Permanent pacing after cardiac transplantation.

OBJECTIVE--To determine the need for long-term pacing and optimum mode of pacing in cardiac transplant recipients. DESIGN--(a) A retrospective review of patient records. (b) A prospective study of pacemaker use by 24 hour ambulatory electrocardiography before and after reprogramming to minimise use of pacemakers. SETTING--Outpatient clinic, supra-regional cardiopulmonary transplant unit. PATIENTS--All 21 patients at this centre who had received permanent pacemakers after cardiac transplantation. 18 of 19 survivors completed the prospective part of the study. MAIN OUTCOME MEASURE--The presence of pacing during a 24 hour ambulatory electrocardiographic recording (programming: 50 beats/min, rate sensor inactivated). RESULTS--21 of 191 (11%) recipients surviving one month or more received permanent pacemakers. The indication was sinus node dysfunction in 13 (62%) and atrioventricular (AV) block in eight (38%). Patients who paced on follow up 12 lead electrocardiograms declined from 38% at three months to 10% at three years after transplantation. After programming to 50 beats/min only five of 18 (28%) patients paced during a 24 hour ambulatory recording. Four of 11 (36%) recipients who received pacemakers for sinus node dysfunction paced compared with one of seven patients (14%) paced for AV block. No patient who had a pacemaker before the 16th day after operation continued to pace whereas five of nine implanted later were used long-term. CONCLUSION--Only five of 18 (28%) patients with pacemakers continued to pace long-term. Continued pacing was more common in those with persistent sinus node dysfunction after the second week after operation but the need for long-term pacing was not predictable.     

Cardiac pacemakers in the transplanted heart: short term with the biatrial anastomosis and unnecessary with the bicaval anastomosis

Sinus node dysfunction occurs commonly after orthotopic heart transplantation and may be caused by surgical trauma, ischemia to the sinus node, rejection, drug therapy and increasing donor age. In the past, using the standard biatrial technique described originally by Lower and Shumway, many series have reported permanent pacing in more than 10% of patients. Unlike sinus node dysfunction in nontransplanted patients, which typically worsens with time, sinus node dysfunction in the transplanted heart usually improves over a period of weeks to months. Delaying the implantation of a permanent pacemaker may render it unnecessary. The development of the bicaval technique for implantation of the donor heart appears to have decreased even further or even eliminated the need for early permanent pacing. Because sinus node dysfunction in the transplanted heart does not predict subsequent development of atrioventricular (AV) node dysfunction, rate-responsive atrial pacing should be used in the majority of cases. Even after appropriate pacing for sinus node dysfunction, the sinus node may recover and permanent pacing may be discontinued. AV conduction abnormalities are far less common and generally occur late after transplantation. Dual-chamber pacing is required and permanent pacing should be continued indefinitely.     

Sinus node function after cardiac transplantation

Objectives. This study aimed to examine changes over time in sinus node function after cardiac transplantation; to determine the incidence, natural history and etiology of sinus node dysfunction in transplant recipients; and to identify any early predictors of long-term sinus node function.Background. Bradyarrhythmias caused by sinus node dysfunction are common immediately after cardiac transplantation. Existing electrophysiologic studies have been limited by small numbers and have reported an unexpectedly high incidence of sinus node dysfunction (~50%) compared with the incidence of bradyarrhythmias in other studies, There have been no previous studies reporting serial electrophysiologic data. Thus, the natural history of sinus node dysfunction after transplantation has not been adequately described.Methods. Serial electrophysiologic studies of sinus node function and 24-h ambulatory electrocardiographic recordings were performed at 1, 2, 3 and 6 weeks and 3 and 6 months after transplantation in 40 adult recipients.Results. The overall incidence of sinus node dysfunction was 17.5% (7 of 40). Six patients (15%) had sinus node dysfunction from week 1; one developed sinus node dysfunction at 3 months. Sinus node recovery time returned to normal by 6 week in all six patients with early sinus node dysfunction, but abnormalities of sinoatrial conduction persisted in two. Two patients who required pacing during ambulatory monitoring at 2 weeks after transplantation (temporary pacemaker 50 beats/min, demand) received a permanent pacemaker. One patient required pacing at 3 weeks and continued to require pacing 6 months after transplantation.Conclusions. The incidence of sinus node dysfunction after cardiac transplantation is lower than has been previously reported in electrophysiologic studies. Sinus node automaticity improves with time, although abnormalities of sinoatrial conduction may persist. The best predictor of permanent pacing requirements is the temporary pacing requirements during 24-h Holter monitoring 2 and 3 weeks after transplantation, with temporary pacing set at 50 beats/min on demand.     

