Cervical Vestibular Evoked Myogenic Potentials (cVEMPs) Evoked by Air-Conducted Stimuli in Patients with Functional Neck Dissection.

OBJECTIVE: Cervical vestibular-evoked myogenic potentials (cVEMPs) are short-latency vestibulocollic reflexes. The damage on any point of the vestibulocollic reflex pathway could affect the cVEMPs. Whether neck dissection has an effect on the sacculocollic pathway, and consequently on cVEMPs, remains unexplored. The aim of this study was to evaluate the cVEMP findings in patients with functional neck dissection without vestibular symptoms. PATIENTS AND METHODS: This cross-sectional study design, 20 patients who had undergone unilateral neck dissection with sparing of the accessory nerve, SCM and internal jugular vein, were included. The response rates (%), cVEMPs parameters such as the prestimulus background EMG [Root mean square (RMS)] activity (µV), P13 and N23 peak latencies (ms), interpeak (N23-P13) interval (ms), scale and non-scale interpeak (N23-P13) amplitudes (µV) were compared between the groups. Amplitude asymmetry ratio (AAR) was calculated. RESULTS: Twenty patients (14 males and 6 females), age was between 38 and 79 years were included in the study. All of the patients had clear cVEMPs on the NOS, whereas 18/20 (90%) patients had on the NDS. P13 and N23 peak latency of the NDS were found to be significantly longer than the NOS (P = 0.01). There was no significant difference in N23-P13 interpeak interval between two sides (P > 0.05). There was a negative correlation between P13 peak latency and post-operative time (P = 0.042; R = ­0.484). Scale and non-scale N23-P13 interpeak amplitudes of the NDS were found to be significantly lower than the NOS (P = 0.03). Mean AAR was found as 0.28 ± 0.16 (0.08-0.76). Seven patients (35%) had abnormal amplitude asymmetry. RMS values, were statistically and significantly lower in NDS compared to NOS (P = 0.01). However, no correlation was observed between the RMS values and peak latency and peak amplitude values (P > 0.05). CONCLUSIONS: cVEMP testing is an easy-to-apply, non-invasive, painless, and recordable test that can be used for evaluations of SAN and SCM function for patients undergoing neck dissection. After neck dissection, VEMP abnormalities can be detected. However, further studies are needed to indicate whether these abnormalities originate within the vestibular system and are due to pathologies originating from the SANs and SCMs. In addition, preoperative and postoperative studies are needed to better guide the clinical application of cVEMP testing.

Mechanisms for the genesis of paroxysmal atrial fibrillation in the Wolff Parkinson-White syndrome: intrinsic atrial muscle vulnerability vs. electrophysiological properties of the accessory pathway.

BACKGROUND: Paroxysmal atrial fibrillation (PAF) develops in up to one-third of patients with the Wolff Parkinson-White syndrome (WPW). The reason for this high incidence of PAF in the WPW syndrome is not yet clearly understood. When PAF appears in patients with WPW syndrome who have anterograde conduction via the accessory pathway (AP), it may be life-threatening if an extremely rapid ventricular response develops degenerating into ventricular fibrillation. METHODS AND RESULTS: Several mechanisms responsible for the genesis of PAF in WPW patients were hypothesized, namely, spontaneous degeneration of atrioventricular reciprocating tachycardia into atrial fibrillation (AF), electrical properties of the APs, effects of APs on atrial architecture, and intrinsic atrial muscle vulnerability. Focal activity, multiple reentrant wavelets, and macroreentry have all been implicated in AF, perhaps under the further influence of the autonomic nervous system. AF can also be initiated by ectopic beats originating from the pulmonary veins, and elsewhere. Several studies demonstrated a decrease incidence of PAF after successful elimination of the AP, suggesting that the AP itself may play an important role in the initiation of PAF. However, PAF still occurs in some patients with the WPW syndrome even after successful elimination of the AP. There is an important evidence of an underlying atrial disease in patients with the WPW syndrome. CONCLUSIONS: Atrial vulnerability has been studied performing an atrial endocardial catheter mapping and analysing abnormal atrial electrograms. Other studies evaluated atrial refractoriness and intraatrial conduction times, suggesting an intrinsic atrial vulnerability as the mechanism of PAF and considering the AP as an innocent bystander. It is our intention to analyse the available data on this particular and interesting topic since AF has a singular prognostic significance in patients with the WPW syndrome, and its incidence is unusually high in the absence of any clinical evidence of cardiac organic disease.

Masseteric repetitive nerve stimulation in the diagnosis of myasthenia gravis.

OBJECTIVE: (1) to develop a method for masseteric repetitive nerve stimulation (RNS) and to obtain normative data for amplitude and area decrement of the muscle (M) response. (2) To investigate myasthenia gravis (MG) patients with masseteric RNS. Masticatory muscles are frequently affected in MG, but no RNS test is available to investigate this district. METHODS: Fifteen healthy subjects and 17 MG patients were examined. The masseteric nerve was stimulated by a monopolar needle (cathode), inserted between the mandibular incisure and the zygomatic arch, and a surface electrode (anode), on the contralateral cheek. Masseteric M response was recorded using surface electrodes on the muscle belly and below the mandibular angle. Stimuli were delivered at 3 Hz in trains of 9, at rest and after isometric effort. RESULTS: Normal subjects: mean amplitude decrement was 0.3+/-1.2% at rest, and 1.9+/-1.3% after isometric effort. PATIENTS: 15 patients (88%) were positive on masseteric RNS; in 3 of these it was the only positive RNS test. The extent of decrement observed in masseter muscle was significantly greater than in trapezius muscle. CONCLUSIONS: Masseteric RNS is a simple and well-tolerated procedure; it offers a new possibility in testing the cranial muscles in disorders of neuromuscular transmission.

Hyperventilation facilitates induction of supraventricular tachycardia: a novel method and the possible mechanism.

INTRODUCTION: Hyperventilation has been demonstrated to alter autonomic function. Sympathomimetic drugs (isoproterenol) and parasympatholytic drugs (atropine) may be needed to facilitate induction of supraventricular tachycardia (SVT). The aim of this study was to test the clinical utility and mechanisms of hyperventilation to facilitate SVT initiation. METHODS AND RESULTS: Fourteen patients with clinically documented SVT (9 AV nodal reentrant tachycardia and 5 AV reciprocating tachycardia) but noninducible during baseline electrophysiologic study were included. Immediately after hyperventilation test (at least 30 respirations/min) for 2 minutes, systolic blood pressure, sinus cycle length, anterograde and retrograde 1:1 conduction, and induced SVT were measured. Arterial blood gas, pH, and heart rate variability before and after hyperventilation were measured. Seven of nine patients with AV nodal reentrant tachycardia and 3 of 5 patients with AV reciprocating tachycardia could be induced immediately after the hyperventilation test. After hyperventilation, anterograde AV and retrograde VA 1:1 conduction were improved, sinus cycle length was decreased, and heart rate variability were decreased in both groups. CONCLUSION: Hyperventilation can facilitate induction of SVT. Improvement of conduction properties and changes of autonomic function are the possible mechanisms.

[Isolated lesion of the accessory nerve]. / De geïsoleerde N. accessorius-laesie.

An isolated accessory nerve lesion was diagnosed in three patients. At clinical investigation of patients with this lesion, paresis of the trapezius muscle is found. This finding can be substantiated by electromyography. An accessory nerve lesion is usually caused by trauma (including surgical trauma) or space-occupying lesions such as tumour or abscess. There are also idiopathic forms. The prognosis is poor. Treatment may include electrostimulation, administration of NSAIDs, nerve transplantation and muscle transposition.