Right ventricular pacing improves right heart function in experimental pulmonary arterial hypertension: a study in the isolated heart

Dynamic aspects of ventricular interaction during exercise in HFpEF and in pre-capillary pulmonary hypertension

AIMS

The contribution of adverse ventricular interdependence remains undervalued in heart failure or pulmonary vascular disease, and not much is known about its dynamic nature during exercise and respiration. In this study, we evaluated ventricular interaction during exercise in patients with heart failure with preserved ejection fraction (HFpEF) and patients with chronic thromboembolic pulmonary hypertension (CTEPH) as compared with healthy controls.

METHODS AND RESULTS

Forty-six subjects (10 controls, 19 CTEPH patients, and 17 HFpEF patients) underwent cardiac magnetic resonance imaging during exercise. Ventricular interaction was determined through analysis of the septal curvature (SC) of a mid-ventricular short-axis slice at end-diastole, end-systole, and early-diastole, both in expiration and inspiration. Exercise amplified ventricular interaction in CTEPH patients and to a lesser extent in HFpEF patients (P < 0.05 for decrease in SC with exercise). Adverse interaction was most profound in early-diastole and most pronounced in CTEPH patients (P < 0.05 interaction group * exercise) because of a disproportionate increase RV afterload (P < 0.05 to both controls and HFpEF) and diastolic pericardial restraint (P < 0.001 for interaction group * exercise) during exercise. Inspiration enhanced diastolic interdependence in CTEPH and HFpEF patients (P < 0.05 vs. expiration). Both at rest and during exercise, SC strongly correlated with RV volumes and pulmonary artery pressures (all P < 0.05).

CONCLUSIONS

Exercise amplifies adverse right-left ventricular interactions in CTEPH, while a more moderate effect is observed in isolated post-capillary HFpEF. Given the strong link with RV function and pulmonary hemodynamic, assessing ventricular interaction with exCMR might be valuable from a diagnostic or therapeutic perspective.

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.

Physical Activity and Its Association with Traditional Outcome Measures in Pulmonary Arterial Hypertension

Rationale Limitation of physical activity is a common presenting complaint for patients with pulmonary arterial hypertension (PAH). Physical activity is thought to be determined by cardiopulmonary function, yet there are limited data that investigate this relationship. Objective We aimed to study the relationship between right ventricular function and daily activity and its impact on health-related quality of life (HRQoL) in PAH. Methods Baseline data for 55 patients enrolled in PHANTOM, an ongoing multicenter randomized controlled trial of anastrozole in PAH were used. Post-menopausal women and men were eligible and underwent six-minute walk testing, echocardiography and completed HRQoL questionnaires. Each patient wore an accelerometer for 7-days. Multivariable linear regression models were used to study the association between tricuspid annular plane systolic excursion (TAPSE) and vector magnitude counts, and between daily activity and HRQoL. Principal component analysis and K-means clustering were used to identify activity-based phenotypes. K-nearest neighbors' classification was applied to an independent cross-sectional cohort from the University of Pennsylvania. Results The mean age of patients in PHANTOM was 61 years. 67% were women with idiopathic PAH as the most common etiology. A 0.4 cm increase in TAPSE was associated with an increase in daily vector magnitude counts (ß:34000, 95%CI:900-67000, p=0.004) after adjustment for age, sex, body mass index, etiology of PAH and wear time. A 1-standard deviation increase in vector magnitude counts was associated with higher six-minute walk distance (ß: 56.1 meters, 95%CI:28.6-83.7, p<0.001) and lower emPHasis-10 scores (ß:-3.3, 95%CI:0.3-6.4, p=0.03). Three activity phenotypes, low, medium, and high, were identified. The most active phenotype had greater six-minute walk distances (p=0.001) and lower emPHasis-10 scores (p=0.009) after adjustment for age, sex, body mass index, WHO functional class and parenteral prostacyclin use. Phenotypes of physical activity were reproduced in the second cohort and were independently associated with six-minute walk distance. Conclusion Better right ventricular systolic function was associated with increased levels of activity in PAH. Increased daily activity was associated with greater six-minute walk distance and better HRQoL. Distinct activity-based phenotypes may be helpful in risk stratification of PAH patients or provide novel endpoints for clinical trials.

Interventional and Surgical Treatments for Pulmonary Arterial Hypertension

Despite significant advancements in pharmacological treatment, interventional and surgical options are still viable treatments for patients with pulmonary arterial hypertension (PAH), particularly idiopathic PAH. Herein, we review the interventional and surgical treatments for PAH. Atrial septostomy and the Potts shunt can be useful bridging tools for lung transplantation (Ltx), which remains the final surgical treatment among patients who are refractory to any other kind of therapy. Veno-arterial extracorporeal membrane oxygenation (V-A ECMO) remains the ultimate bridging therapy for patients with severe PAH. More importantly, VA-ECMO plays a crucial role during Ltx and provides necessary left ventricular conditioning during the initial postoperative period. Pulmonary denervation may potentially be a new way to ensure better transplant-free survival among patients with the aforementioned disease. However, high-quality randomized controlled trials are needed. As established, obtaining the Eisenmenger physiology among patients with severe pulmonary hypertension by creating artificial defects is associated with improved survival. However, right-to-left shunting may be harmful after Ltx. Closure of the artificially created defects may carry some risk associated with cardiac surgery, especially among patients with Potts shunts. In conclusion, PAH requires an interdisciplinary approach using pharmacological, interventional, and surgical modalities.

Asymmetric Regional Work Contributes to Right Ventricular Fibrosis, Inefficiency, and Dysfunction in Pulmonary Hypertension versus Regurgitation

BACKGROUND

Right ventricular (RV) pressure loading from pulmonary hypertension (PH) and volume loading from pulmonary regurgitation (PR) lead to RV dysfunction, a critical determinant of clinical outcomes, but their impact on regional RV mechanics and fibrosis is poorly characterized. The aim of this study was to test the hypothesis that regional myocardial mechanics and efficiency in RV pressure and volume loading are associated with RV fibrosis and dysfunction.

METHODS

Eight PH, six PR, and five sham-control rats were studied. The PH rat model was induced using Sugen5416, a vascular endothelial growth factor receptor 2 inhibitor, combined with chronic hypoxia. PR rats were established by surgical laceration of the pulmonary valve leaflets. Six (n = 4) or 9 (n = 4) weeks after Sugen5416 and hypoxia and 12 weeks after PR surgery, myocardial strain and RV pressure were measured and RV pressure-strain loops generated. We further studied RV regional mechanics in 11 patients with PH. Regional myocardial work was calculated as the pressure-strain loop area (mm Hg ∙ %). Regional myocardial work efficiency was quantified through wasted work (ratio of systolic lengthening to shortening work). The relation of regional myocardial work to RV fibrosis and dysfunction was analyzed.

