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Biomedical subjects

R McKay

Publications and source records attributed to R McKay.

At least 73 records · Page 4Linked to original sources
PubMed1993

Percutaneous balloon pericardiotomy for the treatment of cardiac tamponade and large pericardial effusions: description of technique and report of the first 50 cases.

OBJECTIVES: This study describes the technique, clinical characteristics and results of the first 50 patients undergoing percutaneous balloon pericardiotomy as part of a multicenter registry. BACKGROUND: Percutaneous balloon pericardiotomy involves the use of a percutaneous balloon dilating catheter to create a nonsurgical pericardial window. METHODS: Patients eligible for percutaneous balloon pericardiotomy had either cardiac tamponade (n = 36) or a moderate to large pericardial effusion (n = 14). In addition to clinical follow-up, serial echocardiograms and chest X-ray films were obtained. RESULTS: The procedure was considered successful in 46 patients after a mean follow-up period of 3.6 +/- 3.3 months. Two patients required an early operation, one for bleeding from a pericardial vessel and one for persistent pericardial catheter drainage. Two patients required a late operation for recurrent tamponade. Minor complications of the procedure included fever in 6 of the first 37 patients (studied before the prophylactic use of antibiotic agents), thoracentesis or chest tube placement in 8 and a small spontaneously resolving pneumothorax in 2. Despite the short-term success of this procedure, the long-term prognosis of the 44 patients with malignant pericardial disease remained poor (mean survival time 3.3 +/- 3.1 months). CONCLUSIONS: Percutaneous balloon pericardiotomy is successful in helping to manage large pericardial effusions, particularly in patients with a malignant condition. It may become the preferred treatment to avoid a more invasive procedure for patients with pericardial effusion and a limited life expectancy.

Aged↗
PubMed1993

Left ventricular transvenous electrode dislodgement after Mustard repair for transposition of the great arteries.

An 11-year-old girl who underwent Mustard's operation for complete transposition of the great arteries in infancy, developed Mobitz type II second-degree AV block 8 1/2 years later. A transvenous, active fixation left ventricular lead was inserted and connected to a rate responsive pacemaker. Two years later the lead dislodged due to the child's growth. A new active fixation electrode was positioned in the left ventricle below the pulmonary valve, leaving an electrode loop in the ventricle. Such an approach may prevent lead dislodgement due to growth after intraatrial repair for transposition of the great arteries, but regular radiological or echocardiographic follow-up of lead position is recommended in these patients.

Arrhythmias, Cardiac↗
PubMed1993

Primary repair and autotransplantation of cardiac valves.

The aortic valve is a beautifully designed and balanced structure with precise opening and closing mechanisms. Its design probably cannot be improved upon by man-made mechanical devices, no matter how ingenious. It is logical to use human valves as replacements because of their superior structural configuration. Their chief difficulties are in the troubles of the learning curve of the surgeon to achieve a competent mechanism and the hazard of infection. The pulmonary autograft or translocation of the pulmonary valve to the aortic position offers many advantages, and the long-term results are good. Conservative repair and reconstruction of the aortic valve are increasing in popularity but have a relatively limited application. The mitral valve has a less precise and more adjustable type of mechanism and generous leaflet coaptation. These features make it more amenable to repair, as demonstrated in the clinical series of the technique. Repair is clearly preferable to replacement at present. The tricuspid valve is eminently suitable for reconstruction, but late results are not very good. The disappointing outcome, however, reflects more the severity of underlying cardiac pathology than the effectiveness of the repair.

Heart Valves↗
PubMed1993

Immortalized stem cells from the central nervous system.

A remarkable feature of the early development of the mammalian central nervous system (CNS) is the precise and rapid generation of large numbers of many different neuronal types [1]. We have identified the major neuronal precursor cell and shown that this cell can be immortalized by oncogenes. The immortal precursor cell can be grown in culture and can differentiate when transplanted into the developing brain. The implanted neurons are integrated into the synaptic circuitry of the host brain. These results suggest that implanting cultured precursor cells will provide a powerful strategy to uncover the signals that control the differentiation of this multipotential cell into the many cell types of the adult brain.

Animals↗
PubMed1992

An oligodendrocyte precursor cell line from rat optic nerve.

