Hans Schüller

Automatic Adjustment of Pacemaker Stimulation Output Correlated with Continuously Monitored Capture Thresholds: A Multicenter Study

Pacing threshold is affected by many factors. A pacing system able to confirm capture at each beat and automatically adjust its output close to the actual pacing threshold is highly desirable. This study evaluates the safety and efficacy of the Autocapture function of the Pacesetter Microny SR+. One hundred thirteen patients were recruited from 16 centers in 7 European countries and followed up for 1 year. All pacemakers were implanted with Pacesetters low polarization, bipolar leads. The key feature of Autocapture is the immediate delivery of a 4.5 V safety backup pulse 62.5 ms after any ineffective ongoing low output pulse. Holter recordings confirmed total reliability of this feature without any exit block. The measured evoked response (ER) signal was stable over time. Acute and chronic pacing thresholds measured by VARIO and Autocapture tests correlated (r > 0.79) over the period of the study. The incidence of backup pulses was 1.1% during pacing. With Autocapture programmed ON, the overall total current consumption was 4.1 μA for VVI and 5.0 μA for VVIR pacing. Tbis study proved that the Autocapture safely and reliably regulates the pacemakers output according to the prevailing threshold thus providing maximum patient safety and prolonging service life.

Lessons from the first patient with an implanted pacemaker : 1958-2001

On October 8, 1958 the world’s first pacemaker implantation was performed at the Karolinska Hospital in Stockholm, Sweden. The system had been developed by the surgeon A ◦ ke Senning and the physician inventor Rune Elmqvist. The patient was a 43-year-old engineer suffering from Stokes-Adams syndrome. His name was Arne H.W. Larsson (Fig. 1). At the time Senning was in charge of the experimental laboratory at the newly inaugurated Department of Thoracic Surgery at the Karolinska Hospital in Stockholm. Elmqvist was head of the Electromedical Division at Elema Schonander in Stockholm. He had studied medicine in Lund, Sweden but had not pursued a medical practice. Rather, he had become a self-taught engineer. In 1931 he had designed the first portable optical electrocardiographic (ECG) recorder and in 1948 had introduced the well-known direct writing Mingograf ink jet recorders. When Senning and Elmqvist met in 1950 they began a close cooperation in the development and testing of fibrillators and defibrillators for use in conjunction with open heart surgery, then an experimental procedure. Senning had studied and been inspired by the experimental work of Bigelow and Callaghan1,2 in stimulation for hypothermic cardiac standstill and Zoll who used external chest wall stimulation for management of Stokes-Adams attacks.3,4 During a visit to Minneapolis in 1957, Senning observed C. Walton Lillehei during open heart surgery suture stainless steel electrodes to the ventricle to manage surgically caused atrioventricular (AV) block, after closure of a ventricular septal defect. The wires were led through the thoracic wall and connected to an external pulse generator. This method avoided the discomfort and placement problems in the postoperative patient associated with Zoll’s external pacemaker. Senning considered this to be the beginning of the era of clinical pacing.5,6 On returning to Stockholm, Senning studied Lillehei’s technique experimentally and clini-

Isochromosomes i(8q) or i(9q) in three adenocarcinomas of the lung

We have cytogenetically analyzed three primary adenocarcinomas of the lung. All tumors had chromosome numbers in the triploid region. The multiple structural aberrations included rearrangements of 3p, in two cases affecting the segment 3p14-23, where deletions are characteristically found in small cell lung carcinomas. Isochromosomes for 8q were present in two tumors and i(9q) in one tumor. In the few previously reported cytogenetic analyses of pulmonary adenocarcinomas, all of which examined metastases or cell lines, i(8q) was found in one case and i(9q) in two cases. These isochromosomes, therefore, represent previously unrecognized nonrandom changes in adenocarcinomas of the lung, and might constitute primary aberrations in this tumor type.