RESULTS

In rats, PH and PR induced similar RV dilatation, but fractional area change (%) was lower in PH than in PR. RV lateral wall work was asymmetrically higher in PH compared with sham, while septal work was similar to sham. In PR, lateral and septal work were symmetrically higher versus sham. Myocardial wasted work ratio was asymmetrically increased in the PH septum versus sham. Fibrosis in the RV lateral wall, but not septum, was higher in PH than PR. RV fibrosis burden was linearly related to regional work and to measures of RV systolic and diastolic function but not to wasted myocardial work ratio. Patients with PH demonstrated similar asymmetric and inefficient regional myocardial mechanics.

CONCLUSIONS

Asymmetric RV work and increased wasted septal work in experimental PH are associated with RV fibrosis and dysfunction. Future investigation should examine whether assessment of asymmetric regional RV work and efficiency can predict clinical RV failure and influence patient management.

First in human: the effects of biventricular pacing on cardiac output in severe pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) carries high morbidity and mortality despite available treatment options. In severe PAH, right ventricular (RV) diastolic pressure overload leads to interventricular septal bowing, hindering of left ventricular diastolic filling and reduced cardiac output (CO). Some animal studies suggest that pacing may mitigate this effect. We hypothesized that eliminating late diastole via ventricular pacing could improve CO in human subjects with severe PAH. Using minimal to no sedation, we performed transvenous acute biventricular (BiV) pacing and right heart catheterization in six patients with symptomatic PAH. Hemodynamic measurements were taken at baseline and during BiV pacing at various 20-ms intervals of V-V timing. We compared baseline CO to (1) CO while pacing the RV first by 80 ms (mimicking RV-only pacing), and then to (2) CO during pacing at the V-V timing that resulted in the highest CO. All participants were female, PASP 74 ± 14 mmHg, QRS duration 104 ± 20 ms. Compared with baseline, the CO decreased when the RV was paced first by 80 ms (7.2 ± 1.0 vs. 6.2 ± 1.1 L/min, p = 0.028). Pacing with optimal V-V timing produced CO similar to baseline (7.2 ± 1.0 vs. 7.4 ± 1.4, p = 0.92). Two patients (33%) met the predefined endpoint of a 15% increase in CO during pacing at the optimal V-V timing. In symptomatic PAH, V-V optimized acute BiV pacing does not consistently improve CO. However, acute BiV pacing did improve CO in a subset of this cohort. Further research is needed to identify predictors of response to cardiac resynchronization therapy in this population.

Acute Respiratory Failure in Interstitial Lung Disease Complicated by Pulmonary Hypertension

Interstitial lung disease represents a group of diffuse parenchymal lung diseases with overwhelming morbidity and mortality when complicated by acute respiratory failure. Recently, trials investigating outcomes and their determinants have provided insight into these high mortality rates. Pulmonary hypertension is a known complication of interstitial lung disease and there is high prevalence in idiopathic pulmonary fibrosis, connective tissue disease, and sarcoidosis subtypes. Interstitial lung disease associated pulmonary hypertension has further increased mortality with acute respiratory failure, and there is limited evidence to guide management. This review describes investigations and management of interstitial lung disease associated acute respiratory failure complicated by pulmonary hypertension. Despite the emerging attention on interstitial lung disease associated acute respiratory failure and the influence of pulmonary hypertension, critical care management remains a clinical and ethical challenge.

Impact of right ventricular dyssynchrony on prognosis of patients with idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension is a progressive disease with high mortality with an increasing burden of right ventricular. Right ventricular dyssynchrony was observed in idiopathic pulmonary arterial hypertension, but the association with mortality is unclear. This study aimed to investigate the impact of right ventricular dyssynchrony on the survival of idiopathic pulmonary arterial hypertension. A total of 116 patients with idiopathic pulmonary arterial hypertension were enrolled in this study. All these patients underwent comprehensive clinical evaluation. Right ventricular dyssynchrony was assessed by two-dimensional speckle-tracking echocardiography. The time to peak strain (T_peak) of right ventricular segments were obtained. Right ventricular dyssynchrony was quantified by the standard deviation of the heart rate-corrected T_peak of right ventricular four segments. All patients were followed up and the primary endpoint was all cause of death. Results found patients with significant right ventricular dyssynchrony present with advanced World Health Organization functional class, worse hemodynamic status and right ventricular function. Right ventricular dyssynchrony was an independent predictive factor for the survival of idiopathic pulmonary arterial hypertension. Kaplan–Meier survival curves showed patients with right ventricular dyssynchrony had worse prognosis. In conclusion, right ventricular dyssynchrony analyzed by speckle-tracking echocardiography provided added value to hemodynamic and echocardiographic parameters in evaluating the survival of patients with idiopathic pulmonary arterial hypertension.

Adaptation to acute pulmonary hypertension in pigs

The extent of right ventricular compensation compared to the left ventricle is restricted and varies among individuals, which makes it difficult to define. While establishing a model of acute pulmonary hypertension in pigs we observed two different kinds of compensation in our animals. Looking deeper into the hemodynamic data we tried to delineate why some animals could compensate and others could not. Pulmonary hypertension (mean pressure 45 mmHg) was induced gradually by infusion of a stable thromboxane A₂ analogue U46619 in a porcine model (n = 22). Hemodynamic data (pressure‐volume loops, strain‐analysis of echocardiographic data and coronary flow measurements) were evaluated retrospectively for the short‐term right ventricular compensatory mechanisms and limits (Roehl et al. [2012] Acta Anaesthesiol. Scand., 56:449–58) 10 animals showed stable arterial blood pressures, whereas 12 pigs exhibited a significant drop of 16.4 ± 9.9 mmHg. Cardiac output and heart rate were comparable in both groups. In contrast, right ventricular contractility and coronary flow only rose in the stable group. The unchanging values in the decrease group correlated with an increasing ST‐segment depression and a loss of ventricular synchronism and resulted in a larger septum bulging to the right ventricle. Simultaneously, a reduced left‐ventricular end‐diastolic volume and a missing improvement in contractility in the posterior septal and inferior free wall of the left ventricle have been observed. Our findings suggest that right ventricular compensation during acute pulmonary hypertension is strongly dependent on the individual capability to increase coronary flow. The cause for inter‐individual variability could be the dimension and reactivity of the coronary system.

Pathophysiology, incidence, management, and consequences of cardiac arrhythmia in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension

Arrhythmias are increasingly recognized as serious, end-stage complications of pre-capillary pulmonary hypertension, including pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). Although arrhythmias contribute to symptoms, morbidity, in-hospital mortality, and possibly sudden death in PAH/CTEPH, there remains a paucity of epidemiologic, pathophysiologic, and outcome data to guide management of these patients. This review summarizes the most current evidence on the topic: from the molecular mechanisms driving arrhythmia in the hypertrophied or failing right heart, to the clinical aspects of epidemiology, diagnosis, and management.

