PURPOSE: To determine the functional mechanisms by which interatrial shunting may improve right heart mechanics and systemic perfusion in chronic pulmonary hypertension (CPH).
METHODS: Eight dogs underwent 3 months of progressive pulmonary artery banding, following which right atrial (RA) and right ventricular (RV) end-systolic and end-diastolic pressure volume relations (ESPVR, EDPVR) were calculated using conductance catheters. An 8mm shunt prosthesis (with flow probe) was inserted between the superior vena cava and left atrium (LA), yielding a controlled surgical model of atrial septostomy. Data were obtained: 1) pre-shunt (CPH), 2) Low-Flow Shunt, and 3) High-Flow Shunt (occluding superior vena cava, forcing all flow through the shunt).
RESULTS: With progressive shunting, RVP fell from 72±19 mmHg (CPH) to 54±17 (Low-Flow) and 47±17 (High-Flow) (p<.001). Simultaneously, while RAP fell with shunting (8.8±1.5 vs. 5.8±1.8 vs. 3.8±1.3 mmHg, p<.001), LAP rose (8.3±1.5 vs. 10.6±2.6 vs. 10.8±2.5mmHg, p=.003). Cardiac output (CO) increased from 1.5±0.3 L/min at CPH to 1.8±0.4 L/min Low-Flow (286±105 ml/min, 15% of CO) (p<.001), but returned to 1.6±0.3 L/min at High-Flow (466±172 ml/min, 29% of CO) (p=.008 vs. Low-Flow, p=.21 vs. CPH). Oxygen content progressively fell from 16.6±1.9 ml/dl at CPH to 14.8±1.5 Low-Flow and 13.8±2.1 High-Flow (p=.002), resulting in a modest rise in systemic oxygen delivery from 252±46 ml/min at CPH to 276±50 Low-Flow (p=.07), but substantial fall to 222±50 at High-Flow (p=.005 vs. CPH, p<.001 vs. Low-Flow). With progressive shunting, RA contractility did not change (p=.98), but diastolic function improved (decreased diastolic stiffness) as evidenced by a fall in the slope (1.2±0.5 vs. 0.7±0.1 vs. 0.7±0.4 mmHg/ml; p<.04) and intercept (21±4, 11±6, 9±7 ml; p<.008) of the RA EDPVR.
CONCLUSION: Low-Flow shunting consistently improved RA function, systemic perfusion, and oxygen delivery. With High-Flow, LAP no longer increased, CO fell, and oxygen delivery was compromised beyond pre-shunt.
CLINICAL IMPLICATIONS: With better understanding of its distinct physiologic consequences at different shunt fractions, atrial septostomy may become a saver and thus more widely used therapeutic approach in end-stage patients with CPH.
DISCLOSURE: Andreas Zierer, None.