Long-term follow-up of pacemaker lead systems: establishment of standards of quality.

The functional details of all 5,405 pacemaker leads implanted on Montefiore Medical Center were contemporaneously recorded between 1960 and May 31, 1993. Some models have been observed for as long as 24 years. Ventricular leads with more than 50 and atrial leads with more than 30 implanted units have been continually and repeatedly subjected to actuarial cumulative survival rate (CSR) analysis during which clinical decisions, such as continued lead implantation, cessation of use, or early withdrawal from service, were made. CSR evaluation for many lead models by the Mantel-Haenszel method allowed comparison of the performance of contemporaneous lead models with older and new technologies. No effect on lead longevity, durability, on mode of end of lead service, lead removal independent of function (e.g., for infection), materials, or physiological failure was found due to an operator or anatomical route of venous access. Multifilar silicone rubber insulated leads have longevity (CSR) superior to monofilar silicone rubber leads. The cumulative survival of silicone rubber insulated monofilar models 6901, 6907, continuous lead (CL), 4 mm, and 2 mm was 79%-91%, 20 years after implantation. Multifilar silicone rubber insulated models 6961 and 4116 had a cumulative survival of 99%-100%, 15 years after implantation. Among multifilar polyurethane insulated leads, distinct longevity differences exist between formulations and contemporaneous models that are normally similar, yielding a bimodal longevity distinction; model 6971 (ventricular) has 95% CSR and 6991U (atrial) has 94% CSR, 10 years after implantation. Both performed less well than other contemporaneous models, which approximate 100% CSR. The 10-year CSR for leads implanted between 1960-1975 (Era 1) is 98.7%, and the 10-year CSR of leads implanted between 1981-1985 (Era 3) is 99.4%. Comparison of individual lead models, and all leads of specific eras, allows development of survival expectations and standards of quality for comparison between contemporaneous lead models and different eras of manufacture. As the highest available lead CSR sets the standard, statistical deviation of a model from the best performance of a specific era should be considered as an indication of reduced quality.

DDD pacing mode survival in patients with a dual-chamber pacemaker.

Dual-chamber (DDD) pacing mode survival was assessed by reviewing 486 consecutive initial transvenous DDD pacemaker implantations between December 1981 and December 1988 inclusive, with a mean follow-up time of 33 months. The patients' mean age was 71.4 years and 55% were male; 38% had dominant sinoatrial and 62% had dominant atrioventricular (AV) node disease. Nineteen patients (4%) underwent secondary operative intervention for lead dislodgement (n = 11), lead or pulse generator malfunction (n = 6) or infection (n = 2). During follow-up, 87 patients (18%) had their device permanently reprogrammed out of the DDD mode and 10 others (2%) required temporary reprogramming out of this mode; 12 patients who required device reprogramming were managed in other dual-chamber or atrial pacing modes. Reasons for reprogramming included atrial fibrillation (n = 48; 10%); loss of atrial sensing (n = 26; 5%); recurrent "endless loop" tachycardia (n = 5; 1%); lead dislodgement without repositioning (n = 4; 1%); pulse generator malfunction (n = 1; 1%) and other (n = 5; 1%). The occurrence of atrial fibrillation was associated with dominant sinoatrial disease and a prior history of atrial fibrillation; 19% of atrial sensing loss was attributable to early or faulty pacemaker technology. The DDD mode survival rate at 1, 2, 3, 4 and 5 years was, respectively, 90%, 88%, 84%, 79% and 78%.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical predictors and natural history of atrial fibrillation in patients with DDD pacemakers.

Effective DDD pacing requires that patients remain free of atrial fibrillation (AF). Four hundred eighty-nine consecutive patients undergoing initial transvenous DDD implants were reviewed to determine the incidence of postimplant AF in this population and to assess what factors, known at implant, predicted the later development of AF. The variables analyzed included age, sex, indication for implant (dominant SA or AV node disease), history of AF, atrial electrogram characteristics and pacing threshold, and the status of retrograde conduction. Forty-eight patients (9.8%) developed AF a mean of 23 months postimplant, and 11 of these patients returned to sinus rhythm and were managed once again in DDD for significant periods. A prior history of AF and the presence of dominant sinoatrial disease were far more prevalent in the patients who developed AF (P less than 0.001) though the vast majority of patients with these two independent risk factors remained in sinus rhythm through much or all of their follow-up period. We conclude that the incidence of AF is not of a magnitude to preclude DDD pacing in the vast majority of patients in sinus rhythm at implant.

Survival of implantable pacemaker leads. The Implantable Lead Registry.