Intra-tracheal gene delivery of aerosolized SERCA2a to the lung suppresses ventricular arrhythmias in a model of pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) results in right ventricular (RV) failure, electro-mechanical dysfunction and heightened risk of sudden cardiac death (SCD), although exact mechanisms and predisposing factors remain unclear. Because impaired chronotropic response to exercise is a strong predictor of early mortality in patients with PAH, we hypothesized that progressive elevation in heart rate can unmask ventricular tachyarrhythmias (VT) in a rodent model of monocrotaline (MCT)-induced PAH. We further hypothesized that intra-tracheal gene delivery of aerosolized AAV1.SERCA2a (AAV1.S2a), an approach which improves pulmonary vascular remodeling in PAH, can suppress VT in this model.

OBJECTIVE

To determine the efficacy of pulmonary AAV1.S2a in reversing electrophysiological (EP) remodeling and suppressing VT in PAH.

METHODS

Male rats received subcutaneous injection of MCT (60 mg/kg) leading to advanced PAH. Three weeks following MCT, rats underwent intra-tracheal delivery of aerosolized AAV1.S2a (MCT + S2a, N = 8) or saline (MCT, N = 9). Age-matched rats served as controls (CTRL, N = 7). The EP substrate and risk of VT were determined using high-resolution optical action potential (AP) mapping ex vivo. The expression levels of key ion channel subunits, fibrosis markers and hypertrophy indices were measured by RT-PCR and histochemical analyses.

RESULTS

Over 80% of MCT but none of the CTRL hearts were prone to sustained VT by rapid pacing (P < .01). Aerosolized gene delivery of AAV1.S2a to the lung suppressed the incidence of VT to <15% (P < .05). Investigation of the EP substrate revealed marked prolongation of AP duration (APD), increased APD heterogeneity, a reversal in the trans-epicardial APD gradient, and marked conduction slowing in untreated MCT compared to CTRL hearts. These myocardial EP changes coincided with major remodeling in the expression of K and Ca channel subunits, decreased expression of Cx43 and increased expression of pro-fibrotic and pro-hypertrophic markers. Intra-tracheal gene delivery of aerosolized AAV1 carrying S2a but not luciferase resulted in selective upregulation of the human isoform of SERCA2a in the lung but not the heart. This pulmonary intervention, in turn, ameliorated MCT-induced APD prolongation, reversed spatial APD heterogeneity, normalized myocardial conduction, and suppressed the incidence of pacing-induced VT. Comparison of the minimal conduction velocity (CV) generated at the fastest pacing rate before onset of VT or at the end of the protocol revealed significantly lower values in untreated compared to AAV1.S2a treated PAH and CTRL hearts. Reversal of EP remodeling by pulmonary AAV1.S2a gene delivery was accompanied by restored expression of key ion channel transcripts. Restored expression of Cx43 and collagen but not the pore-forming Na channel subunit Nav1.5 likely ameliorated VT by improving CV at rapid rates in PAH.

CONCLUSION

Aerosolized AAV1.S2a gene delivery selectively to the lungs ameliorates myocardial EP remodeling and VT susceptibility at rapid heart rates. Our findings highlight for the first time the utility of a non-cardiac gene therapy approach for arrhythmia suppression.

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.

Isolated heart model demonstrates evidence of contractile and diastolic dysfunction in right ventricles from rats with sugen/hypoxia-induced pulmonary hypertension

Although extensively used for the study of left ventricular function, limited experience exists with the isolated heart model in the evaluation of right ventricular (RV) function. In particular, no published experience exists with this tool in sugen/hypoxia‐induced pulmonary hypertension (SuHx‐PH), a frequently used model of severe and progressive PH. We sought to characterize markers of RV contractile and diastolic function in SuHx‐PH and to establish their relationship with markers of maladaptive RV remodeling. Hearts were excised from anesthetized Sprague Dawley rats with or without SuHx‐PH and perfused via the aorta using a Langendorff preparation. We explored the Frank–Starling relationship of RV function (RV developed pressure, dP/dt_max, and dP/dt_min; all normalized to RV mass) by increasing RV end‐diastolic pressure (RVEDP) from 0 to 40 mmHg. Functional studies were complemented by quantification of RV pro‐apoptotic signaling (bcl2/bax), procontractile signaling (apelin), and stress response signaling (p38MAPK activation). Pearson's correlation analysis was performed for functional and biochemical parameters. SuHx‐RVs exhibited severe RV dysfunction with marked hypertrophy and decreased echocardiographic cardiac output. For any given RVEDP, SuHx‐RVs demonstrated less developed pressure and lower dP/dt_max, as well as less pronounced dP/dt_min, suggestive of decreased contractile and diastolic function. SuHx‐RVs exhibited decreased bcl2/bax ratios, apelin expression, and p38MAPK activation. Bcl2/bax and apelin RNA abundance correlated positively with RV developed pressure and dP/dt_max and negatively with dP/dt_min. p38MAPK activation correlated positively with RV developed pressure. We conclude that SuHx‐RVs exhibit severe contractile and diastolic dysfunction. Increased pro‐apoptotic signaling and attenuated procontractile and stress response signaling may contribute to these functional alterations.

Right ventricular dyssynchrony and exercise capacity in idiopathic pulmonary arterial hypertension

Survival in patients with pulmonary arterial hypertension (PAH) is determined by right ventricular (RV) function adaptation to afterload. How altered RV function impacts on exercise capacity in PAH is not exactly known.

104 idiopathic PAH (IPAH) patients aged 52±14 years underwent a diagnostic right heart catheterisation, a comprehensive echocardiography including two-dimensional speckle tracking for RV dyssynchrony evaluation and a cardiopulmonary exercise test. Multivariate analyses were performed to identify independent predictors of peak oxygen uptake (peakV′O2).

A first multivariate analysis of only resting haemodynamic variables identified cardiac index, right atrial (RA) pressure and pulmonary arterial compliance as independent predictors, with low predictive capacity (r2=0.31; p<0.001). A second multivariate analysis model which considered only echocardiographic parameters but without RV dyssynchrony, identified RV fractional area change (FAC) and RA area as independent predictors with still low predictivity (r2=0.35; p<0.001). Adding RV dyssynchrony to the second model increased its predictivity (r2=0.48; p<0.001). Repetition of the three multivariate analyses in patients with preserved RVFAC confirmed that inclusion of RV dyssynchrony results in the highest predictive capability of peakV′O2(r2=0.53; p=0.001).

A comprehensive echocardiography with speckle tracking-derived assessment of the heterogeneity of RV contraction improves the prediction of aerobic exercise capacity in IPAH.

