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Biomedical subjects

S Y Ho

Publications and source records attributed to S Y Ho.

At least 127 records · Page 7Linked to original sources
PubMed1997

The morphologically tricuspid valve in hypoplastic left heart syndrome.

OBJECTIVE: Competence of the tricuspid valve is crucial for survival of children with hypoplastic left heart syndrome. We studied the morphology and topology of the valvar and subvalvar structures, trying to identify abnormalities which could impair valvar function. METHODS: A total of 82 specimens with hypoplastic left heart syndrome were examined pathologically. Measurements of valvar dimensions were taken, significant dysplasia of the valvar leaflets was noted and the muscular and tendinous supporting structures determined. The findings were correlated to the subgroups of hypoplastic left heart syndrome. RESULTS: Of the hearts, 10 (12%) showed a bileaflet right atrioventricular valve, 27 (33%) a moderately and 2 (2%) a severely dysplastic tricuspid valve. The majority of the abnormalities was found in hearts with a patent mitral valve. In 79% of the hearts with mitral atresia, the septal surface was concave instead of convex to the right ventricular lumen and the direct tendinous attachments of the septal leaflet replaced by a multitude of freestanding papillary muscles. The number of direct septal attachments was significantly higher in hearts with a patent mitral valve. CONCLUSIONS: The tricuspid valve in hypoplastic left heart syndrome can differ from the valve seen in normal patients. The subvalvar apparatus is different in hearts with mitral atresia, whereas dysplasia of the leaflets occurs more often together with mitral stenosis. These features should be considered in reconstructive operations as well as during diagnostic procedures.

Aortic Valve↗
PubMed1997

Recurrence of accessory pathway conduction after successful radiofrequency ablation: histological findings.

The histological findings from a patient with Wolff-Parkinson-White syndrome (right superior paraseptal accessory pathway) who underwent successful radiofrequency ablation and had recurrence of tachycardia one month later in the absence of overt pre-excitation are reported. Histology revealed three small, oval to circular shaped, whitish, smooth areas on the right endocardial surface, the one being situated at the atrial free wall, and the other two being at the ventricular aspect. A very small hole was present in the interventricular component of the membranus septum. The accessory pathway band passed to either side of the small hole albeit disrupted by fibrous tissue in places. These findings indicate that multiple applications may cause penetration of the myocardium, and to achieve success, complete disruption of the pathway at some point along its course is required. Recurrence of retrograde accessory pathway conduction can be explained with the impedance mismatch hypothesis.

Adult↗
PubMed1997

Evaluation of lipid-coated microbubbles as a delivery vehicle for Taxol in brain tumor therapy.

OBJECTIVE: This work evaluates the potential of lipid-coated microbubbles (LCM) as a delivery vehicle for lipid-soluble antineoplastic agents. We have shown, in rats, the selective affinity of intravenously administered LCM for tumor cells. They are internalized by the tumor cells both in vitro and in vivo. The specificity of LCM for tumors and subsequent incorporation into the cytoplasm could significantly reduce the systemic effects of an agent incorporated into the bubbles, such as Taxol. METHODS: The in vitro methods were as follows. C6 cells (10(5) cells) were treated with Taxol-LCM (6 micrograms/ml), Taxol-Cremophore (6 micrograms/ml), or LCM alone for 8 or 24 hours. Cell death was determined by staining the cells with nuclear staining. Abnormalities of microtubule structures were ascertained by confocal microscopy. The in vivo methods were as follows. Two rat tumor models (C6 and 9L) were used. Rats were treated with single bolus injections or with repetitive (two or three) treatment courses, with respective control animals. Each course consisted of one daily tail vein injection for 5 consecutive days and then 2 days of rest. RESULTS: When compared with either a saline control group or a group receiving Taxol in an oil vehicle, Taxol-LCM reduced tumor progression in Fischer 344 rats inoculated with 9L glioma. The most profound effect was observed with rats treated with three treatment cycles (five daily injections/cycle) separated by two rest periods (2 d/period). CONCLUSION: Both in vitro and in vivo data indicate that Taxol can be incorporated into LCM, can be delivered to the tumor site, and can exert a measurable antitumor biological effect.

Animals↗
PubMed1997

Anatomy of the atrioventricular junctions with regard to ventricular preexcitation.

