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Objective: To determine the validity of predictive equations in calculating oxygen consumption (Vo(2)) in ventilated patients with congenital heart disease., Design: Prospective study., Setting: Cardiac catheterization laboratories and intensive care units of two university teaching hospitals., Patients: A total of 126 patients with congenital heart disease were studied. Of these, 75 patients received anesthesia in the pediatric cardiac catheterization laboratory, and 51 were deeply sedated in the intensive care unit after open heart surgery., Measurements and Main Results: Vo(2) was measured directly in all patients using respiratory mass spectrometry. Estimated values for absolute Vo(2) (mL/min) and indexed Vo(2) (mL.min-1.m-2) were calculated from the four predictive equations published by LaFarge and Miettinen, Lundell et al., Wessel et al., and Lindahl. The agreement between measured and estimated Vo(2) was evaluated by calculating their bias and limits of agreement. A failure of agreement between measured and estimated Vo(2) was noted in both groups of patients, irrespective the equation used, and the agreement was poorer in patients in the intensive care unit. The equation by LaFarge and Miettinen produced the closest estimation in patients at cardiac catheterization with a bias of 4.5 mL/min for absolute Vo(2) and 6.9 mL.min-1.m-2 for indexed Vo(2). A systematic error of overestimating lower and underestimating higher indexed Vo(2) mL.min-1.m-2 was introduced in both groups., Conclusion: Predictive equations do not accurately estimate Vo(2) in ventilated patients with congenital heart disease.

Objective: Postoperative pulmonary hypertension in children after surgical intervention for congenital heart disease has been attributed to failure of the pulmonary endothelium to provide adequate vasodilation. Although we have shown that the impaired vasodilatory component attributable to the l-arginine-nitric oxide pathway is almost completely reversible, a nonrestorable component persists, implying an additional vasoconstrictive mechanism in postoperative pulmonary endothelial dysfunction. In this study of children after surgical intervention for congenital heart disease, we measured endothelin-1 levels and used BQ123, a selective endothelin-A receptor antagonist, together with inhaled nitric oxide to discriminate dysfunctional pulmonary endothelial vasodilation from endothelin-mediated pulmonary vasoconstriction., Methods: All children were examined early after surgical intervention in the intensive care unit. Pulmonary vascular resistance (with respiratory mass spectrometry), as well as arterial and venous endothelin-1 levels (measured by means of a quantitative enzyme-linked immunosorbent assay), were determined in 7 children (age range, 3.3-13.7 months; median age, 6.3 months) with intracardiac shunting defects at baseline and during ventilation with a fraction of inspired oxygen of 0.65, with additional BQ123 (0.1 mg/kg infused over 20 minutes), and with inhaled nitric oxide (20 ppm)., Results: Pulmonary vascular resistance decreased from 7.7 +/- 3.4 at baseline to 6.1 +/- 2.8 Woods units. m(-2) (P =.022) at a fraction of inspired oxygen of 0.65 and to 4.7 +/- 2.7 Woods units. m(-2) (P =.013) during BQ123 infusion. Inhaled nitric oxide had no further effect on pulmonary vascular resistance. Left atrial endothelin-1 levels (1.35-5.12 pg/mL; mean, 2.4 pg/mL) correlated significantly with the decrease in pulmonary vascular resistance in response to BQ123 infusion (r(2) = 0.89, P =.003)., Conclusion: Postoperative elevation of pulmonary vascular resistance in children after surgical intervention for congenital heart disease is responsive to endothelin-A blockade with BQ123. Increased levels of endothelin-1 predict the response to this therapy, which might become an important addition to the clinical armamentarium in postoperative pulmonary hypertensive disease.

Persistent pulmonary hypertension secondary to meconium aspiration syndrome is an important cause of morbidity and mortality in the neonatal population. We investigated the use of the phosphodiesterase-5 inhibitor sildenafil, in its intravenous form, as a pulmonary vasodilator in a model of meconium aspiration syndrome. Pulmonary hypertension was induced in 18 piglets, by endotracheal instillation of human meconium, 6 piglets subsequently received an infusion of intravenous sildenafil for 2 hours, 6 received inhaled nitric oxide for 2 hours, and 6 control animals received no additional intervention. Meconium aspiration increased pulmonary vascular resistance by 70%, and increased oxygenation index by over 100%. Pulmonary vascular resistance remained elevated for the remainder of the study period in control animals. Inhaled nitric oxide reduced the pulmonary vascular resistance by 40% after 2 hours of treatment; intravenous sildenafil completely reversed the increase in pulmonary vascular resistance within 1 hour of commencing the infusion. Neither agent had an effect on systemic hemodynamics. Sildenafil also increased cardiac output by 30%, but while doing so did not adversely influence oxygenation. Intravenous sildenafil is a selective and highly effective pulmonary vasodilator, which is at least as effective as inhaled nitric oxide, in this model of neonatal persistent pulmonary hypertension.