Current Interventional and Surgical Management of Congenital Heart Disease: Specific Focus on Valvular Disease and Cardiac Arrhythmias

Successful outcome in the care of patients with congenital heart disease depends on a comprehensive multidisciplinary team. Surgery is offered for almost every heart defect, despite complexity. Early mortality for cardiac surgery in the neonatal period is ≈10% and beyond infancy is <5%, with 90% to 95% of patients surviving with a good quality of life into the adult years. Advances in imaging have facilitated accurate diagnosis and planning of interventions and surgical procedures. Similarly, advances in the perioperative medical management of patients, particularly with intensive care, has also contributed to improving outcomes. Arrhythmias and heart failure are the most common late complications for the majority of defects, and reoperation for valvar problems is common. Lifelong surveillance for monitoring of recurrent or residual structural heart defects, as well as periodic assessment of cardiac function and arrhythmia monitoring, is essential for all patients. The field of congenital heart surgery is poised to incorporate new innovations such as bioengineered cells and scaffolds that will iteratively move toward bioengineered patches, conduits, valves, and even whole organs.

Altered synchrony of right ventricular contraction in borderline pulmonary hypertension

Imaging studies have shown that pulmonary hypertension (PH) is associated with inhomogenous right ventricular (RV) regional contraction, or dyssynchrony, and that this is of prognostic relevance. This study aimed at the identification and functional significance of RV dyssynchrony in borderline PH defined by a mean pulmonary artery pressure between (mPAP) 20 and 25 mmHg. RV dyssynchrony was measured by 2-dimensional speckle tracking echocardiography in 17 patients with pulmonary arterial hypertension (PAH), 13 patients with borderline PH and 14 controls. Dyssynchrony was defined as the R-R interval-corrected standard deviation of the times to peak-systolic strain for the basal and medium segments of the RV. All the PH patients underwent a right heart catheterization. RV dyssynchrony amounted to 69 ± 34 ms in PAH, 47 ± 23 ms in borderline PH and 8 ± 6 ms in controls, all different from each other (p < 0.05). RV dyssynchrony in borderline PH was the only parameter of RV systolic dysfunction in 11 of 13 (85%) of the patients. RV dyssynchrony was accompanied by postsystolic shortening and correlated to RV fractional area change, not to mPAP or pulmonary vascular resistance. RV dyssynchrony occurs in borderline PH and may reflect early RV-arterial uncoupling.

Right heart-pulmonary circulation unit and cardiac resynchronization therapy

Clinical response to cardiac resynchronization therapy (CRT) has been known for years to be highly variable, with a spectrum of responses from no change or even deterioration of cardiac function to spectacular improvements. In the plethora of clinical, echocardiographic, biohumoral, and electrophysiological predictors of response to CRT and postimplant issues besides patient selection, the role of right ventricular (RV) function has been largely overlooked. In reviewing current evidence, we noticed conflicting results between observational studies and randomized trials not only concerning the impact of baseline RV function on CRT efficacy but also on the effects of CRT on RV size and function. Hence, we aimed to provide a critical reappraisal of current knowledge and unresolved issues on the reciprocal interactions between RV function and CRT, shifting the spotlight on the concept of right heart pulmonary circulation unit and on the clinical and prognostic significance of impaired ventricular-arterial coupling reserve. In this viewpoint, we propose that (1) CRT should not be denied to potential candidate because of "isolated" RV dysfunction and (2) assessment of baseline right heart pulmonary circulation unit and its dynamic response to pharmacological stress should be considered in future studies, as well as in the preimplant evaluation of individual candidates among other clinical factors.

Left Ventricular Diastolic Function Assessment of a Heterogeneous Cohort of Pulmonary Arterial Hypertension Patients

BACKGROUND

Pulmonary arterial hypertension (PAH) is known to trigger right ventricular (RV) remodeling that might compromise left ventricular (LV) filling due to inter-ventricular interdependence. In this study, we aimed to examine standard echocardiographic measurements of LV diastolic function in PAH patients.

METHODS

In this retrospective study, we identified clinical as well as complete echocardiographic data from 128 chronic PAH patients to fully assess LV diastolic dysfunction (LVDD) using standard recommended Doppler guidelines. Accordingly, patients were divided into three groups: LVDD 0, LVDD 1 and LVDD 2.

RESULTS

The mean age of the studied population was 57 ± 14 years with a mean pulmonary artery systolic pressure (PASP) of 55 ± 21 mm Hg. A total of 36% of the study patients had normal LV diastolic function. However, 64% had LVDD with LVDD stage 1 being the most common (48%). In terms of echocardiographic data, significant differences were found among the three LVDD groups in regards to PASP, LV end systolic and diastolic volumes, tricuspid annular plane systolic excursion, right ventricular fractional area change as well as many other tissue Doppler imaging parameters. Finally, just age and PASP were predictors of abnormal LV diastolic function (P < 0.05).

CONCLUSIONS

Impaired relaxation is a common abnormality in PAH patients. Additional studies are warranted to determine whether LVDD alters prognosis or is related to changes in the symptomatic profile of this group of patients.

Why septal motion is a marker of right ventricular failure in pulmonary arterial hypertension: mechanistic analysis using a computer model

Rapid leftward septal motion (RLSM) during early left ventricular (LV) diastole is observed in patients with pulmonary arterial hypertension (PAH). RLSM exacerbates right ventricular (RV) systolic dysfunction and impairs LV filling. Increased RV wall tension caused by increased RV afterload has been suggested to cause interventricular relaxation dyssynchrony and RLSM in PAH. Simulations using the CircAdapt computational model were used to unravel the mechanism underlying RLSM by mechanistically linking myocardial tissue and pump function. Simulations of healthy circulation and mild, moderate, and severe PAH were performed. We also assessed the effects on RLSM when PAH coexists with RV or LV contractile dysfunction. Our results showed prolonged RV shortening in PAH causing interventricular relaxation dyssynchrony and RLSM. RLSM was observed in both moderate and severe PAH. A negative transseptal pressure gradient only occurred in severe PAH, demonstrating that negative pressure gradient does not entirely explain septal motion abnormalities. PAH coexisting with RV contractile dysfunction exacerbated both interventricular relaxation dyssynchrony and RLSM. LV contractile dysfunction reduced both interventricular relaxation dyssynchrony and RLSM. In conclusion, dyssynchrony in ventricular relaxation causes RLSM in PAH. Onset of RLSM in patients with PAH appears to indicate a worsening in RV function and hence can be used as a sign of RV failure. However, altered RLSM does not necessarily imply an altered RV afterload, but it can also indicate altered interplay of RV and LV contractile function. Reduction of RLSM can result from either improved RV function or a deterioration of LV function.NEW & NOTEWORTHY A novel approach describes the mechanism underlying abnormal septal dynamics in pulmonary arterial hypertension. Change in motion is not uniquely induced by altered right ventricular afterload, but also by altered ventricular relaxation dyssynchrony. Extension or change in motion is a marker reflecting interplay between right and left ventricular contractility.

