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T W Riggs

Publications and source records attributed to T W Riggs.

At least 19 recordsLinked to original sources
PubMed2004

A stochastic model of vaccine trials for endemic infections using group randomization.

To clarify the determinants of vaccine trial power for non-typable Haemophilus influenzae, we constructed stochastic SIS models of infection transmission in small units (e.g. day-care centres) to calculate the equilibrium distribution of the number infected. We investigated how unit size, contact rate (modelled as a function of the unit size), external force of infection and infection duration affected the statistical power for detection of vaccine effects on susceptibility or infectiousness. Given a frequency-dependent contact rate, the prevalence, proportion of infections generated internally and the power to detect vaccine effects each increased slightly with unit size. Under a density-dependent model, unit size had much stronger effects. To maximize information allowing inference from vaccine trials, contact functions should be empirically evaluated by studying units of differing size and molecular methods should be used to help distinguish internal vs. external transmission.

Disease Transmission, Infectious↗
PubMed1999

Fetal cardiac asymmetry: a marker for congenital heart disease.

OBJECTIVE: To determine the sensitivity of prenatally detected fetal cardiac asymmetry as a sonographic marker for congenital heart disease. METHODS: The normal ratios of pulmonary artery to aorta diameters and of right ventricle to left ventricle diameters were derived from normal fetuses scanned at 17 weeks or more in a 65-month period. Cross-sectional diameters of cardiac ventricles and great arteries were measured at the level of the valves at the time of the scan. Fetuses with confirmed cardiac anomalies detected prenatally during the study were examined to identify how many had cardiac asymmetry, determined by abnormal ratios. RESULTS: Linear regression analysis of the group of 881 normal fetuses showed the normal pulmonary artery to aorta diameter ratio remained constant throughout pregnancy and the normal right ventricle to left ventricle ratio increased slightly with progressing gestational age. The 90% confidence intervals were 0.79, 1.24 for the right ventricle to left ventricle ratio and 0.84, 1.41 for the pulmonary artery to aorta ratio. Of the 73 fetuses with abnormal hearts, 66% had either ventricular or great artery asymmetry (at least one of the two ratios was abnormal). However, if no asymmetry was present, the cardiac defect was more likely to be a minor one. CONCLUSION: Cardiac asymmetry was present in two-thirds of fetuses with cardiac anomalies diagnosed prenatally. If cardiac asymmetry is found, a more thorough examination of the fetal heart is indicated.

Adult↗
PubMed1999

Recurrence risk of supraventricular tachycardia in pediatric patients.

We analyzed risk of recurrence of supraventricular tachycardia (SVT) in 70 pediatric patients using both Kaplan-Meier survival analysis and logistic regression of likelihood of recurrence, each with covariates: (1) age at onset of SVT; (2) presence of Wolff-Parkinson-White syndrome (WPW), and (3) gender. Among 38 patients who had onset of SVT <1 year, only 11 had a recurrence, while among 32 older patients, 30 had a recurrence of SVT (p < 0.00001, Fisher's exact test). The survival analyses, stratified by age at onset <1 versus >1 year, were significantly different (p < 0.0001) as was stratification by presence of WPW (p < 0.01). Logistic regression analysis showed that the only significant predictor of recurrence was age at onset; the additional information provided by presence of WPW and gender did not significantly add to the prediction of recurrence. The odds ratio of recurrence for age at onset >1 versus <1 year was 34.6, with a 95% confidence interval of 6.98-172.

Adolescent↗
PubMed1997

Sonographic screening to detect fetal cardiac anomalies: a 5-year experience with 111 abnormal cases.

OBJECTIVE: To determine whether there is a difference between the types of cardiac lesions detected as abnormal prenatally and those that are not detected. METHODS: Consecutive fetuses at 14 weeks' gestation or more were scanned in our unit from February 1990 through July 1995 and later were delivered at our hospital. Outcome information was obtained from neonatal echocardiograms and autopsies. Our results were compared to sensitivities for individual cardiac lesions based on pooled data from studies published previously. RESULTS: There were 111 fetuses with cardiac anomalies, of which 73 (66%) were identified correctly as abnormal prenatally. Sensitivities for the most common cardiac lesions were as follows: 87% atrioventricular septal (endocardial cushion) defects, 65% tetralogy of Fallot, 63% transposition of the great arteries, 50% aortic coarctation, and 44% isolated ventricular septal defects. The lesions that went undetected most frequently were isolated septal defects (n = 17); most of these were ventricular and small or moderate in size. Based on our sensitivities and those calculated from previous studies, the fetal cardiac lesions with the highest detection rates involve hypoplastic ventricles and atrioventricular septal defects, followed by lesions of the great arteries and finally by isolated septal defects. CONCLUSIONS: The sensitivity of sonographic screening to defect fetal cardiac anomalies varies with the type of lesion. Isolated septal defects are the most difficult lesions to detect.

Female↗
PubMed1994

Prenatal screening for cardiac anomalies: the value of routine addition of the aortic root to the four-chamber view.

