Abstract
Introduction: In advanced HFpEF, acute phosphodiesterase 5 (PDE5) inhibition leads to favorable change in pulmonary vascular resistance (PVR) and to an increased cardiac output (CO) of variable degree. The determinants of the response are poorely understood. Methods: 47 HFrEF patients (85% males, 57±11 years, NYHA 2.9±0.5, 55% non-ischemic, PAmean 42±8 mmHg, 43% RV dysfunction) underwent clinical exam, echocardiography, biochemical tests and right heart catheterization (RHC) before and after I.V. administration of sildenafil (20 mg). Baseline predictors of absolute and relative (%diff) change of PVR and CO were studied. Results: PDE5i led to highly significant (p<0.001) reduction of pulmonary artery (PA) mean pressure (-11±9 mmHg), PVR (-2.2±1.6 WU;-42±24%), PA wedge pressure (-5.2±7.3 mmHg), CVP (-3.2±2.3 mmHg) and to increase in cardiac output (+0.6±0.7 l/min; +18±23%). PVR decreased more than systemic resistance (PVR/SVR -27±30%diff). Predictors of high CO response (COdiff%) were: low BMI, no diabetes, low baseline CO and severity of mitral or tricuspid regurgitation (r=0.53 or =0.43, both p<0.003). The strongest predictor of high PVR%diff was plasma potassium level. HF etiology, renal function, gender, RAAS inhibitor dose, renin or aldosterone levels were unelated to pulmonary vasoreactivity. Patients who dropped PVR<3 WU after PDE5i had higher plasma K+ (4.1±0.5 vs 4.5±0.3 mmol/L, p=0.01) than those who did not, similar relation was found for K+ and PDE5i-induced change of transpulmonary gradient. Conclusions: The largest increase in CO after PDE5i is observed in HFrEF patients with severe mitral (or tricuspid) regurgitation, probably due to chamber unloading and reduction of regurgitant SV. Pulmonary vasodilator response to PDE5i may be influenced by plasma potassium level. High-normal plasma potassium levels may preserve normal pulmonary vasoreactivity in HFrEF, perhaps by influencing K-channels in pulmonary vascular smooth muscle cells.
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