Invasive techniques that improve the blood supply to the heart also may be used. One of these is percutaneous transluminal coronary angioplasty
,
also known as P.T.C.A., angioplasty, balloon
dilation or balloon angioplasty.
Before performing either of these procedures, a doctor must find the
blocked part of the coronary arteries. This is done using coronary arteriography
, which is done during a procedure called
cardiac catheterization. In this procedure a doctor guides a thin plastic tube (a catheter) through an artery in the arm or leg and into the coronary arteries. Then the doctor injects a liquid dye visible in x-rays through the catheter. High-speed x-ray movies record the course of the liquid as it flows through the arteries. Doctors can identify blockages in the arteries by tracing the liquid’s flow.
Some newer diagnostic tools are available to evaluate how well the heart
works. These tests may be done before or after a heart attack.
Some of these tests are still somewhat experimental and are limited
to larger medical centers.
CAROTID ARTERY STENTING
Carotid artery stenting has recently been introduced at St Vincent's Hospital.
Introduction
Following the encouraging and long-lasting results obtained with angioplasty and stenting in the coronary, renal, and peripheral vascular systems, a natural evolutionary step was the application of these new technologies to the cerebrovascular tree. Preliminary clinical series have suggested that carotid angioplasty followed by stenting can be carried out with an acceptable degree of safety and with excellent angiographic results immediately and at 6 months.[1-7] Although long-term follow-up is not yet available, the low morbidity and mortality associated with these procedures, at least in these early series, make it a viable alternative therapy to carotid endarterectomy (CEA) for a select group of patients.
With advancements in stent technology and the availability of stents exclusively designed for neurovascular use, select intracranial pathologies might be successfully treated with such devices. These include intracranial occlusive disease, prevention of acute and subacute vessel occlusion and as an adjunct to intra-arterial thrombolysis for acute stroke, and intracranial aneurysms.
Angioplasty and Stenting of Intracranial Occlusive Disease
Stenotic lesions located in surgically difficult areas such as the intracranial carotid artery, the intracranial vertebrobasilar system, and the proximal middle cerebral artery are responsible for 5% to 10% of ischemic strokes.[40] Although different extracranial-to-intracranial bypass procedures (superficial temporal artery to middle cerebral artery, occipital artery to posterior inferior cerebellar artery, and superficial temporal artery to superior cerebellar or posterior cerebral artery) have been advocated for the treatment of stenotic lesions in these areas, they are technically demanding and difficult to perform. Additionally, there is no clear-cut evidence supporting their efficacy.
The potential advantages of endovascular revascularization of these surgically inaccessible intracranial vessels by angioplasty and stenting are immediately intuitive. Previous experience with intracranial angioplasty alone for atherosclerotic lesions has shown some promising results.[41-46] However, significant risks related to intimal dissections and subacute thrombosis have been reported;[42-44] this is reminiscent of the initial experience with coronary angioplasty prior to the introduction of stents and antiplatelet agents. New stents with improved flexibility specifically designed for intracranial use might improve the efficacy of cranial vessel repair and enhance the safety of angioplasty by reducing subacute thrombosis and re-establishing lumen patency following vessel dissection.[47]
Angioplasty and Stenting in the Setting of Acute Stroke
One more potential application of angioplasty and stenting is for acute stroke related to intracranial vessel occlusion following intra-arterial thrombolysis. Several reports have now suggested the potential advantages of superselective intra-arterial thrombolysis over other methods of delivery. The Prolyse in Acute Cerebral Thromboembolism Trial (PROACT) was a randomized, controlled, double-blind trial that tested the rate of recanalization, safety, and clinical efficacy of local intra-arterial recombinant prourokinase given within 6 hours of stroke secondary to occlusion of the middle cerebral artery.[48] Recanalization of the middle cerebral artery was found in 58% of patients given the study drug as opposed to only 14% given placebo, and this was statistically significant. The frequency of intracranial hemorrhage, the most feared complication of acute thrombolysis, was not significantly different in the two groups.
Unfortunately, thrombolytic agents, although effective on thrombus lysis, have a paradoxical effect on platelet activation. There is far more experience in the coronary vessels, and the cardiac literature suggests that rethrombosis occurs more commonly in vessels with significant underlying stenoses.[49,50] Thus, in stenotic vessels, immediate or delayed reocclusion after successful revascularization is a major concern. This phenomenon has been observed in the anterior circulation as well as in the posterior circulation: the incidence of reocclusion after successful vertebrobasilar recanalization is as high as 30% and is uniformly fatal.[51] Therefore, a select subgroup of patients with acute ischemic stroke, namely those with an atherosclerotic lesion with superimposed acute thrombosis, is likely to benefit from the addition of stenting to emergency thrombolysis.
Another consideration is the potential use of GPIIb/IIIa antiplatelet blockade in association with thrombolysis, angioplasty, and stenting. Rethrombosis is initiated by platelet activation and may be minimized by platelet inhibition. The benefits of GPIIb/IIIa inhibition must be weighed against the risk of intracranial hemorrhage.[38]
Occlusion of the ostia of small perforating vessels during angioplasty and stenting, with the obvious risk of ischemia or infarction in branches of the basilar, anterior, or middle cerebral arteries, is a poorly understood risk and may limit stent applicability in the cerebral circulation. The feasibility and relative safety of intracranial angioplasty has been reported by several investigators.[40-46] Additional experimental and clinical experience suggest that the risk with intracranial stents is only a theoretical one. In experimental studies, lateral carotid branches that mimic the size and angle of origin of human perforating branches tend to remain patent after stenting.[52] Additionally, in one patient with a fusiform aneurysm of the basilar trunk (a segment notoriously rich in critical small perforating branches) treated by stenting, no problems with perforating branch occlusions were reported.[53]
carotid stenosis before (arrows) and after PTCA/stent
References
