A Randomized Study on the Effects of Pacemaker Programming to a Lower Output on Projected Pulse Generator Longevity

SCHUCHERT, A., et al. : A Randomized Study on the Effects of Pacemaker Programming to a Lower Output on Projected Pulse Generator Longevity. The programmability of cardiac pacemakers enables the physician at follow‐up to adjust the pacing pulse under consideration of the 100% safety margin with respect to the individual pacing threshold. The purpose of reducing the output is to prolong pacemaker longevity. The aims of this prospective, randomized trial were to compare the effects of nominal output versus a lower output on projected pacemaker longevity in single and dual chamber pacemakers. The secondary aim was to assess how many patients can be programmed to 2.5 V/0.4 ms instead of the nominal 3.5‐V setting with ≥ 100% safety margin. The patients received the same types of VVI or DDD pacemakers that were connected in the ventricle to the steroid‐eluting, high impedance pacing lead. At the 3‐month follow‐up, patients with ventricular pacing thresholds ≤ 0.15 ms at 2.5‐V pulse amplitude were randomized to 3.5 V or 2.5 V amplitude at 0.4‐ms pulse duration. Lead function and projected device longevity were assessed with the pacemaker's telemetry 6 and 12 months after implantation. Of patients implanted with a VVI pacemaker, at the 3‐month follow‐up, 3 patients had pacing thresholds > 0.15 ms at 2.5 V and 139 patients could be randomized. A reprogramming to a higher output was necessary in one patient. The mean percentage of ventricular pacing was about 40% throughout the study time. The programming to 2.5‐V output resulted in an insignificant increase of device longevity from 117.9 ± 18.7 months in the nominal group to 123.7 ± 11.9 months at the 12‐month follow‐up (P = 0.16 ). Of patients implanted with a DDD pacemaker, 166 patients underwent randomization. The mean percentage of ventricular pacing was 85% in the ventricle and 35% in the atrium. The 2.5‐V setting significantly prolonged pacemaker longevity from 98.1 ± 21.3 to 112.0 ± 13.6 months (P < 0.0001 ). In three (1%) patients a late increase of the pacing threshold was observed. Due to the low ventricular pacing thresholds, the 2.5‐V/0.4‐ms setting provided, 3 months after implantation, a ≥ 100% safety margin in 99% of the patients. Programming to a lower output slightly increased projected pacemaker longevity compared to the nominal 3.5‐V setting. Longevity increased for 5% in patients with single and for 14% in dual chamber pulse generators.     

Variability in Implantable Cardioverter Defibrillator Pulse Generator Longevity Between Manufacturers

ELLINOR, P.T., et al .: Variability in Implantable Cardioverter Defibrillator Pulse Generator Longevity Between Manufacturers. ICDs are used frequently to treat malignant ventricular arrhythmias. Despite the expanding role of these devices, little is known about the manufacturer variability in the performance of ICD generators. The purpose of this study is to explore the indications for ICD pulse generator replacement and to examine performance differences between the three major manufacturers of ICDs in the United States. The authors performed a retrospective review of ICD pulse generators that were implanted and replaced at Massachusetts General Hospital between February 1998 and March 2002. During the study period, 50 (7%) of the 707 devices in the study cohort were replaced. The most common indication for pulse generator replacement was related to battery performance followed by device recall, upgrade to a dual chamber device, and pulse generator malfunction. After exclusion of the recalled devices, a significantly higher number of pulse generators manufactured by St. Jude Medical (14/229) required replacement for battery depletion or prolonged charge times during the study period compared with devices from Guidant (2/220) or Medtronic (0/273),  P = 0.003  and  P < 0.0001  , respectively. This difference was attributable to reduced longevity in the Angstrom series of defibrillators. (PACE 2003; 26[Pt. I]:71–75)     

