bluuebunny/crossref_metadata_2025_split huggingface dataset:
Double‐Pulse Defibrillation Using Pulse Separation Based on the Fibrillation Cycle Length
Authors: SWEENEY ROBERT J. , GILL ROBERT M. , REID PHILIP R. 
Published: May 2007

Double‐Pulse Defibrillation Using FCL, Introduction: We investigated a method of defibrillation in which two shocks were delivered to the same electrodes with a separation hazed on the cycle length of the fibrillation event (FCL). Methods and Results: In pentobarbital anesthetized dogs, a computerized system determined the FCL from the fibrillation event, computed the desired double‐pulse (DP) shock separation, and immediately delivered the DP shocks. In group 1, energy for 50% success at defibrillation (E50) was measured using separations from 55% to 95% of the FCL and remeasured after administration of flecainide, clofilium, or vehicle to change the FCL. Both drugs increased 1(1 by = 25%. Plots of E50 versus %FCL aligned before and after drug showed that the optimum pulse separation followed the FCL. In group 2, E50s were measured for 55% to 185% FCL separations in clofilium or vehicle‐treated animals. The optimum DP £50 was at 85% FCL and was not significantly different from the single‐shock E50. In group 3, no differences were found when comparing the probability of success versus total energy relationships for single and optimum DP shocks. Group 4 compared E50s for single and DP shocks using a single‐catheter configuration and three‐electrode configurations (catheter‐subdermal patch). E50s for single and DP shocks were equal using the single‐catheter configuration but DP shocks required = 20% more energy in the three‐electrode configurations. Conclusion: In single‐pathway lead configurations, two shocks with 85% FCL separation can be reliably combined to defibrillate using the same total energy as a larger single shock. Since the energy is unchanged but the total duration is doubled, DP shock currents are reduced by 20% to 30%.
Tachycardia‐Induced Cardiomyopathy in a Cardiac Transplant Recipient: Treatment with Radiofrequency Catheter Ablation
Authors: OTT PETER , KELLY PATRICIA A. , MANN DAVID E. , DAMLE ROGER S. , REITER MICHAEL J. , LINDENFELD JoANN 
Published: May 2007

Tachycardia‐Induced Cardiomyopathy. Introduction: Two years after orthotopic cardiac transplantation, a 60‐year‐old man presented with unexplained congestive heart failure and an incessant atrial tachycardia. Methods and Results: Electrophysiologic evaluation identified the underlying arrhythmia as automatic atrial tachycardia with site of origin at the high anterior lateral right atrial wall. Radiofrequency catheter ablation successfully eliminated the tachycardia, which resulted in prompt improvement of this patient's congestive heart failure. Conclusion: This is the first reported case of tachycardia‐induced cardiomyopathy in a cardiac transplant patient. Radiofrequency catheter ablation can he used successfully in this patient population.
Histologic Evolution of Radiofrequency Lesions in an Old Human Myocardial Infarct Causing Ventricular Tachycardia
Authors: BARTLETT THOMAS G. , MITCHELL RICHARD , FRIEDMAN PETER L. , STEVENSON WILLIAM G. 
Published: May 2007

Histology of RF Lesions. Introduction: Radiofrequency (RF) ablation of ventricular tachycardia (VT) late after myocardial infarction may be difficult due to characteristics of the infarct containing the reentry circuit. RF lesions in these infarcts in humans have not been characterized. Methods and Results: Catheter mapping and ablation of VT originating from an anterior wall infarct was performed 8 days and again 12 hours prior to death. Pacing identified a region of abnormal conduction where RF ablation terminated VT. This region contained strips of myocytes sandwiched between endocardial fibrosis and dense scar. RF lesions ranged from 2 × 2 mm to 5 × 10 mm and were up to 3 mm in depth. Acute lesions showed superficial thrombus and early coagulation necrosis without inflammation. Older lesions showed coagulation necrosis, sparse neutrophil infiltrate, minimal granulation tissue, hemorrhage, and mixed inflammatory infiltrate along the lumen without re‐endothelialization. Conclusion: In this patient, RF lesions had sufficient depth but not width to interrupt the thin, but potentially broad, sheets of myocytes in the reentry circuit. In thinned areas, RF lesions can extend to the epicardium. Selecting sites with abnormal electrograms confines RF lesions to the infarct region. Inflammation and hemorrhage could conceivably cause delayed effects of RF.
A Randomized, Double‐Blind, Placebo‐Controlled, Dose‐Ranging Study of Dofetilide in Patients with Inducible Sustained Ventricular Tachyarrhythmias
Authors: ECHT DEBRA S. , LEE JOHN T. , MURRAY KATHERINE T. , VORPERIAN VICKEN , BORGANEELI S. MARCUS , CRAWFORD DIANE M. , FRIEDRICH TIEMAN , RODEN DAN M. 
Published: May 2007