Early polyurethane leads were reported to have a high incidence of materials failure. In 1979 a six-center registry was begun. By October 31, 1989, 7,311 leads had been registered and lead longevity was calculated by individual manufacturer, cumulatively for all manufacturers and for individual leads. Each lead was registered at implant and at removal from service as having been removed for materials failure or for unrelated reasons. Calculations were made for 23 models and for a total of three manufacturers with more than 100 leads implanted. Four thousand seven hundred and sixty three leads (65.1%) were from Medtronic; 2,177 (29.8%) from Cordis; 297 (4.1%) from Intermedics; and 77 (1.0%) were from all others. The 10-year cumulative survival of Medtronic leads was 96.6 +/- 0.4%; for Cordis leads it was 99.9 +/- 0.1% and for Intermediates leads 97.7 +/- 0.9%. Three lead models registered over 100 units and had poorer survival at 5 years than the remainder of all manufacturers' experience. They were #6972 (n = 107) with 78.6 +/- 4.5%; #6991U (n = 294) with 90.6 +/- 1.9%; and #4012 (n = 288) with 97.3 +/- 1.5%. Other possibly failed models did not achieve statistical significance. It can be anticipated that a lead which survives to the seventh year will have prolonged longevity as thereafter additional failures are uncommon.

Atrial electrogram analysis: antegrade versus retrograde.

Automatic discrimination between antegrade and retrograde atrial electrograms would prevent endless loop tachycardia and contribute to tachycardia detection algorithms. We tested its feasibility by comparing antegrade and retrograde atrial electrograms in 129 patients at the time of atrial lead implantation. Only unipolar, passive-fixation, endocardial, right atrial appendage leads were included. The mean antegrade amplitude was 4.2 +/- 2.2 mV, and retrograde 2.4 +/- 1.5 mV (P less than 0.001); the mean antegrade slew rate was 2.6 +/- 2.1 mV/ms, and retrograde 1.3 +/- 1.1 mV/ms (P less than 0.001). Morphology was similar in 84 patients (65%). The antegrade amplitude exceeded the retrograde by 1.0 mV in 67%, and by 0.5 mV in 81% of patients. Morphology and slew rate contributed little to the discriminating power of amplitude alone. Thus, amplitude criteria reliably distinguish antegrade from retrograde atrial activity.

Development of a clinical database for the implant and follow-up of cardioverter systems.

The purpose of a clinical database in AICD follow-up is twofold: to follow the evolution (1) of the patient and (2) of the implanted hardware. The pacemaker implant is performed the same day, whereas the implant of a complete AICD system can span over several days or even weeks. Therefore the first design criteria for the database is to clearly identify a single procedure. AICDs require the use of several leads of different types and functions and each lead has to be followed independently. Therefore the second design criteria is to establish a continuous history for each device implanted. To accomplish this the following method has been devised. The implant patient has a single demographic form and for each new procedure a 'Purpose of Procedure' form is filled out, which is identified by the date the form was initiated and by the patient's ID number. There are separate forms for the defibrillator and for three types of leads (transvenous, epicardial sensing and patch leads). For each hardware implanted a specific form is filled out and keyed to the 'Purpose of Procedure' form. Consequently the patient is monitored through the sequence of 'Purpose of Procedure' forms, the defibrillator and the leads through the hardware forms. Stimulation and sensing threshold measurements are part of the respective hardware forms but the induced tachycardia measurements are separate. At present 56 AICDs have been followed in the database.

Simplifying pacemaker follow-up by the implementation of the NASPE standards on computer interface. North American Society of Pacing and Electrophysiology.

One of the basic limitations for the development and use of more sophisticated pacemakers is the difficulty to provide adequate instrumentation and methodology for the follow-up in the clinical environment. To address this problem, the NASPE (North American Society of Pacing and Electrophysiology) Computer Committee has developed an interface standard to allow communication with the pacemaker programmer through many computer systems. The document recommends the use of the RS 232/c (CCITT V.24) interface with baud rates variable from 300 to 19,200, 7 bit word, no parity and Xon/Xoff protocol. The actual message format consists of an SOH code, a function code describing the action to be taken, a variable code defining the parameter on which the action is to be taken, and the actual numerical data. The CHECKSUM is calculated by summing all the ASCII codes beginning after the SOH code and ending with the last byte preceding the checksum itself. The last seven bits so calculated are attached to the message, and a consecutive ETX code ends the communication. At the receiving end, the checksum is recalculated and compared to the value received. If the two match, the message is accepted. Using this format, compatible computer software and pacemaker programmers can be developed independently and function as a unit. The protocol is capable of real-time ECG transmission.

The role of the computer in cardiac pacemaker technology.

To satisfy the need for even higher performance and smaller size, pacemaker design makes use of the latest available technology. This high level of technology in pacemakers requires an even higher level of technology in the follow-up system. Present methods consisting of independent programmers for each pacer model are confusing to the operator and inadequate. The solution to pacer follow-up developed at Montefiore consists of a three step program: 1) computer-assisted program which guides the personnel interactively through the follow-up; 2) computer-controlled program which enables the person to send identical commands to various programmers and let the computer program identify the various pacer models; and 3) built-in program where the testing and the follow-up are performed internally to the pacer through stored programs. The system is developed in the MIIS version of the MUMPS language but was extensively modified to make conversion to other languages easy.