Age-dependent effects of milrinone and levosimendan on ventricular function and haemodynamics in newborn and mature pigs

A Randomized Porcine Study in Low Cardiac Output of Vasoactive and Inotropic Drug Effects on the Gastrointestinal Tract

BACKGROUND

Splanchnic vasodilation by inodilators is an argument for their use in critical cardiac dysfunction. To isolate peripheral vasoactivity from inotropy, such drugs were investigated, and contrasted to vasopressors, in a fixed low cardiac output (CO) model resembling acute cardiac dysfunction effects on the gastrointestinal tract. We hypothesized that inodilators would vasodilate and preserve the aerobic metabolism in the splanchnic circulation in low CO.

METHODS

In anesthetized pigs, CO was lowered to 60% of baseline by partial inferior caval vein balloon inflation. The animals were randomized to placebo (n = 8), levosimendan (24 μg kg-1 bolus, 0.2 μg kg-1 min-1, n = 7), milrinone (50 μg kg-1 bolus, 0.5 μg kg-1 min-1, n = 7), vasopressin (0.001, 0.002 and 0.006 U kg-1 min-1, 1 h each, n = 7) or norepinephrine (0.04, 0.12, and 0.36 μg kg-1 min-1, 1 h each, n = 7). Hemodynamic variables including mesenteric blood flow were collected. Systemic, mixed-venous, mesenteric-venous, and intraperitoneal metabolites were analyzed.

RESULTS

Cardiac output was stable at 60% in all groups, which resulted in systemic hypotension, low superior mesenteric artery blood flow, lactic acidosis, and increased intraperitoneal concentrations of lactate. Levosimendan and milrinone did not change any circulatory variables, but levosimendan increased blood lactate concentrations. Vasopressin and norepinephrine increased systemic and mesenteric vascular resistances at the highest dose. Vasopressin increased mesenteric resistance more than systemic, and the intraperitoneal lactate concentration and lactate/pyruvate ratio.

CONCLUSION

Splanchnic vasodilation by levosimendan and milrinone may be negligible in low CO, thus rejecting the hypothesis. High-dose vasopressors may have side effects in the splanchnic circulation.

Advances in Diagnosis and Management of Hemodynamic Instability in Neonatal Shock

Shock in newborn infants has unique etiopathologic origins that require careful assessment to direct specific interventions. Early diagnosis is key to successful management. Unlike adults and pediatric patients, shock in newborn infants is often recognized in the uncompensated phase by the presence of hypotension, which may be too late. The routine methods of evaluation used in the adult and pediatric population are often invasive and less feasible. We aim to discuss the pathophysiology in shock in newborn infants, including the transitional changes at birth and unique features that contribute to the challenges in early identification. Special emphasis has been placed on bedside focused echocardiography/focused cardiac ultrasound, which can be used as an additional tool for early, neonatologist driven, ongoing evaluation and management. An approach to goal oriented management of shock has been described and how bed side functional echocardiography can help in making a logical choice of intervention (fluid therapy, inotropic therapy or vasopressor therapy) in infants with shock.

Effects of Combined Milrinone and Levosimendan Treatment on Systolic and Diastolic Function During Postischemic Myocardial Dysfunction in a Porcine Model

It is not known whether there are positive or negative interactions on ventricular function when a calcium-sensitizing inotrope is added to a phosphodiesterase inhibitor in the clinical setting of acute left ventricular (LV) dysfunction. We hypothesized that when levosimendan is added to milrinone treatment, there will be synergetic inotropic and lusitropic effects. This was tested in an anesthetized porcine postischemic global LV injury model, where ventricular pressures and volumes (conductance volumetry) were measured. A global ischemic injury was induced by repetitive left main stem coronary artery occlusions. Load-independent indices of LV function were assessed before and after ventricular injury, after milrinone treatment, and finally after addition of levosimendan to the milrinone treatment. Nonparametric, within-group comparisons were made. The protocol was completed in 12 pigs, 7 of which received the inotrope treatment and 5 of which served as controls. Milrinone led to positive lusitropic effects seen by improvement in tau after myocardial stunning. The addition of levosimendan to milrinone further increased lusitropic state. The latter effect could however not be attributed solely to levosimendan, since lusitropic state also improved spontaneously in time-matched controls at the same rate during the corresponding period. When levosimendan was added to milrinone infusion, there was no increase in systolic function (preload recruitable stroke work) compared to milrinone treatment alone. We conclude that in this model of postischemic LV dysfunction, there appears to be no clear improvement in systolic or diastolic function after addition of levosimendan to established milrinone treatment but also no negative effects of levosimendan in this context.

