Isolated T wave alternans elicited by hypocalcemia in dogs.

Isolated T wave alternans (TWA) could be consistently induced in 13 dogs by infusion of an acid dextrose solution (ACD) and in nine with a 2% EDTA disodium solution. To study the factors concerned in evoking TWA, serial determinations of total and ionized serum calcium (ICa), Mg, K, pH, pCO2 and pO2 were performed. Arterial or LV pressures and LV dp/dt as well as a standard electrocardiographic lead were monitored. TWA appeared after the QT interval was significantly prolonged and was associated with a fall in LV pressure and with mechanical alternans. QT alternans could also be detected in 50% of the cases. ICa levels were significantly reduced at the moment of appearance of the TWA. Data obtained support the conclusion that TWA was the result of a reduction in the level of the ICa, probably interfering with the calcium transport mechanisms of the myocardial cell, although the possibility that the alternans may be due to other effects of the two agents employed unrelated to calcium lowering cannot be excluded.