Differential effects of left anterior descending coronary occlusion on left and right ventricular anterior wall thickening in the conscious pig

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Abstract
Objective: In humans, the left anterior descending coronary artery supplies the left ventricular wall, anterior septum and the paraseptal part of the right ventricular anterior wall. Our aim was to study the effects of acute left anterior descending coronary occlusion on wall thickening in the regions of the left and right ventricular anterior walls supplied by the artery, and in remote, non-ischaemic regions of both ventricles. Methods: Systolic wall thickening (defined as percent thickening with respect to end diastolic wall thickness) was studied in eight conscious pigs every 15 s during 1 min of acute left anterior descending coronary occlusion by a cuff occluder, and every 30 s during 4 min of reperfusion. Pigs were instrumented with ultrasonic microcrystals measuring wall thickness in the anterior walls (left anterior descending artery territory) and lateral walls (left circumflex or right coronary artery territory) of both ventricles, and a left ventricular pressure microtransducer. Results: During control and reperfusion, both anterior walls displayed similar systolic thickening. During coronary occlusion, the left ventricular anterior wall showed paradoxical systolic thinning (dyskinesia) whereas the right ventricular anterior wall showed only hypokinesia. Conclusions: In the presence of equal blood flow deprivation, the right ventricular anterior wall supplied by the left anterior descending coronary artery displays a significantly lesser degree of functional impairment than the left ventricular anterior wall supplied by the same artery. This differential effect may be due to mechanical unloading of the right ventricular anterior wall resulting from left ventricular anterior wall ischaemia. This afterload reduction due to decreased mechanical interaction between the two walls would allow the right ventricular anterior wall to express its contractile reserve in the form of systolic thickening.