title: IKr and IKs remodeling differentially affects QT interval prolongation and dynamic adaptation to heart rate acceleration in bradycardic rabbits.
abstract: Bradycardic ventricular electrical remodeling predisposes to lethal tachyarrhythmias. We investigated the early temporal sequence and reversibility of electrical remodeling in a rabbit complete heart block model subjected to bradycardic ventricular pacing for either 2 or 8 days, with a third group of animals undergoing 8 days of bradycardic pacing followed by 8 days of physiological-rate pacing. At specified time points after complete heart block induction and pacing initiation, steady-state QT interval measurements and variability as well as dynamic QT interval adaptation to abrupt heart rate acceleration were assessed in the absence and presence of isoproterenol. Rapidly (I(Kr)) and slowly (I(Ks)) activating delayed rectifier repolarizing K(+) tail current densities were evaluated using whole cell patch clamp in isolated right ventricular myocytes. Steady-state QT interval prolongation at both 2 and 8 days was associated with moderate I(Kr) reduction. I(Ks) downregulation was apparent by day 2 but more profound at day 8. Dynamic QT interval adaptation was impaired under baseline conditions at day 8 but only during isoproterenol administration at day 2. Both in vivo and cellular manifestations of remodeling reverted toward control values after 8 days of physiological-rate pacing. In conclusion, in this bradycardic model, I(Ks) downregulation 1) proceeds more gradually but more extensively than that of I(Kr) and 2) is most prominently associated with impaired dynamic QT interval adaptation to heart rate acceleration. Isoproterenol blunts the dynamic QT interval response in animals with partially downregulated I(Ks), consistent with stress-related phenomena in known I(Ks)-impaired states. Relative early sparing of I(Ks) could explain the delay in the onset of lethal tachyarrhythmia predisposition in bradycardic electrical remodeling. Reversibility of remodeling supports the potential utility of preventive pacing intervention soon after bradycardia onset.
authors.affiliation: Physiology and Experimental Medicine Program, Hospital for Sick Children Research Institute, University of Toronto, Toronto, Canada.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Suto
authors.forename: Wei
authors.initials: W
authors.lastname: Zhu
authors.forename: Alice
authors.initials: A
authors.lastname: Chan
authors.forename: Gil J
authors.initials: GJ
authors.lastname: Gross
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001919:Bradycardia / Q000188:drug therapy / Q000503:physiopathology*; D015536:Down-Regulation / Q000502:physiology; D006327:Heart Block / Q000188:drug therapy / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D008133:Long QT Syndrome / Q000503:physiopathology*; D008297:Male; D010138:Pacemaker, Artificial; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D011817:Rabbits; D016171:Torsades de Pointes / Q000503:physiopathology; D020257:Ventricular Remodeling / Q000502:physiology
chemical_list: D000318:Adrenergic beta-Agonists; D015221:Potassium Channels; D007545:Isoproterenol; D011188:Potassium