The acute effect of cardiac pacing mode on endothelial vasodilation: prospective, double-blind, cross-over, comparative clinical study

Background: Compared to atrioventricular sequential pacing, ventricular demand pacing is known to have somewhat more deleterious hemodynamic effects, which probably arise from increased sympathetic tonus and inappropriate baroreceptor activation. Endothelial function is affected by various local and systemic factors including baroreceptor activity. The aim of this study was to explore whether cardiac pacing would have any effect on endothelial functions.
Methods: Twelve patients (six male, mean age: 75 ± 9 years) with previously implanted DDD or VDD cardiac pacemakers were included. All patients had stable atrial rhythms during the study. Patients were randomized to either atrial-based pacing mode (VDD or DDD) or ventricular demand pacing mode (VVI) first, and then cross-over was performed with the other pacing mode. Endothelial function was assessed by brachial artery ultrasonography. Basal diameter of the brachial artery, and both flow-mediated dilation (FMD) and endothelium-independent vasodilation with nitroglycerin were measured 1 hour after each pacing mode.
Results: Compared to atrial-based pacing mode, ventricular demand pacing was associated with a significantly worse FMD both as absolute and percentage values (0.17 ± 0.09 mm vs 0.28 ± 0.11 mm, P = 0.015 and 4.84 ± 2.37 % vs 7.00 ± 2.88 %, P = 0.028, respectively). However, there was no significant difference in nitroglycerin-mediated vasodilation values between the two pacing sessions.
Conclusions: Acute ventricular demand pacing (VVI pacing) is clearly associated with attenuation of FMD in patients with atrial-based pacing systems. The attenuation of endothelial vasodilation might have a role in hemodynamic and clinical deterioration in patients with VVI pacemakers.     

Left Ventricular Function During Physiological Cardiac Pacing: Relation to Rate, Pacing Mode, and Underlying Myocardial Disease

The hemodynamic effects of cardiac pacing at different rates and in different modes were studied in 21 patients who were candidates for permanent pacemaker implantation. Nine of these had primary conduction disturbances (PCD), ten had ischemic heart disease (IHD), seven with additional cardiac failure (CHF), and two had hypertrophic cardiomyopathy (HCM). In patients with PCD, atrial (AOO) and AV sequential (DVI) pacing did not change systolic blood pressure and pulse pressure but ventricular (VVI) pacing caused a progressive fall in these measurements, especially as heart rate increased. Ventricular volume and stroke volume (counts) derived from radionuclide ventriculography (RVG) decreased progressively with higher pacing rates, especially during VVI pacing. Cardiac output was maintained during VVI pacing by the increase in heart rate; during AOO and DVI pacing, cardiac output increased. Similar but more marked differences were observed in patients with IHD and CHF and the changes were even greater in the patients with HCM. Left ventricular (LV) ejection fraction changed little with increasing heart rate in PCD but decreased progressively with the onset of ischemia in IHD and CHF. There was no difference in ejection fraction in the different pacing modes. Graphs related to LV contractility (end-systolic pressure-volume relations) showed that AOO pacing produced the highest and VVI pacing produced the lowest curves of myocardial contractility in all patient groups, except that at higher rates the AOO curve shifted down again in patients with IHD and CHF, presumably with the onset of myocardial ischemia. This study showed that physiological pacing produced the best hemodynamic results in all patient groups. Higher pacing rates should be avoided in patients with ischemic heart disease while VVI pacing should not be used in patients with HCM. Blood pressure and RVG studies during temporary pacing are useful in selecting the optimal pacing system in an individual patient when the clinical choice is not clear.     

床边紧急心脏起搏在急诊急救中的应用价值

目的 探讨床边紧急漂浮临时心脏起搏在急诊抢救中的应用价值及优越性.方法 回顾性分析内蒙占医学院第一附属医院近4年床边紧急漂浮临时心脏起搏130例和70例x线指导下临时心脏起搏抢救各种病因引起严重的缓慢型心律失常患者.结果 130例床边紧急漂浮临时心脏起搏患者成功起搏127例(97.69%),电极未到位3例(2.31%),电极脱位3例(2.36%),无严重并发症发生.从就诊到操作开始的时间为5-15 min,穿刺到成功起搏的时间为(4 4±2.5)min;70例x线指导下临时心脏起搏患者成功70例(100%),脱位6例(8.57%),下肢静脉血栓1例(1.43%),心肌穿孔致心包填塞2例(2.86%),从就诊到操作开始的时间为30-90 min,穿刺到成功起搏的时间平均为(3.5±1.5)min.结论 应用床边紧急漂浮临时心脏起搏救治严重缓慢型心律失常方法简便、并发症少,是一种及时、安全、有效的抢救措施,可在急诊急救中推广应用.     

