Demonstration of phase-3 and phase-4 retrograde block in a second concealed accessory pathway after an initial successful radiofrequency ablation of a 'normal' concealed accessory pathway.

We report a patient with concealed Wolff-Parkinson-White syndrome who, following catheter ablation, demonstrated phase-3 and phase-4 retrograde block in a concealed accessory pathway. After an initial 'apparently successful' ablation, retrograde conduction was through the atrioventricular node during constant ventricular pacing. Ventricular extrastimulus testing was performed at a basic drive cycle length of 600 ms. Unexpectedly, ventricular extrastimuli at coupling intervals of 440-380 ms were conducted retrogradely over an accessory pathway, consistent with a phase-3 and phase-4 retrograde block in the accessory pathway. Residual accessory pathway conduction was eliminated in a single ablation session.

Atypical form of the fourth criterion for transient entrainment.

The typical fourth criterion for transient entrainment is defined when both a sudden shortening in conduction interval to and a distinct change in electrogram morphology at a bipolar recording site are demonstrated while performing overdrive pacing of a reentrant tachycardia from a single pacing site at two different constant rates. The purpose of this article was to test the hypothesis that if an intracardiac recording site showing both orthodromic and antidromic capture with entrainment pacing is located suitably distant from the circuit, sudden shortening in conduction interval to that site may occur without any significant change in the bipolar electrogram morphology (i.e., atypical form of the fourth criterion). Atrial overdrive pacing of orthodromic tachycardia was performed in 20 patients with either left anterior (12 patients) or left posterior (8 patients) accessory pathways. We investigated the effects of overdrive pacing from the proximal or distal coronary sinus, specifically effects on the electrogram interval and the electrogram morphology at the right atrial appendage. Overdrive pacing of orthodromic tachycardia from the proximal coronary sinus was performed in 10 of the 12 patients with left anterior accessory pathways; those 10 patients demonstrated the first entrainment criterion at the right atrial appendage site. Overdrive pacing of orthodromic tachycardia at still shorter cycle lengths demonstrated a sudden shortening in conduction interval to the right atrial appendage site. Despite shortening in conduction interval the morphology of the right atrial appendage electrogram was completely or almost identical to that during orthodromic tachycardia, indicating an atypical form of the fourth criterion. This criterion was not demonstrated in patients with left posterior accessory pathways. Thus, atypical fourth entrainment criterion was demonstrated during overdrive pacing of orthodromic tachycardia from the proximal coronary sinus only in patients with left anterior accessory pathways. Demonstration of atypical fourth criterion seems largely dependent on the location of the accessory pathway, the pacing, and the recording sites.

Atypical antidromic resetting during programmed extrastimulation of reentrant ventricular tachycardia.

A patient with reentrant ventricular tachycardia exhibited both the orthodromic and antidromic resetting responses at a single intracardiac recording site during programmed extrastimulation of ventricular tachycardia. The transition from orthodromic to antidromic resetting with extrastimulation demonstrated a sudden shortening in conduction interval to an electrogram recording site and unexpected identical morphology of the spontaneous and captured electrograms at that site, indicating atypical antidromic resetting. This newly observed resetting phenomenon with programmed extrastimulation suggests that the fourth entrainment criterion with overdrive pacing may likely be demonstrated in an atypical form; that is, a sudden shortening in conduction interval to an electrogram recording site may occur without any significant change in the bipolar electrogram morphology at that site when overdrive pacing is performed during tachycardia from a single pacing site at two different constant rates.

Earlier activation of the distal than the proximal site of the coronary sinus may represent retrograde conduction through AV node: significance of recording of far distal coronary sinus.

During retrograde conduction through an accessory pathway (AP) or the atrioventricular (AV) node, earlier activation of the distal recording site than a more proximal site of the coronary sinus (CS) generally indicates retrograde conduction via a distally located AP. Thus, after successful ablation of a left-sided AP, if the distal CS recording site is activated earlier than a more proximal site retrogradely, it is considered to suggest-in the absence of His-bundle recording or more frequently in the setting of poor recording of the low septal right atrial electrogram-a conduction via a second AP (located more distally), and not conduction via the AV node. Yet, we hypothesized that retrograde conduction through the AV node may activate the far distal site of the CS (CSD) earlier than a more proximal site, as the anterior atrial wavefront, coming retrogradely from the AV node and traveling along the anterior mitral annulus, could reach the CSD earlier than a more proximal site. To test this we studied 18 patients with intact retrograde conduction via the AV node, but without evidence of an AP. The CSD was recorded by means of a quadripolar catheter (interelectrode distance of 2-5 mm); retrograde activation sequence at the distal (CSD1-2) versus proximal (CSD3-4) bipolar recording site was determined during ventricular stimulation. In 12 of 18 patients the CSD1-2 recording site was activated 5-10 ms earlier than the CSD3-4 recording site, in 3 of 18 patients the CSD1-2 site was activated 5 ms later than the CSD3-4 site; in the remaining 3 patients both recording sites were depolarized simultaneously. The results indicate that the CSD was often depolarized earlier than a more proximal site by impulses that conducted to the atria retrogradely via the AV node while the quadripolar recording catheter was placed at the CSD. This observation, although not well documented previously, suggests that the sequence of retrograde atrial activation in the CS should be studied carefully in consideration of the actual location of the mapping catheter in order to correctly diagnose the presence or absence of conduction via an AP.

