Ventricular tachycardia produced by hyperosmotic solutions injected into the left main coronary artery in dogs

Abstract

Ao-LAD and Ao-LCX bypass graftings were made in 26 mongrel dogs anesthetized with pentobarbital sodium. Selective injection into the LMC was carried out at a speed of 0.5 ml. per second using a 1.5 ml. quantity of the following fluid: distilled water, 20 per cent hydroxyethyl starch (pH 6.5, 0.1 Osm. per kilogram of water), normal saline (pH 6.4, 0.3 Osm. per kilogram of water), 20 per cent mannitol (pH 6.4, 1.1 Osm. per kilogram of water), 76 per cent Urografin (pH 7.5, 1.4 Osm. per kilogram of water), 10 per cent sodium bicarbonate (pH 9.5, 1.9 Osm. per kilogram of water), 50 per cent glucose (pH 3.3, 3.1 Osm. per kilogram of water), 10 per cent saline (pH 6.3, 3.2 Osm. per kilogram of water) and 30 per cent saline (pH 6.7, 8.5 Osm. per kilogram of water). Injection of 50 per cent glucose produced VT in 27 per cent of the animals, 10 per cent sodium bicarbonate produced VT in 63 per cent, 10 per cent saline produced VT in 100 per cent, respectively. Other fluids did not evoke VT. The ventricular rate of VT at its peak was 176 ± 39.2 beats per minute, and the QRS complexes during paroxysms were, of course, wider than during sinus rhythm but rather narrower than usual (otherwise produced) VT. The VT was elicited under classic total cardiac denervation and under additionally administered propranolol (0.6 mg. per kilogram, intravenously) with atropine (0.15 mg. per kilogram). Also, the induction of A-V block by sectioning the distal part of the His bundle did not effectively block the production of VT. The data obtained from the present experiment suggest the following. (1) Hyperosmolality is the mechanism of the VT. (2) This VT is not reflexly mediated either extrinsically or intrinsically, but it may result from a direct action on the myocardium. (3) Ventricular impulses may originate from just below the bifurcation of the His bundle. (4) The LMC may supply blood to the myocardium by way of its own branches.