Impact of differential right-to-left shunting on systemic perfusion in pulmonary arterial hypertension.

Abstract

OBJECTIVES: This study aimed at identifying the ideal right-to-left shunt-fraction to improve cardiac output (CO) and systemic perfusion in pulmonary arterial hypertension (PHT). BACKGROUND: Atrial septostomy (AS) has been a high-risk therapeutic option for symptomatic drug-refractory patients with PHT. Results have been unpredictable due to limited knowledge of the optimal shunt-quantity. METHODS: In nine dogs, an 8-mm shunt-prosthesis was inserted between the superior vena cava (SVC) and the left atrium. With pulmonary artery (PA) banding, mean (&#xb1; SEM) systolic right ventricular pressure increased from 37 &#xb1; 1 mm Hg at baseline to 44 &#xb1; 1 mm Hg (moderate PHT, P = 0.005) and 50 &#xb1; 2 mm Hg (severe PHT, P < 0.001). Shunt-flow was adjusted by total (forcing all flow through the shunt) or partial occlusion of the SVC and partial or total clamping of the shunt. Caval-, shunt-, and aortic-flow were measured by ultrasonic flow-probes. Blood gases were drawn from the aortic root and PA. RESULTS: At severe PHT, a shunt-flow of 11 &#xb1; 1% of CO (253 &#xb1; 90 mL/min) increased CO significantly by 25% (1.8 &#xb1; 0.1 to 2.4 &#xb1; 0.2 L/min, P = 0.005) causing an increase of systemic oxygen delivery index (DO2 I) by 23% (309 &#xb1; 23 to 399 &#xb1; 32 mL/min/m(2), P = 0.035). Arterial O2 -saturation did not change significantly until a shunt-flow of 18 &#xb1; 2% was exceeded, causing a drop from 96 &#xb1; 1% to 84 &#xb1; 4% (P = 0.013). At moderate PHT, CO or DO2 I did not improve significantly at any shunt-flow. CONCLUSIONS: In severe PHT, a shunt-flow of 11% of CO represented the ideal shunt-fraction. Augmentation of CO compensated for declined O2 -saturation due to right-to-left shunting and improved DO2 I. In moderate PHT, AS is less promising.