Initial Positive Deflection Research Articles

The Application of a New, Modified Algorithm for the Differentiation of Regular Ventricular and Pre-excited Tachycardias.

The three-step Brugada group algorithm is the only published electrocardiographical (ECG) algorithm for differentiating ventricular tachycardia (VT) from pre-excited tachycardia (PXT) as a cause of regular wide QRS complex tachycardia (WCT). This study aimed to improve the diagnostic accuracy of the Brugada group algorithm. This study modified the Brugada group algorithm by adding a new aVR lead criterion (initial positive deflection in lead aVR and the QRS complex area above the baseline is greater than the area below the baseline). The Brugada group algorithm and the new, modified four-step algorithm in 300 WCT ECGs (241 VTs, 59 PXTs) was applied. If any of the criteria were fulfilled, VT was diagnosed; if none were fulfilled, a diagnosis of PXT was established. The test accuracy, VT diagnosis sensitivity, and negative predictive value (NPV) of the new, modified algorithm were significantly greater than that of the Brugada group algorithm: test accuracy 220 of 300 (73%) vs 182 of 300 (61%); sensitivity 73% vs 55% (p<0.001 for both); NPV 40% vs 31% (p=0.0205). The VT diagnosis specificity of the Brugada group algorithm was greater than that of the new, modified algorithm (83% vs 75%; p=0.019). There was no significant difference between the new, modified and Brugada group algorithms in the positive predictive values (92% vs 93%, respectively) for a VT diagnosis, and positive and negative likelihood ratio values (2.87 vs 3.26; 0.36 vs 0.54, respectively). The new, modified algorithm proved to be more sensitive for the differentiation of VT from PXT than the Brugada group algorithm.

PO-04-061 A RARE CASE OF FOCAL LEFT VENTRICULAR OUTFLOW TRACT VENTRICULAR TACHYCARDIA LATE AFTER TRANSCATHETER AORTIC VALVE REPLACEMENT

Transcatheter aortic valve replacement (TAVR) is commonly used to treat severe aortic stenosis (AS). To date there is only one reported case of post-TAVR, new onset, left ventricular outflow tract (LVOT) ventricular tachycardia (VT) which was ablated above the TAVR valve. We report a case of late presenting symptomatic LVOT VT, which was successfully ablated via a trans-septal approach, without fluoroscopy, using intracardiac echocardiography (ICE) and electroanatomic mapping (EAM), thereby, avoiding catheter manipulation in the aorta above the valve. N/A A 68-year-old man underwent TAVR for severe AS with Sapien 3 valve (Edwards Lifescience). Nine months later, the patient developed worsening dyspnea. Echocardiogram showed well seated TAVR valve, and exercise nuclear stress revealed no ischemia. During the stress test, he had slow monomorphic VT at rest, during exercise, and recovery (100-120 bpm). A 24-hour Holter monitor revealed a ventricular arrhythmia burden of 55% with rates between 85 and 112 bpm. The 12-lead ECG of VT had an initial positive deflection in lead I, QS in V1 and V2, and an initial R wave in V3 taller than the sinus QRS, suggesting a septal right ventricular outflow tract (RVOT) vs. LVOT origin. There was no improvement with beta-blocker therapy. An electrophysiology study was performed using ICE and CARTO (Biosense Webster, Diamond Bar, CA). Activation mapping in the septal RVOT revealed a 20ms presystolic electrogram (far field) and an 80% pace map, despite the unipolar signal with QS complex. Radiofrequency ablation performed at this site only mildly suppressed the arrhythmia. The decision was made to map from the LVOT via transseptal access using EAM and real-time markers from Cartosound real time images to accurately visualize the ablation catheter below the TAVR. Earliest activation was beneath the left coronary cusp directly across the RVOT lesions with a sharp 22ms pre-systolic electrogram, unipolar QS, and 90% pace map match. Ablation performed here successfully eliminated the VT even after isoproterenol infusion and programmed stimulation. The patient’s symptoms have resolved, and he remains arrhythmia free. LVOT VA’s may rarely occur post TAVR, although a direct cause cannot be ascertained. This is the first report of successfully ablating the arrhythmia in a TAVR patient using a transeptal, subvalvular approach without fluoroscopy, and avoiding any risks associated with the aortic approach.