Adverse ventricular-ventricular interactions in right ventricular pressure load: Insights from pediatric pulmonary hypertension versus pulmonary stenosis

Right ventricular (RV) pressure overload has a vastly different clinical course in children with idiopathic pulmonary arterial hypertension (iPAH) than in children with pulmonary stenosis (PS). While RV function is well recognized as a key prognostic factor in iPAH, adverse ventricular–ventricular interactions and LV dysfunction are less well characterized and the pathophysiology is incompletely understood. We compared ventricular–ventricular interactions as hypothesized drivers of biventricular dysfunction in pediatric iPAH versus PS. Eighteen iPAH, 16 PS patients and 18 age‐ and size‐matched controls were retrospectively studied. Cardiac cycle events were measured by M‐mode and Doppler echocardiography. Measurements were compared between groups using ANOVA with post hoc Dunnet's or ANCOVA including RV systolic pressure (RVSP; iPAH 96.8 ± 25.4 mmHg vs. PS 75.4 ± 18.9 mmHg; P = 0.011) as a covariate. RV‐free wall thickening was prolonged in iPAH versus PS, extending beyond pulmonary valve closure (638 ± 76 msec vs. 562 ± 76 msec vs. 473 ± 59 msec controls). LV and RV isovolumetric relaxation were prolonged in iPAH (P < 0.001; LV 102.8 ± 24.1 msec vs. 63.1 ± 13.7 msec; RV 95 [61–165] vs. 28 [0–43]), associated with adverse septal kinetics; characterized by rightward displacement in early systole and leftward displacement in late RV systole (i.e., early LV diastole). Early LV diastolic filling was decreased in iPAH (73 ± 15.9 vs. PS 87.4 ± 14.4 vs. controls 95.8 ± 12.5 cm/sec; P = 0.004). Prolonged RVFW thickening, prolonged RVFW isovolumetric times, and profound septal dyskinesia are associated with interventricular mechanical discoordination and decreased early LV filling in pediatric iPAH much more than PS. These adverse mechanics affect systolic and diastolic biventricular efficiency in iPAH and may form the basis for worse clinical outcomes. We used clinically derived data to study the pathophysiology of ventricular–ventricular interactions in right ventricular pressure overload, demonstrating distinct differences between pediatric pulmonary arterial hypertension (iPAH) and pulmonary stenosis (PS). Altered timing of right ventricular free wall contraction and profound septal dyskinesia are associated with interventricular mechanical discoordination and decreased early LV filling in iPAH much more than PS. These adverse mechanics affect systolic and diastolic biventricular efficiency, independent of right ventricular systolic pressure.

Dissecting the Effects of Ischemia and Reperfusion on the Coronary Microcirculation in a Rat Model of Acute Myocardial Infarction

BACKGROUND

Microvascular injury (MVI) after coronary ischemia-reperfusion is associated with high morbidity and mortality. Both ischemia and reperfusion are involved in MVI, but to what degree these phases contribute is unknown. Understanding the etiology is essential for the development of new potential therapies.

METHODS AND FINDINGS

Rats were divided into 3 groups receiving either 30 minutes ischemia, 90 minutes ischemia or 30 minutes ischemia followed by 60 minutes reperfusion. Subsequently hearts were ex-vivo perfused in a Langendorff-model. Fluorescence and electron microscopy was used for analysis of capillary density, vascular permeability and ultrastructure. Most MVI was observed after 30 minutes ischemia followed by 60 minutes reperfusion. In comparison to the 30' and 90' ischemia group, wall thickness decreased (207.0±74 vs 407.8±75 and 407.5±71, p = 0.02). Endothelial nuclei in the 30'-60' group showed irreversible damage and decreased chromatin density variation (50.5±9.4, 35.4±7.1 and 23.7±3.8, p = 0.03). Cell junction density was lowest in the 30'-60' group (0.15±0.02 vs 2.5±0.6 and 1.8±0.7, p<0.01). Microsphere extravasation was increased in both the 90' ischemia and 30'-60' group.

CONCLUSIONS

Ischemia alone for 90 minutes induces mild morphological changes to the coronary microcirculation, with increased vascular permeability. Ischemia for 30 minutes, followed by 60 minutes of reperfusion, induces massive MVI. This shows the direct consequences of reperfusion on the coronary microcirculation. These data imply that a therapeutic window exists to protect the microcirculation directly upon coronary revascularization.

Right ventricular failure due to chronic pressure load: What have we learned in animal models since the NIH working group statement?

Right ventricular (RV) failure determines outcome in patients with pulmonary hypertension, congenital heart diseases and in left ventricular failure. In 2006, the Working Group on Cellular and Molecular Mechanisms of Right Heart Failure of the NIH advocated the development of preclinical models to study the pathophysiology and pathobiology of RV failure. In this review, we summarize the progress of research into the pathobiology of RV failure and potential therapeutic interventions. The picture emerging from this research is that RV adaptation to increased afterload is characterized by increased contractility, dilatation and hypertrophy. Clinical RV failure is associated with progressive diastolic deterioration and disturbed ventricular–arterial coupling in the presence of increased contractility. The pathobiology of the failing RV shows similarities with that of the LV and is marked by lack of adequate increase in capillary density leading to a hypoxic environment and oxidative stress and a metabolic switch from fatty acids to glucose utilization. However, RV failure also has characteristic features. So far, therapies aiming to specifically improve RV function have had limited success. The use of beta blockers and sildenafil may hold promise, but new therapies have to be developed. The use of recently developed animal models will aid in further understanding of the pathobiology of RV failure and development of new therapeutic strategies.

Novel Therapeutic Strategies for Reducing Right Heart Failure Associated Mortality in Fibrotic Lung Diseases

Fibrotic lung diseases carry a significant mortality burden worldwide. A large proportion of these deaths are due to right heart failure and pulmonary hypertension. Underlying contributory factors which appear to play a role in the mechanism of progression of right heart dysfunction include chronic hypoxia, defective calcium handling, hyperaldosteronism, pulmonary vascular alterations, cyclic strain of pressure and volume changes, elevation of circulating TGF-β, and elevated systemic NO levels. Specific therapies targeting pulmonary hypertension include calcium channel blockers, endothelin (ET-1) receptor antagonists, prostacyclin analogs, phosphodiesterase type 5 (PDE5) inhibitors, and rho-kinase (ROCK) inhibitors. Newer antifibrotic and anti-inflammatory agents may exert beneficial effects on heart failure in idiopathic pulmonary fibrosis. Furthermore, right ventricle-targeted therapies, aimed at mitigating the effects of functional right ventricular failure, include β-adrenoceptor (β-AR) blockers, angiotensin-converting enzyme (ACE) inhibitors, antioxidants, modulators of metabolism, and 5-hydroxytryptamine-2B (5-HT2B) receptor antagonists. Newer nonpharmacologic modalities for right ventricular support are increasingly being implemented. Early, effective, and individualized therapy may prevent overt right heart failure in fibrotic lung disease leading to improved outcomes and quality of life.

