Thomas J. Kulik

Efficacy and Safety of Milrinone in Preventing Low Cardiac Output Syndrome in Infants and Children After Corrective Surgery for Congenital Heart Disease

Background—Low cardiac output syndrome (LCOS), affecting up to 25% of neonates and young children after cardiac surgery, contributes to postoperative morbidity and mortality. This study evaluated the efficacy and safety of prophylactic milrinone in pediatric patients at high risk for developing LCOS. Methods and Results—The study was a double-blind, placebo-controlled trial with 3 parallel groups (low dose, 25-&mgr;g/kg bolus over 60 minutes followed by a 0.25-&mgr;g/kg per min infusion for 35 hours; high dose, 75-&mgr;g/kg bolus followed by a 0.75-&mgr;g/kg per min infusion for 35 hours; or placebo). The composite end point of death or the development of LCOS was evaluated at 36 hours and up to 30 days after randomization. Among 238 treated patients, 25.9%, 17.5%, and 11.7% in the placebo, low-dose milrinone, and high-dose milrinone groups, respectively, developed LCOS in the first 36 hours after surgery. High-dose milrinone significantly reduced the risk the development of LCOS compared with placebo, with a relative risk reduction of 55% (P =0.023) in 238 treated patients and 64% (P =0.007) in 227 patients without major protocol violations. There were 2 deaths, both after infusion of study drug. The use of high-dose milrinone reduced the risk of the LCOS through the final visit by 48% (P =0.049). Conclusions—The use of high-dose milrinone after pediatric congenital heart surgery reduces the risk of LCOS.

Use of inhaled nitric oxide and acetylcholine in the evaluation of pulmonary hypertension and endothelial function after cardiopulmonary bypass.

BackgroundIncreased pulmonary vascular resistance is common in congenital heart disease and is exacerbated by cardiopulmonary bypass (CPB). We investigated whether CPB is responsible for pulmonary endothelial dysfunction and contributes to postoperative pulmonary hypertension. Methods and ResultsWe infused the endothelium-dependent vasodilator acetylcholine (ACH) into the pulmonary circulation of pulmonary hypertensive children with congenital heart disease either before (n= 12) or after (n=22) surgical repair on CPB. The dose response to ACH (10−1 to 10–6 M) was recorded for all hemodynamic variables. Nine additional postoperative patients were studied with ACH followed by inhalation of 80 ppm nitric oxide, an endothelium-independent smooth muscle relaxant. Plasma levels of cyclic GMP (cGMP) were measured before and after ACH and nitric oxide administration. Pulmonary vasodilation with 10−1 M ACH was seen in all preoperative patients but was markedly attenuated in postoperative patients. Baseline pulmonary vascular resistance (5.6±1.0 U m2) fell 46±5% in preoperative patients but declined only 11±4% from baseline (5.8±0.9 U m2) in postoperative patients (P<.002). However, inhalation of 80 ppm nitric oxide after ACH infusion in postoperative patients lowered pulmonary vascular resistance by 33±4% (P<.0002 compared with postoperative ACH response) with minimal effects on the systemic circulation. This finding suggests that the capacity for smooth muscle relaxation and pulmonary vasodilation was present in postoperative patients but could not be induced by ACH. Plasma levels of cGMP in postoperative patients were unchanged after acetylcholine infusion but rose more than threefold during pulmonary vasodilation with nitric oxide (P<.0001). This finding is consistent with the purported role of cGMP as the second messenger effecting smooth muscle relaxation in this process. ConclusionsCPB may be responsible for postoperative dysfunction of the pulmonary endothelial cell and may contribute to postoperative pulmonary hypertension in children. Inhaled nitric oxide is a potent pulmonary vasodilator after CPB with minimal systemic circulatory effects. It may have important diagnostic and therapeutic applications in patients with congenital heart disease.