In the normal heart, the atrioventricular junctions surround the orifices of the mitral and tricuspid valves. The septal area of the junctions is much smaller than generally thought, being made up of the fibrous membranous septum and the muscular atrioventricular septum. The left atrioventricular junction gives the potential for muscular atrioventricular contiguities only in relation to the mural leaflet of the mitral valve. The right junction extends from the area posterior to the muscular atrioventricular septum to the supraventricular crest of the right ventricle. Anomalous pathways for conduction, which produce pre-excitation, can be found anywhere within these atrioventricular junctions. The pathways usually are the muscular accessory connections responsible for the Wolff-Parkinson-White syndrome, which can exist in the left, septal, or right junctions. Specific muscular connections are found in the presence of Purkinje cell tumors, diverticulums of the coronary sinus, or when taking origin from nodes of Kent at the acute margin of the ventricular mass. The latter connections are responsible for most examples of so-called Mahaim conduction, and are also described as atriofascicular tracts. The true Mahaim fibers are best described as nodoventricular or fasciculo-ventricular connections, while the pathway previously labelled as atriofascicular by the European Study Group is now best distinguished as an atrio-Hisian tract. The slow and fast pathways into the atrioventricular node are composed or ordinary atrial myocardium, the orientation of the fibers probably producing preferential conduction.

Atrioventricular Node↗
PubMed1997

Architecture of the atrial musculature in and around the triangle of Koch: its potential relevance to atrioventricular nodal reentry.

INTRODUCTION: Recent studies suggest that atrial fibers in the approaches to the AV node form part of the dual pathways recognized electrophysiologically in patients with AV nodal reentrant tachycardia (AVNRT). Our aim was to determine, by gross dissection, the arrangement of the superficial musculature in the area of the triangle of Koch in normal hearts and in hearts with documented AVNRT, hoping to ascertain anatomic features that might contribute to the debate. METHODS AND RESULTS: We used blunt dissection to study the architecture of the superficial atrial musculature in 16 autopsied hearts from adults who died of noncardiac disease. A well-defined pattern of architecture of muscle fibers was found in the region of the triangle of Koch, showing marked variations in 7 of the 16 specimens. The relationship of these fibers to the histologically specialized AV node was confirmed by histology in three cases. Two hearts from patients with known AVNRT, treated by ablation in one, were examined further histologically. These sections showed that the site of ablation was well distant from the histologically discrete AV node. CONCLUSION: The variability in the arrangement of the superficial atrial muscle fibers in the area of the triangle of Koch may be one of the factors influencing the route for impulses entering the AV node. Lesions that ablate nodal reentry are within these atrial fibers rather than the histologically specialized AV node.

Adult↗
PubMed1997

[Effects of no precursor and donor on neuronal activity of rat hippocampal slices].

Using extracellular recording technique, the effects of L-arginine (L-arg), N-nitro-L-arginine (L-NNA), SIN-1 and methylene blue (MB) on spontaneous discharges of neurons in CA1 area of hippocampal slices were examined to determine the role of L-arg: NO pathway and the possible underlying mechanism. The results were as follows: (1) In response to the application of L-arg (1 mmol/L) into the superfusate for 2 min, spontaneous discharge rate (SDR) of 42/54 (77.8%) neurons was decreased significantly, while that of 12/54 (22.2%) neurons showed no change. Following the application of L-NNA (0.15 mmol/L) into the superfusate for 2 min, SDR of 25/29 (86.2%) neurons was increased markedly and that of 4/29 (13.8%) neurons was not affected. The effect of L-NNA might be reversed by pretreatment with L-arg. (2) With application of NO donor SIN-1 (5 mmol/L), SDR of 25 (100%) neurons was decreased in a dose-dependent manner. (3) After superfusing the brain slice with guanylate cyclase inhibitor, MB (3 mumol/L) for 30 min, SDR of 10 units showed significant increase as compared with control. However, MB failed to abolish the effect of L-arg on hippocampal neurons. Taken together, it is likely that NO is released during the resting state of hippocampal neurons and may inhibit the activity of hippocampus, an effect not mediated by the action of guanylate cyclase.

Action Potentials↗
PubMed1997

[Effects of intraventricular and epicardial application of adenosine on electrical activity of medullary PGL neurons].

