Pulmonary venous wedge pressures accurately predict pulmonary arterial pressures in children with single ventricle physiology.

We investigated the relationship between pulmonary venous wedge and pulmonary arterial pressures in patients with single ventricle physiology. This relationship has been studied in other cardiac conditions but not in this unique group of patients. We made 60 paired measurements from one or both lungs in 40 patients, and divided the patients into three groups. Group 1 consisted of patients whose pulmonary blood supply was via an aortopulmonary shunt (n = 14), group 2 included patients with a bi-directional Glenn anastomosis (n = 20), and group 3 included patients with a pulmonary arterial band (n = 6). Venous wedge pressure estimated arterial pressure within 3 mmHg in 59 of 60 paired measurements. Plots of the difference between pulmonary artery and pulmonary venous wedge pressures versus the mean showed excellent correlation, with a mean difference of approximately 1 for group 1 (mean difference, -0.15 +/- 1.3 mmHg) and group 2 (mean difference, 0.52 +/- 1.12 mmHg). The relationship was poor in group 3 (mean difference, -2.00 +/- 4.80 mmHg) but was much better with the exclusion of the one outlying patient in whom pulmonary venous wedge pressure significantly overestimated pulmonary arterial pressure (mean difference, -0.33 +/- 2.07 mmHg). We conclude that pulmonary venous wedge pressure accurately estimates pulmonary arterial pressure in patients palliated for single ventricle physiology, but care must be taken in patients with a pulmonary arterial band.

Sequential magnetic resonance monitoring of pulmonary flow with endovascular stents placed across the pulmonary valve in growing Swine.

BACKGROUND: Patients with endovascular stent implantation for the treatment of right ventricular outflow tract obstruction are often left with incomplete relief of the obstruction and significant pulmonary regurgitation. A noninvasive and reproducible method for monitoring such patients is desirable. MRI in the presence of a stent, however, has to overcome the problem of potential metallic artifacts. METHODS AND RESULTS: Under x-ray fluoroscopic guidance, endovascular nitinol stents were placed across the pulmonary valve in 6 young pigs to induce pulmonary regurgitation. Five additional pigs served as controls. Initial MRI was performed after 2 days (13.5+/-1.8 kg) and follow-up after 3 months (32+/-2.9 kg). Pulmonary flow volumes and regurgitant fraction were quantified by velocity-encoded cine (VEC) MRI through (VEC-TS) and distal to (VEC-DS) the stent. VEC-TS was compared with VEC-DS and volumetric measurements of left and right ventricular stroke volumes provided by cine MRI ("gold standard"). Antegrade and retrograde pulmonary flow volumes by VEC-TS were slightly but significantly less than those with VEC-DS and cine MRI. Excellent correlations (r>0.97) for phasic pulmonary flow volumes as measured by VEC-TS and VEC-DS were shown. Pulmonary regurgitant fraction increased from 32.8+/-15% to 49.6+/-17% (P<0.05) over the course of 3 months with VEC-TS. CONCLUSIONS: MRI demonstrates the progression of pulmonary regurgitation in growing swine. VEC MRI has the ability to quantify pulmonary blood flow inside the lumen of nitinol stents. MRI appears to be ideally suited for monitoring patients with endovascular nitinol stents in the pulmonary artery or pulmonary valve position.

Cardiac catheterization of low birth weight infants.

The increased survival of low birth weight infants means that more of these infants may be candidates for catheter interventions. There are few data on the results of cardiac catheterization in this group. This study aimed to analyze, retrospectively, cardiac catheterization of infants weighing < or =2.5 kg, with emphasis on the results of interventions. The complication rates of interventional and diagnostic procedures were compared. One hundred eleven catheterizations were performed in 107 patients between 1985 and 1998. Thirty-one procedures were interventional. Balloon atrial septostomy (n = 16), balloon pulmonary valvuloplasty (n = 10), balloon pulmonary angioplasty (n = 1), and coil occlusion of collateral vessels (n = 3) were all performed successfully. One infant (3%) died while undergoing myocardial biopsy. The reintervention rate for isolated pulmonary valve stenosis was 25% (2 of 8) at 1 month, 57% (4 of 7) at 6 months, and 71% (5 of 7) at 1 year. Complications were significantly more frequent during interventional (13 of 31, 42%) than during diagnostic (13 of 80, 16%) procedures. The most common complications during interventions were arrhythmias (3 of 31, 10%) and respiratory deterioration (3 of 31, 10%). Cardiac catheterization was technically feasible in all patients. Balloon pulmonary valvuloplasty and atrial septostomy provided good palliation in this patient group. The mortality of interventional procedures was low. The high incidence of respiratory complications suggests that low birth weight infants should undergo elective ventilation for interventional cardiac catheterization.

