The Right Ventricle and Pulmonary Circulation: Basic Concepts

Critical care outcomes in patients with pre-existing pulmonary hypertension: insights from the ASPIRE registry

Pulmonary hypertension (PH) is a life-shortening condition characterised by episodes of decompensation precipitated by factors such as disease progression, arrhythmias and sepsis. Surgery and pregnancy also place additional strain on the right ventricle. Data on critical care management in patients with pre-existing PH are scarce.

We conducted a retrospective observational study of a large cohort of patients admitted to the critical care unit of a national referral centre between 2000–2017 to establish acute mortality, evaluate predictors of in-hospital mortality and establish longer term outcomes in survivors to hospital discharge.

242 critical care admissions involving 206 patients were identified. Hospital survival was 59.3%, 94% and 92% for patients admitted for medical, surgical or obstetric reasons, respectively. Medical patients had more severe physiological and laboratory perturbations than patients admitted following surgical or obstetric interventions. Higher APACHE II (Acute Physiology and Chronic Health Evaluation) score, age and lactate, and lower oxygen saturation measure by pulse oximetry/inspiratory oxygen fraction (S_pO2/F_iO2) ratio, platelet count and sodium level were identified as independent predictors of hospital mortality. An exploratory risk score, OPALS (oxygen (S_pO2/F_iO2) ≤185; platelets ≤196×10⁹·L⁻¹; age ≥37.5 years; lactate ≥2.45 mmol·L⁻¹; sodium ≤130.5 mmol·L⁻¹), identified medical patients at increasing risk of hospital mortality. One (11%) out of nine patients who were invasively ventilated for medical decompensation and 50% of patients receiving renal replacement therapy left hospital alive. There was no significant difference in exercise capacity or functional class between follow-up and pre-admission in patients who survived to discharge.

These data have clinical utility in guiding critical care management of patients with known PH. The exploratory OPALS score requires validation.

Critical care survival is worse in PH patients admitted for medical rather than surgical/obstetric indications. Nevertheless, many show longer term survival and functional recovery. Markers of severity of acute illness at admission are prognostic.https://bit.ly/2YX9Fw9

Inverse modeling framework for characterizing patient-specific microstructural changes in the pulmonary arteries

Microstructural changes in the pulmonary arteries associated with pulmonary arterial hypertension (PAH) is not well understood and characterized in humans. To address this issue, we developed and applied a patient-specific inverse finite element (FE) modeling framework to characterize mechanical and structural changes of the micro-constituents in the proximal pulmonary arteries using in-vivo pressure measurements and magnetic resonance images. The framework was applied using data acquired from a pediatric PAH patient and a heart transplant patient with normal pulmonary arterial pressure, which serves as control. Parameters of a constrained mixture model that are associated with the structure and mechanical properties of elastin, collagen fibers and smooth muscle cells were optimized to fit the patient-specific pressure-diameter responses of the main pulmonary artery. Based on the optimized parameters, individual stress and linearized stiffness resultants of the three tissue constituents, as well as their aggregated values, were estimated in the pulmonary artery. Aggregated stress resultant and stiffness are, respectively, 4.6 and 3.4 times higher in the PAH patient than the control subject. Stress and stiffness resultants of each tissue constituent are also higher in the PAH patient. Specifically, the mean stress resultant is highest in elastin (PAH: 69.96, control: 14.42 kPa-mm), followed by those in smooth muscle cell (PAH: 13.95, control: 4.016 kPa-mm) and collagen fibers (PAH: 13.19, control: 2.908 kPa-mm) in both the PAH patient and the control subject. This result implies that elastin may be the key load-bearing constituent in the pulmonary arteries of the PAH patient and the control subject.