Transcutaneous Cardiac Pacing: Evaluation of Cardiac Activation

ALTAMURA, G., ET AL.: Transcutaneous Cardiac Pacing: Evaluation of Cardiac Activation. The effects of transcutaneous cardiac pacing (TCP) on cardiac activation were evaluated by endocavitary recording (HRA, RVA) in eight patients, in order to test the possibility to obtain a simultaneous atrial and ventricular stimulation. The transcutaneous pacemaker used was the Pace Aid 52 (pacing rate 50–160 ppm, current output 10–150 mA, pulse width 20 sec). The two skin electrodes [surface area 50 cm²) were placed on the chest in anteroposterior position. Ventricular capture was observed in all patients [threshold = 74 ± 14 mA), simultaneous atrial capture was obtained in only four cases (threshold = 138 ± 25 mA). In conclusion, our data show that four-chamber simultaneous stimulation by TCP is possible, but only with pacing energies much higher than those usually required to capture the ventricle. The ability of TCP to simultaneously pace the atria and ventricles, though not relevant in the emergency cardiac stimulation for symptomatic severe bradyarrhythmias, could be useful in the treatment of reentrant supraventricular tachycardias.     

Usefulness of Echocardiography in Cardiac Pacing

The role of echocardiography in cardiac pacing is reviewed. We discuss its usefulness and limitations in the identification of pacing catheters, diagnosis of myocardial wall perforation, evaluation of catheter displacement/malposition, manipulation and positioning of catheters without recourse to fluoroscopy, identification of pacemaker induced thrombosis, diagnosis of venous anomalies and assessment of left atrial function in atrioventricular sequential (DVI) pacing. (PACE, Vol. 5, March-April, 1962)     

Long-Term Performance of Endocardial Pacing Leads

To assess the performance of endocardial pacemaker leads and to identify factors associated with structural lead failure, medical records of 2,611 endocardial pacing leads (in 1, 5W patients) implanted between 1980 and 1991, having at least 1 month of follow-up, were reviewed. Leads without structural failure had normal function at the last follow-up date, or were discontinued for reasons other than structural failure (patient death, infection, dislodgment, lead-pacemaker incompatibility, operative complication, or abandonment by telemetry not related to failure). Leads with suspected structural failures were invasively or noninvasively disconnected because of clinical malfunction (loss of capture or sensing, oversensing, elevated thresholds, or skeletal muscular stimulation). Leads with verified structural failures met the criteria for suspected lead failure and also had a visible defect seen in the operating room or on chest roentgenograms, a change in the impedance interpreted by the physician as lead disruption, or a manufacturer's return product report that confirmed structural failure. Variables analyzed included patients’ age and gender, paced chamber, venous access, insulation materials, fixation mechanism, coaxial design, polarity, and different lead models. The cumulative lead survival at 5 and 10 years were 97.4% and 92.9%, respectively, for suspected failures; and 98.7% and 97.3%, respectively, for verified failures. Leads in older patients (≥ 65 years old), and leads in atrial position had fewer verified failures (P = 0.014 and P = 0.007, respectively). Unipolar leads also tended to perform better according to the verified definition (P = 0.07). The lead Medtronic 4012 had more suspected (P < 0.05) and more verified failures (P < 0.01), the lead CPI 4010 had more verified failures (P < 0.05) than the entire group of ventricular leads. Conclusions: Endocardial pacing leads implanted in atrial position, and implanted in older patients (> 65 years old) seems to have better long-term survival. Some lead models (Medtronic 4012 and CPI 4010) had poor survival rates, that could not be explained by the analyzed variables. The expected performance of endocardial pacing leads varies according to how failure is defined.     

Transcutaneous Cardiac Pacing for Termination of Tachyarrhythmias

ALTAMURA, G., ET AL.: Transcutaneous Cardiac Pacing for Termination of Tachyarrhythmias. Transcutaneous cardiac pacing (TCP) was used for interruption of tachyarrhythmias in 31 patients: 20 with ventricular tachycardia (VT); eight with atrioventricular reentrant tachycardia (AVRT) and three had atrioventricular nodal tachycardia (AVNT). The stimulators used (Pace Aid 50/52) allow pacing at programmable rates (50–160 ppm) and output (10–200 mA at 20-msec pulse duration), when possible overdrive pacing was used. Short bursts of stimuli were delivered with increasing current intensity until interruption of the arrhythmia or to the maximum energy tolerated by the patient. VTs were interrupted in eight of the 20 patients: four of the six (67%) treated by overdrive pacing and four of the 14 (29%) were treated by underdrive pacing. Supraventricular tachycardias (SVT) were terminated in eight of the 11 patients: seven out of eight (88%) AVT, and one out of three AVNT (33%). We observed two cases of arrhythmia worsening: a VT acceleration and induction of ventricular fibrillation in a patient with AVNT. TCP was well tolerated by the majority of the patients. We conclude that TCP is an effective method for interruption of ventricular and supraventricular reentrant tachycardias, but the risk of arrhythmia worsening must be considered.     