Pacing therapy in the elderly

Bradycardia due to sinus node dysfunction and atrioventricular block is more commonly observed in the elderly. Aging is associated with progressive fibrosis in both the sinus node and atrioventricular conduction system (AV node, His bundle, right and left bundles). In the absence of reversible causes implantation of a permanent pacemaker is often required in the patient with symptomatic bradycardia. For elderly patients with sinus node dysfunction, pacing modes that preserve atrioventricular synchrony are associated with a reduced incidence of atrial fibrillation and improved quality of life. For patients with atrioventricular block, the importance of preserving atrioventricular synchrony in the elderly is controversial and is currently being evaluated.     

Development of sinus node disease in patients with AV block: implications for single lead VDD pacing

OBJECTIVE: To investigate the incidence of sinus node disease after pacemaker implantation for exclusive atrioventricular (AV) block. DESIGN: 441 patients were followed after VDD (n = 219) or DDD pacemaker (n = 222) implantation for AV block over a mean period of 37 months. Sinus node disease and atrial arrhythmias had been excluded by Holter monitoring and treadmill exercise preoperatively in 286 patients (group A). In 155 patients with complete AV block, a sinus rate above 70 beats/min was required for inclusion in the study (group B). Holter monitoring and treadmill exercise were performed two weeks, three months, and every six months after implantation. Sinus bradycardia below 40 beats/min, sinoatrial block, sinus arrest, or subnormal increase of heart rate during treadmill exercise were defined as sinus node dysfunction. RESULTS: Cumulative incidence of sinus node disease was 0.65% per year without differences between groups. Clinical indicators of sinus node dysfunction were sinus bradycardia below 40 beats/min in six patients (1.4%), intermittent sinoatrial block in two (0.5%), and chronotropic incompetence in five patients (1.1%). Only one of these patients (0.2%) was symptomatic. Cumulative incidence of atrial fibrillation was 2.0% per year, independent of the method used for the assessment of sinus node function and of the implanted device. CONCLUSIONS: In patients undergoing pacemaker implantation for isolated AV block, sinus node syndrome rarely occurs during follow up. Thus single lead VDD pacing can safely be performed in these patients.     

Trastornos graves de la conducción cardiaca e implante de marcapasos en pacientes con miocardiopatía hipertrófica

The aims of this study were to determine the prevalence of severe cardiac conduction disturbances in a cohort of 451 patients with hypertrophic cardiomyopathy and to describe the characteristics of, and outcomes in, those who required a permanent pacemaker. A pacemaker was implanted in 48 patients (11%): 20 had sinus node dysfunction and 28 had an atrioventricular conduction disturbance. Primary bradyarrhythmia (which was not related to iatrogenic atrioventricular block or therapeutic ablation of the atrioventricular node) was the reason for permanent pacemaker implantation in 36 patients (8%). In 18% of cases, at least one other family member had a permanent pacemaker. In this patient series, a high prevalence of severe cardiac conduction disturbance leading to permanent pacemaker implantation was observed. Severe cardiac conduction disturbance in hypertrophic cardiomyopathy may also have a familial component.     

Congenital cardiac surgery without routine placement of wires for temporary pacing

