The role of elastic restoring forces in right-ventricular filling

Increased Chamber Resting Tone Is a Key Determinant of Left Ventricular Diastolic Dysfunction

BACKGROUND

Twitch-independent tension has been demonstrated in cardiomyocytes, but its role in heart failure (HF) is unclear. We aimed to address twitch-independent tension as a source of diastolic dysfunction by isolating the effects of chamber resting tone (RT) from impaired relaxation and stiffness.

METHODS

We invasively monitored pressure-volume data during cardiopulmonary exercise in 20 patients with hypertrophic cardiomyopathy, 17 control subjects, and 35 patients with HF with preserved ejection fraction. To measure RT, we developed a new method to fit continuous pressure-volume measurements, and first validated it in a computational model of loss of cMyBP-C (myosin binding protein-C).

RESULTS

In hypertrophic cardiomyopathy, RT (estimated marginal mean [95% CI]) was 3.4 (0.4-6.4) mm Hg, increasing to 18.5 (15.5-21.5) mm Hg with exercise (P<0.001). At peak exercise, RT was responsible for 64% (53%-76%) of end-diastolic pressure, whereas incomplete relaxation and stiffness accounted for the rest. RT correlated with the levels of NT-proBNP (N-terminal pro-B-type natriuretic peptide; R=0.57; P=0.02) and with pulmonary wedge pressure but following different slopes at rest and during exercise (R2=0.49; P<0.001). In controls, RT was 0.0 mm Hg and 1.2 (0.3-2.8) mm Hg in HF with preserved ejection fraction patients and was also exacerbated by exercise. In silico, RT increased in parallel to the loss of cMyBP-C function and correlated with twitch-independent myofilament tension (R=0.997).

CONCLUSIONS

Augmented RT is the major cause of LV diastolic chamber dysfunction in hypertrophic cardiomyopathy and HF with preserved ejection fraction. RT transients determine diastolic pressures, pulmonary pressures, and functional capacity to a greater extent than relaxation and stiffness abnormalities. These findings support antimyosin agents for treating HF.

Differential negative effects of acute exhaustive swim exercise on the right ventricle are associated with disproportionate hemodynamic loading

Acute exhaustive endurance exercise can differentially impact the right ventricle (RV) versus the left ventricle (LV). However, the hemodynamic basis for these differences and its impact on postexercise recovery remain unclear. Therefore, we assessed cardiac structure and function along with hemodynamic properties of mice subjected to single bouts (216 ± 8 min) of exhaustive swimming (ES). One-hour after ES, LVs displayed mild diastolic impairment compared with that in sedentary (SED) mice. Following dobutamine administration to assess functional reserve, diastolic and systolic function were slightly impaired. Twenty-four hours after ES, LV function was largely indistinguishable from that in SED. By contrast, 1-h post swim, RVs showed pronounced impairment of diastolic and systolic function with and without dobutamine, which persisted 24 h later. The degree of RV impairment correlated with the time-to-exhaustion. To identify hemodynamic factors mediating chamber-specific responses to ES, LV pressure was recorded during swimming. Swimming initiated immediate increases in heart rates (HRs), systolic pressure, dP/dt_max and -dP/dt_min, which remained stable for ∼45 min. LV end-diastolic pressures (LVEDP) increased to ≥45 mmHg during the first 10 min and subsequently declined. After 45 min, HR and -dP/dt_min declined, which correlated with gradual elevations in LVEDP (to ∼45 mmHg) as mice approached exhaustion. All parameters rapidly normalized postexercise. Consistent with human studies, our findings demonstrate a disproportionate negative impact of acute exhaustive exercise on RVs that persisted for at least 24 h. We speculate that the differential effects of exhaustive exercise on the ventricles arise from a ∼2-fold greater hemodynamic load in the RV than in LV originating from profound elevations in LVEDPs as mice approach exhaustion.NEW & NOTEWORTHY Acute exhaustive exercise differentially impacts the right ventricle (RV) versus left ventricle (LV), yet the underlying hemodynamic basis remains unclear. Using pressure-volume analyses and pressure-telemetry implantation in mice, we confirmed a marked disproportionate and persistent negative impact of exhaustive exercise on the RV. These differences in responses of the ventricles to exhaustive exercise are of clinical relevance, reflecting ∼2-fold greater hemodynamic RV loads versus LVs arising from massive (∼45 mmHg) increases in LV end-diastolic pressures at exhaustion.

