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What is a hemodynamically significant artery stenosis?
Different arterial distributions can tolerate different degrees of stenosis, depending on the metabolic activity of the target organ and the availability of collateral blood supply.
On CTA and MRA, most authors define “significant stenosis” as a diameter reduction of >70%, although a more conservative definition is >50%.
Although the presence of a hemodynamically significant carotid artery lesion is commonly used as an indicator of impaired cerebral circulation, the effect of such lesions on cerebral perfusion pressure and cerebral blood flow has never been determined accurately.
Pressure gradients cannot be measured on CTA and MRA. Although quantitative measurements of the degree of stenosis are important, the presence of clinical symptoms should be the major determinant in the decision to treat an arterial lesion.
Sequential subcritical stenoses result in a pressure decrease that approximates the sum of each stenosis.
Additional signs of hemodynamically significant stenosis are poststenotic dilation of a vessel and delayed enhancement of the target organ.
Early recurrent hemodynamically significant stenosis is unusual and rarely progresses to occlusion.
Even critical stenosis can regress to within normal limits. Redo endarterectomy is seldom necessary.
The challenge remains to define which patients are at risk for symptoms and occlusion.
Research Facts
Study 1
Here are the details of a Study conducted to understand the natural history of hemodynamically significant early recurrent carotid stenosis
Purpose of this Study: The natural history of hemodynamically significant (internal carotid systolic velocity more than 125 cm/s) early recurrent carotid stenosis was studied.
Methods of this Study: Recurrent hemodynamically significant stenosis occurred within 24 months in 49 internal carotid arteries (45 patients) after 883 endarterectomies (5.4%). These patients were then examined with serial scans. Subsequent redo endarterectomy and neurological events were recorded.
Results of this Study: Patients were observed for 9 to 84 months (mean, 53 months).
Arteries with recurrent stenosis were grouped according to the maximal velocity recorded: group I, systolic velocity more than 125 cm/s and less than 280 cm/s (12); group II, systolic velocity more than 280 cm/s or diastolic velocity more than 80 cm/s (21); group III, systolic velocity more than 280 cm/s and diastolic velocity more than 120 cm/s (14); group IV, internal carotid artery occlusion (2).
The mean time to a velocity of more than 125 cm/s was 11 months.
The mean time to peak velocity was 16 months.
During The Follow-UP Period, Five Stenoses Remained Stable. Nineteen Continued To Increase, With Two Eventual Asymptomatic Occlusions (4%). Six Recurrences Ultimately Had Redo Endarterectomy, Two For Symptoms.
Three Of These Developed New Secondary Recurrent Lesions. However, In 25 Arteries (53%), The Velocity Profile Decreased By At Least One Group Classification.
The Mean Time To The Lowest Velocity (TTL) Was 50 Months. Systolic Velocity Ultimately Fell Below 125 Cm/S In 13 Stenoses (SIX In Group I; Five In Group Ii; Two In Group Iii).
Conclusion of this Study: Early recurrent hemodynamically significant stenosis is unusual and rarely progresses to occlusion. Even critical stenosis can regress to within normal limits. Redo endarterectomy is seldom necessary. The challenge remains to define which patients are at risk for symptoms and occlusion. (J Vasc Surg 1999;30:446-52.)
Sources
Hemodynamically significant early recurrent carotid stenosis
