Spontaneous heart activity in pacemaker treated patients with high-grade atrioventricular block. A Holter monitor study

Utility of ambulatory electrocardiography in detecting pacemaker dysfunction in the early postimplantation period

The value of ambulatory electrocardiography (AECG) in detecting pacemaker dysfunction before hospital discharge was assessed in 100 patients a mean of 1.2 days after pacemaker implantation. The incidence of permanent pacemaker dysfunction detected by AECG in the early postimplantation period, the frequency that pacemaker dysfunction detected by AECG was not detected by telemetric monitoring and the frequency that results of AECG led to pacemaker reprogramming before hospital discharge were determined. AECG detected at least 1 type of pacemaker dysfunction in 35% of patients and routine telemetry identified the abnormality in only 8% (p less than 0.001). Pacemaker dysfunction occurred in 42% of patients with dual-chamber devices and 27% of those with single-chamber devices (difference not significant). In the 35 patients who had pacemaker malfunction, a total of 50 instances of pacemaker dysfunction were detected. Failure of atrial capture occurred in 2% of patients, failure of atrial sensing in 9%, failure of atrial output in 1%, failure of ventricular capture in 8%, failure of ventricular sensing in 14%, failure of ventricular output due to myopotential inhibition in 11% and pacemaker-mediated tachycardia in 5%. The results of the AECG led to a clinical intervention in 22 patients (pacemaker reprogramming in 21 patients and lead repositioning in 1 patient) in whom no pacemaker dysfunction was suspected on the basis of telemetry or clinical symptoms. In conclusion, AECG provides additional benefit beyond that of routine telemetry monitoring in identifying pacemaker dysfunction in the early period after implantation.

Characteristics of advanced porous and textured surface pacemaker electrodes

Reduced stimulation thresholds, improved sensing and better attachment have been claimed for totally porous and porous surfaced electrodes. In this study, the potential for clinical use of two new types of porous electrodes and a non-porous, textured high microsurface area electrode, has been evaluated by comparison with equivalent sized, smooth non-porous controls. Eighteen sintered and seven laser drilled porous electrodes, seven-non-porous textured electrodes, and sixteen controls, were implanted singly in the right ventricles of sheep. Measurements of threshold, pacing, sensing and bulk impedances were taken at regular intervals for up 180 days. At sacrifice, only three of the thirteen non-porous controls were attached. All laser porous electrodes, apart from two which were dislodged, were attached, as were eleven of fifteen sintered porous, and five of seven textured non-porous electrodes. Tissue ingrowth was found for both porous electrode types. Stimulation thresholds were not statistically different for all electrode types (p less than 0.05). Pacing and bulk impedances of the two porous and surface textured electrodes were significantly higher (p less than 0.10, p less than 0.05, respectively) than those of controls. The three new electrodes exhibited similar chronic sensing impedance values, 30% less than equivalent non-porous electrodes. The similar sensing performance of the porous and high microsurface area non-porous electrodes indicates that the nature of the external surface, rather than internal porosity, determines sensing impedance. All three new electrode types showed improved attachment and sensing compared with similar smooth electrodes. The laser porous electrode, which permits fixation by tissue ingrowth and maintains simplicity of construction, is promising for routine clinical use.

Electrode-heart interface: definition of the ideal electrode

In dual-chamber pacing in order to maintain the advantages of small pulse generator size and volume, and increased longevity, it becomes necessary to reduce pulse generator output. This may be accomplished by optimizing the electrode-heart interface. New electrode designs may reduce polarization losses; perhaps even newer materials should be considered. The results of accumulated data must be applicable to long-term pacing.

Pulse width dependent increase in the pacemaker automatic interval

From a total of 51 patients equipped with rate and pulse width adjustable pulse generators (Microlith-P 0505, Microthin-PI 0522) implanted over the last 3 years, 10 (19.6%) showed an unexpected drop in pacemaker pulse rate during pulse width programming. For one of the pulse generators used (Microthin-PI 0522), unexpected rate decrease occurred in 7/13 cases (53.8%). For all except one patient, decrease in pacemaker pulse rate corresponded with the total refractory period of the pulse generator ( 320 ms), at a certain pulse width when rate drop first occurred. In seven of the patients the pulse generator automatic interval was extended from 13 ms to 171 ms beyond the refractory period. In two patients it was necessary to replace the pulse generators. Our study strongly proves that this abnormal pacemaker functioning is a result of sensing of the polarization voltage at the pacemaker electrode/tissue interface and/or the T-wave. The polarization voltage is highly dependent on the total pacemaker electrode/tissue interface impedance. Using typical values for pulse generator output and input resistance and output capacitance, Faraday resistance, Helmholtz capacitance and tissue resistance at the electrode/tissue interface it was shown mathematically that in some cases the polarization voltage alone would be of sufficient amplitude and slew rate for pacemaker inhibition. The study demonstrates an urgent need for change in the filter characteristics by making the pulse generators less sensitive in the low frequency region and reducing the polarization voltage by reducing the output circuit capacitance.