Advances in fetal echocardiography

Fetal echocardiography is the primary modality for defining and evaluating fetal cardiac status and requires detailed analysis of the cardiac anatomy from numerous views and Doppler interrogation of the intracardiac structures, great vessels, and umbilical artery. Referrals for fetal echocardiography are determined by fetal, maternal, or familial risk factors; however, approximately 50% of neonates diagnosed with a congenital cardiac defect have no risk factor, and most have undergone an obstetrical ultrasound during the pregnancy that did not detect a cardiac defect. Advances in transducer technology have resulted in the development of small high-frequency transvaginal probes that allow fetal cardiac interrogation earlier during gestation. On the horizon is 3-dimensional fetal echocardiography, which provides rapid image acquisition and tremendous computer image reconstruction ability. At present, the computer image data analysis process is lengthy, and several technical limitations must be overcome before 3-dimensional fetal echocardiography becomes the primary modality of fetal cardiac imaging. New Doppler Tissue Imaging using color Doppler energy mapping allows more precise anatomic definition of the fetal endocardium, facilitating diagnosis of small ventricular septal defects. These new advances, along with improved image resolution, provide obstetricians and pediatric cardiologists with more tools and techniques for earlier and more precise detection of fetuses with cardiac defects.

Echocardiographic Evaluation of Common Atrioventricular Canal Defects: A Study of 206 Consecutive Patients

An accurate echocardiographic evaluation of common atrioventricular canal (CAVC) requires in-depth knowledge of the wide spectrum of morphological and physiological variations in this group of anomalies. In order to evaluate the incidence and morphological distribution of AV canal defects in a large series of patients and to define a systematic approach to the echocardiographic examination, we reviewed the echocardiograms of 206 consecutive patients with CAVC studied at Texas Children's Hospital over a 32-month period. The complete form of CAVC was most common (68.4%) and presented at an earlier age (mean +/- SD: 1.6 +/- 2.4 months). A partial AV canal (ostium primum atrial septal defect [ASD]) was found in 42 patients (20.4%) and their age at presentation was higher (9.2 +/- 10 months). Twenty-three patients (11.2%) had a transitional AV canal. Down syndrome was diagnosed in 34% of patients, the majority of whom (79%) had a complete CAVC. Associated malformations were found in 46% of patients: anomalies of the conotruncus were most frequent (18%), followed by secundum ASD (14.1%), anomalous pulmonary venous connection (11.2%), and heterotaxy syndrome (11.2%). Subaortic obstruction and mitral stenosis were less common. The AV canal was unbalanced in 14.1% of patients, with the right ventricular dominant form being more common than the left ventricular dominant form (10.7% and 3.4%, respectively). Based on our experience, we developed a systematic, segment-by-segment approach to the echocardiographic examination in infants with CAVC. Together with detailed anatomical information, Doppler evaluation provides crucial hemodynamic information that allows planning of surgical repair. (ECHOCARDIOGRAPHY, Volume 13, July 1996)

Intraoperative transesophageal echocardiography in congenital heart surgery. The Texas Children's Hospital experience

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Quantitative morphometric analysis of progressive infundibular obstruction in tetralogy of Fallot. A prospective longitudinal echocardiographic study

BACKGROUND

The morphological hallmark of tetralogy of Fallot is controversial, with much disagreement as to whether the subpulmonary infundibulum in this lesion is hypoplastic. In addition, few quantitative data are available regarding the morphometry of the subpulmonary infundibulum, what anatomic characteristics are acquired in the postnatal period, and at what rate they progress. We also sought to determine whether echocardiographic morphometric analysis of the infundibulum can predict clinical course in infants with tetralogy of Fallot.

