Collateral flow

In the emergency situation, we beheve this technique can be successfully employed in selected patients with symptomatic ischemia due to dissection or atherosclerotic disease despite being on maximal medical therapy. We have also seen patients with carotid occlusion and an isolated cerebral hemisphere (poor collateral flow) benefit from EC-IC bypass. Any potential benefit, however, must... 

The safety of G-CSF stimulation in patients with CAD has been questioned in two recent studies. Hill et al. [138] report the results of administration of 10 mcg/kg/day of G-CSF for 5 days in patients with chronic CAD n = 16). There was no clinical benefit as assessed by exercise stress testing and dobuta-mine cardiac MRI. Additionally two patients in the G-CSF group developed serious adverse events related to the therapy (one non-ST elevation MI one MI causing death). Zbinden et al. [139] also tested the efficacy of the same G-CSF dose in patients with chronic CAD ( = 7). The invasive endpoint collateral flow index was significantly better in the G-CSF treated patients when compared to the placebo group. However, two patients in the G-CSF treated group developed acute coronary syndrome during treatment. 

Increased collateral flow Improved perfusion to ischemic myocardium... 

Entada phaseoloides (L.) Merrill. Guo Gang Long (stem) Entageric acid.33 Antirheumatic, promote collateral flow, relieve blood stasis. 

Tio, R.A., Tkebuchava, T., Scheuermann, T.H., Lebherz, C., Magner, M., Kearny, M. et al. (1999) Intramyocardial gene therapy with naked DNA encoding vascular endothelial growth factor improves collateral flow to ischemic myocardium. Hum. Gene Ther., 10, 2953-2960. 

Additional factors influence the extent of the final infarction. The speed of obstruction may allow collateral arteries to develop, if it occurs gradually (Busch et al. 2003), whereas complete sudden blockade of a major artery by an embolus leaves only some minutes to activate sufficient collateral flow. Hypoxia, hyperglycemia, acidosis, fever, hypotonia, and normal or abnormal variants in vascular anatomy my contribute to the resulting infarction (Hossmann 1999). Basically, the loss of oxygen and... 

The posterior communicating artery offers significant variations in size and is often not sufficiently visible in MRA. If it is utilized for a collateral circulation, it can increase in signal and size, but lacking detection in MR angiography in patients with proximal stenosis does not permit an assessment of the lack of collateral flow (Hartkamp et al. 1999 Hoksbergen et al. 2003). 

Hendrikse and coworkers (2001) investigated whether the presence of borderzone infarcts is related to the collateral ability of the CW in symptomatic and asymptomatic patients with unilateral occlusion of the ICA. They found that in patients with unilateral ICA occlusion, the presence of collateral flow via the posterior communicating artery in the circle of Willis is associated with a low prevalence of borderzone infarcts and that asymptomatic patients with an ICA occlusion do not have an increased collateral function of the CW. Figure 15.10 shows the four patterns of collateral flow via the CW to the hemisphere ipsilateral to the ICA occlusion. 

Fig. 15.10. The four patterns of collateral flow via the circle of Willis to the hemisphere ipsilateral to the ICA occlusion. A1 segment indicates A1 segment of ipsilateral ACA, PcomA indicates posterior communicating artery...

Fig. 15.13. A 76-year-old woman with a subtotal stenosis of the left internal carotid artery shows no sufficient collateral flow and only faint flow signal in the left middle cerebral artery (upper row), severe hypoperfusion (time-to-peak maps) of the left middle cerebral artery territory (middle row) and small acute hemodynamic stroke lesions on DWI (bottom row). The patient was later successfully treated with carotid endarterectomy...

Baumgartner RW, Baumgartner I, Mattie HP et al (1997) Transcranial color-coded duplex sonography in the evaluation of collateral flow through the circle of Willis. Am J Neuro-radiol 18 127-133... 

The circle of Willis. This is formed by the proximal part of the two anterior cerebral arteries connected by the anterior communicating artery, and the proximal part of the two posterior cerebral arteries, which are connected to the distal internal carotid arteries by the posterior communicating arteries. However, approximately 50% of circles have one or more hypoplastic or absent segments, usually one of the communicating arteries, and atheroma may limit the potential for collateral flow (Fig. 4.2). 

Around the orbit. Branches of the external carotid artery can anastomose with branches of the ophthalmic artery if the internal carotid artery is severely stenosed or obstructed. Collateral flow from the external carotid artery into the orbit then passes retrogradely through the ophthalmic artery to fill the carotid siphon, middle cerebral artery and anterior cerebral artery. Sometimes flow may even reach the posterior cerebral artery and vertebrobasilar system. 

During or following a cerebrovascular event, some brain areas may show relative or absolute hyperemia owing to good collateral flow, reperfusion after an occluded artery has been reopened and/or inflammation and vasodilatation in response to hypercapnia. In hyperemic areas, oxygen extraction fraction is low and there is luxury perfusion, indicating that flow is in excess of metabolic requirements, perhaps because the tissue has been irreversibly damaged. 

The near-occluded internal carotid artery (ICA) is markedly narrowed, and flow of contrast into the distal ICA is delayed. After selective injection of contrast into the contralateral carotid artery, significant collateral flow can be seen across the anterior communicating arteries with filling of the middle cerebral artery of the symptomatic hemisphere (top). 

Proof of collateral flow in bleeding oesophageal varices... 

T. Pohl, C. Seiler, M. Billingcr, E. Herren, K. Wustmann, H. Mehta, S. Windecker, F.R. Eberli, and B. Meier, Frequency distribution of collateral flow and factors influencing collateral channel development. Functional collateral channel measurement in 450 patients with coronary artery disease, J Am Coll Cardiol 38,1872-1878 (2001). 

E.F. Unger, S. Banai, M. Shou, D.F. Lazarous, M.T. Jaklitsch, M. Scheinowitz, R. Correa, C. Klingbeil, and S.E. Epstein, Basic fibroblast growth factor enhances myocardial collateral flow in a canine model, Am J Physiol 266, H1588-1595 (1994). 

In both groups of ACS, the ECG pattern may be different according to the following factors (a) duration, severity and extension of ischaemia (b) presence of collateral flow (c) variation of coro-... 

Wustman K, Zbinden S, Windecker S, Meier B, Seiler C. Is there functional collateral flow during vascular occlusion in angiographically normal coronary arteries Circulation 2003 107 2213-2220. 

Fig. 2.4 (a) ACA collateral flow after MCA occlusion, (b) ACA collateral flow. Adapted from Fisher [93]... 

Recurrent transient neurological deficits also occur commonly in patients with ICA stenosis. These deficits generally last for less than 3 min and include transient monocular blindness as well as transient hemispheric neurologic deficits. Their pathologic basis is unknown, though in some cases of transient monocular blindness there is evidence of low flow (the box car appearance of red cell clumps separated by clear space) in the retinal arterioles. The retina may also contain highly refractile cholesterol emboli called Hollenhorst plaques. In many instances of severe carotid stenosis or occlusion, the intracranial collateral flow is sufficient to perfuse the brain and prevent ischemia [17]. 

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