Diagnosis and treatment of right ventricular dysfunction in congenital heart disease

Right ventricular (RV) function is important for clinical status and outcomes in children and adults with congenital heart disease (CHD). In the normal RV, longitudinal systolic function is the major contributor to global RV systolic function. A variety of factors contribute to RV failure including increased pressure- or volume-loading, electromechanical dyssynchrony, increased myocardial fibrosis, abnormal coronary perfusion, restricted filling capacity and adverse interactions between left ventricle (LV) and RV. We discuss the different imaging techniques both at rest and during exercise to define and detect RV failure. We identify the most important biomarkers for risk stratification in RV dysfunction, including abnormal NYHA class, decreased exercise capacity, low blood pressure, and increased levels of NTproBNP, troponin T, galectin-3 and growth differentiation factor 15. In adults with CHD (ACHD), fragmented QRS is independently associated with heart failure (HF) symptoms and impaired ventricular function. Furthermore, we discuss the different HF therapies in CHD but given the broad clinical spectrum of CHD, it is important to treat RV failure in a disease-specific manner and based on the specific alterations in hemodynamics. Here, we discuss how to detect and treat RV dysfunction in CHD in order to prevent or postpone RV failure.

Complications of fluid overload during hysteroscopic surgery: cardiomyopathy and epistaxis - A case report

Background

Hysteroscopic surgery has been used in various gynecological fields. However, massive fluid overload can occur as a complication due to persistent infusion of media for uterine cavity distension. We present the case of a woman who developed cardiomyopathy with pulmonary edema and epistaxis during hysteroscopic surgery.

Case

A 76-year-old female underwent hysteroscopic septectomy. She manifested abrupt, active nasal bleeding and regurgitation in the intravenous line. Heart rate, SpO₂, and PETCO₂ decreased from 55 beats/min to 29 beats/min, from 100% to 56%, and from 31 mmHg to 9 mmHg, respectively. After the operation, brain CT showed bilateral prominent superior ophthalmic vein dilation. Echocardiography showed left ventricle apical ballooning and global hypokinesia. The patient recovered after two days of conservative management, with no sequelae.

Conclusions

Although hysteroscopic surgery is a simple procedure, careful monitoring is necessary to prevent complications from absorption of fluid distending media during the procedure.

Stem Cell Therapy for Hypoplastic Left Heart Syndrome: Mechanism, Clinical Application, and Future Directions

Hypoplastic left heart syndrome is a type of congenital heart disease characterized by underdevelopment of the left ventricle, outflow tract, and aorta. The condition is fatal if aggressive palliative operations are not undertaken, but even after the complete 3-staged surgical palliation, there is significant morbidity because of progressive and ultimately intractable right ventricular failure. For this reason, there is interest in developing novel therapies for the management of right ventricular dysfunction in patients with hypoplastic left heart syndrome. Stem cell therapy may represent one such innovative approach. The field has identified numerous stem cell populations from different tissues (cardiac or bone marrow or umbilical cord blood), different age groups (adult versus neonate-derived), and different donors (autologous versus allogeneic), with preclinical and clinical experience demonstrating the potential utility of each cell type. Preclinical trials in small and large animal models have elucidated several mechanisms by which stem cells affect the injured myocardium. Our current understanding of stem cell activity is undergoing a shift from a paradigm based on cellular engraftment and differentiation to one recognizing a primarily paracrine effect. Recent studies have comprehensively evaluated the individual components of the stem cells' secretomes, shedding new light on the intracellular and extracellular pathways at the center of their therapeutic effects. This research has laid the groundwork for clinical application, and there are now several trials of stem cell therapies in pediatric populations that will provide important insights into the value of this therapeutic strategy in the management of hypoplastic left heart syndrome and other forms of congenital heart disease. This article reviews the many stem cell types applied to congenital heart disease, their preclinical investigation and the mechanisms by which they might affect right ventricular dysfunction in patients with hypoplastic left heart syndrome, and finally, the completed and ongoing clinical trials of stem cell therapy in patients with congenital heart disease.

Pulmonary Arterial Hypertension Emergency Complications and Evaluation: Practical Guide for the Advanced Practice Registered Nurses in the Emergency Department

Pulmonary hypertension (PH) complicates common diseases and can lead to worsening symptoms and increased mortality. A specific group of PH, pulmonary arterial hypertension (PAH), World Health Organization Group 1, may present to the emergency department (ED). We review common ED presentations of patients with PAH such as cardiac arrest/sudden death, right ventricular failure, syncope, hypoxemic respiratory failure, arrhythmias, hemoptysis, pulmonary embolism, chest pain/left main compression syndrome, infection, and considerations for PAH medication administration. We include a case study to illustrate a real example with a positive outcome, and an algorithm for evaluating and triaging patients with PAH in the ED. The ability to recognize, triage, and communicate changes in PAH disease status in a multidisciplinary team approach between the patient, family, specialty pharmacy, and specialized health care providers such as the PH team, is essential for ED providers who are evaluating and treating patients with PAH.