Dofetilide and Ventricular Tachyarrhythmias. Introduction: Dofetilide is a new antiarrhythmic agent with potent Ik blocking properties in vitro. We developed a dose‐ranging, placebo‐controlled study design to define the range of effective doses and to evaluate the clinical electrophysiology of intravenous dofetilide in patients in whom sustained ventricular tachycardia or fibrillation was reproducibly inducible at baseline electrophysiologic testing. Methods and Results: The initial four patients received low doses that were increased in subsequent groups of four if adverse effects were absent. In each group of four patients, one patient was randomly assigned to placebo (double blind). Twenty‐four patients were studied at six incremental loading and maintenance infusion regimens. Dofetilide (0.1 to 8.0 ng/ml.) produced concentration‐related increases in the %δ of QT (r = 0.79, P <0.001). QTc (r = 0.60, P =0.02), RR (r = 0.62, P < 0.02), and right ventricular effective refractory period (cycle length 600 msec; r = 0.68, P = 0.04). Placebo produced no changes in any of these measurements. Sustained ventricular tachycardia or ventricular fibrillation was no longer inducible in 1 of 6 patients receiving placebo and 8 of 18 receiving dofetilide (4 to 13 sec nonsustained ventricular tachycardia was induced in 4 of these 8). One patient developed torsades de pointes at a high concentration (5.3 ng/mL). Conclusions: We conclude that: (1) dofetilide produces concentration‐related Ig blocking effects in patients: (2) an incremental dose‐ranging study design aids in identifying the range of doses demonstrating electrophysiologic effects and efficacy; (3) a concomitant placebo group provides important data to assess reproducibility of results over time; and (4) further studies of dofetilide's efficacy and toxicity should be conducted.
Nonuniform Heating Patterns of Commercial Electrodes for Radiofrequency Catheter Ablation
Authors: MIROTZNIK MARK S. , SCHWARTZMAN DAVID 
Published: May 2007

Heating Patterns of Ablation Electrodes. Introduction: Previous investigations of the biophysics of myocardial ablation using radiofrequency energy have focused mainly on the electrode‐myocardial interface. Relatively little has been written about the overall function of commercial electrodes used for ablation. The purpose of this study was to evaluate the heating patterns of several commercial electrodes used for myocardial ablation. Methods and Results: The specific absorption rate, a unit of measure proportional to the initial rate of rise of the temperature at the electrode‐tissue interface and reflecting the energy deposition from the electrode, was measured during radiofrequency energy application at multiple points around each electrode. These measurements were combined to form a specific absorption rate pattern, which reflected the spatial pattern of energy deposition from the electrode. There was significant nonuniformity of the specific absorption rate pattern of each electrode evaluated. The proximal edge of the electrode and the curvature of the distal portion of the electrode were two sites of accentuated heating relative to the remaining portions of the electrode. The magnitude of this nonuniformity was similar between the 4‐mni length electrodes of different manufacturers, but increased progressively in larger (5‐ and 8‐mm length) electrodes. Conclusions: The heating patterns of commercial electrodes used for myocardial ablation are nonuniform. These data have implications for electrode design and utilization.
Lidocaine and Nisoldipine Attenuate Almokalant‐Induced Dispersion of Repolarization and Early Afterdepolarizations In Vitro
Authors: ABRAHAMSSON CHRISTINA , CARLSSON LEIF , DUKER GÖRAN 
Published: May 2007

