Endovascular stents for coarctation of the aorta: initial results and intermediate-term follow-up.

OBJECTIVES: The aim of this study was to evaluate the use of endovascular stents in native and recurrent coarctation of the aorta (CoA). BACKGROUND: Stents have been used successfully in various locations. Their use in CoA can be an alternative to surgery or balloon angioplasty (BA). METHODS: Thirty-four patients with CoA (13 native and 21 re-coarctation after surgery or BA) with a mean age of 16 +/- 8 years (range 4 to 36 years) underwent attempted stent implantation between 1993 and 1999. Successful outcome was defined as peak systolic pressure gradient after stent implantation < 20 mm Hg. RESULTS: Stents were implanted in 33/34 patients, and successful outcome occurred in 32/33 patients. Peak systolic pressure gradient decreased from 32 +/- 12 mm Hg to 4 +/- 11 mm Hg (p < 0.001). Coarctation site to descending aorta diameter ratio increased from 0.46 +/- 0.16 to 0.92 +/- 0.16 (p < 0.001). Two patients underwent successful stent re-dilation 16 and 21 months after initial implantation. Six patients (18%) developed complications, including two patients who underwent surgery. Follow-up for 29 +/- 17 months (range: 5 to 81 months) demonstrated no evidence of re-coarctation, aneurysm formation, stent displacement or fracture. Systolic blood pressure (SBP) decreased from 136 +/- 21 mm Hg before stent placement to 122 +/- 19 mm Hg at follow-up (p = 0.002). The SBP gradient decreased from 39 +/- 18 mm Hg to 4 +/- 6 mm Hg, and peak Doppler gradient decreased from 51 +/- 26 mm Hg to 13 +/- 11 mm Hg at follow-up (p < 0.001). CONCLUSIONS: Intravascular stent placement for native and recurrent CoA has excellent results in the short and intermediate terms. Long-term outcome remains to be evaluated.

Balloon angioplasty of postsurgical recoarctation in infants: the risk of restenosis and long-term follow-up.

OBJECTIVES: This study was undertaken to evaluate the long-term results of balloon angioplasty (BA) for postsurgical recoarctation in infants. BACKGROUND: Balloon angioplasty is a well-accepted modality for the treatment of recoarctation. However, infants remain a group of concern because of their size, risk for complications and the potential for restenosis with growth. Age <12 months has been determined to be a risk factor for the development of recoarctation after angioplasty for native coarctation. Although studies on postsurgical coarctation have found no relationship between age at angioplasty and the development of recoarctation, few studies specifically addressing infants have been performed. METHODS: Clinical, echocardiographic, hemodynamic and angiographic data on 22 consecutive children <1 year of age who underwent BA between 1986 and 1996 were reviewed. RESULTS: A successful result, defined as a postprocedure gradient of < or =20 mm Hg, was achieved in 20 of 22 (91%) infants with a reduction in the systolic peak pressure gradient from 48 +/- 27 to 9 +/- 10 mm Hg (p < 0.001) and an increase in coarctation diameter from 2.7 +/- 1.1 to 5.2 +/- 1.5 mm (p < 0.001). At long-term follow-up of a median of 56 months (0.6 to 12 years), the restenosis rate after an initial optimal result was 16% (3 of 19). Five (24%) infants required reintervention (2 initially unsuccessful; 3 recoarctation), with a success rate of 95% after two procedures. Suboptimal long-term outcome correlated with a lower infant weight. CONCLUSIONS: Balloon angioplasty can be safely performed in infants, with good long-term results. The risk of restenosis is low and can be successfully managed with repeat angioplasty.

Changes in body composition after a 12-wk aerobic exercise program in obese boys.

