Electrical and mechanical abnormalities in the heart of a schizophrenic patient with hyponatremia derived from water intoxication.

Electrical and mechanical abnormalities were studied in the heart of a schizophrenic male patient with severe hyponatremia and concomitant low plasma osmolarity induced by excessive water intake (so-called "water intoxication syndrome") by recording electrocardiography and echocardiography. There was a significant positive correlation between the plasma osmolarity and serum sodium concentration. The QRS duration of electrocardiography, an index of the ventricular electrical conduction velocity, tended to be prolonged and the left ventricular ejection fraction calculated by echocardiography decreased in proportion to the reduction of the serum sodium concentration. Lowering extracellular sodium concentration theoretically slows electrical conduction velocity, and was observed in this patient. On the other hand, low external sodium concentration should increase cardiac contractility via suppression of the forward mode operation of the sodium-calcium exchange mechanism, thereby increasing the intracellular free calcium concentration. However, this was not the case in our patient, because ejection fraction was not increased but rather significantly decreased with the lowering of serum sodium concentration. We speculate that in patients with water intoxication, the negative inotropism of the heart caused by low plasma osmolarity prevails over the positive inotropism caused by low serum sodium concentration.