[The retriggerable refractory period: a rare cause of apparent sensing malfunctioning in various types of VVI pacemakers].
The retriggerable Refractory Period (RP) is an anti-interference device that causes prolongation of the RP in the presence of rapid false signals. The device starts functioning when a suprathreshold impulse manifests during the second half of the RP of the pacemaker; in such a case the RP itself is retriggered, i.e., re-starts from the moment in which the retrigger occurs. As a consequence, the time during which the pacer cannot be recycled is prolonged. We report a case of unusual pseudo-malfunction caused by the retriggerable RP observed in a patient paced with a Lit 222 Sorin VVI pacemaker. Spontaneous QRS complexes coupled up to 480 ms appeared as not senses, i.e. did not reset the pacemaker, whereas complexes occurring at 510 ms or more from the spike provoked a normal recycling, and complexes coupled at 490-500 ms resulted in partial recycling. This pattern has been interpreted assuming that a spurious signal (probably an afterpotential) occurs shortly after the paced stimulus. Such a signal falls in the retriggerable RP, resulting in prolongation of the RP. Spontaneous QRS, thus, cannot be sensed until 480 ms from the paced impulse. The chest wall stimulation has clarified the principles governing the functioning of the retriggerable RP. When the RP is retriggered three times in the course of a single pacemaker cycle, the pacer varies its mode of functioning, being the pacing rate increased to a value identical to the magnet rate. Furthermore, the RP is extremely prolonged, occupying the 90% of the pacing interval; only impulses occurring during the last 80 ms, thus, are able to reset the PM.(ABSTRACT TRUNCATED AT 250 WORDS)
D000368:Aged; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D004562:Electrocardiography; D004868:Equipment Failure; D006327:Heart Block / Q000503:physiopathology / Q000628:therapy*; D006339:Heart Rate; D006801:Humans; D008297:Male; D010138:Pacemaker, Artificial
Il periodo refrattario retriggerabile: una rara causa di apparente malfunzionamento del sensing in alcuni tipi di pacemaker VVI.