Correlation between QT interval and serum level of calcium

Introduction

The first reported association between long QT interval syndrome and structural disease in the heart was demonstrated by James, Froggatt and James in 1964 (Quart J Med 1964, 33:361–385). A high incidence of long QT interval in critically ill patients has been showed previously (Intensive Care Med 1996, 22:S85). Some causes of long QT interval are electrolyte disturbances, antiarrhythmic and non-antiarrhythmic drugs.

The aim of this study is to evaluate the correlation between serum level of calcium and QT interval in intensive care patients.

Patients and methods

We studied 30 patients (18 men and 12 women) aged more than 12 years old (mean = 52.5 years old) admitted to the intensive care unit. All patients were monitored by the Multi-Function Monitoring System 'Dina Scope DS-330' (Fukuda Denshi Company). Serum electrolytes were determined along their treatment in the intensive care unit. Electrocardiogram (ECG) was recorded daily. The QT interval was correct for the heart rate (QTc) using the Bazett formula (Heart 1920, 7:353). The upper limit of QTc was 0.424 s for men and 0.440 s for women.

Results

Nineteen patients (63.33%) had QTc intervals above the normal limit and 11 (36.67%) had normal values. The most frequent electrolyte disturbance was related with calcium level. From 19 patients of the abnormal QTc group, 12 patients (63.16%) had hypocalcaemia (serum level below 8.5 mg/dl). In the normal QTc group (11 patients) only four patients (36.36%) had hypocalcaemia.

Although there was a high incidence of hypocalcaemia in the abnormal QTc group, according to the Chi-Square test it was not statistically significant (Chi-Square of 2.00).

Conclusion

Our results showed that the most frequent electrolyte disturbance associated with long QT interval was hypocalcaemia. However, our data was not statistically significant. In the future studies with larger groups we might find a significant correlation.