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.

In unselected pacemaker recipients, AAIsafeR reliably prevented V pacing compared with other pacing modes. No adverse effects were reported by any patient. Furthermore, maintaining spontaneous AV conduction protected the patients against ELT episodes.

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.

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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.