Bedside Recordings of His-Bundle Electrograms Using Conventional Twelve-Lead Surface Electrocardiography

Bedside Recording of His Potentials. Introduction: Endocavitary His-bundle electro-grams are usually recorded using high fidelity amplifiers and special filters.
Methods and Results: To evaluate whether similar recordings could be obtained using a 12-lead surface electrocardiograph, we compared recordings obtained during an electrophysiologic study in 33 patients to those obtained by connecting the two poles of the bipolar catheter, used during the study as the His catheter, to the right and left arm leads of the surface electrocardiograph. We recorded His-bundle electrograms using both techniques in all patients. There were no differences in measurements obtained between the two techniques.
Conclusion: His-bundle electrograms can be recorded reliably with a conventional electro-gram without sophisticated systems.     

Bipolar Transvenous Defibrillation: Efficacy of Two Different Positions of the Anode

For most nonthoracotomy defibrillotion lead systems, the transvenous anode can be positioned independently of the right ventricular (RV) cathode. Usually a vertical position in the superior vena cava (SVC) is chosen. However, it is unknown if this position yields the optimal defibrillation threshold (DFT). There-fort, in 15 patients undergoing defibrillator implantation the SVC position was compared in a crossover study design with a horizontal position in the left brachiocephalic vein (BCV). Mean DFT was not different for SVC and BCV (19.2 ± 9.6) vs 18.5 ± 9.1 J) but DFT of individual patients differed by up to 12 joules. A positive correlation between impedance and DFT in the BCV position (r = 0.6; P ≤ 0.05) indicated that the improved geometry of the defibrillation field with the BCV position is opposed by a higher impedance found for this position (63 ± 15 Ω vs 52 ± 7 Ω). Thus, defibrillation is not improved in general although individual patients might benefit.     

Trans venous-Subcutaneous Defibrillation Leads:

Effect of Transvenous Electrode Polarity on DFT. Introduction: The defibrillation threshold (DFT) of a transvenous-subcutaneous electrode configuration is sometimes unacceptably high. To obtain a DFT with a sufficient safety margin, the defibrillation field can be modified by repositioning the electrodes or more easily by a change of electrode polarity. In a prospective randomized cross-over study, the effect of transvenous electrode polarity on DFT was evaluated.
Methods and Results: In 21 patients receiving transvenous-subcutaneous defibrillation leads, the DFT was determined intraoperatively for two electrode configurations. Two monophasic defibrillation pulses were delivered in sequential mode between either the right ventricular (RV) electrode as common cathode and the superior vena cava (SVC) and subcutaneous electrodes as anodes (configuration I) or the SVC electrode as common cathode and the RV and subcutaneous electrodes as anodes (configuration II). In each patient, both electrode configurations were used alternately with declining energies (25, 15, 10, 5, 2 J) until failure of defibrillation occurred. The DFT did not differ between both configurations (18.3 ± 8.2 J vs 18.9 ± 8.9 J; P = 0.72). Eleven patients had the same DFT with both electrode configurations, 5 patients a lower DFT with the RV electrode as cathode, and 5 patients a lower DFT with the SVC as cathode. Four patients had a sufficiently low DFT (≤ 25 J) with only 1 of the 2 configurations.
Conclusion: A change of electrode polarity of transvenous-subcutaneous defibrillation electrodes may result in effective defibrillation if the first electrode polarity tested fails to defibrillate. In general, neither the RV electrode nor the SVC electrode is superior if used as a common cathode in combination with a subcutaneous anodal chest patch.     

Effect of increasing depth of dexmedetomidine anesthesia on upper airway morphology in children

Objective: This prospective study examines the dose–response effects of dexmedetomidine on upper airway morphology in children with no obstructive sleep apnea (OSA). Aim: To determine the effect of increasing doses of dexmedetomidine on static and dynamic magnetic resonance (MR) images of the upper airway in spontaneously breathing children with no OSA. Background: General anesthetics and sedatives attenuate upper airway muscle activity, rendering the airway vulnerable to obstruction. Dose–response effects of dexmedetomidine on upper airway of children are not known. We prospectively examined the dose–response effects of dexmedetomidine on upper airway morphology in children. Methods/Materials: Increasing doses of dexmedetomidine was administered to 23 children scheduled for MR imaging of the brain while breathing spontaneously via the native airway. Static axial and dynamic sagittal midline MR ciné images of the upper airway were obtained during low (1 mcg·kg⁻¹·h⁻¹) and high (3 mcg·kg⁻¹·h⁻¹) doses of dexmedetomidine. The airway anteroposterior diameter, transverse diameter, and cross‐sectional areas were measured manually by two independent observers. Static airway measurements were taken at the level of the nasopharyngeal airway (sagittal images) and retroglossal airway (RGA) (sagittal and axial images). Dynamic change in cross‐sectional area of airway between inspiration and expiration was considered a measure of airway collapsibility. Results: Static axial measurements of RGA did not change with increasing dose of dexmedetomidine. Most sagittal airway dimensions demonstrated clinically modest, although statistically significant, reductions with high dose compared to low dose dexmedetomidine. Although, the dynamic changes in nasopharyngeal and retroglossal area with respiration were marginally greater for high dose than for low dose dexmedetomidine, no subject exhibited any clinical evidence of airway obstruction. Conclusion: Upper airway changes associated with increasing doses of dexmedetomidine in children with no OSA are small in magnitude and do not appear to be associated with clinical signs of airway obstruction. Even though these changes are small, all precautions to manage airway obstruction should be taken when dexmedetomidine is used for sedation.     

Language, memory, and aging: An electrophysiological exploration of the N400 during reading of memory-demanding sentences

Twenty-four young and 24 middle-aged academics carried out a language recognition task in which sentences were presented that made either a high or a low demand on working memory (WM). The sentences ended either normally (i.e., congruent) or with an incongruous word. Middle-aged subjects had smaller WM scores, a marginally slowed down recognition performance, and a smaller and delayed N400 component. The event-related potential (ERP) difference between congruent and incongruent endings was smaller in the high-load condition for younger subjects and totally disappeared for the middle-aged subjects. ERPs for all subjects showed a WM-related positivity in the middle of the sentence and a WM-related negativity at the sentence ending. These shifts could be associated with either storage and retrieval processes or with clause wrap-up processes. Most ERP-effects were dependent on WM capacity. Age differences in sentence processing are not simply explained by age itself but depend to a large extent on individual memory capacity.