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Biomedical subjects

K C Lau

Publications and source records attributed to K C Lau.

At least 37 records · Page 2Linked to original sources
PubMed1992

Accuracy of various methods of localization of the orifice of the coronary sinus at electrophysiologic study.

The coronary sinus (CS) orifice is an important reference point for determining electrode and, thereby, accessory pathway location at electrophysiologic study. The reliability of fluoroscopic landmarks used to identify the CS orifice is not known. This study compared the accuracy of several fluoroscopic landmarks for identifying the CS orifice with the location defined by radiopaque contrast injection of the CS. Forty patients were studied. Radiographic markers of the CS orifice that were examined included: (1) the point at which the CS catheter prolapsed during advancement, (2) the point of maximum convexity of the CS catheter when a superior vena caval approach was used, (3) the right side of the ventricular septum, and (4) the relation to the underlying vertebrae. The least-significant difference method of multiple comparisons was used for statistical analysis. The point at which the CS catheter prolapsed was the most accurate noncontrast method for determining the location of the CS orifice (p less than 0.05), but was possible without the use of excessive force in only 48% of patients. The point of catheter prolapse was a median of 1 mm (range 0 to 11) from the true location of the os. Errors with other examined landmarks ranged up to 3 cm. Identification of the CS orifice is best performed by radiopaque contrast injection. The point of prolapse during catheter advancement in the CS is an accurate alternative when contrast injection is not feasible. Other noncontrast fluoroscopic landmarks are less reliable and are best avoided.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Postnatal development of type I retinal ganglion cells in hamsters: a lucifer yellow study.

The postnatal development of a population of superior colliculus projecting retinal ganglion cells with large somata in hamsters aged from postnatal day (P) 4 to adult was studied by the intracellular injection of Lucifer Yellow. This population of cells was interpreted as Type I cells based on their large soma sizes and dendritic morphology resembling that of mature Type I cells. In addition to the growth of the soma and the dendritic field, transient morphological features such as intraretinal axon collaterals and exuberant dendritic spines, but not somatic spines, were frequently observed on this population of cells in hamsters during development. None of them exhibited any intraretinal axon collaterals after P7. The number of transient spine-like processes on dendrites increased from P4 onwards to reach a peak at P16, decreased abruptly within a few days after the peak, and stabilised to reach the adult level by P30. These developing cells attained the maximum number of dendritic branches by P16 and there seems to be little, if any, reduction in the number of branch points after this time point. In addition, the length of individual branches of dendrites was not increased excessively during development and then shortened during maturation. Thus, the dendritic remodeling of these cells after P16 seems to be mainly the increase of the length of dendrites and the removal of exuberant dendritic spines.

Animals↗
PubMed1992

Pupillary constriction in response to light in rodents, which does not depend on central neural pathways.

We show here that the widely held belief that reflex constriction of the mammalian pupil in response to light depends exclusively upon neural pathways between eye and brain is in need of revision. We investigated the response of the pupil to light in dark-adapted rodents (golden hamsters; hooded rats; albino rats) subjected to a variety of surgical and pharmacological interventions designed to destroy or block all of the neural pathways and structures through which the reflex could be mediated. The interventions included bilateral intraorbital optic nerve section, or unilateral intracranial optic nerve section with enucleation of the contralateral eye, combined in some cases with bilateral removal of the superior cervical ganglia and/or pinealectomy; topical application of atropine; intraocular injection of tetrodotoxin (TTX). Golden hamsters and hooded rats, but not albino rats, retained an effective constriction of the pupil in response to light after all of these interventions, although the constriction was less and slower than in normal animals. These findings show that hamsters and hooded rats have both a neurally mediated fast light reflex that can be eliminated by severing connections between eye and brain, by blockade of cholinergic transmission to iris smooth muscle, and by blockade of action potentials by TTX; and a local, slower constriction in response to light, which remains after all these procedures. We have also confirmed previous observations of Bito and Turansky (1975) that pupillary constriction in response to light occurs in isolated in vitro anterior chamber preparations of hamster and hooded rat eyes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Elimination of transient dendritic spines in ipsilaterally projecting retinal ganglion cells in rats with neonatal unilateral thalamotomy.

Using the DiI and intracellular Lucifer Yellow labeling techniques in the rat, we have demonstrated that the unilateral neonatal thalamotomy does not result in retention of transient dendritic spines of ipsilaterally projecting retinal ganglion cells (IPRGCs), although the thalamotomy is known to retain the normally transient IPRGCs (Chan et al., Dev. Brain Res., 49 (1989) 265-274). These results suggest that the process of elimination or retraction of transient dendritic spines occurs in retinal ganglion cells during development regardless of whether they make connections with appropriate or inappropriate loci in the visual targets, and/or a decrease in interactions with neighboring retinal ganglion cells.

