Single-Chamber Rate Adaptive Pacing

Ventricular rate adaptiie pacemaker are the pacing systems of choice in patients with atrioventricular block and permanent or persistent atrial arrhythmias. A number of different pacemaker models are available, relying on different sensors of activity or metabolic demand. None of the sensors are perfect, each having its own advantages and disadvantages. Rate adaptive pacing is possible in the atrium as well as the ventricle, and at rial systems have a role in the management of patients with a poor sinus node response to exercise (chronotropic incompetence). The major groups of rate adaptive pacemakers are discussed in the following article, together with indications for use and possible future developments.     

Cardiac Output,Stroke Volume,and Pacing Rate: A Review of the Literature and a Proposed Technique for Selection of the Optimum Pacing Rate for an Exercise Responsive Pacemaker

Cardiac Output and Pacing Rate. Introduction : The purpose of this report is to determine the optimal pacing rate for an exercising patient. Methods and Results : From a review of the literature and from our own animal studies, the relationship between cardiac output and pacing rate and that between stroke volume and pacing rate are examined in resting and exercising animal and human subjects. With an adequately wide range of pacing rates, there exists a three-phase relationship between cardiac output and pacing rate. Starting with a low pacing pacing rate, an increase in pacing results in an increase in cardaac output (phase 1), then little change in cardiac output (phase 2), after which there is a decrease in cardiac output (phase 3). However, the relationship between stroke volume and pacing rate does not typically exhibit characteristics that allow identification of the three phases. In resting subjects with impaired ventricles and in exercising subjects, phase 2 is narrow or absent, the cardiac output increasing, then decreasing with an increase in pacing rate. From the experimental data reviewed herein, a technique is proposed for identifying the starting point in selecting the best pacing rate for resting and exercising subjects. The technique relies on identification of the transitions in the three-phase relationship between cardiac output and pacing rate. Conclusion : The best resting pacing rate is at the lower end of phase 2. A tentative first-choice exercise rate is at the middle of the resting phase 2 region. However, a change in cardiac output with a change in pacing rate will allow refinement of this first-choice exercise pacing rate.     

Clinical Experience with Dual-Chamber Rate Responsive Pacemakers

The development of dual-chamber rate responsive pacing is the logical consequence of technical and clinical developments and research in pacemaker technology. The first rate responsive dual-chamber pacemaker was implanted in June 1986 and the successful performance of this device encouraged manufacturers to further develop this technology. The rhythmic corrections that could be achieved were a strong argument to make use of this new technology in patients suffering from combined sinus node and AV nodal disease. DDD rate responsive pacemakers, therefore, have been implanted in 16 patients with a mean follow-up of 10.4 months. No technical complications were encountered, 2 patients died from causes not related to an arrhythmic problem. Of the 14 remaining patients, 12 are still in a dual-chamber rate responsive mode, 2 are in DDD or DDI-mode because of chronotropic competence of the sinus node. Therefore, we, conclude that dual-chamber rate responsive pacing is a reliable mode for long-term physiological pacing. Different features that can be included in a DDDR pacemaker may widen its use so that 85% of pacemaker indications might be covered with the DDDR pacemaker.     

Programming of Rate Responsive Pacemakers

Rate adaptive pacing adds a new dimension to pacemaker therapy. The possibility of near physiological pacing utilizing the piezoelectric sensor is now offered to a broad range of patients with varied clinical problems. Improved cardiac output during exercise increases exercise capabilities and patient satisfaction. Single-chamber rate adaptive pacing has been demonstrated to improve cardiac performance. The expansion of this technology into a dual-chamber pacing unit achieves the combined benefit of AV synchrony with synthesized chronotropic competence. The challenge in clinical practice is to construct an appropriate rate responsive regimen and then to confirm the adequacy and safety of the programmed parameters. Considerable experience with single- and dual-chamber rate adaptive pacemakers led us to develop a protocol for initial pacemaker selection, subsequent programming of these units, and confirmation of optimal function. A practical method for evaluation of rate adaptive pacemaker patients is outlined with programming guidelines.     

