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The potential for conﬂicts of inrest in a relatively captive market have led to accusations that farming interests and practices are not being served by the introduction of genetically modiﬁed crops purchase actonel uk treatment zinc overdose. The expression of the tobacco mosaic virus coat protein within plants order actonel canada symptoms 7 days post iui, which is not sufﬁcient to cause infection purchase actonel canada treatment zygomycetes, does yield resistance to virus infection (Abel et al generic actonel 35 mg otc symptoms of breast cancer. The mechanism of resistance to superinfection is not well understood, although the expression of the coat protein in different tissues of the plant will give rise to different levels of viral resistance (Clark et al. The expression of viral proteins in plant cells has also raised the possibility that other viruses, that are still able to infect the plant, may be able to ‘inherit’ the expressed coat protein. To date, there is no clear evidence that this type of problem might actually occur. For example, transgenic tobacco seedlings constitutively expressing a bean chitinase gene under control of the cauliﬂower mosaic virus 35S promoter showed an increased ability to survive in soil infested with the fungal pathogen Rhizoctonia solani and delayed development of disease symptoms (Broglie et al. An alternative approach is to transfer sets of avirulence genes from the pathogen into the plant (Melchers and Stuiver, 2000). That is, seeds can be produced that will grow into normal plants, but the resulting seeds are sterile. This irreversible modiﬁcation renders the ribosome unable to bind elongation factors and blocks translation. The producer then soaks the seeds in tetracycline to inhibit the binding of the tetracycline repressor to the Cre gene, which can then be transcribed. The sterile seeds retain all the nutritional value of their normal counterparts, but are unable to form new plants. The potential dangers of the terminator gene spreading from the plant to other organisms, coupled with the, real or perceived, control given to the seed producers, particularly in Third World countries, has meant that the technology has yet to be implemented. The safety of the resulting crops, both in terms of the edible product and potential effects on the environment, need to be rigorously assessed. The only realistic way that this can be achieved is through the careful design and thorough analysis of crop trials in a natural setting. Only then will any potentially harmful side-effects of the engineering process be identiﬁed. An obvious exception to this is the cre- ation of cloned animals from adult cells using nuclear transfer technology. The tissue is treated with proteases to break down some of the proteins that hold the cells together and then teased apart to separate the individual cells. These cells are then placed in another dish containing a culture medium with serum and allowed to divide. Primary cells produced in this way do not easily divide outside the animal, and will usually undergo only a few divisions before undergoing senescence. Most cell lines will divide a relatively small number of times (10–20) before entering senescence. Some cell lines, however, do not proceed to senescence and are described as immortal. These cells are said to be ‘transformed’ in that they have undergone a change to make them malignant or immortal. The changes that occur within these cells to make them immortal may result from a viral infection or other change within the cell that leads to unregulated cell division and growth. It is possible to generate stable animal cell lines that harbour extra-chromosomal vectors. Transient transfection represents a rapid way to analyse foreign genes and gene products within cells. For example, many types of gene expression assay rely on the transfection of cells with an appropriate reporter gene, and the collection of data some 24–48 h later. Relative to the generation time of most cell lines (∼16–24 h), this represents a relatively short time between transfection and cell harvesting. Stable cell lines are required for the production of large amounts of a recombinant protein over a prolonged period of time. Technical difﬁculties in producing stable cell lines, arising mainly from the inefﬁciency of the integration process, mean that a clonal cell line can take several months to produce (Power and Meyer, 2000). The transfection of animal cells with genes from other organisms dates back over 40 years (Szybalska and Szybalski, 1962). Animal cells are enclosed by a single membrane, called both the cell membrane and the plasma membrane. The membrane is relatively impermeable and, under normal circumstances, allows only certain materials to pass into and out of the cell. As we have seen with other forms of transformation, the efﬁciency of the process can be greatly increased by various treatments, which are discussed below. Under these circumstances, it is thought that the precipitate settles on the surface of cells and is then internalized through endocytosis (Orrantia and Chang, 1990). By varying the electric ﬁeld strength, and the length of time the cells are exposed to the electric ﬁeld, it is possible to optimize electroporation parameters for almost any cell type. Cationic lipids (those bearing a positive charge) are used for the transport of nucleic acid. The positively charged ‘heads’ project outwards from a hydrophobic core formed by the lipid ‘tails’. These are commercially available lipids that are sold as in vitro transfecting agents, with the latter sold as Lipofectin. Additionally, material brought into the cell through cationic liposomes appears to be able to escape endosome mediated degradation that otherwise presents a major barrier to transfection