Describes a mechanism for a pseudo-endless loop tachycardia in a DDD pacemaker caused by VPC interference and upper rate limit behavior rather than retrograde conduction.
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Clinicians should consider VPC interference with upper rate behavior in apparent endless loop tachycardia; case reports leave open true incidence.
A 3-beat episode of ventricular arrhythmia was recorded in a patient with an AV universal (DDD) pacemaker. This arrhythmia mimicked "endless loop" tachycardia (ELT) because it appeared following a ventricular premature contraction (VPC), its rate approached the preset upper-rate limit and the regular P waves disappeared during the episode. However, as retrograde conduction was absent ELT could not exist. The mechanism of this arrhythmia was based on a combination of interference by VPC of the regular sequence of QRS complexes produced by P wave and the pacemaker commitment to maintain an upper rate limit by prolongation of the programmed pacemaker AV delay.
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Amikam et al. (1984) studied this question.
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