Ventricular Rate Stabilization Algorithm of ICD Causing Dual Chamber Pacing During Ventricular Tachycardia

Some implantable cardioverter-defibrillators (ICD) are designed with a ventricular rate stabilization (VRS) algorithm triggered by sensing a pacemaker-defined ventricular premature complex, for the prevention of short-long-short sequences that may predispose to ventricular tachycardia (VT). The VRS algorithm initiates AV sequential pacing at a relatively fast and decreasing rate according to a programmable sequence. This report describes a complex manifestation of ICD function where activation of the VRS algorithm produced AV sequential pacing during sustained VT. This response occurs when there is an appropriate relationship between the timing cycles of the ICD and a relatively slow VT.     

Adaptive Rate Pacing at Submaximal Exercise: The Importance of the Programmed Upper Rate

The contributions of rate response and different programmed upper rates to sub-maximal exercise were studied in 12 patients with implanted adaptive rate pacemakers (9 Meta, 3 Activitrax). Their median age was 69 years (range 33–80). All were paced from the right ventricle except for one patient with sinoatrial disease who received an atrial Meta pacemaker. In the constant rate pacing (SSI) mode, the reproducibility of a Submaximal stress test (maximum distance covered within a 12-minute walking test) was investigated by repeating the test three times. An initial training effect was obserbed between the first and the second test, but no further increase in walking distance occurred between the second and third test and the distances covered were highly reproducible (r = 0.99). The rate adaptive function was activated with the upper rate randomly programmed to 100, 125, 150, and 165 beats/min. Compared with exercise in the SSI mode, rate adaptive pacing with the upper rate programmed to 125 and 150 beats/min resulted in enhancement of exercise distance (4.7%± 1.2% and 4.4%± 1.2%, respectively, P < 0.005). Upper rates of 100 and 165 beats/min did not improve submaximal exercise performance, and at an upper rate of 165 beats/min, three patients developed complications (angina, dyspnea, and atrial fibrillation). It is concluded that the 12-minute walking test is a reproducible method to assess exercise capacity in pacemaker patients. Adaptive rate pacing improved exercise performance during daily activities, although the extent of the benefit appeared to be small and dependent on the programmed upper rate. An exercise test such as a 12-minute walking test should be performed before a high upper rate is programmed.     

Determining the Optimal Pacing Intervention Rate for Vasovagal Syncope

Introduction: In this study, patients with rate hysteresis pacemakers implanted for vasovagal syncope were re-studied using serial tilt testing to determine whether, once triggered, pacing was more effective if the intervention rate was higher than the standard rate. Methods and Results: Twenty patients (mean age 55.4 years, range 23–81, 14 male) were studied, with randomisation to either initial standard rate (80–90[emsp4 ]beats/min) intervention, or to initial high rate (120[emsp4 ]beats/min) intervention. Although 18 of the 20 reported complete abolition of syncope since pacing, only 8 patients could be objectively assessed. The respective mean time to tilt down after symptom onset with standard and high rate intervention was 193±234[emsp4 ]s and 185±143[emsp4 ]s, (P >0.05). Conclusion: Repeat tilt testing was only of limited value in assessing the benefit of pacing. There was no advantage with high rate intervention in delaying the loss of consciousness (or intolerable symptoms) after the initial onset of symptoms.     

Pace-Termination and Pacing for Prevention of Atrial Tachyarrhythmias: Results from a Multicenter Study with an Implantable Device for Atrial Therapy