Attenuation of Almokalant‐Induced Proarrhythmias In Vitro. Introduction: Treatment with Class III antiarrhythmic agents may lead to increased dispersion or repolarization and early afterdepolarizations (EADs), which are both likely substrates for torsades de pointes. Recent studies in vivo have shown that the prevalence of proarrhythmias induced by Class III agents may be reduced by Na+ or Ca2+‐blocking agents. In the present study, tentative mechanisms for this protective effect were investigated in vitro. Methods and Results: Transmembrane action potentials were recorded simultaneously from rabbit isolated ventricular muscle (VM) and Purkinje fibers (PF). At a basic cycle length (BCL) of 500 msec, the Class III agent almokalant (0.1 μM) increased the dispersion by prolonging the action potential duration (APD) significantly more in the PF (33%± 4.2%, n = 18) than in the VM (17%± 5.9%, n = 18. P < 0.05). In six of the preparations, addition of 1, 5, and 25 μM lidocaine reduced the almokalant‐induced prolongation in a concentration‐dependent manner mainly in the PF, thereby decreasing the dispersion. At 5 μM lidocaine, the remaining prolongation was 7%± 12.2% (P < 0.05 vs time controls) in the PF and 14%± 6.4% in the VM, respectively. In six other preparations, the addition of 0.01, 0.05, and 0.25 μM nisoldipine did not reduce the almokalant‐induced prolongation in the PF and VM, hut attenuated the spike‐and‐dome appearance of the action potential in the PF. In separate experiments performed at a BCL of 1000 msec, EADs developed in 2 of 6 and 5 of 6 PF during superfusion with almokalant (0.3 and 1 μM, respectively) at an API) of 828 ± 41.4 msec. In six separate preparations pretreated with lidocaine (5 μ) the almokalant‐induced prolongation in the PF was less pronounced and EADs were not observed. Pretreatment with nisoldipine (0.05 μM) did not influence the response to almokalant, and in 4 of 6 preparations the APD exceeded 1000 msec. Despite this extensive prolongation, EADs did not appear. Conclusion: At concentrations that did not affect the APD in the VM hut reduced the APD in the PE. lidocaine suppressed almokalant‐induced dispersion and the development of EADs. Nisoldipine, (m the other hand, inhibited almokalant‐induced EADs directly. Hence, (he primary APD‐prolonging effect of a Class III agent may he preserved, but the risk of proarrhythmary reduced, during concomitant treatment with low concentrations of a Na+‐ or Ca2+ blocking agent.
Nonuniform Anisotropy is Responsible for Age‐Related Slowing of Atrioventricular Nodal Reentrant Tachycardia
Authors: ANSELME FREDERIC , FREDERIKS JOOST , PAPAGEORGIOU PANOS , MONAHAN KEVIN M. , EPSTEIN LAURENCE M. , SPACH MADISON S. , JOSEPHSON MARK E. 
Published: May 2007

Age‐Related Slowing of AVNRT. Introduction: AV nodal reentrant tachycardia cycle length has been shown to he longer in the elderly population. Microfibrosis associated with aging producing nonuniform anisotropic conduction or changes in membrane ionic properties could explain this finding. Methods and Results: Forty‐five patients (33 women and 12 men) with typical AV nodal reentrant tachycardia were studied to analyze the effects of age on electrophysiologic characteristics of the tachycardia using high‐density catheter mapping of the triangle of Koch. We classified patients into group A (age ≤ 45 years, mean [± SD] 32.7 ± 8.8, n = 27) and group B (age > 45 years, mean [± SD] 61.1 ± 10.2, n =18). Retrograde atrial activation was recorded during tachycardia by means of a 2‐mm decapolar catheter at the His bundle, a quadripolar catheter at the high right atrium, a multipolar catheter (6 to 10 poles) in the coronary sinus, and a deflectable quadripolar catheter at the posterior triangle of Koch. The AH interval at the AV junction as well as HA intervals at several atrial sites were measured during tachycardia. HA intervals at all atrial recording sites except in the posterior triangle of Koch were significantly longer in group B, as well as the tachycardia cycle length (362 vs 329 msec, P = 0.01). The mean AH interval was prolonged by 24 msec in group B, but this difference did not reach statistical significance. A sequential pattern of retrograde atrial activation during tachycardia was more frequently recorded in group B. Conclusions: Since the delayed activation to the atrium was heterogeneous, transverse nonuniform anisotropic conduction is a likely explanation of these age‐related modifications of AV nodal reentrant tachycardia characteristics.
Evidence for the Presence of M Cells in the Guinea Pig Ventricle
Authors: SICOURI SERGE , QUIST MICHAEL , ANTZELEVITCH CHARLES 
Published: May 2007

