Mechanical support of the pressure overloaded right ventricle: an acute feasibility study comparing low and high flow support

Acute right ventricular failure: pathophysiology, aetiology, assessment, and management

Acute right ventricular failure is a complex and rapidly progressive clinical syndrome, whereby the right ventricle fails to provide adequate left ventricular preload, dilates, and causes systemic venous congestion. Previous research in acute heart failure has primarily focused on the left ventricle. Yet, the need for a better understanding of right ventricular anatomy, physiology, and pathophysiology, as well as of the diagnosis and management of its acute failure is crucial. Diagnosis mandates a high degree of clinical suspicion, as the majority of signs and symptoms are nonspecific. An accurate and prompt identification of the underlying causes, including pulmonary embolism, right ventricular myocardial infarction, acute respiratory distress syndrome, post-cardiac surgery, and decompensated chronic pulmonary hypertension, is therefore essential. This review provides insights into right ventricular anatomy and functioning and discusses the pathophysiology of acute right ventricular failure, its differential aetiologies, clinical presentation, diagnosis, and treatment.

PLACE: Multicenter Study for Right Ventricular Failure on Mechanical Cardiocirculatory Supports

Isolated acute right ventricular failure (aRVF) is associated with poor prognosis in different scenarios. In severe conditions, temporary mechanical cardiocirculatory support (tMCS) is required. PLACE is an international, retrospective, multicenter registry including 17 centers that investigated patients affected by isolated aRVF and treated with various types of tMCS from January 2000 to December 2020. The registry included 644 (69.6% males, mean age: 55 years) patients. The most frequent etiologies were post-left ventricular assist device implantation (LVAD) and postcardiotomy shock. These patients received mostly mechanical circulatory support (MCS) and veno-arterial extracorporeal membrane oxygenation. Mean tMCS duration was 9 days, weaning was achieved in 70.5% of the patients, and the major cause of death on support was multiorgan failure (50.5%). The mortality rate was 45 and 48.4% in-hospital and at 3 month follow-up, respectively. Multivariable logistic regression analysis identified age, aRVF due to acute pulmonary hypertension, bilirubin level, and oliguria or anuria at tMCS implantation as risk factors for in-hospital mortality. Conversely, aRVF after LVAD was found to be associated with a lower risk of early mortality. In-hospital and 3 months mortality occurred in less than half of the aRVF-supported subjects. Furthermore, several preimplant aspects such as age, organ function, and type of tMCS are independently associated with in-hospital and 3 month mortality.

Intraventricular pressure and volume during conventional and automated head-up CPR

BACKGROUND

Active compression-decompression (ACD) CPR, an impedance threshold device (ITD) and automated head and thorax elevation, collectively termed AHUP-CPR, increases cerebral and coronary perfusion pressures, brain blood flow, end-tidal CO2 (ETCO2) and cerebral oximetry (rSO2) in animal models compared with conventional (C) CPR. We tested the hypothesis that cardiac stroke volume (SV) is higher with AHUP-CPR versus C-CPR or ACD + ITD in a porcine cardiac arrest model.

METHODS

Farm pigs (n = 14) were sedated, anesthetized, and ventilated. Hemodynamics, including biventricular pressure-volume loops, were continuously measured. Following 10 min of untreated ventricular fibrillation, C-CPR was performed for 2 min, then ACD + ITD for 2 min in the flat position, and then AHUP-CPR thereafter. Linear mixed-effects model and Pearson correlation comparisons were used for statistical analysis.

RESULTS

Coronary and cerebral perfusion pressures, ETCO2, rSO2, and right (RV) and left (LV) ventricular SV increased progressively and significantly with the implementation of AHUP-CPR (p < 0.05). RV SV with C-CPR was 24.8 ± 2.8 mL (∼48% of baseline) versus 45.2 ± 4.1 with AHUP-CPR (∼90% of baseline) (p < 0.01). LV SV with C-CPR was 17.6 ± 1.8 mL (∼35% of baseline) versus 38.7 ± 6.7 with AHUP-CPR (∼80% of baseline) (p < 0.01).

CONCLUSION

A fundamental and inherent shortcoming of C-CPR, limited cardiac stroke volume, and resultant forward flow, can be overcome with AHUP-CPR. These findings may help explain the better outcomes associated with early use of AHUP-CPR.