Nitric Oxide–Generating Compounds Inhibit Total Protein and Collagen Synthesis in Cultured Vascular Smooth Muscle Cells

Nitric oxide (NO) participates in the regulation of vascular tone and smooth muscle cell proliferation, but little is known of its effect on total protein and matrix synthesis in smooth muscle. We studied the effects of the NO-generating compounds S-nitroso-N-acetylpenicillamine (SNAP, 0.4 to 1.2 mmol/L) and sodium nitroprusside (SNP, 0.1 to 0.5 mmol/L) on total protein (using [3H]leucine) and collagen (using [3H]proline) synthesis in cultured rabbit aortic smooth muscle cells. Both agents caused dose-dependent inhibition of the relative rate of protein (maximum reduction of 87% [SNAP] and 80% [SNP]) and collagen synthesis, as measured by trichloroacetic acid-precipitated label. The magnitudes of percent inhibition of total protein and collagen synthesis were approximately equal. Inhibition of protein synthesis by SNAP and SNP was prevented by hemoglobin (10 mumol/L), suggesting that the protein synthesis inhibition was due to NO release. Inhibition of protein synthesis was reversible after removal of SNAP and SNP and was not caused by damage to the cells. These results suggest that NO may function as a modulator of vascular smooth muscle cell protein synthesis and production of extracellular matrix components.

Optimizing seeding and culture methods to engineer smooth muscle tissue on biodegradable polymer matrices

The engineering of functional smooth muscle (SM) tissue is critical if one hopes to successfully replace the large number of tissues containing an SM component with engineered equivalents. This study reports on the effects of SM cell (SMC) seeding and culture conditions on the cellularity and composition of SM tissues engineered using biodegradable matrices (5 x 5 mm, 2-mm thick) of polyglycolic acid (PGA) fibers. Cells were seeded by injecting a cell suspension into polymer matrices in tissue culture dishes (static seeding), by stirring polymer matrices and a cell suspension in spinner flasks (stirred seeding), or by agitating polymer matrices and a cell suspension in tubes with an orbital shaker (agitated seeding). The density of SMCs adherent to these matrices was a function of cell concentration in the seeding solution, but under all conditions a larger number (approximately 1 order of magnitude) and more uniform distribution of SMCs adherent to the matrices were obtained with dynamic versus static seeding methods. The dynamic seeding methods, as compared to the static method, also ultimately resulted in new tissues that had a higher cellularity, more uniform cell distribution, and greater elastin deposition. The effects of culture conditions were next studied by culturing cell-polymer constructs in a stirred bioreactor versus static culture conditions. The stirred culture of SMC-seeded polymer matrices resulted in tissues with a cell density of 6.4 +/- 0.8 x 10(8) cells/cm3 after 5 weeks, compared to 2.0 +/- 1.1 x 10(8) cells/cm3 with static culture. The elastin and collagen synthesis rates and deposition within the engineered tissues were also increased by culture in the bioreactors. The elastin content after 5-week culture in the stirred bioreactor was 24 +/- 3%, and both the elastin content and the cellularity of these tissues are comparable to those of native SM tissue. New tissues were also created in vivo when dynamically seeded polymer matrices were implanted in rats for various times. In summary, the system defined by these studies shows promise for engineering a tissue comparable in many respects to native SM. This engineered tissue may find clinical applications and provide a tool to study molecular mechanisms in vascular development.

Pediatric Pulmonary Hypertension Guidelines From the American Heart Association and American Thoracic Society

Pulmonary hypertension is associated with diverse cardiac, pulmonary, and systemic diseases in neonates, infants, and older children and contributes to significant morbidity and mortality. However, current approaches to caring for pediatric patients with pulmonary hypertension have been limited by the lack of consensus guidelines from experts in the field. In a joint effort from the American Heart Association and American Thoracic Society, a panel of experienced clinicians and clinician-scientists was assembled to review the current literature and to make recommendations on the diagnosis, evaluation, and treatment of pediatric pulmonary hypertension. This publication presents the results of extensive literature reviews, discussions, and formal scoring of recommendations for the care of children with pulmonary hypertension.