Coronary to pulmonary artery collaterals in patients with pulmonary atresia and ventricular septal defect.

BACKGROUND: The frequency, distribution, and surgical importance of coronary artery to pulmonary artery (CAPA) collaterals have not been established. The aim of this study was to establish prevalence, anatomical pattern, and significance of CAPA in patients with pulmonary atresia and ventricular septal defect (PA/VSD). METHODS: We reviewed cardiac catheterization and operative data of 87 consecutive, unselected patients who underwent one-stage complete unifocalization for PA/VSD and assessed major systemic to pulmonary collaterals from July 1992 to June 1998. RESULTS: CAPA collaterals were diagnosed in 9 of 87 patients (10%). The collaterals originated from the left coronary artery system in 7 patients and the right in 2. Collaterals from the left coronary system arose from the left main coronary artery in 3 patients and the circumflex in 4. All collaterals joined the central pulmonary artery, which bifurcated and supplied both lungs. One collateral from the right coronary system joined the stump of the main pulmonary artery and the other gave origin to a true left pulmonary artery, which was the sole supply to 75% of the left lung. Coronary artery enlargement was seen in 2 patients only. No patient had evidence of myocardial ischemia. Coronary collaterals comprised a dual source of pulmonary blood flow in all but 1 patient. During unifocalization, the CAPA collaterals were ligated at its origin in all cases, and the collateral from the right coronary to the left pulmonary artery was unifocalized. CONCLUSIONS: The prevalence of CAPA collaterals in patients with PA/VSD is approximately 10%. The diagnosis may be missed without appropriate angiograms. We recommend selective ascending aortogram or selective coronary angiogram in all patients.

Balloon arterioplasty of recurrent coarctation after the modified Norwood procedure in infants.

Coarctation of the reconstructed aorta after the modified Norwood procedure for hypoplastic left heart syndrome is a relatively common occurrence that can have significant adverse effects. From 1992-98, 65 infants with hypoplastic left heart syndrome or variants thereof underwent a modified Norwood procedure. Of the 50 survivors of Stage I palliation, 10 (20%) were subsequently diagnosed with clinically significant obstruction of the aortic arch at a median age of 5.1 months. Eight of these patients underwent coarctation balloon arterioplasty. All 8 patients underwent successful dilation of the coarctation, with a decrease in the pressure gradient from 43+/-20 to 4+/-5 mm Hg and an increase in aortic diameter at the site of obstruction from 3.5+/-0.5 to 7.0+/-1.0 mm (both P<0.001). There was also a significant increase in lower extremity systolic blood pressure. Although there was no immediate increase in cardiac output after dilation in most patients, ventricular function was improved in 3 patients within 24-48 hr of the procedure and in all but 2 at the most recent follow-up (median 2 years). Two patients developed bradycardia during wire placement that required cardiopulmonary resuscitation. Two others died suddenly during the follow-up period. All surviving patients have undergone subsequent palliative procedures; none have required repeat intervention for arch obstruction. We found a 20% incidence of coarctation in survivors of the modified Norwood procedure. Balloon arterioplasty is effective in relieving this obstruction, and should be carried out promptly upon diagnosis to minimize its deleterious effects on ventricular function. Balloon dilation, however, should be considered a high-risk procedure in these fragile infants, and special attention must be given to cardiovascular support.

Early and intermediate outcomes after repair of pulmonary atresia with ventricular septal defect and major aortopulmonary collateral arteries: experience with 85 patients.