Initial T wave morphology in the chest leads in patients presenting with anterior ST-segment elevation myocardial infarction and its correlation with spontaneous reperfusion of the left anterior descending coronary artery

Background: T wave inversion in leads with ST-segment elevation after reperfusion therapy is considered a sign of reperfusion. However, the significance of T wave inversion on presentation before the initiation of reperfusion therapy is unclear. Aim of the Work: The current study aimed to assess whether the initial T wave morphology in the electrocardiographic (ECG) at presentation can predict patency of the left anterior descending artery (LAD) in patients with acute anterior ST segment elevation myocardial infarction (STEMI) before undergoing primary percutaneous coronary interventions (PCIs). Methods: This study included ninety patients who presented to the emergency department with acute anterior ST-elevation MI. We excluded patients with bundle branch block, postcoronary artery bypass grafting patients, patients with paced rhythm, and patients who received thrombolytic therapy. The T wave morphology in the 2 leads with maximal ST-segment elevation on the presenting ECG was identified as one of the three morphologies, positive T waves (T+; initial positive deflection ≥0.5 mm above the isoelectric line), biphasic T waves (T+/−; where the T wave initially showed a positive deflection above the ST segment afterward followed by a negative deflection ≥0.5 mm below the isoelectric line), and negative T waves (T−; where the T wave initially showed a negative deflection ≥0.5 mm below the isoelectric line without showing any initial positive deflection). Then, according to the results of the initial angiography, patients were classified into spontaneous reperfusion (SR) (those with thrombolysis in MI [TIMI] II or TIMI III flow in the infarct-related artery [IRA] prior to intervention) or non-SR (those with TIMI 0 or TIMI I flow in the IRA prior to intervention). Results: Ninety consecutive patients (77 males and 13 females) presented by STEMI and treated by primary PCI at cath lab of Ainshams University Hospitals (a 24/7 tertiary referral center for primary PCI) between January 2015 and March 2016 were included in this study, of which 40 patients (44.4%) had positive T waves (T+), 34 patients (37.8%) had negative T waves (T−), and 16 patients (17.8%) had biphasic T waves (T+/−). Initial angiogram showed that 18 patients had SR and 72 patients had no SR. With regard to T wave morphology, negative T waves were significantly present in SR group (66.7% vs. 30.6%, P = 0.004), whereas positive T waves were predominantly present in non-SR (50% vs. 22.2%, P = 0.033). Conclusions: For SR of LAD in anterior STEMI patients, prior to primary PCI, T wave inversion had a good sensitivity of 66.7%, a specificity of 69.4%, and a good negative predictive value of 89.29%.

Zebrafish needle EMG: a new tool for high-throughput drug screens

Zebrafish models have recently been highlighted as a valuable tool in studying the molecular basis of neuromuscular diseases and developing new pharmacological treatments. Needle electromyography (EMG) is needed not only for validating transgenic zebrafish models with muscular dystrophies (MD), but also for assessing the efficacy of therapeutics. However, performing needle EMG on larval zebrafish has not been feasible due to the lack of proper EMG sensors and systems for such small animals. We introduce a new type of EMG needle electrode to measure intramuscular activities of larval zebrafish, together with a method to hold the animal in position during EMG, without anesthetization. The silicon-based needle electrode was found to be sufficiently strong and sharp to penetrate the skin and muscles of zebrafish larvae, and its shape and performance did not change after multiple insertions. With the use of the proposed needle electrode and measurement system, EMG was successfully performed on zebrafish at 30 days postfertilization (dpf) and at 5 dpf. Burst patterns and spike morphology of the recorded EMG signals were analyzed. The measured single spikes were triphasic with an initial positive deflection, which is typical for motor unit action potentials, with durations of ∼10 ms, whereas the muscle activity was silent during the anesthetized condition. These findings confirmed the capability of this system of detecting EMG signals from very small animals such as 5 dpf zebrafish. The developed EMG sensor and system are expected to become a helpful tool in validating zebrafish MD models and further developing therapeutics.