INTRODUCTION: Patients with bradycardia requiring permanent pacing frequently suffer from additional atrial tachyarrhythmias (ATs). This study evaluated the safety and efficacy of atrial antitachycardia pacing (ATP) and the performance of pacing for AT prevention implemented into a new pacemaker. METHODS AND RESULTS: In patients with conventional indications for permanent pacing, an investigational DDDRP pacemaker (Medtronic AT500, model 7253) was implanted. The primary study objectives were to determine the safety of overall device functioning and its efficacy in terminating spontaneous AT. A secondary endpoint was to determine the reliability of AT detection. Pacemaker memory functions were used to analyze the impact of dedicated pacing algorithms on AT prevention. In 33 European and Canadian centers, 325 patients were enrolled (mean follow-up 2.3+/-1.3 months). Complication-free survival at 3 months was 88%. In 2,145 episodes stored with atrial electrograms, AT detection was confirmed in 97%. The algorithm for continuous overdrive pacing increased the percentage of atrial pacing to 97%. After ATP activation, 16,683 of 52,468 AT episodes were treated (120 patients). Of these, 8,903 episodes (53%) were terminated successfully by ATP. No proarrhythmic effect of preventive pacing or atrial ATP was observed. Preventive pacing algorithms increased the median percentage of atrial pacing from 62% to 97%. However, the number of AT/AF (atrial fibrillation) episodes (4.1 vs 4.1 per patient per day) and the time in AT/AF (13.7% vs 12.8%) was not significantly different before and after activation of preventive pacing. CONCLUSION: DDDRP pacing with a new system for AT therapy was safe and associated with successful pace-termination of AT in 53% of episodes. Preventive pacing and atrial ATP algorithms represent two new functions that can be implemented safely into pacemaker systems for nonpharmacologic treatment of ATs in patients requiring pacemaker therapy.     

Echocardiographic Localization of an Inadvertently Placed Pacing Catheter in the Left Ventricle

This report describes a patient in whom a permanent transvenous pacemaker lead was placed unintentionally across the atrial septum and retained in the left ventricle for nearly 11 years before the error was recognized. A 12-lead electrocardiogram showed paced complexes with right bundle branch block configuration. This appearance raised suspicion that the pacemaker electrode might be in the left ventricle and this was confirmed by two-dimensional echocardiography. Two-dimensional echocardiography is useful for the diagnosis of pacing lead malplacement and should be performed in any patient who develops right bundle branch block pattern on the surface electrocardiogram following pacemaker implantation.     

Interactions Between Pacing and Arrhythmia Detection Algorithms in the Dual Chamber Implantable Cardioverter Defibrillator

Dual chamber implantable cardioverter defibrillator (ICD) combines the possibility to detect and treat ventricular and atrial arrhythmias with the possibility of modern heart stimulation techniques. Advanced pacing algorithms together with extended arrhythmia detection capabilities can give rise to new types of device–device interactions. Some of the possible interactions are illustrated by four cases documented in four models of dual chamber ICDs. Functioning of new features in dual chamber devices is influenced by the fact that the pacemaker is not a separate device but a part of the ICD system and that both are being used in a patient with arrhythmia. Programming measures are suggested to optimize use of new pacing algorithms while maintaining correct arrhythmia detection.     

右心室心脏起搏升级双心室起搏的临床应用进展

心脏再同步化治疗是一项成熟应用于临床进展期心力衰竭合并左心收缩功能不全,心脏失同步患者治疗方法。右心室心尖部起搏改变了正常心脏的激动收缩顺序从而导致心脏电机械失同步,心脏收缩功能下降最终发生心力衰竭。适时地将起搏患者右心室起搏系统升级为双心室起搏可以纠正右室起搏导致的心脏失同步,最大限度保持左、右双心室间正常的电激动顺序和收缩同步性,有效地避免了起搏对血流动力学和心功能的不良影响。近来短期研究发现这种起搏系统升级可明显改善心脏活动的同步性,从而改善心功能、提高生活质量。文章综述了右室心尖部起搏的病理生理及升级右室起搏到双室起搏治疗的相关临床试验、显效机制及存在的问题。     

Merits and Limitations of the Mode Switching Rate Stabilization Pacing Algorithms in the Implantable Cardioverter Defibrillator