右室流入道起搏治疗缓慢性心律失常44例临床研究

目的采用右室流入道和传统的右室心尖部起搏两种不同的方法治疗缓慢性心律失常,观察起搏参数、并发症、心电图QRS时限和心功能的变化。方法随机将86例患者分为右室流入道起搏组44例,右室心尖部起搏组42例,分别观察两组起搏器植入时、起搏3和6个月时的起搏参数、并发症、心电图QRS时限和心功能的变化。结果两组不同时期起搏参数、并发症比较,差异无统计学意义;而右室流入道起搏组心电图QRS时限明显短于右室心尖部,心功能改善也显著优于右室心尖部,差异有统计学意义,且心功能改善随起搏时间延长呈逐步好转趋势,而心电图QRS时限不同时期时限较固定。结论采用右室流入道起搏治疗,其心功能改善明显优于传统的右室心尖部起搏,值得在临床上推广。     

运动负荷超声心动图评价起搏器频率适应者的心功能

目的　应用运动负荷超声心动图评价频率适应性起搏器对心功能的影响。方法　对 4 4例植入频率适应性起搏器的患者行运动负荷超声检查 ,分别于非频率适应和频率适应两种起搏状态时进行仰卧位踏车实验。记录踏车运动持续时间、最大负荷量并测定踏车前及踏车高峰时的心率 (HR)和心输出量 (CO)。结果　运动高峰时频率适应性起搏的 HR和 CO明显高于非频率适应性起搏 (P<0 .0 1)。而静息状态下非频率适应性和频率适应性起搏时的 HR和 CO无显著差异 ,这两种起搏方式时的运动持续时间和最大负荷量亦无显著差异。结论　运动负荷超声较静态超声评价心功能有明显优势。运动时频率适应性起搏能明显提高 HR和 CO。     

床旁球囊漂浮电极起搏在心脏术后缓慢性心律失常中应用

目的评估心脏外科术后缓慢性心律失常行床旁球囊漂浮电极导管紧急心脏起搏的可行性和有效性。方法心脏外科术后并发缓慢性心律失常患者21例,均给予漂浮电极导管临时起搏治疗,观察临时起搏手术入路、手术时间、电极导管放置部位及起搏阈值,评估治疗成功率和安全性。结果本组起搏器电极安置经右侧锁骨下静脉15例,经右侧颈内静脉6例;手术时间5-12min;电极导管置入右心室心尖部18例,右心室流出道3例;起搏阈值〈1.0mV;床旁球囊漂浮电极起搏治疗成功率100%,发生导管移位、感知起搏不良各2例,无严重并发症发生。结论床旁球囊漂浮电极起搏操作简单,用于治疗心脏术后缓慢性心律失常安全、可行,疗效确切。     

Septal Short Atrioventricular Delay Pacing: Additional Hemodynamic Improvements in Heart Failure

Controversy exists as to whether short AV delay pacing is beneficial in left ventricular dysfunction with the studies performed coming to disparate conclusions. The right ventricular apical pacing previously studied results in asynchronous contraction and relaxation sequences and may limit the potential benefits of short AV delay pacing. In this study the hemodynamic effects of septal (resulting in a more physiological activation sequence) and apical right ventricular activation were compared in 15 patients with heart failure. VDD pacing with AV delays of 50,100, and 150 msec was evaluated. Apical VDD pacing did not increase the cardiac output significantly, 4.1 ± 0.75 to 4.45 ± 0.74 L/min, whereas septal VDD pacing increased the cardiac output to 4.86 ± 0.79 L/min (P = 0.037). Apical pacing increased the cardiac output in 10 patients and septal pacing in 11 patients. We conclude that selected patients with ventricular dysfunction benefit from short AV delay pacing. Septal ventricular activation confers significant hemodynamic improvements over apical activation.     

