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W G Fisher

Publications and source records attributed to W G Fisher.

11 recordsLinked to original sources
PubMed1997

Adjunctive intracardiac echocardiography to guide slow pathway ablation in human atrioventricular nodal reentrant tachycardia: anatomic insights.

BACKGROUND: Because of the inability of fluoroscopy to image intracardiac structures, the precise anatomic location of successful slow pathway (SP) ablation is controversial. We hypothesized that adjunctive intracardiac echocardiography (ICE) in concert with conventional fluoroscopy and electrogram guidance could identify the anatomic site of successful SP ablation. METHODS AND RESULTS: In 25 patients, radiofrequency ablation was performed in the triangle of Koch directed by biplane fluoroscopy and a 6.2F, 12.5-MHz ICE catheter positioned adjacent to the triangle of Koch. Persistent SP conduction, number of radiofrequency applications, presence of junctional tachycardia, and fluoroscopy times were evaluated. As demonstrated by ICE, anterograde SP ablation was achieved between 2 and 7 mm from the tricuspid valve in imaging planes containing the AV muscular septum in all cases. Radiofrequency energy applications applied at other sites within the triangle of Koch failed to interrupt SP conduction. A mean of three radiofrequency energy applications (3+/-2; range, 1 to 12) successfully ablated all evidence of anterograde SP conduction in all patients studied. Junctional tachycardia was seen in 96% (71/74) of the radiofrequency energy applications. CONCLUSIONS: Radiofrequency ablation at the tricuspid valve's insertion into the AV muscular septum as identified by ICE reliably terminates anterograde SP conduction, supporting the hypothesis that the SP consistently traverses this anatomic location.

Adult↗
PubMed1997

Use of an orthogonal electrode array to identify the successful ablation site in right ventricular outflow tract tachycardia.

A novel approach to localize the origin of a right ventricular outflow tract tachycardia using an ablation catheter having an orthogonally oriented electrode array is described. Bipolar electrogram polarity reversal using minimally filtered (1-500 Hz) electrograms simultaneously acquired in two axes from the ablation catheter permitted accurate localization of the tachycardia focus. A single radiofrequency energy application at the site identified by this technique resulted in successful tachycardia ablation. This technique may facilitate mapping of any arrhythmia which can be modeled as arising from a point source.

Adult↗
PubMed1997

Simultaneous two-photon activation of type-I photodynamic therapy agents.

The excitation and emission properties of several psoralen derivatives are compared using conventional single-photon excitation and simultaneous two-photon excitation (TPE). Two-photon excitation is effected using the output of a mode-locked titanium: sapphire laser, the near infrared output of which is used to promote nonresonant TPE directly. Specifically, the excitation spectra and excited-state properties of 8-methoxypsoralen and 4'-aminomethyl-4,5,8-trimethylpsoralen are shown to be equivalent using both modes of excitation. Further, in vitro feasibility of two-photon photodynamic therapy (PDT) is demonstrated using Salmonella typhimurium. Two-photon excitation may be beneficial in the practice of PDT because it would allow replacement of visible or UV excitation light with highly penetrating, nondamaging near infrared light and could provide a means for improving localization of therapy. Comparison of possible laser excitation sources for PDT reveals the titanium: sapphire laser to be exceptionally well suited for nonlinear excitation of PDT agents in biological systems due to its extremely short pulse width and high repetition rate that together provide efficient PDT activation and greatly reduced potential for biological damage.

Absorption↗
PubMed1996

Activation and entrainment mapping defines the tricuspid annulus as the anterior barrier in typical atrial flutter.

