Impacto da Estimulação Vagal na Indução e Interrupção de Fibrilhação Auricular no Modelo do Coração de Coelho in Vivo

INTRODUCTION: Vagal activity is thought to influence atrial electrophysiological properties and play a role in the initiation and maintenance of atrial fibrillation (AF). In this study, we assessed the effects of acute vagal stimulation (vagus_stim) on atrial conduction times, atrial and pulmonary vein (PV) refractoriness, and vulnerability to induction of AF in the rabbit heart with intact autonomic innervation. METHODS: An open-chest epicardial approach was performed in 11 rabbits (New Zealand; 3.9-5.0 kg), anesthetized and artificially ventilated after neuromuscular blockade. A 3-lead ECG was obtained. Atrial electrograms were recorded along the atria, from right to left (four monopolar electrodes), together with a circular electrode adapted for proximal left PV assessment. Acute vagus nerve stimulation was obtained with bipolar electrodes (20 Hz). Epicardial activation was recorded in sinus rhythm, and the conduction time from right (RA) to left atrium (LA), and from RA to PVs, was measured in basal conditions and during vagus_stim. The atrial effective refractory period (ERP) and dispersion of refractoriness (Disp_A) were analyzed. Vulnerability to AF induction was assessed at the right (RAA) and left (LAA) atrial appendages and the PVs. Atrial stimulation (50 Hz) was performed alone or combined with vagus_stim. Heart rate and blood pressure were monitored. RESULTS: In basal conditions, there was a significant delay in conduction from RA to PVs, not influenced by vagus_stim, and the PV ERPs were shorter than those measured in LA and LAA, but without significant differences compared to RA and RAA. During vagus_stim, conduction times between RA and LA increased from 16+8 ms to 27+6 ms (p < 0.05) and ERPs shortened significantly in RA, LAA and LA (p < 0.05), but not in RAA. There were no significant differences in Disp_A. AF induction was reproducible in 45% of cases at 50 Hz and in 100% at 50 Hz+vagus_stim (p < 0.05). The duration of inducible AF increased from 1.0 +/- 0.2 s to 12.0 +/- 4.5 s with 50 Hz+vagus_stim (p < 0.01). AF lasted >10 s in 45.4% of rabbits during vagus_stim, and ceased after vagus_stim in 4 out of these 5 cases. In 3 animals, PV tachycardia, with fibrillatory conduction, induced with 50 Hz PV pacing during vagus_stim. CONCLUSIONS: Vagus_stim reduces interatrial conduction velocity and significantly shortens atrial ERP, contributing to the induction and duration of AF episodes in the in vivo rabbit heart. This model may be useful for the assessment of autonomic influence on the pathophysiology of AF.

Imaging the Hypoglossal Nerve

The hypoglossal nerve is a pure motor nerve. It provides motor control to the intrinsic and extrinsic tongue muscles thus being essential for normal tongue movement and coordination. In order to design a useful imaging approach and a working differential diagnosis in cases of hypoglossal nerve damage one has to have a good knowledge of the normal anatomy of the nerve trunk and its main branches. A successful imaging evaluation to hypoglossal diseases always requires high resolution studies due to the small size of the structures being studied. MRI is the preferred modality to directly visualize the nerve, while CT is superior in displaying the bony anatomy of the neurovascular foramina of the skull base. Also, while CT is only able to detect nerve pathology by indirect signs, such as bony expansion of the hypoglossal canal, MRI is able to visualize directly the causative pathological process as in the case of small tumors, or infectious/inflammatory processes affecting the nerve. The easiest way to approach the study of the hypoglossal nerve is to divide it in its main segments: intra-axial, cisternal, skull base and extracranial segment, tailoring the imaging technique to each anatomical area while bearing in mind the main disease entities affecting each segment.

A Posterior Interosseous Nerve Syndrome Associated With Spontaneous Rupture of the Extensor Pollicis Longus Tendon

Posterior interosseous nerve entrapment syndrome and spontaneous rupture of the extensor pollicis longus tendon are rare conditions. The authors describe the bizarre combination of a spontaneous rupture of the extensor pollicis longus tendon in a 82-year-old lady with a posterior interosseous nerve syndrome. As far as the authors know, this is the first description of such an association in the literature. Surgical exploration revealed compression of the posterior interosseous nerve at the proximal portion of the supinator muscle and at Henry's leash. The nerve was freed, and the tendon of the extensor index proprius was transferred to the extensor pollicis longus. Six months after the procedure, the patient had resumed her daily activities, showing a good functional result.