M Cells in the Guinea Pig. Introduction: Recent studies have described the presence of M cells in the deep layers of the canine and human ventricle displaying electrophysiologic and pharmacologic features different from those of epicardial (EPI) and endocardial (ENDO) cells. The M cell is distinguished electrophysiologically by the ability of its action potential to prolong disproportionately to that of other myocardial cells with slowing of the stimulation rate and pharmacologically by its unique sensitivity to Class III antiarrhythmic agents. The present study was designed to test the hypothesis that similar cells are present in the guinea pig ventricle. Methods and Results: We used a dermatome to obtain thin strips of left ventricular free wall from the hearts of guinea pigs (8 to 14 weeks old) and standard microelectrode techniques to record transmembrane activity. Action potential duration measured at 90% repolarization (APD90) was significantly longer in mid‐myocardial (MID) cells than in surface EPI or ENDO cells at all basic cycle lengths (BCLs) tested. At a BCL of 300 msec, APD90 was 102 ± 21, 136 ± 9, and 95 ± 15 msec in EPI, MID, and ENDO cells (mean ± SD; n = 12). At a BCL of 5000 msec, APD90 was 133 ± 14, 185 ± 24, and 135 ± 13 msec in EPI, MID, and ENDO cells ([K+]0= 4 mM). Thus, APD‐rate relations were more pronounced in the MID cells. MID cells were also more sensitive to agents with Class III actions (e.g., d,I‐sotalol: 10 to 100 μM), exhibiting a greater APD prolongation than EPI or ENDO. d,I‐Sotalol also induced early afterdepolarizations in MID cells hut not in EPI or ENDO cells. The rate of rise of the action potential upstroke (Vmax) was significantly greater in MID cells: 129 ± 13, 240 ± 42, and 192 ± 28 V/sec in EPI, MID, and ENDO cells (n = 10 to 18). Conclusion: Our results demonstrate the existence of important transmural electrical heterogeneity in guinea pig ventricular myocardium. The study provides data in support of the existence of M cells in the mid‐myocardial layers of the guinea pig ventricle exhibiting longer APDs and a greater sensitivity to agents with Class III antiarrhythmic action.
Spectral Turbulence Versus Time‐Domain Analysis of Signal‐Averaged ECG Used for the Prediction of Different Arrhythmic Events in Survivors of Acute Myocardial Infarction
Authors: COPIE XAVIER , HNATKOVA KATERINA , STAUNTON ANNE , JOH CAMM A. , MALIK MAREK 
Published: May 2007

Spectral Turbulence SAECG After MI. Introduction: Spectral turbulence analysis of the signal‐averaged ECG (SAECG) combines spectral analysis with statistical evaluation of spectrograms of individual parts of the QRS complex. It has been suggested that it may be superior to conventional time‐domain analysis of the SAECG. Methods and Results: This study compared the power of conventional time‐domain (40 to 250Hz) and spectral turbulence analyses of SAECG for the prediction of cardiac death, ventricular tachycardia, sudden arrhythmic death, and arrhythmic events (ventricular tachycardia or fibrillation, and/or sudden arrhythmic death) after acute myocardial infarction in 603 patients. The population excluded patients with bundle branch block and other conduction abnormalities. During the first 2 years of follow‐up, there were 40 cardiac deaths, 21 cases of ventricular tachycardia, 11 sudden arrhythmic deaths, and 29 arrhythmic events. The positive predictive accuracy of spectral turbulence analysis was significantly higher than time‐domain analysis for cardiac death at most levels of sensitivity (e.g., 26% vs 20% at 40% sensitivity, P < 0.05). The positive predictive accuracies of the two techniques were not statistically different for the prediction of ventricular tachycardia. For the prediction of sudden arrhythmic death and arrhythmic events, the positive predictive accuracy of spectral turbulence was better than that of time‐domain analysis only at the higher levels of sensitivity (9% vs 2%, P < 0.001 for sudden arrhythmic death at 60% sensitivity, and 14% vs 11%, P < 0.05 for arrhythmic events at 60% sensitivity). Conclusions: Spectral turbulence analysis is essentially equivalent to time‐domain analysis for the prediction of arrhythmic events after myocardial infarction. However, it performed significantly better than time‐domain analysis for the prediction of cardiac death.
Origin and Morphogenetic Movements of the Pores of the Contractile Vacuoles in Paramecium qurelia
Authors: KING ROBERT L. 
Published: May 2007

