How Angioplasty Works

Derived from Greek words meaning shaping of a vessel, today the term is applied to what has become termed minimally, or non, invasive surgery of blood vessels, and is a point where the Interventional Radiologist, a discipline fathered by Nobel prize winner Charles Dotter, has to some extent taken over the role of the surgeon, and to a large extent offered forms of treatment outside the surgeon’s capabilities.

The purpose of any angioplasty procedure is to enlarge the opening of a vessel whose cavity has become narrow (stenosed), obstructed by clot formed on the wall (thrombus), or mobile and lodged in the vessel (embolus), or an enlarging plaque of lipids that shouldn’t be there  (atherosclerosis). In nearly all instances the vessel is an artery, but recently a question has been raised about narrowing of veins associated with multiple sclerosis and studies of angioplasty on veins in that condition are in progress.

The Anatomy of an Artery
Arterial structures vary in size from the largest, the aorta, to the smallest arteriole about to branch into capillaries. The function of an artery is the passive transmission of blood, hence, like an arterial highway, its structure depends on the load it bears. The pressure on the wall of the aorta is higher than on the wall of the least arteriole, their structure is commensurate to their function.
The innermost layer, endothelium is known in the capillaries to have important hormonal functions, but it acts mechanically in the artery to provide a smooth surface for passage of blood. The middle and outer layers are composed of fibrous tissue with a proportion of elastic tissue. The vessels closest to the heart have to be able to expand as a wave of blood pulses through them, and the restoration of size is by the elastin fibres; vessels furthest from the heart have least expansion, everyone knows a simple cut does not rhythmically spurt blood.

Pathologic Conditions of the Arteries
An artery is a muscle walled tube, in terms of pathology, the condition in question may be due to the tube itself, or to some factor blocking the tube, or both.

Arteriolosclerosis, otherwise known as small artery disease, is a condition associated in particular with type two diabetes, and with hypertension (abnormally raised blood pressure). Three different changes may occur in arterioles (the smallest type of artery), degenerative changes and thickening may occur on the inner surface, in the wall or both. The result is narrowing of the lumen, and partial or complete obstruction of blood flow.

Arteriosclerosis, otherwise known as hardening of the arteries. The wall of the artery has changed its character, become scarred and calcified, to the point it may be shown on an X-ray, just like bone, both are seen because of their calcium content.

Atherosclerosis, also a hardening of the arteries, but in addition there are formed plaques of yellow cheesy like material which swells the wall and may burst into the interior of the artery providing an adhesive surface for clot formation. The mechanism is far from fully understood, the more that is learnt, the more there remains to discover. It is accepted that there is a process of depositing cholesterol and other lipids in association with inflammation (there’s a chicken and egg issue), the inflammation provokes scarring, the wall of the artery thickens and there is occlusion, partial or total, to blood flow.

Mechanism of Angioplasty
There are two steps, dilating the constricted vessel, and keeping it dilated. The procedure is invasive, infection can be caused because the skin is penetrated. Although angioplasty is essentially a radiologic procedure and is carried out using an X-ray machine and fluoroscopy like television, it must be conducted with maximum attention to preventing the introduction of infection. It is usually conducted without general anesthetic, but the area of the cut is “numbed” as the dentist numbs the area of the tooth he is operating on.

A catheter, that is a thin flexible tube, is inserted through a small cut in the skin, and into an artery, generally the femoral artery at the groin. Watching the progress of this special catheter as it is inserted and pushed along the artery, the doctor conducting the procedure follows its progress on the television monitor until it reaches the point of obstruction. This can be determined by squirting fluid (contrast) that shows on the X-ray and identifies the narrow point. Once at this point the doctor expands the collapsed balloon end of the catheter to distend the obstruction. The improvement is demonstrated by the free flow of contrast fluid. At this point he may or may not decide to insert a stent. There are many kinds, but essentially it is a mesh that can be collapsed to reduce its size until it is placed, and then expanded to keep the arterial wall opened and the flow of blood made free.

Applications of Angioplasty
Coronary artery occlusion is treated in many centers by angioplasty without resort to the “clot buster” technique. It is also performed on the carotid arteries of the neck, the renal arteries of the kidneys, and the arteries of the leg.

Aneurysms are localized distensions of a vessel, usually an artery. Sometimes they are resected and replaced, an alternative is to provide a safe internal lumen within the aneurysms by means of a stent inserted with the angioplasty technique.

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