Effects of a cardiac glycoside on regional function, blood flow, and electrograms in conscious dogs with myocardial ischemia

Abstract

We studied the effects of coronary occlusion and of subsequent ouabain administration on regional myocardial function, flow, and electrograms in 14 conscious dogs. Coronary occlusion resulted in a graded loss of regional function as reflected by measurements of segment length (SL), velocity of SL shortening and myocardial 'work' from the normal to severely ischemic zones, along with graded flow (radioactive microsphere technique) reductions and graded elevation of the regional S-T segment. Ouabain, 20 μg/kg, improved function in the normal zone, in which stroke shortening rose by 0.23 ± 0.07 mm (mean ± SE) and 'work' rose by 30.2 ± 9.5 mm Hg.mm. In moderately ischemic segments, stroke shortening rose by 0.60 ± 0.05 mm and 'w ork' rose by 58.1 ± 6.1 mm Hg.mm. In the majority of severely ischemic segments, stroke shortening and 'work' also increased; the average effect in all severely ischemic segments was an increase in stroke shortening of 0.35 ± 0.10 mm and in 'work' of 31.5 ± 9.9 mm Hg.mm. In addition, ouabain reduced S-T elevation by 0.90 ± 0.20 mV in moderately ischemic zones and by 3.14 ± 0.35 mV in severely ischemic zones, and increased flow by 28 ± 6% and 46 ± 9% in moderately and severely ischemic zones, respectively. All these changes were significant, P<0.01. Thus, ouabain caused an improvement in perfusion of ischemic tissue, which was associated with significant enhancement of stroke shortening and 'work'. Most strikingly, ouabain returned normal systolic shortening to 10 severely ischemic segments which previously were akinetic.