Preliminary clinical experience with the first dual chamber pacemaker defibrillator.

The lack of specificity of VT detection is a significant shortcoming of current ICDs. In a French multicenter study, 18 patients underwent implantation of the Defender 9001 (ELA Medical), an ICD utilizing dual chamber pacing and arrhythmia detection. Over a mean follow-up period of 7.1 +/- 4.5 months, 176 tachycardia episodes recorded in the device memory were analyzed, and physician diagnosis was compared with that by the device. All 122 VT/VF episodes were correctly diagnosed, as were 51 of 53 supraventricular tachyarrhythmias. Two episodes of AF with rapid regular ventricular rates were treated as VT, and a third episode, treated as VT, could not be diagnosed with certainty. A dual chamber pacemaker defibrillator offers improved diagnostic specificity without loss of sensitivity, in addition to the hemodynamic benefit of dual chamber pacing.

[Environment and permanent cardiac pacing]. / Environnement et stimulation cardiaque définitive.

The increasing technological sophistication of cardiac pacemakers make them potentially more vulnerable to electrical interference. The clinical consequence are of variable importance depending on the type of pacemaker and the nature of the interference. Electrical interference is present in the domestic, industrial and, above all, the medical environment. Apart from controlling the sources of emission, prevention requires standards of protection for the casing and electronic circuitry. Patient education remains primordial.

Clinical results of low energy unipolar or bipolar activated carbon tip leads.

Biocompatibility of carbon makes it a good candidate for a pacing electrode. Moreover, activation of the electrode creates microporosity, which increases the surface area and reduces polarization losses. Chronic thresholds noninvasively measured on a large population of patients implanted with vitreous carbon electrodes of one manufacturer are significantly lower than those caused by polished platinum tip electrodes of the same manufacturer with similar electrode design.

Advantages and disadvantages of various upper and lower rate responses.

The advantages and disadvantages of several types of upper and lower rate responses are presented. The optimal response is dependent upon the programmable parameters and the relationship to natural cardiac cycles. The ideal physiologic pacemaker will provide several different choices for rate response. In addition, it will provide the physician with the means to verify the physiologic effects of the particular response.

How should the software pacemaker be programmed during manufacturing and after implantation?

The different possibilities for programming modern pacemakers are discussed. A pacemaker based on hardware alone provides highly reliable pacing within narrow limits. On the other hand, a totally software-based pacemaker would provide maximum flexibility in terms of programming but would remain more susceptible to errors in software. A middle solution might be one that divides the program between passive ROM and active RAM memories. This alternative may provide sophistication without sacrificing safety.

Detection and characteristics of retrograde P waves.

Clinical evaluation performed on an external prototype of a programmable VDD pacemaker showed a high risk of induction of pacemaker-mediated tachycardia. In these tests tachycardia was observed following magnet removal, premature atrial and ventricular complexes, myopotential oversensing, detection of electrical interference and other events. The high risk and poor predictability of pacemaker-mediated tachycardia suggest that VDD (or DDD) pacemakers should provide automatic means to control this kind of tachycardia without undue loss of the hemodynamic benefits which can be provided by these units.

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.