Guidelines for vasodilator therapy of congestive heart failure in infants and children

Critical Heart Failure and Shock

OBJECTIVES

The objectives of this review are to discuss the clinical assessment, pathophysiology, and management of shock, with an emphasis on circulatory physiology, cardiopulmonary interactions, and pharmacologic strategies to optimize systemic oxygen delivery. These principles will then be applied to the clinical syndromes of heart failure and cardiogenic shock that are seen in children.

DATA SOURCE

MEDLINE, PubMed.

CONCLUSION

An understanding of essential circulatory physiology and the pathophysiology of shock are necessary for managing patients at risk for or in a state of shock. A timely and accurate assessment of cardiac function, cardiac output, and tissue oxygenation and the means by which to enhance the relationship between oxygen delivery and consumption are essential in order to optimize outcomes.

Sodium-nitroprusside-induced cyanide toxicity in pediatric patients

BACKGROUND

Sodium nitroprusside (SNP) is often used as a continuous infusion intravenous vasodilator in pediatric patients. However, cyanide toxicity can occur with SNP therapy. Scant literature is available determining the safety of SNP therapy, the incidence of cyanide toxicity or the risk factors for cyanide toxicity in pediatric patients.

OBJECTIVE

To review the literature concerning the safety of intravenous SNP with regard to cyanide toxicity in the pediatric patient population.

METHODS

A MedLine search was used to identify articles pertaining to SNP therapy and cyanide toxicity in pediatric patients.

CONCLUSIONS

Sodium nitroprusside seems to be safe when used in critically ill pediatric patients. Cyanide toxicity may occur in patients with specific risk factors. Routine monitoring of cyanide levels may not be warranted.

Postoperative management in patients with complex congenital heart disease

Life-threatening problems occur in the neonate and infant after cardiac surgery because of the interplay of diminished cardiac output (CO), increased metabolic demand, inflammatory responses to cardiopulmonary bypass, and maladaptive responses to stress. Therefore, the postoperative management of patients with complex congenital heart defects is directed at optimization of oxygen delivery to maintain end-organ function and promote wound healing. Traditionally, assessment of circulation in the postoperative congenital heart patient has depended on indirect assessment of CO using parameters such as blood pressure, pulses, capillary refill, and urine output. Because of the limitations of indirect and observer-dependent assessment of CO, we rely on objective measures of tissue oxygen levels for the complex postoperative patient. We have found that continuous monitoring of the mixed venous saturation (SvO2) allows for identification of acute changes in systemic oxygen delivery and frequently precedes other indicators of decreased CO. The postoperative patient can be expected to have a period of decreasing CO, and the need for intervention should be anticipated because critical low output syndrome will develop in a subset of patients. Strategies for postoperative care are developed based on the diagnosis and procedure, but optimizing SvO2 is a consistent goal. A uniform approach to airway maintenance, vascular access, and drug infusions, all universal concerns during the perioperative period, minimizes the potential for these predictable and necessary interventions to result in morbidity or mortality. Management of the postoperative single ventricle patient targets stabilization of the systemic vascular resistance through the use of vasodilators to improve systemic perfusion and simplify ventilator management. Management of any individual patient should be driven by objective analysis of available data and must include efforts to re-evaluate the treatment plan as well as to identify unanticipated problems.

Severely impaired cardiac autonomic nervous activity after the Fontan operation

BACKGROUND

Elevated neurohumoral activity and an abnormal cardiopulmonary response to exercise are well-established characteristics in patients after the Fontan operation. However, there have been few studies addressing cardiac autonomic nervous activity (CANA) in these patients.

METHODS AND RESULTS

We evaluated CANA in 63 post-Fontan patients and 44 controls. Cardiac parasympathetic nervous activity (PSNA) was estimated by heart rate (HR) changes after cholinergic blockade, HR variability, and arterial baroreflex sensitivity. Cardiac sympathetic nervous activity was estimated by the heart to mediastinum [(123)I]metaiodobenzylguanidine activity ratio (H/M) and the HR increase (DeltaHR) after isoproterenol infusion (beta). DeltaHR and peak oxygen uptake (VO(2)) were measured by exercise test. There was no difference in beta between the Fontan group and controls. PSNA and H/M were markedly lower than in controls (P<0.001). PSNA and beta were related to DeltaHR (P<0.05); however, peak VO(2) was not correlated with DeltaHR. Neither PSNA nor H/M was associated with clinical features, including hemodynamics, type of repair, number of surgical procedures, age at Fontan operation, or follow-up period, and administration of an angiotensin-converting enzyme inhibitor did not improve the impaired CANA in these patients.

