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Lerman BB, Stein KM, Markowitz SM. Idiopathic right ventricular outflow tract tachycardia: a clinical approach. Pacing Clin Electrophysiol 1996; 19:2120-37. [PMID: 8994952 DOI: 10.1111/j.1540-8159.1996.tb03287.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Right ventricular outflow tract (RVOT) tachycardia is the most common form of idiopathic ventricular tachycardia (VT). Phenotypically, RVOT tachycardia segregates into two predominant forms, one characterized by repetitive monomorphic nonsustained VT and the other by paroxysmal exercise induced sustained VT. There is an increasing body of evidence to support the concept that both forms of tachycardia reflect disparate clinical manifestations of an identical cellular mechanism (i.e., cAMP-mediated triggered activity), which is identified clinically by the tachycardia's sensitivity to adenosine. The clinical characteristics, natural history, and approaches to therapy of RVOT tachycardia are delineated herein.
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Affiliation(s)
- B B Lerman
- Department of Medicine, New York Hospital-Cornell University Medical Center, NY 10021, USA.
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52
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Betsuyaku T, Takano H, Hirao N, Nakano N, Yoshida I, Yotsukura A, Sakurai M, Kitabatake A. A case of adenosine-sensitive ventricular tachycardia in a very elderly male. JAPANESE CIRCULATION JOURNAL 1996; 60:901-7. [PMID: 8958200 DOI: 10.1253/jcj.60.901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The best-known type of adenosine-sensitive ventricular tachycardia is idiopathic and of right ventricular outflow origin; however, there is little information about other types of adenosine-sensitive ventricular tachycardia. Idiopathic adenosine-sensitive ventricular tachycardia is common in the young. An 87-year-old man with ventricular tachycardia was admitted to our hospital. His ventricular tachycardia was sensitive to adenosine triphosphate, edrophonium, verapamil, and Valsalva's maneuver. He had experienced no anginal episodes. His ventricular tachycardia was thought to be idiopathic. We report this very rare case of adenosine-sensitive ventricular tachycardia, which was not derived from the right ventricular outflow tract, in a very elderly male.
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Affiliation(s)
- T Betsuyaku
- Department of Cardiovascular Medicine, School of Medicine, Hokkaido University, Japan
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53
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Song Y, Belardinelli L. Electrophysiological and functional effects of adenosine on ventricular myocytes of various mammalian species. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:C1233-43. [PMID: 8897829 DOI: 10.1152/ajpcell.1996.271.4.c1233] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The goal of this study was to determine the electrophysiological and functional effects of adenosine on ventricular myocytes of guinea pig, rabbit, rat, and ferret hearts. Adenosine (100 microM) shortened the action potential durations of rat and ferret myocytes by 14 +/- 1 and 57 +/- 7%, reduced the amplitudes of cell twitch shortening by 13 +/- 1 and 54 +/- 5%, and increased outward currents by 15 +/- 4 and 55 +/- 5%, respectively, but had no effect on guinea pig and rabbit myocytes. The properties of adenosine-activated outward current in rat and ferret ventricular myocytes indicated that this current is the adenosine-sensitive K+ current [IK(Ado)]. Adenosine had no significant effect on basal Ca2+ current but specifically inhibited isoproterenol-stimulated L-type Ca2+ current in myocytes of all species studied. Binding studies revealed that the density of A1 adenosine receptors (A1AdoR) was highest in ferret and lowest in rabbit myocytes, but the differential effects of adenosine among species could not be solely explained by differences in A1AdoR density. In summary, adenosine shortened the action potential and reduced the twitch shortening of rat and ferret but not of guinea pig and rabbit ventricular myocytes. Shortening of the action potential was associated with the activation of IK(Ado). The anti-beta-adrenergic action of adenosine appeared to be independent of species.
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Affiliation(s)
- Y Song
- Department of Medicine, University of Florida Medical School, Gainesville 32610, USA
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54
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Abstract
Idiopathic ventricular tachycardia (VT) is a term that refers to tachycardia that arises from ventricles devoid of apparent structural abnormalities. This form of VT is now recognized to be related to several distinct entities and includes a reentrant form typically located in the region of the left posterior fascicle, an automatic form that may originate from either ventricle, and a form that originates from the right ventricular outflow tract. This last type can account for up to 80% of cases of idiopathic VT and with few exceptions can be further subdivided into repetitive monomorphic VT and paroxysmal stress-induced VT. Evidence has accumulated suggesting that both forms of VT are related to cAMP-mediated triggered activity. The experimental underpinnings of this conclusion as well as the clinical characteristics of this form of idiopathic VT are elucidated in this review.
