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Biomedical subjects

L M Davis

Publications and source records attributed to L M Davis.

At least 19 recordsLinked 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↗
PubMed1991

Dimensions of the human posterior septal space and coronary sinus.

Accurate anatomic localization of accessory pathways during preoperative electrophysiologic study and during operative mapping depends on a knowledge of the dimensions of the posterior septal space and the left free wall. These dimensions were therefore studied in 48 human cadaver hearts. Mean distance from the coronary sinus orifice to the left margin of the posterior septal space was 2.3 +/- 0.4 cm and mean length of the left free wall was 5.0 +/- 1.0 cm. The posterior septal space at the level of the valve anuli extended a mean of 3.4 +/- 0.5 cm around the epicardium. The width of the posterior septum measured in the coronary sinus was related to heart weight and a combination of body weight and patient age (p less than 0.05). The probability of an accessory pathway being located in the left free wall or the posterior septum during catheter mapping was calculated for various distances from the coronary sinus orifice for adults of different ages and body weights. In adults, accessory pathways located in the proximal 1.5 cm of the coronary sinus are almost always in the posterior septum. Those located between 1.5 and 3 cm from the coronary sinus orifice may be in either the left free wall or the posterior septum, and those located greater than 3 cm from the coronary sinus orifice are almost invariably in the left free wall.

Adolescent↗
PubMed1991

Molecular analysis of chromosomal rearrangements using pulsed field gel electrophoresis and somatic cell hybrids.

Many human genetic diseases, including some cancers, are characterized by consistent chromosome abnormalities, such as deletions and translocations. Analyses of these mutations often prove crucial to the eventual cloning and characterization of the gene(s) responsible for the disease. Two methods for analyzing these chromosome abnormalities have been developed in recent years: somatic cell hybridization and pulsed field gel electrophoresis (PFGE). Somatic cell hybridization is a technique for segregating an aberrant chromosome from its normal homologue in a cell derived from an unrelated species, which is usually a rodent. Panels of such hybrids dividing a given chromosomal region into increasingly smaller units can be constructed and used specifically to map DNA probes into those units. PFGE can then be used to define precise physical distances between such an array of chromosome abnormalities. Demonstrations of these analytic techniques are presented, using as an example chromosomal abnormalities involving human chromosome band 11p13, the locus for the Wilms' tumor, aniridia, genitourinary abnormality, and mental retardation (WAGR) syndrome.

Aniridia↗
PubMed1991

A tumor chromosome rearrangement further defines the 11p13 Wilms tumor locus.

A sporadic Wilms tumor, WT-21, with an (11;14)-(p13;q23) reciprocal translocation has been identified. The translocation is found in tumor cells, but not in the patients' circulating lymphocytes. Molecular analysis of somatic cell hybrids segregating the derivative translocation chromosomes reveals a submicroscopic interstitial deletion at the translocation breakpoint, as well as a cytologically undetectable interstitial deletion in the nontranslocation chromosome 11, resulting in a homozygous deletion in 11p13. Pulsed-field gel analysis of tumor DNA indicates that the two deletions are indistinguishable, and the homozygously deleted region is less than 875 kb. The homozygously deleted regions of three other sporadic Wilms tumors overlap with the deleted region in WT-21, and the candidate cDNA clone for the 11p13 Wilms tumor gene described by Call et al. (Cell 60, 509-520, 1990) is included in the deleted region. These findings strengthen previous conclusions regarding the obligate location for the 11p13 WT locus and support the suggestion that the Wilms tumor gene has been cloned.

Animals↗
PubMed1991

Rapid DNA sequencing based upon single molecule detection.

We are developing a laser-based technique for the rapid sequencing of 40-kb or larger fragments of DNA at a rate of 100 to 1000 bases per second. The approach relies on fluorescent labeling of the bases in a single fragment of DNA, attachment of this labeled DNA fragment to a support, movement of the supported DNA fragment into a flowing sample stream, and detection of individual fluorescently labeled bases as they are cleaved from the DNA fragment by an exonuclease. The ability to sequence large fragments of DNA will significantly reduce the amount of subcloning and the number of overlapping sequences required to assemble megabase segments of sequence information.

Base Sequence↗
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

What is the best method for assessing the long-term outcome of surgery for accessory pathways and atrioventricular junctional reentrant tachycardias?