BACKGROUND: The importance of anatomic barriers in the atrial flutter reentry circuit has been well demonstrated in canine models. It has been shown previously that the crista terminalis and its continuation as the eustachian ridge form a posterior barrier. In this study we tested the hypothesis that the tricuspid annulus forms the continuous anterior barrier to the flutter circuit. METHODS AND RESULTS: Thirteen patients with typical atrial flutter were studied. A 20-pole halo catheter was situated around the tricuspid annulus. A mapping catheter was used for activation and entrainment mapping from seven sequential sites around the tricuspid annulus and from three additional sites including the tip of the right atrial appendage, at the fossa ovalis, and in the distal coronary sinus. Sites were considered to be within the circuit when the postpacing interval minus the flutter cycle length and the stimulus time minus the activation time were < or = 10 ms; sites were considered to be outside the circuit when these intervals were > 10 ms. All seven annular sites were within the circuit; activation occurred sequentially around the annulus and accounted for 100% of the flutter cycle length. The fossa ovalis, the distal coronary sinus, and the right atrial appendage were outside the circuit. CONCLUSIONS: Closely spaced sites around the tricuspid annulus are activated sequentially, and are all within the flutter circuit according to entrainment criteria. This demonstrates that the tricuspid annulus constitutes a continuous anterior barrier constraining the reentrant wave front of human counterclockwise atrial flutter.

Aged↗
PubMed1995

Radiofrequency catheter modification of the sinus node for "inappropriate" sinus tachycardia.

BACKGROUND: Radiofrequency catheter ablation is the treatment of choice for patients with paroxysmal supraventricular tachycardias refractory to medical therapy. However, in symptomatic patients with inappropriate sinus tachycardia resistant to drug therapy, catheter ablation of the His' bundle with permanent pacemaker insertion is currently applied. We evaluated the safety and efficacy of radiofrequency modification of the sinus node as alternative therapy for patients with inappropriate sinus tachycardia. METHODS AND RESULTS: Sixteen patients with disabling episodes of inappropriate sinus tachycardia refractory to drug therapy (4.2 +/- 0.3 drug trials) underwent either total sinus node ablation or sinus node modification. The region of the sinus node was identified as the region of earliest atrial activation in sinus rhythm during electrophysiological study. This region was further defined by use of intracardiac echocardiography (ICE) in 9 patients, in whom it was found that an ablation catheter could be guided reliably and maintained on the crista terminalis. Radiofrequency energy was delivered during tachycardia between either a standard 4-mm or custom 10-mm thermistor-imbedded catheter tip and a skin patch. Total sinus node ablation was performed successfully in all 4 patients in whom it was attempted and was characterized by a junctional escape rhythm. Sinus node modification was successfully achieved in all 12 patients in whom it was attempted and was characterized by a 25% reduction in the sinus heart rate. For the group as a whole, exercise stress testing after ablation revealed a gradual chronotropic response, with a significant reduction in maximal heart rate (132.8 +/- 6.5 versus 179.5 +/- 3.6 beats per minute [bpm]; P < .001) without evidence of an exaggerated heart rate response to a light workload (103.0 +/- 4.1 versus 139.5 +/- 3.5 bpm; P < .001). Twenty-four-hour ambulatory ECG monitoring revealed a significant decrease in maximal heart rate and mean heart rate after ablation (167.2 +/- 2.6 versus 96.7 +/- 5.0 bpm, P < .001, and 125.6 +/- 5.0 versus 54.1 +/- 5.3 bpm, P < .001, respectively). There was a significant decrease in the number of applications of radiofrequency energy required in patients undergoing modification of the sinus node when guided by ICE compared with fluoroscopy alone (3.6 +/- 0.8 versus 10.4 +/- 2.1; P < .01) as well as a decrease in fluoroscopy time (33.0 +/- 9.5 versus 58.5 +/- 8.4 minutes). After a mean follow-up period of 20.5 +/- 0.3 months, there were no recurrences of inappropriate sinus tachycardia in patients who underwent a total sinus node ablation. However, 2 patients who had a total sinus node ablation subsequently required permanent pacing because of symptomatic pauses, and 1 patient developed an ectopic atrial tachycardia. After a mean follow-up of 7.1 +/- 1.7 months, there were two recurrences of inappropriate sinus tachycardia in patients who underwent sinus node modification. However, no significant bradycardia or pauses were observed. Complications encountered during the study included 1 patient who developed transient right diaphragmatic paralysis and another patient who developed transient superior vena cava syndrome. CONCLUSIONS: Sinus node modification is feasible in humans and should be considered as an alternative to complete atrioventricular junctional ablation for patients with disabling inappropriate sinus tachycardia refractory to medical management. Sinus node modification may be aided by ICE.