METHODS AND RESULTS

Twenty-one infants with tetralogy of Fallot (median age at initial study, 1.6 months) were prospectively followed with serial echocardiograms until the time of first surgical intervention (median age at surgery, 10 months). Selected video still frames were digitized off-line with a computerized system. Compared with age-matched normal control infants (n = 37), the following indexed infundibular dimensions in patients with tetralogy of Fallot were significantly smaller: length (1.86 +/- 0.54 versus 2.7 +/- 0.56 cm/BSA0.5, P < .0001), cross-sectional area (1.6 +/- 0.49 versus 4.7 +/- 1.3 cm2/BSA, P < .0001), and volume (1.24 +/- 0.62 versus 7.2 +/- 3 mL/BSA1.5, P < .0001). The following measurements were increased in tetralogy patients: infundibular septal thickness (0.83 +/- 0.21 versus 0.54 +/- 0.06 cm/BSA0.5, P = .0002) and infundibular free-wall thickness (0.62 +/- 0.13 versus 0.49 +/- 0.06 cm/BSA0.5, P = .006). The angle between infundibular septum and ventricular septum had a greater degree of anterosuperior deviation in tetralogy patients, resulting in a larger infundibuloventricular septal angle (77 +/- 8.2 degrees versus 31 +/- 6.5 degrees, P < .0001). During follow-up, infundibular volume in tetralogy patients decreased from 1.24 +/- 0.62 to 0.81 +/- 0.47 mL/BSA1.5 (P = .002), correlating with infundibular septal thickness (r = -.63, P < .003). The mean rate of decrease of indexed infundibular volume was 0.1 +/- 0.13 mL.BSA-15.mo-1. Correlation analysis revealed a nonlinear correlation between the degree of infundibular septal malalignment and indexed infundibular volume (r = .93, P < .0001). Tetralogy patients who required early surgical intervention (4.8 +/- 0.9 versus 10.7 +/- 1.7 months, P < .0001) had a smaller infundibulum at presentation (0.92 +/- 0.35 versus 1.41 +/- 0.67 mL/BSA1.5, P = .04) and an accelerated rate of infundibular narrowing (0.17 +/- 0.18 versus 0.06 +/- 0.08 mL.BSA-1.5.mo-1, P = .04).

CONCLUSIONS

Compared with normal infants, the subpulmonary infundibulum in tetralogy of Fallot is characterized by a smaller volume, shorter and thicker infundibular septum, and anterosuperior deviation of the infundibular septum. Infundibular obstruction in tetralogy patients is progressive, with an average rate of decrease in indexed infundibular volume of 0.1 +/- 0.13 mL.BSA-1.5.mo-1. Infants who are likely to require early therapeutic intervention may be identified on their initial echocardiogram as having an infundibular volume of < 0.9 to 1.0 mL/BSA1.5.

Effects of chronic exercise on blood volume expansion and hematologic indices during pregnancy

OBJECTIVE

To compare blood volumes and hematologic indices between nine aerobically trained, physically active pregnant women who continued to exercise throughout gestation and five healthy yet sedentary gravidas.

METHODS

Subjects were tested on three occasions: 25 and 36 weeks of pregnancy and 12 weeks postpartum. Plasma volumes were estimated by dye dilution with Evans blue. Blood samples were taken from the antecubital vein with the subjects resting in a seated, semirecumbent position. In addition to plasma volume estimations, blood samples were analyzed for hematocrit ratio, hemoglobin concentration, red cell count, and plasma protein concentration. Blood volumes and red cell volumes were calculated from plasma volume estimates and hematocrit ratios.

RESULTS

Average birth weight and length of gestation did not differ between the subject groups. Analysis of variance indicated that absolute blood volume measures were significantly greater (P < .01) in the physically active compared to sedentary subjects at all three test times. Similar results were found for plasma and red cell volumes (P < .01). Blood volumes relative to body weight were significantly higher in physically active subjects (P < .01) than in their sedentary counterparts at 25 weeks (88.5 versus 75.5 mL/kg) and at 36 weeks (88.4 versus 70.9 mL/kg), as well as at 12 weeks postpartum (72.2 versus 57.6 mL/kg). All vascular volumes were significantly (P < .001) lower at 12 weeks postpartum compared to those seen during pregnancy in both subject groups. Hematologic indices of hematocrit ratio, hemoglobin concentration, red cell count, and plasma protein concentration were all greater (P < .001) at 12 weeks postpartum than during pregnancy.

CONCLUSIONS

Physically active women possessed significantly greater vascular volumes than their sedentary counterparts. Although this difference was maintained throughout gestation as the active gravidas continued to exercise, there was no apparent effect on pregnancy outcome.

Effects of maternal aerobic fitness on cardiorespiratory responses to exercise

We hypothesized that aerobically fit women who continued to exercise throughout pregnancy would have enhanced cardiorespiratory responses to exercise. Physically active (N = 10) and sedentary (N = 6) subjects were compared during steady-state (15 min) semi-recumbent cycle exercise performed at a given heart rate (HR; 140 b.min-1) twice during pregnancy (25 wk, 36 wk) and 12 wk postpartum. Indirect calorimetry was used to measure volumes and fractional concentrations of expired gases. Cardiac output was estimated via CO2 rebreathing. Data were analyzed with repeated measures ANOVA. Caloric expenditure during exercise was significantly (P < 0.001) greater in the physically active (7.2 kcal.min-1) compared with sedentary (4.7 kcal.min-1) subjects. Alveolar ventilation and cardiac output responses to exercise were proportionally greater (P < 0.001) in the aerobically fit subjects. Ventilatory equivalents for O2 and physiological dead space/tidal volume ratios were significantly (P < 0.01) lower in the physically active subjects during exercise. In contrast, ratings of perceived exertion during exercise did not differ between subject groups. It appears that a physically active woman's enhanced cardiorespiratory responses to acute exercise are maintained during pregnancy if she continues her aerobic fitness program throughout gestation.