The presence of a patent arterial duct may complicate the course of the patient on veno-arterial extracorporeal membrane oxygenation (ECMO). While surgical ligation has been traditionally used as a definitive treatment for this problem, transcatheter closure may have advantages. This is the first report of transcatheter occlusion of a patent arterial duct in an infant on ECMO support.

It is unknown if nitric oxide (NO) modulates the balance between systemic or myocardial O2 delivery ( DO2) and consumption VO2 during inotropic stimulation with the beta-adrenergic agonist dobutamine. Accordingly, we measured systemic and left ventricular (LV) DO2 and during dobutamine infusion to a peak of 10 microg .kg-1 .min-1, before and after inhibition of NO synthesis with i.v. N(omega)-nitro- L-arginine ( L-NNA, 25 mg.kg-1) in 11 anesthetized ewes instrumented with aortic, pulmonary arterial and coronary sinus catheters, an ultrasonic coronary artery flow probe and a pulmonary arterial thermistor to measure cardiac output. L-NNA reduced systemic DO2 by 19% (2.1+/-0.5 ml.min-1.kg-1, P<0.005) but increased systemic by 13% (0.4+/-0.1 ml.in-1.g-1, P<0.05), whereas LV DO2 and rose by 44% (4.3+/-1.3 ml.min-1).100 g-1, P<0.005) and 47% (3.1+/-0.9.min-1.100 g-1, P<0.025) respectively. Dobutamine increased systemic DO2 by 61% (5.3+/-0.9 ml.min-1.kg-1, P<0.001) and systemic by 10% (0.32+/-0.12 ml.min-1.kg-1, P<0.01), with no effect of L-NNA on either response ( P>0.9). As a result, while was 0.5 ml.min(-1).kg-1 higher at any given level of DO2 ( P<0.001), the slope of the systemic DO2- relation was unchanged after L-NNA. By contrast, LV DO2 increased by 152% (15.6+/-2.2 ml.min-1.100 g-1, P<0.001) and by 184% (12.7+/-1.9 ml.min-1.100 g-1, P<0.001), but because the slope of both dose-response curves was reduced by 48% after L-NNA ( P<0.001), the LV DO2- relationship was unaffected by inhibition of NO synthesis. These results suggest that NO modulated the baseline balance between systemic, but not myocardial, DO2 and. However, NO did not additionally alter dobutamine-related changes in either systemic or myocardial DO2 and balance.

Objective: Young children with congenital cardiac defect and airway obstruction leading to ventilator dependency present a significant clinical challenge with uncertain outcome., Design: Retrospective review of our experience with self-expanding metal stents in these young children between 1996-2000., Results: Airway stenting has been undertaken in five such children (four boys, one girl) at our institution. Their mean age was 7.4 months (range 2-14 months), and four of the five had undergone congenital cardiac surgery and could not be weaned from the ventilator following surgery. These five children were ventilator dependent for a mean of 112 days (range 40-210 days, median 71). A total of ten self-expanding metal stents were inserted (4-11 mm in diameter and 15-33 mm in length). The sites stented included the trachea (two stents), the left main bronchus (three stents) and the bronchus intermedius (five stents). Four of these five children were successfully weaned from the ventilator and extubated after a mean time interval of 6 days (range 2-11 days, median 5.5) after stenting. One child failed to wean from the ventilator, required tracheostomy and is ventilator dependent after 8 months. There was one death 2 months after extubation but unrelated to the airway. Three children remain well and asymptomatic 24, 36 and 54 months after stenting., Conclusions: Airway stenting in such young children is an infrequent procedure often undertaken in dire circumstances. We have found it valuable in enabling ventilator-dependent children to be extubated with encouraging early results. Their long-term outlook remains uncertain and is dependent on the underlying cardiac status.

Infection with varicella zoster virus, leading to chicken pox in susceptible hosts, is usually a benign self-limiting disease conferring immunity in those affected. Cardiac complications are rare, but when present may lead to severe morbidity or mortality. We have recently encountered three children, all of whom developed significant cardiac complications secondary to infection with varicella. Myocarditis has long been associated with such infection. The pathological mechanism is presumed similar to other cardiotropic viruses, where both direct cytopathic and secondary auto-immune effects contribute to myocardial cellular destruction and ventricular dysfunction. Complications include arrhythmias and progression to dilated cardiomyopathy. Pericarditis, and secondary pericardial effusion, related to infection with the virus is most commonly associated with secondary bacterial infiltration. Both cardiac tamponade and chronic pericardial constriction may result. Endocarditis complicating varicella has only been described in the last fifteen years, and is associated with the emergence of virulent strains of both streptococcus and staphylococcus, the two organisms most commonly associated with endocarditis. The exact mechanism by which varicella causes secondary bacterial endocarditis remains unclear. Whilst cardiac complications of infection with the varicella zoster virus are rare, the resulting complications are potentially life threatening. Evidence of varicella-induced carditis must be aggressively pursued in any child with signs of acute cardiac decompensation in whom chicken pox is confirmed or suspected.