We have established permanent cell lines from the optic nerve of the rat with a temperature sensitive immortalizing oncogene (Simian Virus 40 large T-antigen carrying both the tsA58 and U19 mutations). The oncogene was transduced into primary cultures via a replication deficient retrovirus, and infected cells were selected with the antibiotic G418. A clonal cell line (tsU19-5) displayed some properties of oligodendrocyte precursors: it proliferated, bound the monoclonal antibody A2B5 (which recognizes minor ganglioside species), and expressed the intermediate filament vimentin and the enzyme 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNP) at 33 degrees C (the permissive temperature for the oncogene). At 39 degrees C (the non-permissive temperature), some cells had the potential to differentiate further, and expressed several oligodendrocyte specific components: galactocerebroside, myelin basic protein, proteolipid protein and CNP. These results suggest that conditional oncogenes can establish neural precursor cell lines which are still capable of differentiation in vitro.

Animals↗
PubMed1992

Thrombolysis with tissue-type plasminogen activator following cardiac surgery in children.

Three children with major intracardiac or vascular thrombosis following cardiac operations were treated with intravenous recombinant tissue-type plasminogen activator. The first patient, aged 10 yr, developed a left atrial thrombus following replacement of the mitral valve with a Björk-Shiley prosthesis. The second patient, aged 16 months, had a right atrial thrombus following a modified Fontan procedure for tricuspid atresia. Both were successfully treated with a short course of intravenous tissue plasminogen activator. The third patient, aged 19 months, developed the Budd-Chiari syndrome with occlusion of the inferior caval vein following a modified Fontan operation for double inlet left ventricle. Even though near-complete thrombolysis and recanalization of the inferior caval vein was achieved with three courses of tissue plasminogen activator on successive days, she died with failure of multiple organs. In all cases, the diagnosis was established by cross-sectional and Doppler echocardiography, and the response to therapy was monitored using the same technique. Thrombolytic therapy with systemic tissue-type plasminogen activator was safe and effective in the postoperative period, with no major haemorrhagic complications.

Cardiac Surgical Procedures↗
PubMed1992

Reconstituting animals from immortal precursors.

Several recent experiments have shown that immortal neural and muscle cells retain the specific temporal and spatial properties of their precursor cells in the animal. In addition, the immortal cells retain the ability to differentiate in vitro and, after transplantation, in vivo. The results of these experiments suggest that the use of precursor cell lines may lead to powerful approaches for understanding the mechanisms that generate the ordered distribution of cell types in mammals.

Animals↗
PubMed1992

Multipotential stem cells in the vertebrate CNS.

The functional differences between the many mature neuronal types make the origins of cellular diversity in the nervous system one of the most intriguing problems in biology. This paper discusses recent experiments which explore the mechanisms generating cell diversity in the vertebrate central nervous system, focusing particularly on the immediate precursor to neurons and on neuronal differentiation. Transplantation experiments have been used to explore regional and temporal differences in the cells of the neuroepithelium. The effects of specific genes on neuronal development have been examined by mutational analysis in transgenic mice and in established neuronal stem cell lines. The combination of methods now available allow increasingly powerful dissection of the molecular and cellular mechanisms that generate the large number of different neurons in the vertebrate brain.

Animals↗
PubMed1992

Morphology of the ventriculoaortic junction in critical aortic stenosis. Implications for hemodynamic function and clinical management.

The clinical presentation of infants with critical aortic stenosis, as well as the results of surgical treatment, differs from obstruction of the left ventricular outflow tract in older children. To investigate a possible anatomic basis for this situation, we performed a detailed morphometric study of 21 hearts from infants who had critical aortic stenosis and 11 normal hearts from infants less than 3 months of age. In each of the hearts with critical aortic stenosis, only one commissure extended to the sinutubular ridge. The other two commissures were represented by folds in the aortic wall that suspended the leaflet below the level of the sinutubular junction. The leaflet thus had a free edge shorter than the circumference of the sinus, in contrast with the normal valve, in which leaflets always were longer than the circumference of their supporting sinus. Analysis of the fibrous triangles on the ventricular aspect of abnormal valves showed a symmetric three-sinus arrangement. In all but one specimen, however, only the triangle related to the mitral valve was fully developed. Although incision of both rudimentary commissures to the aortic wall should achieve some relief of obstruction, these morphologic features strongly mitigate against surgical restoration of normal function or growth in aortic valves having the morphology observed in this series of hearts.

