Significance of QTc Interval in Chronic Hypoparathyroidism and its Correlates

Abstract

Abstract 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. Objective To assess the significance of QTc interval in chronic hypoparathyroidism and its correlates. Methods This was an observational cohort study at a tertiary care center. Eighty-eight nonsurgical patients with 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 intact parathyroid hormone. Results The mean QTc in the 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 < .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 = .02). Of patients with cHypoPT 21.6% had arrhythmic symptoms. They had significantly higher mean QTc (P = .02) and also tended to have lower mean serum total calcium during follow-up (P = .06). In multivariable regression, female gender, higher current age, higher body mass index, 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 the curve being 0.72 (95% CI 0.51, 0.93). Conclusion One-fifth of patients with cHypoPT had arrhythmic symptoms and a significant proportion had prolonged QTc. This highlights the need for close monitoring of patients with cHypoPT 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.