OBJECTIVE: Temporary pacing wires have been associated with serious postoperative complications. Recommendations for their routine use after open heart surgery are decades old, and may not reflect current surgical techniques and outcomes. METHODS: The electronic web-enabled medical records of all patients undergoing congenital cardiac surgery from February, 2002, through December, 2005, were reviewed, excluding patients undergoing implantation of pacemakers as a primary procedure, or those undergoing ligation of a patent arterial duct. RESULTS: There were 1193 surgical procedures performed, 1041 with cardiopulmonary bypass. Median age of the patients was 5.8 months, with a range from 0 days to 54 years, weighing 6.2 kilograms, with a range from 1 to 114 kilograms. Mortality prior to discharge was 2.5%, and median postoperative stay was 6 days. No deaths were attributed to arrhythmias. Temporary pacing wires were placed 14 times (1.2%). Indications for placement included sinus nodal dysfunction in 8 patients, preoperative in 4 and intraoperative in 4, high degree atrioventricular block in 4 patients, and intraoperative atrial flutter in 2 patients. Of these patients, 4 (0.3%) eventually underwent permanent implantation of a pacemaker, 2 for persistent sinus nodal dysfunction, and 2 for persistent atrioventricular block. Postoperative junctional ectopic tachycardia requiring antiarrhythmic therapy occurred in 9 patients (0.8%). All recovered without incident, and none were treated with temporary pacing. CONCLUSIONS: The diminished risk of unexpected postoperative arrhythmias in the current era alleviates the necessity for routine placement of temporary pacing wires. Those institutions with experienced surgical and cardiac critical care teams may be able to predict the need for temporary pacing wires preoperatively or intraoperatively.     

Stability of AV conduction in sick sinus node syndrome patients with implanted atrial pacemakers

Single-chamber atrial pacing is effective in the management of sinus node dysfunction, subject to the uncertainty of long-term atrioventricular conduction. Despite the accepted observation that many patients with sinus node dysfunction also have atrioventricular conduction disease, data do not exist on the development of atrioventricular block in those patients with permanent single-chamber atrial pacing. Of 70 patients who received single-chamber atrial pacing from 1967 to 1982 (mean duration of pacing was 33 months), only two patients of 58 (3.4%) of those with sinus node dysfunction developed atrioventricular (AV) block—after 14 months in one patient and after 23 months of successful atrial pacing in the other. None of the 12 patients paced for tachyarrhythmia management developed AV block. Of the 70 patients, 37 had assessment of AV conduction by incremental atrial pacing at the time of implant and 20 patients underwent atrial pacing on the basis of surface ECG and clinical judgment. Electrophysiologic studies were conducted only in those patients being paced for control of supraventricular arrhythmias. Only 5 of the 70 patients required conversion to ventricular pacing for technical difficulties; three of these conversions occurred in the early 1970's before the advent of atrial tined or J leads; one was for irreparable lead fracture and only one occurred in a patient with a newer design atrial lead. In conclusion, progression to AV block in patients with permanent atrial pacing is uncommon; formal electrophysiologic studies are necessary mainly in patients with supraventricular arrhythmias; and in the majority of patients, AV conduction can be assessed at the time of implant. Continued improvement in atrial leads should make atrial pacing even more successful.     

Complications of pacemaker therapy in adults with congenital heart disease: A multicenter study

Background

This study aims to investigate indications and complications of permanent cardiac pacing in adults with congenital heart disease (CHD).

Methods and results

Two-hundred and seventy-four CHD patients were identified who underwent permanent pacemaker implantation between 1972 and 2009. The indication for pacing was acquired sinus node or AV node conduction disease (63%), sinus node or AV node conduction disease after cardiac surgery (28%), and drug/arrhythmia-related indications (9%). Patients with complex CHD received a pacemaker at younger age (23 versus 31 years, p < 0.0001) and more often received an epicardial pacing system (51% versus 23%, p < 0.0001) compared to those with simple or moderate CHD. Twenty-nine patients (10.6%) had a periprocedural complication during the primary pacemaker implantation (general population: 5.2%). The most common acute complications were lead dysfunction (4.0%), bleeding (2.6%), pocket infection (1.5%) and pneumothorax (1.5%). During a median follow-up of 12 years, pacemaker-related complications requiring intervention occurred in 95 patients (34.6%). The most common late pacemaker-related complications included lead failure (24.8%), pacemaker dysfunction/early battery depletion (5.1%), pacemaker migration (4.7%) and erosion (4.7%). Pacemaker implantation at younger age (< 18 years) was an independent predictor of late pacemaker-related complication (adjusted hazard ratio 1.68, 95% confidence interval 1.07 to 2.63, p = 0.023).

Conclusions

The risk of periprocedural complications seems higher in the CHD population compared to the general population and more than one-third of CHD patients encountered a pacemaker-related complication during long-term follow-up. This risk increases for those who receive a pacemaker at younger age.     

