Significance of QTc interval in chronic hypoparathyroidism and its correlates.

Context: Hypocalcemia predisposes patients with chronic hypoparathyroidism (cHypoPT) to an increased risk of QTc prolongation and life-threatening arrhythmias. Information on clinical and biochemical correlates of QTc in cHypoPT is limited.
Design and Setting: Observational cohort study at tertiary-care-center.
Subjects and Methods: Eighty-eight non-surgical cHypoPT (mean age 44.1 ± 15.4 years, 45 males) were assessed for QTc interval and its possible correlates including arrhythmic symptoms (palpitation/giddiness/syncope), serum total-calcium, phosphate, 25(OH)D and iPTH.
Results: The mean QTc in HypoPT cohort was 428 ± 34 ms with 13.6% having prolonged QTc. There was a significant inverse correlation between QTc interval and serum total-calcium measured on the same day (r = -0.43, p < 0.001). The mean serum total-calcium was significantly lower in patients with prolonged QTc (7.05 ± 1.94 vs. 8.49 ± 1.01 mg/dL, p = 0.02). 21.6% of cHypoPT patients had arrhythmic symptoms. They had significantly higher mean QTc (p = 0.02) and also tended to have lower mean serum total-calcium during follow-up (p = 0.06). In multivariable regression, female gender, higher current-age, higher BMI, and low serum total-calcium showed significant association with prolonged QTc. For every mg/dL decrease in serum total-calcium, QTc increased by 13 ms. Receiver-operating-characteristic analysis revealed serum total-calcium at cut-off of 8.3 mg/dL discriminated prolonged QTc with area-under-curve being 0.72 [95% CI: 0.51,0.93].
Conclusion: One-fifth of cHypoPT had arrhythmic symptoms and a significant proportion had prolonged QTc. This highlights the need for close monitoring of cHypoPT patients for arrhythmic symptoms and QTc prolongation. The serum total-calcium should be maintained to at least 8.3 mg/dL to minimize the risk of potentially life-threatening arrhythmia in cHypoPT.
(© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)