Two-dimensional echocardiographic anatomy of atrioventricular alignment discordance with situs concordance

Relationships between the atria and the ventricles are commonly described in terms of either atrioventricular (AV) alignments (or connections) or AV situs (i.e., the type of atrial situs and the type of ventricular situs or ventricular loop). With either method of analysis, only one type of AV relationship (situs or alignment) is diagnosed specifically and is considered to be predictive of the other type of AV relationship. The two-dimensional echocardiographic characteristics of two patients with incongruent AV situs and alignments are described for the first time. Patient 1 had situs solitus of the viscera and atria (S), ventricular D-loop (D), and solitus normally related great arteries (S), or (S,D,S) segmental combination with concordant AV situs. However, the right-sided right atrium drained into the inferior and right-sided left ventricle, and the left-sided left atrium drained into the superior and left-sided right ventricle. Hence AV alignment discordance was present. Patient 2 had visceroatrial situs solitus (S), ventricular D-loop (D), and double-outlet right ventricle with a rightward aortic valve (D), or (S,D,D) segmental set (AV situs concordance). Similar to patient 1, AV alignment discordance was demonstrated. In both patients the diagnosis was established by two-dimensional echocardiography and subsequently confirmed by cardiac catheterization. The key to accurate echocardiographic diagnosis of this congenital heart disease was independent analysis of the AV alignments and the segmental situs of the three main cardiac segments. This diagnosis was determined by scanning from the parasternal, subxiphoid, and apical windows.(ABSTRACT TRUNCATED AT 250 WORDS)

Indomethacin for preterm labor: fetal toxicity in a dizygotic twin gestation

Indomethacin was given for the treatment of preterm labor in a twin pregnancy at a dosage of 200 mg/day for 7 days beginning at 34 weeks and 5 days' gestation. During treatment, one twin developed closure of the ductus arteriosus, tricuspid regurgitation, right ventricular dysfunction, and pericardial effusion. Severe oligohydramnios in both amniotic sacs appeared as well. All findings resolved within 7 days of discontinuation of the medication. The infants, delivered vaginally at 37 weeks' gestation, were alive and well at a 2-month follow-up visit. We believe that all fetuses of mothers treated with indomethacin should be closely monitored for early evidence of decreased amniotic fluid volume and constriction of the ductus arteriosus.

Maturational differences in the isolated isovolumic rabbit heart

To determine maturational differences in myocardial pressure work, oxygen consumption, and stability, we evaluated an isolated retrogradely perfused isovolumic rabbit heart model in newborns (0-6 days of age, mean 3.3 +/- 1.9 days), immatures (4-6 wk) and adults (5-7 mo). To reduce ischemic time and cardiac trauma, the hearts were isolated and instrumented within the chest cavity. By design, there were no significant age-related differences in coronary flow per gram, heart rate, or resting pressure. Left ventricular developed pressure was similar at all ages, but myocardial oxygen consumption was much lower in newborns and immatures than in adults. Coronary resistance was lower in the younger hearts. There were no significant age-related differences in contractility, left ventricular stiffness, or myocardial pH. All hearts were stable for 120 min, but thereafter immatures and adults deteriorated more rapidly than newborns. The study demonstrates that this model is technically suitable for the study of age-related differences in cardiac physiology. Furthermore, newborn and immature hearts are able to more efficiently use oxygen to develop left ventricular pressures, possibly due to a lower wall tension.

