Prognostic role of pulmonary impedance estimation to predict right ventricular dysfunction in pulmonary hypertension

Impact of right ventricular and pulmonary vascular characteristics on Impella hemodynamic support in biventricular heart failure: A simulation study

BACKGROUND

Impella (Abiomed, Danvers, MA, USA) is a percutaneous ventricular assist device commonly used in cardiogenic shock, providing robust hemodynamic support, improving the systemic circulation, and relieving pulmonary congestion. Maintaining adequate left ventricular (LV) filling is essential for optimal hemodynamic support by Impella. This study aimed to investigate the impact of pulmonary vascular resistance (PVR) and right ventricular (RV) function on Impella-supported hemodynamics in severe biventricular failure using cardiovascular simulation.

METHODS

We used Simulink® (Mathworks, Inc., Natick, MA, USA) for the simulation, incorporating pump performance of Impella CP determined using a mock circulatory loop. Both systemic and pulmonary circulation were modeled using a 5-element resistance-capacitance network. The four cardiac chambers were represented by time-varying elastance with unidirectional valves. In the scenario of severe LV dysfunction (LV end-systolic elastance set at a low level of 0.4 mmHg/mL), we compared the changes in right (RAP) and left atrial pressures (LAP), total systemic flow, and pressure-volume loop relationship at varying degrees of RV function, PVR, and Impella flow rate.

RESULTS

The simulation results showed that under low PVR conditions, an increase in Impella flow rate slightly reduced RAP and LAP and increased total systemic flow, regardless of RV function. Under moderate RV dysfunction and high PVR conditions, an increase in Impella flow rate elevated RAP and excessively reduced LAP to induce LV suction, which limited the increase in total systemic flow.

CONCLUSIONS

PVR is the primary determinant of stable and effective Impella hemodynamic support in patients with severe biventricular failure.

The Right Ventricular-Arterial Compliance Index: A Novel Hemodynamic Marker to Predict Right Heart Failure Following Left Ventricular Assist Device

The development of right heart failure (RHF) in patients with advanced heart failure following left ventricular assist device (LVAD) implantation remains difficult to predict. We proposed a novel composite hemodynamic index-the right ventricular-arterial compliance index (RVACi), derived from pulmonary artery pulse pressure (PAPP), ejection time (ET), heart rate (HR), and cardiac output (CO), with and expressed as mm Hg·s/L. We then conducted a retrospective, single-center analysis comparing the predictive value of RVACi for the development of RHF or unplanned right ventricular (RV) mechanical circulatory support following LVAD implantation against existing hemodynamic indices. One hundred patients were enrolled after screening 232 patients over a 10 year period, with 74 patients having complete hemodynamic data for RVACi calculation. There was good correlation between pulmonary arterial capacitance ( R ² = 0.48) and pulmonary vascular resistance ( R ² = 0.63) with RVACi, but not RV stroke work index or pulmonary artery pulsatility index. Reduced baseline RVACi (52 ± 23 vs . 92 ± 55 mm Hg·s/L; p = 0.02) was the strongest hemodynamic predictor of unplanned RV mechanical circulatory support requirement in patients following LVAD insertion. Composite pulsatile hemodynamic indices including RVACi may provide additional insight over existing hemodynamic indices for the prediction of RHF and need for RV mechanical circulatory support.

Dissecting contributions of pulmonary arterial remodeling to right ventricular afterload in pulmonary hypertension

