Patient-initiated autonomous pacemaker tachycardia.

Multiparameter programmable DDD pacemakers are said to have an uncountable number of possible parameter combinations. It is probable that a number of these combinations, particularly when triggered by one or more critically timed native events, will result in bizarre and unanticipated rhythms sustained entirely within the timing circuit of the pulse generator. We report the occurrence and analysis of one such rhythm termed a sustained autonomous pacemaker tachycardia. In this rhythm, both atrial and ventricular outputs occur at the maximum tracking rate of the pacemaker with an apparently shortened AV interval. Once initiated, the ability to sustain the tachycardia requires that the maximum tracking rate interval exceed the atrial escape interval. It will then continue until the pulse generator is programmed to parameters that alter this critical timing or a properly timed ventricular sensed event occurs. It is anticipated that this will be only one of many similar rhythms encountered in patients treated with complex devices from all the manufacturers. In the future, once such a rhythm is noted and its mechanism identified, modifications of the basic circuit design will allow these parameters to be used without danger to the patient and without having to limit the options of the device.