What is a CORONARY INTERVENTION?
Initially coronary balloon angioplasty was the only intervention but now coronary stents are the most common treatment for significantly blocked coronary vessels. It is also possible to have a high speed diamond tipped drill passed through a calcified blockage to smooth the vessel wall and allow expansion with the deployment of a metal stent. The metal stent itself is a stainless steel or cobalt chromium slotted tube which is crimped onto a balloon. The balloon in a fully deflated form is passed through the coronary vessel and then positioned across the area of narrowing and fully expanded up against the wall at very high pressure up to 360 psi. This stent is then firmly wedged internally as a physical scaffold holding the artery open until a slow healing process has covered the struts of the stent with natural body skin. The stents are biologically inert and hence are not rejected by the body and most stents are now coated with various drugs which are designed to reduce the ingrowth of healing tissue to a minimum.
STENTING TECHNIQUE: After diagnostic angiogram pictures are obtained, a guiding photo is placed in front of the Cardiologist for accurate positioning of stents. Then, with the use of x-ray guidance, a guiding catheter is passed from either the wrist or the groin up to the entrance of the artery with the severe blockage. A very soft, thin guide wire is passed smoothly down the artery through the center of the blockage and positioned in the downstream vessel. A small sausage shaped balloon is passed across this guide wire in a deflated shape and positioned across the blockage and fully inflated to partially open the artery, the balloon is then removed leaving the wire in place and then a stent crimped on to a balloon is passed again over the wire and under x-ray imaging, the balloon is inflated to its full diameter to high pressure forcing the stent against the inside edge of the pipe acting as an internal scaffold and preventing any collapse of the arterial wall. Normal flow down the coronary artery is then demonstrated inside the stented segment to ensure that the artery is smooth throughout its length and then all the guide wire and balloon equipment is removed. During the balloon inflation inside the stent, patients may feel a transient tightness or chest pain which improves immediately after removal of the balloon. Importantly, some patients may have multiple blockages and therefore may require more than one procedure to achieve a complete re-opening of all blockages.
STENT TECHNOLOGY: After the initial enthusiasm for bare metal stenting some patients developed early regrowth of blockage inside the stent due to an exaggerated scarring or healing process. The promising development of a drug eluting stent led to the ability to control the bodyís healing process and the ingrowth of scar tissue was minimized with the slow release of a drug from the surface of the stent over the first 8 weeks after stent deployment.
Even with this drug eluting technology, approximately 6 to 7% of drug eluting stents still develop excess scar tissue ingrowth associated also with some inflammation around the edges of the stent.
A further very promising new technology has led to the availability of a biodegradable stent which has tended to overcome these limitations of metallic stents.
This is a non metallic stent composed of a polylactic acid substrate which is self dissolving within a two year period of deployment leaving no trace of stent struts and a normally reactive healthy artery.