Effect of pressure-controlled intermittent coronary sinus occlusion on pacing-induced myocardial ischemia in domestic swine.

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Abstract
This study tested the hypothesis that pressure-controlled intermittent coronary sinus occlusion (PICSO) would be useful in ameliorating myocardial ischemia under conditions characterized by preserved, but reduced (relative to demand), myocardial blood flow. Studies were conducted in closed-chest, sedated domestic swine prepared with an artificial stenosis that reduced luminal diameter of the animal's left anterior descending coronary artery by 80%. Measurements of hemodynamics, regional myocardial blood flow, and oxygen, lactate, and nucleoside metabolism were obtained in 10 animals (1) before placement of stenosis, (2) 30 min after insertion of stenosis, (3) after 30 and 60 min of PICSO, and (4) 30 min after discontinuation of PICSO. Two groups of control animals were studied to observe the natural history of metabolic markers of ischemia. Control group I consisted of four animals studied concurrently and subjected to the same protocol except for the fact that PICSO was not applied. Control group II consisted of eight additional animals studied as a group. A specially designed balloon-tipped catheter positioned in the proximal portion of the animal's great cardiac vein was used to provide PICSO. Heart rate was controlled by atrial pacing (rate, 145 beats/min) through the study. After placement of the stenosis, flow in endocardial and transmural layers distal to the stenosis declined significantly (p less than .01) vs control. Application of PICSO failed to increase arterial inflow distal to the stenosis in any myocardial layer. Myocardial aerobic metabolism was adversely affected by stenosis and changed from consumption of lactate, inosine, and hypoxanthine before stenosis to production at 30 min after stenosis. Although PICSO was associated with reduced production and a return toward consumption of lactate, inosine, and hypoxanthine, a similar pattern of changes in lactate, inosine, and hypoxanthine metabolism was observed in control animals over a comparable period of time. In addition, regional myocardial oxygen extraction and consumption were not changed vs poststenosis levels by PICSO. However, in comparison with controls, PICSO did accelerate the rate of resolution of myocardial ischemia as assessed by lactate metabolism. At 30 min of PICSO (or sham) the change vs poststenosis was +33.6 +/- 25.0 mumol/min/100 g in the PICSO but only +6.7 +/- 29.7 in the control group (p = .05). We conclude, therefore, that even though PICSO did not alter the final level of myocardial ischemia under conditions modeled in this study it did accelerate its rate of resolution, an effect that may be beneficial clinically.

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