Different responses of left ventricular systolic function to changes in right ventricular volume and shortening--comparison between aorto-femoral vein and aorto-left atrium shunts in dog hearts.

It has been reported that left ventricular end-systolic volume decreases during arteriovenous shunt and increases during subclavian artery-left atrium shunt at a constant end-systolic pressure. The mechanism of the opposing changes in end-systolic volume during the two types of shunt is not clear. One possible cause is that left ventricular pump function with enhanced right ventricular ejection differs from that without enhancement. To investigate this hypothesis, we studied the two types of shunt (Aorto-femoral vein shunt, AoFV; aorto-left atrium shunt, AoLA) with matched reduction of systemic vascular resistance in open-chest dogs with beta-blockade. Both right and left ventricular volumes and shortenings were assessed from short-axis views by two-dimensional (2D)-echocardiogram. Left ventricular end-systolic short-axis area decreased from 76 +/- 3 to 62 +/- 3% in AoFV shunt (p less than 0.05), but tended to increase in AoLA shunt (76 +/- 4 in control state vs 81 +/- 5% in AoLA, NS) in spite of a similar reduction in left ventricular end-systolic pressure. There was no difference in left ventricular shortening, but significant differences were observed in right ventricular shortening (50 +/- 8 in AoFV vs 24 +/- 7% in AoLA, p less than 0.05) and right ventricular short-axis area at end-diastole (142 +/- 6 in AoFV vs 96 +/- 3% in AoLA, p less than 0.01), and at end-systole (92 +/- 8 in AoFV vs 73 +/- 7% in AoLA, p less than 0.05) between the two types of shunt. We conclude that the different changes in left ventricular end-systolic short-axis area found in the two shunts are not caused by the different left ventricular shortenings, but by the different right ventricular mechanical actions. These findings suggest that left ventricular pumping action in the high output state changes, depending on whether it is accompanied by augmented ejection of the right ventricle or not.