Objective: To determine: 1) if dobutamine elicited a thermogenic response during postnatal development; and 2) if this response impacted on the balance between systemic O(2) delivery (DO(2)) and O(2) consumption (VO(2)), and involved one or a combination of adrenoceptor subtypes., Design: Prospective non-randomized unblinded study., Setting: University research laboratory., Subjects: Thirty-five Border-Leicester cross lambs used in a main study performed at 1-2 days (n=7), 7-10 days (n=7), and 6-8 weeks (n=8), and in a adrenoceptor blockade substudy performed at 1-2 days (n=13)., Interventions: Lambs were instrumented under anaesthesia and dobutamine was infused at incremental rates of 1-40 microg/kg per minute. In separate subgroups of 1-2 day-old lambs, dobutamine was infused after selective or combined alpha1, beta 1, and beta 2-adrenoceptor blockade., Measurements: Cardiac output, aortic and pulmonary arterial blood gases, and body temperature were measured. DO(2) and VO(2) were calculated., Main Results: Dobutamine increased DO(2) similarly at all three ages. Dobutamine also increased VO(2) in the absence of muscle shivering, but the average rise in 1-2 day-old lambs was sevenfold to 12-fold greater (P<0.001) than in 7-10 day-old and 6-8 week-old animals, was associated with an increase in systemic O(2) extraction, and accounted for approximately 90% of the rise in DO(2). Body temperature rose by 1.3+/-0.5 degrees C in 1-2 day-old animals (P<0.001), but was unchanged in 7-10 day-old or 6-8 week-old lambs. In 1-2 day-old lambs, rises in DO(2), VO(2), and body temperature induced by dobutamine were not affected by selective alpha1, beta1 or beta2 adrenoceptor blockade, but were markedly attenuated by combined adrenoceptor blockade., Conclusions: A substantial rise in VO(2) which accompanied a pronounced thermogenic effect of dobutamine in newborn lambs utilized most of the associated increase in DO(2) and appeared to be dependent on activation of multiple adrenoceptor subtypes.

Abnormal loading and distension of the right ventricle may induce arrhythmia through the process of mechanoelectrical feedback. Nonetheless, the electrophysiological effects of right ventricular distension are ill-defined and the mechanisms which underpin mechanoelectrical feedback in the right ventricle are unknown. We examined the effects of changes in right ventricular load (complete occlusion of both caval veins or the main pulmonary artery) in 14 anaesthetised lambs, instrumented with right ventricular surface electrodes and strain gauges for recording monophasic action potential and segment length, and an integrated conductance and micromanometer-tipped catheter for measurement of right ventricular pressure and volume. Caval occlusion did not alter right ventricular segment length and monophasic action potential duration. By contrast, pulmonary arterial occlusion increased the segment length and decreased the monophasic action potential duration at 25, 50 and 70% repolarisation by 29 +/- 6, 22 +/- 4 and 17 +/- 3 ms, respectively (all P < 0.01). Of the 42 pulmonary arterial occlusions, 38 were associated with early afterdepolarisations (EADs) which increased progressively in magnitude as the occlusion was maintained until, in 32, overt arrhythmia was observed. By contrast, none of the four occlusions in which EADs were not observed resulted in arrhythmia. As a result, the proportion of occlusions which resulted in arrhythmia were greater in those associated with EADs than in those which were not (P = 0.002). Right ventricular distension alters the pattern of repolarisation, precipitates early afterdepolarisations and results in a variety of ventricular arrhythmia, including ventricular tachycardia.

Objective: We sought to define the contemporary clinical effect of increased pulmonary vascular resistance in infants after congenital heart operations with cardiopulmonary bypass., Methods: Fifteen infants (median age, 0.31 years; median weight, 5.1 kg) underwent cardiac operations involving cardiopulmonary bypass (range, 49-147 minutes). Pulmonary vascular resistance was measured in the immediate postoperative period in the intensive care unit by means of the direct Fick principle, with respiratory mass spectrometry to measure oxygen consumption. The effect of ventilation with an inspired oxygen fraction of 0.65, with additional infusion of L -arginine, substance P, and inhaled nitric oxide, was assessed and subsequently correlated with the length of mechanical ventilation from the end of cardiopulmonary bypass to successful extubation., Results: Overall, pulmonary vascular resistance at baseline (11.7 +/- 5.6 WU. m(2)) could be reduced to a minimum of 6.1 +/- 3.5 WU. m(2). The ventilatory time was 0.86 to 14.9 days (median, 1.75 days) and correlated directly with the lowest pulmonary vascular resistance value achieved during the pulmonary vascular resistance study (r (2) = 0.64, P <.01). The patient subgroup with mechanical ventilation of greater than 2 days had significantly higher pulmonary vascular resistance at all stages of the study protocol, and in this group there was a correlation of cardiopulmonary bypass time and ventilatory support time (r (2) = 0.48, P <.05)., Conclusion: Increased pulmonary vascular resistance, either directly or as a surrogate of the systemic inflammatory response after cardiopulmonary bypass, continues to have a significant effect on postoperative recovery of infants after cardiac operations.