CONCLUSIONS

After the Fontan procedure, postsynaptic beta-sensitivity is maintained and is important in DeltaHR during exercise as is PSNA, although DeltaHR does not determine exercise capacity. The lack of a relationship between CANA and clinical features implies that, in addition to surgical damage, the Fontan circulation per se may impair CANA. Angiotensin-converting enzyme inhibitor administration does not change this abnormality.

Activity of the renin–angiotensin–aldosterone and sympathetic nervous system and their relation to hemodynamic and clinical abnormalities in infants with left-to-right shunts

We studied neurohormonal, clinical and invasively measured hemodynamic data of 47 infants with left-to-right shunts and varying degrees of congestive failure. When referred to a clinical heart failure score, plasma renin activities (r=0.71) and norepinephrine levels (r=0.43) are significantly increased. Arterial hypotension seems to be the hemodynamic trigger of renin release (r=-0.72), but not decreased systemic cardiac index (r=-0.43), the magnitude of the left-to-right shunt (r=0.33) or a reduced ejection fraction (r=0.12). These data indicate neurohormonal activation in infants with left-to-right shunts with preserved myocardial function is similar to the activation in adults with heart failure secondary to myocardial pump failure. These findings have to be considered for optimal medical treatment of these infants with angiotensin-converting enzyme inhibitors or beta-blockers.

Vasodilators in the treatment of pediatric heart failure

The goals of heart failure therapy have shifted from purely hemodynamic manipulation to a combination of hemodynamic and neurohumoral modulation. Vasodilators with neurohumoral modulatory properties [such as ACE inhibitors (ACEi) and third generation beta-blockers] have become the cornerstone of chronic heart failure therapy. These newer agents have proven to improve morbidity and mortality in adults with chronic heart failure. Pure vasodilators still have a place in the treatment of acute decompensated heart failure and in patients who are intolerant to ACEi or beta-blocker therapy. In decompensated heart failure management, improvement of cardiac output is of paramount importance and restoration of normal hemodynamics takes priority over modulation of cardiac maladaptation. Under these circumstances agents that improve contractility and modify cardiac preload and afterload are used. In the intensive care unit setting inodilators offer the advantage of an added positive inotropic effect. NO donors play an important role when close titration of blood pressure is also needed. It is the purpose of this manuscript to address principles and current practice regarding the use of vasodilators in pediatric heart failure. ACE inhibitors and third generation beta-blockers due to their importance in today's therapeutic approach to heart failure are the focus of more detailed articles in this issue of Progress in Pediatric Cardiology.

Overview of the management of pediatric heart failure

For the most part of this the century heart failure syndrome was understood as a pump failure disorder with hemodynamic consequences stemming from the same myocardial dysfunction. In addition supply and demand theories were used to explain the nature of symptoms. As a result, therapeutic strategies were directed at correcting the abnormal hemodynamic conditions and normalizing the delivery of the much needed nutrients. Improvement of cardiac pump function with inotropic drugs and abnormal circulatory conditions with afterload and preload modifications became therapeutic goals and standards of care. However, while vasodilators and inotropic drugs immediately improved symptoms, hemodynamics and functional status, in the long term they either did not affect or worsen the natural history of heart failure. In pediatrics, this is further complicated by the lack of large scale trials addressing issues pertinent to the particularities that affect heart failure in children. In the late 1980s and 1990s heart failure has evolved into a more complex, multiple and interactive pathophysiologic disorder. Today not only the abnormal hemodynamics but also the biological disorders are pharmacologic targets. The reversal or slowing of myocardial maladaptation has become one of the most important therapeutic goals. With this end in mind therapeutic strategies may seem counterintuitive and paradoxical, such as the use of beta-blockers. This review will address the current thinking and therapeutic modalities used today in the treatment of heart failure syndrome in the adult population. We also discuss some of the issues why we think that these principles can be extrapolated to the pediatric population.

