title: Upper rate lockout: an unexpected feature of rate adaptive atrioventricular delay.
abstract: We present a case in which use of rate adaptive AV delay resulted in unexpected pacemaker 2:1 AV block when the patient's atrial rate exceeded the pacemaker maximum tracking rate but was below the predicted multiblock rate. "Lockout" of normal upper rate behavior was accompanied with the requirement of a slower atrial rate for reassociation than loss of atrial tracking, a form of upper rate hysteresis. The mechanism of upper rate lockout is discussed, along with potential ways to avoid the problem. The use of software based pacemakers with an extended range of programmable options allows the most flexibility in optimizing pacemaker performance in an individual patient.
authors.affiliation: Clinical Cardiac Electrophysiology Laboratory, Likoff Cardiovascular Institute, Hahnemann University, Philadelphia, Pennsylvania 19102.
authors.forename: S E
authors.initials: SE
authors.lastname: Hessen
authors.forename: R C
authors.initials: RC
authors.lastname: Sheppard
authors.forename: S P
authors.initials: SP
authors.lastname: Kutalek
mesh_terms: D001283:Atrioventricular Node / Q000502:physiology*; D002648:Child; D004867:Equipment Design; D005260:Female; D006801:Humans; D010138:Pacemaker, Artificial