BACKGROUND: Pulmonary atresia with ventricular septal defect (VSD) and major aortopulmonary collaterals (MAPCAs) is a complex lesion with marked heterogeneity of pulmonary blood supply. Traditional management has involved staged unifocalization of pulmonary blood supply. Our approach has been to perform early 1-stage complete unifocalization in almost all patients. METHODS AND RESULTS: Since 1992, 85 patients with pulmonary atresia, VSD, and MAPCAs have undergone unifocalization (median age, 7 months). Complete 1-stage unifocalization and intracardiac repair were performed through a midline approach in 56 patients, whereas 23 underwent unifocalization in a single stage with the VSD left open, and 6 underwent staged unifocalization through sequential thoracotomies. There were 9 early deaths. During follow-up (1 to 69 months), there were 7 late deaths. Actuarial survival was 80% at 3 years. Among early survivors, actuarial survival with complete repair was 88% at 2 years. Reintervention on the neo-pulmonary arteries was performed in 24 patients. CONCLUSIONS: Early 1-stage complete unifocalization can be performed in >90% of patients with pulmonary atresia and MAPCAs, even those with absent true pulmonary arteries, and yields good functional results. Complete repair during the same operation is achieved in two thirds of patients. There remains room for improvement; actuarial survival 3 years after surgery is 80%, and there is a significant rate of reintervention. These results must be appreciated within the context of the natural history of this lesion: 65% of patients survive to 1 year of age and slightly >50% survive to 2 years even with surgical intervention.

Results of 102 cases of complete repair of congenital heart defects in patients weighing 700 to 2500 grams.

BACKGROUND: Published data suggest that low birth weight is a risk factor for poor outcome in corrective surgery for many cardiac defects. Congenital heart defects in low birth weight infants are typically managed with supportive therapy or palliative operations, with definitive repair delayed. The morbidity associated with such approaches is high. METHODS: Since 1990 complete repair of congenital heart defects (other than patent ductus arteriosus) has been performed in 102 infants no larger than 2500 g (median 2100 g, range 700-2500 g), including 16 no larger than 1500 g. Defects included ventricular septal defect (n = 22), tetralogy of Fallot complexes (n = 20), transposition complexes (n = 13), aortic coarctation (n = 12), interrupted arch (n = 10), truncus arteriosus (n = 8), atrioventricular septal defect (n = 6), total anomalous pulmonary venous return (n = 5), and other (n = 6). RESULTS: Preoperative morbidity was more common among patients referred late for surgical correction. There were 10 early deaths (10%) attributable to cardiac failure (n = 4), arrhythmia (n = 1), multiorgan failure (n = 1), sepsis (n = 1), idiopathic coronary artery intimal necrosis (n = 1), foot gangrene (n = 1), and pulmonary hemorrhage (n = 1). No patient had postbypass intracerebral hemorrhage. At follow-up (median 36 months) there were 8 late deaths, and 8 patients underwent 10 reinterventions. There was no evidence of neurologic sequelae attributable to the operation. CONCLUSIONS: In general, delaying repair of congenital heart defects in low birth weight infants does not confer a benefit and is associated with higher preoperative morbidity. Complete repair of both simple and complex lesions can be achieved in such cases with good results. Growth after repair approximates the normal curve for low birth weight infants without heart disease. It is recommended that such infants, especially when they have symptoms, undergo early surgical repair rather than prolonged medical management or other forms of palliation.

Intramyocardial hematoma causing cardiac tamponade after repair of Ebstein malformation: erroneous echocardiographic diagnosis as intracavitary thrombus.

Intramyocardial hematoma is an uncommon lesion, most often occurring after chest trauma, aortic valve disease, acute myocardial infarction, or coronary artery bypass surgery. We describe a 17-year-old patient who experienced cardiac tamponade after repair of Ebstein malformation. The malformation was caused by an enlarging intramyocardial hematoma that extended from the right atrium to the atrialized right ventricle. The hematoma was incorrectly diagnosed by echocardiography as an intracavitary thrombus, and the correct diagnosis was recognized only at the time of surgical intervention.