Beta-blocker therapy of severe congestive heart failure in infants with left to right shunts

We report on the clinical and neurohumoral effects of adding low-dose propranolol to conventional therapy with digoxin and diuretics in 6 infants with severe congestive heart failure due to large left-to-right shunts. A significant decrease in heart failure scores and a decrease of the highly activated renin-angiotensin-1 aldosterone system by approximately 70% strongly suggests a beneficial effect of this new therapeutic approach.

Recent advances in the treatment of congestive heart failure

Treatment of heart failure should include correction of the underlying cause. These causes include large left to right shunts, obstructive lesions, arrhythmias, primary myocardial disease etc. The main pharmacological therapy includes inotropic agents, vasodilators and diuretics. Inotropic agents increase myocardial contractility and include digoxin, intravenous dopamine, dobutamine and isoproterenol. Vasodilators improve cardiac pump performance by decreasing the vascular resistance and/or increasing the venous capacitance. Commonly used vasodilator agents include angiotensin converting enzyme inhibitors (captopril, enalapril etc.), hydralazine, prazosin hydrochloride etc. Diuretics inhibit salt and water reabsorption promoting their excretion. Furosemide, thiazide diuretics, aldactone, are commonly used diuretics. Electrolyte and acid-base imbalance can occur on chronic diuretic therapy. Cardiac transplantation is considered for patients where all medical management has failed.

Computer simulation of circulation in patient with total cavo-pulmonary connection: inter-relationship of cardiac and vascular pressure, flow, resistance and capacitance

The aim is to develop a computer model representative of the circulation in a patient with a uni-ventricular heart surgically palliated by a total cavo-pulmonary connection (TCPC). The effects of known hazardous exposures on this type of circulation are investigated. A model of the cardiovascular system is built using standard components such as transmission lines, restrictors and capacitances. The chamber of the heart consists of a volume connected to checkvalves, and an oscillating source flow connected to the volume represents the pumping of the heart. The following are simulated: exposure to cold, heat, high altitude, accelerating forces, blood loss, reduction in ventricular function, atrioventricular-valve regurgitation and treatment with afterload-reducing agents. During simulations, all the parameters can be changed, independently of each other, and the resulting changes in flow, resistance and pressure are recorded. Exposure to cold, reduced ventricular function and atriventricular-valve regurgitation result in a decrease in cardiac output (14, 58 and 45%, respectively). At high altitude, an increase of 18% is noted in the central venous pressure. Afterload-reducing agents increase the cardiac output by 8% and reduce central aortic pressure by 23%. Blood loss results in a marked reduction in perfusion pressure. It is concluded that the computer model is a useful instrument for simulation of a TCPC or Fontan circulation. The original criteria for this surgical procedure are those showing the most marked haemodynamic responses to different stimulus.

Management of functional pulmonary atresia with isoproterenol in a neonate with Ebstein's anomaly

Ebstein's anomaly is a rare congenital cardiac anomaly showing significant clinical manifestations with a high mortality rate in the neonatal period. The prognosis of the patient is essentially determined by the severity in morphological changes, however, high pulmonary vascular resistance in the neonatal period may aggravate tricuspid regurgitation and lead to functional pulmonary atresia. We describe a critically ill neonate with morphologically mild Ebstein's anomaly who was successfully managed with intensive care including isoproterenol administration for functional pulmonary atresia. Isoproterenol is a potent pulmonary vasodilator with inotropic and chronotropic effects, and seemed to decrease the pulmonary vascular resistance allowing increased antegrade blood flow to the pulmonary artery and improved cardiac output. If tachycardia is not present, isoproterenol administration is recommended in critically ill neonates with anatomically mild Ebstein's anomaly and no associated cardiac defects.

[Treatment of acute heart failure in infants]

The treatment of congestive heart failure in infants must be etiological and symptomatic. Vasodilators, inotropic agents and diuretics are the main therapeutics used in the symptomatic treatment. Guidelines for the emergency treatment according to the main etiologies are presented.

