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

Differential Effects of Pharmacologic and Mechanical Support on Right-Left Ventricular Coupling

BACKGROUND

Percutaneous ventricular assist devices are increasingly relied on to maintain perfusion for cardiogenic shock patients. Optimal medical management strategies however remain uncertain from limited understanding of interventricular effects. This study analyzed the effects of pharmacologic and left-sided mechanical support on right ventricular function.

METHODS

A porcine model was developed to assess biventricular function during bolus pharmacologic administration before and after left-sided percutaneous ventricular assist and in cardiogenic shock.

RESULTS

The presence of mechanical support increased right ventricular load and stress with respect to the left ventricle. This shifted and exaggerated the relative effects of commonly used vasoactive agents. Furthermore, induction of cardiogenic shock led to differential pulmonary vascular and right ventricular responses.

CONCLUSIONS

Left ventricular ischemia and mechanical support altered interventricular coupling. Resulting impacts of pharmacologic agents indicate differential right heart responses and sensitivity to treatments and the need for further study to optimize biventricular function in shock patients.

Repetitive milrinone therapy in ambulatory advanced heart failure patients

BACKGROUND

Advanced heart failure (HF) patients usually poorly tolerate guideline-directed HF medical therapy (GDMT) and suffer high rates of morbidity and mortality. The use of continuous inotropes in the outpatient settings is hampered by previous data showing excess morbidity. We aimed to assess the safety and efficacy of repetitive, intermittent, short-term intravenous milrinone therapy in advanced HF patients with an intention to introduce and up-titrate GDMT and improve functional class.

HYPOTHESIS

Repetitive, intermittent milrinone therapy may assist with the stabilization of advanced HF patients.

METHODS

Advanced HF patients treated with beta-blockers and implanted with defibrillators were initiated with repetitive, intermittent short-term intravenous milrinone therapy at our HF outpatient unit. Patients were prospectively followed with defibrillator interrogation, functional class assessment, B-natriuretic peptide (BNP) levels, and echocardiography parameters.

RESULTS

The cohort included 24 patients with a mean 330 ± 240 days of milrinone therapy exposure. Mean age was 73 ± 6 years with male predominance (96%). Following milrinone therapy, median BNP levels decreased significantly (882 [286-3768] to 631 [278-1378] pg/ml, p = .017) with a significant reduction in the number of patients with New York Heart Association (NYHA) Class III and IV (p = .012, 0.013) and an increase in number of patients on GDMT. Importantly, the number of total sustained ventricular tachycardia events and HF hospitalizations did not change.

CONCLUSIONS

In this small cohort of advanced HF, repetitive, intermittent, short-term milrinone therapy was found to be safe and potentially efficacious.

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.

Increasing carbohydrate oxidation improves contractile reserves and prevents hypertrophy in porcine right heart failure

In heart failure, myocardial overload causes vast metabolic changes that impair cardiac energy production and contribute to deterioration of contractile function. However, metabolic therapy is not used in heart failure care. We aimed to investigate the interplay between cardiac function and myocardial carbohydrate metabolism in a large animal heart failure model. Using magnetic resonance spectroscopy with hyperpolarized pyruvate and magnetic resonance imaging at rest and during pharmacological stress, we investigated the in-vivo cardiac pyruvate metabolism and contractility in a porcine model of chronic pulmonary insufficiency causing right ventricular volume overload. To assess if increasing the carbohydrate metabolic reserve improves the contractile reserve, a group of animals were fed dichloroacetate, an activator of pyruvate oxidation. Volume overload caused heart failure with decreased pyruvate dehydrogenase flux and poor ejection fraction reserve. The animals treated with dichloroacetate had a larger contractile response to dobutamine stress than non-treated animals. Further, dichloroacetate prevented myocardial hypertrophy. The in-vivo metabolic data were validated by mitochondrial respirometry, enzyme activity assays and gene expression analyses. Our results show that pyruvate dehydrogenase kinase inhibition improves the contractile reserve and decreases hypertrophy by augmenting carbohydrate metabolism in porcine heart failure. The approach is promising for metabolic heart failure therapy.

Changes in overall ventricular myocardial architecture in the setting of a porcine animal model of right ventricular dilation

BACKGROUND

Chronic pulmonary regurgitation often leads to myocardial dysfunction and heart failure. It is not fully known why secondary hypertrophy cannot fully protect against the increase in wall stress brought about by the increased end-diastolic volume in ventricular dilation. It has been assumed that mural architecture is not deranged in this situation, but we hypothesised that there might be a change in the pattern of orientation of the aggregations of cardiomyocytes, which would contribute to contractile impairment.