Background: While unifocalization techniques have improved the treatment options in patients with pulmonary atresia, ventricular septal defect (PA-VSD), and major aortopulmonary collaterals (MAPCAs), severe airflow limitation contributes to significant early postoperative morbidity and mortality. Although this has been attributed to bronchospasm, characteristically it is refractory to bronchodilators, suggesting that other mechanisms may play a role., Methods and Results: The clinical course and preoperative angiograms of patients who underwent unifocalization were reviewed. Patients who developed airflow limitation early after surgery underwent fiberoptic bronchoscopy. In addition, the anatomy of the MAPCAs was examined in 14 heart-lung blocks from patients with PA-VSD. Twenty-two procedures were performed in 16 children. Three developed marked airflow limitation early after surgery, necessitating prolonged high-pressure ventilation. Bronchoscopy demonstrated tracheobronchial epithelial necrosis in 2 and signs of tracheobronchial ischemia in the third. Two were successfully extubated after 15 and 16 days, but the third died after 57 days of ventilatory support. Review of the preoperative angiograms demonstrated an extensive peribronchial arterial supply arising from a MAPCA in 1 of the patients who developed severe airway necrosis after unifocalization. This was also obvious in a second patient, but the MAPCA was not included in the unifocalization. In 7 autopsy specimens, MAPCAs contributed to a peribronchial or peritracheal vascular network. Dissection of the distribution of these branches in 2 specimens revealed extensive intrapulmonary peribronchial anastomoses., Conclusions: Airflow limitation early after unifocalization is related to airway ischemia resulting from interruption of the tracheobronchial blood supply during mobilization of MAPCAs.

Background: Impaired right ventricular function has been implicated as a cause of reduced maximal exercise capacity after the Mustard operation for transposition of the great arteries., Methods and Results: Fourteen asymptomatic survivors of the Mustard operation were studied. Each underwent conventional cardiac catheterization, and after satisfactory hemodynamics were confirmed, load-independent indexes of ventricular function were derived by conductance catheter during dobutamine infusion (0, 5, and 10 microg x kg(-1) x min(-1)). Seven patients also underwent upright exercise testing on a bicycle ergometer with analysis of respiratory gas exchange by continuous mass spectrometry. Accessible pulmonary blood flow was measured at each workload with an automated acetylene rebreathing technique. All patients exercised to a satisfactory end point (respiratory quotient >1.1). Maximum oxygen consumption during exercise was impaired compared with predicted values (mean, 77%; P:<0.02). Both exercise and dobutamine infusion were associated with an increase in cardiac index and heart rate and a reduced stroke volume index response. This was despite significantly improved indexes of myocardial contraction (end-systolic pressure volume relation, P:<0.001), preload recruitable stroke work index (P:<0.01), VA coupling (P:<0.001), and isovolumic relaxation (P:<0.001) during dobutamine infusion. There were no changes observed in end-diastolic pressure-volume relations, but there was failure to augment ventricular filling manifest by absence of change in dV/dt (P:=NS)., Conclusions: The stroke volume response to exercise stress is reduced in patients after the Mustard operation. A similar failure to augment stroke volume occurs during dobutamine stress despite appropriate responses in load-independent indexes of contraction and relaxation. This is due to failure to augment right ventricular filling rates during tachycardia, presumably as a result of impaired AV transport, consequent to the abnormal intra-atrial pathways.

In recent years, post-operative intensive care of the child with congenital cardiac disease has placed an emphasis on earlier weaning from mechanical ventilation. We describe our experience of postoperative fast-tracking of children undergoing cardiac surgery during a charitable mission in Venezuela, where resources and equipment were severely limited. During our stay, 11 children, with a median age of 2 years, underwent total correction of tetralogy of Fallot. The median duration of ventilation was 2.5 hours, and all patients were extubated within 12 hours of surgery. Effective analgesia was achieved without the need for continuous intravenous infusions of opiates. This experience shows that early extubation can safely be carried out in well-selected patients after surgery to correct congenital cardiac malformations. This allows faster throughput of patients, and helps provide an efficient and cost-effective service.