Aortic Valve↗
PubMed1991

Replacement of the aortic valve or root with a pulmonary autograft in children.

Between January 1967 and December 1988, 34 patients ranging in age from 3 to 18 years (mean, 14 +/- 3.6 years) underwent replacement of the aortic valve or root with their own pulmonary valve. The indication for operation was left ventricular outflow obstruction in 16 patients (47%), aortic regurgitation in 14 (41%), mixed aortic valve disease in 3 (9%), and failure of a previously implanted aortic homograft in 1 (3%). There were four early deaths, all before 1971, giving a hospital mortality of 11.8% (70% confidence interval, 6% to 20%). Surviving patients have been followed up a cumulative total of 214 patient-years, the longest period of observation being 16 years 8 months. Late mortality was 13.3% (70% confidence interval, 7% to 23%), and 4 other patients required removal of the pulmonary autograft for endocarditis. Actuarial rates at 16 years were 74% +/- 11% for freedom from reoperation on the left ventricular outflow tract, 80% +/- 10% for freedom from reoperation on the right ventricular outflow tract, and 77% +/- 10% for late survival. There was no instance of primary structural degeneration in the pulmonary autograft, and all surviving patients were in New York Heart Association functional class I without medication. This experience demonstrates that the pulmonary autograft can achieve good early and medium-term results in young patients. Should growth potential be realized, it might constitute the ideal biological valve for the left ventricular outflow in children.

Adolescent↗
PubMed1991

The myth of the aortic annulus: the anatomy of the subaortic outflow tract.

Surgical repair of the small aortic root is limited in part by the very structure of the outflow tract from the left ventricle. The root is not constructed on the basis of a ringlike annulus supporting the leaflets of the aortic valve. The only truly circular structure within the outflow tract is the junction of the aortic wall with the underlying ventricular structures, themselves partly muscular and partly fibrous. This circular ventriculoarterial junction is crossed by the semilunar attachments of the leaflets of the aortic valve, producing an interlinking arrangement between the expanded aortic sinuses and three triangles of fibrous tissue placed beneath the apexes of the commissures between the valve leaflets. The triangles form extensions of the left ventricle that are related, in part, to the pericardial cavity surrounding the heart. The arrangements of the attachment of the leaflets in malformed valves with two (or only one) effective leaflets are highly abnormal, although these valves are usually produced on the template of three aortic sinuses. The valve with two leaflets rarely gives problems during childhood. In valves producing "critical stenosis", there is usually only one effective leaflet, a condition due to incomplete liberation of two of the anticipated three commissures. Detailed study shows that, in these malformed hearts, the attachment of the leaflets is much more annular than in normal valves, with inadequate formation of the fibrous triangles.

Aortic Valve↗
PubMed1991

Identifying and manipulating neuronal stem cells.

Fetal brain tissue has been shown to have clear behavioral effects when transplanted into adult lesioned brains. These results have focused attention on the cell types of the embryonic brain. Transplantation experiments using primary cells are beginning to define the plasticity of these cells and the times when they become committed to specific neuronal fates. Growth factors have been defined that regulate the proliferation of these cells in culture. Cell lines have been established that express stem cell properties and that are capable of differentiation when implanted into the developing brain. In this article we review this work on mammalian neuroepithelial stem cells and discuss how these studies might contribute to the therapeutic use of brain transplants.

Animals↗
PubMed1991

Traumatic ventricular septal defect: serial follow-up with Doppler ultrasound.

A three-year-old girl presented with a gunshot wound of the chest. Cross-sectional and Doppler echocardiography enabled precise location of the bullet, and assessment of the haemodynamic effects of the traumatic ventricular septal defect. Serial ultrasound examination in the acute stage confirmed that the bullet was well embedded in the left ventricular myocardium, and the ventricular septal defect was restrictive, enabling conservative management.

Cardiac Catheterization↗
PubMed1991

Results of balloon pulmonary valvuloplasty as a palliative procedure in tetralogy of Fallot.