Outcome of pediatric patients treated with extracorporeal life support after cardiac surgery

BACKGROUND Extracorporeal life support (ECLS) has been used for over two decades in select patients after cardiac surgery. We previously described factors associated with death in this population. We now review our recent experience to reassess factors related to mortality. METHODS All pediatric patients who received ECLS support within 7 days after surgery between July 1995 and June 2001 were examined to describe clinical features associated with survival. We compared the results with our prior report to assess changes in practice and outcome. RESULTS Seventy-four patients were followed. Fifty percent survived to discharge. Hospital survival was not significantly related to patient age, cannulation site, or indication. Thirty-five percent of patients required hemofiltration while on ECLS and were significantly less likely to survive (23% vs 65%). A multivariate analysis combining all children from our prior report with the present cohort revealed that patients who received hemofiltration were five times more likely to die (odds ratio 5.01, 95% confidence interval 2.11-11.88). Children with an adequate two-ventricular repair had lower risk of death (odds ratio 0.42, 95% confidence interval 0.19-0.91) after adjusting for patient age, study period, and hours elapsed before initiation of ECLS after surgery. CONCLUSIONS Patients with an adequate two-ventricle repair have significantly higher hospital survival, whereas those with single ventricle physiology or need for dialysis have decreased survival.

Development and characterization of a cloned rat pulmonary arterial smooth muscle cell line that maintains differentiated properties through multiple subcultures.

BackgroundPulmonary hypertension is associated with abnormal pulmonary arterial contractility and growth. The mechanisms for these abnormalities are largely unknown. To study these processes, we sought to develop an in vitro system. Even though cultured aortic and pulmonary artery smooth muscle cells (SMCs) have been of considerable value in studying smooth muscle biology, one drawback of this system has been that these cells often lose differentiated properties in an unpredictable manner when they are passaged in culture. In addition, there appear to be significant differences in physiological and pathological responses between the systemic and pulmonary circulations, many of which could be directly related to the smooth muscle. We therefore established a cloned population of rat pulmonary arterial SMCs (PASMCs) that maintain differentiated properties through multiple subcultures. Methods and ResultsPASMCs were obtained initially by enzymatic dissociation from pulmonary arteries of adult Sprague-Dawley rats. From these cells, clones were isolated. The cloned cells retained expression of functional surface receptors for angiotensin II, norepinephrine, and α-thrombin and high levels of the smooth muscle isoforms of α-actin, myosin heavy chain, myosin regulatory light chain, and α-tropomyosin mRNAs even after multiple passages. The cells could also be transfected and processed exogenous transcripts in a smooth muscle-specific fashion. ConclusionsThese cloned PASMCs retain many differentiated characteristics and should be valuable for future studies of pulmonary vascular smooth muscle cell biology.

Effect of Mechanical Forces on Growth and Matrix Protein Synthesis in the In Vitro Pulmonary Artery Analysis of the Role of Individual Cell Types

The effect of mechanical stimuli on pulmonary artery growth and matrix tissue synthesis (and how individual cell types in the vessel wall respond to such stimuli) is incompletely characterized. Rabbit pulmonary arteries were placed in tissue culture medium and subjected to varying magnitudes of stretch or hydrostatic pressure (separately) for 4 days. The rate of protein synthesis in smooth muscle cells (by quantitative autoradiography) was positively related to the magnitude of stretch, as were the percentage of procollagen type I-positive cells and the rate of cell replication. In adventitial fibroblasts, stretch increased the rate of replication but not of protein synthesis. Hydrostatic pressure had little or no effect on the variables measured in either smooth muscle cells or fibroblasts. Stretch also increased the rate of elastin and collagen synthesis in the whole pulmonary artery segment, and after 4 days of stretch, the contents of actin and elastin were increased. Removal of the endothelium did not affect stretch-induced protein, collagen, or elastin synthesis but augmented stretch-induced smooth muscle replication. These data suggest that in the intact pulmonary artery, stretch, but not pressure, can stimulate hypertrophy and hyperplasia in smooth muscle cells and hyperplasia in fibroblasts. Matrix protein synthesis and accumulation are also increased by stretch. Neither stretch-mediated growth nor matrix protein synthesis required endothelium in this model.