The effects of intraventricular injection and epicardial application of adenosine on spontaneous electrical activity of nucleus paragigantocellularis lateralis (PGL) neurons in rostral ventrolateral medulla (RVLM) were examined in 35 anesthetized rats with sinoaortic denervation and vagotomy. The results obtained were as follows: (1) The spontaneous discharge of 121 PGL neurons (mean discharge rate: 22.5 +/- 1.9 spikes/s) were recorded in 35 rats. (2) In response to intraventricular injection of adenosine (0.5 mumol/kg), mean arterial pressure (MAP) was initially increased by 1.7 +/- 0.2 kPa(P < 0.001) and subsequently decreased by 4.6 +/- 0.5 kPa(P < 0.001), while the heart rate (HR) was decreased by 126.5 +/- 12.3 bpm (P < 0.001). Of 35 PGL spontaneous discharge units responsive to intraventricular injection of adenosine, 30 showed an average increase from 21.9 +/- 2.6 to 29.2 +/- 3.4 spikes/s (P < 0.001), 3 with no change, while 2 with a decrease. (3) Following epicardial application of 20 mmol/L adenosine, the BP and HR were not significantly changed, while the spontaneous discharge of 22 PGL neurons were increased from 18.8 +/- 1.9 to 26.9 +/- 2.8 spikes/s (P < 0.001), and that of 3 neurons was not changed. (4) The excitatory response of PGL neurons to intraventricular injection or epicardial application of adenosine was completely inhibited by pretreatment with selective adenosine A1-receptor antagonist 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 500 micrograms/kg). (5) Following epicardial application of phenol or bilateral stellate ganglionectomy, adenosine failed to affect the activity of PGL neurons. The results obtained indicate that adenosine may stimulate cardiac sympathetic afferents through adenosine A1-receptor, thereby resulting in the activation of PGL neurons.

Action Potentials↗
PubMed1996

Fibrous matrix of ventricular myocardium in tricuspid atresia compared with normal heart. A quantitative analysis.

BACKGROUND: The collagen matrix is a small component of the myocardium, but it provides a supportive framework. An increase in collagen in the pressure-overloaded ventricle is known to cause myocardial stiffness. However, little is known about the collagen matrix in the volume-overloaded ventricle, particularly in relation to congenital heart disease. METHODS AND RESULTS: We examined a total of 53 hearts with tricuspid atresia and 58 normal hearts matched for age. Using a microscopic-morphometric method, we analyzed the percentage per field area occupied by interstitial fibrous tissue in four sites in the ventricular mass for each specimen. A comparison of sampling sites showed no significant variations between normal and malformed hearts. Results from a homogeneity of regression co-efficients analysis suggested that the two groups shared the same basic relation of proportion of fibrosis with age. The use of ANCOVA, however, revealed a clear separation between the extents of fibrous tissue in the two groups of hearts. CONCLUSIONS: The myocardium of hearts with tricuspid atresia is consistently more fibrotic than normal heart and is probably an inherent part of the malformation. This difference could explain, at least in part, the clinical observation that the left ventricle is frequently abnormal, even at an early age.

Adolescent↗
PubMed1996

Surgical anatomy of the coronary circulation in hearts with discordant atrioventricular connections.

We examined the arrangement of the coronary arterial and cardiac venous systems in 46 specimens with discordant atrioventricular connections so as to identify any structural abnormalities and to consider their surgical implications in terms of anatomical biventricular repair. Grossly abnormal arterial courses were seen in 11 hearts (24%). A substantial branch supplying the morphologically right ventricular outflow tract, which could restrict a ventriculotomy, was found in 61% of cases. The coronary sinus received all the morphologically right ventricular veins, as well as the posterior interventricular vein, in 40 hearts, this pattern being in contrast to the pattern in the normal heart. The morphologically left ventricular and anterior interventricular veins, all of which drain via the coronary sinus in the normal heart, were frequently connected independently to the morphologically right atrium in the specimens with discordant connections, the drainage occurring through the spaces between the pectinate muscles. These direct drainages are at risk of potential damage either by extensive intra-atrial maneuvers or by postoperative intraatrial thrombosis. It is predicted, therefore, that surgical results can be improved still further when account is taken of this vascular anatomy of the heart itself.

Cadaver↗
PubMed1996

The nature of the annular attachment of a common atrioventricular valve in hearts with isomeric atrial appendages.