UNLABELLED: Previous studies have shown that vigorous aerobic training programs for obese children result in minimal weight changes, and concluded that they may not be beneficial. Weight change alone may not detect important beneficial changes in body composition associated with vigorous training in these children. Fifteen obese boys (aged 9-12 yr, body mass index (BMI) 31.8+/-6.5, average percent body fat (%BF) 41+/-4.2) underwent a supervised aerobic and resistance training program (12 wk, 2 days/wk for 30 min/session), to investigate the effects on weight and body composition. After the 3-month training period, weight loss averaged only 1.5+/-1.0 kg (not significant), but total body fat decreased by 4.1+/-1.8 kg (p<0.05) and fat-free mass (FFM) increased by 2.6+/-1.1 kg (p<0.05) based on hydrostatic weighing. As a result, %BF fell by 10% (p<0.01). There was a 5.8+/-2.8 mL/kg/min (p<0.05) increase in peak volume of oxygen uptake (VO(2)), along with a 248+/-120 kcal/d (p<0.05) increase in resting energy expenditure (REE). Activity questionnaires showed a significant increase in high intensity recreational activities (6.5+/-1.5 vs 3.5+/-0.5 h physical activity/wk; p<0.01) in the home and a significant decrease in low intensity activities (7+/-2.0 vs 12+/-3.5 h TV viewing/wk; p<0.01). CONCLUSIONS: Vigorous supervised aerobic training in obese boys has beneficial effects on body composition, fitness and leisure time activities that are not apparent by measurement of changes in body weight alone.

Inhaled nitric oxide therapy in a critically ill neonate with Ebstein's anomaly.

The successful use of nitric oxide (NO) inhalation in a critically ill neonate with Ebstein's anomaly of the tricuspid valve is reported for the first time. This use of inhaled NO therapy suggests a therapeutic intervention that directly addresses the pathophysiologic process of severe neonatal Ebstein's anomaly.

Single coronary artery complicating stent implantation for homograft stenosis in tetralogy of Fallot.

Successful stent implantation for conduit stenosis has been described; however, this procedure may be complicated by compression of adjacent structures during expansion. We report on a rare case of a single right coronary artery system complicating stent implantation for relief of homograft stenosis in tetralogy of Fallot.

Cardiovascular abnormalities in patients with X-linked hypophosphatemia.

Treatment for X-linked hypophosphatemia (XLH; vitamin D metabolites and phosphate salts) may result in hypercalcemia, hypercalciuria, nephrocalcinosis, and hyperparathyroidism. Cardiovascular abnormalities occur in association with these complications, but have not been reported in XLH. We hypothesized that such abnormalities may occur in XLH and evaluated cardiovascular status in 13 patients with this disease. All patients were asymptomatic and had normal cardiovascular physical examinations and Holter studies. Serum calcium and creatinine clearance were normal in all. However, all patients had mild to moderate nephrocalcinosis. Left ventricular hypertrophy was diagnosed by electrocardiogram in three and by ultrasonography in seven children. Baseline blood pressure (BP) was normal (mean +/- SD, 116 +/- 15/74 +/- 6 mm Hg). During exercise stress testing, systolic BP increased in all patients, but the maximal systolic pressure was less than that in healthy age- and sex-matched controls (156 +/- 20 vs. 175 +/- 23; P = 0.002, by t test). An abnormal increase in diastolic BP occurred at all levels of work load in XLH patients; their peak exercise diastolic BP was 91 +/- 12 vs. 72 +/- 6 mm Hg in controls (P < 0.0001, by t test). Whether these abnormal findings are primary defects in XLH or represent complications of treatment is unclear. Patients with XLH should be monitored closely for the development of hypertension and left ventricular hypertrophy. Investigation of the mechanisms involved and establishment of therapeutic guidelines are indicated.

Hepatic and gastrointestinal oxygen and lactate metabolism during low cardiac output in lambs.