Contribution of synchronized atrial systole to left ventricular contraction in the newborn pig heart.

Synchronized atrial contraction may be much more important in the newborn, who has a faster heart rate and a less compliant ventricle, than in the adult. We therefore investigated the extent by which synchronized atrioventricular contraction contributes to cardiac output and cardiac work in a neonatal circulation, and whether this effect can be fully explained by the Starling mechanism. In neonatal piglets, left ventricular pressure and volume (conductance catheter) were measured during atrial and ventricular pacing. By manipulating preload during atrial pacing, end-systolic pressure and volume, stroke work, and dP/dtmax were compared at the same end-diastolic volume as indices of contractility. Finally, end-diastolic pressure-volume relationships were assessed to investigate the validity of using end-diastolic pressure as an indicator of preload. We found a significant contribution of synchronized atrial contraction; cardiac output increased 27% when pacing mode was switched form ventricular to atrial. The mechanism by which this was achieved is entirely the enhancement of ventricular filling and thus the Starling effect; contractility was unaffected by pacing mode. This large and important effect can be explained by slowed relaxation (compared with the adult ventricle), which impairs passive filling during the ventricular relaxation phase, and makes active filling during atrial contraction more important. In addition, we found that the use of end-diastolic pressure as an indicator of preload, instead of end-diastolic volume, leads to serious misinterpretations, due to not only the nonlinearity of this relationship, but also the possible shifts in this relationship with certain interventions.

Evaluation of Gianturco coils for closure of large (> or = 3.5 mm) patent ductus arteriosus.

OBJECTIVES: This report evaluates the use of Gianturco coils to close large patent ductus arteriosus (PDAs) (> or = 3.5 mm) and describes transvenous delivery of 0.052-in. (0.132-cm) Gianturco coils. BACKGROUND: Coil closure of PDAs has become increasingly popular. However, the technique has significant limitations when used to close large PDAs. This report evaluates patient characteristics, PDA anatomy, hemodynamic variables, delivery technique and coil geometry to determine predictors of success. METHODS: Between January 1995 and January 1997, 16 of 118 patients undergoing catheterization for PDA closure were found to have large PDAs. Their median age and weight were 14 months (range 3 months to 43 years) and 8.5 kg (range 3.5 to 73), respectively. The mean PDA diameter was 4.3 mm (range 3.5 to 5.9). Closure of PDAs was attempted using transcatheter delivery of 0.038-in. (0.096-cm) and 0.052-in. coils. Differences in clinical, anatomic, hemodynamic and technical variables between successes and failures were compared. RESULTS: Eleven (69%) of 16 patients had successful closure of their PDA. Failures occurred only in patients < 8 months of age with an indexed PDA diameter > 7 mm/m and a pulmonary/systemic flow ratio > or = 2.8:1. Use of 0.052-in. coils tended to reduce the incidence of embolization and the number of coils needed for closure. CONCLUSIONS: Patients > 8 months of age can have successful closure of large PDAs with currently available Gianturco coils. The 0.052-in. Gianturco coils can be used safely to close large PDAs in infants as small as 6 kg. Increased experience and improved coil design may improve closure rates of large PDAs in infants.

Acute elevation of coronary venous pressure does not affect left ventricular contractility in the normal and stressed swine heart: implications for the Fontan operation.

OBJECTIVE: After the Fontan operation the right atrium and, thus, the coronary sinus are connected to the pulmonary arterial system, which causes the coronary venous pressure to increase. We investigated the acute effects of elevation of coronary venous pressure on baseline hemodynamics, coronary venous flow, and left ventricular contractility. METHODS: In acutely instrumented pigs, during complete right heart bypass and during constant cardiac output, pressure in the right atrium, right ventricle, and coronary sinus was altered by a height-adjustable reservoir. At various levels of coronary venous pressure (up to 4 kPa or up to 30 mm Hg), flow from the reservoir was measured and left ventricular hemodynamics and contractility were measured from catheter-derived left ventricular pressure and (conductance) volume data. Contractility of the left ventricle was assessed by the end-systolic pressure-volume relationship derived during an unloading intervention by adjusting the bypass pump speed. RESULTS: Left ventricular end-diastolic pressure increased slightly (about 5%) with each kilopascal increase in coronary venous pressure, most likely related to diastolic ventricular interaction. No other changes in hemodynamic parameters occurred. Neither coronary venous flow nor left ventricular contractility was influenced by changes in coronary venous pressure. Imposing myocardial stress with dobutamine, 10 microg/kg per minute, did not change these findings. CONCLUSION: Increasing coronary venous pressure to 4 kPa in the intact circulation with intact autoregulation does not affect coronary flow or left ventricular contractility. We found no experimental evidence for the usefulness of diversion of the coronary sinus to the left atrium during Fontan-type operations