OBJECTIVE: To clarify the precise anatomic arrangement of the annular attachment of a common atrioventricular valve in the setting of visceral heterotaxy. METHODS: One hundred and twelve autopsied specimens with isomeric atrial appendages were studied. RESULTS: Annular hinge points with a planar orientation were found in only 7 hearts. All others showed a nonplanar and undulating arrangement, including 7 with Ebsteins's malformation. When the posterior half of the valvar attachment was taken as a reference plane, the anterior part deviated superiorly, the distance from the plane to the anterior point being 6.7 +/- 4.9% of the circumferential length of the annulus. The ratio of the antero-posterior diameter to the width of the annulus was smaller in hearts with biventricular connections (0.77 +/- 0.15) than in those with double inlet ventricle (0.89 +/- 0.17, P < 0.001). Reflecting this, the ratio of superior deviation of the anterior valvar annulus compared to the antero-posterior diameter was greater in hearts with biventricular atrioventricular connections (P = 0.016), particularly in those with isomeric right appendages. No significant differences were found when the data was analyzed according to variations in ventricular morphology. CONCLUSIONS: The precise evaluation of the annular structure of a common atrioventricular valve may well prove to be of clinical significance so as optimally to achieve valvar annuloplasty.

Ebstein Anomaly↗
PubMed1996

Value and impact of necropsy in paediatric cardiology.

OBJECTIVE: To assess the current value of necropsy in paediatric cardiology and cardiothoracic surgery and determine its potential impact on clinical practice. DESIGN AND SETTING: Descriptive study of all paediatric cardiac deaths occurring over four years in a tertiary referral centre. Data were obtained from reviewing the hospital files, available necropsy records and specimens, and audit reports. PATIENTS: Paediatric patients with congenital or acquired heart disease, who died of a cardiac cause between January 1992 and July 1995. Inclusion criteria were that the diagnosis of heart disease was made before death, and that patients were managed thereafter medically and/or surgically at the referral centre. The value of necropsy was assessed according to its contribution in establishing the cause of death (confirmed, clarified, precise cause of death uncertain) and the anatomy (simple confirmation or additional information provided). For cases not submitted to necropsy the clinical information relating to the cause of death was assessed and the case assigned as cause of death firm, uncertain, or unknown. RESULTS: One hundred and six deaths were identified (61 males, age at death: one day to 20 years). Seventy occurred early (a month or less) after surgery and were graded as postoperative deaths. The rest were considered to be either medical or late surgical deaths. Necropsy was performed in 59 (55.6%). The precise cause of death was confirmed in 33 (55.9%), clarified in 22 (37.3%), and remained uncertain in four (7.8%). Additional information regarding the anatomy was found in eight (13.6%) cases. In five cases (8.5%) the necropsy detected findings which, if known before death, would probably have improved outcome. For the patients dying without a necropsy, the cause of death remained uncertain in 10 (21.3%) and unknown in seven (14.9%). In 36% of cases, therefore, a firm cause of death that might have been provided by a necropsy was missing. CONCLUSION: In paediatric cardiology necropsy continues to provide clinically relevant information at a high level. It remains vital for ensuring quality of medical care, in instigating improvements in future management, and increasing understanding of congenital heart disease. The procedure should therefore be sought actively in all cases.

Adolescent↗
PubMed1996

Ventricular myoarchitecture in tetralogy of Fallot.

BACKGROUND: Little attention has been paid to the architecture of the muscle fibres of the ventricular walls in congenitally malformed hearts. In this study the gross pattern of myocardial fibres in normal hearts was compared with that in cases of tetralogy of Fallot. METHODS AND RESULTS: After morphological examination nine specimens with tetralogy were dissected to study the ventricular myoarchitecture. Changes were found in the shape of the malformed ventricles. The ventricular walls were arranged in layers in all hearts. Superficial and deep layers were present in both ventricles, with the superficial layer showing a more oblique orientation in the specimens with tetralogy than in normal hearts. Modifications of muscle fibre that were related to the type of malformation were seen in the deep layer. A middle layer was present in the left ventricles of normal hearts and specimens with tetralogy: this showed a horizontal orientation in both groups. In contrast, a middle layer was found in the right ventricle only in specimens showing tetralogy. CONCLUSIONS: The malformed hearts showed modifications in ventricular shape, in the arrangement of muscle in the right ventricle, and in the overall myoarchitecture. These changes could well be the consequence of the same agent (or agents) that caused the structural defect.