Poster 117 Electrophysiological Assessment of the Sural Nerve in Mice Treated with Saline and Cisplatin: A Pilot Study

distal latency with preserved distal amplitude and mild partial sensory conduction block at the wrist. 2. Right median thenar CMAP was reduced in amplitude with initial positive deflection; normal amplitude was restored with stimulation over the ulnar nerve. Median CMAP at lumbrical II was mildly delayed with borderline decreased amplitude. 3. Needle EMG examination of the right APB was normal. Impression: 1. Mild to moderate right median neuropathy at the wrist (carpal tunnel syndrome). 2. Right Riche-Cannieu anastomosis. Discussion: Riche-Cannieu anastomosis is a common neuroanatomical variant involving a deep ulnar motor-to-recurrent median branch anastomosis. The “all ulnar hand“ may initially appear on nerve conduction studies to resemble a severe median neuropathy. This misdiagnosis may lead to unnecessary surgical intervention. Conclusions: Riche-Cannieu anastomosis should be included in the differential when median thenar CMAP is severely reduced in the setting of well-preserved thenar musculature.

A new approach to confirming or excluding ventricular pre-excitation on a 12-lead ECG

The purpose of this study was to determine simple features of the standard 12-lead electrocardiogram (ECG) and incorporate them in a stepwise algorithm that would help confirm or exclude the presence of ventricular pre-excitation. We retrospectively analysed multiple variables on pre- and post-ablation ECGs in 238 patients with manifest accessory pathways that had been successfully ablated. A new variable, PR dispersion, was defined as a difference between maximum and minimum PR intervals on a single 12-lead ECG. A logistic regression analysis showed the combination of the following criteria to be powerful in the confirmation of the diagnosis in patients with suspected delta wave: presence of both PR interval < or = 120 ms and PR dispersion > or = 20 ms, absence of initial positive deflection (septal R wave) in lead augmented voltage right arm (aVR), and horizontal QRS transition in lead V1 or before. A stepwise algorithm was developed based on these criteria. Of the total 476 ECGs, seven patients with pre-excitation and one patient with normal ECG were misdiagnosed using the algorithm. Even though the retrospectively determined sensitivity and specificity of the three stepwise criteria were high (97% and 99%, respectively) a prospective study evaluating the algorithm is needed. Using a stepwise approach is a very sensitive and specific technique for excluding or confirming ventricular pre-excitation on a 12-lead ECG.

Epicardial transcatheter ablation through the coronary sinus in a patient with a biventricular device and left ventricular outflow tract ventricular arrhythmias

Left ventricular outflow tract (LVOT) may be a source of isolated ventricular premature beats (VPBs), frequently in short VT runs, resistant to drug therapy. In highly symptomatic pts, radiofrequency catheter ablation (RFCA) can be effective, either from the endocardial or from the epicardial site. We report the case of a 50 years old patient, female, with primitive DCM and severe LV dysfunction (LVEF 20%), LBBB, NYHA class IV, who received a biventricular ICD in 2002, because of clinical episodes of VT. Despite amiodarone and previous RFCA of sustained VT circuits, frequent VPBs were still present at Holter monitoring (21.019 /24 h) even in prolonged sequences, conditioning 6 ICD’s interventions in the last 2 months. Most of VPBs and documented VT runs showed an inferior axis morphology, with an initial positive deflection in the first precordial leads and R/S ratio in V3 >1, suggesting a possible LVOT origin. This was the target of a further RFCA procedure. After informed consent was given, the RVOT was firstly mapped with unsatisfactory results. Using a 4 mm. irrigated tip electrode, a detailed mapping of the endocardial LVOT was then performed, from the anterior MV aspect to the aortic cusps, with better results in terms of prematurity, compared to RVOT, but no 12/12 concordance at pacemapping. Despite the presence of a CRT device, with a 4F lead positioned in the lateral CS branch, an epicardial LVOT mapping through the CS was attempted. After the detection of −48 ms prematurity and 12/12 concordance at pacemapping, successful RFCA was performed at the anterior aspect of LVOT in the anterior CS branch, with RF power titration (from 10 to 20 W, 3 pulses of 1 min.). A fast, complete and stable suppression of VPBs was evident, with no periprocedural or late complications. At 1, 3 and 6 months follow-up, no further ICD’s interventions were documented, the LVEF and NYHA class improved (respectively to 40 % and class II), while the total number of daily VPBs was <100 at repeated Holter recordings, with the same drug therapy. To our knowledge, this is a first case describing epicardial RFCA from CS in presence of a CRT device.

