Cardiac pacing leads.

Many of the advances that have been seen in the last decade concerning the functionality, size, and longevity of cardiac pacemakers have been dependent upon concomitant advances in cardiac pacing leads. The most difficult component of a pacing lead to develop has been the insulator. There are many choices for physicians implanting pacing leads: active versus passive fixation, standard impedance versus high impedance and polyurethane versus silicone. The current state of affairs of cardiac pacing leads is quite good in that we have leads that have excellent electrical properties and appear to be more resistant to the hostile environment into which the lead is placed. In spite of this, the goal of a perfect lead remains elusive and there continues to be many challenges in lead design.

False-positive behavior with the dP/dt sensing pacemaker: a rare complication of a physiological sensor.

As with "nonphysiological" devices, sensors that directly measure physiological variables have the potential to measure unexpected signals and for the physiological parameter being measured to respond in an unexpected manner. We present the case of a dP/dt sensing pacing system that functioned normally for 2 months and then developed upper rate behavior due to the sensing of a high frequency artifact on the pressure recording. Our case and others cited reinforce the need for future physiological rate responsive pacemakers to incorporate a second sensor to provide for backup rate response in cases of inappropriate rate response.

Reprogramming pacemakers enhances longevity and is cost-effective.

BACKGROUND: Historically, the majority of pulse generators implanted in the United States remain at the nominal programmed settings from the time of implant. While these nominal settings typically allow a sufficient safety margin to prevent later loss of capture with potential chronic threshold rise, the pulse generator with significant use would not be expected to last longer than that predicted by the manufacturer. However, improvements in lead technology have resulted in significantly lower chronic capture thresholds, which would permit lower programmable output settings while still allowing acceptable safety margins. Such changes could result in a significant reduction in long-term battery drain and translate into longer generator life. METHODS AND RESULTS: One hundred eighty consecutive patients undergoing implantation of permanent pacemakers at our institution were studied to determine the impact of reprogramming on pulse generator longevity and cost. Of these patients, 122 completed 6 months of follow-up at our institution and had pulse generators implanted that were capable of measuring battery current. We compared the estimated longevity based on battery current at nominal settings with that based on settings achieved in follow-up. The final settings were determined by the patient's physician using standard safety margins. The predicted longevity was 6.95 +/- 1.59 years at nominal implant settings and 11.16 +/- 2.71 years at final programmed settings (P < .001). Therefore, reprogramming extends the estimated pulse generator longevity by 4.25 +/- 2.14 years (64%) at a mean cost of $110 per patient (+37 per year extended). CONCLUSIONS: Reprogramming of permanent pacemakers is efficacious and cost-effective.

Defibrillator twiddler's syndrome causing device failure in a subpectoral transvenous system.

Twiddler's syndrome is well described as a complication of cardiac pacing. Defibrillator twiddler's syndrome has been recently reported with abdominal implantations of epicardial and transvenous defibrillator systems. We report a case of a patient with a transvenous defibrillator system implanted with the pulse generator placed in the subpectoral plane. The patient developed twiddler's syndrome, which resulted in retraction of both leads. This caused inappropriate shocks due to sensing both the atrial and ventricular electrograms. While the subpectoral position leaves the generator deeper and more difficult for the patient to access, it may not lessen the chance of twiddler's syndrome. It is possible that the subpectoral position may actually predispose the patient to this malady.

Effects of atrial fibrillation and atrial flutter on the signal-averaged electrocardiogram.

In conclusion, atrial flutter can create significant errors in the automated time-domain analysis of the SAECG that are only apparent when the study is repeated in sinus rhythm, thus lowering the predictive accuracy of the technique in patients with atrial flutter. Atrial fibrillation rarely creates problems with time-domain analysis of the SAECG. These findings suggest that, unless the performance of a specific signal-averaging device has been evaluated in patients with atrial flutter and found to have acceptable error rates, patients with atrial flutter should not have SAECGs performed for postinfarction risk assessment.

P wave morphology during atrial pacing along the atrioventricular ring. ECG localization of the site of origin of retrograde atrial activation.