Indications for Pacing in Patients with Congenital Heart Disease

Background: Advances in pacing technology have increased indications for antibradycardia pacing and new indications have appeared for treatment of atrial tachycardia and cardiac failure in patients with congenital heart disease (CHD).
Methods and Results: Implantation of a pacemaker is mandatory for symptomatic children with complete atrio-ventricular block (CAVB). In asymptomatic neonates and infants, prophylactic pacing is indicated when the ventricular rhythm is <55 beats per minute (bpm) or 70 bpm in case of significant cardiac malformations. Beyond one year of age, PM implantation is recommended in children with an average heart rate <50 bpm or long pauses on 24-hour recordings. Post-operative block that persists 7 days after cardiac surgery is a class I indication for pacing. Postoperative heart block may also be transient, but patients with residual conduction abnormalities and a long HV interval have a high risk of late sudden death and should be paced. After cardiac surgery, atrial pacing may also be considered, in patients with severe sinus bradycardia and symptoms, or in those requiring antiarrhythmic drugs for tachy-bradycardia syndrome; in case of failure of antiarrhythmic drugs, antitachycardia atrial pacing now appears to be safe and efficacious. Finally, cardiac resynchronization therapy may apply to children with congenital heart block and cardiomyopathy, as well as to the population with CHD. Methods and results are described in the section dedicated to resynchronization.
Conclusion: Cardiac pacing indications have extended beyond prevention of sudden death and pacemaker implantation is now indicated to improve quality of life of patients with CHD and as a bridge to cardiac transplantation.     

Transcutaneous pacemakers

Transcutaneous pacing (TP) is technically the fastest, easiest, and least physically invasive of the accepted modes of cardiac pacing. Although first introduced in the early 1950s, TP was abandoned because of cutaneous nerve pain, skeletal muscle contraction, and local tissue burns associated with the use of the technique. The advent of transvenous pacing caused a further decline in interest in TP. Recent investigations suggest that this pacing mode has value when immediate pacemaker therapy is needed in the prehospital or hospital setting. As a result of the renewed interest in TP, the cardiovascular nurse should be aware of this therapy. The article presents a general overview of TP with emphasis on nursing care.     

临时心脏起搏在急性中毒并严重缓慢心律失常的疗效研究

目的 探讨在临时心脏起搏术支持下对急性中毒并严重缓慢心律失常进行中毒抢救的,临床意义.方法 对38例急性中毒并严重缓慢心律失常患者在急诊救治过程中随机采用临时心脏起搏器治疗(起搏组,18例)和药物治疗(对照组,20例),再进行解毒治疗.结果 起搏组18例经床旁临时心脏起搏术右心室起搏成功并置入临时心脏起搏器,配合解毒治疗措施后心律失常改善有效率为100%,而对照组为60%,2组比较差异有统计学意义(x2=19.7,P<0.01).中毒治愈率起搏组为88.9%,对照组为65.0%,2组比较差异有统计学意义(x2=8.2,P<0.05).结论 床旁临时心脏起搏术在抢救急性中毒并严重缓慢性心律失常患者的疗效确切,能有效提高患者的抢救成功率.     

Permanent cardiac pacing for brady-arrhythmia

The indications for and technology associated with permanent cardiac pacing have undergone major changes during the past decade. In contrast to the 1970s, most patients now receive cardiac pacing devices subsequent to the diagnosis of sick sinus syndrome. However, since this condition is prevalent in elderly patients, it is crucial that indications for pacing be critically evaluated and pacing recommended only for those with documented symptoms or marked abnormalities indicative of high risk for a subsequent cardiac event. This is particularly important because pacing has not been shown to influence survival in these patients. The technological advances in pacing devices during the last ten years now provide many desirable options. As a result, available pacemakers range from very simple to highly complex; accordingly, they have a wide range of prices. It is more important than ever to carefully select the appropriate pacing device for a given patient, since its cost, longevity, and required follow-up may differ greatly.     

双心室起搏与右心室起搏对充血性心力衰竭急性心功能的影响

目的最近研究提示心脏再同步治疗有效地改善了慢性心肌病心力衰竭患者心功能。本研究旨在探讨双心室和右心室起搏对心功能的相对影响。方法 15例慢性心力衰竭患者心功能Ⅲ级,左心室射血分数〈35%,QRS〉130ms和二尖瓣反流。安装心房-双心室再同步起搏器。彩色多普勒超声心动图观察心功能变化。结果急性双心室和右心室起搏并未影响左心室内径和短轴缩短率,也不影响左心室射血速度和排血量。左心室压力上升和下降峰速率无明显变化。等容收缩时间缩短（P〈0.05）,但不影响等容舒张时间。增加Z比例（P〈0.05）。缩短二尖瓣反流时间（P〈0.05）,对二尖瓣环和三尖瓣环运动幅度和峰速率无明显影响。双心室和右心室起搏之间无明显差别。结论双心室起搏改善了慢性心肌病心功能。双心室和右心室起搏无明显差别。双心室起搏是一种有前途的心脏再同步治疗方法。     

