The effect of acute alterations in blood sodium on the electrocardiogram

Abstract

Experiments were designed to induce hypernatremia and hyponatremia acutely in the intact dog for the purpose of establishing associated electrocardiographic changes. Blood sodium levels were measured simultaneously and continuously by a stable sodium sensitive glass electrode system. Elevation of blood sodium, averaging 41% above the original level (R.28–56%), resulted in diminution in amplitude of P and QRS, an increase in the QT/RR ratio, and divergence of mean T frontal vector from the mean QRS frontal vector. Additional changes were a slight fall in serum potassium, a fall in pH, and a fall in mean blood pressure. Electrocardiographic changes took place when there had been only a 5% to 15% elevation in blood sodium levels. A dilutional fall in blood sodium, averaging 24% below the original level (R.18–34%), resulted in slowing of the heart rate, a diminution in amplitude of P, and an increase in amplitude of QRS and T. QT/RR ratio changes were variable and usually minor. Additional changes were a slight fall in serum potassium and pH. The electrocardiographic changes also took place with a 5% fall in blood sodium. It should be noted that arrhythmias were exceptional and occurred only in one experiment (hypernatremia) out of the 24 performed. The electrocardiographic changes described were consistent and did not appear to be due to other electrolyte changes or alterations in blood volume. The results can be partially correlated with those obtained from action potential measurements with sodium variation.