CARDIAC CONDUCTION IN PATIENTS WITH HYPERCALCEMIA DUE TO PRIMARY HYPERPARATHYROIDISM

OBJECTIVE To assess whether hypercalcaemia due to primary hyperparathyroidism is associated with significant cardiac arrhythmias. DESIGN AND PARTICIPANTS The prevalence of cardiac arrhythmias and conduction disturbances was evaluated by 12-lead ECG and 24-hour long-term ECG during presurgical hypercalcaemia and after post-surgical normalization of serum calcium values in 20 patients with primary hyperparathyroidism. RESULTS After surgery, mean +/- SD calcium levels decreased from 2.85 +/- 0.1 to 2.40 +/- 0.1 mmol/l (P < 0.001). There was a significant increase in OT-intervals (0.36 +/- 0.05 vs 0.39 +/- 0.05) and QTc-intervals (0.38 +/- 0.04 vs 0.42 +/- 0.03) after surgery (P < 0.01). Long-term ECG showed no change in the minimal heart rate 47 +/- 8 vs 48 +/- 7 beats/min or in the longest RR interval 1.6 +/- 0.5 vs 1.6 +/- 0.5 s (P NS). There was no difference in the prevalence of supraventricular or ventricular arrhythmias. No episode of high-grade AV-block was observed before surgery. Circadian heart rate rhythm did not change between investigations. CONCLUSIONS It is concluded that moderate hypercalcaemia, in spite of causing a shortening of the repolarization phase (QT-interval), has no clinically significant effect on cardiac conduction.