of parasites, and completely aborted the infection in nearly all cases. The other three drugs failed to sterilize any of the cases treated, and were not even effective as suppressants.The pentaquines, however, proved quite toxic to the host and, even in the dosages used, retarded the normal rate of weight gain. Pyrimethamine had a similar effect, and in addition interfered with normal feathering. Neither of these effects, whether due to pentaquines or pyrimethamine, was recovered from after treatment stopped.