Hybrid fibrillation potentials and positive sharp waves.

Fibrillation potential configurations are characterized as initially positive triphasic waveforms, whereas positive sharp waves appear biphasic with an initial positive deflection. Careful observation of single muscle fiber discharges in denervated muscle, however, can reveal many different-appearing and stable firing waveforms that resemble a bifid positive sharp wave or some form of combined fibrillation potential and positive sharp wave. In this investigation, a number of atypical-appearing single muscle fiber discharges are hypothesized to arise from particular interactions between the muscle fiber and recording electrode. Single muscle fiber potentials are modeled as originating from a single denervated muscle fiber's former endplate and midfiber region as well as from the fiber's tendinous termination for both a compressed and sealed end effect. The modeled waveforms' appearance corresponds well to those obtained clinically and the necessary interpotential summated templates' temporal domains are feasible for action potential termination at the electrode with subsequent reinitiation beyond the proposed peri-electrode compressed region. It is hypothesized that the majority of hybrid waveforms are the result of a single muscle fiber action potential terminating at a recording electrode while also initiating a "skipped" activation of the muscle fiber past the electrode resulting in the summation of two distinct time-locked waveforms.

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF

Abstract. We document the detailed dynamics of the dayside aurora in the \\sim1200-1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic field (IMF) under negative IMF By conditions. Features not documented in previous work are elucidated by using two meridan scanning photometers (separated by 2 h) and an all-sky auroral imager in Ny Ålesund, Svalbard (75.5°MLAT) in combination with magnetograms from stations on Svalbard, covering the latitude range 71°75°MLAT. The initial auroral response may be divided into three phases consisting of: (1) intensification of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and ~100 km equatorward shift of its equatorward boundary, at ~75°MLAT, (2) eastward and poleward expansions of the cusp aurora, reaching the 1430 MLT meridian after 5-6 min, and (3) east-west expansion of the higher-latitude aurora (at ~77°78°MLAT) in the postnoon sector. The associated magnetic disturbance is characterized by an initial positive deflection of the X-component at stations located 100-400 km south of the aurora, corresponding to enhanced Sunward return flow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the first 15 min, accompanied by corresponding pulsations in the convection current, was followed by a strong westward contraction of the cusp aurora when the ground magnetograms indicated a temporary return to the pre-onset level. These observations are discussed in relation to the Cowley-Lockwood model of ionospheric response to pulsed magnetopause reconnection.Key words. Mangetospheric physics (magnetopause · cusp and boundary layers; solar wind-magnetosphere interactions; auroral phenomena)

