PTCA using drug-eluting stents

Stent implantation is a procedure used in the treatment of stenotic (narrowed) coronary arteries. In comparison to uncoated, bare metal stents, drug-eluting stents reduce the risk of restenosis occurring in previously treated sections (in-stent restenosis).

What is PTCA using drug-eluting stents?

A patient with coronary artery stenosis may have a stent implanted during cardiac catheterization. When compared to simple balloon angioplasty, stent treatment will reduce the risk of restenosis in a previously treated section. Stents do not have to be bare metal, and may be coated in certain medicines (drug-eluting stents) which significantly reduce the rate of in-stent restenosis.

Historical origins and development

Stents developed as a result of advances in the field of balloon angioplasty, and were intended to address two specific problems that can occur during or after a simple balloon angioplasty procedure.

Using a balloon to dilate a stenotic vessel usually results in a small tear (dissection) in the vessel wall. Although these tears are usually only partial, and only affect the inner layers of the vessel, balloon dilation can lead to parts of the inner lining coming away from the vessel wall, creating a partial or complete blockage. Prior to the introduction of stent technology, larger tears often resulted in the patient requiring emergency bypass surgery, whereas stents can now be used to support the vessel wall from the inside. This re-establishes normal blood flow and avoids the need for emergency surgery.

Another problem typically associated with balloon angioplasty is restenosis of a previously widened section of a blood vessel (in-stent restenosis). When balloon angioplasty results in a tear forming inside a diseased vessel, this can lead to an overgrowth of scar tissue, which in turn can result in restenosis of a previously treated section. Although the introduction of stents has helped to counteract this problem, the use of bare metal stents is associated with restenosis in up to a third of all treated sections, with the exact rate of restenosis dependent upon the characteristics of the previously treated section (length of lesion, vessel diameter, degree of calcification). The fact that the rate of restenosis observed in patients with diabetes is significantly higher than that observed in other patients has prompted researchers to investigate ways of addressing the problems faced by this sub-group of patients.

Using an animal model, Sollot et al., were able to show that the chemotherapy drug Paclitaxel can be used to prevent restenosis following balloon angioplasty. Gallo et al. were able to demonstrate similar effects in relation to rapamycin, a drug that regulates cell growth. Since then, large clinical studies have been carried out to test the clinical effects these products (or their derivatives) produce during catheter-based treatment for coronary heart disease. The implantation of such stents was shown to reduce the rate of restenosis down to single digit values.

Problems associated with this treatment include a reduced rate of healing due to the need for prolonged antiplatelet therapy, and a risk of late stent thrombosis. Changes in stent design, however, have resulted in these phenomena becoming less common.

What conditions are treated with this procedure?

  • Coronary heart disease in patients with angina pectoris
  • Coronary heart disease in patients without angina pectoris but with evidence of disruption in normal blood flow
  • Acute myocardial infarction (heart attack)
  • Subacute myocardial infarction (heart attack)

What is the purpose of this type of treatment, and what are the results?

A PTCA procedure is performed in order to treat coronary artery stenosis, and to alleviate the symptoms of angina pectoris associated with physical exertion.

Once the degree of narrowing reaches approximately 75%, normal blood supply is impeded during episodes of physical exertion. This leads to the heart receiving insufficient amounts of oxygen, which in most patients will lead to exercise-induced chest pain known as angina pectoris. It is possible for patients with diabetes to remain asymptomatic even when there is clear evidence of a disruption in normal blood flow. This may be due to specific nerve damage that is typically found in patients with diabetes.

Treatment of stenosis using balloons and/or stents leads to blood flow being restored to a previously narrowed section. Depending on the nature of the patient's concomitant disease, and the characteristics of the stenosis, treatment may involve either bare metal or drug-eluting stents, in order to prevent the treated blood vessel from becoming blocked again a few months after treatment.

Successful treatment leads to significant improvements in the patient's exercise capacity, and may even lead to the patient being able to reduce the number of drugs previously required to support tissue perfusion. All patients will require long-term drug-based treatment to prevent or slow the progression of vascular disease in untreated vessels. All patients who undergo stent treatment will be required to take anticoagulant medication in order to avoid the treated vessel becoming blocked. Patients who undergo stent treatment using drug-eluting stents usually require antiplatelet drugs for a duration of 3-12 months. The exact duration of drug treatment is dependent upon the type of stent used, the type of vessel treated, and whether treatment was performed following a heart attack.

As far as patients with clinically stable coronary heart disease are concerned, PCTA does not represent a life-prolonging solution or prevent heart attacks, except in a few very specific cases.

What happens during PTCA using drug-eluting stents?

  • The patient is positioned on the catheterization table and is prepped and draped.
  • After the entry site has been disinfected and numbed using a local anesthetic, a tiny incision is made in the artery.
  • A guide wire is used to introduce a sheath into the artery.
  • A catheter is introduced and advanced to the coronary artery.
  • The guide wire is used to cross the stenosis inside the coronary artery.
  • The guide wire is then used to advance a stent to the site of the stenosis.
  • A balloon is inflated to expand the stent.
  • Balloon and catheter are removed, and the entry site is dressed with a pressure bandage, or closed using a wound closure system.
  • The patient is moved to the ward for observation, and can usually be discharged the day after the procedure.

Sources

  • Peterson KL, Nicod P (Hrsg.) Cardiac Catheterization. Methods, Diagnosis, and Therapy. 1st ed. Saunders. Philadelphia, Toronto, Montreal, Sydney, Tokyo. 1997.
  • Topol EJ: Textbook of Interventional Cardiology. 5th ed. Saunder, Elsevier. Philadelphia 2008.
  • Krakau I: Das Herzkatheterbuch. [The Book of Cardiac Catheterization] Thieme Stutgart, New York 1999.
  • Liistro F, Stankovic G, Di Mario C et al. Circulation. 2002;105(16):1883-6.
  • Sousa JE, Costa MA, Abizaid A et al. Circulation. 2001;103(2):192-5.
 
 
 
 
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