Time Course of Transvenous Pacemaker Stimulation Impedance, Capture Threshold, and Electrogram Amplitude

To examine the time course of atrial and ventricular stimulation impedance, capture threshold, and electrogram amplitude, we obtained noninvasive telemetric data in 63 patients who underwent implantation of unipolar, endocardial pacing leads and a second-generation dual chamber pacemaker with expanded bidirectional telemetry, including stimulation impedance, endocardial electrograms, and automatic capture threshold determination. On follow-up of 9-20 months (mean, 15 months), all but six patients continued to pace in the DDD mode. To validate measurements made with telemetry, invasive measurements made directly with a pacing system analyzer at time of implant were compared with immediate postimplant telemetric measurements. Significant correlation of acute stimulation impedance was noted in both atrial (r = .7, p less than .001) and ventricular (r = .8, p less than .001) lead systems. The atrial stimulation impedance decreased from 538 ohms at implant to 471 ohms at 13 months (p less than .01); the ventricular stimulation impedance similarly declined from 545 ohms to 485 ohms at 13 months (p less than .01). Capture thresholds peaked at one month, then declined: atrial, 1.2 V at implant vs 2.2 V at 1 month (p less than .008) and 1.4 V at 13 months; ventricular, 1.1 V at implant vs 1.9 V at 1 month (p less than .001) and 1.3 V at 13 months. There were no significant changes noted in atrial or ventricular electrogram amplitude following implantation. We conclude that there is close correlation of invasive recordings with those made telemetrically with this pacemaker at time of implant.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Influence of Endocardial Electrode Fixation Status on Acute and Chronic Atrial Stimulation Threshold and Atrial Endocardial Electrogram Amplitude

The endocardial atrial electrogram or "P wave amplitude" (PWA) and pacemaker atrial stimulation thresholds are important parameters determining correct pacing system function. Pacemaker lead fixation mechanism and lead age may negatively influence these parameters. Therefore, we compared acute and chronic PWA and atrial stimulation thresholds in 33 patients with permanent transvenous atrial screw-in leads, follow-up 647 days +/- 297 days; and in 31 patients with nonscrew leads, follow-up 855 days +/- 512 days (P = ns). Results: The PWA differed between the two lead types acutely (1.97 mV +/- 0.8 mV for screw-in versus 2.48 mV +/- 1.1 mV for nonscrew-in leads; P less than 0.05), but not chronically (2.21 mV +/- 0.8 mV vs 2.2 mV +/- 1.2 mV; P = ns). Acute and chronic atrial pacing thresholds did not differ between groups. We also analyzed an early interim PWA in a subgroup of patients (mean 31 days after implantation). The nonscrew fixation group interim PWA was 1.76 mV +/- 0.9 mV versus 2.7 mV +/- 1.2 mV at implant (P less than 0.001). The screw-in lead interim PWA was 2.04 mV +/- 0.9 mV versus 1.97 mV +/- 0.7 mV at implant (P = ns). Conclusions: (1) A significantly higher endocardial PWA occurs at the time of lead implantation in nonscrew versus screw-in lead groups, but the chronic PWA does not differ between the two groups. (2) A transient but marked early (mean approximately 31 days) attenuation of the PWA occurs only with nonscrew-in leads. (3) Atrial threshold stimulation energies do not differ between the two lead groups acutely or during follow-up.     

Clinical Testing of a New Pacemaker Function to Monitor Ventricular Capture

Automatic beat-by-beat capture functions are designed to minimize the pacing energy delivered, while maintaining the highest safety by delivering an immediate back-up stimulus in case of loss of capture. The objective of this study was to estimate the lowering of ventricular pacing amplitude allowed by such a function, compared to amplitudes usually set manually in routine practice. An automatic ventricular pacing threshold test is launched every 6 hours to measure the automatic capture threshold (AT). From AT the function calculates: (1) the "capture amplitude" (V_c) = AT + 0.5 V at a minimum output of 1 V and (2) the "safety amplitude " (V_s) = twice AT at a minimum output of 2.5 V. The function preferentially uses V_c and verifies capture after each paced beat. In case of loss of capture, a back-up spike is delivered and V_s is implemented until the next threshold measurement. We estimated the ventricular amplitude delivered by the pacemaker from data stored in the pacemaker memory. We compared these values with the pacing amplitude typically programmed manually (MPA) by physicians at twice AT and a minimum of 2.5 V. Data from 57 recipients of Talent 3 DR pacemakers were analyzed. Complete data sets were available in 25 patients at 1 day, 28 at 1 month, and 39 between 1 day and 1 month. No loss of capture or ventricular pause was observed on 53 ambulatory electrocardiograms (ECG); and pulse amplitude automatically delivered by the device was significantly lower than the MPA at each of the three time points analyzed. This new beat-by-beat capture function allows a significant lowering of the pacing amplitude compared to manual settings, while preserving a 100% safety.     