The success of surgery for supraventricular tachycardia (SVT) is evaluated by a variety of methods in different hospitals. Unfortunately, the predictive values of these methods are not known. We therefore compared the various methods in 261 patients undergoing surgery for SVT at Westmead Hospital since 1981. Surgical outcome was assessed by early tests during the first week after surgery (serial 12-lead electrocardiograms, telemetric monitoring of the electrocardiogram, and electrophysiological study performed using epicardial wires); later tests at 6 months after surgery (12-lead electrocardiograms and electrophysiological study); and symptomatic review done by telephone interview at a median of 34 months after surgery. Early tests were obtained in 97%, later tests were obtained in 76%, and symptomatic review was obtained in 98% of patients. All of the examined tests were inaccurate methods of surgical assessment compared with the late electrophysiological study. A large proportion of the patients proven to be surgical failures at the late electrophysiological study were not detected by early tests (83%), by later electrocardiograms (66%), or by symptomatic assessment (41%). Accurate assessment of surgical outcome requires a late electrophysiological study to permit comparison of surgical techniques. Late electrophysiological study also provides accurate information on the current risks and benefits of proposed surgery for communication to patients to enable them to make an informed decision on future treatment. Most patients are willing to have a late electrophysiological study and usually benefit from clarification of their true surgical outcome.

Cardiac Pacing, Artificial↗
PubMed1991

Factors affecting the development of pneumothorax associated with thoracentesis.

This study is a retrospective survey of the variables that may influence the development of pneumothorax after thoracentesis. In a 30-month period, a computer search of hospital records identified 342 thoracenteses, of which 154 were done with conventional techniques by the clinical services, and 188 were done with sonographic guidance. Other factors surveyed included the patients' age, sex, underlying pulmonary disease, and overall clinical condition; the size of the effusion; the type of tap (diagnostic or therapeutic); the amount and type (exudate or transudate) of fluid acquired; and the size of the needles used. The technique used was the most significant single risk factor affecting the development of pneumothorax (18% for clinical vs 3% for sonography-guided thoracenteses). The incidence of pneumothorax decreased when a smaller amount of pleural fluid was aspirated (mean, 246 ml aspirated from patients who did not vs 472 ml from those who did develop pneumothorax) and when thin needles were used (4% pneumothorax with 20-gauge or smaller and 18% with larger than 20-gauge needles). The other factors surveyed did not influence the development of pneumothorax. Our results show that sonography-guided thoracentesis is complicated by pneumothorax significantly less often than is thoracentesis done with conventional techniques. Use of the smallest possible needle and aspiration of the smallest possible amount of fluid will also result in fewer cases of pneumothorax.

Adult↗
PubMed1990

Proarrhythmic effects of antiarrhythmic drugs.

Drugs that are described as antiarrhythmic drugs may actually aggravate arrhythmia in several ways and these are termed proarrhythmic effects. The most common type of proarrhythmia is a paradoxical increase in the frequency of episodes of the target arrhythmia. This type of effect had not been suspected until recently and has not been widely publicized. It is a phenomenon common to all antiarrhythmic drugs when they are used to treat arrhythmias based on a re-entrant mechanism (the most common mechanism of clinical arrhythmias). Different drugs vary in their tendency to produce this type of proarrhythmic response. These differences are explicable in terms of the relative effects of the drugs on refractoriness and conduction times in the re-entrant circuit. Proarrhythmic effects are most important in the treatment of ventricular tachycardias because recurrences are often fatal. Proarrhythmic effects on ventricular tachycardia can now be predicted at electrophysiological study before commencement of long-term therapy, and potentially dangerous treatment can be avoided. The key to proper treatment to proarrhythmia is to recognize that it is a drug-induced problem and to withdraw the offending drug.

Aged↗
PubMed1990

Mapping small DNA sequences by fluorescence in situ hybridization directly on banded metaphase chromosomes.

A procedure for mapping small DNA probes directly on banded human chromosomes by fluorescence in situ hybridization has been developed. This procedure allows for the simultaneous visualization of banded chromosomes and hybridization signal without overlaying two separate photographic images. This method is simple and rapid, requires only a typical fluorescence microscope, has proven successful with DNA probes as small as 1 kilobase, is applicable for larger probes, and will greatly facilitate mapping the vast number of probes being generated to study genetic disease and define the human genome. Human metaphase chromosomes were prepared from phytohemagglutinin-stimulated lymphocyte cultures synchronized with bromodeoxyuridine and thymidine. Probes were labeled with biotin-dUTP, and the hybridization signal was amplified by immunofluorescence. Chromosomes were stained with both propidium iodide and 4',6-diamidino-2-phenylindole (DAPI), producing R- and Q-banding patterns, respectively, allowing unambiguous chromosome and band identification while simultaneously visualizing the hybridization signal. Thirteen unique DNA segments have been localized to the long arm of chromosome 11 by using this technique, and localization of 10 additional probes by using radioactive in situ hybridization provides a comparison between the two procedures. These DNA segments have been mapped to all long-arm bands on chromosome 11 and in regions associated with neoplasias and inherited disorders.

Base Sequence↗
PubMed1990

Somatic cell hybrid and long-range physical mapping of 11p13 microdissected genomic clones.