via endocytosis. For example, the oocytes of the African clawed frog Xenopus laevis, which can be harvested in large numbers from the ovaries of adult female frogs, are approximately 1 mm in diameter and have a correspondingly large nucleus. The efﬁciency of the integration process varies considerably in different organisms. Further analysis, however, revealed that the pattern of expression was non-uniform and failed to correct the underlying histological and functional abnormalities of the disease. The introns sequences removed during splicing are shown in red encoded on both strands of the genome such that they overlap each other. Viral infection primarily occurs in monkey kidney cells, but the virus is capable of infecting a variety of mammalian cell types and, depending on the cell type infected, can either undergo a lytic or a lysogenic life-cycle (Das and Niyogi, 1981). If a foreign gene replaces, for example, a late gene, then the virus cannot replicate properly. Additionally, the virus produces large numbers of progeny (up to 105 virions per infected cell), which means that viral particles, recombinant or otherwise, can be puriﬁed in large amounts with ease. The lack of integration may, however, be advantageous if adenoviral vectors are used in gene therapy trails (see below). Additionally, tissue speciﬁc gene expression is possible with adenoviral vectors if the foreign gene is placed under the control of cell-speciﬁc promoter and enhancer elements, e. Additionally, since they do not integrate into the host genome, they cannot bring about mutagenic effects caused by random integration events.
It is diffcult to specify specifc volumes of blood coaguLaTion facToRs and pLaTeLeTs loss that should be an indication for reoperation buy discount actonel 35 mg online medicine ads. Probably the most useful indication is that the volume of chest tube In neonates and young infants it is usually wise to admin- output is increasing after 3 or 4 hours rather than decreas- ister both platelets and cryoprecipitate following a major ing actonel 35 mg cheap treatment for hemorrhoids. Evidence of hemodynamic compromise with a falling procedure order actonel 35 mg free shipping symptoms stiff neck, such as an arterial switch proven actonel 35mg medications hard on liver. Shunt thrombosis after a Norwood operation is a life- hyperthermia exacerbates neurologic injury after deep threatening event as is coronary thrombosis after an arterial hypothermic circulatory arrest. The infuence of hemodilu- recovery in children after minimum versus full-length ster- tion on outcome after hypothermic cardiopulmonary bypass: notomy. It has several advantages, including the fact that it is immediately available, sterile, nonimmunoreactive and One of the most important basic principles of surgery for free. Autologous pericardium can be used in its fresh state, congenital heart disease is that operations should be designed either pedicled or as a free graft, or it can be used as a free to incorporate growth potential. Whether fxed or by careful use of in-situ tissues, creation and subsequent slid- unfxed, pericardium has the important advantage that there ing or rotation of autologous faps, as well as transfer of free is minimal bleeding through suture holes. However, situations arise where autologous formable to complex three-dimensional shapes in contrast to tissue is not available and a choice must be made between Dacron, which has a tendency to kink inwards resulting in the various biomaterials that are available. Although the pericardium itself will review the properties, advantages and disadvantages of a thicken and fbrose over time, there is little adjacent fbrous number of biomaterials used in various applications for con- reaction such as is seen with Dacron. There are numerous situations where patches are employed in Glutaraldehyde Treatment of Autologous Pericardium congenital cardiac surgery. Aldehyde fxa- a patch is used to direct blood from one chamber to another tion is the same process that is used in tanning animal skins chamber or to a great artery, it may be described as a “baf- to make leather. The pericardium should be clipped to card- fe,” for example, the intraventricular baffe constructed as board to prevent shrinkage and to ensure that the edges are part of the Rastelli procedure for correction of transposition not rolled (Fig. In contrast to nonmedical dehyde determines the degree of fxation and can be varied applications of the term baffe, such as sound baffes or baf- according to the planned use of the patch. Usually between fes in storage tanks, a baffe in a congenital heart operation 1 15 and 30 minutes is appropriate. The patch should then should totally seal and separate the blood inside the baffe be removed from its cardboard backing and should be thor- from the blood outside. A baffe often has a complex three- oughly rinsed in saline in the same way that a porcine valve dimensional shape and therefore imposes stringent demands is rinsed to remove residual glutaraldehyde. The patch can be cut and shaped with the expectation that when it is exposed to pressure it will retain approxi- Pericardium mately the same shape and size. Despite fxation, pericar- dium retains a degree of elasticity and conformability that Autologous Pericardium allows it to be shaped into complex baffes with almost no A patient’s own pericardium, ‘autologous pericardium’ is risk of kinking and infolding. The edges of fresh pericar- one of the most useful materials for application as a patch dium tend to roll and are diffcult to suture unless held under 247 248 Comprehensive Surgical Management of Congenital Heart Disease, Second Edition have been investigated for application both with autologous and bovine pericardium. Some centers have used fresh pericardium to construct conduits and