Early pacemaker twiddler syndrome.

Twiddler's syndrome is a well-known complication of pacemaker treatment. It was first described by Bayliss et al. when a patient manipulated and rotated the pulse generator in the pocket so many turns that it resulted in lead dislodgment, diaphragmatic stimulation and loss of capture. In this case report we present a patient who managed to rotate her dual chamber pulse generator so quickly after implantation that exit block occurred within 17 h. She had wound the two leads as far as their tips in a perfect formation around the pulse generator.

Thin co-radial bipolar leads: technology and clinical performance.

While bipolar leads offer advantages such as better sensing performance than unipolar leads, their use has been limited by a larger lead diameter and reports about a high failure rate of several bipolar lead models. This has led to the development of thin bipolar leads using a special technology which aims at improving lead safety. Leads with monofilar thin conductors (drawn filled tube) which are individually coated with a very resistant material (ETFE) have been developed. Using a co-radial instead of co-axial bipolar conductor design, the lead diameter could be reduced to 4.5 F compared to 6-7 F of conventional bipolar leads. Bench testing demonstrated a significant improvement of this lead technology with respect to degradation of insulation material by biochemically reactive solutions. Also mechanical characteristics such as resistance to tearing forces and compression showed a high lead durability. From our own experience, co-radial bipolar leads show a favorable electrical performance with the exception of a relatively low pacing impedance. Also during long-term follow-up, the rate of lead failure was very low. These findings are corroborated by other clinical studies which also demonstrated good handling characteristics of thin bipolar leads during implantation.

Alternative to the transvenous approach in pediatric pacing - long-term experiences with bipolar epicardial pacing leads.

BACKGROUND: Cardiovascular anatomy and limited venous access may preclude the implantation of endocardial pacing systems in children as well as adults with congenital heart disease. Thus, the implantation of myo/epicardial pacing leads is required in these patients. The less favorable long-term results experienced in the past with myocardial screw-in leads are often used to justify the transvenous approach whenever possible, even in infants. However, encouraging preliminary results were reported from modern bipolar steroid eluting epicardial pacing leads. Further follow-up data are now warranted to obtain arguments for the dispute regarding the preferable or optimal pacing approach in infants and small children. Methods From January 1994 to November 2000 a total of 64 bipolar steroid-eluting epicardial pacing leads (Medtronic CapSure Epi 10366 and 4968, Medtronic, Inc, Minneapolis, MN, USA) were implanted in 52 children at our institutions (52 electrodes in ventricular and 12 in atrial position). The median age of the children was 25.5 months (range 0.03 to 193 months). As part of a prospective multicenter study these leads were continuously followed in combination with AutoCapture devices since December 1996. Results Telemetry data demonstrated at discharge low pacing thresholds both for the ventricular (0.8±0.37Volt @ 0.5ms) and the atrial leads (0.8±0.4Volt @ 0.5ms) as well as excellent sensing signals (P wave 2.9±1.4mV and R wave 10.6±5.5mV) without significant changes during follow-up up to 24 months. AutoCapture controlled pacing could be applied in 46/52 (88%) children rendering a calculated battery service life of 14.8±2.9 years with a VVIR device (Regency SR 5130, St. Jude Medical, Sylmar, CA, USA) and 10.8±1.1 years with a dual chamber device (Affinity DR 5330, St. Jude Medical, Sylmar, CA, USA). Apart from the necessity to reposition three leads in the immediate postoperative period no late lead related complications have been experienced during follow-up. Conclusions The new steroid-eluting bipolar epicardial pacing lead demonstrates a high reliability and consistent extraordinary pacing as well as sensing thresholds. AutoCapture controlled pacing is feasible in most patients and may result in marked battery service life extension. Hence epicardial pacing can now be highly recommended as the first choice for permanent pacing in infants and children.

[Atrial fibrillation--new knowledge yields new therapeutic possibilities]. / Förmaksflimmer--ny kunskap ger nya behandlingsmöjligheter.