Pulmonary hypertension subjects exhibit right ventricular transient exertional dilation during supine exercise stress echocardiography

Pulmonary hypertension is a condition with high morbidity and mortality. Resting transthoracic echocardiography is a pivotal diagnostic and screening test for pulmonary hypertension. The role of exercise stress echocardiography in the diagnosis of pulmonary hypertension is not well-established. We studied right ventricular size changes during exercise using exercise stress echocardiography to assess differences between normal and pulmonary hypertension patients and evaluate test safety, feasibility, and reproducibility. Healthy control and pulmonary hypertension patients performed recumbent exercise using a bicycle ergometer. Experienced echocardiography sonographers recorded the following resting and peak exercise right ventricular parameters using the apical four chamber view: end-diastolic area; end-systolic area; mid-diameter; basal diameter; and longitudinal diameter. Two cardiologists masked to clinical information subsequently analyzed the recordings. Parameters with acceptable inter-rater reliability were analyzed for statistical differences between the normal and pulmonary hypertension patient groups and their association with pulmonary hypertension. We enrolled 38 healthy controls and 40 pulmonary hypertension patients. Exercise stress echocardiography testing was found to be safe and feasible. Right ventricular size parameters were all readily obtainable and all had acceptable inter-observer reliability except for right ventricular longitudinal diameter. During exercise, healthy controls demonstrated a decrease in right ventricular end-systolic area, end-diastolic area, mid-diameter, and basal diameter (P < 0.05). Conversely, pulmonary hypertension patients demonstrated an increase in right ventricular end-systolic area, end-diastolic area, and mid-diameter (P < 0.05). These changes were unaffected by multivariate corrections. The sensitivity for pulmonary hypertension of an increase in right ventricular size was 97.2% with a negative predictive value of 95.2%. The ROC C-statistic for increase in right ventricular size was 0.93. This transient exertional dilation (TED) of the right ventricle is observed in pulmonary hypertension patients but not in healthy controls. Recumbent right ventricular exercise stress echocardiography is a feasible and safe diagnostic test for pulmonary hypertension which warrants additional study.

Ventriculo-arterial coupling detects occult RV dysfunction in chronic thromboembolic pulmonary vascular disease

Chronic thromboembolic disease (CTED) is suboptimally defined by a mean pulmonary artery pressure (mPAP) <25 mmHg at rest in patients that remain symptomatic from chronic pulmonary artery thrombi. To improve identification of right ventricular (RV) pathology in patients with thromboembolic obstruction, we hypothesized that the RV ventriculo-arterial (Ees/Ea) coupling ratio at maximal stroke work (Ees/Ea_{max sw}) derived from an animal model of pulmonary obstruction may be used to identify occult RV dysfunction (low Ees/Ea) or residual RV energetic reserve (high Ees/Ea). Eighteen open chested pigs had conductance catheter RV pressure-volume (PV)-loops recorded during PA snare to determine Ees/Ea_{max sw} This was then applied to 10 patients with chronic thromboembolic pulmonary hypertension (CTEPH) and ten patients with CTED, also assessed by RV conductance catheter and cardiopulmonary exercise testing. All patients were then restratified by Ees/Ea. The animal model determined an Ees/Ea_{max sw} = 0.68 ± 0.23 threshold, either side of which cardiac output and RV stroke work fell. Two patients with CTED were identified with an Ees/Ea well below 0.68 suggesting occult RV dysfunction whilst three patients with CTEPH demonstrated Ees/Ea ≥ 0.68 suggesting residual RV energetic reserve. Ees/Ea > 0.68 and Ees/Ea < 0.68 subgroups demonstrated constant RV stroke work but lower stroke volume (87.7 ± 22.1 vs. 60.1 ± 16.3 mL respectively, P = 0.006) and higher end-systolic pressure (36.7 ± 11.6 vs. 68.1 ± 16.7 mmHg respectively, P < 0.001). Lower Ees/Ea in CTED also correlated with reduced exercise ventilatory efficiency. Low Ees/Ea aligns with features of RV maladaptation in CTED both at rest and on exercise. Characterization of Ees/Ea in CTED may allow for better identification of occult RV dysfunction.