The Etiology and Management of Critical Acute Right Heart Failure

Right ventricular failure contributes to the morbidity and mortality of acute myocardial function, massive pulmonary embolism, and chronic pulmonary hypertension. Understanding how the normal physiology of the right ventricle (RV) is disrupted is integral to managing patients who present with RV decompensation. Therapeutic advances in mechanical circulatory support, pharmacotherapies to reduce afterload, mechanical and chemical lytic therapies for acute pulmonary embolism have improved outcomes of patients by offloading the RV. In this report we provide an overview of the physiology of the RV, medical management (volume optimization, hemodynamic targets, rhythm management), along with critical care-specific topics (induction with mechanical ventilation, sedation strategies, and mechanical circulatory support) and provide a framework for managing patients who present with leveraging principles of preload, contractility, and afterload. Last, because of the complexity of right ventricular failure management, and the complexity of presentation, we also discuss the role of team-based approach (cardiogenic shock and pulmonary embolism response teams), and highlight its benefits at improving outcomes.

Contemporary treatment of right ventricular failure

Right ventricular failure (RVF) is a clinical syndrome resulting from structural and functional changes in the right ventricle (RV), leading to inadequate blood flow to the pulmonary circulation and elevated systemic venous pressures. Factors modulating RV function include afterload, preload, contractility, and interventricular dependency. The pathophysiology of RVF involves complex interactions, such as maladaptive hypertrophy, metabolic reprogramming, inflammation, fibrosis, apoptosis, and endothelial dysfunction. Therapeutic strategies are limited for RVF, as basic and clinical research has historically focused mainly on the left ventricle. Novel pharmacological interventions targeting metabolism, calcium homeostasis, oxidative stress, extracellular matrix remodeling, endothelial function, and inflammation are needed to address RVF effectively. This review explores the etiology, mechanisms, and pathophysiology of RVF, drugs directly targeting the RV myocardium, the intricate biological processes between RV and pulmonary vascular remodeling, surgical and device therapies, and future perspectives on managing RVF.

Right Ventricular Pressure Waveform Analysis-Clinical Relevance and Future Directions

Continuous measurement of pressure in the right atrium and pulmonary artery has commonly been used to monitor right ventricular function in critically ill and surgical patients. This approach is largely based upon the assumption that right atrial and pulmonary arterial pressures provide accurate surrogates for diastolic filling and peak right ventricular pressures, respectively. However, due to both technical and physiologic factors, this assumption is not always true. Accordingly, recent studies have begun to emphasize the potential clinical value of also measuring right ventricular pressure at the bedside. This has highlighted both past and emerging research demonstrating the utility of analyzing not only the amplitude of right ventricular pressure but also the shape of the pressure waveform. This brief review summarizes data demonstrating that combining conventional measurements of right ventricular pressure with variables derived from waveform shape allows for more comprehensive and ideally continuous bedside assessment of right ventricular function, particularly when combined with stroke volume measurement or 3D echocardiography, and discusses the potential use of right ventricular pressure analysis in computational models for evaluating cardiac function.

Computational models of ventricular mechanics and adaptation in response to right-ventricular pressure overload

Pulmonary arterial hypertension (PAH) is associated with substantial remodeling of the right ventricle (RV), which may at first be compensatory but at a later stage becomes detrimental to RV function and patient survival. Unlike the left ventricle (LV), the RV remains understudied, and with its thin-walled crescent shape, it is often modeled simply as an appendage of the LV. Furthermore, PAH diagnosis is challenging because it often leaves the LV and systemic circulation largely unaffected. Several treatment strategies such as atrial septostomy, right ventricular assist devices (RVADs) or RV resynchronization therapy have been shown to improve RV function and the quality of life in patients with PAH. However, evidence of their long-term efficacy is limited and lung transplantation is still the most effective and curative treatment option. As such, the clinical need for improved diagnosis and treatment of PAH drives a strong need for increased understanding of drivers and mechanisms of RV growth and remodeling (G&R), and more generally for targeted research into RV mechanics pathology. Computational models stand out as a valuable supplement to experimental research, offering detailed analysis of the drivers and consequences of G&R, as well as a virtual test bench for exploring and refining hypotheses of growth mechanisms. In this review we summarize the current efforts towards understanding RV G&R processes using computational approaches such as reduced-order models, three dimensional (3D) finite element (FE) models, and G&R models. In addition to an overview of the relevant literature of RV computational models, we discuss how the models have contributed to increased scientific understanding and to potential clinical treatment of PAH patients.