Effects of Acute Autonomic Modulation on Atrial Conduction Delay and Local Electrograms Duration in Paroxysmal Atrial Fibrillation

Slowed atrial conduction may contribute to reentry circuits and vulnerability for atrial fibrillation (AF). The autonomic nervous system (ANS) has modulating effects on electrophysiological properties. However, complex interactions of the ANS with the arrhythmogenic substrate make it difficult to understand the mechanisms underlying induction and maintenance of AF. AIM: To determine the effect of acute ANS modulation in atrial activation times in patients (P) with paroxysmal AF (PAF). METHODS AND RESULTS: 16P (9 men; 59±14years) with PAF, who underwent electrophysiological study before AF ablation, and 15P (7 men; 58±11years) with atrioventricular nodal reentry tachycardia, without documentation or induction of AF (control group). Each group included 7P with arterial hypertension but without underlying structural heart disease. The study was performed while off drugs. Multipolar catheters were placed at the high right atrium (HRA), right atrial appendage (RAA), coronary sinus (CS) and His bundle area (His). At baseline and with HRA pacing (600ms, shortest propagated S2) we measured: i) intra-atrial conduction time (IACT, between RAA and atrial deflection in the distal His), ii) inter-atrial conduction time (interACT, between RAA and distal CS), iii) left atrial activation time (LAAT, between atrial deflection in the distal His and distal CS), iv) bipolar electrogram duration at four atrial sites (RAA, His, proximal and distal CS). In the PAF group, measurements were also determined during handgrip and carotid sinus massage (CSM), and after pharmacological blockade of the ANS (ANSB). AF was induced by HRA programmed stimulation in 56% (self-limited - 6; sustained - 3), 68.8% (self-limited - 6; sustained - 5), and 50% (self-limited - 5; sustained - 3) of the P, in basal, during ANS maneuvers, and after ANSB, respectively (p=NS). IACT, interACT and LAAT significantly lengthened during HRA pacing in both groups (600ms, S2). P with PAF have longer IACT (p<0.05), a higher increase in both IACT, interACT (p<0.01) and electrograms duration (p<0.05) with S2, and more fragmented activity, compared with the control group. Atrial conduction times and electrograms duration were not significantly changed during ANS stimulation. Nevertheless, ANS maneuvers increased heterogeneity of the local electrograms duration. Also, P with sustained AF showed longer interACT and LAAT during CSM. CONCLUSION: Atrial conduction times, electrograms duration and fractionated activity are increased in PAF, suggesting a role for conduction delays in the arrhythmogenic substrate. Acute vagal stimulation is associated with prolonged interACT and LAAT in P with inducible sustained AF and ANS modulation may influence the heterogeneity of atrial electrograms duration.

Intraocular Pressure Correlates with Optic Nerve Sheath Diameter in Patients with Normal Tension Glaucoma

PURPOSE: 1. Identify differences in optic nerve sheath diameter (ONSD) as an indirect measure of intracranial pressure (ICP) in glaucoma patients and a healthy population. 2. Identify variables that may correlate with ONSD in primary open-angle glaucoma (POAG) and normal tension glaucoma (NTG) patients. METHODS: Patients with NTG (n = 46) and POAG (n = 61), and healthy controls (n = 42) underwent B-scan ultrasound measurement of ONSD by an observer masked to the patient diagnosis. Intraocular pressure (IOP) was measured in all groups, with additional central corneal thickness (CCT) and visual field defect measurements in glaucomatous patients. Only one eye per patient was selected. Kruskal-Wallis or Mann-Whitney were used to compare the different variables between the diagnostic groups. Spearman correlations were used to explore relationships among these variables. RESULTS: ONSD was not significantly different between healthy, NTG and POAG patients (6.09 ± 0.78, 6.03 ± 0.69, and 5.71 ± 0.83 respectively; p = 0.08). Visual field damage and CCT were not correlated with ONSD in either of the glaucoma groups (POAG, p = 0.31 and 0.44; NTG, p = 0.48 and 0.90 respectively). However, ONSD did correlate with IOP in NTG patients (r = 0.53, p < 0.001), while it did not in POAG patients and healthy controls (p = 0.86, p = 0.46 respectively). Patient's age did not relate to ONSD in any of the groups (p > 0.25 in all groups). CONCLUSIONS: Indirect measurements of ICP by ultrasound assessment of the ONSD may provide further insights into the retrolaminar pressure component in glaucoma. The correlation of ONSD with IOP solely in NTG patients suggests that the translaminar pressure gradient may be of particular importance in this type of glaucoma.