have described an impressive degree of enlargement, although aneurysmal dilation is also seen. Fresh pericardium has been used as an in- (a) situ patch, for example to supplement the pulmonary venous atrium in the Senning procedure4 or to enlarge the pulmo- nary veins for congenital pulmonary vein stenosis. Cryopreserved Homograft (Allograft) Pericardium Allograft pericardium is collected by tissue banks from cadav- ers and after antibiotic treatment is cryopreserved using the same process used for storage of allograft valves. Allograft pericardium has several disadvantages relative to autologous pericardium. Over the longer term, it is probable that it has a risk of calcifcation despite the absence of glutaraldehyde treatment (b) most likely because of immune factors. The anterior pericardium is Pericardium harvested from cows (bovine) and treated with harvested. The glutaraldehyde must be thoroughly rinsed from essentially no risk of disease transmission. However, both bovine and equine peri- aneurysmal dilation is reduced by fxation, particularly if the cardium are thicker and less pliable and conformable than patch will be exposed to systemic pressure. The combination of a powerful The disadvantages of fxation of pericardium are rela- immune response to the xenograft tissue (probably a reaction tively minor. Over the longer term, glutaraldehyde fxation to the residual cellular debris in particular) and the effect of can predispose to a mild degree of calcifcation. The fact the aldehyde results in a severe degree of calcifcation often that the size of the patch is fxed may be a disadvantage if in as short a time as a few months. It also costs more than there is hope that the patch might enlarge with time, thereby autologous pericardium. Finally, glutaraldehyde is toxic and should be handled with care and in such a way that cryoPreserved Homograft (allograft) arterial Wall the surgical team is not exposed to its fumes. It is particu- larly important to color glutaraldehyde immediately after it Allograft arterial wall is excellent material for patch plasty is poured into a bowl on the sterile surgical feld with a dye, enlargement of stenotic vessels. It is usually quite hemo- such as methylene blue, so that it is not confused with crys- static and conforms well to irregular contours. It has sev- talloid solutions and inadvertently irrigated into the surgical eral disadvantages however. Methylene blue may have the added beneft of reduc- is very expensive (several thousand dollars) and it requires ing late calcifcation. Numerous other anticalcifcation agents time for thawing and rinsing (about 20 minutes). Allograft Choosing the Right Biomaterial 249 pulmonary artery wall is often unpredictable as to the size it will stretch to when under pressure. There is a risk of calci- fcation particularly for aortic allografts, although this risk appears to be less with patches of allograft than for allograft tube-graft conduits. Porcine intestinal submucosa Porcine intestinal submucosa has been developed for use as both a pericardial substitute, as well as for septal defect clo- sure. It contains elements of the extracellular matrix which encourage ingrowth of host cells. It has been used in a num- ber of noncardiac surgical settings, including orthopedic and urological reconstructions and is also being explored for application as a biomatrix for myocardial replacement. On the other hand, if a Dacron patch lies closely adjacent to a syntHetic PatcHes semilunar valve, the fbrosis is a disadvantage so that Dacron should probably be avoided in this setting. Dacron Another disadvantage of Dacron is that it is much less Dacron (polyethylene terephthalate) is a synthetic polymer elastic and conformable than biologic materials, such as peri- that was developed by the DuPont company in the 1950s cardium and homograft arterial wall. Although this does not during the period immediately following the Second World present a problem when it is used as a fat patch for simple War when there was an explosion of knowledge in the feld septal defect closure, it is a problem when it is used for con- of plastics technology. This is particularly true in was more stable and resistant to degradation when in a bio- smaller children where the wall tension in a small diameter logic milieu than some of its polymer cousins, such as Nylon baffe is not suffcient to straighten out any inward kinks. It often broke down after several years and ful to avoid Dacron for baffe construction in small children required surgical replacement for the recurrent septal defect and particularly in neonates and infants. These small defects are read- learned from development of Dacron vascular grafts (see ily detected by color Doppler and are often a cause of need- below). Serial echo studies demonstrate that ful property of allowing water vapor to pass through it while these hemodynamically insignifcant defects gradually close water does not. This There are a number of situations in congenital cardiac sur- is useful in some situations and a disadvantage in others.