Single-pass lead VDD pacing system in children and adolescents: report of twenty-four patients

The dual-chamber pacing systems allow for AV synchrony, but generally require the placement of two separate transvenous leads. Single-lead atrioventricular synchronous pacing system (VDD) using single-pass leads has been accepted as therapeutic alternative for atrioventricular block with normal sinus node function. The aim of this study is to evaluate clinical performance of single-pass lead VDD pacing systems in 24 consecutive patients in a ten-year period. The study group includes 17 (70.8%) male and 7 (28.8%) female patients.The mean age and mean weight during pacemaker implantation was 10.4 +/- 3.8 years (4-17 years) and 30 +/- I I kg (13.5-55 kg), respectively. The patients have been followed for 7-84 months (median 42 months). The percentage of atrial sensing-ventricular pacing changed from 75 to 99.9% at the last control. During the follow-up period, pacing mode was changed to VVIR due to complete loss of AV synchrony in five patients (21%). Four of them had underlying cardiac disease. In these patients loss of AV synchrony might be related to cardiac enlargement/abnormal cardiac anatomy or small atrial dipole-ventricular tip length. Despite the loss of AV synchrony in post surgical AV block or dilated cardiomyopathy, single-lead VDD pacing systems can be successfully used in children with complete AV block and normal sinus node function. Patients and lead selection should be taken into consideration for the maintenance of AV synchrony.     

Natural history of sinus node disease treated with atrial pacing in 213 patients: implications for selection of stimulation mode.

OBJECTIVES. This study was designed to analyze the incidence and determinants of complications and long-term survival in sinus node disease treated with atrial pacing. BACKGROUND. Knowledge of the natural history of sinus node disease treated with different pacing modes is imperfect, and controversy exists regarding the optimal pacemaker therapy. METHODS. A consecutive series of 213 patients with sinus node disease initially treated with atrial pacing was studied for a median follow-up period of 60 months. The end points studied were permanent atrial fibrillation, high grade atrioventricular (AV) block, P wave undersensing, pacing mode change, reoperation and death. Several prognostic factors were evaluated statistically and the survival rate was compared with that of a matched general population. RESULTS. The incidence rate of permanent atrial fibrillation during follow-up was 7% (1.4%/year). The risk of this arrhythmia increased substantially with age greater than or equal to 70 years at pacemaker implantation. Only 2 of the 15 patients who developed permanent atrial fibrillation required ventricular pacing. High grade AV block occurred in 8.5% (1.8%/year) and its incidence was much greater in patients with complete bundle branch block or bifascicular block (35%) than in patients without such conduction disturbances (6%). A change to ventricular or dual-chamber stimulation was necessary in 14% of all patients, primarily because of early lead dislodgment or high grade AV block. Surgical intervention with maintenance of atrial pacing was required in 7% of patients. The survival rates of 97% at 1 year, 89% at 5 years and 72% at 10 years did not differ significantly from those of a matched general population. CONCLUSIONS. In sinus node disease, atrial pacing can be successfully applied during long-term follow-up. Patients with complete bundle branch or bifascicular block in addition to sinus node disease should initially receive a dual-chamber pacemaker, but routine application of dual-chamber stimulation does not appear to be warranted.     

Clinical study of double-chamber stimulation. Apropos of 50 cases followed-up for 1 to 5 years

The authors report their experience of dual chamber pacing in 29 men and 21 women of mean age 71 +/- 4 years. 35 had sinus node dysfunction associated with node-His bundle conduction disorders; 31 presented with neurological symptoms and 4 with heart failure (due to pacemaker syndrome in 1 case). Sinus node dysfunction was diagnosed by surface ECG in 25 cases and after electrophysiological studied in only 10 cases. Fifteen patients had atrioventricular block without sinus node dysfunction: 2 of them were young subjects, 1 had pacemaker syndrome and 12 were actual or potential heart failure patients for whom preservation of the atrial systole was justified. Nine patients presented with neurological symptoms. 43 (86%) had cardiac or arterial disease associated with cardiac rhythm and conduction disorders. The percutaneous single subclavian vein approach was used in 36 cases (78%). 41 active and 9 passive fixation electrodes were utilized. The mean follow-up period was 25 months (12 to 70 months), with a cumulative figure of 1,253 months/patients. Two late re-operations for displacement of the atrial electrode were performed. Dual chamber pacing was abandoned, 14 months on average after implantation, in 9 patients (18%), on account of arrhythmias in 4 of them. Three cases of tachycardia from "electronic re-entry" and 6 cases of supraventricular arrhythmia transferred to the ventricle by the pacemaker were observed. Sixteen patients (32%) died 12 +/- 4 months on average after surgery: 12 (33%) had sinus node dysfunction and 4 (26%) had AV block. Death was caused by a cardiovascular disease in 12 cases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pre-implant determinants of adequate long-term function of single lead VDD pacemakers.