高龄老年人右室心尖部及室间隔上部起搏对心功能的影响

【目的】探讨高龄老年人右室心尖部（RVA）和室间隔上部（RVUS）起搏对心功能的影响,寻找最佳起搏部位。【方法]89例行DDD起搏器治疗的患者：男84例,女5例,平均年龄84（75～95）岁,分为RVA组44例,RVUS组45例。对比分析两组起搏器间术前、术后3个月、6个月和1年心脏超声指标：心排血量（CO）、每搏输出量（sV）、射血分数（EF）、左室舒张末内径（LVDd）和血脑利钠肽（BNP）等的变化。【结果】RVA组治疗后心功能较起搏治疗前恶化,且随着起搏时间的延长恶化程度加重,而RVUS组心功能较起搏治疗前明显改善,且随着起搏时间的延长改善的越明显,与RVA组比较,具有统计学意义（P〈0．05）。【结论】高龄老年人RVUS优于RVA,可明显改善心功能,值得在高龄老年人中推广。     

Ventricular Pacing from the Middle Cardiac Vein Mimicking Supraventricular Morphology

A case is described in which ventricular pacing from the middle cardiac vein produced an electrocardiographic pattern which mimicked the morphology of the normally conducted beats. The possible etiologies of this unusual phenomenon and its implications concerning the functional anatomy of the normal conduction system in the human heart are discussed.     

The Effect of Ventricular Activation Sequence on Cardiac Performance During Pacing

The aim of this study was to evaluate the importance of a normal ventricular activation pattern for cardiac performance. In nine mongrel clogs, atrial pacing was compared to AV synchronous pacing at three different A V delays (150, 100, and 60 nis). In six dogs, proximal septal AV synchronous pacing was compared to apical A V synchronous pacing at three different A V delays. AV synchronous pacing was performed after RF induced complete heart block. Hemodynarnics were evaluated by assessment of positive and negative dP/dt, cardiac output, and left ventricular and pulmonary pressures. Atrial pacing was superior to AV synchronous pacing with respect to positive and negative dP/dt and cardiac output. This difference was present at all AV delays. Proximal septal pacing was associated with a higher positive and negative dP/dl compared to apical pacing at all AV delays. Left ventricular activation time was significantly shorter during proximal septal pacing than during apical pacing (88 ± 4 vs 115 ± 4 ms, P < 0.001). We conclude that atrial and proximal septal pacing improves cardiac function and shortens the ventricular activation time compared to apical AV synchronous pacing independent of the AV interval.     

Computer Simulation of Cardiac Pacing

A mathematical model of the cardiac conduction system, including external pacemakers, has been developed. The heart is modeled as a network in which the impulse propagation is described by differential equations; several arrhythmia-generating mechanisms, such as modulated parasystole, reflection, macro and micro re-entry and block, can be simulated. Different kinds of pacemaker modes have been incorporated in the model, thus making it possible to simulate the interaction between the heart and the pacemaker. The model can be tuned by the user according to electrophysiological data so that pacemaker programs can be tested under different underlying conditions. During a simulation, the program generates ECG signals and pacemaker diagnostic diagrams. This model can be used for training and testing, and also as a support system when searching for the optimal pacing therapy for a particular patient.     