Atrial fibrillation (AF) is the most common cardiac arrhythmia prompting treatment. Advances in our knowledge of the pathophysiology of AF provide the basis for new and improved treatment modalities. Thus, focal excitation and localised impulse conduction defects are possible trigger factors which can be counteracted by focal ablation and pacing synchronisation, respectively. Perpetuation of AF, caused by continuous multisite re-entry, is promoted by successive shortening of repolarisation. Internal defibrillation and anatomical limitation of re-entry are treatments that counteract perpetuation of the arrhythmia. Current knowledge of AF and the application of new treatments are discussed by the Lund AF research group.

The patient alert system--pilot study of built-in warning systems for pacemakers.

Malfunction of a pacing system can be life-threatening for a pacemaker-dependent patient. It would be desirable for implantable pulse generators to have a built-in automatic warning system capable of alerting the patient as soon as a potentially dangerous disorder is detected. In this study, seven patients (mean age, 72.6 +/- 10.7 years) with slow, chronic atrial fibrillation underwent implantation of a dual-chamber pulse generator with a custom-made "alert electrode" connected to the atrial port of the pulse generator to stimulate the underlying pectoral muscle. The muscle was temporarily stimulated while the pacemaker was in VVIR mode. The lowest amplitude sufficient to alert the patient (perception threshold) was 1.6 +/- 0.58 V at 0.45 ms during implantation and 1.2 +/- 0.5 V at 0.45 ms chronically. In a second phase, alerts outside of the office were issued using a special software routine capable of delivering stimuli at programmable date and time.

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.

Practical aspects of rate adaptive atrial (AAI,R) pacing: clinical experiences in 44 patients.

Forty-four patients with sinus node disease and chronotropic incompetence but no evidence of AV conduction disturbances were treated with rate adaptive atrial (AAI,R) pacemakers. Medtronic Activitrax and Siemens Sensolog activity sensing single chamber pulse generators were used. Twenty-four patients (55%) had the bradycardia-tachycardia syndrome. The mean follow-up time is 20 +/- 14 months (range 1-48, median 17 months). All patients remain alive. Two patients were reoperated upon for lead problems without change of pacing mode. One patient developed symptomatic second-degree Wenckebach block during follow-up, and received a DDD,R system. Although 22 of the patients were treated with antiarrhythmic drugs postoperatively, no further cases of significant AV conduction disturbances were seen. During rapid atrial pacing, exercise-induced enhancement of AV conduction was a consistent finding, although less pronounced in patients treated with beta-blocking drugs. One patient developed permanent atrial fibrillation with an adequate ventricular rate. By systematic reprogramming procedures, QRS complex sensing through the atrial electrode could be demonstrated in 25 patients (23/28 with unipolar and 2/16 with bipolar leads). It could be counteracted effectively by pulse generator program selection in all cases. Forty-two of 44 patients (95%) remain in AAI,R pacing with normal function. Rate adaptive atrial pacing can be successfully applied in this patient group.

Reversal of lethal citrate intoxication by intravenous infusion of calcium. An experimental study in pigs.

Intravenous infusions of 750 and 1000 ml 2.2% sodium citrate were given over a 60 min period to 17 pigs to study its effect on aortic pressure, electrocardiogram, ionised calcium, and citrate clearance. In group 1 (seven pigs) the animals did not receive calcium and the median survival time was 30 min (range 20-70 min). In groups 2 and 3 (five in each group) the pigs were treated with calcium chloride infusions (1 ml 10% calcium chloride to 10 ml citrate) and they all survived. In group 1 the ionised calcium concentrations in blood fell to values below 0.4 mmol/l, after which the blood pressure dropped abruptly. In the animals treated with calcium the mean ionised calcium concentration fell to 0.6 mmol/l, whereas total calcium increased to more than 7 mmol/l. The aortic pressure was consistently within normal values in the groups treated with calcium, but in the group that was not treated the blood pressure fell dramatically. There was no correlation between electrocardiographic changes and ionised calcium concentrations. In summary, calcium was an effective antidote to lethal citrate intoxication, and the only reliable method of determining the necessary dose of calcium was monitoring of ionised calcium concentrations.

