title: Dynamic assessment of the electrocardiographic QT interval during citrate infusion in healthy volunteers.
abstract: OBJECTIVE
  To investigate changes in the electrocardiographic QT interval during rapidly induced, sustained hypocalcaemia in healthy volunteers.
  
  
  METHODS
  Serial rate corrected QT measurements were made during and after a variable rate trisodium citrate infusion designed to "clamp" the whole blood ionised calcium concentration 0.20 mmol/l below baseline for 120 min.
  
  
  METHODS
  12 healthy teetotallers aged 19- 36 years who were not receiving medication known to influence calcium homoeostasis.
  
  
  METHODS
  Whole blood ionised calcium concentration and QaTc intervals (onset of the Q wave to T wave apex divided by the square root of the RR interval).
  
  
  RESULTS
  Mean (SD) ionised calcium concentration decreased from 1.18 (0.03) mmol/l preinfusion to values close to target (0.98 mmol/l) between 10 and 120 min. The QaTc interval lengthened from a baseline of 0.309 (0.021) to a maximum 0.343 (0.024) s0.5 at 10 min before returning to a stable level from 15 to 120 min (0.334 (0.023) and 0.330 (0.023) s0.5 respectively). The change from baseline of both variables expressed as a ratio (delta QaTc/ delta [Ca2+]) was greater during rapid induction of hypocalcaemia (at 5 and 10 min) than at other times during and after the infusion (P < 0.02).
  
  
  CONCLUSIONS
  The disproportionate prolongation of QaTc interval during prompt induction of hypocalcaemia suggests rate dependency which can be represented by a hysteresis relation between (ionised calcium, QaTc) coordinates. This finding may have clinical implications.
authors.affiliation: University of Western Australia, Department of Medicine, Fremantle Hospital.
authors.forename: T M
authors.initials: TM
authors.lastname: Davis
authors.forename: B
authors.initials: B
authors.lastname: Singh
authors.forename: K E
authors.initials: KE
authors.lastname: Choo
authors.forename: J
authors.initials: J
authors.lastname: Ibrahim
authors.forename: J L
authors.initials: JL
authors.lastname: Spencer
authors.forename: A
authors.initials: A
authors.lastname: St John
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000494:pharmacology*; D002951:Citrates / Q000494:pharmacology*; D019343:Citric Acid; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000187:drug effects; D006801:Humans; D006996:Hypocalcemia / Q000503:physiopathology*; D008297:Male
chemical_list: D000925:Anticoagulants; D002951:Citrates; D019343:Citric Acid