We previously observed young lambs to be more tolerant of hypoxia; compared with older lambs, they accumulate lactate at a slower rate during comparable reduction in cardiac output, and have a greater percent decrease in cardiac output before onset of systemic lactate accumulation. To determine the mechanism of lactic acidosis and the cause for this "tolerance," we reduced cardiac output progressively in seven chronically catheterized conscious lambs (16.4 + 5.1 d) and measured hepatic and gastrointestinal (GI) blood flow (radioactive microspheres) and delivery, uptake, and extraction of lactate and O2. Hepatic O2 consumption declined proportionately below a critical hepatic O2 delivery (approximately 2 mL O2/min/kg), corresponding to the systemic O2 delivery associated with the onset of systemic lactate accumulation. As hepatic O2 delivery decreased below the critical value, there was initially net hepatic lactate uptake and then a change to net production when the O2 delivery decreased below approximately 1 mL O2/min kg. The GI tract had net lactate production at rest, but surprisingly switched to lactate uptake as cardiac output decreased. The mechanism of lactic acidosis was failure of hepatic lactate uptake to increase despite increased hepatic lactate delivery, as reported in adults subjects. However, in contrast, there was "true" hepatic dysfunction and lactate production only at the lowest levels of cardiac output, after onset of systemic lactate accumulation. Moreover, we speculate that tolerance of young lambs to hypoxia is at least due to two factors: 1) hepatic lactate uptake is maintained beyond the "critical" O2 delivery and fall in hepatic O2 consumption, and 2) there is a switch to lactate uptake by the GI tract serving to buffer the lactate.

Transcatheter closure of the patent ductus arteriosus: a comparative study between occluding coils and the Rashkind umbrella device.

This study was performed to evaluate the efficacy of transcatheter coil closure of the patent ductus arteriosus in comparison to our experience with the Rashkind umbrella device. Transcatheter coil closure of the patent ductus arteriosus has been reported with encouraging results. We present our experience with ducti up to 5.0 mm in diameter and report the short-term follow-up. We compare the results with our previous experience with the Rashkind umbrella device. Seventy-one patients underwent transcatheter coil closure. Median age was 3.1 years, and median weight was 13.6 kg. Mean ductus diameter was 2.0 +/- 1.1 mm. These were compared with 105 patients who underwent transcatheter closure using a single Rashkind umbrella device. The median age was 3.2 years and the median weight was 14.0 kg. The mean ductus diameter for this group was 2.1 +/- 0.6 mm. The ductus murmur in the coil group disappeared in all patients. Immediate (< or = 24h), complete closure was achieved in 89% of the coil group as compared to 71% for the Rashkind umbrella device group (P < 0.005). Closure rate for the coil group was 97% at the 6-month follow-up, vs. 82% for the Rashkind umbrella device group at the 6-12 month follow-up (P < 0.05). In almost all patients requiring more than one coil, the ductus was crossed serially from the aortic end. All patients with ductus diameter > or = 3.0 mm required two or more coils. Eleven coils in six patients embolized to the pulmonary arteries. All coils except one were retrieved with subsequent successful foil placement. Sixty-seven patients (94%) in the coil group were discharged in < or = 24 h. Transcatheter closure of the patent ductus arteriosus using multiple coils is a more effective technique than the Rashkind umbrella closure and has excellent short-term results. This can be performed safely as an outpatient procedure.

Implantation of balloon-expandable stents for coarctation of the aorta: implantation data and short-term results.

We report the immediate results and the short-term follow-up in a group of selected patients with coarctation of the aorta who underwent endovascular stent implantation. Balloon-expandable stents were implanted in 6 patients (mean age 19.8 +/- 5.1 years) with coarctation of the aorta (4 recurrent and 2 native) who underwent a total of 7 procedures (6 implantation and 1 further expansion). The systolic peak pressure gradient was decreased from 36.7 +/- 16.9 to 13.3 +/- 23.2 mm Hg (P < 0.005). There was a 66% increase in the mean coarctation diameter from 9.3 +/- 1.7 to 15.6 +/- 3.1 mm (P = 0.001) with the ratio of the coarctation to descending aorta diameter, measured at the level of the diaphragm, increasing from 0.49 +/- 0.1 to 0.81 +/- 0.2 (P < 0.005). The dilatation was successful in expanding the stent to an acceptable diameter in 5 of 6 patients. One patient underwent successful further expansion of a stent implanted 22 months previously. There were no immediate complications during balloon expansion and stent implantation. One patient suffered a femoral arterial bleed requiring surgical repair. There was one unrelated death. All patients were hypertensive (systolic blood pressure > 140 mm Hg) prior to stent implantation. At mean follow-up of 8 months, 3 patients are normotensive. There was no recurrence of coarctation, aortic dissection, or aneurysm formation in the patients in whom stent implantation was successful. These findings indicate that balloon-expandable stent implantation for coarctation of the aorta in selected patients is a safe and effective alternative approach for relieving the obstruction with a low complication rate and no recoarctation at short-term follow-up.