OBJECTIVE: To determine whether the addition of the aortic-root view would detect more congenital cardiac anomalies than a standard four-chamber view alone. METHODS: The study included fetuses of 14 weeks' gestation or more who were scanned in our unit during a 28-month period. Outcome information was obtained from postnatal echocardiograms and autopsies. Abnormal hearts were classified as to whether the four-chamber or aortic-root view was abnormal. RESULTS: There were 5967 fetuses in whom a four-chamber view could be obtained. In 5111 of these, an aortic-root view could also be obtained. The four-chamber view detected 24 (47%) of the 51 fetuses with abnormal hearts. Adding the aortic-root view increased the sensitivity to 78%. CONCLUSIONS: Visualization of the aortic root is a quick and easy means of evaluating the aortic outflow tract during routine scanning. Adding the aortic-root view to the standard four-chamber view will result in the detection of most cardiac anomalies prenatally.

Echocardiography↗
PubMed1993

Abnormal right ventricular filling in patients with dilated cardiomyopathy.

Doppler echocardiograms of the tricuspid and mitral valves were recorded along with the electrocardiogram and respiration in six patients with dilated cardiomyopathy and 20 normal children. There was significant respiratory variation in right ventricular filling in the patients with dilated cardiomyopathy. Four variables of early diastolic right ventricular filling increased with inspiration: the peak E velocity (mean increase 55%, p < 0.05), the E/total area (mean increase 32%, p < 0.001), the E/A area (mean increase 74%, p < 0.001), and peak E/A ratio (mean increase 72%, p < 0.01), whereas the peak A velocity did not change significantly and the A/total decreased (mean decrease 27%, p < 0.001). Thus, abnormalities of right ventricular filling worsened during expiration and improved with inspiration. Inspiration enhances right ventricular venous return and thus improves indices of right ventricular filling in patients with cardiomyopathy.

Cardiomyopathy, Dilated↗
PubMed1991

Dizygotic twins concordant for truncus arteriosus.

Persistent truncus arteriosus (TA) is an uncommon congenital cardiovascular malformation, which comprises between 0.4% and 4% of all congenital heart defects. Occurrence of TA in siblings has been reported infrequently. Twins concordant for isolated TA appear to have been reported only once previously. In this paper, we describe dizygotic twin females who were concordant for isolated TA.

Diseases in Twins↗
PubMed1990

Physiologic peripheral pulmonic stenosis in infancy.

We studied 14 premature infants with the clinical diagnosis of peripheral pulmonic stenosis (PPS) and 15 normal full-term neonates by echocardiographic Doppler examinations. The PPS group had an average main pulmonary artery (PA) diameter similar to the control group (0.91 vs 0.96 cm, difference not significant), but had smaller branch PA diameters: right PA = 0.41 vs 0.50 cm, p less than 0.001, and left PA = 0.41 vs 0.49 cm, p less than 0.001. The PPS group also had greater peak velocities in the main PA (76 vs 63 cm/s, p less than 0.05), right PA (193 vs 118 cm/s, p less than 0.001) and left PA (187 vs 123 cm/s, p less than 0.001). Similarly, the ratio of peak velocity in the branch/main PA was greater for the PPS group: right/main PA peak velocity = 2.91 vs 1.92, p less than 0.01, and left/main PA peak velocity = 2.73 vs 1.99, p less than 0.05. The calculated right ventricular output for the PPS group was more than the control group: 437 vs 261 ml/min/kg, p less than 0.001. Hematocrits were not done on the control group, but the PPS group had an average hematocrit which was low (34%). It is concluded that patients with PPS have mild underdevelopment of the PA branches, with consequent increased flow velocity and turbulent flow. This turbulent flow may be contributed to by increased cardiac output and mild anemia.

Blood Flow Velocity↗
PubMed1990

Doppler echocardiographic evaluation of left ventricular diastolic function in adolescents with diabetes mellitus.

Doppler echocardiograms of the mitral valve were recorded along with electrocardiograms and respirations from 20 diabetics and 16 normal subjects, all aged 10 to 15 years. E and A areas (the components of the total velocity-time integral in the early passive period of ventricular filling [E] and the late active period of atrial emptying [A], respectively), the peak E and A velocities (cm/s) and the 1/3 area fraction (or the proportion of filling in the first 1/3 of diastole) were measured. Each of the following was significantly greater for the normal subjects versus diabetic patients: peak E (96 +/- 14 vs 81 +/- 14 cm/s, p less than 0.005), E/total area (0.74 +/- 0.04 vs 0.69 +/- 0.06, p less than 0.005) and peak E/A velocity ratio (2.38 +/- 0.55 vs 1.92 +/- 0.55, p less than 0.05). The mean heart rates and ages were not significantly different for the 2 groups. The remaining parameters (peak A velocity, A/total area, E/A area, and 1/3 area fraction) were also not significantly different for the 2 groups. This study is the first to demonstrate diastolic dysfunction in pediatric patients with diabetes and may indicate abnormalities of ventricular relaxation or compliance in diabetes mellitus.

Adolescent↗
PubMed1989

Respiratory influence on right and left ventricular diastolic function in normal children.