Low-energy epicardial pacing in children: the benefit of autocapture

BACKGROUND Permanent cardiac pacing in children results commonly in augmented energy consumption because of the high pacing rates and the ample stimulation safety margin applied in children. Cardiovascular anatomy and limited venous access sometimes preclude the otherwise preferred endocardial approach. In this multicenter patient series, we studied the feasibility, safety, and energy saving obtained by a combination of steroid-eluting epicardial leads with autocapture devices capable of ongoing adjustment of the stimulation output to the prevailing threshold. METHODS Autocapture devices (Pacesetter Microny SR+/- and Regency SR+/-; Pacesetter, Solna, Sweden) and steroid-eluting epicardial pacing leads (Medtronic CapSure Epi 10366; Medtronic, Inc, Minneapolis, MN) were implanted in 14 children. Thresholds, telemetry data, evoked response, and polarization signals were obtained at discharge and follow-up, and battery service life was calculated. RESULTS During a median follow-up of 6.5 months, autocapture pacing was applied in 12 of 14 children. The automatically adjusted pulse amplitude of autocapture devices demonstrated low-energy pacing with no significant changes between discharge and 6 months follow-up (1.1 +/- 0.3 versus 0.9 +/- 0.3 V). Autocapture-programmed pacemakers had calculated life spans of 7.8 +/- 1.4 years (Microny) and 21.0 +/- 1.6 years (Regency). No adverse effects were noted. CONCLUSIONS Autocapture-controlled pacing with bipolar epicardial pacing leads is feasible and safe in children. Autocapture programming results in substantial energy savings and extends battery life markedly.

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.

Threshold Tracking Pacing Based on Beat by Beat Evoked Response Detection: Clinical Benefits and Potential Problems

Continuous monitoring of pacemaker stimulation thresholds and automatic adjustment of pacemaker outputs were among the longstanding goals of the pacing community. The first clinically successful implementation of threshold tracking pacing was the Autocapture feature which has accomplished automatic ventricular capture verification for every single stimulus by monitoring the Evoked Response (ER) signal resulting from myocardial depolarization. The Autocapture feature not only decreases energy consumption by keeping the stimulation output slightly above the actual threshold, but also increases patient safety by access to high-output back-up pulses if there is loss of capture. Furthermore, it provides valuable documentation of stimulation thresholds over time and serves as a valuable research tool. Current limitations for its widespread use include the requirements for implantation of bipolar low polarization leads and unipolar pacing in the ventricle. Fusion/pseudofusion beats with resultant insufficient or even non-existent ER signal amplitudes followed by unnecessary delivery of back-up pulses and a possible increase in pacemaker output is not an uncommon observation unique to the Autocapture feature. The recent incorporation of the Autocapture algorithm in dual chamber pacemakers has been challenging because of more frequent occurrence of fusion/pseudofusion beats in the presence of normal AV conduction. Along with a review of the previously published studies and our clinical experience, this article discusses the clinical advantages and potential problems of Autocapture.

Combipolar sensing in dual chamber pacing: is there still a need for bipolar leads in the atrium?

LINDE, C., et al.: Combipolar Sensing in Dual Chamber Pacing: Is There Still a Need for Bipolar Leads in the Atrium? Bipolar leads have been shown to provide superior sensing conditions compared to unipolar leads as bipolar sensing is less susceptible to interference. However, the mechanical long‐term integrity and longevity of bipolar leads is inferior to that of unipolar leads. A prospective randomized, multicenter study was performed to investigate a new atrial detection configuration called combipolar sensing. This new sensing concept is designed for the use of conventional unipolar leads in the atrium and the ventricle. While the atrial stimulation is unipolar, atrial sensing is accomplished in a bipolar way using the ventricular lead tip as the indifferent electrode. A modified dual chamber pacemaker provided with this sensing concept was implanted in 26 patients. At predischarge and at the 1‐ and 3‐month follow‐ups no significant differences in atrial sensing thresholds and P wave amplitudes were found between the unipolar and the combipolar sensing configuration at rest or during provocation. Myopotential inhibition could be demonstrated in 22 patients during unipolar sensing at sensitivity settings as “low” as 2 mV. In contrast, during combipolar sensing it could only be demonstrated in one patient once and only at the highest atrial sensitivity of 0.5 mV. Combipolar atrial sensing is feasible under normal conditions and during provocation. Myopotential interference is negligible. Thus, combipolar sensing offers comparable atrial sensing to bipolar without the disadvantages of a bipolar lead.

A Software Sensor Using Neural Networks for Detection of Patient Workload

The morphology of intracardiac electrograms (IEGMs) was used for pacemaker patient workload estimation. The body posture also was studied as another characteristic. The IEGMs were obtained and recorded via temporary transcutaneous leads connected to the implanted pacemaker. IEGMs were recorded during exercise and at rest. Recordings at rest were performed in different body positions. The morphology was analyzed visually in order to observe changes due to workload and posture. The recordings were digitized and processed by a computer‐simulated neural network. The network was used as an automatic IEGM classifier based on the morphology. Our results show that the morphology of the IEGM may be used as an indicator of patient workload and body posture. The necessary information is found mainly in the ST segment. We conclude that neural networks seem to be useful in an active cardiac device.