Beta-receptor downregulation in congenital heart disease: a risk factor for complications after surgical repair?

Incidence of adverse events requiring intervention after initiation of oral beta-blocker in pediatric cardiac intensive care patients

Only limited clinical data are available to establish the risk factors for adverse events and their frequency among children who have received oral beta-blockers in a critical care unit setting. The authors aimed to analyze the frequency of adverse events experienced by children treated with oral beta-blockers in a cardiovascular intensive care unit (CVICU) and sought out independent risk factors for these adverse events in a tertiary care hospital. The primary end point in this retrospective descriptive study was the incidence of adverse events associated with enteral beta-blocker administration, and the secondary end point was the incidence of readmission to the CVICU after transfer of patients to an acute care floor. At least one clinical adverse event occurred for 38% of the patients. Specifically, the profile of the clinical adverse events included bradycardia in 27 patients (11%), hypoglycemia in 46 patients (19%), and the initiation or escalation of inotropes in 36 patients (15%) after oral beta-blocker administration. Additionally, 41 patients (17%) were readmitted to the CVICU after transfer during the same hospital admission. The patients receiving propranolol were predisposed to have at least one adverse event (p = 0.045). No other patient-specific characteristics significantly predisposed patients to adverse events. The patients admitted after a cardiac procedure had fewer readmissions to the intensive care unit (ICU) during the same hospital admission (p = 0.002). The results demonstrated that adverse events are relatively common among patients receiving oral beta-blockers in a CVICU population. Because these children have less physiologic reserve, more must be done to ensure that the correct beta-blocker is prescribed to avoid clinically significant adverse events that may hamper the recovery of these patients and lead to increased ICU time.

Cardiovascular catecholamine receptors in children: their significance in cardiac disease

Adrenoceptors and dopamine receptors are grouped together under the name 'catecholamine receptors.' Catecholamines and catecholaminergic drugs act on catecholamine receptors located on or near the cardiovascular system. The physiological effects of catecholamine receptor stimulation are only partly understood. The catecholaminergic drugs used in critical care medicine today are not selective, or are, at best, in part selective for the various catecholamine receptor subtypes. Many patients, however, depend on them. A variety of animal models has been developed to unravel catecholamine distribution and function. However, the identification of species heterogeneity makes it imperative to determine catecholamine receptor distribution and function in humans. In addition, age-related alterations in catecholamine receptor distribution and function have been identified in human adults. This might have implications for our understanding of the effect of catecholamines in pediatric patients. This article will focus on the pediatric population and will review currently available in vitro data on the distribution and the function of catecholamine receptors in the cardiovascular system of fetuses and children. Also discussed are relevant young animal models and in vivo hemodynamic effects of cardiotonic drugs acting on the catecholamine receptor in children requiring major cardiac surgery. A better understanding of these topics might provide clues for new, receptor subtype-selective, therapeutic approaches in newborns and children with cardiac disease.

Role of β-blocker therapy in pediatric heart failure

Heart failure is becoming an increasingly common and significant problem in the field of pediatric cardiology. The numerous types of cardiomyopathies, and more recently, long-term survival of patients with congenital heart disease, have added to a growing patient population. Over the last several decades, our knowledge base regarding mechanisms of disease and therapeutic intervention in adult patients with heart failure has drastically changed. The most recent and important breakthrough in the pharmacologic treatment of heart failure has been the particular role of β-blocker therapy. This medication has led to significant improvements in survival and symptoms in adults, with less convincing findings in limited studies in pediatrics. The ability to study the benefits of this therapy in patients has been challenging owing to the heterogeneity of the patient population and lack of large sample sizes. However, as we investigate the mechanisms behind the disease process, the differences that exist between disease conditions and ages, and the significant alterations that may exist at the molecular and genetic level, our understanding of β-blocker therapy in pediatric heart failure will improve, and ultimately may lead to patient-specific therapy.

Clinical methods for the evaluation of endothelial function - a focus on resistance arteries

Endothelial dysfunction is a key event in the pathophysiology of cardiovascular diseases and appears as a strong independent predictor of cardiovascular events. In this context, biological evaluation of endothelial circulating markers can be helpful. However, functional tests using pharmacological stimuli appear more specific for the study of resistance arteries. These methods consist in the evaluation of the endothelium-dependent changes in regional vascular flow in response to local infusion of substances that act through endothelial receptors without modification of systemic arterial pressure and in comparison with a non endothelium-dependent relaxation. Flow is measured by Doppler and intravascular ultrasound in coronary circulation, laser Doppler in skin and by venous occlusion plethysmography in peripheral muscular arteries. Similar studies can be performed ex vivo using isolated resistance arteries obtained from fat subcutaneous biopsies. In addition, other information can be obtained from reactive hyperemia and the study of the flow-mediated dilatation of conduit arteries to enable a selective and comprehensive approach of the heterogeneity of endothelial function in pathophysiology.

Effects of therapeutic beta blockade on myocardial function and cardiac remodelling in congenital cardiac disease

BACKGROUND

Cardiac remodelling is now recognised as an important aspect of cardiovascular disease progression and is, therefore, emerging as a therapeutic target in cardiac failure due to different etiologies. Little is known about the influence of different therapies for cardiac failure on the remodelling seen in infants with congenital cardiac disease.

METHODS

During follow-up of a prospective and randomized trial, we investigated therapeutic effects on neurohormonal activation, ventricular function, and myocardial gene expression. We compared the data from 8 infants with severe congestive heart failure due to left-to-right shunts, who received digoxin and diuretics alone, to 9 infants who received additional treatment with propranolol.

RESULTS

In these infants, beta-adrenergic blockade significantly reduced highly elevated levels of renin, from 284 +/- 319 microU/ml compared to 1061 +/- 769 microU/ml. Systolic ventricular function was normal in both groups, but diastolic ventricular function was improved in those receiving propranolol, indicated by significantly lower left atrial pressures, lower end-diastolic pressures, and less pronounced ventricular hypertrophy, the latter estimated by lower ratios of myocardial wall to ventricular cavity areas on average of 42%. Further hemodynamic parameters showed no significant differences between the groups, except for the lower heart rate in infants treated with propranolol. In those treated with digoxin and diuretics, there was a significant downregulation of beta2-receptor and angiotensin-2 receptor genes, and up-regulation of endothelin A receptor and connective tissue growth factor genes, that were partially prevented by additional treatment with propranolol.

CONCLUSIONS

Beta-blockade is a new therapeutic approach for congestive heart failure in infants with congenital cardiac disease, producing with significant benefits on neurohormonal activation, diastolic ventricular function, and cardiac remodelling.