A Novel Method for Deriving Pressure-Volume Loops in Stable cfLVAD Patients: Validation and Insights into Myocardial Oxygen Consumption, Energetics and Efficiency

Abstract

Introduction: Assessment of left ventricular (LV) recovery under continuous-flow left ventricular assist device (cfLVAD) support is hampered by concomitant pump support. We describe derivation of non-invasive pressure-volume (PV) loops in cfLVAD patients and demonstrate an application in the assessment of recovery. Methods: Using controller parameters and non-invasive arterial pressure waveforms, central aortic pressure, outflow conduit pressure gradient and instantaneous left ventricular pressure (LVP) were calculated. Instantaneous LV volumes (LVV) were calculated from echocardiographic left ventricular end-diastolic volume (LVEDV) accounting for the integral of pump flow with respect to time and aortic ejection volume derived from the pump speed waveform. PV loops were derived during pump speed adjustment and following bolus intravenous Milrinone to assess changes in loading conditions and contractility respectively. Results: Fourteen patients were studied, generating 77 non-invasive PV loops. Baseline non-invasive LVEDP correlated with invasive PAWP (r2 = 0.57, RMSE 5.0, p = 0.003). Measured non-invasively, Milrinone significantly increased LVEF (40.3 ± 13.6 vs 36.8 ± 14.2%, p < 0.0001), maximum dPdt (623 ± 126 vs 555 ± 122 mmHg/s, p = 0.006), and end-systolic elastance (1.03 ± 0.57 vs 0.89 ± 0.38 mmHg/mL, p = 0.008), consistent with its expected inotropic effect. Milrinone reduced MVO2 (0.15 ± 0.06 vs 0.16 ± 0.07 mL/beat, p = 0.003) and improved myocardial efficiency (43.7 ± 14.0 vs 41.2 ± 15.5%, p = 0.001). Reduced pump speed caused increased LVEDV (190 ± 80 vs 165 ± 71 mmHg, p < 0.0001) and LVEDP (14.3 ± 10.2 vs 9.9 ± 9.3 mmHg, p = 0.024), consistent with a predictable increase in preload. There was increased MVO2 (0.16 ± 0.07 vs 0.14 ± 0.06 mL/beat, p < 0.0001) despite unchanged stroke work (p = 0.24), reflecting decreased myocardial efficiency (39.2 ± 12.7 vs 45.2 ± 17.0%, p = 0.003). Conclusions: Non-invasive PV loops can accurately detect changes in load and contractility, and may help detect LV recovery under cfLVAD support.