Use of extracorporeal life support as a bridge to pediatric cardiac transplantation

BACKGROUND Extracorporeal life support (ECLS) has been used for post-cardiotomy rescue, but its use as a bridge to heart transplantation (OHT) in patients with post-surgical or end-stage ventricular failure remains controversial. METHODS Records were reviewed for patients receiving ECLS for ventricular failure from January 1991 to August 2001. Patients listed for OHT were analyzed separately. Listing for OHT requirements were improbable myocardial recovery, absence of contraindications (central nervous system damage, high pulmonary resistance, ongoing infection, etc.), and parental consent. Outcome variables included patient demographics, diagnosis, days from ECLS initiation to United Network for Organ Sharing (UNOS) listing (latency), list time, renal function, and survival to discharge. RESULTS Of 145 patients with ventricular failure who received ECLS, 21 pediatric patients were UNOS listed. Of 124 non-listed patients, 57 (46%) survived to discharge. All but 3 survivors were separated from ECLS in </=7 days. Twelve underwent OHT and 10 survived to discharge (list time, 6 days; median ECLS time, 14 days). Five had ECLS discontinued without undergoing OHT (1 later underwent OHT, 2 survived to discharge). Five experienced complications while receiving ECLS and died without undergoing OHT. Six of 9 patients who required dialysis for renal failure died. Of 11 infants listed, 4 were weaned from ECLS without undergoing OHT (2 survived to discharge), 5 had OHT (ECLS support, 4 days; 4 survived to discharge) and 2 died (ECLS support, 16 and 47 days). CONCLUSIONS (1) Extracorporeal life support can be used as a bridge to OHT (even among the infant population) for at least 2 weeks with acceptable survival and hospital discharge rates, and (2) renal insufficiency with the concomitant requirement for dialysis decreases the likelihood of survival before and after OHT.

Resting coronary flow and coronary flow reserve in human infants after repair or palliation of congenital heart defects as measured by positron emission tomography

OBJECTIVE Coronary physiology in infants with congenital heart disease remains unclear. Our objective was to better understand coronary physiology in infants with congenital heart disease. METHODS We used positron emission tomography with nitrogen 13-labeled ammonia to measure myocardial perfusion at rest and with adenosine (142 micrograms/kg/min x 6 minutes) in five infants after anatomic repair of a congenital heart lesion (group I), and in five infants after Norwood palliation for hypoplastic left heart syndrome (group II). The groups were matched for age, weight, and time from the operation. RESULTS Resting coronary flow in the left ventricle in group I was 1.8 +/- 0.2 ml/min/gm; resting flow in the right ventricle in group II was 1.0 +/- 0.3 ml/min/gm (p = 0.003). Coronary flow with adenosine was 2.6 +/- 0.5 ml/min/gm in group I and 1.5 +/- 0.7 ml/min/gm in group II (p = 0.02). Absolute coronary flow reserve was the same in both groups (1.5 +/- 0.2 in group I vs 1.6 +/- 0.3 in group II, p = 0.45). Oxygen delivery was reduced in group II compared with group I at rest (16.1 +/- 4.2 ml/min/100 gm vs 28.9 +/- 4.42 ml/min/100 gm, p = 0.02) and with adenosine (25.5 +/- 8.1 ml/min/100 gm vs 42.3 +/- 5.8 ml/min/100 gm, p = 0.02). CONCLUSIONS Infants with repaired heart disease have higher resting flow and less coronary flow reserve than previously reported for adults. After Norwood palliation, infants have less perfusion and oxygen delivery to the systemic ventricle than do infants with a repaired lesion. This may in part explain why the outcome for patients with Norwood palliation is less favorable than for others.