AIMS: An inherent limitation of single lead VDD pacing is the inability to stimulate the atria. Reprogramming and upgrading the pacemaker system may be required when sinus node dysfunction, atrial undersensing, or atrial fibrillation develop. We evaluated whether routine clinical information is sufficient to select patients to benefit in long-term from VDD pacing. METHODS AND RESULTS: We collected data on 12-lead and monitored electrocardiograms and routine clinical information at implantation of a VDD pacing system in 350 consecutive patients with grade II or III atrioventricular conduction block. The age at implantation was 74.5 +/- 8.0 years, and the follow-up lasted 1.5 +/- 1.5 years. The cumulative maintenance of VDD pacing mode was 91.%. Loss of VDD mode was due to permanent atrial fibrillation in 16 (4.6%), sinus node dysfunction in six (1.7%). atrial undersensing in 11 (3.1%). Chronic atrial fibrillation developed in 23% of patients who had heart enlargement in chest x-ray and a history of paroxysmal atrial fibrillation or flutter. A criterion of normal sinus rate at implantation sufficiently predicted adequate sinus node function. Poor atrial sensing was not predicted by pre-implant characteristics. CONCLUSIONS: According to our data, adequate sinus-driven atrial rate and no history of paroxysmal atrial fibrillation and cardiac enlargement predict maintenance of the VDD pacing mode in elderly patients treated for heart block. Routine information available at implantation is sufficient to guide acceptance of single lead VDD pacing therapy.     

Cardiac bradyarrhythmia

Permanent cardiac pacing was introduced in 1958 and till the end of 70s this method saved lives in particular of the patients with advanced atrioventricular block. The implantation technique has changed from complicated thoracotomy to endovasal approaches. The introduction of physiological AV sequenced atrioventricular pacing marked a significant progress in this field. Acute haemodynamic studies documented positive effect of the atrial contribution. Numerous studies subsequently analyzed the influence of different pacing regimes on total and specific cardiovascular mortality and morbidity. It can be concluded that on the basis of present evidence-based medicine the use of physiological pacing is clearly indicated in the patients with expressed sinus bradycardia and AV block of a higher degree. Atrial pacing remains an ideal solution for the patients with isolated sinus node dysfunction and sufficient atrioventricular conduction capacity. Research is continued in order to clarify how to influence the occurrence of ventricular fibrillation by permanent cardiac pacing including the use of preventive algorithms. This topic has not yet been reliably and unambiguously concluded. Biventricular pacing is currently established and recognized not only for typical indications in cases of bradyarrhythmias but also to solve primary haemodynamic problems in the patients with advanced heart failure and evidence of ventricular dyssynchrony.     

Permanent pacemaker use after cardiac transplantation: completing the audit cycle.

OBJECTIVE: To determine the effects of delaying permanent pacemaker implantation in cardiac transplant recipients from less than tree weeks to three weeks or more post transplantation-a change prompted by an earlier audit. DESIGN: Retrospective review of resting 12 lead electrocardiograms and prospective 24 hour ambulatory electrocardiograms. Comparison of pacemaker usage before (period 1) and after (period 2) the policy change in November 1990. SETTING: Outpatient department, supra-regional cardiopulmonary transplant unit. PATIENTS: All 30 consecutive orthotopic cardiac transplant recipients who received a permanent pacemaker within one month of transplantation between May 1985 and August 1995. MAIN OUTCOME MEASURES: Presence of pacing on the 12 lead electrocardiogram and during 24 hour ambulatory electro-cardiogram monitoring (pacemaker programmed to 50 beats per minute). RESULTS: 16/152 (10.5%) cardiac transplant recipients received permanent pacemakers in period 1 compared with 14/180 (7.8%) in period 2 (P = NS). Evidence of pacing was seen on 12 lead electrocardiograms at three months in 37.5% recipients in period 1 compared with 78.6% in period 2 (P = 0.03). At six months pacemaker usage had declined to 18.8% in period 1 and 35.7% in period 2 and at three years to 13.3% in period 1 and 40% in period 2 (P = NS for both). 21% patients in period 1 paced on ambulatory 24 hour monitoring compared with 38.5% in period 2 (P = NS). CONCLUSIONS: Delaying permanent pacemaker implantation to three weeks or more after cardiac transplantation reduced the proportion of permanent pacemaker implantations, slightly but not significantly. There was a significant increase in permanent pacemaker usage at three months post transplantation with trends towards increased usage at later times, suggesting more appropriate selection of patients for permanent pacing.     