Melatonin as a preventive and curative therapy against pulmonary hypertension

Pulmonary hypertension (PH) is characterized by elevated pulmonary arterial pressure, which leads to right ventricular (RV) hypertrophy and failure. The pathophysiological mechanisms of PH remain unclear but oxidative stress is believed to contribute to RV dysfunction. Melatonin is a powerful antioxidant and is cardioprotective against ischemia-reperfusion injury and hypertension. Therefore, we hypothesized that a chronic treatment with melatonin, given as a curative or preventive therapy, may confer cardiovascular benefits in PH. PH was induced in Long Evans rats (n ≥ 6 per group), with a single subcutaneous injection of monocrotaline (MCT, 80 mg/kg). Melatonin was given daily in the drinking water, with the treatment starting either on the day of the injection of MCT (dose testing: melatonin 75 ng/L and 6 mg/kg), 14 days after the injection of MCT (curative treatment: 6 mg/kg), or 5 days before the injection (preventive treatment: 6 mg/kg). The development of PH was assessed by measuring RV hypertrophy, RV function, cardiac interstitial fibrosis, and plasma oxidative stress. Compared with controls, MCT-treated rats displayed RV hypertrophy and dysfunction, increased interstitial fibrosis, and elevated plasma oxidative stress. A chronic melatonin treatment (75 ng/L or 6 mg/kg) reduced RV hypertrophy, improved RV function and reduced plasma oxidative stress. Curative and preventive treatment improved RV functional and plasma oxidative stress parameters and reduced cardiac interstitial fibrosis. Our data demonstrate that melatonin confers cardioprotection in this model of PH. As melatonin is an inexpensive and safe drug, we propose that clinical investigation of the effects of melatonin on RV function in patients with PH should be considered.

Ebstein anomaly review: what's now, what's next?

Ebstein anomaly accounts for 1% of all congenital heart disease. It is a right ventricular myopathy with failure of tricuspid valve delamination and highly variable tricuspid valve morphology that usually results in severe regurgitation. It is the only congenital heart lesion that has a range of clinical presentations, from the severely symptomatic neonate to an asymptomatic adult. Neonatal operation has high operative mortality, whereas operation performed beyond infancy and into adulthood has low operative mortality. Late survival and quality of life for hospital survivors are excellent for the majority of patients in all age brackets. Atrial tachyarrhythmias are the most common late complication. There have been more techniques of tricuspid repair reported in the literature than any other congenital or acquired cardiac lesion. This is largely due to the infinite anatomic variability encountered with this anomaly. The cone reconstruction of Ebstein anomaly can achieve near anatomic restoration of the tricuspid valve anatomy. Early and intermediate results with these repairs are promising. Reduced right ventricular function continues to be a challenge for some patients, as is the need for reoperation for recurrent tricuspid regurgitation. The purpose of this article is to outline the current standard of care for diagnosis and treatment of Ebstein anomaly and describe innovative strategies to address poor right ventricular function and associated right-sided heart failure.

Treatment for pulmonary arterial hypertension-associated right ventricular dysfunction

Pulmonary arterial hypertension (PAH) includes a heterogeneous group of diseases characterized by pulmonary vasoconstriction and remodeling of the lung circulation. Although PAH is a disease of the lungs, patients with PAH frequently die of right heart failure. Indeed, survival of patients with PAH depends on the adaptive response of the right ventricle (RV) to the changes in the lung circulation. PAH-specific drugs affect the function of the RV through afterload reduction and perhaps also through direct effects on the myocardium. Prostacyclins, type 5 phosphodiesterase inhibitors, and guanylyl cyclase stimulators may directly enhance myocardial contractility through increased cyclic adenosine and guanosine monophosphate availability. Although this may initially improve cardiac performance, the long-term effects on myocardial oxygen consumption and function are unclear. Cardiac effects of endothelin receptor antagonists may be opposite, as endothelin-1 is known to suppress cardiac contractility. Because PAH is increasingly considered as a disease with quasimalignant growth of cells in the pulmonary vascular wall, therapies are being developed that inhibit hypertrophy and angiogenesis, and promote apoptosis. The inherent danger of these therapies is a further compromise to the already ischemic, fibrotic, and dysfunctional RV. More recently, the right heart has been identified as a direct treatment target in PAH. The effects of well established therapies for left heart failure, such as β-adrenergic receptor blockers, inhibitors of the renin-angiotensin system, exercise training, and assist devices, are currently being investigated in PAH. Future treatment of patients with PAH will likely consist of a multifaceted approaches aiming to reduce the pressure in the lung circulation and improving right heart adaptation simultaneously.

Wall Thickness, Pulmonary Hypertension, and Diastolic Filling Abnormalities Predict Response to Postoperative Biventricular Pacing

OBJECTIVE

Post-cardiopulmonary bypass biventricular pacing improves hemodynamics but without clearly defined predictors of response. Based on preclinical studies and prior observations, it was suspected that diastolic dysfunction or pulmonary hypertension is predictive of hemodynamic benefit.

DESIGN

Randomized controlled study of temporary biventricular pacing after cardiopulmonary bypass.

SETTING

Single-center study at university-affiliated tertiary care hospital.

INTERVENTIONS

Patients who underwent bypass with preoperative ejection fraction ≤40% and QRS duration ≥100 ms or double-valve surgery were enrolled. At 3 time points between separation from bypass and postoperative day 1, pacing delays were varied to optimize hemodynamics.

PARTICIPANTS

Data from 43 patients were analyzed.

MEASUREMENTS AND MAIN RESULTS

Cardiac output and arterial pressure were measured under no pacing, atrial pacing, and biventricular pacing. Preoperative echocardiograms and pulmonary artery catheterizations were reviewed, and measures of both systolic and diastolic function were compared to hemodynamic response. Early after separation, improvement in cardiac output was positively correlated with pulmonary vascular resistance (R(2) = 0.97, p<0.001), ventricle wall thickness (R(2) = 0.72, p = 0.002)), and E/e', a measure of abnormal diastolic ventricular filling velocity (R(2) = 0.56, p = 0.04). Similar trends were seen with mean arterial pressure. QRS duration and ejection fraction did not correlate significantly with improvements in hemodynamics.

CONCLUSIONS

There may be an effect of biventricular pacing related to amelioration of abnormal diastolic filling patterns rather than electrical resynchronization in the postoperative state.

Novel technologies and devices for monitoring and treating pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature associated with significant morbidity and mortality. Despite significant advances in the past 2 decades with the development of pharmacological therapies to target key molecular pathways of PAH, there remains an ongoing need for novel technologies and devices for diagnosis, monitoring, and treatment to improve PAH outcomes. The advent of sophisticated imaging tools, including cardiac magnetic resonance imaging, positron emission tomography, and speckle tracking echocardiography, offer novel opportunities for advanced, noninvasive assessment of right ventricular function, the most powerful predictor of death in patients with PAH. Noninvasive cardiac output monitors and implantable hemodynamic sensors are among the additional promising novel technologies that might offer daily access to hemodynamic data to influence clinical decision-making and potentially improve outcomes. Percutaneous interventional therapeutics might offer a nonpharmacological treatment option in select patients with PAH, ranging from the percutaneous creation of right to left shunts, pulmonary artery denervation, and right ventricular pacing. Finally, mechanical circulatory support with durable ventricular assist devices offers hope to one day provide a realistic strategy to treat life-threatening right ventricular failure in PAH. Future clinical trials and carefully designed prospective observational studies will be needed to evaluate the full potential of many of these novel devices and technologies for monitoring and treating PAH.