Pulmonary hypertension (PH) is defined as an elevation in the right ventricle (RV) afterload, characterized by increased hemodynamic pressure in the main pulmonary artery (PA). Elevations in RV afterload increase RV wall stress, resulting in RV remodeling and potentially RV failure. From a biomechanical standpoint, the primary drivers for RV afterload elevations include increases in pulmonary vascular resistance (PVR) in the distal vasculature and decreases in vessel compliance in the proximal PA. However, the individual contributions of the various vascular remodeling events toward the progression of PA pressure elevations and altered vascular hemodynamics remain elusive. In this study, we used a subject-specific one-dimensional (1D) fluid-structure interaction (FSI) model to investigate the alteration of pulmonary hemodynamics in PH and to quantify the contributions of vascular stiffening and increased resistance towards increased main pulmonary artery (MPA) pressure. We used a combination of subject-specific hemodynamic measurements, ex-vivo mechanical testing of arterial tissue specimens, and ex-vivo X-ray micro-tomography imaging to develop the 1D-FSI model and dissect the contribution of PA remodeling events towards alterations in the MPA pressure waveform. Both the amplitude and pulsatility of the MPA pressure waveform were analyzed. Our results indicated that increased distal resistance has the greatest effect on the increase in maximum MPA pressure, while increased stiffness caused significant elevations in the characteristic impedance. The method presented in this study will serve as an essential step toward understanding the complex interplay between PA remodeling events that leads to the most severe adverse effect on RV dysfunction.

Relationship of TAPSE Normalized by Right Ventricular Area With Pulmonary Compliance, Exercise Capacity, and Clinical Outcomes

BACKGROUND

While tricuspid annular plane systolic excursion (TAPSE) captures the predominant longitudinal motion of the right ventricle (RV), it does not account for ventricular morphology and radial motion changes in various forms of pulmonary hypertension. This study aims to account for both longitudinal and radial motions by dividing TAPSE by RV area and to assess its clinical significance.

METHODS

We performed a retrospective analysis of 71 subjects with New York Heart Association class II to III dyspnea who underwent echocardiogram and invasive cardiopulmonary exercise testing (which defined 4 hemodynamic groups: control, isolated postcapillary pulmonary hypertension, combined postcapillary pulmonary hypertension, and pulmonary arterial hypertension). On the echocardiogram, TAPSE was divided by RV area in diastole (TAPSE/RVA-D) and systole (TAPSE/RVA-S). Analyses included correlations (Pearson and linear regression), receiver operating characteristic, and survival curves.

RESULTS

On linear regression analysis, TAPSE/RVA metrics (versus TAPSE) had a stronger correlation with pulmonary artery compliance (r=0.48-0.54 versus 0.38) and peak VO2 percentage predicted (0.23-0.30 versus 0.18). Based on the receiver operating characteristic analysis, pulmonary artery compliance ≥3 mL/mm Hg was identified by TAPSE/RVA-D with an under the curve (AUC) of 0.79 (optimal cutoff ≥1.1) and by TAPSE/RVA-S with an AUC of 0.83 (optimal cutoff ≥1.5), but by TAPSE with only an AUC of 0.67. Similarly, to identify peak VO2 <50% predicted, AUC of 0.66 for TAPSE/RVA-D and AUC of 0.65 for TAPSE/RVA-S. Death or cardiovascular hospitalization at 12 months was associated with TAPSE/RVA-D ≥1.1 (HR, 0.38 [95% CI, 0.11-0.56]) and TAPSE/RVA-S ≥1.5 (HR, 0.44 [95% CI, 0.16-0.78]), while TAPSE was not associated with adverse outcomes (HR, 0.99 [95% CI, 0.53-1.94]). Among 31 subjects with available cardiac magnetic resonance imaging, RV ejection fraction was better correlated with novel metrics (TAPSE/RVA-D r=0.378 and TAPSE/RVA-S r=0.328) than TAPSE (r=0.082).

CONCLUSIONS

In a broad cohort with suspected pulmonary hypertension, TAPSE divided by RV area was superior to TAPSE alone in correlations with pulmonary compliance and exercise capacity. As a prognostic marker of right heart function, TAPSE/RVA-D <1.1 and TAPSE/RVA-S <1.5 predicted adverse cardiovascular outcomes.