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Affiliation(s)
- B B Lerman
- Department of Medicine, New York Hospital-Cornell University Medical Center, New York 10021, USA
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55
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Ishida S, Ito M, Takahashi N, Fujino T, Akimitsu T, Saikawa T. Caffeine induces ventricular tachyarrhythmias possibly due to triggered activity in rabbits in vivo. JAPANESE CIRCULATION JOURNAL 1996; 60:157-65. [PMID: 8741241 DOI: 10.1253/jcj.60.157] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Caffeine induces delayed afterdepolarizations (DADs) and triggered activity in isolated cardiac tissue. We investigated the ability of caffeine to induce triggered ventricular arrhythmias in rabbits in vivo. During continuous infusion of caffeine at doses of 0.3 or 1.0 mg/kg per min, ventricular pacing was performed with 50 stimuli with a cycle length of 220 msec (basic pacing train) every 5 min until ventricular tachycardia (VT) was induced. The effects of programmed stimulation and pharmacologic agents on the induction of ventricular ectopic beats (VEBs) were examined. Pacing protocols were carried out in the presence of vagal-induced slowing of sinus rhythm. VT was induced by a basic pacing train during the infusion of caffeine at 1.0 mg/kg per min, but not at 0.3 mg/kg per min. An increase in the pacing rate or the number of stimuli resulted in 1) a decrease in the first postpacing interval, and 2) an increase in the number of postpacing VEBs. Induction of VT was suppressed by intravenous bolus injections of verapamil, propranolol and adenosine. At the time of the initial induction of VT, the plasma concentration of caffeine was 87 +/- 2 micrograms/ml and the plasma level of norepinephrine increased from 666 +/- 166 pg/ml at baseline to 1121 +/- 245 pg/ml. These results suggest that catecholamine-associated triggered activity may be responsible for caffeine-induced VT.
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Affiliation(s)
- S Ishida
- Department of Laboratory Medicine, School of Medicine, Oita Medical University, Japan
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56
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57
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Affiliation(s)
- M A Cook
- Department of Pharmacology and Toxicology, University of Western Ontario, London, Canada
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58
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Miura M, Ishide N, Numaguchi H, Takishima T. Diversity of early afterdepolarizations in guinea pig myocytes: spatial characteristics of intracellular Ca2+ concentration. Heart Vessels 1995; 10:266-74. [PMID: 8904002 DOI: 10.1007/bf01744906] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We classified early afterdepolarizations (EADs) into subgroups according to the spatial features of the intracellular Ca2+ concentration ([Ca2+]i). Myocytes were enzymatically isolated from guinea pig ventricles. When fura-2 salt was applied through a whole cell patch pipette after the formation of a gigaohm seal, the membrane potential was measured using the current, clamp technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional microelectrode technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV system. EADs were induced after superfusion with potassium-free Tyrode solution. Irrespective of the fura-2 loading procedure, EADs could be classified into those with spatially synchronous fluorescence changes (n = 26 from eight hearts) and those with heterogeneous changes (n = 20 from three hearts). EADs with synchronous features took off from a higher membrane potential (> or = -34 mV) than EADs with heterogeneous features (< or = -57 mV). These results suggest that EADs have at least two constituents.