Long-Term Follow-Up of Biventricular Pacing Using a Totally Endocardial Approach in Patients with End-Stage Cardiac Failure

Background: Besides standard left ventricular (LV) stimulation via the coronary sinus, a transseptal approach allows left ventricular endocardial stimulation. We report our long-term observations with biventricular stimulation, using a strictly endocardial system for patients presenting with severe congestive heart failure .
Methods: Six patients with nonischemic cardiomyopathy (mean age = 60 ± 9.6 years, women) in New York Heart Association (NYHA) functional class III (n = 5) or IV, despite optimal drug therapy, and a mean LV ejection fraction of 24 ± 3%, underwent implantation of biventricular stimulation systems between April 1998 and March 1999. All presented with left bundle branch block and an increased LV end-diastolic diameter (mean = 66 ± 5 mm). In all patients, a bipolar pacing lead was implanted in the lateral LV wall using a direct transseptal approach. After implantation, all patients received oral anticoagulation.
Results: QRS duration decreased from 184 ± 22 ms to 108 ± 11 ms. NYHA functional class decreased to II in all patients within 1 month. Over a 85 ± 5 month follow-up, two patients underwent cardiac transplantation, 2 and 4 years after device implantation, respectively; two patients died of end-stage heart failure 4 years after system implantation; and two patients were alive in functional class II. One patient, who experienced syncope due to fast ventricular, underwent implantation of an ICD. One transient ischemic attack occurred in a patient whose anticoagulation was temporarily interrupted .
Conclusions: Long-term endocardial biventricular stimulation via a transseptal approach was safe and effective in this small population. This approach needs to be further compared with conventional epicardial pacing via the coronary sinus     

Long-Term Clinical Performance of a Central Venous Oxygen Saturation Sensor for Rate Adaptive Cardiac Pacing

Rate adaptive ventricular pacemakers using central venous oxygen saturation (O₂Sat) to control the pacing rate have been implanted in 14 patients (mean age 71 years), with a mean follow-up period of 44 months (range 2–63 months). In eight patients the pacemakers were replaced due to signs of battery depletion after an implant duration of 39–58 months. During bicycle exercise testing the O₂Sat decreased on average from 61%± 4% at rest to 36%± 4% (P < 0,0001) at peak exercise, and the maximum pacing rate was 122 ± 5 beats/min. The time delay until the O₂Sat bad dropped 10%, 65%, and 90% of the total reduction during exercise was 4.8 ± 0.9 seconds, 39.8 ± 3.8 seconds, and 71.3 ± 7.5 seconds, respectively. The O₂Sat decreased 9.4%± 2% (P <0.005) from resting supine to resting sitting. Oxygen breathing increased the telemetered O₂Sat from the pacemaker by 8.4 %± 1 % (P < 0.001). During follow-up the O₂Sats were relatively stable in 50% of the patients, but demonstrated significant fluctuations in the others. At 1-year invasive follow-up O₂Sat measured by the pacemaker decreased 22%± 2%, and in blood samples from the right ventricle 22%± 2% from rest to 3 minutes exercise at 25 watts. There was a significant correlation between O₂Sat measured by the pacemaker and in blood samples from right ventricle (n = 105; r = 0.73; P < 0.001). In two patients the O₂Sat dropped significantly during pneumonia. In another patient episodes of angina pectoris was associated with low O₂Sat and a concomitant fast pacing rate.     

Steroid Eluting High Impedance Pacing Leads Decrease Short and Long-Term Current Drain: Results from a Multicenter Clinical Trial.