Mechanical Circulatory Support in Right Ventricular Failure

Right ventricular dysfunction presents unique challenges in patients with cardiopulmonary disease. When optimal medical therapy fails, mechanical circulatory support is considered. Devices can by classified according to whether they are deployed percutaneously or surgically, whether the pump is axial or centrifugal, whether the right ventricle is bypassed directly or indirectly, and whether the support is short term or long term. Each device has advantages and disadvantages. Acute mechanical circulatory support is a suitable temporizing strategy in advanced heart failure. Future research in right ventricular mechanical circulatory support will optimize device management, refine patient selection, and ultimately improve clinical outcomes.

Intensive care management of right ventricular failure and pulmonary hypertension crises

Pulmonary hypertension (PH), an often unrelenting disease that carries with it significant morbidity and mortality, affects not only the pulmonary vasculature but, in turn, the right ventricle as well. The survival of patients with PH is closely related to the right ventricular function. Therefore, having an understanding of how to manage right ventricular failure (RVF) and acute pulmonary hypertensive crises is imperative for clinicians who encounter these patients. This review addresses the management of these patients in detail, addressing: (a) the pathophysiology of RVF, (b) intensive care monitoring of these patients in the intensive care unit, (c) imaging of the right ventricle, (d) intubation and mechanical ventilation, (e) inotrope and vasopressor selection, (f) pulmonary vasodilator use, (g) interventional and surgical procedures for the acutely failing right ventricle, and (h) mechanical support for RVF.

First in vivo assessment of RAS-Q technology as lung support device for pulmonary hypertension

Objectives:

To assess the in vivo hemodynamic effects on the pressure overloaded right ventricle of RAS-Q^® technology, the world’s first gas exchanger with a fully integrated compliance.

Methods:

In six acute in vivo trials RAS-Q was implanted in sheep between the pulmonary artery and left atrium. Right ventricular pressure overload was induced by pulmonary artery banding. Pressures and flows were recorded in baseline, moderate and severe pulmonary hypertension conditions. In one trial, RAS-Q was benchmarked against the pediatric Quadrox-i^®.

Results:

With 1.00 and 1.17 L/min, RAS-Q delivered 31% and 39% of the total cardiac output in moderate and severe pulmonary hypertension, respectively. Pulmonary artery pressures and mean pulmonary artery pressure/mean arterial blood pressure ratio successfully decreased, implying a successful right ventricular unloading. Cardiac output was restored to normal levels in both pulmonary hypertension conditions. With both devices in parallel, RAS-Q provided three times higher flow rates and a 10 times higher pressure relief, compared to the pediatric Quadrox-i.

Conclusion:

A gas exchanger with a fully integrated compliance better unloads the right ventricle compared to a non-compliant gas exchanger and it can restore cardiac output to normal levels in cases of severe pulmonary hypertension.

Delineating the molecular and histological events that govern right ventricular recovery using a novel mouse model of pulmonary artery de-banding

AIMS

The temporal sequence of events underlying functional right ventricular (RV) recovery after improvement of pulmonary hypertension-associated pressure overload is unknown. We sought to establish a novel mouse model of gradual RV recovery from pressure overload and use it to delineate RV reverse-remodelling events.

METHODS AND RESULTS

Surgical pulmonary artery banding (PAB) around a 26-G needle induced RV dysfunction with increased RV pressures, reduced exercise capacity and caused liver congestion, hypertrophic, fibrotic, and vascular myocardial remodelling within 5 weeks of chronic RV pressure overload in mice. Gradual reduction of the afterload burden through PA band absorption (de-PAB)-after RV dysfunction and structural remodelling were established-initiated recovery of RV function (cardiac output and exercise capacity) along with rapid normalization in RV hypertrophy (RV/left ventricular + S and cardiomyocyte area) and RV pressures (right ventricular systolic pressure). RV fibrotic (collagen, elastic fibres, and vimentin+ fibroblasts) and vascular (capillary density) remodelling were equally reversible; however, reversal occurred at a later timepoint after de-PAB, when RV function was already completely restored. Microarray gene expression (ClariomS, Thermo Fisher Scientific, Waltham, MA, USA) along with gene ontology analyses in RV tissues revealed growth factors, immune modulators, and apoptosis mediators as major cellular components underlying functional RV recovery.

