News - Part 5

The Greenfield Vena Cava Filter: Operative TechniqueOperative Technique
Anatomic definition of a patients IVC is mandatory prior to filter placement, as the device has a finite maximal diameter. In addition to congenital abnormalities in the venous system, cavae with diameters greater than 28 mm (so-called “megacavae”) may be encountered. Indeed, the one report of significant proximal filter migration was due to inadvertent placement in a massively dilated segment of the IVC. Venocavography will also alert the physician to the presence of clot in the IVC or the renal veins. Such clot may prevent the struts of the filter from completely opening and engaging the caval wall. This situation, once recognized, can be dealt with by suprarenal filter placement. Read the rest of this entry »

Mobin-Uddin Filter
In order to appreciate the development of the Greenfield filter, it is necessary to understand what has previously been available. The Mobin-Uddin filter was the first widely used transvenous device, having been introduced in the 1960s. It resembles an umbrella and consists of six stainless steel spokes radiating from a central hub. A thin fenestrated Silastic sheet covers the metal on each side but allows protrusion of the spokes by 2 mm. In its original design, the filter expanded to 23 mm in cross-sectional diameter, having been developed in such fashion based on autopsy studies of human vena cava morphology. However, due to filter migration in man, the filter was increased in size to its current 28 mm. This has helped reduce the number of proximally migrating filters but has not eliminated the problem. In one report 20 of 1,981 (1 percent) of 23 mm filters proximally migrated vs two of234 (0.85 percent) 28 mm filters; and in another report, 0.4 percent of the 28 mm filters migrated. This filter is efficacious in preventing pulmonary embolism; however, complications have been recognized, including caval thrombosis in 33 to 85 percent of patients, proximal migration of the filter resulting in death, venous stasis sequelae related to filter placement, and a higher than expected rate of recurrent pulmonary embolism perhaps related to the high incidence of caval thrombosis. natural breast enhancement Read the rest of this entry »

The Greenfield Vena Cava FilterTnterruption of the inferior vena cava (IVC) has been used for several decades as a means of protecting patients with lower extremity deep venous thrombosis (DVT) from pulmonary embolism (PE). The long history of this approach has been marked, as expected, by an evolution of the techniques employed. It took some years before it became apparent that unilateral interruptive procedures (femoral vein ligation) were inadequate and needed to be replaced by I VC interruption. It took additional time to appreciate that I VC ligation had a number of deficiencies and was best replaced by partially-occlusive, and preferably less invasive, procedures. During the past 20 years, trans-venous approaches have developed that obviate the need for general anesthesia with its attendant risks, costs, and delays. A number of transvenous devices have been described; however, only two have gone into widespread use: the Mobin-Uddin umbrella filter, and more recently, the Greenfield filter. Other devices, such as the Hunter balloon, birds nest filter, and the nitinol wire filter, have been reported, but are not in general use. Read the rest of this entry »

Different pathophysiologic hypotheses have been proposed to explain these findings. Firstly, trigger substances might enter the systemic circulation through the right-to-left shunt instead of being trapped in the pulmonary capillaries. These trigger substances could induce cerebral vascular instability or increased excitability of the CNS and provoke migraine attacks. In individuals without a right-to-left shunt or after percutaneous closure, a larger amount of trigger substances is needed to induce migraine by overwhelming the filter capacity of the lungs. These trigger substances are proposed to be vasoactive chemicals such as serotonin or (micro) emboli. The latter might also explain the increased risk of ischemic stroke or transient ischemic attack in patients with migraine with aura. This increased risk might be explained by the elevated levels of platelet activation and platelet/leukocyte interaction in patients with migraine. The same interactions have been reported in the pathophysiology of ischemic stroke. Moreover, it has been shown that the incidence of subclinical brain infarction diagnosed with magnetic imaging is higher in patients with migraine with aura when compared to control sub-jects. As mentioned, the effect of shunt closure on the occurrence of migraine seemed to be more pronounced in patients who had migraine with aura. In support of this hypothesis, aura is accompanied by hypoperfusion of the occipital cortex, and emboli seem to have a predilection to embolize in this brain area. Consistent with this hypothesis is the finding that anticoagulant and high-dose antiplatelet therapy seems to decrease the incidence of migraine. comments
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The Relationship Between Migraine and Right-to-Left Shunt: Migraine CriteriaIn contrast, Yankovsky and Kuritzky reported aggravation of migraine with aura into a daily pattern after closure of an ASD in a single patient. The latter was also suggested by Mortelmans et al, who found an aggravation of migraine with aura after percutaneous ASD closure with relatively larger Amplatzer ASD devices. However, the reason for this observation remains unexplained. It is hypothesized that an increased nickel release from the closing device might induce cortical-spreading depressions. These depressions have been suggested to be associated with migraine with aura. However, Mortel-mans et al suggested that microthrombi formed on the left-sided disk during the endothelization process could embolize and provoke migraine attacks. Indeed, even macrothrombi seem not to be so uncommon after device closure. further
In almost all reports that describe the relationship between shunt closure and migraine, the diagnosis of migraine and migraine with aura was based on the International Headache Criteria, except for the report by Azarbal et al. In their study, the presence or absence of migraine was self-reported by patients on the basis of a diagnosis made by either their primary care physician or their neurologist. However, in this study the validated Migraine Disability Assessment Questionnaire was used to assess migraine severity.
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We and others> have described the changes in prevalence of migraine after percutaneous PFO closure. These data are summarized in Table 1. All studies, except for the study by Schw-erzmann et al, showed a significant reduction in the prevalence of migraine and migraine with aura after percutaneous PFO closure. The relative reduction in prevalence of migraine varied from 29 to 59%. For migraine with aura, the relative reduction in prevalence was even more pronounced and varied from 33 to 74%. purchase prozac online
Although Schwerzmann et al could not identify a significant decrease in prevalence of migraine, they found a reduction in the frequency of migraine attacks by 62% in patients with migraine without aura and 54% in those with migraine with aura. The major criticism of these studies was their retrospective and nonrandomized design. However, recently, Anzola et al reported a case-control study that showed a significant overall improvement of migraine after percutaneous PFO closure in comparison to medical treatment during a 1-year follow-up. This seems to be independent of migraine subtype and of previous cerebrovascular disease.
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The Relationship Between Migraine and Right-to-Left Shunt: Occurrence of Right-to-Left Shunt and MigraineIn patients with migraine, the prevalence of a right-to-left shunt seems to be higher when compared to the general population. Two investigational groups used transcranial Doppler ultrasound to determine right-to-left shunts in patients with migraine. A right-to-left shunt was found in 23% of the patients with migraine without aura. Forty-one to 48% of the patients with migraine with aura had a detectable right-to-left shunt. However, in only 16 to 20% of the control group could a detectable shunt be found. Similar findings were reported by Schwerzmann et al using transoesophageal echocardiography, who found that only PFOs with large shunts were found more often in patients with migraine with aura compared to control subjects. These observations suggest that migraine, particularly migraine with aura, may be associated with right-to-left shunting, especially in larger shunts. Link
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