几种药物对高原脱适应者血液流变学的影响

目的探讨银杏叶片、复方红景天、复方党参和刺五加片对高原脱适应者血液流变学的影响。方法将驻守海拔5170m 1年的57名健康青年于返回平原前5天随机分为5组,分别口服银杏叶片(12人)、复方红景天(12人)、刺五加 (11人)、复方党参(11人)和安慰剂(11人),返回平原后第7天停药。停约后清晨采空腹静脉血检测全血粘度、全血还原粘度、血浆粘度、红细胞刚性指数、红细胞聚集指数、红细胞变形指数。结果复方红景天组和复方党参组较安慰剂组全血粘度、红细胞压积、全血还原粘度、血浆粘度、红细胞刚性指数、红细胞聚集指数、红细胞变形指数均降低,有显著性意义(P<0．01或0．05),银杏叶片组较安慰剂组全血粘度中切(30s-1)、全血低切还原粘度、血浆粘度降低,有显著性意义(P<0．01或0．05);复方红景天组和复方党参组较刺五加组全血粘度、全血低切还原粘度、血浆粘度、红细胞刚性指数均降低,有显著性意义(P<0．01或0．05)。结论复方红景天、复方党参和银杏叶片三种药物均具有改善组织微循环及血液流变性的作用,使红细胞变形能力增强,血液粘度下降,血流速度增加。且复方红景天和复方党参要优于银杏叶片。     

Determinants of Subsidiary Ventricular Pacemaker Suppression in Man

To investigate the relative contribution of the duration and rate of overdrive to subsidiary ventricular pacemaker suppression, in six patients with complete heart block after His-bundle ablation, ventricular overdrive stimulation studies were performed. The studies, which were spread over a mean follow-up period of 745 days, were carried out invasively with a temporary lead (one patient) as well as nonin-vasively with the implanted pacemakers and chest wall inhibition (five patients). The overdrive pacing rate was increased in steps of 10 beats/min, and the pacing duration was 15, 30, 60, 90, and 120 seconds at each level. A recovery period of 2 minutes was allowed after each overdrive stimulation. Incremental ventricular overdrive stimulation at increasing pacing durations consistently caused progressive suppression of ventricular impulse formation. Nonparamelric variance analysis demonstrated a significant (P < 0.0001) influence of both the pacing rate and duration on ventricular recovery time. Nonlinear regression showed an exponential increase in recovery time with incremental pacing rate and a biphasic increase in recovery time with incremental pacing duration. Beyond a pacing duration of 60 seconds ventricular impulse suppression was primarily dependent upon the pacing rate. A nonlinear regression model was applied to predict the number of heals required for return of the escape rhythm toward prepacing control values. The predicted maximum mean number of beats was 15.4 ± 5.9 and independent of the rate and duration of pacing, although, the initial temporary instability of the escape rhythm was directly related to the degree of overdrive.     

Electrogram Signals Recorded from Acute and Chronic Pacemaker Implantation Sites in Pacemaker Patients

Electrogram signals recorded from typical pacemaker implantation sites may be useful for a variety of pacemaker system functions including pacemaker follow-up, atrial and ventricular sensing (event detection), and triggered electrogram storage. We quantified the electrical characteristics of pacemaker pocket electrograms using a subcutaneous electrode array (SEA) in a population of 48 patients undergoing initial or replacement pacemaker implantation. SEA recorded intrinsic R wave amplitudes measured peak to peak averaged 118 μV and 65 μV for the two recorded SEA electrograms and were significantly different (P < 0.001); paced R wave amplitudes averaged 180 μV and 110 μV. P wave amplitudes averaged 39 μV and 26 μV. No statistically significant difference in amplitudes were observed between acute versus chronic pacemaker pocket or indication for pacing (A V block, sick sinus syndrome). Signal to noise ratios, using R wave amplitude as signal, were lower in the SEA electrogram on average (11 dB) compared to the intracardiac electrogram (27 dB), but sufficient for diagnostic assessment. R wave/P wave ratios for SEA signals were lower than surface and intracardiac values 3.1 and 2.7 compared to a range of 6.2–9.8, indicating a relative enhancement of P waves to R waves in SEA signals. In summary, SEA electrograms are of sufficient amplitude and signal quality (signal to noise ratio) to hold promise for future implantable device features such as electrogram telemetry, enhanced sensing, and diagnostic data storage.     