Diminished venous vascular capacitance in patients with univentricular hearts after the Fontan operation.

Patients who have undergone Fontan's operation are known to have impaired cardiac output response to dynamic exercise. This may be due to either poor cardiac function or a limited ability to mobilize blood from capacitance vessels due to increased resting venous tone. We tested the latter hypothesis by determining venous vascular capacitance at rest and during orthostatic stress produced by lower body negative pressure (LBNP) in 6 subjects who had undergone the Fontan operation and 6 healthy age-, sex-, height-, and weight-matched controls. Resting blood volume was similar for Fontan and control subjects (79 +/- 6 vs 70 +/- 3 ml/kg body weight, respectively), while central venous pressure (CVP) was elevated in Fontan subjects (18.4 +/- 1.0 vs 3.5 +/- 0.9 mm Hg, p < 0.05). Forearm venous capacitance at a distending pressure of 40 mm Hg was less in Fontan subjects than in controls (2.6 +/- 0.1 vs 3.9 +/- 0.5 ml/100 ml), while resting plasma norepinephrine level was elevated in Fontan subjects (255 +/- 28 vs 144 +/- 9 pg/ml, p < 0.05). The increase in calf volume (1.6 +/- 0.2 vs 2.3 +/- 0.2 ml) and decrease in CVP (-5.0 +/- 0.5 vs -6.7 +/- 1.1 mm Hg) during -30 mm Hg LBNP were smaller for Fontan than control subjects (p < 0.05). Reduced forearm venous capacitance and diminished pooling of blood into capacitance vessels of the leg during orthostatic stress indicated higher venous tone in Fontan than control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

The transition from fetal to neonatal circulation: normal responses and implications for infants with heart disease.

The primary function of the circulatory system of both the fetus and newborn is to deliver oxygen to metabolizing organs and return deoxygenated blood to the gas exchange organ to replenish the oxygen and eliminate the waste product CO2. In the fetus, the gas exchange organ is the placenta, and its vascular connections are in a parallel arrangement with the other systemic organs, remote from the pulmonary circulation. In order to supply deoxygenated blood to the placenta and return oxygenated blood to the systemic organs, a series of extracardiac shunts (ductus venosus, ductus arteriosus) and an intracardiac communication (foramen ovale) are necessary. With birth, the function of gas exchange is transferred from the placenta to the lungs, and therefore from the systemic circulation to the pulmonary circulation. The venous and arterial circulations are separated, and not only are the fetal shunts unnecessary, but their persistence may lead to circulatory compromise. The transition from the fetal to the neonatal circulation thus includes elimination of the placental circulation, lung expansion, and increase in lung blood flow so that the entire cardiac output can be accommodated, and closure of the foramen ovale, ductus arteriosus, and ductus venosus. For most congenital structural heart disease, the fetal shunt pathways allow redistribution of ventricular blood flows so that systemic blood flow is adequate and fetal growth and development are usually normal. Uncomplicated VSDs do not alter the circulation significantly in either the fetus or immediate newborn period, with the important exception of premature infants. With severe left heart obstruction, the burden of systemic and pulmonary blood flow is transferred to the fetal right ventricle, with reversal of blood flow at the foramen ovale, and systemic blood flow almost entirely transmitted via the ductus arteriosus. This "ductal-dependent" systemic circulation is poorly tolerated in the newborn, because normal closure of the ductus arteriosus progressively decreases systemic blood flow and progresses to circulatory failure and shock. Severe right heart obstruction is also well tolerated in the fetus, because the combined fetal cardiac output can be transferred to the aorta, with the ductus arteriosus supplying predominantly lung blood flow. After birth, such "ductal-dependent" pulmonary blood flow can lead to critically low levels of pulmonary blood flow and severe cyanosis with closure of the ductus arteriosus. An understanding of fetal hemodynamics and the acute and chronic changes that occur with transition to the newborn circulation are important for the care of normal newborns and are crucial to the recognition, diagnosis, and management of the newborn with significant congenital heart disease.

