Cytoplasmic calcium regulation and the electrocardiogram in patients with primary hyperparathyroidism

Primary hyperparathyroidism (HPT) is a disease caused by an abnormal cytosolic regulation of calcium concentration [Ca++]i leading to an increased secretion of parathyroid hormone and thereby increased levels of extracellular calcium. It is well known that the QT-interval measured at electrocardiography (ECG) is shortened in HPT subjects. Whether this is due to an abnormal intracellular handling of calcium also in the heart or to the raised extracellular calcium levels is not known. In order to study the extent to which the deranged extra- and intracellular levels of calcium in HPT patients were related to ECG characteristics, [Ca++]i was determined in vitro by microfluorometry in surgery-removed parathyroid cells at extracellular calcium concentrations of 0.5 mM and 30.0 mM and ECG was recorded preoperatively in 42 HPT patients and in 15 subjects operated on for atoxic goitre. Serum calcium and plasma-ionized calcium also were measured preoperatively. The QT-interval and ST-segment duration were both shortened in the HPT patients compared to controls (P < 0.001). [Ca++]i at 3.0 mM extracellular calcium divided by that at 0.5 mM was correlated to the QT-interval, when measured at the onset of the T-wave (QoT, r = 0.39, P < 0.03) and early diastolic phase (end of T-wave to onset of p-wave, r = -0.34, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)