Background: Postoperative pulmonary hypertension in children after congenital heart surgery is a risk factor for death and is associated with severe acute changes in both pulmonary vascular resistance and lung mechanics., Objective: To examine the impact of changes in pulmonary blood flow on lung mechanics in preoperative children with congenital heart disease, in order to assess the cause-effect relation of pulmonary vascular-bronchial interactions., Design: Prospective, cross sectional study., Setting: Cardiac catheterisation laboratory, general anaesthesia with mechanical ventilation., Interventions: Variation of pulmonary blood flow (Qp) by either balloon occlusion of an atrial septal defect before interventional closure, or by complete occlusion of the pulmonary artery during balloon pulmonary valvuloplasty for pulmonary valve stenosis., Main Outcome Measures: Ventilatory tidal volume (Vt), dynamic respiratory system compliance (Cdyn), respiratory system resistance (Rrs)., Results: 28 occlusions were examined in nine patients with atrial septal defect (median age 9.5 years) and 22 in eight patients with pulmonary stenosis (median age 1.2 years). Normalisation of Qp during balloon occlusion of atrial septal defect caused no significant change in airway pressures and Rrs, but there was a small decrease in Vt (mean (SD): 9.61 (0.85) to 9.52 (0.97) ml/kg; p < 0.05) and Cdyn (0.64 (0.11) to 0.59 (0.10) ml/cm H(2)O*kg; p < 0.01). These changes were more pronounced when there was complete cessation of Qp during balloon valvuloplasty in pulmonary stenosis, with a fall in Vt (9.71 (2.95) to 9.32 (2.84) ml/kg; p < 0.05) and Cdyn (0.72 (0.29) to 0.64 (0.26) ml/cm H(2)O*kg; p < 0.001), and there was also an increase in Rrs (25.1 (1. 7) to 28.8 (1.6) cm H(2)O/litre*s; p < 0.01). All these changes exceeded the variability of the baseline measurements more than threefold., Conclusions: Acute changes in pulmonary blood flow are associated with simultaneous changes in lung mechanics. While these changes are small they may represent a valid model to explain the pathophysiological impact of spontaneous changes in pulmonary blood flow in clinically more critical situations in children with congenital heart disease.

Objective: To assess longitudinal changes in systemic ventricular diastolic function late after the Fontan procedure., Design and Patients: Prospective study of 13 patients at 2.8 (2.0) years (early) and again at 11.4 (2.0) years (late) after the Fontan procedure by Doppler echocardiography with simultaneous ECG, phonocardiogram, and respirometer., Setting: Tertiary paediatric cardiac centre., Results: The isovolumic relaxation time (IVRT) was significantly longer, and E wave deceleration time, E and A wave velocities, and E:A velocity ratio were reduced compared to normal both early and late after the procedure. The mean (SD) z score of IVRT decreased significantly from +2.50 (1.00) to +1.24 (0.80) (p = 0.002), and the z score of the E wave deceleration time decreased from -1.69 (1.31) to -2.40 (1.47) (p = 0.03) during follow up. The A wave deceleration time also tended to decrease (early 80 (12) ms v late 73 (11) ms, p = 0.13) with increased follow up. There were no changes of the E and A wave velocities and E:A velocity ratio. The E wave velocity was inversely related to IVRT both early (r = -0.82, p = 0.001) and late (r = -0.59, p = 0.034) after the operation. The prevalence of diastolic flow during isovolumic relaxation decreased from 85% (11/13) to 38% (5/13) (p = 0.04), while that of mid diastolic flow increased from 23% (3/13) to 77% (10/13) (p = 0.02) between the two assessments., Conclusions: Left ventricular diastolic function remains highly abnormal late after the Fontan procedure. The longitudinal changes demonstrated on follow up are compatible with reduction of left ventricular compliance in addition to persisting abnormalities of relaxation.

Objective: We sought to assess oxygen consumption and its determinants in children shortly after undergoing cardiopulmonary bypass operations., Methods: Twenty children, aged 2 months to 15 years (median, 3.75 years), undergoing hypothermic cardiopulmonary bypass operations were studied during the first 4 hours after arrival in the intensive care unit. Central and peripheral temperatures were monitored. Oxygen consumption was continuously measured by using respiratory mass spectrometry. Oxygen delivery was calculated from oxygen consumption and arterial and mixed venous oxygen contents, which were sampled every 30 minutes. Oxygen extraction was derived by the ratio of oxygen consumption and oxygen delivery. Arterial blood lactate levels were measured every 30 minutes., Results: There was a correlation between oxygen consumption and age in patients older than 3 months (r = -0.76). Mean oxygen consumption increased by 14.7% during the study. The increase in oxygen consumption was correlated with the increase in central temperature (r = 0.73). Nine patients had an arterial lactate level above 2 mmol/L on arrival. There were no significant differences in oxygen consumption, oxygen delivery, and oxygen extraction between the group with lactate levels between 2 and 3 mmol/L and the groups with normal lactate levels both on arrival and at 2 hours. One patient with a peak lactate level of 6.8 mmol/L had initially low oxygen delivery (241.3 mL. min(-1). m(-2))., Conclusions: During the early hours after a pediatric cardiac operation, the increase in oxygen consumption is mainly attributed to the increase in central temperature. Oxygen consumption is negatively related to age. Mild lactatemia is common and does not appear to reflect oxygen delivery or oxygen consumption or a more complicated recovery.