Cardiac pacing in the elderly

Sinus node disease and atrioventricular block are common etiologies of symptomatic bradyarrhythmias in the elderly and remain the leading indications for permanent pacemaker implantation. In fact, the vast majority (>80%) of all pacemakers are implanted in the elderly. Whereas indications of pacemaker therapy have been largely unchanged over the past several years, several questions, such as differences in pacemaker mode selection, remained unanswered. Recent large, randomized, multicenter trials have evaluated the benefits of pacemaker therapy in sinus node dysfunction and acquired atrioventricular block and have provided us with further insights into the difference between atrial- and ventricular-based pacing in these syndromes. Further evaluation of the most appropriate pacing mode in the elderly as well as the outcome of pacing in the elderly are addressed in this review.     

Long-term reliability of AAI mode pacing in patients with sinus node dysfunction and low Wenckebach block rate.

AIMS: To compare the risk of atrioventricular (AV) conduction disturbance between patients with sinus node dysfunction on AAI pacing who had a low or high Wenckebach block rate (WBR). METHODS AND RESULTS: Patients with sinus node dysfunction and normal AV conduction those underwent an electrophysiological study were studied. The patients were classified into two groups: Group L was with the patients with a WBR of 100 to 129 per minute and Group H was with the patients with a WBR > or = 130 per minute. All patients followed up every 3-6 months after an AAI pacemaker implantation. A total of 102 patients, including 35 Group L and 67 Group H, were followed for 90 +/- 44 months. Six patients died from non-cardiac cause and five patients required a new atrial lead implantation due to lead failure during follow-up. Symptomatic bradycardia requiring a new ventricular lead implantation developed in four patients (annual incidence 0.5%). In Group L, two patients developed AV block (annual incidence 0.7%). In Group H, two patients developed bradycardic atrial fibrillation (annual incidence 0.4%). Kaplan-Meier analysis revealed no significant difference between the two groups (P = 0.2983). CONCLUSION: These results suggest that a long-term risk of developing AV conduction disturbance is low even in patients with a WBR of 100 to 129 per minute.     

Sick sinus syndrome due to cardiac amyloidosis

In a patient suffering from cardiac amyloidosis a case of sick sinus syndrome, manifested by markedly prolonged recovery time of the sinus node, was documented by an atrial pacing study. The first A-V junctional escape interval was markedly prolonged following the termination of the atrial pacing, pointing to a coexisting A-V nodal dysfunction. The patient required a permanent artificial pacemaker implantation.     

Pacemaker utilization during permanent atrial fibrillation in patients who received pacemaker implantation for sinus node dysfunction

Patients who have pacemakers and sinus node dysfunction frequently have atrial fibrillation (AF). The need for continued pacemaker therapy after conversion to permanent AF remains uncertain. This study showed that, among 174 patients who received pacemaker implantation for sinus node dysfunction, 38% (n = 62) had the minimum intrinsic ventricular rate of >60 beats/min after conversion to AF. The pacemaker memory showed that 30 patients (18%) never used ventricular pacing during permanent AF. The study results suggest that patients who have a stable intrinsic ventricular rate during permanent AF by serial assessment may no longer need continued pacemaker therapy.     

15例植入型起搏系统作临时起搏的临床应用

目的 探讨利用植入型起搏系统脉冲发生器外置作为临时起搏临床应用的可行性.方法 15例房室阻滞或窦性心动过缓需行临时起搏患者,经锁骨下静脉径路植入永久起搏系统的心室主动导线,头端固定于右心室间隔部,连接外置脉冲发生器,行临时起搏.结果 15例患者均顺利完成临时起搏过程.结论 植入型起搏系统脉冲发生器外置可作为临时起搏应用.