The Biological Bases of Group 2 Pulmonary Hypertension

Pulmonary hypertension (PH) is a potentially fatal condition with a prevalence of around 1% in the world population and most commonly caused by left heart disease (PH-LHD). Usually, in PH-LHD, the increase of pulmonary pressure is only conditioned by the retrograde transmission of the left atrial pressure. However, in some cases, the long-term retrograde pressure overload may trigger complex and irreversible biomechanical and biological changes in the pulmonary vasculature. This latter clinical entity, designated as combined pre- and post-capillary PH, is associated with very poor outcomes. The underlying mechanisms of this progression are poorly understood, and most of the current knowledge comes from the field of Group 1-PAH. Treatment is also an unsolved issue in patients with PH-LHD. Targeting the molecular pathways that regulate pulmonary hemodynamics and vascular remodeling has provided excellent results in other forms of PH but has a neutral or detrimental result in patients with PH-LHD. Therefore, a deep and comprehensive biological characterization of PH-LHD is essential to improve the diagnostic and prognostic evaluation of patients and, eventually, identify new therapeutic targets. Ongoing research is aimed at identify candidate genes, variants, non-coding RNAs, and other biomarkers with potential diagnostic and therapeutic implications. In this review, we discuss the state-of-the-art cellular, molecular, genetic, and epigenetic mechanisms potentially involved in PH-LHD. Signaling and effective pathways are particularly emphasized, as well as the current knowledge on -omic biomarkers. Our final aim is to provide readers with the biological foundations on which to ground both clinical and pre-clinical research in the field of PH-LHD.

Survival Benefit of Obese Patients With Pulmonary Embolism

OBJECTIVE

To investigate the impact of obesity and underweight on adverse in-hospital outcomes in pulmonary embolism (PE).

PATIENTS AND METHODS

Patients diagnosed as having PE based on International Statistical Classification of Diseases and Related Health Problems, 10th Revision, German Modification code I26 in the German nationwide inpatient database were stratified for obesity, underweight, and normal weight/overweight (reference group) and compared regarding adverse in-hospital outcomes.

RESULTS

From January 1, 2011, through December 31, 2014, 345,831 inpatients (53.3% females) 18 years and older were included in this analysis; 8.6% were obese and 0.5% were underweight. Obese patients were younger (67.0 vs 73.0 years), were more frequently female (60.2% vs 52.7%), had a lower cancer rate (13.6% vs 20.5%), and were more often treated with systemic thrombolysis (6.4% vs 4.3%) and surgical embolectomy (0.3% vs 0.1%) vs the reference group (P<.001 for all). Overall, 51,226 patients (14.8%) died during in-hospital stay. Obese patients had lower mortality (10.9% vs 15.2%; P<.001) vs the reference group and a reduced odds ratio (OR) for in-hospital mortality (OR, 0.74; 95% CI, 0.71-0.77; P<.001) independent of age, sex, comorbidities, and reperfusion therapies. This survival benefit of obese patients was more pronounced in obesity classes I (OR, 0.56; 95% CI, 0.52-0.60; P<.001) and II (OR, 0.63; 95% CI 0.58-0.69; P<.001). Underweight patients had higher prevalence of cancer and higher mortality rates (OR, 1.15; 95% CI, 1.00-1.31; P=.04).

CONCLUSION

Obesity is associated with decreased in-hospital mortality rates in patients with PE. Although obese patients were more often treated with reperfusion therapies, the survival benefit of obese patients occurred independently of age, sex, comorbidities, and reperfusion treatment.

The natural matching of harmonic responses in the pulmonary circulation

Key points

The right ventricle of the mammal heart is highly sensitive to the afterload imposed by a combination of the pulmonary circulation and the retrograde contribution of the left heart.

Right ventricular afterload can be analysed in terms of pulmonary artery input impedance, which we were able to decompose as the result of the harmonic frequency responses of the pulmonary vessels and the left heart attached in series.

Using spectral methods, we found a natural matching between the pulmonary vasculature and the left chambers of the heart. This coupling implies that the upstream transmission of the left heart frequency‐response has favourable effects on the pulmonary tree.

This physiological mechanism protects the right ventricle against acute changes in preload, and its impairment may be a relevant contribution to right ventricle dysfunction in pulmonary hypertension.

Abstract

The right ventricle (RV) of the mammal heart is highly sensitive to the afterload imposed by the pulmonary circulation, and the left heart (LH) retrogradely contributes significantly to this vascular load. Transmission‐line theory anticipates that the degree of matching between the frequency responses of the pulmonary vasculature and the LH should modulate the global right haemodynamic burden. We measured simultaneous high‐fidelity flow (pulmonary artery) and pressure (pulmonary artery and left atrium) in 18 healthy minipigs under acute haemodynamic interventions. From these data, we decomposed the impedance spectra of the total right‐circulation system into the impedance of the pulmonary vessels and the harmonic response of the LH. For frequencies above the first harmonic, total impedance was below the pulmonary impedance during all phases (P < 0.001; pooled phases), demonstrating a favourable effect of the LH harmonic response on RV pulsatile load: the LH harmonic response was responsible for a 20% reduction of pulse pulmonary artery pressure (P < 0.001 vs. a theoretical purely‐resistive response) and a 15% increase of pulmonary compliance (P = 0.009). This effect on compliance was highest during acute volume overload. In the normal right circulation, the longitudinal impedance of the pulmonary vasculature is matched to the harmonic response of the LH in a way that efficiently reduces the pulmonary pulsatile vascular load. This source of interaction between the right and left circulations of mammals protects the RV against excessive afterload during acute volume transients and its disruption may be an important contributor to pulmonary hypertension.

