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T R Lloyd

Publications and source records attributed to T R Lloyd.

71 records · Page 4Linked to original sources
PubMed1990

Sympathetic innervation improves the contractile performance of neonatal cardiac ventricular myocytes in culture.

We propose that sympathetic innervation could contribute to the improvement in cardiac contractility that normally occurs during neonatal life because these processes are developmentally coincident. Effects of sympathetic innervation were studied in primary cultures of isolated, not previously innervated ventricular cardiomyocytes from neonatal rats. Innervation was produced by addition of autologous neurons from the thoracolumbar sympathetic ganglia, and amplitude and frequency of myocyte contraction were measured by on-line video motion analysis. Sympathetic innervation significantly (P less than 0.0001) increased amplitude of contraction (by 34 +/- 8%) and decreased contraction frequency (by 36 +/- 3%). The effect of innervation on myocyte contractility was not attenuated by adrenoceptor blockade (10(-6) M propranolol and 10(-6) M phentolamine), but could be reproduced using medium conditioned by cocultures of neurons and myocytes. Sympathetic innervation improves the contractility of isolated cardiomyocytes, indicating that autonomic innervation contributes to maturation of cardiac function.

Animals↗
PubMed1990

Emulation of conduction system functions in the hearts of early mammalian embryos.

The conduction system functions of atrioventricular sequential contractions, atrioventricular delay, and coordination of ventricular contraction were examined in rat embryos at the earliest functional stage of cardiac development (before cardiac looping, n = 6) and shortly after looping (n = 15). Atrioventricular sequential contractions were observed in all embryos, and contractions appeared to originate in the left sinus horn. Atrioventricular delay was present in both prelooped (132 +/- 32 ms) and looped (141 +/- 15 ms) hearts. Before looping, contractions traveled from proximal ventricle to bulbus cordis, a distance of 253 +/- 27 microns, in 72 +/- 22 ms. After looping, contractions crossed an increased intraventricular distance (520 +/- 28 microns, p less than 0.005) in substantially less time (16 +/- 7 ms, p less than 0.005). Sinoatrial and atrioventricular nodal functions are emulated in both prelooped and looped hearts of early mammalian embryos, and His-Purkinje system function is emulated in looped hearts.

Animals↗
PubMed1989

Age at death in the hypoplastic left heart syndrome: multivariate analysis and importance of the coronary arteries.

Survival analysis of 63 fatal cases of the hypoplastic left heart syndrome was undertaken to determine whether morphologic measurements related to coronary blood flow would predict the length of postnatal survival. Cross-sectional areas of the ascending aorta and proximal left and right coronary arteries, left and right ventricular mass, coronary artery dominance pattern, and the presence of discrete coarctation were determined from autopsy specimens. These values were used to construct survival functions using Cox regression. Survival was significantly prolonged in cases with larger cross-sectional areas of the left (p less than 0.005) and right (p less than 0.05) coronary arteries, right ventricular mass (p less than 0.005), and combined ventricular mass (p less than 0.005). A multivariate model was developed that included combined left and right coronary artery cross-sectional areas, right ventricular mass, and the ratio of combined coronary artery area-to-combined ventricular mass. This model also significantly (p less than 0.001) predicted instantaneous risk of death, and again larger covariate values were associated with longer survival. These results suggest that myocardial perfusion is an important determinant of survival in these infants.

Age Factors↗
PubMed1988

Concealed atrial parasystole following the Senning operation.

A patient with sick sinus syndrome following the Senning operation was also found to have concealed atrial parasystole during intracardiac electrophysiological study. This atrial parasystolic pattern could be converted to atrial bigeminy by changing the atrial drive rate.

Arrhythmias, Cardiac↗
PubMed1987

Balloon dilation valvuloplasty of bioprosthetic valves in extracardiac conduits.

Six patients, aged 8 to 20 years, with valved right ventricle to pulmonary artery conduits were catheterized for balloon dilation valvuloplasty of stenotic and calcified bioprosthetic valves. Conduit stenosis was severe in all cases, with peak-to-peak systolic pressure gradients of 62 to 100 mm Hg (mean 79 mm Hg) and right ventricular systolic pressures of 87 to 115 mm Hg (mean 100 mm Hg). Three patients had good results, with residual peak-to-peak systolic pressure gradients of 20, 25, and 35 mm Hg. In two other patients, repeated balloon rupture before full inflation occurred, and residual gradients were high (55 and 60 mm Hg). One patient had substantial proximal and distal conduit obstruction in addition to valvular stenosis, and balloon dilation valvuloplasty was not attempted. No complications occurred in five patients; one patient required iliac vein exploration to remove an avulsed balloon fragment. Balloon dilation valvuloplasty can relieve bioprosthetic valve stenosis and postpone conduit replacement in some patients.

Adolescent↗
PubMed1986

Morphologic determinants of coronary blood flow in the hypoplastic left heart syndrome.