COMPARISON OF THREE METHODS FOR RECORDING TIBIAL H REFLEX

Recording the tibial H reflex from the calf is routine in clinical electromyography. Two widely used methods are Hugon's and Braddom and Johnson's. Both methods produce an H wave with an initial positive deflection. Another method, the "half and half" method, generates an H wave with an initial negative deflection. To compare these methods, H-reflex responses were recorded in the right calf of 20 normal adults with each method using identical amplifier and stimulator settings. Stimulus current was increased by increments of 0.5-1.0 mA until the H reflex and motor (M) wave responses reached maximum amplitudes (Hmax, Mmax). H wave to M wave (H/M) amplitude ratios were calculated. The half-and-half method produced greatest Hmax, Mmax, and H/M ratio. Wave form configuration for the half-and-half method was biphasic with an initial negative deflection; it was triphasic with an initial positive deflection with the other methods. The shapes of M and H waves were similar in two methods but dissimilar in one. Because of the greater amplitude and the initial negative deflection, the H wave may be easier to detect with the half-and-half method and may present a latency that is more easily determined. For these reasons, the half-and-half method is recommended for measuring amplitude and latency in clinical settings.

Effect of xenon on central nervous system electrical activity during sevoflurane anaesthesia in cats: comparison with nitrous oxide

We have compared the effects of xenon and nitrous oxide on central nervous system (CNS) electrical activity during sevoflurane anaesthesia in cats by recording the electroencephalogram (EEG), multi-unit activity of the midbrain reticular formation (R-MUA) and somatosensory evoked potentials (SEP). Basal anaesthesia with 2% and 5% sevoflurane was used. With 2% sevoflurane, 70% xenon initially produced rhythmic slow waves which were followed by bursts of high-amplitude sharp waves interrupted by low amplitude slow waves on the EEG. Xenon induced an initial increase, followed by a decrease in R-MUA. Nitrous oxide 70% decreased the amplitude of the EEG activity which was associated with an increase in R-MUA. Xenon suppressed the amplitude of both the initial positive and negative deflections of the SEP to a greater extent than nitrous oxide. With 5% sevoflurane anaesthesia, both anaesthetics increased the frequency of spikes on the EEG and facilitated R-MUA. These findings indicate that xenon has a stimulatory action on CNS background activity and a suppressive action on CNS reactive capability which is more potent than that of nitrous oxide.

Spatio-temporal dynamics of attention to color: evidence from human electrophysiology.

This study characterized patterns of brain electrical activity associated with selective attention to the color of a stimulus. Multichannel recordings of event-related potentials (ERPs) were obtained while subjects viewed randomized sequences of checkerboards consisting of isoluminant red or blue checks superimposed on a grey background. Stimuli were presented foveally at a rapid rate, and subjects were required to attend to the red or blue checks in separate blocks of trials and to press a button each time they detected a dimmer target stimulus of the attended color. An early negative ERP component with an onset latency of 50 ms was sensitive to stimulus color but was unaffected by the attentional manipulation. ERPs elicited by attended and unattended stimuli began to diverge after approximately 100 ms following stimulus onset. Inverse dipole modelling of the attended-minus-unattended difference waveform indicated that an initial positive deflection with an onset latency of 100 ms had a source in lateral occipital cortex, while a subsequent negative deflection with an onset at 160 ms had a source in inferior occipito-temporal cortex. Longer-latency attention-sensitive components were localized to premotor frontal areas (onset at 190 ms) and to more anterior regions of the fusiform gyrus (onset at 240 ms). These source localizations correspond closely with cortical areas that were identified in previous neuroimaging studies as being involved in color-selective processing. The present ERP data thus provide information about the time course of stimulus selection processes in cortical areas that subserve attention to color.

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc. Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negativity with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.

Cholinergic, GABAergic, and dopaminergic influences on visually evoked field potentials in the superficial optic tectum of Bufo marinus

Field potentials (FPs) were recorded from the dorsal surface of the toad's ( Bufo marinus) optic tectum (OT) in response to onset (ON) and offset (OFF) of diffuse illumination. FPs showed initial positive deflections P1 ∗ due to presynaptic axonal inputs; subsequent negative N1 and N2 waves and positive P2 and P3 waves reflected summated excitatory and inhibitory postsynaptic processes, respectively, in superficial tectal laminae. The influence of neuropharmaca on the visually evoked FPs was investigated. Acetylcholine led to an initial increase and a subsequent decrease of the N1 and P2 waves, e.g., suggesting a cholinergic retinotectal transmission and a delayed ACh-receptor desensitization. The effects on N1, N2, and P2, P3 waves were differently strong in response to ON- and OFF-stimulation. After administration of alpha-tubocurarine, the N1 and P2 waves were reduced, while in the first OFF response the N2 and P3 waves were remarkably enlarged, particularly the former. GABA led to an unexpected increase of all waves, whereas picrotoxine showed opposite effects, suggesting a special GABAergic excitatory mechanism. Dopamine, L-dopa, or apomorphine did not influence the visually evoked FPs.