Balloon pulmonary valvuloplasty was attempted in 67 patients with tetralogy of Fallot at a median age of 5 months (range 0.03 to 52 months) for relief of cyanosis. In three patients, the valve could not be crossed and an aortopulmonary shunt was performed. In 35 patients, follow-up angiography was performed 3 to 30 months (average 12) after valvuloplasty. In 24 of these 35 patients (group A), the stenosis had been adequately palliated by valvuloplasty; the other 11 patients (group B) had required an aortopulmonary shunt 1 month (range 0 to 3 months) after valvuloplasty. The two groups were similar (p greater than 0.1) with respect to age at valvuloplasty, pulmonary anulus diameter, ratio of pulmonary artery to descending aorta diameter before valvuloplasty and interval to follow-up angiography. In contrast to patients in group B, patients in group A had a significant immediate improvement in systemic arterial oxygen saturation (p less than 0.01) and a significant increase in pulmonary anulus diameter at follow-up angiography (p less than 0.001). The growth of the branch pulmonary arteries was similar (p greater than 0.1) in the two groups. Among 42 patients who have had surgical correction, a transannular patch for right ventricular outflow tract reconstruction was used in 27 (64%); there was no difference between groups A and B with respect to its use. Eight patients died (three after repair) and death could not be directly attributed to valvuloplasty in any. Balloon valvuloplasty promotes growth of the pulmonary valve anulus and pulmonary arteries and is a useful alternative to an aortopulmonary shunt in patients with small pulmonary arteries or associated complex intracardiac defects.

Angiocardiography↗
PubMed1991

Renal function after cardiopulmonary bypass in children: comparison of dopamine with dobutamine.

We have compared low dose dopamine with dobutamine in conserving renal function in 142 children younger than 10 yr undergoing cardiopulmonary bypass (CPB). Patients were allocated randomly to receive a continuous infusion of either dopamine 2.5 micrograms kg-1 min-1 (group 1) or dobutamine 2.5 micrograms kg-1 min-1 (group 2) from the time of induction of anaesthesia. Administration of inotropes and diuretics was controlled strictly to agreed regimens. There was no clinical or statistically significant difference between the two groups in postoperative urine output, serum concentration of creatinine, fractional sodium excretion or need for diuretic therapy. This was true also of the subgroup of patients who received no other inotropic support. However, the subgroup of patients in group 1 who underwent periods of CPB in excess of 2 h (n = 17) had persistently greater postoperative serum concentrations of creatinine. Low dose dopamine did not appear to be superior to dobutamine for protection of renal function in these patients.

Acute Kidney Injury↗
PubMed1991

Critical aortic stenosis in early infancy. Anatomic and echocardiographic substrates of successful open valvotomy.

To establish noninvasive criteria by which to manage infants with critical aortic stenosis, we examined 20 heart specimens from infants under 3 months of age and reviewed the clinical course and real time echocardiograms of 20 patients in the same age group. All 20 infants underwent open valvotomy, and in five cases both echocardiographic and postmortem measurements were available for the same heart. The anatomic specimens showed a spectrum of valvular, ventricular, and vascular abnormalities that could be accurately identified by echocardiography. A small left ventricular cavity was usually associated with a narrow ventriculoarterial junction, small ascending aorta, and narrow subaortic region. In these hearts, the mitral valve had a single or grossly hypoplastic papillary muscle with short or "arcuate" tendinous cords. A dilated left ventricular cavity had wider inflow and outflow orifices, and the tension apparatus of the mitral valve was either normal or supported by hypertrophic papillary muscles, at the other end of the spectrum. The survivors (n = 15) and nonsurvivors (n = 5) of open valvotomy showed significant differences in the echocardiographic dimensions of the left ventricle (p less than 0.005), the subaortic region (p less than 0.05), the ventriculoaortic junction (p less than 0.05), the ascending aorta (p less than 0.005), and the mitral valve orifice (p less than 0.001). Moreover, the papillary muscle of the mitral valve was invariably single or hypoplastic with short tendinous cords in the early nonsurvivors. Infants with unfavorable cardiac anatomy tended to present earlier (p less than 0.05) and to have a lower systemic blood pressure (p less than 0.05), and they required prostaglandin E2 to maintain right ventricular support of the circulation through a persistent arterial duct. This study suggests that patients with a small left ventricle (echocardiographic inflow dimension less than 25 mm), a narrow ventriculoaortic junction (less than 5 mm), and a small mitral valve orifice (less than 9 mm) will not achieve a satisfactory surgical result from aortic valvotomy. Such patients should be considered for cardiac transplantation or the Norwood-type of palliation for hypoplastic left heart syndrome.

Aortic Valve↗