Dynamic assessment of the electrocardiographic QT interval during citrate infusion in healthy Volunteers

• Main Authors: Davis, T.M.E, Balbir, Singh, Choo, KE, Jamal, Ibrahim, Spencer, Janine L., A St, John
• Format: E-Article
• Language: English
• Published: British Medical Association 1995
• Subjects: R Medicine (General)
• Online Access: http://ir.unimas.my/id/eprint/15843/1/Dynamic%20assessment%20of%20the%20electrocardiographic%20%28abstract%29.pdf; http://ir.unimas.my/id/eprint/15843/; https://www.researchgate.net/publication/15573497_Dynamic_assessment_of_the_electrocardiographic_QT_interval_during_citrate_infusion_in_healthy_Volunteers
• Institution: Universiti Malaysia Sarawak

To investigate changes in the electrocardiographic QT interval during rapidly induced, sustained hypocalcaemia in healthy volunteers. 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. 12 healthy teetotallers aged 19- 36 years who were not receiving medication known to influence calcium homoeostasis. 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). 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). 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.