QT(C)-MEASUREMENTS - A CASE-CONTROL STUDY ON SERUM ELECTROLYTES .2.

This is a report on a prospective case-control study, in which a group of patients with an electrocardiographic diagnosis of QT(c)-prolongat ion (cases) was compared with a group of patients with a normal QT(c) (controls) for the presence of potential causative factors. Twelve cas es and twelve carefully-matched controls were entered during a 1-year recruitment period. Ventricular arrhythmias were more frequent amongst the cases than amongst the controls (7/12 the cases, only 2/12 contro ls). Blood was sampled around the time of the ECG-recording in all pat ients. Forearm exercise (pumping) to increase venous blood pooling was prohibited before this blood sampling. The serum cation levels (potas sium, calcium, magnesium) were determined in one central laboratory. S erum potassium levels were inversely correlated with the QT(c)-interva l. Such a correlation was not found for the other two cations, althoug h calcium levels also tended to be lower in patients with a long QT(c) . The findings, in addition, suggest that serum potassium values in th e lower normal range (i.e. < 4 meq/l) might predispose to the developm ent of ventricular arrhythmias. In view of these results, the diagnost ic work-up of a patient with a long QT(c) is incomplete without a seru m -K+, and possibly serum -Ca2+, assessment.