Survival and Mortality in 3,701 Pacemaker Patients: Arguments in Favor of Pacemaker Reuse

This study analyzed the results of 3,701 patients implanted with cardiac pacemakers at the Centre Chirurgical du Val d'Or between 1976 and 1981. Two pacemaker populations were compared; those having a new pacemaker and (hose implanted with a reused pacemaker. There were no statistically significant differences between the two groups, either in terms of indications for implantation or in terms of actuarial survival of patients. In addition, there was no significant change in survival of the pulse generator. The reutilization of pacemakers appeared to be in no way detrimental to patients.     

The Superfast Atrial Recharge Pulse: A Cause of Pectoral Muscle Stimulation in Patients Equipped with a Unipolar DDD Pacemaker

Pectoral muscle stimulation may cause serious discomfort to patients equipped with a pulse generator. Insulation defects of the lead, connector problems and defective coating of the pacemaker can are common causes of local muscle contractions. This report describes pectoral muscle stimulation caused by the atrial superfast recharge pulse incorporated into the atrial channel of a commercially available unipolar DDD pacemaker. As pectoral muscle stimulation could not be eliminated by reprogramming the pacemaker to a lower atrial output in some patients a redesign of the pacemaker is highly required.     

短时程脊髓电刺激联合臭氧对神经病理性疼痛患者机械痛阈值、炎性因子的影响

目的：探究短时程脊髓电刺激联合臭氧对神经病理性疼痛患者机械痛阈值、疼痛程度以及炎症因子的影响。方法：选取2021年2月至2023年1月我院收治的神经病理性疼痛患者90例。将90例NP患者根据随机数字表法分为研究组（n=45）和对照组（n=45）,对照组在X线透视引导下植入电极进行短时程脊髓电刺激（tSCS）治疗,连续治疗2周;研究组在对照组的基础上联合臭氧治疗,予疼痛触发点行臭氧注射,每周2次,共治疗2周。记录并比较两组机械痛阈值、视觉模拟评分(VAS),检测两组肿瘤坏死因子-α（tumor necrosis factor-alpha,TNF-α）、白细胞介素-6（interleukin 6,IL-6）表达水平,评价两组治疗后的临床疗效。结果：治疗后,研究组总有效率为82.22%（37/45）,对照组总有效率为62.22%（28/45）,差异有统计学意义（P<0.05）;治疗后,两组患者机械痛阈值明显升高（P<0.05）,且研究组的机械痛阈值明显高于对照组（P<0.05）;两组治疗后VAS评分以及血清TNF-α、IL-6水平显著降低（P<0.05）,且研究组明显低于对照组（P<0.05）。结论：短时程脊髓电刺激联合臭氧能有效治疗神经病理性疼痛,提升患者的机械痛阈值,缓解患者疼痛,并降低血清炎症因子水平。     

玉树地震外来卫生应急人员急性高原反应及其影响因素分析

目的分析玉树地震后外来卫生应急人员急性高原反应发生情况及引起急性高原反应的危险因素,为日后高原地区开展大规模医疗应急救援时有效保障应急救援人员的安全和健康提供科学依据。方法从参加2010年4月14日玉树地震的25支救援队伍中随机选取来自不同海拔地区的4支队伍,共67名队员进行问卷调查,了解他们急性高原反应发生情况及其危险因素。结果 67名被调查者中有54名(81%)作出应答,其中93%为男性,中位年龄36岁(24～55岁),有34人(63%)发生急性高原反应。单因素分析结果显示:居住在海拔<100 m者高原反应评分高于居住在海拔>1000 m者(分别为10分和5.2分,P=0.005);未到过高海拔地区者的高原反应评分高于曾到过高海拔地区者(分别为10分和6.4分,P=0.039);事先在海拔>2000 m地区停留不同天数者的高原反应评分不同(停留≥3天者为5.7分,停留≤1天者为9.4分,P=0.011);随身行李重量不同者的高原反应评分不同(≥25 kg者为9.8分,≤25 kg者为5.5分,P=0.002)。多元线性回归分析结果显示:原居住地海拔低和进入高原前的适应时间短是高原反应程度的影响因素[y=2.89–0.187×原居住地高度(每100 m)–2.43×进入玉树前在海拔超过2000 m地区的停留时间(d)]。结论既往经历和到达高原地区前的准备情况是影响急性高原反应的重要因素,应采取有效措施保护进入高原地区的应急救援人员的安全和健康。     