Students' ratings of otolaryngology clerkship activities: the role of residents.

The present study was conducted with a sample of junior medical students at Jefferson Medical College to investigate the factors that influence students' overall satisfaction with the otolaryngology clerkship. The most important factor related to their overall satisfaction in the clerkship was their experience with residents, followed by experience with attending physicians, quality of rounds, and of lectures. The number of patients the students encountered, and number of rounds and lectures were deemed less important. Based on these findings, the authors of this paper concluded that the residents' role in teaching should be emphasized and students' satisfaction with the otolaryngology clerkship may be enhanced by developing residents' skills in teaching students.

Reexamination of relationships between students' undergraduate majors, medical school performances, and career plans at Jefferson Medical College.

A reexamination of the possible relationships between medical students' undergraduate academic majors and their medical school performances and career plans seems appropriate, given the continuing changes in the characteristics of the medical school applicant pool in the last several years. This study investigated these relationships by comparing cognitive and noncognitive characteristics of medical students who had had different undergraduate majors. The study sample consisted of 812 students who entered Jefferson Medical College between 1985 and 1988. They were classified into six categories based on their undergraduate majors: biological, chemical and physical, social and behavioral, other sciences, humanities and arts, and indeterminate majors. Results indicated that performances in the basic science component of medical education were about the same for students with different undergraduate majors. The groups had similar rates of delayed graduation, but the attrition rate was highest for students who had majored in humanities and arts. The students in undergraduate disciplines traditionally oriented toward medicine (biological, physical, and chemical sciences) were younger and had made the decision to become a physician at earlier ages than had their counterparts with undergraduate majors in social sciences and humanities. Also, the groups differed with regard to their estimates of their future incomes and plans for professional activities after graduation. Similarities concerning the students' preferred professional activities were also noticed among the groups.

Effects of serotonin, GABA and glycine on the activity of pause neurons during vestibular nystagmus in the cat.

Pause neurons (PNs), found in the pontine raphe nuclei, are important in the regulation of fast eye movements. The present study focuses on transmitters regulating the activity of the PNs. Extracellular spikes of single PNs and ocular motor nerve discharges were simultaneously recorded during horizontal vestibular nystagmus in the alert cat. Several transmitter candidates were iontophoretically applied, while methysergide, a serotonin antagonist, was administered both systemically and topically. The following data supported the conclusion that PNs are probably under the control of two different types of neurons, and the firing of PNs may be caused partly by GABAergic, but not by glycinergic neurons: 1) serotonin markedly decreased the spontaneous firing of the PNs; 2) methysergide abolished the inhibitory effect of serotonin on the PN firing; however, a pause pattern was maintained under this condition; 3) GABA moderately suppressed the firing but only in 25% of PNs; and 4) glycine hardly changed the PN firing in any case examined.

Neurotransmitter effects on inhibitory burst neurons in the cat.

The present experiment was designed to determine which neurotransmitter influences the burst pattern in the firing of the inhibitory burst neurons (IBN) during vestibular nystagmus. Cats were anesthetized with ether and mounted in a stereotaxic apparatus on a turntable, implanted stimulation electrodes, removed occipital bone and aspirated the vermal part of cerebellum. After the operation ether was discontinued. The recordings took place with the cats in an alert condition created by upper cervical cord transsection, artificial respiration and local anesthesia by infiltrating 0.5% lidocaine into the semilunar ganglions every two hours. We also employed iontophoretic application of the various drugs: GABA, muscimol, glycine, serotonin (5-HT) and bicuculline through seven-barrelled glass micropipettes. GABA or muscimol did not influence nystagmus rhythm, but both chemicals caused strong suppression of burst activities in IBN. Since this inhibitory effect of GABA was suppressed by the simultaneous application of bicuculline, IBNs appear to be controlled by GABAA receptor. Glycine and 5-HT did not change the firing pattern of IBN. Application of bicuculline itself caused an increase of tonic discharges of IBN. These findings suggest that IBN receive inhibitory impulses from the higher GABAergic neurons.

Further clinical experiences with middle-ear implantable hearing aids: indications and sound quality evaluation.

Since 1983, when the 5-year project on the middle-ear implantable hearing aids (MEI) was completed, we have been concentrating our studies on the clinical application of the partially implantable MEI (PMEI). The study was on the indication of implantation, improvement of the implantation operation, follow-up of the implanted patients, minor modification of the MEI, preparation of necessary surgical tools, and so on. Clinical study was also necessary for our team to finally confirm the clinical usefulness of this device. The present report is focussed mostly on the problem of indication for the application of PMEI.

Frequency-selective auditory brain-stem response in newborns and infants.

The efficacy of the frequency-selective auditory brain-stem response (ABR) in new borns and infants was assessed using an auditory stimulus of a 1-kHz tone pip and compared with the results of click-evoked ABR. In subjects whose responses to conventional behavioral audiometry were obtained at intensities of 40 to 70 dB, the ABR thresholds evoked by 1-kHz tone pips and clicks lay between 5 and 20 dB hearing threshold level (HTL). In subjects who did not respond to conventional behavioral audiometry at the intensity of 70 dB, ABR thresholds in each auditory stimulus were elevated by 35 to 70 dB HTL, and no responses were noted at 80 to 90 dB HTL. These results indicate that frequency-selective ABR can be applied clinically as an objective method of audiometry for newborns and infants.