Hemodynamic evaluation before and after closure of fenestrated Fontan. An acute study of changes in oxygen delivery.

BACKGROUND: Acute changes in hemodynamics and oxygen delivery accompanying temporary occlusion of atrial defects in 14 patients after a fenestrated Fontan procedure were evaluated at a median interval of 32 days after surgery to identify candidates for permanent transcatheter closure of their defects. METHODS AND RESULTS: Patients ranged in age from 9 months to 33 years and in weight from 7.9 to 69 kg. Right atrial (RA), left atrial (LA), and aortic pressures, mixed venous (SmvO2) and aortic (SaO2) oxygen saturation, and whole-body oxygen consumption (VO2) were measured, and systemic blood flow (Qs), systemic oxygen transport (SOT), and oxygen extraction were calculated before and after occlusion. SmvO2, VO2, and RA pressures did not change, but SaO2 increased from 84 +/- 6% to 95 +/- 3% (p less than 0.05), and LA pressures fell from 5.1 +/- 3.6 to 3.7 +/- 2.2 mm Hg (p less than 0.05). Qs fell from 2.4 +/- 0.7 to 1.8 +/- 0.41.min-1.m-2 (p less than 0.05), SOT fell from 425 +/- 154 to 366 +/- 112 ml.O2.min-1.m-2 (p less than 0.05), and oxygen extraction increased from 0.40 +/- 0.12 to 0.46 +/- 0.13 (p less than 0.05). Only one patient did not undergo definitive closure of his defect because of a marked decrease in Qs and SOT with a significant rise in RA pressure. CONCLUSIONS: Although delayed closure of an atrial defect in these patients improved morbidity and mortality, the complete separation of the venous and systemic circulations was accomplished at the expense of decreased Qs and oxygen delivery despite the improved level of arterial oxygenation. The resting levels of oxygen extraction are elevated and will be associated with decreased exercise capability. The long-term benefits of closure of these fenestrations are yet to be shown.

Fenestrated Fontan operation with delayed transcatheter closure of atrial septal defect. Improved results in high-risk patients.

Ten patients, each with two or more risk factors for morbidity and death, underwent a fenestrated Fontan procedure in which a 4 to 6 mm circular fenestration was left between the systemic and pulmonary venous chambers. None died; a similar group of high-risk patients without fenestration had a mortality rate of 2 of 8. Patients with fenestration had significantly less drainage from the chest tube, less need for inotropic support, and shorter intensive care and hospital stays than did patients without fenestration. Comparison with a group of low-risk patients undergoing the Fontan operation showed no statistical difference in these postoperative parameters. Fenestrations were closed in all 10 patients at from 9 days to 6 months after operation by means of the transcatheter clamshell occluder device. Two patients had left pulmonary artery balloon angioplasty and three patients had other atrial communications closed with additional clamshell devices. During short-term follow-up periods averaging 18 months, all patients were clinically well; however, one patient with mitral atresia required reoperation for obstruction between the left atrium and the tricuspid valve, not related to the clamshell device. These data indicate that fenestration may be one method of achieving lower morbidity and mortality rates among high-risk patients undergoing the Fontan procedure.

Balloon angioplasty for recurrent coarctation of aorta. Immediate and long-term results.