Intraorbital Abducens Nerve Schwannoma

BACKGROUND: Schwannomas of the abducens nerve are extremely rare tumors. The tumor may be located within the cavernous sinus or more often at the prepontine region. However, literature research has identified only one case of isolated schwannoma of the orbit, arising from the terminal branches of the abducens nerve to the lateral rectus muscle. This is only the second report of an abducens nerve schwannoma located entirely intraconal. CASE DESCRIPTION: We report a case of an intraorbital abducens nerve schwannoma in a 42-year-old man with no signs of neurofibromatosis. The lesion resulted in progressive diplopia and focal abducens palsy. The clinical, radiologic, and pathologic features are presented. RESULTS: We point the particular aspects and discuss the possible treatments and approaches to preserve nerve function. CONCLUSIONS: Being a benign lesion, one of the goals has always been total removal. The knowledge of the correct anatomic features made us believe that the VI nerve function could be preserved. Our case is the first example of a total removal with eye abduction preserved. Because of that, we believe that it is reasonable to aim for these goals in future cases.

Brachial Plexus Morphology and Vascular Supply in the Wistar Rat

Introduction: The rat is probably the animal species most widely used in experimental studies on nerve repair. The aim of this work was to contribute to a better understanding of the morphology and blood supply of the rat brachial plexus. Material and Methods: Thirty adult rats were studied regarding brachial plexus morphology and blood supply. Intravascular injection and dissection under an operating microscope, as well as light microscopy and scanning electron microscopy techniques were used to define the microanatomy of the rat brachial plexus and its vessels. Results: The rat brachial plexus was slightly different from the human brachial plexus. The arterial and venous supply to the brachial plexus plexus was derived directly or indirectly from neighboring vessels. These vessels formed dense and interconnected plexuses in the epineurium, perineurium, and endoneurium. Several brachial plexus components were accompanied for a relatively long portion of their length by large and constant blood vessels that supplied their epineural plexus, making it possible to raise these nerves as flaps. Discussion: The blood supply to the rat brachial plexus is not very different from that reported in humans, making the rat a useful animal model for the experimental study of peripheral nerve pathophysiology and treatment. Conclusion: Our results support the homology between the rat and the human brachial plexus in terms of morphology and blood supply. This work suggests that several components of the rat brachial plexus can be used as nerve flaps, including predominantly motor, sensory or mixed nerve fibers. This information may facilitate new experimental procedures in this animal model.

Sciatic Nerve High Division: Two Different Anatomical Variants

Introduction: Sciatic nerve variations are relatively common. These variations are often very significant in several fields of Medicine. The purpose of this paper is to present two such variants and discuss their clinical implications. Material and Methods: Three Caucasian cadavers with no prior history of lower limb trauma or surgery were dissected and found to present anatomical variants of the sciatic nerve. Results: In all cases the sciatic nerve divided above the popliteal fossa. In two cases (cadavers 1 and 2) it divided on both sides in the inferior portion of the gluteal region in its two terminal branches: the common fibular and the tibial nerves. In another case (cadaver 3) the sciatic nerve was found to divide inside the pelvis just before coursing the greater sciatic notch. The common fibular nerve exited the pelvis above the pyriformis muscle and then passed along its posterior aspect, while the tibial nerve coursed deep to the pyriformis muscle. Discussion: According to the literature, the anatomical variant described in cadaver 3 is considered relatively rare. This variant can predispose to nerve entrapment and thus to the pyriformis syndrome, sciatica and coccygodynia. The high division of the sciatic nerve, as presented in cadavers 1 and 2, can make popliteal nerve blocks partially ineffective. Conclusion: The anatomical variants associated with a high division of the sciatic nerve, must always be born in mind, as they are relatively prevalent, and have important clinical implications, namely in Anesthesiology, Neurology, Sports Medicine and Surgery.

Optic Nerve Drusen: Find the Differences

Introdução: Os drusens do disco ótico são anomalias congénitas do desenvolvimento da cabeça do nervo ótico, correspondendo a depósitos hialinos calcificados, localizados anteriormente à lâmina crivosa. O seu diagnóstico é maioritariamente acidental, em doentes normalmente assintomáticos. Material e Métodos: Os autores apresentam 5 casos clínicos de doentes com idades de apresentação compreendidas entre 6 e 12 anos, observados na Consulta de Oftalmologia Pediátrica e Estrabismo, à qual foram referenciados por diferentes motivos. Resultados: Nos casos clínicos apresentados os motivos de consulta foram diminuição da acuidade visual, estrabismo divergente, cefaleias com suspeita de papiledema e rotina. O exame oftalmológico e os meios complementares de diagnóstico realizados, nomeadamente retinografia, ecografia ocular, tomografia de coerência ótica e campos visuais, contribuíram para o diagnóstico de drusens do nervo ótico. Foram ainda encontrados erros refractivos em 4 dos casos descritos. Conclusão: Salienta-se a importância de uma história clínica e observação detalhadas para o diagnóstico diferencial e despiste de patologias oftalmológicas concomitantes, em doentes com drusens do disco ótico e seus familiares.