title: "Locked-in" sensitivity in the managed ventricular pacing mode.
abstract: Two cases of "locked-in" sensitivity in the managed ventricular pacing mode are reported. Patient A was a 22-year-old man with a history of hypertrophic obstructive cardiomyopathy and a prophylactic dual-chamber automatic implantable cardioverter-defibrillator who manifested paradoxic T-wave oversensing on the ventricular lead at a sensitivity setting of 1.2 mV but not earlier when the sensitivity had been set to 0.9 mV. Patient B was a 74-year-old patient with ischemic cardiomyopathy and a dual-chamber defibrillator who presented with persistent paradoxic undersensing of the P wave on the atrial lead even at the maximal sensitivity of 0.15 mV, although P-wave sensing was normal earlier when sensitivity was set to 0.3 mV. The phenomenon and the mechanism for its behavior are described.
authors.affiliation: Division of Cardiology, University Health Network, Toronto, Ontario, Canada. krishnakumar.nair@uhn.on.ca
authors.forename: Krishnakumar
authors.initials: K
authors.lastname: Nair
authors.forename: Raja
authors.initials: R
authors.lastname: Selvaraj
authors.forename: Sheila
authors.initials: S
authors.lastname: Watkins
authors.forename: Douglas
authors.initials: D
authors.lastname: Cameron
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial; D009202:Cardiomyopathies / Q000628:therapy; D002312:Cardiomyopathy, Hypertrophic / Q000628:therapy; D017147:Defibrillators, Implantable; D004867:Equipment Design; D004868:Equipment Failure; D006325:Heart Atria / Q000294:innervation* / Q000473:pathology; D006352:Heart Ventricles / Q000294:innervation* / Q000473:pathology; D006801:Humans; D008297:Male; D012032:Refractory Period, Electrophysiological; D018879:Ventricular Premature Complexes / Q000628:therapy*; D055815:Young Adult