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Affiliation(s)
- M Miura
- The First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan
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59
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Xu J, Hurt CM, Pelleg A. Digoxin-induced ventricular arrhythmias in the guinea pig heart in vivo: evidence for a role of endogenous catecholamines in the genesis of delayed afterdepolarizations and triggered activity. Heart Vessels 1995; 10:119-27. [PMID: 7673081 DOI: 10.1007/bf01744478] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The mechanisms of digoxin-induced ventricular arrhythmias were studied in vivo using a novel experimental model. Anesthetized guinea pigs were instrumented with custom-made electrode catheters which enabled the monitoring and recording of right atrial, right ventricular, and His bundle electrograms, midmyocardial monophasic action potentials (MAP), and systemic arterial blood pressure. Intravenous digoxin induced ventricular arrhythmias ranging from ventricular premature contractions (VPCs) to ventricular fibrillation (VF). These were associated with delayed afterdepolarizations (DADs) observed on the MAP recordings. The severity of the arrhythmias depended on the dose of digoxin. Short bursts of ventricular pacing neither terminated nor suppressed episodes of ventricular tachycardias (VTs). A direct relationship existed between the paced ventricular cycle length and the coupling interval between the last paced beat and the first ectopic beat (r = 0.913, P < 0.001, n = 10) and between the amplitude of the DADs and the pacing rate (r = 0.972, P < 0.05, n = 7). The increased contractility (LV dp/dt) and heart rate evoked by isoproterenol (0.1 microgram/kg) did not induce DADs in the absence of digoxin. Verapamil terminated the digoxin-induced VTs in 15 of 16 animals and abolished the associated DADs in 7 of 7 animals. Adenosine terminated the VTs in 15 of 19 animals and abolished the DADs in 8 of 10 animals. Digoxin induced VT in only 1 of 6 animals treated with reserpine (5 + 5 mg/kg) 24 and 48h prior to experimentation. However, subsequent intravenous isoproterenol (0.2 micrograms/kg) induced VT and DADs, both of which were abolished by verapamil, in all 6 animals.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J Xu
- Likoff Cardiovascular Institute, Medical College of Pennsylvania, Philadelphia, USA
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60
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Li GR, Feng J, Shrier A, Nattel S. Contribution of ATP-sensitive potassium channels to the electrophysiological effects of adenosine in guinea-pig atrial cells. J Physiol 1995; 484 ( Pt 3):629-42. [PMID: 7623281 PMCID: PMC1157949 DOI: 10.1113/jphysiol.1995.sp020692] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
1. Adenosine caused dose-dependent action potential abbreviation in multicellular guinea-pig atrial preparations, an action antagonized by glyburide (IC50, 31 microM) in both physiological and low-chloride superfusate. 2. When 5 mM ATP was included in pipettes for whole-cell voltage clamp of isolated guinea-pig atrial myocytes, adenosine (10 microM) increased the holding current at -40 mV from 41 +/- 8 to 246 +/- 31 pA (mean +/- S.E.M., P < 0.01), and glyburide (20 microM) returned the holding current to 69 +/- 11 pA (P < 0.01 vs. adenosine alone). Acetylcholine (10 microM) also increased the holding current, but its effects were not altered by glyburide. 3. Both adenosine and acetylcholine induced an additional current component in response to 500 ms voltage steps. Glyburide partially inhibited the adenosine-induced current, but did not alter the effect of acetylcholine. In the presence of maximally effective acetylcholine concentrations, adenosine increased membrane conductance (P < 0.01), although to a lesser extent than in the absence of acetylcholine. 4. Single K+ channel activity was seen in only one of eight cell-attached patches in the absence of adenosine or acetylcholine (0.5 mM Ba2+ in bath and pipette solutions). With acetylcholine (10 microM) in the pipette, inwardly rectifying channels (conductance, 41 +/- 5 pS) were seen in five of six patches. With adenosine (10 microM) in the pipette, single-channel activity was seen in twelve of fourteen patches with two populations of channels, one similar to that induced by acetylcholine and another higher-conductance channel (72 +/- 5 pS) that showed less inward rectification. Glyburide (20 microM) suppressed the high-conductance channel (68 +/- 2 pS) leaving a single channel type with a conductance of 36 +/- 5 pS and strong inward rectification. 5. We conclude that K+ATP channels contribute to the electrophysiological actions of adenosine on guinea-pig atrium in the presence of physiological intracellular ATP levels, and may therefore play a role in the cardiac electrophysiological effects of adenosine in the absence of myocardial ischaemia.
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Affiliation(s)
- G R Li
- Department of Medicine, Montreal Heart Institute, Quebec, Canada
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61
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Tan HL, Hou CJ, Lauer MR, Sung RJ. Electrophysiologic mechanisms of the long QT interval syndromes and torsade de pointes. Ann Intern Med 1995; 122:701-14. [PMID: 7702233 DOI: 10.7326/0003-4819-122-9-199505010-00009] [Citation(s) in RCA: 173] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
PURPOSE To review the current understanding of the mechanisms and treatment of the long QT interval syndromes and torsade de pointes. DATA SOURCES Personal databases of the authors and a search of the MEDLINE database from 1966 to 1994. STUDY SELECTION Experimental and clinical studies and topical reviews on the electrophysiologic mechanisms and treatment of torsade de pointes were analyzed. RESULTS The long QT interval syndromes have been classified into acquired and hereditary forms, both of which are associated with a characteristic type of life-threatening polymorphic ventricular tachycardia called torsade de pointes. The acquired form is caused by various agents and conditions that reduce the magnitude of outward repolarizing K+ currents, enhance inward depolarizing Na+ or Ca2+ currents, or both, thereby triggering the development of early afterdepolarizations that initiate the tachyarrhythmia. The hereditary form appears to result from an abnormal response to adrenergic or sympathetic nervous system stimulation. At least some cases of the hereditary long QT interval syndromes may result from a single gene defect that alters the intracellular regulatory proteins responsible for the modulation of K+ channel function. Treatment of the acquired form is primarily directed at identifying and withdrawing the offending agent, although emergent therapy using maneuvers and agents that favorably modulate transmembrane ion currents can be lifesaving. In torsade de pointes associated with the hereditary long QT interval syndromes, early diagnosis leading to treatments designed to both shorten the QT interval and block the beta-adrenergic-induced instability of the QT interval is essential. CONCLUSIONS The long QT interval syndromes and torsade de pointes are potentially life-threatening conditions caused by various agents, conditions, and genetic defects. The mechanisms responsible for these conditions and available treatment options for them are reviewed.
