Inside The Exam Room™ 11/21/2006
ANGIOPLASTY Part 1
By Mark Ombrellaro, MD
In the treatment of vascular disease, angioplasty is a minimally invasive technique that can be used to improve blood flow through a narrowed or blocked section of artery. Historically, Dotter is credited with performing the first angioplasty. In 1963, he developed a technique where he gradually enlarged (dilated) the flow channel of a narrowed artery by inserting a series of small tapered catheters (stiff plastic tubes) of increasing diameters. Using this technique, he was able to gradually stretch the narrowed part of the artery and improve the blood flow through it. At this time, the technique required making an incision into the artery big enough to allow passage of the various sized tubes. The technique worked best when moving from a larger to a smaller vessel but was problematic when trying to treat a larger upstream vessel. In 1965, he used a balloon catheter, rather than the dilators, to stretch out the narrowed vessel segment. In 1974, Gruntzig improved upon this technique by developing a flexible, double lumen balloon catheter design which is the predecessor of modern day angioplasty equipment. A balloon catheter consists of an inflatable balloon fixed on the tip of a long, small diameter flexible tube. This type of construction allows a very low profile device to achieve the same type of results in a more controlled and precise fashion. The advantage of a low profile device is that it can be introduced into the artery through a needle stick rather than an actual incision. Currently, angioplasty catheters vary with respect to the length of the shaft and the diameter and length of the balloon. Balloons are fixed to the shaft as a one piece unit and are not detachable. When choosing an angioplasty catheter, Balloon dimensions (diameters and lengths) refer to their inflated state. Most of the angioplasty balloons are constructed of polyethylene plastic with some being compliant (more stretchy and can be over dilated by adding more pressure) and others being non-compliant (can not be overstretched). With a non-compliant balloon, it can be brought to its rated or” nominal” diameter (as stated on the packaging) and will typically not go above this size. With a compliant balloon, a range of diameters can be achieved depending upon the amount of pressure added to the balloon. The same balloon catheter can be reused within the same patient if repeated dilatations become necessary. Once the artery is adequately treated, the entire balloon/ catheter device is removed.
How does angioplasty actually work? The mechanism of action is considered to be a combination of several events such as pushing fluid out of the plaque (accounting for 6-12% of the increase in the luminal diameter), compacting or “smashing “ the plaque into the artery wall (accounting for 1-2% of the increase in the luminal diameter), and disruption of both the plaque as well as the inner and middle segments (intima and media) of the arterial wall itself (accounting for 85-95% of the increase in the luminal diameter). Angioplasty is basically a technique where a balloon is used to make a controlled tear within the artery in order to stretch it out. Conceptually, you can think about it like over stretching a sock: if you stretch it too much and break the elastic fibers, it remains dilated and will no longer stay up.
In the treatment of peripheral vascular disease, one must consider that no type of treatment, whether it is medical, minimally invasive, or surgical, is able to affect a permanent cure. The goals of all are to improve blood flow but both the natural history of the disease process itself, as well as the body’s healing response to injury will ultimately manifest itself as some type of recurrence. This is not to say that treatment of vascular disease is futile. On the contrary, vascular therapies are quite successful in treating symptomatic cardiac disease; peripheral vascular disease; and preventing organ, tissue, and limb loss. However one must consider the risks and anticipated benefits of all treatment options in order to determine which is the best for that particular circumstance. On one hand, medical treatment of PVD with walking programs may help improve blood flow by up to 5-10% in a compromised limb but may take up to a year to achieve this effect. Surgical treatments, such as bypass, give a more immediate and durable result, yet are obviously more invasive. Angioplasty represents a compromise between durability, risk, and invasiveness and is more of a middle ground between surgical and medical therapies.