CONCLUSION

We established a novel gradual de-PAB mouse model and used it to demonstrate that established pulmonary hypertension-associated RV dysfunction is fully reversible. Mechanistically, we link functional RV improvement to hypertrophic normalization that precedes fibrotic and vascular reverse-remodelling events.

Establishment of adult right ventricle failure in ovine using a graded, animal-specific pulmonary artery constriction model

BACKGROUND

Right ventricle failure (RVF) is associated with serious cardiac and pulmonary diseases that contribute significantly to the morbidity and mortality of patients. Currently, the mechanisms of RVF are not fully understood and it is partly due to the lack of large animal models in adult RVF. In this study, we aim to establish a model of RVF in adult ovine and examine the structure and function relations in the RV.

METHODS

RV pressure overload was induced in adult male sheep by revised pulmonary artery constriction (PAC). Briefly, an adjustable hydraulic occluder was placed around the main pulmonary artery trunk. Then, repeated saline injection was performed at weeks 0, 1, and 4, where the amount of saline was determined in an animal-specific manner. Healthy, age-matched male sheep were used as additional controls. Echocardiography was performed bi-weekly and on week 11 post-PAC, hemodynamic and biological measurements were obtained.

RESULTS

This PAC methodology resulted in a marked increase in RV systolic pressure and decreases in stroke volume and tricuspid annular plane systolic excursion, indicating signs of RVF. Significant increases in RV chamber size, wall thickness, and Fulton's index were observed. Cardiomyocyte hypertrophy and collagen accumulation (particularly type III collagen) were evident, and these structural changes were correlated with RV dysfunction.

CONCLUSION

In summary, the animal-specific, repeated PAC provided a robust approach to induce adult RVF, and this ovine model will offer a useful tool to study the progression and treatment of adult RVF that is translatable to human diseases.

The right treatment for the right ventricle

PURPOSE OF REVIEW

Right ventricular (RV) function is an important determinant of morbidity and mortality in patients with pulmonary arterial hypertension (PAH). Although substantial progress has been made in understanding the development of RV failure in the last decennia, this has not yet resulted in the development of RV selective therapies. In this review, we will discuss the current status on the treatment of RV failure and potential novel therapeutic strategies that are currently being investigated in clinical trials.

RECENT FINDINGS

Increased afterload results in elevated wall tension. Consequences of increased wall tension include autonomic disbalance, metabolic shift and inflammation, negatively affecting RV contractility. Compromised RV systolic function and low cardiac output activate renin-angiotensin aldosterone system, which leads to fluid retention and further increase in RV wall tension. This vicious circle can be interrupted by directly targeting the determinants of RV wall tension; preload and afterload by PAH-medications and diuretics, but is also possibly by restoring neurohormonal and metabolic disbalance, and inhibiting maladaptive inflammation. A variety of RV selective drugs are currently being studied in clinical trials.

SUMMARY

Nowadays, afterload reduction is still the cornerstone in treatment of PAH. New treatments targeting important pathobiological determinants of RV failure directly are emerging.

Evaluation and Management of Right-Sided Heart Failure: A Scientific Statement From the American Heart Association

Background and Purpose:

The diverse causes of right-sided heart failure (RHF) include, among others, primary cardiomyopathies with right ventricular (RV) involvement, RV ischemia and infarction, volume loading caused by cardiac lesions associated with congenital heart disease and valvular pathologies, and pressure loading resulting from pulmonic stenosis or pulmonary hypertension from a variety of causes, including left-sided heart disease. Progressive RV dysfunction in these disease states is associated with increased morbidity and mortality. The purpose of this scientific statement is to provide guidance on the assessment and management of RHF.