Management of pulmonary hypertension and right heart failure in the intensive care unit

Management of acute right ventricular failure, both with and without coexisting pulmonary hypertension, is a common challenge encountered in the intensive care setting. Both right ventricular dysfunction and pulmonary hypertension portend a poor prognosis, regardless of the underlying cause and are associated with significant morbidity and mortality. The right ventricle is embryologically distinct from the left ventricle and has unique morphologic and functional properties. Management of right ventricular failure and pulmonary hypertension in the intensive care setting requires tailored hemodynamic management, pharmacotherapy, and often mechanical circulatory support. Unfortunately, our understanding of the management of right ventricular failure lags behind that of the left ventricle. In this review, we will explore the underlying pathophysiology of the failing right ventricle and pulmonary vasculature in patients with and without pulmonary hypertension and discuss management strategies based on evidence-based studies as well as our current understanding of the underlying physiology.

Validation of an arterial constitutive model accounting for collagen content and crosslinking

During the progression of pulmonary hypertension (PH), proximal pulmonary arteries (PAs) increase in both thickness and stiffness. Collagen, a component of the extracellular matrix, is mainly responsible for these changes via increased collagen fiber amount (or content) and crosslinking. We sought to differentiate the effects of collagen content and cross-linking on mouse PA mechanical changes using a constitutive model with parameters derived from experiments in which collagen content and cross-linking were decoupled during hypoxic pulmonary hypertension (HPH). We employed an eight-chain orthotropic element model to characterize collagen's mechanical behavior and an isotropic neo-Hookean form to represent elastin. Our results showed a strong correlation between the material parameter related to collagen content and measured collagen content (R(2)=0.82, P<0.0001) and a moderate correlation between the material parameter related to collagen crosslinking and measured crosslinking (R(2)=0.24, P=0.06). There was no significant change in either the material parameter related to elastin or the measured elastin content from histology. The model-predicted pressure at which collagen begins to engage was ∼25mmHg, which is consistent with experimental observations. We conclude that this model may allow us to predict changes in the arterial extracellular matrix from measured mechanical behavior in PH patients, which may provide insight into prognoses and the effects of therapy.

STATEMENT OF SIGNIFICANCE

The literature has proposed several constitutive models to describe the mechanical effects of arterial collagen but none separates collagen content from crosslinking. Given that both are critical to arterial mechanics, the novel model described here does so. Furthermore, our novel model is well tested by experimental data; model parameters were reasonably correlated with measured collagen content and crosslinking and the model-predicted collagen transition stretch was consistent with that obtained experimentally. Given that arterial collagen structural changes and collagen engagement are critical to arterial stiffening in several disease states, this model, by linking mechanical and biological properties, may allow us to predict important biological changes during disease progression from measured mechanical behavior.

In vivo and in vitro measurements of pulmonary arterial stiffness: A brief review

During the progression of pulmonary hypertension (PH), proximal pulmonary arteries (PAs) undergo remodeling such that they become thicker and the elastic modulus increases. Both of these changes increase the vascular stiffness. The increase in pulmonary vascular stiffness contributes to increased right ventricular (RV) afterload, which causes RV hypertrophy and eventually failure. Studies have found that proximal PA stiffness or its inverse, compliance, is strongly related to morbidity and mortality in patients with PH. Therefore, accurate in vivo measurement of PA stiffness is useful for prognoses in patients with PH. It is also important to understand the structural changes in PAs that occur with PH that are responsible for stiffening. Here, we briefly review the most common parameters used to quantify stiffness and in vivo and in vitro methods for measuring PA stiffness in human and animal models. For in vivo approaches, we review invasive and noninvasive approaches that are based on measurements of pressure and inner or outer diameter or cross-sectional area. For in vitro techniques, we review several different testing methods that mimic one, two or several aspects of physiological loading (e.g., uniaxial and biaxial testing, dynamic inflation-force testing). Many in vivo and in vitro measurement methods exist in the literature, and it is important to carefully choose an appropriate method to measure PA stiffness accurately. Therefore, advantages and disadvantages of each approach are discussed.