Hemodynamic effects of chronic prenatal ventricular pacing for the treatment of complete atrioventricular block.

BACKGROUND: Increasing the heart rate of the fetus with cardiac failure caused by complete AV block (CAVB) may allow delivery of a full-term, stable neonate with preserved ventricular function. Direct fetal pacing may be a feasible method to achieve this, but the effect of pacing on the structure and function of the rapidly developing fetal heart is unknown. METHODS AND RESULTS: CAVB was created in fetal lambs at 80% gestation by cryoablating the AV node. Epicardial ventricular pacing at 130 bpm was achieved by use of a pacemaker placed under the pectoral muscles. The fetus was returned to the uterus and allowed to continue to term. Ventricular function was assessed 1 week after birth in 7 lambs with CAVB and 10 control lambs. By use of the conductance catheter technique, the end-systolic pressure-volume relationship was determined at different heart rates, pacing conditions, and inotropic states. The contractility was not different between the two groups at their baseline heart rates and rhythms or when they were paced synchronously compared with asynchronously. Also, both groups responded significantly and similarly to inotropic manipulation, indicating preserved contractile reserve. Finally, in both groups, increased heart rates were associated with increased contractility, indicating an intact force-frequency relationship. CONCLUSIONS: We conclude that chronic epicardial ventricular pacing is well tolerated by the fetus, can be successfully applied as a treatment for CAVB, and does not adversely affect myocardial function in the rapidly developing, immature heart.

One-stage complete unifocalization in infants: when should the ventricular septal defect be closed?

BACKGROUND: The decision whether to close the ventricular septal defect at the time of unifocalization in patients with pulmonary atresia, ventricular septal defect, and major aortopulmonary collaterals may be difficult. The purpose of this study was to develop morphologic and physiologic methods to aid in deciding whether to close the ventricular septal defect in patients undergoing one-stage unifocalization. METHODS: Between July 1992 and April 1996, 27 infants with pulmonary atresia, ventricular septal defect, and aortopulmonary collaterals were treated at our institution. Midline complete unifocalization was performed in 25 patients-the ventricular septal defect was closed in 17 and left open in eight. Two patients with severe distal collateral stenoses underwent staged unifocalization. Pulmonary artery and collateral sizes were measured from preoperative angiograms and used to calculate the indexed cross-sectional area of the total neopulmonary artery bed. An intraoperative pulmonary flow study previously validated with experiments in neonatal lambs was performed in six patients: the unifocalized neopulmonary arteries were perfused with a known flow and pulmonary artery pressures were recorded. RESULTS: The neopulmonary artery index was greater in patients who underwent ventricular septal defect closure than in those who did not (p = 0.001), although the values did overlap. This index correlated with the postoperative right ventricular/left ventricular pressure ratio (p = 0.037). Mean pulmonary artery pressures obtained during the intraoperative flow study and after bypass were comparable. CONCLUSION: The total neopulmonary artery index correlates with postrepair right ventricular/left ventricular pressure ratio and is useful in deciding when to close the ventricular septal defect if it is larger than 200 mm2/m2. The pulmonary flow study is helpful in deciding whether to close the ventricular septal defect in all patients.

Left ventricular pressure and volume data acquisition and analysis using LabVIEW.