Adult↗
PubMed1995

Radiofrequency catheter modification of sinus pacemaker function guided by intracardiac echocardiography.

BACKGROUND: The sinus P wave arises from a pacemaker complex distributed along the crista terminalis. We investigated the feasibility of modification of sinus pacemaker function using graded applications of radiofrequency energy along the crista terminalis in dogs to achieve sinus rate control. METHODS AND RESULTS: Modification of sinus pacemaker function (30 +/- 5% reduction in intrinsic heart rate with retention of a normal P-wave axis) was performed in 11 dogs (group 1). Total sinus pacemaker ablation (> 50% reduction in intrinsic heart rate with development of a low ectopic atrial or a junctional rhythm) was performed in 4 dogs (group 2). Intracardiac echocardiography was used to identify the crista terminalis as an anatomic marker of sinus node location. Sinus pacemaker modification caused a significant decrease in intrinsic heart rate (31% reduction, P < .001), heart rate responsiveness to isoproterenol (30% reduction, P < .0001), and average (20% reduction, P = .0002) and maximal (22% reduction, P = .0007) heart rates during 24-hour Holter monitoring. In 6 of the 11 animals, the targeted rate reduction of 30 +/- 5% was accurately achieved (mean, 31.6 +/- 4.3%; P < .001), and in the other 5, significant reduction of intrinsic heart rate was achieved but with greater variation (28.0 +/- 17.3%, P < .005). Corrected sinus node recovery time was not prolonged. After modification, earliest activation was mapped to the crista terminalis inferior to the lesion in all animals. In long-term follow-up (3.7 +/- 1.0 months), effects were maintained. After total sinus pacemaker ablation, junctional and low atrial escape pacemakers were unstable. CONCLUSIONS: This study demonstrates the feasibility of modification of sinus pacemaker function for sinus rate control using catheter-based radiofrequency ablation guided by intracardiac echocardiography. This can be done while pacemaker stability and attenuated responsiveness to autonomic influences are preserved. Intracardiac echocardiography accurately defined the crista terminalis and provided a reliable means to anatomically localize catheter position in relation to the sinus node.

Animals↗
PubMed1994

Comparison of budesonide and disodium cromoglycate for the treatment of seasonal allergic rhinitis in children.

BACKGROUND: Budesonide and disodium cromoglycate (DSCG) are commonly used agents for the treatment of seasonal allergic rhinitis. The comparative efficacy, however, of these agents in the pediatric population has not been reported. OBJECTIVE: The efficacy of nasally administered budesonide (400 micrograms/day, administered twice daily) was compared with that of DSCG (31.2 mg/day, administered six times per day) for the treatment of seasonal allergic rhinitis in children. METHODS: A single-blind parallel group study was carried out in 56 children (mean age 12 years) with seasonal allergic rhinitis. Treatment was for 3 weeks, during which patients assessed nasal symptoms, eye symptoms, and overall efficacy. RESULTS: Over the 3-week period, mean scores for the nasal symptoms of blocked nose, itchy nose, and sneezing were significantly lower with budesonide therapy than with DSCG. P values were .021, .0032, and .0016, respectively. Both treatment groups reported reduced scores for runny nose and eye symptoms; no statistically significant difference was observed between budesonide and DSCG. The global efficacy assessment scores show significantly more patients benefited from budesonide therapy than from DSCG treatment. CONCLUSIONS: The results suggest that nasally administered budesonide has greater efficacy than DSCG in the treatment of seasonal allergic rhinitis in children.

Adolescent↗
PubMed1993

Catheter-based three-dimensional electrogram acquisition and analysis system.

