Aims Heart failure with preserved ejection fraction (HFpEF) is characterized by complex pathophysiology including an im-paired diastolic reserve. We recently showed that milrinone favourably modifies filling pressures at rest and during exertion in HFpEF patients; however, the responsible mechanism is uncertain. The objective of this study was to develop a clearer understanding of the acutely modifiable physiologic parameters that may be targeted in HFpEF.
Methods and results We conducted computer modelling simulations based on invasive haemodynamic assessments, by right heart catheterization, in HFpEF patients at baseline and in response to milrinone. Our aim was to develop a detailed understanding of the physiologic mechanisms, which accounted for the observed actions. The resultant circulatory model of HFpEF encompassed the left ventricular (LV) end-systolic and end-diastolic pressure–volume relations, together with stressed blood volume, heart rate, and arterial mechanics. To support the modelled action of milrinone, we conducted complementary LV conductance catheter and echocardiography studies in sheep to evaluate LV end-systolic and enddiastolic pressure–volume relations. In HFpEF patients, the acute haemodynamic effects of intravenous milrinone (n = 10) administration com-pared with placebo ( n = 10) included significant reductions in right atrial pressure (7 ± 1 to 3 ± 1 mmHg, P < 0.001) and pulmonary capillary wedge pressure (13 ± 1 to 8 ± 1 mmHg, P < 0.001), while cardiac index increased (2.77 ± 0.19 to 3.15 ± 0.14 L/min/m2, P < 0.05), and mean arterial pressure remained unchanged (95 ± 2 to 93 ± 3 mmHg, P = ns). Computer simulations showed that these haemodynamic effects were explained by a concomitant 31% reduction in stressed blood volume together with 44% increase in LV end-systolic elastance (LV Ees). Individually, changes in these parameters were not sufficient to explain the haemodynamic effects of milrinone. In vivo studies conducted in sheep (n = 5) showed that milrinone reduced LV filling pressure (8.0 ± 0.8 to 2.7 ± 0.6 mmHg, P < 0.01 ) and increased LV Ees(0.96 ± 0.07 to 2.07 ± 0.49,P < 0.05), while no significant effect on LV stiffness was observed (0.038 ± 0.003 to 0.034 ± 0.008, P = not significant).
Conclusions These data demonstrate that stressed blood volume in HFpEF represents a relevant physiologic target in HFpEF; however, concomitant modulation of other cardiovascular parameters including LV contractility may be required to achieve desirable haemodynamic effects .