Renal responses to hypoxemia during renin-angiotensin system inhibition in fetal lambs

The role of the renin-angiotensin system (RAS) in modulating the renal hemodynamic and functional responses to hypoxemia was studied in chronically catheterized fetal lambs (132-143 days gestation; term 145 days) before and during administration of either captopril or [Sar1-Gly8]ANG II. Base-line mean arterial blood pressure decreased significantly after administration of either captopril or [Sar1-Gly8]ANG II. This decrease was associated with a significant decline in renal vascular resistance (RVR) in captopril-treated fetuses, whereas no changes in RVR were observed in [Sar1-Gly8]ANG II-treated fetuses. However, the decline in renal blood flow (RBF) and the rise in RVR associated with hypoxemia in control fetuses were not attenuated significantly during inhibition of the RAS using either captopril or [Sar1-Gly8]ANG II. Moreover neither captopril nor [Sar1-Gly8]ANG II blunted the hypertensive response associated with fetal hypoxemia. The renal functional response to captopril was different from the response observed during infusion of [Sar1-Gly8]ANG II. Administration of [Sar1-Gly8]ANG II produced significant decreases in urinary flow rate (UFR), glomerular filtration rate (GFR), and urinary electrolyte (Na+, K+, Cl-) excretion rates, whereas no changes were observed during captopril infusion. The effects of hypoxemia on renal function were not modified after captopril. However, [Sar1-Gly8]ANG II tended to increase UFR and GFR, but these changes were pressure-dependent and not directly related to inhibition of the RAS. This study suggests that the RAS is not an important mediator of the fetal renal hemodynamic and functional responses to hypoxemia.

Factors controlling aldosterone secretion during hypoxemia in fetal lambs

Factors modulating the fetal aldosterone response to hypoxemia were studied in three groups of chronically catheterized fetal lambs between 131 and 143 days of gestation (term, 145 days). One group (control group) received an infusion of 5% dextrose in water; the second group (captopril-treated group) was given captopril, an inhibitor of angiotensin-converting enzyme; the third group (captopril plus dexamethasone-treated group) received dexamethasone in addition to captopril. In all groups of fetuses, hypoxemia was associated with a significant increase in plasma K+ concentration (+0.7 +/- 0.1 meq/liter). In control fetuses, changes in plasma aldosterone concentration during hypoxemia correlated closely with changes in plasma K+ concentration r = 0.79; P less than 0.001) and with changes in plasma angiotensin II concentration (r = 0.77; P less than 0.001). In the captopril-treated fetuses, the rise in plasma aldosterone concentration during hypoxemia correlated closely with plasma K+ (r = 0.79; P less than 0.001) but not with plasma angiotensin II values (r = 0.17). No significant correlation was found between percent changes in maternal aldosterone and percent changes in fetal aldosterone during hypoxemia and following recovery (r = 0.36; P greater than 0.1) in captopril-treated fetuses. Administration of dexamethasone to fetuses receiving captopril completely inhibited the rise in plasma aldosterone associated with hypoxemia. Taken together, the present results suggest that the rise in plasma aldosterone during hypoxemia is not related to the level of activity of the renin-angiotensin system but depends probably on the increased secretion of adrenocorticotrophin by the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)

Near-fatal Kearns-Sayre syndrome. A case report and review of clinical manifestations

The Kearns-Sayre syndrome is a relatively uncommon condition which occurs in childhood and is characterized by neurologic dysfunction and abnormalities in atrioventricular (AV) conduction. The high mortality rate is directly attributable to the cardiovascular manifestations of this syndrome. We report a case, with documentation of a "near-fatal" episode, and review the pertinent clinical features of the syndrome.

Renal and adrenal responses to converting-enzyme inhibition in fetal and newborn life

The renal and adrenal responses to a continuous infusion of the angiotensin-converting enzyme (ACE) inhibitor captopril were studied in 27 chronically catheterized sheep fetuses (less than 120 days gestation, n = 15, and greater than 130 days gestation, n = 12; term being 145 days) and in 12 newborn lambs between 8 and 21 days of age. Total renal blood flow did not change during ACE inhibition. However, the renal vascular resistance decreased significantly in newborn lambs (-21.8 +/- 5.7%) and in fetuses greater than 130 days (-21.7 +/- 4.7%) but not in fetuses less than 120 days. A significant decrease in filtration fraction (-19.2 +/- 6.5%) was observed in newborn lambs. No changes in urinary kallikrein and prostaglandin excretion rate were observed during ACE inhibition in any group of animals. ACE inhibition produced similar declines in blood pressure in both groups of fetuses (-10.2 +/- 3% in fetuses less than 120 days and -9.5 +/- 4.6% in fetuses greater than 130 days) and in newborn lambs (-13.4 +/- 2.1%). The percent changes in plasma renin activity were similar in all groups of animals. However, a significant decline in plasma aldosterone concentration was observed only in newborn lambs (from 130 +/- 31 to 64 +/- 9 pg/ml). These results suggest that the renin-angiotensin system might have physiological significance during maturation, but that this role seems to be more important in near-term fetuses (greater than 130 days) and postnatally than early in gestation.