A pericardial patch is sutured into and ventricular level shunts without pulmonary hyperten- the pulmonary arteriotomy and right ventriculotomy during sion cheap 35mg actonel overnight delivery medicine in balance, hypercarbia to achieve a pH of 7 purchase genuine actonel on line treatment 2nd 3rd degree burns. Hypotension prior to initiation of car- appropriate enlargement of the infundibulum buy generic actonel 35 mg on-line medications education plans. The incision diopulmonary bypass is likely to be the result of excessive should not extend into the body of the ventricle purchase actonel 35mg on line treatment 2014. Because the atria of infants and young children tive procedures elsewhere had a median age of 13 weeks and with atrioventricular canal defects tend to be relatively small a median weight of 4. The mitral valve cleft was closed and noncompliant, the height of the V wave correlates well in 31 of the 34 patients. One patient had moderate intraopera- with the severity of mitral and tricuspid regurgitation. We concluded from this study and from our ongoing experience with this regurgitation should be assessed at a time when blood pres- technique at Children’s National Medical Center that repair sure is in an age-appropriate range. In patients requiring both of the particular advantages of this technique is that it can be inotropic support and systemic vasodilation, milrinone is a applied even in the neonatal period since there is no need to good choice. Thirty-day mortality subtyped as 60 partial, 27 transitional, 120 complete, and 8 was 1. It will be important to review in longer-term follow- up whether this results in any restriction to growth of the associated cardiac defects (p < 0. After a follow-up time of 34 months, the results were repair and hence we believe the advantage of the Australian equivalent to those of standard repair. The authors most current results of the classic single-patch and two-patch emphasize the importance of cleft closure. The authors were standard single-PatCh rePair of ComPlete aV Canal unable to identify any predictors of mortality by multivari- ate analysis. The authors examined 46 patient related, morpho- 47 cleft closure operated on between 1999 and 2009. Median logic, procedure-related and postoperative variables for pre- age at operation was 3. The early mor- ated with a decreased incidence of postoperative pulmonary hypertension emphasizing the importance of earlier age at tality was 2. Freedom Another large series describing results of the single-patch from late mitral valve reoperation was similar for both technique is the report by Crawford and Stroud from the groups. No signifcant morphological predictors of mitral Medical University of South Carolina published in 2001. The mean age moderate or worse mitral regurgitation in the early postoper- at surgery was 10. Actuarial survival including operative deaths was well as improved growth and decreased ventricular volume. In nine previous atrioventricular canal repair signifcantly improves patients, mitral valve repair was possible and in one mitral clinical status with a sustained improvement in ventricular valve replacement. Freedom from lowing mitral valve replacement was noted in a more recent late reoperation from mitral regurgitation did not decrease report from Boston. The patients who presented with congestive infants underwent mitral valve replacement. Tissue valves heart failure in the frst year of life had a high incidence of performed particularly poorly in this situation in infancy. None of these patients had Down syndrome versus replacement for prosthetic stenosis 5–69 months (mean 30 an incidence of 19% in patients who did not present early. This report emphasizes the disadvantages of was a higher risk of need for reoperation. Mortality was prosthetic mitral valve replacement in the infant in that there high at 36%. The authors conclude that left-sided obstruc- is inevitable outgrowth of the prosthesis and a lifelong need tive lesions should be anticipated in children with primum for anticoagulation. An alternative technique for repair of the mitral year survival was 94% and 40-year survival was 76%. This was associated with improved sur- The authors estimated that 14% of patients require reop- vival. Surgery at age less than 20 years was also associ- eration for mitral regurgitation within 10 years of initial ated with improved survival. They describe a novel technique of leafet augmen- 11% of patients, most commonly for mitral valve regurgita- tation using autologous pericardium to augment the bridg- tion. Left ventricular outfow tract obstruction occurred in ing leafets of the atrioventricular valve. This technique 36 patients of whom seven required reoperation to relieve was applied in eight patients and was compared with 68 obstruction. Supraventricular arrhythmias were observed in other patients who underwent either conventional repair 16% of patients after surgery and were more common with (54 patients) or valve replacement (14 patients). Complete heart block no early deaths or major complications following the patch occurred in 3% of patients. The authors believe that the results of the patch repair technique compare favorably with the 68 ComPlete aV Canal with tetralogy of fallot patients who underwent conventional surgery. An alterna- tive method for dealing with severe and irreparable mitral In 1986, Vargas et al. The prosthesis is placed entirely Fallot at Children’s Hospital between 1975 and 1985. Although clinical results with this technique annular outfow patch was used in 10 of the 13 patients. There have been and continue to be satisfactory, the late hemody- were no hospital deaths. The authors also present in this paper the results of an autopsy study of 13 patients. The estimated survival at 5 years after defnitive repair Complete Atrioventricular Canal 533 was 82%. Overall, 30% of the survi- complete atrioventricular septal defect: relation between vors required a reoperation. Predicting disease in Down syndrome: an imbalance in biosynthesis feasibility of biventricular repair of right-dominant unbalanced of thromboxane A2 and prostacyclin. The architecture of the conduction system in congeni- ular canal defect in presence of Down syndrome (letter to the tal heart disease. The atrioventricular con- left-sided obstructive lesions in patients with atrioventricular duction system in persistent common atrioventricular canal canal without Down’s syndrome. Outcome after Morphometric analysis of unbalanced common atrioventricu- repair of atrioventricular septal defect with tetralogy of Fallot.