Little is known about the changes in systemic and pulmonary vascular responses to dobutamine that occur during postnatal development. To address this question, vascular pressures and cardiac output were measured in anesthetized 1- to 2-d-old (n = 6), 7- to 10-d-old (n = 7), and 6- to 8-wk-old lambs (n = 6) while dobutamine was infused incrementally in the dose range of 0.5-40 microg x kg(-1) x min(-1). Dobutamine reduced pulmonary vascular resistance in the three age groups (all p<0.005). However, although this reduction reached a plateau over the infusion range of 15-40 microg x kg(-1) x min(-1) at all ages, its magnitude was less (p<0.02) in 1- to 2-d-old lambs (24+/-2%) than in 7- to 10-d-old (41+/-7%) or 6- to 8-wk-old lambs (42+/-6%). Over the same infusion range, dobutamine produced a fall in systemic vascular resistance (all p<0.005) that was proportionally similar in 1- to 2-d-old (51+/-3%), 7- to 10-d-old (48+/-3%), and 6- to 8-wk-old lambs (42+/-6%). In separate subgroups of 1- to 2-d-old lambs, pulmonary and systemic responses to dobutamine were not affected by pretreatment with selective alpha1-, beta1-, or beta2-adrenoceptor antagonists. Taken together, these findings suggest that the pulmonary but not systemic vasodilator response to dobutamine in lambs is blunted in the initial days after birth, and that this pulmonary effect is not directly related to the adrenoceptor-stimulating properties of dobutamine.

A low cardiac output state is an important cause of morbidity and mortality following repair of tetralogy of Fallot (ToF). This is often refractory to conventional measures. The cardiac output of these patients is highly dependent on diastolic pulmonary arterial flow which is enhanced during spontaneous respiration, but much reduced by intermittent positive pressure ventilation (IPPV). We report the successful use of negative pressure ventilation (NPV) as haemodynamic therapy in three children with a low output secondary to restrictive right ventricular (RV) physiology following ToF repair. NPV produced a significant haemodynamic improvement, with increases in cardiac output of greater than 100 % in two of the children. By augmenting pulmonary blood flow, and hence cardiac output, NPV has a role as adjunctive haemodynamic therapy in patients with a low output secondary to diastolic RV dysfunction, in whom early extubation is not possible.

Aims: To compare changes in global haemodynamics as well as anterior cerebral and superior mesenteric artery perfusion after dopamine treatment., Methods: Anterior cerebal and superior mesenteric artery perfusion was measured using Doppler ultrasonography in hypotensive preterm neonates in whom cardiac output increased (group 1, n=10) or decreased (group 2, n=40) after dopamine treatment., Results: Despite a lower dopamine infusion rate, the blood pressure increase (mm Hg) in group 2 [Delta=13(1); mean(SE)] exceeded that in group 1 [Delta=8(1)], while systemic vascular resistance (mm Hg/l/min/kg) rose in group 2 [Delta=106 (37)], but was unchanged in group 1 [Delta=9 (6)]. Anterior cerebral artery blood velocity and resistance were unaffected by dopamine. However, compared with unchanged values in group 1, superior mesenteric artery blood velocity fell by 14.7(4.8) cm/s and resistance increased by 4.1(0.7) mm Hg/cm in group 2., Conclusions: These results suggest that, in a portion of hypotensive preterm neonates, the increase in blood pressure induced by dopamine is related to a predominant vasoconstrictor action and is associated with a fall in bowel perfusion.

There has been increasing interest in the study of ventricular function in the patient with congenital heart disease. Numerous indexes have been derived for the assessment of ventricular function, suggesting that none is ideal. While the derivation of some measures of ventricular function have relied on advanced mathematical principles, it is still possible for the non-mathematician to obtain important insights into ventricular function from an assessment of the events which underpin the cardiac cycle. In this review, I use the mechanics of the cardiac cycle to introduce basic concepts of ventricular function for the non-expert. In this way, I analyse ventricular systolic and diastolic performance and describe the contribution of regional variability of function to overall performance. This approach also highlights the role of the ventricle in overall cardiovascular and metabolic homeostasis.

Objective: To assess the interaction between pulmonary hemodynamics and respiratory mechanics during acute pulmonary hypertension., Patients: Ventilated and paralysed children treated with inhaled nitric oxide because of post-operative pulmonary hypertension., Interventions: Weaning of inhaled nitric oxide., Measurements: Air flow and airway pressure, calculation of dynamic respiratory system compliance and respiratory system resistance for each breath by multiple linear regression., Results: In four patients, increases in pulmonary arterial pressure from 26.1 to 56.7 mm Hg (p<0.001) during weaning off nitric oxide were associated with decreases in tidal volume (from 9.7-->8.2 ml/kg, p<0.01) and reductions in dynamic respiratory system compliance (from 0.52-->0.34 cm H20/ml/kg, p<0.001), while respiratory system resistance was unchanged., Conclusions: Impaired ventilation during acute pulmonary hypertension is predominantly related to a reduction in respiratory system compliance.

