Myocardial hypertrophy after pulmonary regurgitation and valve implantation in pigs

Norepinephrine and dobutamine improve cardiac index equally by supporting opposite sides of the heart in an experimental model of chronic pulmonary hypertension

BACKGROUND

Pulmonary hypertension is a significant risk factor in patients undergoing surgery. The combined effects of general anaesthesia and positive pressure ventilation can aggravate this condition and cause increased pulmonary blood pressures, reduced systemic blood pressures and ventricular contractility. Although perioperative use of inotropic support or vasopressors is almost mandatory for these patients, preference is disputed. In this study, we investigated the effects of norepinephrine and dobutamine and their ability to improve the arterio-ventricular relationship and haemodynamics in pigs suffering from chronic pulmonary hypertension.

METHOD

Pulmonary hypertension was induced in five pigs by banding the pulmonary artery at 2-3 weeks of age. Six pigs served as controls. After 16 weeks of pulmonary artery banding, the animals were re-examined under general anaesthesia using biventricular conductance catheters and a pulmonary artery catheter. After baseline measurements, the animals were exposed to both norepinephrine and dobutamine infusions in incremental doses, with a stabilising period in between the infusions. The hypothesis of differences between norepinephrine and dobutamine with incremental doses was tested using repeated two-way ANOVA and Bonferroni multiple comparisons post-test.

RESULTS

At baseline, pulmonary artery-banded animals had increased right ventricular pressure (+ 39%, p = 0.04), lower cardiac index (- 23% p = 0.04), lower systolic blood pressure (- 13%, p = 0.02) and reduced left ventricular end-diastolic volume (- 33%, p = 0.02). When incremental doses of norepinephrine and dobutamine were administered, the right ventricular arterio-ventricular coupling was improved only by dobutamine (p < 0.05). Norepinephrine increased both left ventricular end-diastolic volume and left ventricular contractility to a greater extent (p < 0.05) in pulmonary artery-banded animals. While the cardiac index was improved equally by norepinephrine and dobutamine treatments in pulmonary artery-banded animals, norepinephrine had a significantly greater effect on mean arterial pressure (p < 0.05) and diastolic arterial pressure (p < 0.05).

CONCLUSION

While norepinephrine and dobutamine improved cardiac index equally, it was obtained in different manners. Dobutamine significantly improved the right ventricular function and the arterio-ventricular coupling. Norepinephrine increased systemic resistance, thereby improving arterial pressures and left ventricular systolic function by maintaining left ventricular end-diastolic volume.

Animal models of right heart failure

Right heart failure may be the ultimate cause of death in patients with acute or chronic pulmonary hypertension (PH). As PH is often secondary to other cardiovascular diseases, the treatment goal is to target the underlying disease. We do however know, that right heart failure is an independent risk factor, and therefore, treatments that improve right heart function may improve morbidity and mortality in patients with PH. There are no therapies that directly target and support the failing right heart and translation from therapies that improve left heart failure have been unsuccessful, with the exception of mineralocorticoid receptor antagonists. To understand the underlying pathophysiology of right heart failure and to aid in the development of new treatments we need solid animal models that mimic the pathophysiology of human disease. There are several available animal models of acute and chronic PH. They range from flow induced to pressure overload induced right heart failure and have been introduced in both small and large animals. When initiating new pre-clinical or basic research studies it is key to choose the right animal model to ensure successful translation to the clinical setting. Selecting the right animal model for the right study is hence important, but may be difficult due to the plethora of different models and local availability. In this review we provide an overview of the available animal models of acute and chronic right heart failure and discuss the strengths and limitations of the different models.

Animal Models of Repaired Tetralogy of Fallot: Current Applications and Future Perspectives

Tetralogy of Fallot is the most common cyanotic congenital heart disease. Despite ongoing improvements in the initial surgical repair, there are lingering concerns regarding the long-term outcomes that may be complicated by right ventricular dysfunction, right ventricular dyssynchrony, and sudden cardiac death. The mechanisms leading to these late complications remain incompletely understood. Experimental animal models have been developed as preclinical steps to gain better insight into the pathophysiology of diseases and to develop new therapeutic strategies. This article summarizes the various types of experimental animal models of repaired tetralogy of Fallot published to date in the literature, with the aim of achieving a greater understanding of the deleterious mechanisms that may lead to these known late and sometimes lethal complications. In addition to analysing the type of animals that can be used according to a given study's objectives, needs, and constraints, the present review also evaluates the type of dysfunction that can be reproduced in our model according to the research objectives, as well as the different types of studies in which these models can be used. In view of all that, we propose a decision algorithm to create an animal model of repaired tetralogy of Fallot. This synthesis should furthermore help in the development of future studies and in the design of new experimental models, thus allowing greater insight into this disease, while not forgetting the ultimate goal of broadening future therapeutic measures to reduce the morbidity and mortality of this prevalent congenital heart disease.

Isolated pulmonary regurgitation causes decreased right ventricular longitudinal function and compensatory increased septal pumping in a porcine model

Aim

Longitudinal ventricular contraction is a parameter of cardiac performance with predictive power. Right ventricular (RV) longitudinal function is impaired in patients with free pulmonary regurgitation (PR) following corrective surgery for Tetralogy of Fallot (TOF). It remains unclear whether this is a consequence of the surgical repair, or whether it is inherent to PR. The aim of this study was to assess the relationship between longitudinal, lateral and septal pumping in a porcine model of isolated PR.

Methods

Piglets were divided into a control (n = 8) group and a treatment (n = 12) group, which received a stent in the pulmonary valve orifice, inducing PR. After 2–3 months, animals were subjected to cardiac magnetic resonance imaging. A subset of animals (n = 6) then underwent percutaneous pulmonary valve replacement (PPVR) with follow‐up 1 month later. Longitudinal, lateral and septal contributions to stroke volume (SV) were quantified by measuring volumetric displacements from end‐diastole to end‐systole in the cardiac short axis and long axis.

