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Biomedical subjects

P Hurzeler

Publications and source records attributed to P Hurzeler.

10 recordsLinked to original sources
PubMed1986

Transtelephonic monitoring of 25,919 implanted pacemakers.

In order to evaluate the behavior of lithium-powered cardiac pacemakers, a database of 25,919 lithium-powered pacing systems including 23,517 single and 2,402 dual chambered pacemaker generators were followed in 21,750 patients. Of this group, 11,319 were currently active in addition to 7,560 who died, as well as 2,871 patients who terminated their follow-up service prior to the end-of-life of the pacemaker system. A total of 23,517 single chambered pacemakers were followed for 719,173 months of pacing. The mean time to explant for generator malfunctions was 42 months and for all pacing system malfunctions it was 38 months compared to 31.9 months and 28.6 months, respectively, for the 2,402 dual chambered units that were observed for 38,718 months. In the single chambered units, the most frequent reason for explant was battery exhaustion (37% of explants) followed by lead problems (26%) compared to 49% and 12%, respectively, for the dual chambered units. The incidence rates, defined as a transtelephonic test result, required physician decision for action or clarification of the pacing mode or program parameters and showed a high incidence rate immediately post-implant; thereafter, there was a relatively trouble-free period until the 36th month when capture, sensing, and battery problems began to occur at a steady rate reaching 4% at the end of 48 months. Similarly, for dual chambered units, an 8% incidence rate was seen within the first 3 months, followed by a quiescent period until the 28th month when the incidence rate jumped to 16%.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment Design↗
PubMed1977

A comparison of unipolar and bipolar electrograms for cardiac pacemaker sensing.

Simultaneous unipolar and bipolar electrograms were recorded and compared from 49 pacemaker patients with bipolar endocardial electrodes. Average bipolar depolarization signal voltage equalled that of unipolar but showed greater variation. Bipolar and unipolar slew rates were equal in both mean and variance. The proximal pole voltage had little effect on the bipolar result in 8% of the cases, tended to cancel the tip voltage in 49% of the cases and augmented the tip voltage in 43% of the electrograms. The average bipolar R wave duration was 28% less, the T wave amplitude 34% less, and the ST-segment elevation 37% less than the unipolar values. By consistently attenuating the undersirable T waves and ST elevations, while leaving the depolarization signal unaffected, the bipolar electrode offered the advantage of a superior signal-to-noise ratio for sensing depolarization. In one case, however, the bipolar signal was so small as to cause a clinical sensing failure.

Arrhythmias, Cardiac↗
PubMed1977

The ventricular endocardial electrogram and pacemaker sensing.

During cardiac pacemaker implantation and pulse generator replacement, unipolar, right ventricular electrograms were recorded from 133 patients (77 at implantation and 56 at pulse generator replacement) at 200 mm. per second with a band pass of 0.1 to 2,000 Hz on photographic paper. Each signal was analyzed for electrogram structure, peak-to-peak voltage deflection, ST-segment displacement, and maximum voltage deflection/time (slew rate [dv/dt]). The QRS designation of the peripheral electrocardiogram was used for the endocardial electrogram wave forms, which are sufficiently similar to allow QRS terminology to be used. Of the acute electrograms (at implantation) 58 per cent had a small Q followed by an R wave which was 10 per cent or more of the S amplitude; 30 per cent had an R wave less than 10 per cent of the S; all had a straight line segment, within the QRS complex, exhibiting maximum amplitude and slew rate and a large ST-segment elevation. In 12 per cent the Q was followed by an R wave only. The mean voltage was 12.4 mv. +/- 5.5, the slew rate mean 2.9 v. per second +/- 1.5, and the ST displacement 4.0 mv. +/- 2.6. All chronic (over 6 months after implantation) electrograms but one had no ST-segment elevation, and all had an inverted T wave and a straight line segment extending from the highest to the lowest peaks of the QRS complex. The chronic voltage amplitude is 15 per cent lower and the slew rate 41 per cent lower than that of the acute electrogram. The margin of amplitude and slew rate required at implantation to maintain adequate postimplant sensing must accommodate these changes. The possibility of satisfactory pacing threshold associated with poor sensing exists. Knowledge of the amplitude and slew rate allows the determination of the optimal position for electrode placement and the sensitivity required for satisfactory pulse generator selection, design, and operation.

Electrocardiography↗
PubMed1975

Pulse duration variation and electrode size as factors in pacemaker longevity.

For the past 4 years, we have used highly efficient Medtronic electrodes (Nos. 6901 and 6907), with small surface areas, for cardiac pacemakers. We have found that chronic thresholds average 1.6 Ma. at a 1 msec. pulse duration, compared to 4.9 Ma. for the conventional Medtronic No. 5816 electrodes. These electrodes have been used in association with Medtronic Models 5961 and 5931, ventricular-inhibited and asynchronous pulse generators in which output current and voltage are fixed and pulse duration is variable. Drain from the generator battery is directly related to impulse duration and is reduced at shorter durations. The strength-duration curve of cardiac stimulation suggests and actual long-term pacing has been achieved at an average of 0.2 to 0.3 msec., rather than the conventional 1.0 msec. Drain from the battery is one fourth that of pacemakers of 1970 and one half that of present day, conventional units. This fact suggests that a realistic average life of the pulse generator is 4 years or more.

Differential Threshold↗
PubMedDate not supplied

Endocardial electrograms and pacemaker sensing.

Endocardial electrograms in 77 acute cases (at time of pacemaker implant) and 56 chronic cases (at time of pulse generator replacement, with electrodes in service for at least 6 months) were recorded. The peak-to-peak voltage and rate of rise, or slew rate, were compared acutely and chronically. Both parameters must simultaneously exceed given thresholds to trigger the sensing circuits of implantable pacemakers. The average chronic slew rate was half the average acute value. The maximum slew rate and voltage swing occur during the intrinsic deflection as a virtually straight line segment of the electrogram. The findings are consistent with the predictions of a mathematical model for genesis of the electrogram, and also with a model for explaining acute-to-chronic changes in stimulation current thresholds.

Electrocardiography↗