P wave morphology during atrial pacing along the atrioventricular (AV) ring was evaluated to develop electrocardiographic (ECG) criteria for identifying the site of origin of the atrial activation wave during reentrant supraventricular tachycardia. Because P wave morphology changes as the pattern of atrial activation changes, the P wave should show characteristic morphologies during reentrant supraventricular tachycardia with use of either accessory AV pathways or the AV node for retrograde atrial activation. In 14 patients, 12-lead ECGs were recorded during bipolar atrial pacing at sites in the coronary sinus vein (along the mitral annulus) and along the atrial endocardium of the tricuspid annulus. P wave morphology was graded for each lead at each site. Sensitivity, specificity, and predictive value of ECG criteria for left versus right and anterior versus posterior atrial pacing sites were evaluated. Data were obtained from 14 sites along the AV ring, including 71 recordings at 6 sites in the coronary sinus vein and 94 recordings at 8 sites along the tricuspid annulus. These recordings were further divided into 54 anterior sites and 80 posterior sites, as well as 62 recordings along the right free wall and 32 recordings along the right atrial septum. The predictive value of a positive P wave in lead I indicating right atrial site of origin was 98.9%, and that for a negative or isoelectric P wave in lead I indicating a left atrial site of origin was 94.6%. Negative P wave in leads II, III, and aVF indicated a posterior site of origin, with a predictive value of 91.2%. The predictive value of a negative or isoelectric P wave in lead V1 indicating a right atrial free wall site was 87.5%. Thus, P wave morphology can be used to localize the site of origin of the atrial depolarization wave to a region along the AV ring.

Steroid elution improves the stimulation threshold in an active-fixation atrial permanent pacing lead. A randomized, controlled study. Model 4068 Investigators.

BACKGROUND: Prior work suggests that the addition of a steroid-eluting reservoir to a passive-fixation permanent pacemaker lead improves the stimulation threshold; however, no large randomized study has addressed this tissue. Over the last several years, there has been an increase in enthusiasm for the use of active-fixation permanent pacemaker leads for various reasons in spite of the generally accepted notion that active-fixation leads have higher stimulation thresholds. METHODS AND RESULTS: This multicenter, randomized, controlled study examined the difference in performance between a standard active-fixation atrial lead (Medtronic model 4058) and a steroid-eluting lead (Medtronic model 4068). Stimulation thresholds were obtained in a four-point strength-duration fashion. Evaluations of sensing and impedance were performed as well. These evaluations were performed at implantation, at weeks 1 through 4, and at weeks 6, 12, 24, and 52. Stimulation thresholds were significantly better in the steroid lead than in the nonsteroid lead at each measurement point from 1 week to 12 months. The mean 1.6-V stimulation threshold at 12 months was 0.19 +/- 0.2 ms in the steroid lead and 0.41 +/- 0.30 ms in the control lead. No acute peaking was observed with the steroid lead, whereas significant peaking was observed with the control lead. There was no difference in long-term sensing or impedance. CONCLUSIONS: Inclusion of a steroid-eluting reservoir in an active-fixation permanent pacing lead improved stimulation thresholds in both the subacute and chronic periods and therefore should extend pulse-generator longevity.

Treatment of patients with prior exit block using a novel steroid-eluting active fixation lead. Model 4068 Investigators.

An increased interest has developed in active fixation leads for several reasons. Exit block is an uncommon complication that is seen with both active and passive fixation leads. Exit block has not been a significant problem with passive fixation steroid-eluting leads and has been treated with these leads. A new steroid-eluting active fixation lead was examined for its performance in patients in whom exit block had previously occurred. The lead function was evaluated prospectively in 24 patients with a history of exit block (15 ventricular and 9 atrial). The results in patients with atrial exit block are encouraging with an average chronic stimulation threshold of 0.19 msecs at 2.5 volts. Results in the ventricle are less encouraging with 3 occurrences of recurrent exit block in 15 patients; however, the remaining patients had a good mean threshold of 0.21 +/- 0.11 msecs at 2.5 volts. There were a remarkable number of non-lead related complications suggesting that this is a substantially different group than routine implantations.

Modeling and closed-loop pharmacologic control of the ventricular rate during induced atrial fibrillation in anesthetized dogs.

An automated drug delivery system that provides closed-loop feedback control of the ventricular rate during atrial fibrillation is described. The control system was designed using a mathematical model of the effect of esmolol infusion in the ventricular rate. The model was developed in system identification experiments with anesthetized dogs in which atrial fibrillation was induced and maintained by rapid atrial pacing. A control system of variable structure, which incorporates a transient controller and a regulator, was designed to perform satisfactorily over a wide range of subject responses to drug infusion. The transient controller brings the ventricular rate to the setpoint with little overshoot. When the ventricular rate is near the setpoint, the drug infusion rate is calculated by the regulator. The drug infusion rate is constrained to ensure smooth transitions in the hemodynamic state of the patient and for safety. Feasibility of the system was demonstrated in computer simulations and animal experiments.