Results

PR resulted in a lower longitudinal contribution to RV stroke volume, compared to controls (60.0 ± 2.6% vs. 73.6 ± 3.8%; P = 0.012). Furthermore, a compensatory increase in septal contribution to RVSV was observed (11.0 ± 1.6% vs. −3.1 ± 1.5%; P < 0.0001). The left ventricle (LV) showed counter‐regulation with an increased longitudinal LVSV. Changes in RV longitudinal function were reversed by PPVR.

Conclusion

These findings suggest that PR contributes to decreased RV longitudinal function in the absence of scarring from cardiac surgery. Measurement of longitudinal RVSV may aid risk stratification and timing for interventional correction of PR in TOF patients.

Effects of milrinone and epinephrine or dopamine on biventricular function and hemodynamics in right heart failure after pulmonary regurgitation

Right ventricular failure (RVF) secondary to pulmonary regurgitation (PR) impairs right ventricular (RV) function and interrupts the interventricular relationship. There are few recommendations for the medical management of severe RVF after prolonged PR. PR was induced in 16 Danish landrace pigs by plication of the pulmonary valve leaflets. Twenty-three pigs served as controls. At reexamination the effect of milrinone, epinephrine, and dopamine was evaluated using biventricular conductance and pulmonary catheters. Seventy-nine days after PR was induced, RV end-diastolic volume index (EDVI) had increased by 33% ( P = 0.006) and there was a severe decrease in the load-independent measurement of contractility (PRSW) (−58%; P = 0.003). Lower cardiac index (CI) (−28%; P < 0.0001), mean arterial pressure (−15%; P = 0.01) and mixed venous oxygen saturation (SvO2) (36%; P < 0.0001) were observed compared with the control group. The interventricular septum deviated toward the left ventricle (LV). Milrinone improved RV-PRSW and CI and maintained systemic pressure while reducing central venous pressure (CVP). Epinephrine and dopamine further improved biventricular PRSW and CI equally in a dose-dependent manner. Systemic and pulmonary pressures were higher in the dopamine-treated animals compared with epinephrine-treated animals. None of the treatments improved stroke volume index (SVI) despite increases in contractility. Strong correlation was detected between SVI and LV-EDVI, but not SVI and biventricular contractility. In RVF due to PR, milrinone significantly improved CI, SvO2, and CVP and increased contractility in the RV. Epinephrine and dopamine had equal inotropic effect, but a greater vasopressor effect was observed for dopamine. SV was unchanged due to inability of both treatments to increase LV-EDVI.

Cardiac natriuretic Peptide gene expression and plasma concentrations during the first 72 hours of life in piglets

Plasma measurement of cardiac natriuretic peptides constitutes promising markers of congenital heart disease. However, concentrations change rapidly and dramatically during the first days after delivery even in healthy neonates, which complicates clinical interpretation. It is unknown whether these changes in plasma concentrations are explained by corresponding changes in the cardiac gene expression. We quantified the chamber-specific mRNA levels of ANP (A-type natriuretic peptide) and BNP (B-type natriuretic peptide) and plasma pro-ANP and BNP-32 concentrations in healthy piglets during the first 72 hours of life (from 2 litters, n = 44). Chamber-specific ANP and BNP mRNA levels reflected hemodynamic neonate changes at birth but did not correlate with circulating natriuretic peptide concentrations. However, plasma pro-ANP and creatinine concentrations were closely correlated (P < .0001; r = 0.73). Plasma pro-ANP levels were highest on the day of delivery (5580 pmol/L [4320-6786] decreasing to 2484 pmol/L [1602-2898] after 72 hours, P < .0001). During the 72 hours, gel chromatography suggested that the translational products in circulation and in atrial tissue were immature, ie, unprocessed pro-ANP. In contrast to pro-ANP, BNP-32 plasma concentrations were low at delivery and peaked after 48 hours (12 [10.5-20.6] vs. 88.8 [71.7-101.4] pmol/L, P < .0001). To conclude, ANP and BNP gene expression differs considerably between cardiac chambers in the first 72 hours of life in healthy piglets, resembling the transition from fetal to neonate circulation. However, the cardiac gene expression does not explain plasma concentrations.

Percutaneous pulmonary valve replacement after different duration of free pulmonary regurgitation in a porcine model: effects on the right ventricle

BACKGROUND

Free pulmonary regurgitation (PR) after surgical correction of Tetralogy of Fallot (ToF) with transannular patching can lead to irreversible right ventricular (RV) failure. However, the optimal timing of valve replacement is still debated.

METHODS AND RESULTS

Thirty six pigs were included in the study. Twenty one pigs had a bare metal stent placed in the pulmonary annulus inducing free PR and 9 animals served as control. Six animals died prematurely due to procedural complications. The 21 animals were divided into 3 groups with differential duration of PR (1, 2, 3 months, respectively) after which PPVR was performed. After 1 month with competent valve the animals were euthanized. Cardiac magnetic resonance (CMR) and right heart catheterization were performed serially. Free PR led to severe dilation of the RV in all three groups compared to matched controls (p<0.001). Final RV volume after one month with competent pulmonary valve was modeled. Increase in RV volume from baseline to valve replacement (ΔRV) was the only predictor of RV recovery (p<0.001) and increases in ΔRV beyond 120 mL/m2 were predictive of very low probability of recovery. A total of 5 animals did not recover.

CONCLUSIONS

Recovery of right ventricular function after free PR by treatment with PPVR was successful in the majority of animals. Increases in RV volume during PR were the only predictor of non-recovery after PPVR and duration of PR did not in itself predict treatment success.