Background: Cardiovascular collapses, syncopes, and sudden deaths have been observed following the rapid administration of intravenous vitamin K. Our objectives were to characterize the effects of vitamin K on cardiac action potentials and to evaluate effects of vitamin K on sodium and potassium currents, namely I(Na), I(Kr), and I(Ks).
Methods and results: Guinea pig hearts (n = 21) were paced at a cycle length of 250 msec and exposed to vitamin K at 1.15-4.6 micromol/L (2.5-10 mg/L). Monophasic action potential duration measured at 90% repolarization (MAPD(90)) was not significantly reduced (-1.6 +/- 0.3 msec; P >.05; N.S.) at 1.15 micromol/L, but increased by 6.5 +/- 0.4 msec (P <.05) at 2.3 micromol/L. MAPD(90) was not measurable at 4.6 micromol/L, as a result of inexcitability. Patch-clamp experiments in ventricular myocytes demonstrated a approximately 50% reduction in I(Na) by 10 micromol/L vitamin K and a concentration-dependent reduction of the K(+) current elicited by short depolarizations (250 msec; I(K250)). Estimated IC(50) for I(K250), mostly representing I(Kr), was 2.3 micromol/L. Vitamin K was less potent to block the K(+) current elicited by long depolarizations (5,000 msec; I(K5000)), mostly representing I(Ks), with an estimated IC(50) over 100 micromol/L.
Conclusions: Therapeutic concentrations ( approximately 1.5 micromol/L) of intravenous vitamin K modulate cardiac action potential by blocking ionic currents involved in cardiac depolarization and repolarization.