Pacemaker lead technology has changed considerably over the past decades. The widespread use of low polarization highly porous electrodes and steroid elution electrodes has resulted in low chronic pacing thresholds, as well as a decrease in the incidence of exit block. Efforts to develop pacing leads with high impedance might theoretically lead to lower lead current drain, which is a component of battery capacity. Pulse generator longevity can be increased without sacrificing pacemaker capabilities if pacing current drain can be decreased. Decreasing the size of the stimulation electrode results in increased pacing impedance, and if pacing thresholds are unchanged, a decreased current drain is predicted by Ohm's law (I = V/R). There is limited data available on the pacing characteristics of large numbers of patients with high impedance leads, despite their recent general availability and increasing widespread use. This multicenter, controlled trial examined the differences in performance between standard steroid-eluting pacing leads in the atrium (Medtronic model 5524) and ventricle (Medtronic model 5024), and new high impedance steroid-eluting pacing leads in the atrium (Medtronic model 5534) and ventricle (Medtronic model 5034). Measurements of bipolar pacing thresholds at 2.5 V, pacing impedance, and sensing thresholds were determined within 24 hours of pacemaker implantation, and at 0.5, 1, 3, 6 and 12 months after pacemaker implantation in 609 patients. Pacing and sensing thresholds were similar for the control and high impedance leads at all times except for a slightly larger R wave with the high impedance leads at implantation and 12 months. The mean impedance of the high impedance pacing leads in the atrium and ventricle at 12 months was 992 ± 175 and 1,080 ± 220 Ω, compared to 522 ± 69 and 600 ± 89 Ω for the standard pacing leads in the atrium and ventricle (P ≤ 0.001 for the high impedance leads compared to standard leads in each chamber). The mean atrial lead current (measured at 2.5 V) at 12 months was 2.6 ± 0.5 mA with the high impedance lead, and 4.9 ± 0.7 mA with the standard lead in the atrium (P ≤ 0.001). In the ventricle, the mean lead current at 12 months was 2.4 ± 0.4 mA with the high impedance pacing lead and 4.3 ± 0.6 mA with the standard lead (P ≤ 0.001). High impedance leads are associated with lower lead current drain than standard pacing leads in the atrium and ventricle for up to 1 year. No clinically important differences in sensing characteristics was noted with the high impedance leads in the atrium or ventricle compared to standard pacing leads. High impedance leads may result in increased pulse generator longevity.     

Permanent Ventricular Pacing Via the Great Cardiac Vein

Two cases of left ventricular pacing via the great cardiac vein are presented. A 64-year-old female with a mechanical prosthetic tricuspid valve and slow atrial fibrillation had a failed attempt at pacing from the middle cardiac vein. In a 58-year-old male with hypertrophic obstructive cardiomyopathy and brodycardia tachycardia svndrome. transvenous permanent pacing could not be achieved via the right ventricle or middle cardiac vein. In both cases, successful pacing via the great cardiac vein was achieved but with an elevated stimulation threshold. These cases illustrate an alternate transvenous route when difficulties occur using standard ventricular pacing sites.     

Choice of the Optimum Pulse Duration for Precordial Cardiac Pacing: A Theoretical Study

In precordial pacing with skin-surface electrodes, the goal is to excite the ventricles with minimal stimulation of overlying tissues. A theoretical analysis is presented to identify the relevant factors; the two most important are electrode location and pulse duration. Using the basic law of stimulation, we developed a model which indicates that the optimum pulse duration for the closed-chest pacing pulse is one that is long with respect to the membrane time constant of cardiac muscle. Current-versus-duration curves are presented for pacing and pain, based on experimentally obtained data. For pacing with minimum pain, the optimum stimulus duration was found to be about 10 ms.     

气管内紧急心脏起搏抢救心跳骤停的临床应用

目的:探讨紧急床边气管内心脏起搏在心肺复苏中的成功率。方法:对50例心跳骤停患者紧急行改良气管导管插管,插管成功后即行气管内心脏起搏。结果:50例中41例有起搏信号,起搏成功率为82%,28例临床有效,临床有效率为56%,其中21例复苏成功,复苏成功率为42%。结论:紧急床边气管内心脏起搏设备、操作简单,不影响胸外按压和进行其它急救措施,是抢救心跳骤停的一种有效措施。     

Long-Term Performance of Epimyocardial Pacing Leads in Adults: Comparison with Endocardial Leads

The long-term performance of epimyocardiaJ pacing leads in children is well established, but few studies have analyzed the performance in adults. This issue has clinical relevance in view of the increased use of epimyocardial leads with implantable cardioverter defibrillator and antitachycardia pacing systems. We analyzed 93 epimyocardial pacing "systems" (121 leads: 65 unipolar, 28 bipolar) in adult patients (age 57 ± 16 years), implanted since January 1980. Two different models were studied: Medtronic 4951 "Stab–on" (n = 35) and Medtronic 6917/6917A "Screw-in" (n = 58). A control group was created by randomly matching each epimyocardial system with two endocardial leads, according to age and year of implant. Epimyocardial and endocardial leads were followed-up for 44 ± 35 and 43 ± 35 months, respectively (P = NS). Freedom from failure for epimyocardial leads was 0.91 (95% Confidence Interval [95% CI] = 0.82 to 0.96) at 5 years, and 0.91 f95% CI = 0.69 to 0.98) at 10 years. No difference was found between the two analyzed models. Freedom from failure for endocardial leads was 0.97 (95% CI = 0.93 to 0.99) and 0.90 (95% CI = 0.61 to 0.97) at 5 and 10 years, respectively. Epimyocardial Jeads had a significantly poorer short-term survival than endocardiaJ leads, secondarily to earlier "technique related" failures (P = 0.03; relative riskc 3.0; Wilcoxon test). However, overall long-term performance was similar to endocardial leads. Epimyocardial pacing leads, meticulously implanted and tested, have a long-term performance similar to endocardial pacing leads.     