METHODS

We created pulmonary valvular regurgitation by open chest, surgical suturing of its leaflets in seven piglets, performing sham operations in seven control animals. Using cardiovascular magnetic resonance imaging after 12 weeks of recovery, we demonstrated significantly increased right ventricular volumes in the test group. After sacrifice, diffusion tensor imaging of their hearts permitted measurement of the orientation of the cardiomyocytes.

RESULTS

The helical angles in the right ventricle approached a more circumferential orientation in the setting of right ventricular RV dilation (p = 0.007), with an increased proportion of surface-parallel cardiomyocytes. In contrast, this proportion decreased in the left ventricle. Also in the left ventricle a higher proportion of E3 angles with a value around zero was found, and conversely a lower proportion of angles was found with a numerical higher value. In the dilated right ventricle the proportion of E3 angles around -90° is increased, while the proportion around 90° is decreased.

CONCLUSION

Contrary to traditional views, there is a change in the orientation of both the left ventricular and right ventricular cardiomyocytes subsequent to right ventricular dilation. This will change their direction of contraction and hinder the achievement of normalisation of cardiomyocytic strain, affecting overall contractility. We suggest that the aetiology of the cardiac failure induced by right vetricular dilation may be partly explained by morphological changes in the myocardium itself.

Expression of Recombinant Phosphodiesterases 3A and 3B Using Baculovirus Expression System

Background

Phosphodiesterase 3A (PDE3A) and phosphodiesterase 3B (PDE3B) play a critical role in the regulation of intracellular level of adenosine 3´,5´-cyclic monophosphate (cyclic AMP, cAMP) and guanosine 3´,5´-cyclic monophosphate (cyclic GMP, cGMP). Subsequently PDE3 inhibitors have shown to relax vascular and inhibit platelet aggregation in cardiovascular disease.

Objectives

In this study, our aim was to establish a method of expression for the recombinant human PDE3A and PDE3B proteins in insect cells using baculovirus expression system in order to investigate the activity of the expressed PDE3A and PDE3B proteins.

Materials and Methods

The full length human PDE3A and PDE3B cDNA were cloned into recombinant baculovirus and transfected into the SF9 insect cells. Recombinant proteins were collected at 48 h, 60 h, 72 h, and 84 h post transfection. Transfection of recombinant baculovirus was verified by the morphological changes of the SF9 cells. Expression of human PDE3A and PDE3B was detected by using RT-PCR and western blot, respectively. The ¹²⁵I RIA method was used to determine the level of adenosine 3´,5´-cyclic monophosphate cAMP and cGMP, correspondingly. The activity of the expressed PDE3A and PDE3B proteins were investigated by cAMP and cGMP dsgradation with or without addition of milrinone, a potent and selective PDE inhibitor.

Results

Recombinant human PDE3A and PDE3B proteins were stably expressed in SF9 cells and could be detected by distinct morphological changes in the SF9 cells, RT-PCR, and western blot at 48 h post-transfection. The molecular weights of the recombinant PDE3A and PDE3B molecular weights proteins were about 120 KDa and 135 KDa, respectively. Results of ¹²⁵I RIA assay showed that the levels of cAMP and cGMP were significantly decreased after incubation with the expressed PDE3A and PDE3B proteins. Furthermore, degradation of cAMP and cGMP through the activity of PDE3A and PDE3B was suppressed following to the addition of milrinone.

Conclusions

Recombinant human PDE3A and PDE3B could be expressed in SF9 cells using baculovirus expression system, and thus provides the basic material for studying human PDE3A and PDE3B activity.

Hypoxic hepatitis during the perioperative period in patients with severe pulmonary disease and cor pulmonale

Hypoxic hepatitis (HH) is characterized by marked and transient elevations in liver enzyme levels in the absence of other potential causes of liver injury. Although rare, it can occur in the presence of hemodynamic instability and hypoxemia in patients with cor pulmonale. We report two cases of perioperative HH in patients with severe pulmonary disease and cor pulmonale. The first case is of a patient with cor pulmonale who underwent hemiarthroplasty for a femur fracture. Transient hypotension developed during spinal anesthesia and severe hypoxemia were observed in the postoperative period. After surgery, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels suddenly increased to 3740 and 817 U/L, respectively. The second case is of a patient with congestive heart failure and cor pulmonale whose blood pressure and oxygen saturation decreased during induction of general anesthesia and after surgery, and AST, ALT, and lactic dehydrogenase levels increased to 1291, 1292, and 2710 U/L, respectively. The liver enzyme levels normalized within 7–14 days in both cases. We speculate the diagnosis of these cases as HH.