Objective: To determine whether inotropic responses to the beta-adrenergic agonist dobutamine are potentiated by systemic inhibition of nitric oxide synthase (NOS) with the L-arginine analogue N omega-nitro-L-arginine (L-NNA), and to establish to what extent any observed responses are related to the increase in aortic blood pressure accompanying systemic NOS inhibition., Methods: Dobutamine was infused incrementally at rates of 1, 2.5, 5 and 10 micrograms/kg/min in 15 open-chest, anaesthetised ewes before and after inhibition of NO synthesis with i.v. L-NNA (n = 8), or elevation of mean aortic blood pressure to the same extent as attained with NOS inhibition using proximal arterial occlusion (n = 7)., Results: By the peak infusion rate, dobutamine increased the maximal rate of rise of left ventricular pressure (LV dP/dtMAX) by 100% (p < 0.001) and reduced LV stroke work by 18% (p < 0.01). L-NNA and arterial occlusion increased resting mean aortic blood pressure by 55 +/- 4 and 51 +/- 3 mmHg respectively. Compared to dobutamine alone, subsequent peak dobutamine-related increases in LV dP/dtMAX were augmented by 76% after L-NNA and by 88% after arterial occlusion (both p < 0.001). Moreover, dobutamine increased LV stroke work by 23% at infusion rates of 1-5 micrograms/kg/min (p < 0.001) after L-NNA, and by 17% at an infusion rate of 1 microgram/kg/min (p < 0.01) after arterial occlusion., Conclusions: Systemic NOS inhibition potentiates the effects of dobutamine on LV isovolumic and pumping performance in the intact circulation, but this potentiation is in large part related to the increase in arterial blood pressure accompanying NOS inhibition.

Objective: To assess the impact of the bidirectional cavopulmonary shunt, total cavopulmonary connection, and baffle fenestration on outcome of the Fontan operation in our unit., Method: We reviewed 123 bidirectional cavopulmonary shunts and 264 Fontan operations performed from 1980 to 1995. Analysis of pulmonary artery size (right and left main and lower lobe branches) before and after bidirectional cavopulmonary shunt was performed. Outcome of the Fontan operation was analysed in various time periods to assess the effect of prior bidirectional cavopulmonary shunt, use of the lateral tunnel, and fenestration., Results: Operative risk for the bidirectional cavopulmonary shunt was 4% (CI = 2-10%) with a survival of 89% (CI = 83-95%) at 36 months. Probability of conversion to Fontan operation at 36 months was 49% (CI = 38-61%). Pulmonary artery size (Nakata and lower lobe indices) fell after bidirectional cavopulmonary shunt (P = 0.0006). Fontan risk dropped from 8.5% (1980-1987) to 1.8% (1988-1995) (P = 0.02), coinciding with the use of the bidirectional cavopulmonary shunt. There was no further risk reduction after introduction of the lateral tunnel and baffle fenestration, although these comparisons are limited by relatively small numbers. Duration of hospital stay related to pleural effusions was lowest for patients with a fenestrated lateral tunnel operation (P < 0.05)., Conclusion: The bidirectional cavopulmonary shunt is a suboptimal stimulus for pulmonary artery enlargement, but may reduce the risk of Fontan operation in selected children. Fenestrated lateral tunnel operations have reduced the duration of postoperative pleural effusions.

Background: Infective endocarditis is an uncommon but serious disease in children. Optimal treatment strategy, especially surgical indications, continues to evolve., Methods: Retrospective review of 98 patients treated for infective endocarditis during the past 13 years at the Royal Children's Hospital, including medically and surgically treated patients., Results: Thirty of 98 patients had surgical intervention with 6.7% hospital mortality, and 76% survival probability at 45 months. The remaining patients were treated medically, with 10% hospital mortality and 52% 5-year survival probability. The incidence of structural heart disease, congestive heart failure, and spectrum of organisms was similar in the two groups., Conclusions: Despite advances in antibiotic therapy, early surgical intervention is required in a significant subset. Concurrent intracardiac repair may be appropriate.

Pulmonary arterial size was measured during cineangiography in 23 patients, 1.9 months before, and 14 months after bidirectional cavopulmonary connection (BCPC). Measurements were standardized for body surface area using the method of Nakata and co-workers (pulmonary artery index). There was a significant reduction in pulmonary artery index after BCPC. These data suggest that pulmonary arterial growth is impaired after the creation of a BCPC. This may be related to an absolute reduction in pulmonary arterial flow, and/or the loss of systolic expansion of the pulmonary artery.