Microdissection and microcloning of banded human metaphase chromosomes have been used to construct a genomic library of 20,000 clones that is highly enriched for chromosome 11p13 DNA sequences. Clones from this library have been mapped on a panel of human-rodent somatic cell hybrids that divides the region from distal p12 to proximal p14 into seven physical intervals, A total of 1500 clones has been isolated, 250 clones have been characterized, and 58 clones have been mapped. Six of the clones were used to complete a long-range physical map of 7.5 megabases through the region. Two of the clones are localized to the Wilms tumor (WT) region, three are localized to the aniridia (AN2) region, and two are localized to the region between WT and AN2. The library represents DNA sequences spanning a distance of approximately 13 x 10(6) base pairs, with an average density of one clone per 37,000 base pairs.

Animals↗
PubMed1989

Long-range restriction map around 11p13 aniridia locus.

Using two random DNA markers, and pulsed field gel electrophoresis, a 1.5-Mb physical map surrounding the 11p13 aniridia locus (AN2) has been assembled. The map was constructed using a combination of single- and double-restriction digests on DNA from normal controls and a patient transmitting familial aniridia. The aniridia patient has a chromosome translocation and the two DNA markers flank the breakpoint. This 11p13 breakpoint lies no further than 100 kb from the DNA marker 1104 (D11S95), located on the centromeric side of the breakpoint. Two CpG islands, separated by 550 kb and flanking the translocation, suggest an upper limit to the size of the gene.

Aniridia↗
PubMed1988

Two anonymous DNA segments distinguish the Wilms' tumor and aniridia loci.

The association of Wilms' tumor with aniridia (the WAGR complex) in children with 11p13 chromosomal abnormalities has been established, but the paucity of molecular probes in 11p13 has hampered identification of the responsible genes. Two new anonymous DNA segments have been identified that map to the WAGR region of 11p13. Both DNA probes identify a cytologically undetectable deletion associated with a balanced chromosome translocation inherited by a patient with familial aniridia, but not Wilms' tumor. The same two DNA segments are also included in the distal p13-p14.1 deletion of another patient, who has aniridia, Wilms' tumor, and hypogonadism, but they are not included in the p12-p13 deletion of a third patient, who does not have aniridia but has had a Wilms' tumor. The discovery of this aniridia deletion and these two DNA segments that physically separate the Wilms' tumor and aniridia loci should facilitate identification of the genes in the WAGR locus, beginning with the aniridia gene.

Animals↗
PubMed1988

Four new DNA markers are assigned to the WAGR region of 11p13: isolation and regional assignment of 112 chromosome 11 anonymous DNA segments.

One hundred eighty-three human single copy clones were isolated from the Livermore Laboratory chromosome 11 library (ID code LL11NSO1) and 112 of them were mapped to chromosome 11. Using a panel of somatic cell hybrids segregating chromosome 11 translocations and short arm deletions, 54 of the clones were assigned to one of nine segments on the short arm of chromosome 11; the remainder were assigned to the long arm. Nine of these clones map to 11p13, and four of the nine [57(D11S89), 530(D11S90), 706(D11S93), and 1104(D11S95)] are confined to the same segment within p13 that contains catalase (CAT), the beta subunit of follicle stimulating hormone (FSHB), and the Wilms' tumor-aniridia (WAGR) gene complex.

Catalase↗
PubMed1986

The chromosome 11 gene map: genes for growth and development, Wilms' tumor deletions, and cancer chromosome breakpoints.

Human chromosome 11 is clearly a model autosome encoding genes and characteristics associated with both normal and abnormal growth and development, and several significant disorders. A fine-structure molecular, genetic, and physical map of this chromosome would add considerably to our knowledge of the organization and control of human genes and to an understanding of normal and abnormal human biology.

Animals↗
PubMed1985

Application of molecular genetics to prenatal diagnosis and carrier detection in the hemophilias: some limitations.

Prenatal diagnosis and carrier detection in the hemophilias have received much attention in recent years. The error rate in prenatal diagnosis by fetoscopy is less than 1%; fetoscopy is not possible, however, until the second trimester of pregnancy. Carrier detection based on bioassays of plasma has an irreducible error rate (approximately 5%?), because of the "lyonization" phenomenon in heterozygous women, and the final results are always probabilistic. New DNA methods promise to alleviate these difficulties. Prenatal diagnosis can be accomplished in the first trimester. "Lyonization" is bypassed in carrier detection, and the results may sometimes be essentially nonprobabilistic. But the DNA methods have certain limitations of their own which are not widely appreciated. Aside from cost and the necessity to adopt a new technology, there are inherent genetic problems: mothers must be heterozygous for both a disease gene and a marker gene, final results are probabilistic if the marker gene lies outside the disease gene, and multiple marker genes are often in linkage disequilibrium. We have concluded that a clinical unit planning to use the DNA methods must also maintain the conventional methods at a high level of performance.

Crossing Over, Genetic↗