To automate analysis of left ventricular pressure-volume data, we used LabVIEW to create applications that digitize and display data recorded from conductance and manometric catheters. Applications separate data into cardiac cycles, calculate parallel conductance, and calculate indices of left ventricular function, including end-systolic elastance, preload-recruitable stroke work, stroke volume, ejection fraction, stroke work, maximum and minimum derivative of ventricular pressure, heart rate, indices of relaxation, peak filling rate, and ventricular chamber stiffness. Pressure-volume loops can be graphically displayed. These analyses are exported to a text-file. These applications have simplified and automated the process of evaluating ventricular function.

Perinatal left ventricular performance in fetal sheep: interaction between oxygen ventilation and contractility.

Left ventricular (LV) output nearly triples at birth, in association with increases in serum catecholamines. Similar increases in catecholamines in utero, however, do not increase output. We hypothesized that catecholamines increase contractility in utero, but that output cannot increase until LV loading conditions are changed by oxygen ventilation. To address this hypothesis, we studied nine fetal sheep acutely placed in a warm water bath (40 degrees C). Conductance and manometric catheters were placed in the LV to generate pressure-volume loops during caval occlusion in the nonventilated and oxygen-ventilated states, each under control, dobutamine, and propranolol conditions. Contractility was estimated by the end-systolic pressure-volume relationship, preload by end-diastolic volume, and afterload by arterial elastance. Oxygen ventilation increased LV output 1.4-fold, despite a decrease in contractility to about three-fourths of the nonventilated value. Heart rate remained constant, whereas preload increased and afterload decreased significantly. During oxygen ventilation, dobutamine increased output to 2.3 times the control, nonventilated value, associated with increases in contractility and heart rate and no change in preload and afterload. Although dobutamine increased contractility and heart rate similarly in the nonventilated and oxygen ventilated states, output increased significantly more during ventilation. Similarly, propranolol decreased contractility and heart rate equally in both states, but output decreased far more during ventilation. Thus, oxygen ventilation is associated with advantageous changes in LV load such that the positive inotropic and chronotropic effects of dobutamine are translated into greater increases in LV output.

The effect of sarcoplasmic reticulum blockade on the force/frequency relationship and systolic contraction patterns in the newborn pig heart.

We investigated the relationship between heart rate and contractility in seven anaesthetized young piglets by measuring contractility at different atrial pacing rates. To study the origin of this relationship we repeated the measurements after blocking the sarcoplasmic reticulum calcium release channel with ryanodine. We assessed contractility using indices derived from instantaneous left ventricular pressure and volume measured by micromanometric and conductance catheters during rapid inferior vena cava occlusion, thus generating the end-systolic pressure-volume relationship, which was characterized by its slope Ees, and the maximum rate of change of ventricular pressure (dP/dtmax)/end-diastolic volume relationship, also characterized by its slope. All animals showed an increase in contractility with increasing heart rate (intact force/frequency relationship) which was abolished after ryanodine. The most striking effect of ryanodine on baseline haemodynamics was the dramatic decrease of dP/dtmax to about 50% of its original value, while peak developed pressure and Ees did not change. We conclude that the young piglet, despite its immaturity, has a functional sarcoplasmic reticulum, illustrated by an intact force/frequency relationship. In addition, blockade of the sarcoplasmic reticulum in vivo has profoundly different effects during early and late systole, indicating that indices of contractility derived during different parts of the cardiac cycle represent different aspects of systole.

Aortoventriculoplasty with the pulmonary autograft: the "Ross-Konno" procedure.

