title: Relative refractoriness of left ventricular contraction underlies human tachycardia-induced mechanical and electrical alternans.
abstract: BACKGROUND
  Mechanical alternans (MA) and electrical alternans (EA) are predictors of cardiac events. Experimental studies have suggested that refractoriness of calcium cycling underlies these cardiac alternans. However, refractoriness of left ventricular contraction has not been examined in patients with cardiac alternans.
  
  
  METHODS
  In 51 patients with miscellaneous heart diseases, incremental right atrial pacing was performed to induce MA and EA. MA was quantified by alternans amplitude (AA: the difference between left ventricular dP/dt of a strong beat and that of a weak beat), and AA at 100/min (AA100) and maximal AA (AAmax) were measured. EA was defined as alternation of T wave morphology in 12-lead electrocardiogram. Relative refractoriness of left ventricular contraction was examined by drawing the mechanical restitution curve under a basal coupling interval (BCL) of 600 ms (100/min) and was assessed by the slope at BCL (Δmechanical restitution). Postextrasystolic potentiation (PESP) was also examined and the slope of PESP curve (ΔPESP) was assessed as a property to alternate strong and weak beats.
  
  
  RESULTS
  MA and EA were induced in 19 patients and in none at 100/min or less, and at any heart rate in 32 and in 10, respectively. AA100 and AAmax correlated positively with Δmechanical restitution and negatively with ΔPESP. Patients with EA had a significantly larger Δmechanical restitution and a significantly larger absolute value of ΔPESP than those without.
  
  
  CONCLUSIONS
  In patients with MA and EA, the left ventricular contractile force during tachycardia is under relative refractoriness and prone to cause large fluctuation of contractile force.
authors.affiliation: Department of Cardiovascular Biology and Medicine, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kashimura
authors.forename: Makoto
authors.initials: M
authors.lastname: Kodama
authors.forename: Tohru
authors.initials: T
authors.lastname: Watanabe
authors.forename: Komei
authors.initials: K
authors.lastname: Tanaka
authors.forename: Yuka
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Yukako
authors.initials: Y
authors.lastname: Ohno
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Obata
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ito
authors.forename: Satoru
authors.initials: S
authors.lastname: Hirono
authors.forename: Haruo
authors.initials: H
authors.lastname: Hanawa
authors.forename: Tohru
authors.initials: T
authors.lastname: Minamino
mesh_terms: D002304:Cardiac Pacing, Artificial / Q000379:methods*; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction; D017180:Tachycardia, Ventricular / Q000150:complications / Q000503:physiopathology*; D018487:Ventricular Dysfunction, Left / Q000209:etiology / Q000503:physiopathology*
keywords: T wave alternans; postextrasystolic potentiation; pulsus alternans