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.

Effects of milrinone and epinephrine or dopamine on biventricular function and hemodynamics in an animal model with right ventricular failure after pulmonary artery banding

Right ventricular (RV) failure due to chronic pressure overload is a main determinant of outcome in congenital heart disease. Medical management is challenging because not only contractility but also the interventricular relationship is important for increasing cardiac output. This study evaluated the effect of milrinone alone and in combination with epinephrine or dopamine on hemodynamics, ventricular performance, and the interventricular relationship. RV failure was induced in 21 Danish landrace pigs by pulmonary artery banding. After 10 wk, animals were reexamined using biventricular pressure-volume conductance catheters. The maximum pressure in the RV increased by 113% ( P < 0.0001) and end-diastolic volume by 43% ( P < 0.002), while left ventricular (LV) pressure simultaneously decreased ( P = 0.006). Concomitantly, mean arterial pressure (MAP; −16%, P = 0.01), cardiac index (CI; −23%, P < 0.0001), and mixed venous oxygen saturation (SvO2; −40%, P < 0.0001) decreased. Milrinone increased CI (11%, P = 0.008) and heart rate (HR; 21%, P < 0.0001). Stroke volume index (SVI) decreased (7%, P = 0.03), although RV contractility was improved. The addition of either epinephrine or dopamine further increased CI and HR in a dose-dependent manner but without any significant differences between the two interventions. A more pronounced increase in biventricular contractility was observed in the dopamine-treated animals. LV volume was reduced in both the dopamine and epinephrine groups with increasing doses In the failing pressure overloaded RV, milrinone improved CI and increased contractility. Albeit additional dose-dependent effects of both epinephrine and dopamine on CI and contractility, neither of the interventions improved SVI due to reduced filling of the LV.

Inotropic therapy for right ventricular failure in newborn piglets: effect on contractility, hemodynamics, and interventricular interaction

OBJECTIVES

To investigate the effect of right ventricular stunning on interventricular relationships in newborn piglets and to determine the effect of three commonly used inotropic treatment strategies.

DESIGN

Randomized, placebo-controlled animal study.

SETTING

Aarhus University Hospital, animal laboratory.

SUBJECTS

Twenty-eight newborn (4-d old) farm-bred piglets.

INTERVENTIONS

Acute right ventricular failure was induced by 10 cycles of alternating 3 minutes of ischemia and reperfusion of the right coronary artery. After right ventricular failure was induced, treatment with epinephrine + milrinone, dopamine + milrinone, dobutamine, or control (saline) was initiated, and the animals were observed for 180 minutes.

MEASUREMENTS AND MAIN RESULTS

Right and left ventricular systolic and diastolic variables were measured using pressure-volume loops recorded by conductance catheters. Arterial and central venous pressures were recorded, and cardiac index was determined by placing a flow probe around the pulmonary artery. Whole-body perfusion was evaluated by measuring pH and lactate in arterial blood samples. Induction of right ventricular stunning resulted in decreased ejection fraction (51% ± 4% vs 40% ± 12%, p = 0.0004); caused an interventricular septum deviation, decreased mean arterial pressure (49 ± 10 mm Hg vs 43 ± 11 mm Hg, p = 0.03), and increased blood lactate (1.85 ± 0.6 mM vs 5.79 ± 3.16 mM, p < 0.00001); and led to a decrease in blood pH (7.37 ± 0.08 vs 7.23 ± 0.13, p < 0.00001). A mortality rate greater than 50% was observed in the control group. All inotropic interventions increased contractility significantly in both the left and right ventricle. The effect of dobutamine on right ventricular failure decreased after 30 minutes and was indistinguishable from the control group after 3 hours. Dobutamine-treated animals had lower perfusion pressures and blood pH compared with epinephrine + milrinone and dopamine + milrinone groups.