External noninvasive cardiac pacing in out-of-hospital cardiac arrest

External noninvasive cardiac pacing was applied outside the hospital to 19 patients who had experienced cardiopulmonary arrest and 1 patient with life-threatening bradycardia. Seven patients developed electrocardiographic evidence of pacemaker capture, although only 2 had palpable pulses. The patient with bradycardia was successfully paced. This study demonstrates the feasibility of cardiac pacing in out-of-hospital cardiac arrest but confirms the poor prognosis of asystolic cardiac arrest even with the application of pacing.     

Four-chamber pacing in patients with poor ejection fraction but normal QRS durations undergoing open heart surgery

Background: Poor ejection fraction (EF) comprises a critical risk factor in cardiac bypass surgery (CABG). It has been unclear, whether biventricular or four-chamber pacing confers benefit upon patients with intact atrioventricular and interventricular conduction especially following surgery.
Methods: Twenty-one consecutive patients with an EF ≤ 35% underwent hemodynamic evaluation (continuous pressures and thermodilution) 3, 6, and 18 hours post-CABG and biatrial (AA), biatrial-right ventricular (AAV), and biatrial-biventricular (AAVV) pacing were compared.
Results: Patients (65 ± 9 years) presented with an average EF of 29.5% (15–35%). 514 measurements of cardiac index (CI) were taken. Nineteen patients (91%) showed highly significant increases in CI with AAVV as compared to AA pacing (P < 0,001) at all times post surgery. The increase in CI with pacing mode varied from 6% to 25% and decreased with time following surgery. No consistent difference in CI was seen between four-chamber (AAVV) and biventricular pacing (AVV). The QRS-widths prior to surgery never exceeded 120 ms; postoperatively QRS-complexes widened in all patients on average by 15.9 ms ±6 and returned to starting values by 48 hours.
Conclusions: Biventricular pacing improves CI in patients with poor EF following cardiac surgery in the absence of preoperative atrioventricular- or interventricular conduction block. This benefit decreases with time after surgery as the QRS width returns to preoperative values. Four-chamber pacing did not confer additional benefit as compared to biventricular pacing in this series. Biventricular pacing should be considered as an adjunct in patients with critically low EF undergoing cardiac surgery.     

心脏临时起搏在老年患者围手术期中的应用及护理

目的总结心脏临时起搏在老年患者围手术期中应用的护理经验。方法回顾分析21例老年围手术期患者应用心脏临时起搏器的护理,包括心理护理、术中配合、术后心率、心律监测及临时起搏器的护理等。结果 21例床边安置临时起搏器均获得成功,手术顺利完成,18例术后3 d内去除起搏电极后自主心率恢复良好,3例出现起搏器依赖, 须安置永久起搏器。结论术前加强心理护理,取得患者配合,术中根据患者年龄特点做好起搏频率及起搏阈的调节,术后加强心率、心律监测及临时起搏器的护理等是确保起搏器有效工作、使手术顺利完成的关键。     

Is DDD Pacing Superior to VVI,R? A Study on Cardiac Sympathetic Nerve Activity and Myocardial Oxygen Consumption at Rest and During Exercise

Rate responsive ventricular pacing (VVI,R) has been demonstrated to equal atrial synchronous ventricular pacing (DDD) with regard to hemodynamics and exercise tolerance. Whether the two modes are also comparable, with regard to cardiac metabolic effects, is not yet dear. We assessed central hemodynamics, cardiac sympathetic nerve activity fcardiac norepinephrine overflow), and myocardial oxygen consumption in 16 patients treated with rate responsive atrial synchronous ventricular pacemakers (DDD,R), due to high degree AV block. The study was performed at rest and during supine exercise at two workloads (30 ± 12 and 68 ± 24 watts, respectively) during VDD and rate matched VVI pacing (VVI_m). Ventricular rates at rest and during both workloads were almost identical. Cardiac output at rest tended to be higher in the VDD mode, due to a slightly higher stroke volume. Central pressures including right atrial pressure and pulmonary capillary wedge pressure were similar in the pacing modes. The coronary sinus blood flow, the coronary sinus arteriovenous oxygen difference, and the myocardial oxygen consumption did not differ between the two pacing modes. Cardiac norepinephrine overflow was similar in the two pacing modes, at rest or during exercise. Thus, we found no significant differences between VDD and VVI_m pacing with regard to central hemodynamics, cardiac sympathetic nerve activity (cardiac norepinephrine overflow), or myocardial oxygen consumption either at rest or during moderate exercise.     

