边界处电偶联对1D生物起搏器的作用 — 一种仿真研究

现在生物起搏器越来越引起学者们的关注. 本文旨在研究边界处的电偶联对生物起搏器起搏及驱动能力的影响. 首先利用各向异性的反应扩散方程,建立了包含生物起搏器的1D心室组织模型. 基于该模型,仿真了不同边界电偶联对应的起搏器初次起搏时间、特殊位置细胞的动作电位、心电的传导过程等参考项,发现减弱边界处的电偶联对生物起搏器的起搏能力具有一定的增强作用;然而,当电偶联足够小时,起搏器的电兴奋却不能有效传出,导致其驱动心室组织失败. 另外,本文探讨了边界电偶联的大小与起搏器最小尺寸之间的关系,发现电偶联越小,起搏器成功起搏所需的细胞数量越少,但是细胞数量变化并不明显. 因此,仅仅减弱电偶联对生物起搏器有一定的增强作用,但如果生成高效的起搏器,仍需辅助其它措施.     

Left ventricular endocardial pacing in cardiac resynchronisation therapy: Moving from bench to bedside

In cardiac resynchronisation therapy, failure to implant a left ventricular lead in a coronary sinus branch has been reported in up to 10% of cases. Although surgical insertion of epicardial leads is considered the standard alternative, this is not without morbidity and technical limitations. Endocardial left ventricular pacing can be an alternative as it has been associated with a favourable acute haemodynamic response compared with epicardial pacing in both animal and human studies. In this paper, we discuss left ventricular endocardial pacing and compare it with epicardial surgical implantation. Ease of application and procedural complications and morbidity compare favourably with epicardial surgical techniques. However, with limited experience, the most important concern is the still unknown long-term risk of thromboembolic complications. Therefore, for now endovascular implants should remain reserved for severely symptomatic heart failure patients and patients at high surgical risk of failed coronary sinus implantation.     

Minimizing cows’ stress when calves were early weaned using the two-step method with nose flaps

Early weaning may be used in beef cattle production to improve reproduction rates in range conditions. However, weaning causes a stress response in cows, which may be especially strong in early weaning management, as the bond between the cow and the calf is still strong. We hypothesized that weaning calves in two steps, with the aid of anti-sucking devices (nose flaps) would reduce the behavioural stress response in the cows separated from their calves 2 months after parturition. We compared the behaviour frequency and weight change in cows that were weaned abruptly, by separation of the calf on day 0 of the study, or in two steps, consisting of the use of anti-sucking nose flaps for 5 days before permanent separation; a third group was not weaned to serve as control. Thirty-six crossbred multiparous Aberdeen Angus×Hereford cows and their calves (n=12/treatment) were managed in three paddocks with similar pasture availability, with four dyads from each treatment per paddock. Cows’ behaviour was observed by direct visual instantaneous sampling, at 10 min intervals from days −3 to 11. Weaning the calves in two steps clearly attenuated the behavioural stress response observed in abruptly weaned cows, which included reductions in grazing and lying, and increases in pacing, walking and vocalizing. Our results corroborate those previously shown for cows nursing older calves, and indicate that step weaning can reduce the behavioural stress response of cows at weaning, even when the calf is weaned shortly after birth, when the bond between the cow and calf is still very strong.     

Ventricular pacing – Electromechanical consequences and valvular function

Although great strides have been made in the areas of ventricular pacing, it is still appreciated that dyssynchrony can be malignant, and that appropriately placed pacing leads may ameliorate mechanical dyssynchrony. However, the unknowns at present include:1. The mechanisms by which ventricular pacing itself can induce dyssynchrony;2. Whether or not various pacing locations can decrease the deleterious effects caused by ventricular pacing;3. The impact of novel methods of pacing, such as atrioventricular septal, lead-less, and far-field surface stimulation;4. The utility of ECG and echocardiography in predicting response to therapy and/or development of dyssynchrony in the setting of cardiac resynchronization therapy (CRT) lead placement;5. The impact of ventricular pacing-induced dyssynchrony on valvular function, and how lead position correlates to potential improvement.This review examines the existing literature to put these issues into context, to provide a basis for understanding how electrical, mechanical, and functional aspects of the heart can be distorted with ventricular pacing. We highlight the central role of the mitral valve and its function as it relates to pacing strategies, especially in the setting of CRT. We also provide future directions for improved pacing modalities via alternative pacing sites and speculate over mechanisms on how lead position may affect the critical function of the mitral valve and thus overall efficacy of CRT.     