The position of the contractile vacuoles in non‐dividing Paramecium aurelia, as judged by that of the pores, is relatively constant both laterally and longitudinally, as is the distance between them. Some variability of the distance between the pores persists from the recent fission among the smaller animals of normal shape. At the onset of fission two new vacuoles appear, one anterior to each of the old vacuoles; all the vacuoles must undergo relocation because their mean positions now are somewhat removed from that in the non‐dividing animals. The pores of the front daughter are too close together: the anterior pore is too far back, and the posterior is too far forward; likewise the pores of the hind daughter are too close together: the anterior too far forward as well as the posterior. The relocation does not begin until shortly before separation of the daughters and is practically complete by the time the daughters have assumed their normal length/width ratio after separation. A neuroneme connects the pore to one of the basal granules adjacent to its place of origin, now far removed.Occasionally more than one new pore appears at the usual time and place during very early fission; these are very close together and usually serve a single vacuole. However, most of them fail to survive the relocation following this and the next fission, so they are found in the posterior position very rarely. But, in some individuals they may survive and serve a single or separate vacuoles. In a certain clone of Paramecium aurelia multiple pores and vacuoles are rather frequent; these are, of course, the result of the tendency to produce multiple pores and vacuoles at the time of fission.
Mating Type Inheritance at Conjugation in Variety 4 of Parameciurn aurelia*
Authors: Nanney David L. 
Published: May 2007

SUMMARY. The pattern of mating type distribution observed at conjugation under different conditions in stock 51, variety 4, of Paramecium aurelia is presented. When the two mating types (VII and VIII) found in this variety are crossed, each pair member usually gives rise to two caryonides of its own mating type. Either parent may, however, give rise to progeny unlike itself. When cytoplasmic fusion is induced by antiserum treatment, the two members of a pair characteristically yield progeny of the same mating type, and the progeny are usually mating type VIII. The direction of change can be influenced to some extent by the temperature at which conjugation occurs; changes from VII to VIII are more frequent at the higher temperatures.A modification of mating type distribution is observed when conjugation occurs in the unstable clones designated as “selfing caryonides”. Changes are frequent under these circumstances, but are predominantly from type VIII to type VII—precisely the reverse direction observed when pure clones are crossed. The relative frequencies of the changes in the two directions are again influenced by the temperature at which conjugation occurs. These observations indicate a separation of two normally correlated macronuclear functions—the activity in determining the phenotype (mating type) of the cell and the activity in determining the cytoplasmic conditions responsible for nuclear differentiation in the following generation. An interpretation of these results, based on macronuclear heterogeneity, is suggested.
A Contribution to the Systematics and Morphology of Endoparasitic Trichodinids from Amphibians, with a Proposal of Uniform Specific Characteristics
Authors: LOM JIRI 
Published: May 2007

SYNOPSIS. Trichodina urinicola was found in newts, Triturus cristatus and T. taeniatus, in three localities in Czechoslovakia. The ciliate populations showed important differences on the basis of which they were separated as three new forms of this species: T. urinicola f. typica, T. urinicola f. bohemica, both from Triturus cristatus, and T. urinicola f. taeniatus from Triturus taeniatus. The great variability of trichodinids is evident from the literature as well as from our own observations, so that these new forms are to be regarded as provisional ones until it is possible to decide on the basis of a large number of observations the extent of specificity and variation of individual endozoic species of Trichodina. A detailed description of these forms is given as well as a comparison with the known species of trichodinids inhabiting the urinary tract of amphibians. A brief comment on the present taxonomy of the Urceolaridae in general is outlined.The need for a uniform description of these ciliates is emphasized; in connection with this, the taxonomic value of individual body characters is discussed. Special attention is paid to the adhesive disk of Trichodina, the structure of which is of greatest importance in the taxonomy of this group. On the basis of Dogel's and Fauré‐Fremiet's descriptive methods employed in study of trichodinids, a proposal of a uniform description of Trichodina is made which involves all the important features of these protozoa.