Methods:

The writing group used systematic literature reviews, published translational and clinical studies, clinical practice guidelines, and expert opinion/statements to summarize existing evidence and to identify areas of inadequacy requiring future research. The panel reviewed the most relevant adult medical literature excluding routine laboratory tests using MEDLINE, EMBASE, and Web of Science through September 2017. The document is organized and classified according to the American Heart Association to provide specific suggestions, considerations, or reference to contemporary clinical practice recommendations.

Results:

Chronic RHF is associated with decreased exercise tolerance, poor functional capacity, decreased cardiac output and progressive end-organ damage (caused by a combination of end-organ venous congestion and underperfusion), and cachexia resulting from poor absorption of nutrients, as well as a systemic proinflammatory state. It is the principal cause of death in patients with pulmonary arterial hypertension. Similarly, acute RHF is associated with hemodynamic instability and is the primary cause of death in patients presenting with massive pulmonary embolism, RV myocardial infarction, and postcardiotomy shock associated with cardiac surgery. Functional assessment of the right side of the heart can be hindered by its complex geometry. Multiple hemodynamic and biochemical markers are associated with worsening RHF and can serve to guide clinical assessment and therapeutic decision making. Pharmacological and mechanical interventions targeting isolated acute and chronic RHF have not been well investigated. Specific therapies promoting stabilization and recovery of RV function are lacking.

Conclusions:

RHF is a complex syndrome including diverse causes, pathways, and pathological processes. In this scientific statement, we review the causes and epidemiology of RV dysfunction and the pathophysiology of acute and chronic RHF and provide guidance for the management of the associated conditions leading to and caused by RHF.

Treatment strategies for the right heart in pulmonary hypertension

The function of the right ventricle (RV) determines the prognosis of patients with pulmonary hypertension. While much progress has been made in the treatment of pulmonary hypertension, therapies for the RV are less well established. In this review of treatment strategies for the RV, first we focus on ways to reduce wall stress since this is the main determinant of changes to the ventricle. Secondly, we discuss treatment strategies targeting the detrimental consequences of increased RV wall stress. To reduce wall stress, afterload reduction is the essential. Additionally, preload to the ventricle can be reduced by diuretics, by atrial septostomy, and potentially by mechanical ventricular support. Secondary to ventricular wall stress, left-to-right asynchrony, altered myocardial energy metabolism, and neurohumoral activation will occur. These may be targeted by optimising RV contraction with pacing, by iron supplement, by angiogenesis and improving mitochondrial function, and by neurohumoral modulation, respectively. We conclude that several treatment strategies for the right heart are available; however, evidence is still limited and further research is needed before clinical application can be recommended.

Low-flow support of the chronic pressure-overloaded right ventricle induces reversed remodeling

BACKGROUND

Mechanical right ventricular (RV) support in pulmonary arterial hypertension patients has been feared to cause pulmonary hemorrhage and to be detrimental for the after-load-sensitive RV. Continuous low-flow pumps offer promise but remain insufficiently tested.

METHODS

The pulmonary artery was banded in 20 sheep in this study. Eight weeks later, a Synergy micro-pump (HeartWare International, Framingham MA) was inserted in 10 animals, driving blood from the right atrium to the pulmonary artery. After magnetic resonance imaging, hemodynamics and RV pressure-volume loop data were recorded. Eight weeks later, RV function was assessed in the same way, followed by histologic analysis of the ventricular tissue.

RESULTS

During the 8 weeks of support, RV volumes and central venous pressure decreased significantly, whereas RV contractility increased. Pulmonary artery pressure increased modestly, particularly its diastolic component. RV contribution to total right-sided cardiac output increased from 12 ± 12% to 41 ± 9% (p < 1 × 10^-4). After pump inactivation, and compared with 8 weeks earlier, RV volumes had significantly decreased, tricuspid valve regurgitation had almost disappeared, and RV contractility had significantly increased, resulting in significantly increased RV forward power (0.25 ± 0.05 vs 0.16 ± 0.06 W, p = 0.014). Fulton index and RV myocyte size were significantly smaller, and without changes in fibrosis, when compared with controls.

CONCLUSIONS

Prolonged continuous low-flow RV mechanical support significantly unloads the chronic pressure-overloaded RV and improves cardiac output. After 8 weeks, RV hemodynamic recovery and reverse remodeling begin to occur, without increased fibrosis.