Effect of neuropeptide-Y on tectal field potentials in the toad

Field potentials (FP) recorded from the surface of toad's optic tectum (OT) to electrical stimulation of the contralateral optic nerve (ON) show initial positive deflections P *, followed by negative wave N and positive wave P; the former result from axonal inputs, the latter two resemble excitatory and inhibitory postsynaptic processes, respectively. Electrostimulation of the pretectum ipsilaterally to the recorded OT — preceeding ON-stimulation — strongly attenuates the N wave, suggesting pretectotectal inhibitory influences. The N wave of the tectal FP evoked by ON-stimulation is reduced, too, after application of the neuropeptide-Y (NPY) to the tectal surface. Previous authors have shown that frog's pretectum contains NPY immunoreactive pretectotectal projecting cells.

Estrogen-sensitive neurons in the female rat ventral tegmental area: a dual route for the hormone action

1. Electrical stimulation of the ventral part of the midbrain central gray (CG) elicited antidromic action potentials in 136 neurons in the ventral tegmental area (VTA) of 23 urethan-anesthetized ovariectomized female rats. 2. Antidromic action potentials were positive-negative biphasic and completed mostly within 2.4 ms. Many had a notch in their initial positive deflection, at which antidromic potentials often failed to propagate into the neuronal soma. 3. The latency for antidromic activation ranged 1.0-10.5 ms, and the threshold was 100-1,700 microA. The relative refractory period was 0.8-2.8 ms. In 23 neurons (17%) gradual changes in stimulus intensity caused latency jumps, suggesting that their axons terminate or spread into branches in stimulation sites. 4. The parameters for antidromic activation were compared among 12 animals with a subcutaneous Silastic capsule of estrogen and 11 others with a blank capsule. Estrogen raised the mean threshold from 675 +/- 40 (SE) microA (n = 69) to 908 +/- 40 microA (n = 67). At the same time, estrogen significantly decreased the probability of the antidromic propagation from 63 to 41%. No changes were detected in the latency or the refractory period. 5. The probability distribution of the threshold was different in ovariectomized animals from that in estrogen-treated animals. Estrogen increased the number of cells with thresholds in the 1,300- to 1,500-microA range. 6. The probability of antidromic propagation was stable in each neuron to stimuli repeated at 1.0 Hz. Electrical stimulation of the preoptic area (POA) with a 30-s train of 50-microA pulses at 100 Hz increased the probability of antidromic propagation into the soma.(ABSTRACT TRUNCATED AT 250 WORDS)

Component-specific effects of physostigmine on the cat visual evoked potential.

Pattern visual evoked potentials (VEPs) were recorded from the pial surface of the cat primary visual cortex prior to and following the intravenous administration of physostigmine, an agent which blocks the enzyme responsible for the breakdown of synaptically released acetylcholine. The control VEP was composed of a small initial positive deflection (P1), a subsequent large negative wave (N1) and a second large positive wave (P2). Following physostigmine, the amplitude of P1-N1 was diminished whereas that of N1-P2 increased. These effects were long lasting and were blocked by prior treatment with scopolamine, a result consistent with mediation by a muscarinic cholinergic pathway. Waveform subtraction revealed that the physostigmine-sensitive component had a slow, negative polarity waveform while the physostigmine-insensitive component was also slow, but positive in polarity. The fundamental nature of these components remains to be assessed. Nevertheless, the results indicate that waveforms of different polarity combine algebraically to yield the conventional VEP.

