Myocardial responses to chelation.

The phenomena of displacement and immobilization of calcium ions by chelation is being studied in an increasing number of clinical states. Chelation therapy in hypercalcmmia (Holland et al., 1953; Spencer et al., 1956), calcium deposition in coronary arteries (Meltzer et al., 1960) and peripheral vessels (Clarke et al., 1960) and in skin (Muller et al., 1959), and in the treatment of digitalis toxicity (Cohen et al., 1959) are under scrutiny and therefore careful analysis of the myocardial action of chelating drugs is warranted. In a 28-month study, 125 intravenous infusions of disodium ethylenediaminetetraacetate (disodium edathamil or EDTA) were administered to 58 subjects. Chelation produced four characteristic though occasionally variable responses of ventricular, atrial, and atrio-ventricular (A-V) junctional tissue: (1) suppression of ectopic ventricular beats and ventricular tachycardia, (2) slight slowing of the sino-atrial pacemaker, (3) improvement of A-V nodal conduction in first degree, second degree, and advanced heart block, and (4) increased automaticity of idioventricular pacemakers in complete heart block. Since the slowest effective rate of administration is the safest rate (Spencer et al., 1952), the total quantity of calcium chelated was determined for periods of administration varying from one-half to eleven hours.