CONCLUSIONS

In newborn piglets, dobutamine had a nonsustained effect on right ventricular failure, resulting in decreased contractility and impaired perfusion compared with both dopamine and epinephrine administered in combination with milrinone.

Milrinone and levosimendan during porcine myocardial ischemia -- no effects on calcium overload and metabolism

BACKGROUND

Although inotropic stimulation is considered harmful in the presence of myocardial ischaemia, both calcium sensitisers and phosphodiesterase inhibitors may offer cardioprotection. We hypothesise that these cardioprotective effects are related to an acute alteration of myocardial metabolism. We studied in vivo effects of milrinone and levosimendan on calcium overload and ischaemic markers using left ventricular microdialysis in pigs with acute myocardial ischaemia.

METHODS

Anaesthetised juvenile pigs, average weight 36 kg, were randomised to one of three intravenous treatment groups: milrinone 50 μg/kg bolus plus infusion 0.5 μg/kg/min (n = 7), levosimendan 24 μg/kg plus infusion 0.2 μg/kg/min (n = 7), or placebo (n = 6) for 60 min prior to and during a 45 min acute regional coronary occlusion. Systemic and myocardial haemodynamics were assessed, and microdialysis was performed with catheters positioned in the left ventricular wall. (45) Ca(2+) was included in the microperfusate in order to assess local calcium uptake into myocardial cells. The microdialysate was analysed for glucose, lactate, pyruvate, glycerol, and for (45) Ca(2+) recovery.

RESULTS

During ischaemia, there were no differences in microdialysate-measured parameters between control animals and milrinone- or levosimendan-treated groups. In the pre-ischaemic period, arterial blood pressure decreased in all groups while myocardial oxygen consumption remained stable.

CONCLUSIONS

These findings reject the hypothesis of an immediate energy-conserving effect of milrinone and levosimendan during acute myocardial ischaemia. On the other hand, the data show that inotropic support with milrinone and levosimendan does not worsen the metabolic parameters that were measured in the ischaemic myocardium.

Metabolic effects of three different inotropic strategies in the newborn piglet myocardium

INTRODUCTION

Neonates undergoing congenital heart surgery frequently need post-operative inotropic support. Knowledge about the effect of inotropes on myocardial metabolism in the newborn heart is limited, and the choice of inotropic therapy is based mainly on evidence from studies in adults. The aim of this study was to compare the effect of three inotropic strategies on the myocardial metabolism in a neonatal pig model.

METHODS

Newborn piglets were randomised to intravenous infusions with: adrenaline and milrinone; dopamine and milrinone; dobutamine in haemodynamically equivalent doses; or isotonic saline, through 3 h. Microdialysis catheters were inserted in the myocardium of the left and right ventricle, and concentrations of lactate, pyruvate, glycerol, and glucose were measured in the microdialysate. In myocardial biopsies, tissue lactate and intracellular glycogen concentrations were determined, and arterial blood samples were analysed for lactate and glucose.

RESULTS

No statistically significant differences were observed in haemodynamics between the three interventions. Metabolic variables demonstrated a consistent increase in lactate concentration in blood, myocardial dialysate, and biopsies in milrinone-adrenaline-treated animals. The lactate concentration remained stable in all other groups in all samples. The myocardial lactate/pyruvate ratio did not increase and was not significantly different between groups.

CONCLUSION

Milrinone and adrenaline induced significantly higher lactate levels in neonatal piglets. The increase was not caused by myocardial ischaemia, but rather due to a beta-stimulation-induced glycolysis.