Vagal stimulation suppresses ischemia-induced myocardial interstitial norepinephrine release

Although electrical vagal stimulation exerts beneficial effects on the ischemic heart such as an antiarrhythmic effect, whether it modulates norepinephrine (NE) and acetylcholine (ACh) releases in the ischemic myocardium remains unknown. To clarify the neural modulation in the ischemic region during vagal stimulation, we examined ischemia-induced NE and ACh releases in anesthetized and vagotomized cats. In a control group (VX, n = 8), occlusion of the left anterior descending coronary artery increased myocardial interstitial NE level from 0.46+/-0.09 to 83.2+/-17.6 nM at 30-45 min of ischemia (mean+/-SE). Vagal stimulation at 5 Hz (VS, n = 8) decreased heart rate by approximately 80 beats/min during the ischemic period and suppressed the NE release to 24.4+/-10.6 nM (P < 0.05 from the VX group). Fixed-rate ventricular pacing (VSP, n=8) abolished this vagally mediated suppression of ischemia-induced NE release. The vagal stimulation augmented ischemia-induced ACh release at 0-15 min of ischemia (VX: 11.1+/-2.1 vs. VS: 20.7+/-3.9 nM, P < 0.05). In the VSP group, the ACh release was not augmented. In conclusion, vagal stimulation suppressed the ischemia-induced NE release and augmented the initial increase in the ACh level. These modulations of NE and ACh levels in the ischemic myocardium may contribute to the beneficial effects of vagal stimulation on the heart during acute myocardial ischemia.     

Clinical profile and outcomes of semi-permanent pacing in a tertiary care institute in southern India

BackgroundSemi-permanent pacing (SPP) includes the placement of a permanent lead through the internal jugular vein and connection to a pulse generator on the skin outside the venous access site.AimTo evaluate the clinical profile and outcomes of semi-permanent pacing in a tertiary care institute in Southern India.MethodsThis is a retrospective observational study. All patients admitted and requiring management with semi-permanent pacing from January 2017 to June 2020 were included.ResultsFrom January 2017 to June 2020, 20 patients underwent semi-permanent pacing (SPP) with a median age of 54 (21–74) years. Males comprised a majority of the patients (55%). Hypertension was noted in 50% of patients and 30% were diabetic. The right internal jugular vein was the most common access in 95% of patients. The most common indication for semi-permanent pacing was pocket site infection in 30% of patients. There were no procedural complications. The median duration on SPP was 7 (5–14) days and the median duration of hospital stay was 13 (8–21) days. Permanent pacemaker implantation was done in 55% of patients. Mortality in our study group was 15% with 10% dying due to cardiogenic shock (post resuscitated cardiac arrest) and 5% dying due to non-cardiac cause (Epidural hematoma).ConclusionIn our study, semi-permanent pacing was noted to be a safe procedure and was more commonly indicated in emergent conditions with complete heart block secondary to underlying reversible causes and in the management of pocket site infection.     

The vagus nerve, food intake and obesity

Food interacts with sensors all along the alimentary canal to provide the brain with information regarding its composition, energy content, and beneficial effect. Vagal afferents innervating the gastrointestinal tract, pancreas, and liver provide a rapid and discrete account of digestible food in the alimentary canal, as well as circulating and stored fuels, while vagal efferents, together with the sympathetic nervous system and hormonal mechanisms, codetermine the rate of nutrient absorption, partitioning, storage, and mobilization. Although vagal sensory mechanisms play a crucial role in the neural mechanism of satiation, there is little evidence suggesting a significant role in long-term energy homeostasis. However, increasing recognition of vagal involvement in the putative mechanisms making bariatric surgeries the most effective treatment for obesity should greatly stimulate future research to uncover the many details regarding the specific transduction mechanisms in the periphery and the inter- and intra-neuronal signaling cascades disseminating vagal information across the neuraxis.     

Electrocardiographic patterns in biventricular pacing delivered by second-generation cardiac resynchronization devices

Background

With increasing use of cardiac resynchronization therapy (CRT), treating physicians should be familiar with different electrocardiographic (ECG) patterns of left ventricular (LV) lead and biventricular (BiV) pacing. However, there are a few publications on ECG patterns during BiV pacing.

Retrieval of a Micra transcatheter pacing system in a heart with a preexisting lead

We report the case of a 74-year-old man with a previously implanted pacemaker lead. He had undergone Medtronic? Micra Transcatheter Pacing System (TPS, Medtronic plc, MN, USA) implantation because of lead fracture. We implanted a new TPS and retrieved the dislodged one. We used a multiple-loop snare (EN snare^®) and an 8.5F steerable sheath (Agilis NXT; St. Jude Medical, St Paul, MN, USA). The TPS was obstructed by the chordae tendineae of the tricuspid valve and the pacemaker lead. We pushed the TPS to the apex site; this enabled us to move the TPS away from the chordae tendineae and pacemaker lead. The TPS body was caught in the inferior vena cava and was successfully retrieved. To our knowledge, this is the first case reporting TPS retrieval in a heart with preexisting lead.     

A Novel pacing option in patients with endomyocardial fibrosis: A case series

Endomyocardial fibrosis (EMF) is characterized by fibrous tissue deposition on the endocardial surface leading to impaired filling of one or both ventricles, resulting in either right or left heart failure or both. Although Sinus node dysfunction and tachyarrhythmia - atrial fibrillation, ventricular tachycardia, have been commonly reported, complete heart block (CHB) necessitating a pacemaker is rare in EMF. Transvenous pacing is technically limited by fibrotic obliteration of the affected ventricle that results in poor lead parameters, and alternative pacing strategy like epicardial pacing may be required in many. We report three cases of EMF, who were treated with an alternative pacing strategy.