The impact of ECPELLA on haemodynamics and global oxygen delivery: a comprehensive simulation of biventricular failure

BACKGROUND

ECPELLA, a combination of veno-arterial (VA) extracorporeal membrane oxygenation (ECMO) and Impella, a percutaneous left ventricular (LV) assist device, has emerged as a novel therapeutic option in patients with severe cardiogenic shock (CS). Since multiple cardiovascular and pump factors influence the haemodynamic effects of ECPELLA, optimising ECPELLA management remains challenging. In this study, we conducted a comprehensive simulation study of ECPELLA haemodynamics. We also simulated global oxygen delivery (DO2) under ECPELLA in severe CS and acute respiratory failure as a first step to incorporate global DO2 into our developed cardiovascular simulation.

METHODS AND RESULTS

Both the systemic and pulmonary circulations were modelled using a 5-element resistance‒capacitance network. The four ventricles were represented by time-varying elastances with unidirectional valves. In the scenarios of severe LV dysfunction, biventricular dysfunction with normal pulmonary vascular resistance (PVR, 0.8 Wood units), and biventricular dysfunction with high PVR (6.0 Wood units), we compared the changes in haemodynamics, pressure-volume relationship (PV loop), and global DO2 under different VA-ECMO flows and Impella support levels.

RESULTS

In the simulation, ECPELLA improved total systemic flow with a minimising biventricular pressure-volume loop, indicating biventricular unloading in normal PVR conditions. Meanwhile, increased Impella support level in high PVR conditions rendered the LV-PV loop smaller and induced LV suction in ECPELLA support conditions. The general trend of global DO2 was followed by the changes in total systemic flow. The addition of veno-venous ECMO (VV-ECMO) augmented the global DO2 increment under ECPELLA total support conditions.

CONCLUSIONS

The optimal ECPELLA support increased total systemic flow and achieved both biventricular unloading. The VV-ECMO effectively improves global DO2 in total ECPELLA support conditions.

Prognostic role of pulmonary impedance estimation to predict right ventricular dysfunction in pulmonary hypertension

BACKGROUND

The effect of pulmonary hypertension (PH) on right ventricular (RV) afterload is commonly defined by elevation of pulmonary artery (PA) pressure or pulmonary vascular resistance (PVR). In humans however, one-third to half of the hydraulic power in the PA is contained in pulsatile components of flow. Pulmonary impedance (Zc) expresses opposition of the PA to pulsatile blood flow. We evaluate pulmonary Zc relationships according to PH classification using a cardiac magnetic resonance (CMR)/right heart catheterization (RHC) method.

METHODS

Prospective study of 70 clinically indicated patients referred for same-day CMR and RHC [60 ± 16 years; 77% females, 16 mPAP <25 mmHg (PVR <240 dynes.s.cm-5 /mPCWP <15 mmHg), 24 pre-capillary (PrecPH), 15 isolated post-capillary (IpcPH), 15 combined pre-capillary/post-capillary (CpcPH)]. CMR provided assessment of PA flow, and RHC, central PA pressure. Pulmonary Zc was expressed as the relationship of PA pressure to flow in the frequency domain (dynes.s.cm-5 ).

RESULTS

Baseline demographic characteristics were well matched. There was a significant difference in mPAP (P < 0.001), PVR (P = 0.001), and pulmonary Zc between mPAP<25 mmHg patients and those with PH (mPAP <25 mmHg: 47 ± 19 dynes.s.cm-5 ; PrecPH 86 ± 20 dynes.s.cm-5 ; IpcPH 66 ± 30 dynes.s.cm-5 ; CpcPH 86 ± 39 dynes.s.cm-5 ; P = 0.05). For all patients with PH, elevated mPAP was found to be associated with raised PVR (P < 0.001) but not with pulmonary Zc (P = 0.87), except for those with PrecPH (P < 0.001). Elevated pulmonary Zc was associated with reduced RVSWI, RVEF, and CO (all P < 0.05), whereas PVR and mPAP were not.

CONCLUSIONS

Raised pulmonary Zc was independent of elevated mPAP in patients with PH and more strongly predictive of maladaptive RV remodelling than PVR and mPAP. Use of this straightforward method to determine pulmonary Zc may help to better characterize pulsatile components of RV afterload in patients with PH than mPAP or PVR alone.