Background: The 7250 Jewel AF Medtronic model of ICD is the first implantable device in which both therapies for atrial arrhythmias and pacing algorithms for atrial arrhythmia prevention are available. Feasibility of that extensive atrial arrhythmia management requires correct and synergic functioning of different algorithms to control arrhythmias. Methods and results: The ability of the new pacing algorithms to stabilize the atrial rate following termination of treated atrial arrhythmias was evaluated in the marker channel registration of 600 spontaneously occurring episodes in 15 patients with the Jewel AF. All patients (55±15 years) had structural heart disease and documented atrial and ventricular arrhythmias. Dual chamber rate stabilization pacing was present in 245 (41%) of episodes following arrhythmia termination and was a part of the mode switching operation during which pacing was provided in the dynamic DDI mode. This algorithm could function as the atrial rate stabilization pacing only when there was a slow spontaneous atrial rhythm or in presence of atrial premature beats conducted to the ventricles with a normal AV time. In case of atrial premature beats with delayed or absent conduction to the ventricles and in case of ventricular premature beats, the algorithm stabilized the ventricular rate. The rate stabilization pacing in DDI mode during sinus rhythm following atrial arrhythmia termination was often extended in time due to the device-based definition of arrhythmia termination. This was also the case in patients, in whom the DDD mode with true atrial rate stabilization algorithm was programmed. Conclusions: The rate stabilization algorithms in the Jewel AF applied after atrial arrhythmia termination provide pacing that is not based on the timing of atrial events. Only under certain circumstances the algorithm can function as atrial rate stabilization pacing. Adjustments in availability and functioning of the rate stabilization algorithms might be of benefit for the clinical performance of pacing as part of device therapy for atrial arrhythmias.     

希氏束起搏进展

希氏束起搏是一种生理性的起搏模式。较传统右心室起搏相比,能够改善电-机械活动的同步性及血流动力学,有较好的临床获益。本文就希氏束起搏的研究进展做一综述。     

Permanent HIS bundle Pacing Feasibility in Routine Clinical Practice: Experience from an Indian Center

There is a paucity of experience regarding His bundle pacing (HBP) at laboratories initially attempting the procedure, especially in the Indian scenario. Patient who underwent HBP were selected for pacing therapy or in lieu of cardiac resynchronization therapy (CRT) at a single center. Among 22 patients attempted, 19 patients underwent successful implant, achieving selective HBP in 14 patients. There was a significant improvement in left ventricular ejection fraction (LVEF) (49.3 ± 9.3 vs. 36.7 ± 9.2) in the LV dysfunction subgroup (n = 6). Over a follow-up of 15 ± 6.5 months, thresholds were stable in all except one patient, and there was no requirement of lead revision. In summary, we found that HBP is a feasible option for achieving physiological pacing.     

特殊心房起搏程序预防和治疗心房颤动研究进展

心房颤动是临床上最常见的心律失常之一,严重影响了患者的生活质量,增加病死率。根据心房颤动发生的电生理机制,许多起搏器公司设计了可以减少或预防心房颤动发生的起搏程序。现就这些特殊程序的具体工作原理做一综述。     

生理起搏现代概念

近年来,随着多项大规模临床试验的揭晓,生理性起搏的概念也发生了较大变化。在起搏模式上应用各种程控方式尽可能的减少右室起搏,鼓励自身传导。采用能尽量模拟心脏正常传导及最小的血流动力学改变的起搏部位。生物起搏器能更生理性的恢复心脏的起搏和传导功能,将是未来发展的方向。而远程监控、远程随访、病情监测等多种新功能提高了起搏器的工作效率,扩展了起搏器的功能。现就起搏模式和部位的生理化以及生物起搏器、起搏器的远程监控技术等方面的研究进展进行综述。     

生理性起搏临床研究及进展

右心室起搏已被证实同心力衰竭、心房颤动、病死率等有密切关联,促使起搏治疗新一轮的革新。生理性起搏是近来心脏起搏器临床研究的重要方向,目前国内外主要通过优化起搏功能、选择起搏部位最小化心室起搏。以尽可能的生理性起搏,维持整个循环系统的稳定,从而提高患者生活质量并指导起搏器临床应用。