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Affiliation(s)
- H L Tan
- Stanford University School of Medicine, California, USA
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62
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Lerman BB, Engelstein ED. Increased defibrillation threshold due to ventricular fibrillation duration. Potential mechanisms. J Electrocardiol 1995; 28 Suppl:21-4. [PMID: 8656114 DOI: 10.1016/s0022-0736(95)80004-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The duration of ventricular fibrillation (VF) that precedes a high energy shock has been recognized as a critical determinant of defibrillation outcome. Factors such as metabolic acidosis or alkalosis do not affect outcome. The authors hypothesized that release of myocardial adenosine during VF could potentially mediate the time-dependent effects of VF duration on defibrillation. Defibrillation threshold (DFT) was therefore determined in dogs during concurrent infusion of adenosine and dipyridamole (a nucleoside transport blocker). Transthoracic DFT increased by approximately 50%, whereas transmyocardial DFT increased by approximately 100% in a separate group of dogs. These effects of adenosine on DFT were abolished when the dogs were autonomically denervated, suggesting that the deleterious effects of adenosine on DFT are due to its antiadrenergic mechanism of action. These data indicate that adenosine release during VF can markedly increase DFT. Since adenosine myocardial release during VF is time dependent, it is likely that adenosine plays a significant role in mediating the increase in threshold that is dependent on the duration of VF.
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Affiliation(s)
- B B Lerman
- Department of Medicine, New York Hospital-Cornell University Medical Center, NY 10021, USA
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63
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64
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Provenzano SC, Paschoal AT. Is There a Place for Aminophylline in Cardiopulmonary Resuscitation? Chest 1994. [DOI: 10.1378/chest.106.5.1637] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
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65
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Kumar R, Joyner RW. An experimental model of the production of early after depolarizations by injury current from an ischemic region. Pflugers Arch 1994; 428:425-32. [PMID: 7530837 DOI: 10.1007/bf00374561] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
An ischemic myocardial region contains cells with a depolarized resting membrane potential. This depolarization leads to an intercellular current flow between the ischemic region and the surrounding normal myocardial cells which has been termed an "injury current". We have devised an experimental model system in which an isolated guinea pig ventricular cell is electrically coupled to a model depolarized cell in order to evaluate the effects of this injury current on the electrical properties of a normal ventricular cell exposed to drugs which increase calcium current or decrease potassium current. Using low doses of isoproterenol, forskolin, or Bay K 8644 (or 8-bromo-cyclic adenosine monophosphate in the pipette) we found that the action potential duration of the isolated cell was lengthened, but that early afterdepolarizations (EADs) were not produced unless the cell was also coupled to a depolarized cell model representing an adjacent ischemic region. A similar prolongation of the action potential was produced by low doses of quinidine, but EADs were not produced unless coupling to a depolarized cell model was added. EADs could not be produced in any cells in the absence of the drugs even though the coupling to the depolarized cell model was increased up to the level at which the action potential was indefinitely prolonged. At higher isoproterenol concentrations, EADs or spontaneous activity were produced without coupling to the depolarized cell model. Under these conditions, coupling of the cell to a cell model with normal resting membrane potential stopped the spontaneous activity and prevented the occurrence of EADs even with high levels of resistive coupling.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R Kumar
- Todd Franklin Cardiac Research Laboratory, Children's Heart Center, Department of Pediatrics, Emory University, Atlanta, GA 30323
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66
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Bertolet BD, Hill JA. Adenosine: diagnostic and therapeutic uses in cardiovascular medicine. Chest 1993; 104:1860-71. [PMID: 8252974 DOI: 10.1378/chest.104.6.1860] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Affiliation(s)
- B D Bertolet
- Department of Medicine, University of Florida Health Sciences Center, Gainesville
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67
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Affiliation(s)
- J A Gatell
- Department of Anesthesiology, Syosset Community Hospital, NY
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