BACKGROUND: As angioplasty techniques have been refined and larger low-profile balloons developed, a nonsurgical approach to recoarctation has become available. Several reports have documented both the efficacy and safety of this procedure. However, there are little data available on the long-term follow-up of these patients. This report details the initial results and long-term evaluation of both the relief of obstruction and the presence of hypertension after balloon angioplasty for recurrent coarctation. METHODS AND RESULTS: Balloon angioplasty for recurrent coarctation of the aorta was performed 29 times in 26 patients at a median age of 4 years and 9 months (range, 4 months to 29 years), with eight patients less than 1 year old. Initial surgical techniques were end-to-end anastomosis in 11 patients, subclavian flap aortoplasty in 11 patients, and patch aortoplasty in four patients. Angioplasty was performed at a median interval of 2 years and 7 months (range, 4 months to 23 years) after surgery. Mean peak systolic pressure difference across the coarctation decreased from 40.0 +/- 16.8 to 10.3 +/- 9.5 mm Hg (p less than 0.05) after the initial angioplasty, and mean diameter of the aortic lumen at the coarctation site increased from 5.8 +/- 3.5 to 9.0 +/- 4.3 mm (p less than 0.05). There was no mortality, and only one patient developed an aneurysm (4%). Three patients underwent repeat angioplasty for a pressure difference of more than 20 mm Hg. Long-term follow-up is available on 24 of 26 patients with a mean follow-up of 42 +/- 24 months (range, 12-88 months). Mean peak systolic pressure difference across the area of coarctation decreased from 40.3 +/- 17.4 before angioplasty to 8.5 +/- 8.3 mm Hg after final angioplasty (p less than 0.05) and 7.5 +/- 7.5 mm Hg at follow-up. Mean peak systolic blood pressure in the upper extremities decreased from 133.1 +/- 14.9 before angioplasty to 111.1 +/- 14.1 mm Hg at long-term follow-up (p less than 0.05). CONCLUSIONS: Balloon angioplasty should be considered the treatment of choice for relief of recurrent aortic coarctation.

Transesophageal echocardiographic guidance of transcatheter closure of atrial septal defect.

Transcatheter closure of atrial septal defect (ASD) was accomplished in 10 of 11 patients aged 13 months to 46 years (weight range 11 to 77 kg). Transesophageal echocardiography (TEE) was used simultaneously with fluoroscopic imaging in 4 of these patients aged 4.5 to 46 years (weight range 19 to 77 kg). TEE was used to ascertain defect size, position and number of defects and to ascertain appropriate seating of the defect occluder within the atrial defect. In 2 patients TEE-assisted transcatheter ASD closure was accomplished after previous attempts at transcatheter ASD closure, unaided by TEE, had been unsuccessful. The only unsuccessful ASD closure procedure occurred in the smallest patient in the series (an 11-kg 13-month-old), a child who was too small to undergo TEE using our 11-mm diameter endoscopic probe. The concomitant use of TEE with fluoroscopic imaging provides information that is unique and complementary and may improve the efficacy and safety of the transcatheter technique for ASD closure. The recent availability of a 7-mm diameter TEE probe will extend the use of TEE into the infant age group and may decrease the discomfort and potential morbidity of TEE in older patients.

Response to low cardiac output: developmental differences in metabolism during oxygen deficit and recovery in lambs.

When cardiac output is critically lowered, whole body O2 consumption decreases and an O2 deficit accumulates. With restoration of cardiac output, an excess O2 consumption is expected in order to "repay" some or all of the O2 deficit. We tested the hypothesis that young lambs, with higher resting O2 consumption, cardiac output and growth rates than older lambs, would repay less of their O2 deficit because they have a higher proportion of nonessential metabolism. We reduced cardiac output acutely by inflating a Foley catheter in the right atrium of spontaneously breathing, sedated lambs at ages 2 (n = 5) and 8 (n = 5) wk. Each lamb was studied with low cardiac output periods of 30 and 60 min on different days. Aortic and pulmonary artery blood pressures, gases, and O2 saturations, venous Hb, and arterial lactate concentrations were measured every 10 min during baseline, low output, and 60 min of recovery. Oxygen consumption was monitored continuously. Oxygen deficit and excess O2 of recovery were calculated from the time integral of the difference between O2 consumption at baseline and during the respective study period. The average percent decreases in cardiac output (66.4 and 64.6%) and O2 consumption (38.1 and 35.1%) were similar in the 2- and 8-wk groups, respectively. There was no consistent relation between O2 deficit and O2 repayment in either age group. However, on average the 2-wk group repaid a significantly lower percentage (3 +/- 16%, mean +/- SEM) than 8-wk-olds (76 +/- 29%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hemoglobin concentration on critical cardiac output and oxygen transport.

