Primary Hyperparathyroidism and Shorter QTc Intervals

People with primary hyperparathyroidism (PHPT) have shorter QTc intervals but no increased rates of arrhythmia on pre-operative electrocardiogram (EKG) compared with people with thyroid disease (TD), according to a study in the Journal of Clinical Endocrinology and Metabolism.

Researchers retrospectively reviewed the electronic medical records of patients aged ≥40 years who underwent parathyroidectomy for PHPT or thyroidectomy for nontoxic goiter at an urban medical center from January 1, 2013, to August 9, 2018.

A total of 1242 patients were included (PHPT group, n = 619; TD control group, n= 623). The overall cohort had a median age of 60.5 years at surgery (interquartile range [IQR], 53.6-67.9), 80.8% were female, and 64.5% were White.

Preoperatively, a higher proportion of patients in the PHPT group had a history of hyperlipidemia than the control group (48.8% vs 36.2%, respectively, P < .001) and hypertension (50.1% vs 42.2%, respectively, P < .001). The PHPT group also had a significantly higher preoperative median serum calcium level (10.7 [10.4-11.1] vs 9.5 [9.3-9.8] mg/dlL respectively, compared with a normal range of 8.8-10.3 mg/dL; P < .001) and parathyroid hormone level (90 [66-122.2] vs 42 [35.8–50.4] pg/mL, respectively, compared with a normal range of 15- 85 pg/mL; P < .001).

Use of 12-lead EKG found no significant differences in the frequency of normal sinus rhythm, sinus bradycardia, or tachycardia, or atrial fibrillation between the 2 groups. Unadjusted analyses showed that the PHPT group had a lower median heart rate, longer PR interval, and shorter QT (386 [368-406] vs 398 [376-418] ms, respectively, P < .001) and QTc interval (412 [395.8-426.9] vs 426 [410-441.5] ms, respectively, P < .001) vs the control group.

Adjusted models showed that PHPT was not associated with the frequency of left bundle branch block (LBBB), heart rate, PR interval, or uncorrected QT, but QTc was still significantly shorter in the PHPT group than in the control group (414 ms [±24] vs 422 ms [±24], respectively, adjusted P value < .01).

In addition, calcium were levels significantly correlated with QT (r = –0.20, P < .001) and QTc (r = –0.28, P < .001) intervals but not with other EKG factors.

The researchers noted that their findings were limited to retrospective data, and EKGs were performed at various facilities. Furthermore, use of the Bazett correction can overestimate the QT interval at higher heart rates and underestimate it at lower heart rates, and data were lacking for serum calcium levels for a majority of the control group. .

“While the results are reassuring, further studies are needed to investigate the long-term consequences of short QTc in PHPT, specifically, the lifetime risks of developing clinically significant cardiac events and mortality,” the study authors stated.

Reference

Stewart LA, Steinl GK, Huang BL, et al. Primary hyperparathyroidism is associated with shorter QTc intervals, but not arrhythmia. J Clin Endocrinol Metab. Published online November 9, 2021. doi:10.1210/clinem/dgab820