The right ventricle of the mammal heart is highly sensitive to the afterload imposed by a combination of the pulmonary circulation and the retrograde contribution of the left heart.

Right ventricular afterload can be analysed in terms of pulmonary artery input impedance, which we were able to decompose as the result of the harmonic frequency responses of the pulmonary vessels and the left heart attached in series.

Using spectral methods, we found a natural matching between the pulmonary vasculature and the left chambers of the heart. This coupling implies that the upstream transmission of the left heart frequency‐response has favourable effects on the pulmonary tree.

This physiological mechanism protects the right ventricle against acute changes in preload, and its impairment may be a relevant contribution to right ventricle dysfunction in pulmonary hypertension.

Prognostic Value of Time Interval Between Mitral and Tricuspid Valve Opening in Patients With Heart Failure

BACKGROUND

We used dual Doppler echocardiography to measure the time interval between the mitral and tricuspid valve opening (MO-TO time), which we expected would reflect the balance between left and right ventricular hemodynamics. Methods and Results: We prospectively enrolled 60 patients with heart failure (HF) and sinus rhythm. The MO-TO time was measured in addition to routine echocardiography parameters, invasive hemodynamic parameters and plasma B-type natriuretic peptide (BNP) level in all patients. Patients were divided into 2 groups based on the MO-TO time: MOP (mitral opening preceding tricuspid opening), and TOP (tricuspid opening preceding mitral opening) groups. We followed up the predefined adverse outcomes (cardiovascular [CV] death and hospitalization due to worsening HF) for 1 year. Pulmonary artery wedge pressure (PAWP) and mean pulmonary artery pressure (mPAP) were higher in the MOP than in the TOP group (P<0.001; P<0.001, respectively). The probability of an adverse CV outcome was higher in the MOP than in the TOP group (log-rank test; P=0.002). Addition of MOP improved the predictive power of univariate predictors (mitral E/A ratio and BNP) in the bivariate Cox analysis (P=0.017, P=0.024, respectively).

CONCLUSIONS

MOP reflects pulmonary hypertension caused by left heart disease and has prognostic value in predicting adverse CV events in patients with HF.

Assessment of pulmonary arterial compliance evaluated using harmonic oscillator kinematics

We hypothesized that K_PA, a harmonic oscillator kinematics-derived spring constant parameter of the pulmonary artery pressure (PAP) profile, reflects PA compliance in pediatric patients. In this prospective study of 33 children (age range = 0.5–20 years) with various cardiac diseases, we assessed the novel parameter designated as K_PA calculated using the pressure phase plane and the equation K_PA = (dP/dt_max)²/([Pmax – Pmin])/2)², where dP/dt_max is the peak derivative of PAP, and Pmax – Pmin is the difference between the minimum and maximum PAP. PA compliance was also calculated using two conventional methods: systolic PA compliance (sPAC) was expressed as the stroke volume/Pmax – Pmin; and diastolic PA compliance (dPAC) was determined according to a two-element Windkessel model of PA diastolic pressure decay. In addition, data were recorded during abdominal compression to determine the influence of preload on K_PA. A significant correlation was observed between K_PA and sPAC (r = 0.52, P = 0.0018), but not dPAC. Significant correlations were also seen with the time constant (τ) of diastolic PAP (r = −0.51, P = 0.0026) and the pulmonary vascular resistance index (r = −0.39, P = 0.0242). No significant difference in K_PA was seen between before and after abdominal compression. K_PA had a higher intraclass correlation coefficient than other compliance and resistance parameters for both intra-observer and inter-observer variability (0.998 and 0.997, respectively). These results suggest that K_PA can provide insight into the underlying mechanisms and facilitate the quantification of PA compliance.

Multimodality Evaluation of the Right Ventricle: An Updated Review

The assessment of the volumes, function, and mechanics of the right ventricle (RV) is very challenging because of the anatomical complexity of the RV. Because RV structure, function, and deformation are very important predictors of cardiovascular morbidity and mortality in patients with heart failure, pulmonary hypertension, congenital heart disease, or arrhythmogenic RV cardiomyopathy, it is of great importance to use an appropriate imaging modality that will provide all necessary information. In everyday clinical practice, 2-dimensional echocardiography (2DE) represents a method of first choice in RV evaluation. However, cardiac magnetic resonance (CMR) remained the gold standard for RV assessment. The development of new imaging tools, such as 3-dimensional echocardiography (3DE), provided reliable data, comparable with CMR, and opened a completely new era in RV imaging. So far, 3DE has shown good results in determination of RV volumes and systolic function, and there are indications that it will also provide valuable data about 3-dimensional RV mechanics, similar to CMR. Two-dimensional echocardiography-derived strain is currently widely used for the assessment of RV deformation, which has been proven to be a more significant predictor of functional capacity and survival than CMR-derived RV ejection fraction. The purpose of this review is to summarize currently available data about RV structure, function, and mechanics obtained by different imaging modalities, primarily 2DE and 3DE, and their comparison with CMR and cardiac computed tomography.