Is cardiac resynchronization therapy for right ventricular failure in pulmonary arterial hypertension of benefit?

Pulmonary arterial hypertension is a manifestation of a group of disorders leading to pulmonary vascular remodeling and increased pulmonary pressures. The right ventricular (RV) response to chronic pressure overload consists of myocardial remodeling, which is in many ways similar to that seen in left ventricular (LV) failure. Maladaptive myocardial remodeling often leads to intraventricular and interventricular dyssychrony, an observation that has led to cardiac resynchronization therapy (CRT) for LV failure. CRT has proven to be an effective treatment strategy in subsets of patients with LV failure resulting in improvement in LV function, heart failure symptoms, and survival. Current therapy for pulmonary arterial hypertension is based on decreasing pulmonary vascular resistance, and there is currently no effective therapy targeting the right ventricle or maladaptive ventricular remodeling in these patients. This review focuses on the RV response to chronic pressure overload, its effect on electromechanical coupling and synchrony, and how lessons learned from left ventricular cardiac resynchronization might be applied as therapy for RV dysfunction in the context of pulmonary arterial hypertension.

Interventricular Dyssynchrony Using Tagging Magnetic Resonance Imaging Predicts Right Ventricular Dysfunction in Adult Congenital Heart Disease

PURPOSE

Right ventricular (RV) failure and ventricular dyssynchrony are strong determinants of prognosis in patients with adult congenital heart disease (ACHD). The aim of this study was to investigate the relationship between interventricular dyssynchrony (IVD) using cine-tagged magnetic resonance imaging (MRI) and RV dysfunction in ACHD patients.

MATERIALS AND METHODS

Sixty-seven patients with ACHD (38 with repaired tetralogy of Fallot; 22 with atrial septal defect; seven with ventricular septal defect) underwent tagging MRI. Time curves of myocardial circumferential strains for RV and left ventricular (LV) free walls were delivered from short-axis cine-tagging images. Contraction delay between RV and LV free walls was computed by cross-correlation analysis of the two strain time curves and was defined as the IVD time (msec).

RESULTS

IVD was significantly greater for patients with RV ejection fraction (RVEF) <40% (116 ± 58 msec) than for patients with RVEF ≥ 40% (65 ± 54 msec) and was significantly greater for patients with RV systolic pressure ≥ 40 mm Hg (112 ± 59 msec) than for patients with RV systolic pressure <40 mm Hg (49 ± 28 msec). Receiver operating characteristic analysis revealed optimal IVD thresholds for detecting patients with RVEF <40% with C-statistics of 0.76 and patients with RV systolic pressure ≥ 40 mm Hg with C-statistics of 0.81.

CONCLUSION

Quantification of IVD was possible using RV and LV strains derived from tagging MRI. IVD, represented as the time difference between LV and RV contractions, correlates with RV dysfunction. IVD may thus offer an indicator for RV failure in ACHD.

Right heart adaptation to pulmonary arterial hypertension: physiology and pathobiology

Survival in patients with pulmonary arterial hypertension (PAH) is closely related to right ventricular (RV) function. Although pulmonary load is an important determinant of RV systolic function in PAH, there remains a significant variability in RV adaptation to pulmonary hypertension. In this report, the authors discuss the emerging concepts of right heart pathobiology in PAH. More specifically, the discussion focuses on the following questions. 1) How is right heart failure syndrome best defined? 2) What are the underlying molecular mechanisms of the failing right ventricle in PAH? 3) How are RV contractility and function and their prognostic implications best assessed? 4) What is the role of targeted RV therapy? Throughout the report, the authors highlight differences between right and left heart failure and outline key areas of future investigation.

ESC Working Group on Myocardial Function Position Paper: how to study the right ventricle in experimental models

The right ventricle has become an increasing focus in cardiovascular research. In this position paper, we give a brief overview of the specific pathophysiological features of the right ventricle, with particular emphasis on functional and molecular modifications as well as therapeutic strategies in chronic overload, highlighting the differences from the left ventricle. Importantly, we put together recommendations on promising topics of research in the field, experimental study design, and functional evaluation of the right ventricle in experimental models, from non-invasive methodologies to haemodynamic evaluation and ex vivo set-ups.

Myocardial effects of local shock wave therapy in a Langendorff model

OBJECTIVE

Applying shock waves to the heart has been reported to stimulate the heart and alter cardiac function. We hypothesized that shock waves could be used to diagnose regional viability.

METHOD

We used a Langendorff model to investigate the acute effects of shock waves at different energy levels and times related to systole, cycle duration and myocardial function.

RESULTS

We found only a small time window to use shock waves. Myocardial fibrillation or extrasystolic beats will occur if the shock wave is placed more than 15 ms before or 30 ms after the onset of systole. Increased contractility and augmented relaxation were observed after the second beat, and these effects decreased after prolonging the shock wave delay from 15 ms before to 30 ms after the onset of systole. An energy dependency could be found only after short delays (-15 ms). The involved processes might include post-extrasystolic potentiation and simultaneous pacing.

CONCLUSION

In summary, we found that low-energy shock waves can be a useful tool to stimulate the myocardium at a distance and influence function.

Electromechanical dyssynchrony and resynchronization of the failing heart

Patients with heart failure and decreased function frequently develop discoordinate contraction because of electric activation delay. Often termed dyssynchrony, this further decreases systolic function and chamber efficiency and worsens morbidity and mortality. In the mid- 1990s, a pacemaker-based treatment termed cardiac resynchronization therapy (CRT) was developed to restore mechanical synchrony by electrically activating both right and left sides of the heart. It is a major therapeutic advance for the new millennium. Acute chamber effects of CRT include increased cardiac output and mechanical efficiency and reduced mitral regurgitation, whereas reduction in chamber volumes ensues more chronically. Patient candidates for CRT have a prolonged QRS duration and discoordinate wall motion, although other factors may also be important because ≈30% of such selected subjects do not respond to the treatment. In contrast to existing pharmacological inotropes, CRT both acutely and chronically increases cardiac systolic function and work, yet it also reduces long-term mortality. Recent studies reveal unique molecular and cellular changes from CRT that may also contribute to this success. Heart failure with dyssynchrony displays decreased myocyte and myofilament function, calcium handling, β-adrenergic responsiveness, mitochondrial ATP synthase activity, cell survival signaling, and other changes. CRT reverses many of these abnormalities often by triggering entirely new pathways. In this review, we discuss chamber, circulatory, and basic myocardial effects of dyssynchrony and CRT in the failing heart, and we highlight new research aiming to better target and implement CRT, as well as leverage its molecular effects.