Atrial and ventricular stimulation threshold development: a comparative study in patients with a DDD pacemaker and two identical carbon-tip leads.

The atrial and ventricular pacing threshold development during the first postoperative year was studied in a group of patients receiving DDD pacemakers. Identical carbon-tip endocardial leads were implanted in atrium and ventricle. Atrial and ventricular voltage stimulation thresholds were measured at implantation, and noninvasively at 1 and 12 months thereafter. The atrial amplifier sensitivity required for adequate P wave sensing during follow-up was also determined. The possible influence of a number of factors upon atrial and ventricular threshold evolution was statistically assessed. The threshold data were complete in 57 patients (mean age +/- SD, 65.2 +/- 12.4 years). Thirteen patients had a diagnosis of sinus node disease, whereas 44 had not. Patient age and diagnosis did not significantly influence atrial or ventricular stimulation threshold development. Atrial sensing thresholds were not related to atrial stimulation thresholds during follow-up. Atrial pacing thresholds were higher than ventricular thresholds at pacemaker implantation (P less than 0.00005), but the postoperative threshold rise and thresholds at 1 and 12 months postoperatively did not differ significantly between the atrium and ventricle. The ratio of chronic to acute stimulation thresholds was higher on the ventricular than on the atrial level (0.001 greater than P greater than 0.0005). The chronic atrial threshold showed a logarithmic relation to the threshold at implantation (P = 0.0006); postoperative threshold rise was not a significant determinant of the chronic atrial threshold (P = NS). On the ventricular level, the reverse was seen: The chronic threshold was related to the postoperative threshold rise (P = 0.0015, logarithmic relation), but not to the implantation threshold (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute atrial endocardial P wave amplitude and chronic pacemaker sensitivity requirements: relation to patient age and presence of sinus node disease.

Data are reviewed from 88 patients who received double, passive-fixation unipolar endocardial leads for DDD pacemaker treatment. Identical electrodes were used in the right atrium and the right ventricle. Intra-atrial P wave amplitudes, intraventricular QRS complex amplitudes, and atrial and ventricular pacing thresholds were determined at implantation. The intra-atrial P wave amplitudes were not significantly correlated to the intraventricular QRS complex amplitudes. No significant correlation was found between the atrial stimulation thresholds and the ventricular pacing thresholds. The intra-atrial P wave amplitude showed a significant inverse and logarithmic correlation with patient age (P = 0.007). Furthermore, patients with sinus node disease had significantly lower intra-atrial P wave amplitudes (P = 0.04) than patients without this abnormality. The acute atrial and ventricular pacing thresholds and the intraventricular QRS complex amplitude were not correlated to patient age or presence of sinus node disease. Patients requiring higher atrial amplifier sensitivity settings during follow-up were significantly older (P less than 0.05) than those in whom lower atrial sensitivities were sufficient. A postoperative attenuation of the atrial electrogram was detectable by sensitivity programming procedures in 29 of the patients (35%). This phenomenon did not significantly relate to patient age or presence of sinus node disease. No case of permanent atrial undersensing occurred. It is suggested that the lower intra-atrial P wave amplitudes in older patients and patients with sinus node disease reflect degenerative changes in the atrial myocardium. The statistical relations found appear to motivate special attention to atrial sensing in these patient groups.

Far-field QRS complex sensing via the atrial pacemaker lead. II. Prevalence, clinical significance and possibility of intraoperative prediction in DDD pacing.

