Patients With Primary Hyperparathyroidism Have Shorter QT/QTc Intervals

Abstract Background: Previous studies suggest that patients with primary hyperparathyroidism (PHPT) have subclinical cardiovascular disease, but data regarding cardiac conduction abnormalities are limited. The aim of this study was to assess cardiac conduction abnormalities in patients with PHPT compared to controls with thyroid disease (TD). Method: We conducted a retrospective analysis of patients over 40 years of age who underwent parathyroidectomy or thyroidectomy at a single tertiary institution between 2013 and 2018. Demographics and EKG parameters from pre-operative EKG reports were compared using the Mann-Whitney U and Chi Square tests. Regression was used to compare EKG differences between the PHPT and control groups adjusted for sex, age, and other variables found to be significant on univariate analysis. Results: A total of 1181 patients were analyzed, 51% in the PHPT group (n=602) and 49% in the TD group (n=579). The median age was 60.5 years (IQR 53.5–67.9) and there was no difference in sex between the cohorts. PHPT patients had a higher prevalence of hyperlipidemia (HLD, 49% vs 36%, p<0.001) and hypertension (HTN, 50.7% vs 42.1%, p<0.01), but had no differences in EKG rhythm patterns or prevalence of arrhythmia compared to TD patients. As expected, mean serum calcium levels were higher for the PHPT group, 10.74 (0.66) vs 9.53 (0.44). However, the PHPT group included both normocalcemic and hypercalcemic patients. The PHPT group had a lower median QT interval compared to the TD group, 386ms (IQR 368–406) vs 398ms (IQR 376–418), p<0.001 and a higher median PR value, 158ms (IQR 144–174.5) vs 156ms (IQR 143.5–171), p<0.05. More PHPT patients (n=21, 3.5%) had a short QTc interval (<360ms males/<370ms females), compared to TD controls (n=1, 0.2%). Among PHPT patients with a short QT interval, the proportion of patients with hypercalcemia (95%) was higher than that of the PHPT group overall (75%). On multivariable analysis, PHPT patients had a shorter QT interval than TD controls after controlling for sex, age, HLD, HTN. There was no difference between PHPT and TD when serum calcium was included in the model, suggesting that calcium mediates the relationship between QT interval and disease status. Conclusion: PHPT patients have shorter QT/QTc intervals compared to TD controls, but no increased prevalence of arrythmia at baseline. While the QT interval was associated with degree of serum calcium elevation, these findings in a large cohort suggest that PHPT is not associated with arrythmia at baseline among those undergoing parathyroidectomy.