Conventional time-domain electrogram (EGM) characteristics have a poor positive predictive value for successful accessory pathway (AP) ablation location. The authors hypothesized that a computer-generated three-dimensional electrogram (3D-EGM) of myocardial activation along the atrial aspect of the tricuspid or mitral annulus created from sequentially obtained, signal-averaged endocardial bipolar EGMs and time aligned to a known myocardial reference could improve AP localization and ablation. Serial signal-averaged EGMs, digitized at 4 KHz and filtered from 1 to 2,500 Hz, were sampled at known locations along the atrioventricular ring. Up to 15 EGMs were time aligned to a known myocardial activation reference and displayed as a 3D-EGM. Time-domain 3D-EGMs were then analyzed for morphologic characteristics corresponding to effective radiofrequency ablation location in 33 patients with leftsided APs, 5 with posteroseptal APs, and 5 with right free wall APs. A characteristic retrograde atrial 3D-EGM polarity reversal identified AP insertion sites in all free wall locations with a 97% sensitivity, 46% specificity, and 72% positive predictive value. Posteroseptal APs were characterized by left posterior paraseptal atrial 3D-EGM polarity reversal, but proximal coronary sinus activation preceded endocardial activation in all. Three-dimensional electrogram polarity reversal of the retrograde atrial activation vector has a high sensitivity and positive predictive value for effective ablation location patients with left and right free wall APs, but should be used with caution in patients with posteroseptal APs.

Adult↗
PubMed1992

NASPE Young Investigator Awardee 1992. Three-dimensional electrogram mapping improves ablation of left-sided accessory pathways.

Conventional electrogram mapping techniques for localization of accessory pathways during radiofrequency ablation procedures are time consuming and often inaccurate. We hypothesized that a computer generated, three-dimensional electrogram of retrograde atrial activation created from signal-averaged sequential endocardial bipolar electrograms (collected from the atrial aspect of the mitral annulus using a single transseptal catheter and then time aligned to a known myocardial activation reference) would improve left-sided accessory pathway atrial insertion site identification and increase ablation efficiency. Ablation efficiency was defined by procedure time, fluoroscopy time, duration of radiofrequency energy required to achieve initial accessory pathway block, cumulative ablation energy per procedure, and number of radiofrequency energy applications. Patients with single left-sided accessory atrioventricular connections were studied. Standard mapping results in 31 patients (group A) were compared to a three-dimensional electrogram approach used in 26 patients (group B). Three-dimensional electrogram mapping reduced procedure time (group A 3.8 +/- 1.6 vs group B 2.8 +/- 0.9 hours, P < 0.004), fluoroscopy time (group A 45.3 +/- 35.0 vs group B 25.1 +/- 10.5 min, P < 0.02), time to accessory pathway block (group A 2.6 +/- 1.5 vs group B 1.2 +/- 0.5 sec, P < 0.002), cumulative radiofrequency energy (group A 2126 +/- 2207 vs group B 636 +/- 586 joules, P < 0.0008), and radiofrequency energy applications (group A 5.0 +/- 4.4 vs group B 1.7 +/- 1.2, P < 0.0002). We conclude that three-dimensional electrogram mapping improves left-sided accessory pathway atrial insertion localization, reduces ablation procedure time and radiation exposure, and improves ablation efficiency.

Adult↗
PubMed1989

Schistosomiasis: role of endogenous opioids in suppression of gonadal steroid secretion.

1. Radioimmunoassay of the opiate, beta-endorphin, in mouse sera, indirect measurement of estrogen by examination of vaginal smears and indirect measurement of androgens by electrophoresis of major urinary proteins (MUP) revealed that beta-endorphin increases while estrogen and androgen levels decrease in mice with chronic Schistosoma mansoni infection. 2. Injections of the opiate antagonist, naltrexone, reversed the effects of schistosomiasis on estrogen and androgen levels. 3. Because opiates are known to inhibit the secretion of releasing hormones by the hypothalamus, the data suggest that the inhibition of hypothalamic-pituitary-gonadal function that occurs in chronically infected male and female mice results from excessive beta-endorphin. 4. It is also suggested that the excessive beta-endorphin may be secreted by T-lymphocytes and possibly macrophages involved in the cell-mediated immune response (CMIR) to the ova.

Androgens↗