BACKGROUND: For patients with complex left ventricular outflow tract obstruction, including hypoplastic aortic anulus with or without severe diffuse subaortic stenosis, various aortoventriculoplasty procedures (e.g., Konno procedure and its modifications; extended aortic allograft root replacement) are important management options. In younger patients, however, reoperation for valve replacement is inevitably required, and anticoagulation issues pose additional problems. The pulmonary autograft provides a promising option for aortic valve replacement as part of the aortoventriculoplasty procedure in children. Long-term follow up shows that the pulmonary autograft functions well as the systemic arterial (neoaortic) valve and that valve growth occurs. METHODS: Between July 1993 and May 1995, 11 patients 4 days to 17 years old (median 12 months) underwent aortoventriculoplasty with pulmonary autograft (Ross-Konno procedure). The diagnoses were aortic stenosis with or without subaortic stenosis (n = 8), Shone complex (n = 2), and interrupted aortic arch with subaortic stenosis (n = 1). On average, 1.9 previous interventions had been performed per patient, including a previous Konno procedure in one patient. The aortic root was replaced with a pulmonary autograft valve. The left ventricular outflow tract was enlarged with a Dacron polyester fabric patch in two patients, with an allograft aortic patch in two patients and a right ventricular infundibular free wall muscular extension harvested in continuity with the autograft in seven patients. RESULTS: Intraoperative transesophageal echocardiographic assessment revealed mild aortic insufficiency in one patient. One patient had a residual left ventricular outflow tract gradient of 15 mm Hg. Significant complications were cardiac tamponade from bleeding (n = 1) and complete heart block necessitating a permanent pacemaker (n = 1). Follow-up ranged from 2 weeks to 16 months. To date, there have been no late deaths or reoperations. Follow-up echocardiography revealed mild autograft insufficiency in one patient and a 16 mm Hg residual left ventricular outflow tract gradient in one patient. CONCLUSIONS: Initial experience suggests that aortoventriculoplasty with the pulmonary autograft is an excellent alternative for young patients with complex left ventricular outflow tract obstruction. Because the pulmonary autograft has been shown to grow after implantation, reoperation on the left ventricular outflow tract is likely to be avoided.

Fetal chemoreception: a developing story.

The central and peripheral chemoreceptors are critical to the efficient uptake and delivery of oxygen and the removal of carbon dioxide after birth. However, the importance and activity of fetal chemoreception has been questioned, since oxygen uptake and carbon dioxide removal are not regulated in the lungs in the fetus. Early studies suggested that chemotransduction-the conversion of a chemical stimulus to cardiovascular and ventilatory responses via the integration of chemoreceptor stimulation, neural afferent activity and neurohormonal effector mechanisms-was immature in its individual components or their interaction. However, it now appears that the chemoreceptor cascade is structurally and functionally intact in the late-term fetus, and responds actively to normal and other chemical stimuli. The differences between fetal and postnatal chemotransduction appear to be primarily dependent on the central inhibition of the ventilatory response, the inhibitory area being localized to the lateral pons. It appears to be mediated in part by a placental factor which is removed at birth, allowing for the expression of the ventilatory response. The suppression of this response is also responsible for the difference in the heart rate response: the postnatal tachycardia is caused by the lung inflation reflex; when abolished, bradycardia is seen, just as in the fetus. Despite the suppression of the ventilatory component of chemoreception, the fetal carotid chemoreceptor is more important than the aortic, even though it has been considered to be more important to ventilatory than to cardiovascular stability. This review discusses current knowledge of the various components of the mature chemoreceptor cascade, and presents the fetal story within that framework.

Effect of drugs on chemoreceptor responsiveness in fetal sheep.

This study was designed to examine the effects of the drugs ketamine, morphine, pentobarbital, and propranolol on fetal chemoreceptor responsiveness. Eleven fetal lambs (gestational age 125-133 d) were chronically instrumented with a catheter in a hindlimb artery and vein and a forelimb artery; a carotid arterial oximeter catheter was placed in six of these fetuses. An inflatable cuff occluder was placed around the maternal hypogastric artery. Acute fetal hypoxemia was induced repeatedly by reducing uterine blood flow. Fetal heart rate, arterial pressure, and carotid arterial oxygen saturation were monitored continuously before and after administering ketamine, morphine, pentobarbital, or propranolol to the fetus. The ratio delta heart rate/delta O2 saturation has been shown previously to be a reproducible index of chemoreflex response. The differences in baseline values and changes with drugs were compared by multiple regression analysis coded by effects. Chemoreflex response was markedly attenuated by ketamine and morphine but not by pentobarbital or propranolol. Because the cardiovascular response to hypoxemia is blunted by some drugs, caution should be exercised in interpreting heart rate responses to hypoxemia in the fetus when these drugs have been administered to the mother.