The diameters of the ascending aorta, coronary ostia, and proximal coronary arteries were measured in autopsy specimens from 51 infants with hypoplastic left heart syndrome and 18 normal infant heart specimens. Standard cross sections were prepared from 35 of the hypoplastic left heart syndrome hearts, and histologic indices of myocardial viability and fibrosis were determined. The diameters of the coronary arteries and ostia in hypoplastic left heart syndrome were not different from the values in control specimens. Little fibrosis was found but extensive myocardial necrosis was present. The degree of fibrosis and necrosis did not correlate significantly with any of the arterial or ostial diameters. The extent of myocardial preservation in the hypoplastic left heart syndrome, which may substantially limit the success of surgical palliation, cannot be predicted from these morphologic measurements. The observed myocardial damage appeared to be acquired postnatally, implying that early vigorous treatment of these infants may be necessary to preserve myocardial function.

Aorta↗
PubMed1986

Effect of intralipid on the neonatal pulmonary bed: an echographic study.

The effect of Intralipid infusion on pulmonary vascular resistance was studied prospectively by serial echocardiography on 13 occasions in six low birth weight infants. After 90 minutes of Intralipid infusion, the ratio of right ventricular preejection period to ejection time (RVPEP/ET) rose from 0.232 +/- 0.025 (mean +/- SD) to 0.285 +/- 0.035 (P = 0.0001). Of the 13 infusions studied, six (43%) resulted in RVPEP/ET values suggestive of pulmonary hypertension. Six LBW infants were observed over the same time period without Intralipid infusion, and RVPEP/ET did not change (0.209 +/- 0.035 vs 0.194 +/- 0.024). The increase in RVPEP/ET with Intralipid administration could not be explained by differences in preload or contractility, and most likely reflects an increase in pulmonary vascular tone. Caution in the use of Intralipid is recommended in infants who would be at particular risk from increased pulmonary vascular resistance.

Echocardiography↗
PubMedDate not supplied

Access to the left atrium for delivery of radiofrequency ablation in young patients: retrograde aortic vs transseptal approach.

Reported experience with the transseptal approach to the left atrium for delivery of radiofrequency energy in the young patient is limited. To compare two approaches for radiofrequency ablation (RFA) in the left atrium we reviewed our experience from January 1, 1991, through February 1, 1999, in 154 procedures performed on 136 patients (mean age 12.2 years). The patients were grouped by either the retrograde aortic route (R, n = 30) or the transseptal atrial route (T, n = 106). No significant differences were found in age, weight, height, supraventricular tachycardia cycle length, or electrocardiograph characteristics (manifest vs concealed accessory pathway) between the two approaches. Comparison of the transseptal group to the retrograde aortic group revealed a significant difference in the number of catheters (mean = 4 R vs 3 T, p < 0.0001), total fluoroscopic time (71.3 min R vs 43.0 min T, p = 0.0007), diagnostic fluoroscopic time (40.2 min R vs 16.6 min T, p < 0.0001), ablation fluoroscopic time (44.7 min R vs 25.3 min T, p = 0.019), and procedure time (5.0 hours R vs 4.1 hours T, p < 0.0001). No significant difference was found in success rate, number of radiofrequency applications, or major complication rate. These data suggest that although outcomes and major complication rates are similar for the two groups, the use of fewer catheters and shorter fluoroscopic times warrant consideration of the transseptal atrial approach in young patients.

Adolescent↗
PubMedDate not supplied

Iodixanol pharmacokinetics in children.

The objective of this report was to study the elimination pharmacokinetics of iodixanol in children. Iodixanol (Visipaque, Nycomed Inc., Wayne, PA, USA) is a new iso-osmolar iodinated radiocontrast agent. We hypothesized that elimination of this agent would be dependent on age-related differences in renal clearance. Seven centers enrolled 43 patients. Cardiac catheterization was performed in 41 patients and cranial computed tomography in 2. Patients were entered into 5 age groups: newborn to <2 months, 2 to <6 months, 6 months to <1 year, 1 to <3 years, and 3 to 6 months of age that is comparable to normal adults. Prolonged elimination in children <6 months of age is related to renal immaturity.

Age Factors↗
PubMedDate not supplied

Neonatal cardiac catheterization: A 10-year transition from diagnosis to therapy.

To assess the changing role of cardiac catheterization in the care of the neonate, a retrospective review of all catheterizations between January 1984 to December 1985 (group I) and January 1994 to December 1995 (group II) at C.S. Mott Children's Hospital was performed. Neonatal cardiac catheterization was performed more frequently (p = 0.02) in group I, comprising 14% (110 of 772) of all catheterizations versus 11% (93 of 880) in group II. Access was performed by cutdown in 15 patients (13 venous and 2 arterial), all in group I. In group I, 20 of 110 patients (18%) had balloon atrial septostomies; no other catheter interventions were performed. Interventions were more frequent (p = 0.003) and varied in group II, including 15 septostomies, 17 balloon valvuloplasties (13 pulmonary and 4 aortic), 2 coil embolizations of collaterals, and 1 cardiac biopsy. Despite the higher prevalence and complexity of interventions in group II, fluoroscopy times (median; range: 16 min; 2-55 vs 16 min; 1-107) were similar in both groups (p = not significant) as well as the prevalence of complications. Neonatal cardiac catheterizations are performed less frequently than they were a decade ago at our institution, and therapeutic interventions have become more common. Despite these changes, fluoroscopy time and the rate of complications have not increased.

Cardiac Catheterization↗