The optimal management of infants with pulmonary atresia with intact ventricular septum (PA.IVS) remains a controversy. Attempts have been made to base the surgical approach on various geometrical or morphological characteristics of the right ventricle (RV). However, the overall results remain poor when compared to other complex congenital heart defects. Forty-eight neonates with PA.IVS were admitted to our unit between 1980 and 1992. The management plan has evolved to be based entirely on the echocardiographic assessment of the state of development of the infundibulum of the RV. In neonates with a well-formed infundibulum (n = 31), the initial palliation consisted mainly of pulmonary valvotomy (without cardiopulmonary bypass) and PTFE shunt from the left subclavian artery to the main pulmonary artery. There was one death from initial palliation in this subgroup. If necessary, the RV cavity was later enlarged by excision of the hypertrophic muscle of both the trabecular and infundibular portions, before finally attempting biventricular repair. The actuarial probability of achieving a biventricular repair at 40 months of age was 60% (95% CL = 39.5% to 71.3%). Thirteen patients have undergone biventricular repairs with one late death over a total follow-up of 1,720 patient months. In one patient, the RV failed to grow satisfactorily, necessitating a Fontan procedure. Seventeen patients without a well-formed infundibulum were approached with a Fontan procedure in mind. The initial palliation in these patients consisted of a modified Blalock-Taussig shunt only. Ten have undergone a Fontan procedure so far and five are awaiting such repairs. In this group there were four operative deaths: two after initial palliation, and two after Fontan procedures. In patients with a well-developed infundibulum, the actuarial survival probability was 93% (95% CL = 74% to 98%) at 8 months with no further late deaths over 120 months follow-up, whereas in patients without a well-formed infundibulum it was 75% at 40 months (95% CL = 46% to 89%). The overall survival probability at 104 months was 77% (95% CL = 51% to 90%).

Whereas abnormalities of the morphological tricuspid valve are common in the setting of discordant atrioventricular connections, there are only a few postmortem reports of abnormalities of the mitral valve in this condition. This report describes two patients with discordant atrioventricular connections, in whom important abnormalities of the mitral valve were found during life by cross sectional echocardiography.

Objective: To study regional wall motion of the systemic ventricle in patients after the Fontan operation., Design and Patients: Systemic ventricular angiograms of 15 patients after the Fontan operation and of 11 unoperated patients with a univentricular atrioventricular connection were digitised frame by frame. Strict criteria for abnormal wall motion were used so that minor abnormalities were not considered., Results: Incoordinate contraction of the ventricular wall was found in five of the 11 patients before and in four of the 15 patients after the Fontan operation (NS). Only three of the 11 patients before the Fontan operation, showed incoordination of ventricular relaxation, but incoordinate relaxation was seen in 12 of the 15 patients after operation (p less than 0.01)., Conclusions: Whereas incoordination of ventricular contraction was common in patients with a univentricular atrioventricular connection, before or after the Fontan operation, incoordinate relaxation of the ventricular wall was a common consequence of the Fontan operation and was rare in patients before operation.

Objective: To assess whether regional abnormalities of ventricular function are present in patients after the Fontan operation and to explore the implications of any such abnormalities for ventricular filling., Design and Patients: Prospective study in which 25 patients after the Fontan operation were compared with 25 healthy controls and 12 patients with a univentricular atrioventricular connection, before the Fontan operation., Interventions: Doppler echocardiography, with simultaneous electrocardiogram, phonocardiogram, and respirometer., Results: Isovolumic relaxation time was significantly longer in patients after the Fontan operation than in normal children (p less than 0.001) or the preoperative patients (p = 0.001). Systolic intraventricular flow was detected in 60% of patients after the Fontan operation and in 42% of preoperative patients. After the Fontan operation 80% of patients showed intraventricular flow during isovolumic relaxation compared with 8% of normal children and none of the preoperative patients., Conclusions: Incoordinate ventricular relaxation is common after the Fontan operation. This may have important implications for ventricular diastolic filling, pulmonary blood flow, and cardiac output in these patients.

Objective: To document whether the act of respiration influences pulmonary blood flow in patients after the Fontan operation., Design: Prospective study in which patients acted as their own controls., Setting: Supraregional paediatric cardiology centre., Patients: Sixteen patients who had undergone atriopulmonary anastomosis (Fontan operation) for the treatment of congenital heart disease., Intervention: Doppler assessment of pulmonary artery flow patterns with a simultaneous respirometer, electrocardiogram and phonocardiogram., Results: Total (mean (1SD) ) forward pulmonary flow was 63.6 (35)% higher during inspiratory cardiac cycles than during expiratory ones., Conclusions: The act of breathing provides an additional energy supply to pulmonary blood flow in patients after the Fontan operation.

The development of abnormal flow has been described in patients with incoordinate motion of the ventricular wall. In all cases so far documented, these abnormal patterns of flow have been restricted to the ventricular cavity, and the atrioventricular valve remained closed. We identified a patient after a Fontan operation in whom the degree of ventricular mural incoordination was of such severity that the atrioventricular valve remained open and atrioventricular flow occurred for 140 msec after the onset of QRS complex. As far as we know, this phenomenon has not previously been described.

Pulmonary blood flow patterns were studied during the application of varying extrathoracic pressure in 2 patients after total cavopulmonary anastomosis. The application of negative extrathoracic pressure was associated with large increases in pulmonary blood flow, while positive extrathoracic pressure, caused retrograde flow away from the lungs. These preliminary observations suggest that negative extrathoracic pressure may be useful as a means of respiratory support in patients after right heart bypass procedures.

An oral solution containing lactulose and L-rhamnose was administered to six patients with cystic fibrosis. Intestinal absorption of both sugars was assessed by measurement of their urinary excretion. The lactulose: L-rhamnose excretion ratio was raised, supporting the hypothesis of an intestinal component to the malabsorption of cystic fibrosis.