Present Day Pacemakers for Pulse Generator Exchange: Is 3.5 V a Sufficient Nominal Setting for the Pulse Amplitude?

Projected pacemaker longevity is calculated according to the nominal setting, which is 3.5 V for pulse amplitude in most present day pacemakers. The aim of this study was to test whether the nominal ventricular output setting of 3.5 V and 0.4 ms provides a 100% safety margin if these pacemakers are connected to implanted ventricular pacing leads. The study included 24 patients undergoing pulse generator exchange. The new pacemaker was either a Thera DR (n = 21) or Them SR (n = 3) device. Ventricular pacing leads were implanted 70 ± 38 months previously. Intraoperative measurements included pacing threshold at 0.5-ms pulse duration, impedance, and R wave amplitude. To achieve a 100% safety margin with 3.5 V, the cut-off pacing threshold is 1.7 V. At discharge it was assessed whether ventricular pulse amplitude remained at > 3.5 V or was programmed to > 3.5 V. At pulse generator exchange, pacing threshold was 1.2 ± 0.5 V, including four patients with pacing thresholds > 1.7 V. Impedance was 587 ± 189 Ω and R wave amplitude was 12.8 ± 4.8 mV. At discharge, ventricular pulse amplitude remained at the nominal setting in 13 patients, including 2 patients with high pacing thresholds at pacemaker exchange, and was programmed to < 3.5 V in 7 patients. Ventricular pulse amplitude was programmed to > 3.5 V in four patients. Two of these patients had high pacing thresholds (> 1.7 V/0.5 ms) at pulse generator exchange; the other two patients were programmed to > 3.5 V, although 3.5 V already provided a 100% safety margin. After pulse generator exchange, 92% of the patients could be paced with a 3.5- V pulse amplitude. Pacemakers were programmed in four patients > 3.5 V, but in only two of them to obtain a sufficient safety margin. High pacing thresholds at pulse generator exchange did not generally predict high pacing thresholds at discharge.     

External Non-invasive Cardiac Pacing: A Comparative Hemodynamic Study of Two Techniques with Conventional Endocardial Pacing

Out-of-hospital therapy for cardiac arrest due to bradyarrhythmias or asystole is pharmacologic and the outcome is uniformly dismal. Optimal therapy for the latter disturbances may be artificial cardiac pacing, but conventional invasive pacing techniques are not employed or are of limited value in the out-of-hospital and emergency department setting. This investigation compared the hemodynamic effects of two techniques of non-invasive external pacing: 1) transcutaneous transthoracic pacing (TTP) and 2) tongue-to-epigastrium pacing (TEP), with conventional transvenous right ventricular endocardial pacing (RVEP) in a closed-chest, chronic heart block canine model. All techniques significantly increased (p less than .001) cardiac output (CO). However, CO and mean arterial pressure (MAP) measured during external pacing with either non-invasive technique were significantly greater than that during RVEP (p less than .001). TEP produced vigorous skeletal muscle stimulation and, in the canine model, it produced contraction resulting in impaired ventilation, hypoxemia, and a decrease in systemic vascular resistance. TTP in this model resulted in improved MAP and CO when compared with control and RVEP values and did not affect arterial or mixed venous blood gas values. Thus, this study demonstrates that noninvasive TTP is comparable to RVEP in its hemodynamic effects. TTP may offer definitive non-invasive therapy for a subset of victims of out-of-hospital cardiac arrest.