Recording compound action potentials from the optic nerve in man and monkeys

Compound action potentials were recorded from the optic nerve in patients undergoing neurosurgical operations and in rhesus monkeys. The stimuli were short light flashes delivered by light-emitting diodes that were bonded to plastic contact lenses positioned on one or both eyes, and potentials were recorded simultaneously from electrodes placed on the scalp. Potentials recorded from the optic nerve in man have an initial small positive deflection, with a latency of about 45 msec, followed by a negativity with a latency of 60–70 ,msec. The wave form depends on the recording site on the optic nerve and, occasionally, oscillations with a frequency around 100 Hz were seen in the responses from the optic nerve. There was considerable individual variation in the shape and size of the recorded potentials, but most potentials recorded simultaneously from an electrode placed on Oz with a reference electrode on the forehead appeared as positive deflections with latencies of about 80 msec and, occasionally, with a small positivity with a latency of about 45 msec. Compound action potentials recorded from the optic nerve near the ocular globe in the rhesus monkey in response to similar light flashes appeared as negative deflections with latencies of about 17 msec. The potentials recorded at the chiasm appeared as initial positive deflections, with the latency of the earliest peak being about 35 msec, on which oscillations with frequencies of about 100–150 Hz occasionally could be seen. The recordings from electrodes placed on the scalp (Cz-Oz and Cz-shoulder) in the monkey showed a positive peak with a latency of about 65 msec. In some animals a small negative peak with a latency of 40 msec was seen.

Self-assessment examination: 1987 pretest on electrodiagnosis

1. When doing an electromyogram (EMG) on the left lower extremity and its related paraspinals, you find diphasic potentials with a large initial positive deflection spontaneously firing irregularly and confined to the lumbar paraspinal, extensor hallucis longus. and flexor digitorum longus muscles. EMG testing in other muscles in this extremity is normal. The left peroneal nerve conduction velocity is 46 misec below the fibular head and 48 misec across the fibular head. The most likely diagnosis is ( 1) S 1 radiculopathy (2) L4 radiculopathy (3) L5 radiculopathy (4) upper motor neuron disease (5) peroneal palsy

Cell size, projection path, and localization of estrogen-sensitive neurons in the rat ventromedial hypothalamus.

Antidromic action potentials were recorded in and around the ventromedial nucleus of the hypothalamus (VMN) of the ovariectomized female rat following stimulation of the central gray matter of the mesencephalon (CG). The animals had either the lateral or caudal trajectory of the VMN efferent disrupted by a small knife cut. Changes in the polarity, peak-to-peak amplitude, and the duration of the initial positive deflection of the antidromic action potentials were recorded for each response as the recording electrode was advanced at 10-micron intervals from the point of detection of the potential until its deterioration. Seventy-four recordings in which potentials exceeded 2 mV at the maxima were subjected to further analysis. The mean spatial spread of the extracellular antidromic action potentials, which was measured by moving the recording electrode at 10-micron intervals, was significantly larger in responses in 17 animals bearing the posterior knife cut (n = 41) than those in 15 animals with the lateral knife cut (n = 33). Mean peak-to-peak amplitude was also significantly greater in responses from the posterior-cut animals than in those from the lateral-cut ones. In the former, action potentials were completed with a shorter time lapse than the latter. In the posterior-cut animals, estrogen treatment of the ovariectomized rats significantly lowered antidromic activation thresholds and shortened absolute refractory periods for CG stimulation. Estrogen had no detectable effect on the excitability of cells that survived the lateral cut. Histological analyses located antidromically driven cells in the posterior-cut animals in the rostral extremity of the VMN and the adjacent retrochiasmatic area; those in the lateral-cut animals were scattered in and around the VMN, caudad to the former. These results suggest that rostral VMN neurons with large soma and laterally projecting axons are responsible for estrogen-dependent autonomic, neuroendocrine, and behavioral functions, such as reproduction and feeding.