Aging↗
PubMed1991

Permanent junctional reciprocating tachycardia misdiagnosed as 'cardiomyopathy'.

In a nine-year-old female, cardiac failure was erroneously attributed to idiopathic cardiomyopathy and cardiac transplantation was planned. The actual cause of cardiac failure was permanent junctional reciprocating tachycardia (PJRT), a rare form of supraventricular tachycardia. The diagnostic error was discovered before transplantation was performed and the arrhythmia was treated surgically. This resulted in return of near normal cardiac function.

Cardiomyopathies↗
PubMed1991

Patients with two types of atrioventricular junctional (AV nodal) reentrant tachycardia. Evidence that a common pathway of nodal tissue is not present above the reentrant circuit.

BACKGROUND: The site of the reentrant circuit in atrioventricular (AV) junctional reentrant tachycardia has not been defined; in particular, the existence of a common pathway of AV nodal tissue above the reentrant circuit is controversial. METHODS AND RESULTS: Two types of AV junctional reentrant tachycardia were induced in each of three patients at electrophysiological study. In one type of tachycardia (anterior), the onset of atrial activity occurred from 0 to 12 msec before the onset of ventricular activation, and earliest atrial activity was recorded near the His bundle. In the second type of tachycardia (posterior), the ventriculoatrial intervals were longer (76-168 msec), and earliest atrial activity was recorded near the mouth of the coronary sinus. In individual patients, the two types of tachycardia had different cycle lengths. Posterior AV junctional reentrant tachycardia was not a fast-slow form of AV junctional reentry in at least two of the three patients. Surgical cure was attempted in two patients. In one patient, anterior AV junctional reentrant tachycardia was abolished by dissection of the anterior perinodal atrium, but posterior AV junctional reentrant tachycardia could still be induced. At reoperation 4 months later, dissection of the posterior perinodal atrium abolished posterior AV junctional reentrant tachycardia while preserving AV conduction. CONCLUSION: Differences in ventriculoatrial intervals and cycle lengths and the results of selective surgery suggest that the two types of AV junctional reentrant tachycardia used different reentrant circuits. These observations imply that a common pathway of AV nodal tissue is not present above the reentrant circuit and suggest that perinodal atrium is part of these circuits.

Adolescent↗
PubMed1990

Effects of visual or light deprivation on the morphology, and the elimination of the transient features during development, of type I retinal ganglion cells in hamsters.

Intracellular injection of Lucifer Yellow (LY) was used to study the detailed morphology of the normal visually deprived, and light-deprived superior colliculus projecting Type I retinal ganglion cells (RGCs) in hamsters. The soma size of the normal Type I cells ranged from 337 to 583 microns 2 with a mean of 436 microns 2. Two to six primary dendrites were observed in these cells. The mean dendritic field diameter was 495 microns and ranged from 309 to 702 microns. The dendritic field diameter of this population of cells exhibited an eccentricity dependence. Quantitative comparisons between the normal and visually deprived or light-deprived Type I RGCs indicated that the morphology of these three groups of cells were similar to each other in terms of the soma size, dendritic field diameter, branching pattern, and total length of the dendrites. During the normal development of cats and hamsters, several transient features, such as exuberant dendritic spines and intraretinal axonal branches, have been observed in the developing RGCs. The complete elimination of these transient features occurs at about 3 and 2 weeks after the opening of the eyes in cats and hamsters, respectively. In the present study, the hypothesis whether visual experience or light stimulation is required for the elimination of these transient features during development was examined. After studying a total of 115 mature Type I RGCs, which included cells from the normal, visually deprived and light deprived animals, no transient feature was observed. We conclude that visual or light deprivation has no effect on the morphological development of superior colliculus projecting Type I RGCs in hamsters, and the elimination of the transient features on the Type I RGCs during development does not depend on visual experience or light stimulation.

Animals↗
PubMed1990

Incessant ventricular tachycardia in infancy.

Two infants with incessant tachycardia uncontrolled by multiple drug treatment were thought initially to have supraventricular tachycardia. Careful examination of the 12-lead electrocardiogram suggested ventricular tachycardia, which was confirmed by electrophysiological studies. Intra-operative mapping showed that the arrhythmia arose from the posterior left ventricular free wall in one infant and at the left ventricular apex in the other. Cryoablation of these foci led to cessation of ventricular tachycardia. Myocardial biopsy showed hamartomatous involvement in the first infant and normal tissue in the other. In the first infant the incessant arrhythmia was cured but in the other it recurred 4 months later. The origin of the recurrent tachycardia was adjacent to the previously cryoablated arrhythmogenic area. This area was also cryoablated, leading to disappearance of the ventricular tachycardia. Both patients are free of arrhythmia 10 months and 3 months after their surgery. Surgically ablatable lesions are common in infants with incessant ventricular tachycardia. Early diagnosis and prompt surgical treatment usually can effect 'cure' of this potentially fatal problem in childhood.