Novel therapeutic approaches to preserve the right ventricle

The right ventricle (RV) is increasingly recognized for its role in heart disease. In fact, RV function is a strong predictor of outcome in patients with cardiovascular disease. Although the focus in heart failure has been on the left ventricle (LV), recently the spotlight has been shifting to include the RV. The RV and LV have different embryological origins and respond differently to stressors and to therapies. Newer therapies targeting the RV have been investigated in an attempt to improve right-ventricular adaptation to cardiovascular diseases. In this review, we summarize the differences between the RV and LV and focus on novel therapies that target the RV.

Effects of exercise on monocrotaline-induced changes in right heart function and pulmonary artery remodeling in rats

Pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT) is an experimental protocol of right heart failure. We analyzed the role of exercise training on the right ventricle structure and function, pulmonary artery remodeling, and GSK-3β expression. Rats were divided among the following groups: sedentary control (SC), sedentary monocrotaline (SM), trained control (TC), and trained monocrotaline (TM). Rats underwent exercise training for a period of 5 weeks, with 3 weeks post-MCT injection. Rats in the SM and TM groups presented with an increase in right ventricle hypertrophy indexes and lung congestion. The right ventricular end diastolic pressure (RVEDP), right ventricular systolic pressure (RVSP), and its minimum and maximal pressure derivates were increased in the SM and TM groups. The right ventricle interstitial volume pulmonary artery thickness and p-GSK-3β/GSK-3β were increased in the MCT groups as compared with the control groups. The TM group had a reduction in interstitial volume, p-GSK-3β/GSK-3β ratio, pulmonary artery thickness, RVEDP, and an increase in intramyocardial vessels volume as compared with the SM group. The overall results have shown that the exercise protocol used promoted positive changes in right ventricle and pulmonary artery remodeling. These observations also suggest that structural remodeling may be influenced by signaling proteins, such as GSK-3β.

Arrhythmias in pulmonary arterial hypertension

Cardiac arrhythmias are important contributors to morbidity and mortality in patients with pulmonary arterial hypertension (PAH). Such patients manifest a substrate resulting from altered autonomics, repolarization abnormalities, and ischemia. Supraventricular arrhythmias such as atrial fibrillation and flutter are associated with worsened outcomes, and maintenance of sinus rhythm is a goal. Sudden death is a relatively common issue, though the contribution of malignant ventricular arrhythmias versus bradyarrhythmias differs from non-PAH patients. Congenital heart disease patients with PAH benefit from catheter ablation of medically refractory arrhythmias. Clinical studies of defibrillator/pacemaker therapy for primary prevention against sudden death in PAH patients are lacking.

The effects of asymmetric ventricular filling on left-right ventricular interaction in the normal rat heart

Heart failure is characterised by ventricular dysfunction and with the potential for changes to ventricular volumes constraining the mechanical performance of the heart. The contribution of this interaction from geometric changes rather than fibrosis or metabolic changes is unclear. Using the constant pressure Langendorff-perfused rat heart, the volume interaction between left ventricle (LV) and right ventricle (RV) was investigated. RV diastolic stiffness (P < 0.001) and developed pressure (P < 0.001) were significantly lower than LV. When the RV was fixed at the end-diastolic volume (EDV) or EDV + 50 %, both LV systolic and diastolic performance were unaffected with increasing LV balloon volume. However, at fixed LV volume, RV systolic performance was significantly decreased when LV volume increased to EDV + 50 % when RV volume was increased incrementally between 50 and 300 μl (P < 0.001). Systolic interaction in RV was noted as declining RV peak systolic load with increasing LV systolic pressure (P < 0.05) and diastolic interaction was noted for RV when LV volume was increased from EDV to EDV + 50 % (P < 0.05). RV diastolic wall stress was increased with increasing LV balloon volume (P < 0.05), but LV wall stress was unaltered at fixed RV balloon volume. Taken together, increasing LV volume above EDV decreased systolic performance and triggered ventricular constraint in the RV but the RV itself had no effect on the performance of the LV. These results are consistent with overload of the LV impairing pulmonary perfusion by direct ventricular interaction with potential alteration to ventilation-perfusion characteristics within the lung.

Cardiovascular modeling in pulmonary arterial hypertension: focus on mechanisms and treatment of right heart failure using the CircAdapt model

In recent years, increased understanding of cardiovascular system dynamics has led to the development of mathematical models of the heart and circulation. Models that enable realistic simulation of ventricular mechanics and interactions under a range of conditions have the potential to provide an ideal method with which to investigate the effects of pulmonary arterial hypertension and its treatment on cardiac mechanics and hemodynamics. Such mathematical models have the potential to contribute to a personalized, patient-specific treatment approach and allow more objective diagnostic decision-making, patient monitoring, and assessment of treatment outcome. This review discusses the development of mathematical models of the heart and circulation, with particular reference to the closed-loop CircAdapt model, and how the model performs under both normal and pathophysiological (pulmonary hypertensive) conditions.

Biventricular pacing improves left ventricular function by 2-D strain in right ventricular failure

BACKGROUND

We used speckle-tracking echocardiography to test the hypothesis that regional left ventricular (LV) strain would improve during optimized biventricular pacing (BiVP) in acute right ventricular (RV) pressure overload (PO).

MATERIALS AND METHODS

Complete heart block and RVPO were induced in five open-chest fully anesthetized pigs. BiVP was optimized by adjusting atrioventricular and interventricular delays to maximize cardiac output derived from an aortic flow probe. LV short axis views were obtained during atrio-RV pacing (RVP), atrio-LV pacing (LVP), and BiVP. Intraventricular synchrony was assessed by comparing speckle-tracking echocardiography-derived time to peak (TTP) strain in the anterior septal (AS) and posterior wall segments. Segmental function was assessed using radial strain.

RESULTS

Cardiac output was higher with optimized (RV first) BiVP than with LVP (0.96 ± 0.26 L/min versus 0.89 ± 0.27 L/min; P = 0.05). AS TTP strain (502 ± 19 ms) during LVP was prolonged versus BiVP (392 ± 58 ms) and versus RVP (390 ± 53 ms) (P = 0.0018). AS TTP strain during LVP was prolonged versus posterior (502 ± 19 ms versus 396 ± 72 ms, P = 0.0011). No significant difference in TTP strain in these segments was seen with BiVP or RVP. Posterior strain (20% ± 5%) increased 66% versus AS strain (12% ± 6%) during BiVP (P = 0.0029). A similar increase occurred during RVP (posterior 20% ± 3% versus AS 12% ± 7%, P = 0.0002). Posterior strain did not increase during LVP.

CONCLUSIONS

BiVP and RVP restore intraventricular LV synchrony and increase regional function versus LVP during RVPO. RV pre-excitation unloads the RV and reduces the duration of AS contraction, facilitating synchrony of all LV segments and increasing free wall LV contraction.