We previously found limited tolerance to acute reduction in cardiac output in lambs at the nadir of their physiological anemia [Am. J. Physiol. 253 (Heart Cir. Physiol. 12): H100-H106, 1987]. To determine the effect of hemoglobin concentration [Hb] on critical cardiac output, critical systemic O2 transport, and peripheral O2 extraction, we performed 31 experiments in 12 one-mo-old lambs at four [Hb] (means +/- SD in g/dl): 7.4 +/- 0.6, 10.5 +/- 0.5, 14.5 +/- 0.5, and 16.5 +/- 0.6. Desired [Hb] was obtained by exchange transfusion with packed red cells or plasma. Cardiac output was reduced by inflation of a balloon-tipped catheter in the right atrium, and critical levels were defined at the point where O2 consumption decreased and/or arterial blood lactate concentration increased in response. With lower [Hb], cardiac output was unchanged, systemic O2 transport was reduced, and fractional O2 extraction was increased, keeping O2 consumption constant at base line. As [Hb] was reduced, critical cardiac output was significantly higher, whereas critical systemic O2 transport was independent of [Hb], as were fractional O2 extraction and mixed venous PO2 at the critical point. Thus peripheral O2 extraction was not affected by changes in [Hb] during progressive decreases in cardiac output. We conclude that 4-wk-old lambs have decreased tolerance to reductions in cardiac output and systemic O2 transport because their relative anemia provides them with a base-line cardiac output and systemic O2 transport close to the critical level.

Aneurysms of the right ventricular outflow tract after tetralogy of Fallot repair: role of radiology.

Eight patients with aneurysms of the right ventricular outflow tract patch following tetralogy of Fallot repair were found to have residual distal obstructions. The site of such an obstruction must be carefully documented preoperatively because failure to relieve significant distal obstruction may result in recurrent aneurysm formation. Chest radiography; echocardiography, including Doppler analysis; and cardiac catheterization, including angiocardiography, each have a role in the detection and evaluation of this complication.

Postnatal changes in critical cardiac output and oxygen transport in conscious lambs.

We lowered cardiac output progressively in a controlled, stepwise fashion in conscious, unsedated lambs to determine the critical cardiac output or systemic oxygen delivery (the level at which oxygen consumption decreased abruptly). With the use of incremental inflation of a balloon-tipped catheter placed in the right atrium to lower cardiac output, we examined the response of oxygen consumption, systemic oxygen transport, fractional oxygen extraction, arterial lactate, and blood pressure. We studied lambs at 2 (n = 5), 4 (n = 5), and 8 wk (n = 6) of age and found that the 4-wk-old lambs reached critical values of cardiac output and systemic oxygen transport with the smallest proportional decreases from base-line values. Therefore, the 4-wk-old lambs were the least tolerant of acute decreases in cardiac output. We also found that fractional oxygen extraction was able to increase even after critical systemic oxygen transport was achieved. Furthermore, we found at every age that lactic acid accumulation began when the critical level of cardiac output was reached.

A simple method for reducing cardiac output in the conscious lamb.

We have developed a method for reducing cardiac output in a controlled stepwise fashion using awake, intact, unsedated lambs. The method involves placing a balloon-tipped (Foley) catheter into the right atrium from a jugular vein isolated by a small neck incision. Systemic venous return and cardiac output are limited by balloon inflation. With each balloon inflation the animal reaches a new and stable cardiac output, which allows the measure of steady-state hemodynamic and metabolic variables. We have been able to decrease cardiac output to as low as 20% of the resting cardiac output and maintain a stable preparation. The reductions in cardiac output are quickly reversible by balloon deflation. Animal survival allows repeated study. We present data from five lambs studied between 26 and 36 days of age. Alterations in O2 consumption, O2 transport, O2 extraction, blood pressure, and arterial lactate concentration are examined in response to decrements in systemic blood flow and are consistent with changes seen in response to a reduction of cardiac output by other methods.