Primary Hyperparathyroidism is Associated with Shorter QTc Intervals, but not Arrhythmia.

CONTEXT Primary hyperparathyroidism (PHPT) is associated with subclinical cardiovascular disease, but data regarding cardiac conduction abnormalities are limited. OBJECTIVE AND DESIGN Retrospective cross-sectional comparison of cardiac conduction in patients with PHPT or thyroid disease (TD). PARTICIPANTS AND SETTING Patients ≥40 years old who underwent parathyroidectomy or thyroidectomy at a single tertiary institution from 2013-2018. METHODS AND OUTCOMES Demographics and pre-operative electrocardiogram (EKG) parameters were compared using the Mann-Whitney U, Chi Square tests, and linear regression. RESULTS A total of 1,242 patients were included: 49.8% PHPT (n=619) and 50.2% TD (n=623). Median age was 60.5 years (IQR 53.6-67.9). Compared to controls, PHPT patients had higher median serum calcium [10.7 mg/dL (IQR 10.4-11.1) vs 9.5 mg/dL (IQR 9.3-9.8), p<0.001] as expected, as well as, a higher prevalence of hyperlipidemia (49% vs 36%, p<0.001) and hypertension (50.1% vs 42.2%, p<0.01). Based on EKG, there was no difference in PR interval or the prevalence of arrhythmia, atrioventricular block, ST segment/T wave changes, premature ventricular complexes, right bundle branch block or left bundle branch block after adjusting for covariates. The PHPT group had a lower mean corrected QT interval (414ms (+/- 24) vs 422ms (+/- 24), p<0.01), adjusted for covariates. Serum calcium predicted QTc independently of age, sex, and other covariates. CONCLUSIONS In the largest study to date, PHPT patients had shorter QTc intervals compared to TD controls, but no increased prevalence of arrhythmia based on pre-operative EKG.