Cryosurgery↗
PubMed1990

Electrophysiological study in supraventricular tachycardia.

Supraventricular tachycardia is a common clinical problem. Although its primary mortality is usually low, it often causes significant life long symptoms. It can be life threatening when associated with rapidly conducting accessory atrioventricular connections or nodo-ventricular fibres. Electrophysiological study is now the "gold standard" investigation for diagnosis of this problem. It is also an essential tool for choosing therapeutic options. It is safe and cost effective and should be available in all major hospitals. Since surgical cure is currently feasible for almost all forms of supraventricular tachycardia with a high success rate and a low mortality, electrophysiological study and arrhythmia surgery should be offered to symptomatic patients early in the course of disease. Catheter ablation of supraventricular tachycardia is presently investigational but may in the future become the standard treatment for some forms of supraventricular tachycardia if the cure rate and risk of the procedure can be improved so that they are superior to surgery.

Cardiac Pacing, Artificial↗
PubMed1989

Axillary artery counter-current aortography in the newborn with aortic arch obstruction.

13 newborn infants with aortic coarctation were evaluated by counter-current aortographic technique. The right radial or brachial artery approach (2 cases in each group) did not give successful aortic arch imaging while the right axillary artery approach resulted in adequate imaging in each of 9 cases investigated. In 2, the axillary artery was transiently weakened but returned to normal within 24 h. No other complications were encountered. Axillary artery counter-current aortography is a safe and relatively non-invasive procedure which can be used to image the aortic arch in the newborn babies when other non-invasive diagnosis of aortic arch obstruction is tentative.

Aortic Coarctation↗
PubMed1989

Left ventricular function in beta thalassaemia major.

The left ventricular dimension and posterior wall dynamics were studied by computer assisted analysis of M mode echocardiography in 25 normal children (group 1) and 32 transfusion dependent children with beta thalassaemia major who had no evidence of heart failure (group 2). Twenty seven of those in group 2 remained well but five died of cardiac decompensation within 12 months. Compared with group 1, the left ventricular fractional shortening and ejection fraction were normal in those in group 2 who survived but diminished in those who died. Evaluation of left ventricular dimension and posterior wall dynamics during systole (peak shortening rate, peak velocity of circumferential fibre shortening, and peak posterior wall thickening rate) showed similar findings in that only the group who died had abnormal values. The left ventricular dimension and posterior wall diastolic dynamics (peak relaxation rate, normalised peak relaxation, peak wall thinning, and normalised peak wall thinning rate), however, showed progressively slower rates in all the children in group 2. The findings suggest that left ventricular diastolic dysfunction occurs early in myocardial impairment in patients with beta thalassaemia major. When there are abnormalities in both diastole and systole, the myocardial impairment is advanced and the prognosis is poor.

Adolescent↗
PubMed1989

Congenital cardiovascular malformations in Chinese children with Down's syndrome.

149 Chinese children (70 boys, 79 girls) with Down's syndrome and congenital heart disease were studied. Diagnosis of the cardiac abnormality was made by cardiac catheterisation in 119, two-dimensional echocardiography in 23 and autopsy in 7. The commonest lesion was ventricular septal defect which was present in 43.6%, a higher frequency than that reported in Caucasians. Other common lesions included atrioventricular septal defect (15.4%), atrial septal defect (13.4%), tetralogy in Fallot (13.4%) and patent ductus arteriosus (12.1%). Multiple lesions occurred in 36% of the cases, with patent ductus arteriosus, the most frequent coexisting lesion. Other cyanotic congenital heart conditions were very rare and coarctation of aorta was not seen. An aberrant right subclavian artery arising from the descending aorta was present in 16.5% and abnormalities of the radial artery at the wrist were found in 19%. The literature on patterns of congenital heart diseases seen in Down's syndrome was reviewed.

Asian People↗
PubMed1987

Balloon atrial septostomy under two-dimensional echocardiographic control.

Balloon atrial septostomy was performed under two-dimensional echocardiographic control in 18 consecutive neonates. Initially, a subcostal long-axis view was used to guide the catheter into the right atrium. Then, by tilting the transducer medially, a plane traversing the inferior vena caval-right atrial junction, foramen ovale, and left atrium was obtained to direct the manipulation of the catheter into the left atrium and monitor the septostomy procedure. As the catheter was always in view, catheter manipulation was easy and complications were avoided.

Cardiac Catheterization↗