To study the prevalence and significance of far-field QRS complex sensing via unipolar atrial electrodes, we attempted to provoke this phenomenon postoperatively in 119 patients with DDD pacemakers. It occurred in 42 patients (35%), with different types of atrial electrodes. In 27 cases with documented far-field QRS complex sensing, selection of an adequate atrial amplifier sensitivity eliminated the problem; in the remaining 15 cases, other program adjustments were necessary. In all patients DDD pacing could be maintained, and no reoperations were required. In a retrospective analysis of a subgroup of 26 patients, all having received endocardial unipolar carbon tip electrodes in the right atrial appendage, the possibility of predicting subsequent far-field QRS complex sensing was studied. The occurrence thereof was not significantly related to patient age or sex, indication for pacing, or routinely obtained electrophysiological measurements. Potential far-field QRS complex sensing via the atrial electrode is significantly common in patients with DDD pacemakers. Patient characteristics and intraoperatively measured intraatrial signal amplitudes are not useful in predicting the postoperative occurrence of the phenomenon. As a rule, it can be handled effectively by pulse generator reprogramming.

Far-field QRS complex sensing via the atrial pacemaker lead. I. Mechanism, consequences, differential diagnosis and countermeasures in AAI and VDD/DDD pacing.

Unintended sensing of QRS complexes via atrial pacemaker leads may cause disorders of pacemaker function in AAI, VDD and DDD pacing. The consequences of this phenomenon depend upon the pacing mode and the timing of the inappropriate sensing as related to the technical characteristics of the pulse generator. With AAI pacemakers, "inappropriate pacemaker bradycardia" may be seen or P-wave undersensing may be simulated. With VDD and DDD systems a special kind of pacemaker mediated tachycardia or apparent P-wave undersensing may result. With knowledge of the underlying mechanisms, differential diagnosis is possible. The countermeasures available are discussed.

Tachycardias initiated by automatic antitachycardia pacemakers.

Available automatic tachycardia-terminating pacemakers cannot distinguish between physiological and pathological tachycardia and, consequently, electrical stimulation during sinus tachycardia can occur. In order to evaluate whether this might be an arrhythmogenic problem or not, the cardiac response in eight patients having paroxysmal supraventricular tachycardia treated with tachycardia-terminating pacemakers was studied during exercise. After tachycardia recognition, the implanted pulse generator automatically emits single or double critically timed premature stimuli for termination of the arrhythmia. Post-implantation examinations revealed successful tachycardia termination by the pacemaker at rest, without the addition of any antiarrhythmic drugs, in all eight patients. During exercise tests, the sinus rate in seven patients exceeded the programmed tachycardia trigger rate resulting in triggered pacemaker stimulation. The native supraventricular tachycardia was initiated in four cases. In one of these patients, two short episodes of probable ventricular tachycardia were also recorded. This study demonstrates the clinical value of post-implantation assessments with exercise tests concerning the problem of pacemaker-initiated tachyarrhythmias. Tachycardia-terminating devices can induce tachycardias, and individual precautions must be taken in order to prevent or minimize the risk of pacemaker reversion of sinus rhythm to paroxysmal tachycardia or hazardous arrhythmias.

Ventricular arrhythmia or supraventricular arrhythmia with aberrant conduction? An electrocardiographic study in halothane-anaesthetized children undergoing adenoidectomy.

The electrocardiograph (ECG) was recorded continuously in 20 children undergoing adenoidectomy during halothane anaesthesia. Five surface ECG leads and an oesophageal lead were used. In 11 children, there were QRS complexes which had a shape distinctly different from that of the ordinary sinus-evoked beats. Except in one child, these anomalous QRS complexes first made their appearance during surgery, although the arrhythmia continued until 0-1 min after adenoidectomy in some children. The severity ranged from that of occasional anomalous QRS complexes with uniform shape to that of a fast irregular rhythm with a variety of QRS shapes. Although the anomalous QRS complexes were premature, P waves and P-P intervals were unchanged. In some children, there appeared to be ventricular capture beats and fusion beats. Because of this, and in view of evidence gathered from studies in animals, by other authors, we considered it likely that the anomalous beats were ventricular in origin.