Transcutaneous cardiac pacing

Transvenous cardiac pacing is currently the pacing procedure of choice in patients with severe, life-threatening bradyarrhythmias that do not respond to pharmacotherapy. However, pacing catheters can be difficult to insert and frequently fail to capture in severely hypotensive patients. Therefore, there has been a recent resurgence of interest in external pacing methods. Newer transcutaneous cardiac pacing units are easy to apply and especially suited for unconscious patients with severe, life-threatening bradyarrhythmias. There is no operator danger and, if need be, cardiopulmonary resuscitation can continue while the electrodes are in place and the unit is operating. Human and animal studies to date have shown that there are no significant short-term clinical hazards or pathologic abnormalities when using this technique.     

Comparative Left Ventricular Function Following Atrial, Septal, and Apical Single Chamber Heart Pacing in the Young

Ventricular pacing, typically initiated from a RV apical electrode, inherently causes abnormal biventricular activation, decreases LV function, and causes histopathological changes. Since pacing initiated in childhood can he expected to have a more protracted course compared with the adult, the consequences of this alteration in LV hemodynamics gain added significance among the young pacemaker recipient. The purpose of this study was to evaluate the potential of improving paced LV function by a septal electrode implant site. Acute alterations in cardiac index, LV pressure, and contraction indices, including dP/dt, Vmax. and Vpm, were compared among 22 patients (median age 10 years) with normal cardiac anatomy during intracardiac electrophysiological studies. LV hemodynamics were measured during intrinsic rhythms and following 15 minutes of atrial, HV apical, and septal pacing at an appropriate exercise rate for age of 150 ppm. Results showed a significant decrease in LV dP/dt, Vmax, and Vpm, and increase in LV end-diastolic pressure only with apical pacing. Septal pacing, in spite of loss of any atrial contribution to ventricular filling, maintained comparable indices with intrinsic and atrial paced rhythms. This study demonstrates that normalized LV function is maintained by septal and deteriorates with apical pacing acutely among young, nonischemic hearts. Continued evaluation of appropriate pacing electrode designs to permit septal implant is needed to ensure optimal chronically paced LV function.     

Hemodynamic Benefits of Right Ventricular Outflow Tract Pacing: Comparison with Right Ventricular Apex Pacing

To assess optimal hemodynamics in relation to stimulation site during right ventricular pacing, 17 consecutive patients who underwent cardiac catheterization were studied. In all patients, right ventricular apex and right ventricular outflow tract stimulation was performed at 85, 100, and 120 beats/min. Cardiac index at both pacing sites was compared using the left ventricular outflow tract continuous wave Doppler technique. Comparison of the two stimulation sites demonstrated that right ventricular outflow tract pacing resulted in a higher cardiac index at 85 beats/min (2.42 ± 1.2 vs 2.04 ±1.0 L/min per m², P < 0.002) at 100 beats/min (2.78 ± 1.4 vs 2.35 ± 1.1 L/min perm², P < 0.001) and 120 beats/min (3.00 ± 1.5 vs 2.61 ± 0.9 L/min perm², P < 0.001). From a total of 51 paired observations, 45 showed an increase in cardiac index during outflow tract pacing as compared to apex pacing. Right ventricular outflow tract pacing at 120 beats/min resulted in a lower cardiac index than right ventricular apex pacing in patients with significant coronary artery disease and/or impaired left ventricular function (ejection fraction ≤ 50%), whereas right ventricular outflow tract pacing produced higher cardiac indices in the absence of these abnormalities. Right ventricular outflow tract pacing resulted in higher cardiac indices as compared to apex pacing in all other subgroups at all other pacing sites tested. It is concluded that stimulation of the right ventricular outflow tract offers a significant hemodynamic benefit during single chamber pacing as compared to conventional apex pacing, particularly in the absence of significant coronary artery disease and/or left ventricular dysfunction.