Effect of 2 Hours' Exposure to Simulated High Altitude (4,500 m) on Human Red Cell Metabolism

During acute exposure to high altitude (2 hours) the red cell metabolism is altered. A pH-induced increase in phosphofructokinase activity together with a decrease in the level of the monophosphoglycerates are the most prominent features of the changes. Despite the increase in pH, the level of 2,3-diphos-phoglycerate is not altered, probably because of a reduction in the concentration of inorganic phosphate. Besides 2,3-DPG neither ATP, ADP, lactate, or pyruvate levels are changed significantly during exposure of this duration. The results are interpreted as being due to a combined effect of alkalosis and a decrease in the concentration of inorganic phosphate.     

高压氧治疗高原脱习服症者血液流变学指标的变化

目的探讨高压氧（HBO）治疗对高原脱习服症者血液流变学指标的影响。方法对驻守海拔5,000m以上地区1年的20名男性青年,在返回平原（海拔1,400m）第2天开始进行HBO治疗,连续治疗10d。治疗前后清晨采空腹静脉血检测全血黏度、全血还原黏度、血浆黏度、红细胞变形指数和红细胞压积（Hct）。结果HBO治疗后较治疗前全血黏度高切、中切、低切、全血高切还原黏度、全血低切还原黏度均降低,有显著性差异（P〈0．05）,血浆黏度、全血高切相对指数、全血低切相对指数、红细胞变形指数、Hct降低,有非常显著性差异（P〈0．01）。结论HBO具有改善高原脱习服症者组织微循环及血液流变性的作用,使血液黏度下降,血流速度增加。     

Irregular Ventricular Stimulation in the DDI Mode of a Dual Chamber Pacemaker With Atrial-Based Lower Rate Timing

This report describes two patients with atrial fibrillation in whom an implanted CHORUS DDD pacemaker programmed to the DDI mode produced an irregular ventricular stimulation rate. The lower rate timing of these devices is atrial-based only when an atrial event opens an AV interval shorter than the programmed AV delay. In the DDI mode, if Api represents the time when an atrial paced event (Ap) would have occurred if it had not been inhibited by a previous atrial sensed event (As), then Api-Vp constitutes the implied AV interval where Vp is a paced ventricular event. Although the As-Vp interval (As-Api+Api-Vp) generates an atrial refractory period during its entire duration, the pacemaker can sense an atrial event (A r ) during the implied AV interval. A r cannot start another AV delay, but it can initiate the atrial-based lower rate interval. This timing mechanism can cause irregular prolongation of Vp-Vp intervals to a value longer than the programmed lower interval with a maximal extension equal to the programmed AV delay. Such behavior of the CHORUS pacemaker should not be interpreted as malfunction.     

药物对高原人体运动血液流变学的干预效应

目的探讨药物对高原人体运动前后血液流变学的影响。方法对进驻海拔4100m高原20天的40名健康青年随机分为红景天组、乙酰唑胺组、西氏胶囊组和对照组,每组10人,在安静时、服药前、后及踏阶运动后分别检测红细胞压积(HCT)、血液粘度(η     

心肺复苏后早期低氧血症与预后的分析

目的:探讨心肺复苏自主循环恢复后早期低氧血症与预后的关系。方法:228例心肺复苏后患者早期监测动脉氧分压PaO2并相应进行危险度分层,研究心肺复苏后早期低氧血症与预后的关系。结果:全组心肺复苏后患者大多均有不同程度的低氧血症,低氧血症越严重存活率越低。结论:心肺复苏后早期大多存在低氧血症,低氧血症是影响预后的存活危险因素。     