Doppler echocardiograms of the tricuspid and mitral valves were recorded with electrocardiogram and respirations in 20 normal children aged 1.5 to 11 years. Four variables of early diastolic left ventricular (LV) filling decreased with inspiration: the peak E velocity (mean decrease 8%, p less than 0.0001), the ratio of E/A areas (mean decrease 12%, p less than 0.001), the peak E/A velocity ratio (mean decrease 14%, p less than 0.005) and the 1/3 area fraction (mean decrease 12%, p less than 0.001). Variables of late active atrial emptying (peak A velocity and A/total area ratio) were unchanged with respiration. There was a significant increase in the right ventricular (RV) peak E (mean increase 26%, p less than 0.0001) and peak A velocities (mean increase 18%, p less than 0.0001) and mean heart rate (5% increase) with inspiration. The enhancement of RV filling was similar for early and late diastolic filling, since each of the variables generated from their ratios were not significantly changed with inspiration. Inspiration significantly enhances RV venous return, while the LV response to inspiration is a complex interplay among preload, afterload and ventricular interdependence. Assessment of pediatric RV and LV diastolic function should include standardization for phase of respiration.

Child↗
PubMed1989

Doppler echocardiographic evaluation of right and left ventricular diastolic function in normal neonates.

Doppler echocardiograms of the tricuspid and mitral valves were recorded along with the electrocardiogram and respiration in 22 normal full-term neonates. A computer-interfaced digitizer pad was utilized to measure the following: peak E and A velocities (cm/s); E and A areas (the components of the total velocity-time integral in the early passive period of ventricular filling [E] and the late active period of atrial emptying [A], respectively) and the 1/3 area fraction (or the proportion of filling in the first 1/3 of diastole). All of the variables of right (tricuspid) versus left (mitral) ventricular filling were significantly different on the 1st day of life. Respective values were peak E velocity (cm/s) 44.6 +/- 10.0 (tricuspid) versus 53.2 +/- 9.3 (mitral), p less than 0.01; peak E/A ratio 0.84 +/- 0.14 versus 1.15 +/- 0.17, p less than 0.0001; E/total area 0.58 +/- 0.07 versus 0.63 +/- 0.05, p less than 0.005; E/A area ratio 1.05 +/- 0.23 versus 1.63 +/- 0.40, p less than 0.0001; 1/3 area fraction 0.31 +/- 0.04 versus 0.41 +/- 0.04, p less than 0.0001; peak A velocity (cm/s) 53.0 +/- 8.4 versus 47.6 +/- 5.8, p less than 0.05 and A/total area 0.57 +/- 0.09 versus 0.41 +/- 0.09, p less than 0.001; the mean heart rate (beats/min) was not significantly different: 121 +/- 8 versus 120 +/- 7. Most of the variables remained significantly different on the 2nd day of life, but the level of significance was the same or less for all measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Cesarean Section↗
PubMed1985

Functional aortic valve atresia in transposition of the great arteries.

The criterion for the diagnosis of functional atresia of a patient semilunar valve is met when the pressure in a ventricle remains lower than that in the related great artery throughout systole so that no forward flow can occur. Functional pulmonary valve atresia has been well recognized in infants with normally related great arteries and massive tricuspid valve incompetence. The cardiac physiology and anatomy of an infant with transposed great arteries and functional aortic valve atresia is reported for the first time. The peak systolic pressure in the right ventricle was 30 mm Hg and in the aorta 64 mm Hg. The causes for right ventricular incompetence were abnormalities of the tricuspid valve and hypoplasia of the ventricular free wall. Three other cases with similar ventricular anatomy and physiology but with anatomic atresia of the aortic valve are reviewed. The possibility that under these physiologic circumstances during fetal life functional atresia develops first, and that anatomic fusion of idle semilunar cusps develops as a secondary phenomenon, is discussed.

Aortic Valve↗
PubMed1984

The surgical management of left ventricular outflow tract obstruction due to tricuspid valve pouch in complete transposition of the great arteries.

Subpulmonary stenosis in transposition of the great arteries, resulting from a tricuspid valve pouch bulging into the left ventricular outflow tract through a ventricular septal defect, can be missed at the time of operation in the flaccid, nonbeating heart unless preoperative diagnosis has been established. In our experience, six patients were found to have this lesion. In four patients the tricuspid valve pouch was recognized preoperatively. At operation, retraction of the tricuspid valve pouch into the right ventricle, patch closure of the ventricular septal defect, and a Mustard procedure were performed in three patients; the fourth is awaiting correction following initial palliation with a subclavian-pulmonary shunt. In the other two, the ventricular septal defect was partially or completely obliterated by a tricuspid valve pouch that was missed preoperatively and during exploration at the time of the Mustard procedure. Residual left ventricular outflow tract obstruction was subsequently corrected with a left ventricle-pulmonary artery valved conduit. Echocardiographic and angiocardiographic examinations offer helpful signs for the diagnosis of tricuspid valve pouch. Transatrial retraction of the redundant tricuspid valve tissue into the right ventricle, patch closure of the ventricular septal defect, and Mustard operation are the procedures of choice. A left ventricle-pulmonary artery valved conduit may be required for residual unresectable left ventricular outflow tract obstruction.

Cardiomyopathy, Hypertrophic↗