Adolescent↗
PubMed1996

Electroporation of cell membranes: a review.

The study of the electroporation on biomembranes has become one of the most exciting topics in the biophysical and biotechnological areas. Researchers all over the world have been focused on four major areas: measurements of transmembrane potential (TMP); dynamics of electroporation such as time sequence, properties of electropores such as size, structure, and population; membrane permeabilization and breakdown theory; and the effects of secondary factors such as ions type and cell growth stage on electroporation. This article reviews some of the recent discoveries and theories on this subject. Studies on TMP and pore dynamics remain a difficult task. Since the area of electroporation on a biomembrane is small (less than 0.1% of total surface area) and the time sequence of electropores is in the submicrosecond range measuring devices with subtle detection and time resolution are required. While more and more studies have shown the formation sequence of electropore(s) at specific locations on various biomembranes, the pore(s) widening process and the subsequent membrane breakdown mechanisms remain controversial. The influence of electromechanical stress or transmembrane potential on membrane discharge and rupture seems to be a function of various factors such as membrane properties, external medium, and the protocols of electroporators.

Cell Division↗
PubMed1996

[Effects of endothelin on the electrical activity of sino-atrial pacemaker cells of rabbit].

The effects of endothelin-1 (ET-1) on the electrophysiological activity of pacemaker cells of rabbit sino-atrial node were examined by using intracellular microelectrode technique. The results obtained were as follows: (1) With superfusion of ET-1 (1-30 nmol/l), the velocity of diastolic depolarization (VDD) of pacemaker cells was significantly decreased in a concentration dependent manner, resulting in a reduced rate of pacemaker firing (RPF). (2) The decreases in RPF and VDD induced by ET-1 could be virtually blocked by pretreatment with ET(A) receptor blocker BQ-123 (20 or 100 micrograms/L). It was strongly suggested that the electrophysiological effects of ET-1 on the pacemaker cells were mediated by the ET(A) receptor. (3) The negative chronotropic action of ET-1 on the pacemaker cells was totally abolished by pretreatment with a kind of KATP channel blocker glibenclamide (10 mumol/L). On the basis of above results, it appears that the binding of ET-1 with ET(A) receptor may induce an activation of KATP channels with resultant increase in K+ current so as to decrease the velocity of diastolic depolarization in the pacemaker cells.

Animals↗
PubMed1996

Anatomy of the aortic root with particular emphasis on options for its surgical enlargement.

BACKGROUND AND AIMS OF THE STUDY: The aortic root is a frequent site of surgical intervention, both in adults and children, yet there is ambiguity about the precise nature and relation of the various structures composing the aortic root. The present review aims to clarify these ambiguities and to explain the morphological basis of surgical procedures for enlargement of the aortic root. MATERIALS AND METHODS: Using autopsied specimens of normal hearts, the morphology of the attachment of the leaflets, the interleaflet triangles and the circular ventriculo-arterial junction of the aortic root were studied in detail, paying special regard to fibrous and muscular continuity, relation to the atrioventricular conduction axis, and the coronary arterial branching. Surgical dissections and incisions required for enlargement of the aortic root were simulated in these specimens. RESULTS: It was evident that the locus of attachment of aortic valvar leaflets takes the form of three (semilunar) crescents. This attachment is not circular, as the word 'annulus' suggests, neither does it correspond to the anatomical ventriculo-arterial junction. During implantation of a mechanical valve in the aortic position, a circular prosthetic valve ring is sutured on to the attachments of the native valvar leaflets. This must entail some distortion when the sutures are tied. Analysis of autopsied specimens showed that, on completion of the process of suturing, the location of the prosthetic valve is close to the anatomic ventriculo-arterial junction-one of the true annular regions of the aortic root. CONCLUSIONS: The continuity of the aortic valvar leaflets and the interleaflet triangles with structures such as the aortic (anterior) leaflet of the mitral valve posteriorly, and with the muscular ventricular septum anteriorly, provide an opportunity for surgeons to enlarge the aortic root by widening of the anatomic ventriculo-arterial junction.

Adult↗