久居高原对健康青年男性左心室功能和质量影响的研究

目的 研究长期移居高原对健康青年男性左心室功能和质量的影响.方法 对平原青年男性官兵51例,长期移居3 700 m高原的青年男性官兵53例(A组),长期移居3 700 m高原再进4 400m高原50 d的青年男性官兵42例(B组)分别进行血压、心率、指脉氧饱和度及彩色多普勒心脏超声的检测.结果 移居高原两组左室收缩末内径、左心室质量指数显著低于平原对照组(P＜0.05),移居高原A组左室收缩末容积显著低于平原对照组(P＜0.01),移居高原B组室间隔厚度、左心室质量显著低于平原对照组(P＜0.05);移居高原两组左室射血分数、短轴缩短率、每搏输出量、心输出量均显著高于平原对照组(P＜0.05),移居高原B组心脏指数显著高于平原对照组(P＜0.01);移居高原两组心率显著高于平原对照组(P＜0.01),血氧饱和度则显著低于平原对照组(P＜0.01),移居高原B组血氧饱和度显著低于移居高原A组(P＜0.01).结论 久居高原后左心室收缩功能显著高于平原对照组,舒张功能显著低于平原对照组,而久居高原后短期无更高海拔暴露的健康青年男性左室质量与平原对照组无显著差异.     

Telemetry Guided Pacemaker Programming: Impact of Output Amplitude and the Use of Low Threshold Leads on Projected Pacemaker Longevity

In a prospective study, a low threshold screw-in electrode (Medtronic 5078, group I. n = 9) was compared to a conventional active fixation lead (Biotronik Y60BP, group II. n = 9) to investigate whether lower pacing thresholds really translate into longer projected service life of the pacemaker. The leads were implanted in the atrium and were connected to a dual chamber pacing system which included the same ventricular lead (Medtronic 5024) and the same pulse generator model (Intermedics 294–03) in both groups. Eighteen months after implantation, atrial and ventricular pacing thresholds were measured as the charge delivered per pulse [μC] at 0.5, 1.0. 1.5, 2.0, and 3.5 V, respectively. For chronic output programming in both channels, patients capturing at 0.5 V were set to 1.0 V, those capturing at 1.5 V were permanently programmed to 2.0 V with the double of the charge threshold as the safety margin for pacing (“safety charge”). A combination of atrial and ventricular output settings was optimal, if it resulted in minimum battery current drain [μA] as measured by pacemaker telemetry. In both groups, current consumption [μA] decreased significantly as output amplitude was decreased, exhibiting its lowest value at 1.0 V in either channel. All ventricular leads could be programmed to the optimum output amplitude of 1.0 V in groups 1 and 2. As the 2:1 “safety charge” values were almost identical, the ventricular channel essentially contributes the same amount to the battery drain of the pacing system in both groups. In the atrium, all patients of group 1 could be programmed to the optimum output amplitude of 1.0 V with an average pulse duration of 0.42 ± 0.15 ms. In group 2, however, all patients had to be programmed to 2.0 V with a mean pulse width of 0.52 ± 0.15 ms. With the atrial and ventricular output being optimized, the average battery drain of the whole pacing system was 12.19 ± 0.63 μA in group 1 versus 14.42 ± 0.32 μA in group 2 (P < 0.001). As patients were chronically programmed to these output settings, this difference translates into a clinically relevant gain in projected pacemaker longevity of 17 months or 18.3 % (121 ± 4 vs. 104 ± 2 months; P < 0.001). Thus, programming a 2:1 safety margin in terms of charge and optimizing the output parameters by real-time telemetry of the battery current is a useful approach to reduce battery current drain. Making the most of modern lead technology with a different performance in only one channel of an otherwise identical DDD pacing system translates into a significant prolongation of projected pacemaker service life which is of great importance with the increasing awareness of health care expenditures. The gain in projected longevity is mainly due to the option of reducing the output amplitude which is still significantly beneficial well below the nominal voltage of the power source.     

Selective Dysfunction of Ventricular Electrode-Endocardial Junction Following DC Cardioversion in a Patient with a Dual Chamber Pacemaker

A patient with a dual chamber pacemaker received two transthoracic (anterior-anterior paddle position) shocks for VF. Subsequent analysis of stimulation thresholds revealed a marked rise in the ventricular threshold only. Later, she received three additional shocks (anterior-posterior paddle position) during electrophysiological study to terminate episodes of induced VT. Following these, the ventricular stimulation threshold was > 10 Vat 2.0 ms. The selective damage at the ventricular site in this patient led us to carry out in vitro studies that revealed a preferential shunting of high electrical energy into the ventricular lead, as compared to the atrial lead, following a DC shock. These observations may explain the selective pacing malfunction observed in our patient.