High-performance liquid chromatography using electrochemical detection for the determination of prazosin in biological samples

For the quantitation of prazosin a sensitive high-performance liquid chromatographic (HPLC) method was developed. This HPLC analysis method uses an electrochemical detection technique for the identification and quantitation of prazosin. In this assay the serum samples were deproteinized by using a simple acetonitrile precipitation technique that was followed by n-hexane extraction. Prazosin in the deproteinized serum sample was separated by an isocratic elution with an ODS Hypersil HPLC column (150 x 4.6 mm) using a mobile phase consisting of 0.05 M Na2HPO4-acetonitrile (60:40), pH 8.4. Prazosin that was eluted from the column was detected using a Coulochem II electrochemical detector. The precision of this assay method was assessed by performing inter- and intra-assay analyses by spiking prazosin free fetal bovine serum samples with 20 and 40 ng/ml concentrations of prazosin. In the intra-assay the recovery was 95.40 +/- 4.82% and 97.80 +/- 3.40%, respectively, for 20 and 40 ng/ml concentrations of prazosin that were used to spike the serum samples. This electrochemical detection HPLC assay method could be very useful in monitoring plasma levels of prazosin.

Inhibition of angiotensin converting enzyme with enalapril maleate in infants with congestive heart failure

We studied the inhibition of angiotensin converting enzyme (ACE) in eight infants with congestive heart failure (CHF) poorly controlled with digoxin and diuretics, treated orally with 0.25 mg kg-1 enalapril maleate once a day. Baseline ACE activities were compared between these infants and control children without CHF or ACE inhibitor. Except for one infant who vomited, inhibition of ACE activity was 75.5 +/- 12.2%, 75.5 +/- 10.5% and 51.7 +/- 12.2%, at 4, 12 and 24 h after drug intake respectively. There was no correlation between postnatal age and inhibition of ACE activity. In infants with CHF, mean baseline ACE activity was significantly higher than in control infants (36.4 +/- 7.2 mu ml-1 vs 26.9 +/- 6.9 mu ml-1, P < 0.05). These results were very similar to those seen in adults.

Acute hemodynamic effects of captopril in children with a congestive or restrictive cardiomyopathy

The acute hemodynamic effects of captopril were evaluated at cardiac catheterization in 16 children (age, 0.3-18 years) with cardiomyopathy. Twelve children had congestive cardiomyopathy, whereas four had restrictive cardiomyopathy. Hemodynamic measurements were obtained 30 and 60 minutes after the oral administration of captopril (0.5 mg/kg). Blood pressures were measured in the aorta, pulmonary artery, right atrium, and pulmonary capillary wedge position; cardiac outputs were measured by the thermodilution technique. Hemodynamic data could not be obtained after the administration of captopril in one child with congestive cardiomyopathy because of an immediate, severe hypotensive response. In 11 of 12 children with congestive cardiomyopathy, cardiac index increased by 22%, from 2.3 to 2.8 l/min/m2 (p less than 0.05), and stroke volume increased by 22%, from 23 to 28 ml/m2 (p less than 0.05). Systemic vascular resistance decreased from 32 to 21 units.m2 (p less than 0.01), but the mean aortic pressure did not change significantly. In contrast, four children with restrictive cardiomyopathy had no change in cardiac output after captopril, but there was a trend toward significant arterial hypotension (mean aortic pressure decreased from 78 to 59 mm Hg). Thus, captopril acutely reduced systemic vascular resistance and increased both cardiac output and stroke volume in children with congestive cardiomyopathy. In children with restrictive cardiomyopathy, however, captopril did not affect cardiac output, but it did decrease aortic pressure. These data indicate that captopril may benefit children with a congestive cardiomyopathy but that captopril probably should not be used in children with restrictive disease.

Physiologic sequelae of prematurity: the nurse practitioner's role. Part III. Congestive heart failure

The premature infant with resultant respiratory disease may also have signs and symptoms of impending congestive heart failure that have a variety of causes. The nurse practitioner can be instrumental in the early identification and treatment of congestive heart failure. This article, the third in a series, provides a discussion of the pathophysiology, signs and symptoms, data collection, treatment modalities, and parental education that can assist parents when coping and dealing with congestive heart failure in their premature infant.