HEART HEALTH

Dr. Steve Karas

THIRTY YEARS ago, the first coronary angioplasty was performed by Dr. Andreas Gruentzig in Zurich.  The procedure involved snaking a balloon-tipped catheter to the heart from the femoral artery in the groin.  By inflating the balloon in a narrowed portion of the coronary artery which is a vessel that supplies blood to heart muscle, it became possible to improve blood flow to the heart without major surgery.

Since this revolutionary event, significant advances have been made in the techniques for treating coronary blockages without invasive surgery.  Probably the most significant advance in the field was the introduction of stents in the 1990s.  Stents are small metallic devices which are implanted in the coronary artery during angioplasty.  Stents remain permanently in place, preventing elastic recoil which may occur after balloon angioplasty.  The risk of recurrent narrowing following angioplasty, also known as restenosis, was significantly lower in patients treated with stents when compared to those that undergo balloon angioplasty alone.

Even after coronary stenting, however, about 15-20 percent of patients would develop restenosis.  This phenomenon appears to be related to the in-growth of cells around the metallic struts of the stent.  This process can be compared to the formation of scar tissue at the site of tissue trauma such as a cut or deep abrasion.  Patients with diabetes and those with small vessels have even higher rates of restenosis.  Many of the patients developing recurrent narrowing would ultimately require major coronary bypass surgery.

STENTS are small metallic devices which are implanted in the coronary artery during angioplasty. Stents remain permanently in place, preventing elastic recoil which may occur after balloon angioplasty.

Attention subsequently focused on ways to decrease the amount of tissue growth within vessels following coronary stenting.  A variety of drugs which inhibit cell growth were tested, but none showed any benefit when given systemically in pill form.   Then came a novel idea:  Would these agents be more effective if they could be bound directly to the stent?  If so, then extremely small quantities of drug could be delivered to a precise location over a long period of time without subjecting patients to the systemic effects of the drug.

Drug-eluting Stents
In the late 1990’s, medical device companies began aggressive programs to develop and test drug-eluting stents.  Early results were promising.  This effort culminated in the approval by the U.S. Food and Drug Administration of the Cordis Cypher stent in 2003.  The Cypher utilized Sirolimus, a potent inhibitor of tissue growth first discovered as a byproduct of bacteria found in soil from Easter Island.  The following year, Boston Scientific’s Taxus stent was also approved.

The drug used in the Taxus stent is Paclitaxel, a chemotherapy agent originally derived from the bark of the Pacific Yew tree.  Although Sirolimus and Paclitaxel work in different ways to prevent tissue growth, both Cypher and Taxus stents were associated with similar, dramatic reductions in restenosis.  Initial studies showed recurrence rates of about five percent, or 3-4 times less often than the bare metal stents, within one year of implantation of either product.

These impressive data led to the swift adoption of drug-eluting stents by the cardiology community. Within a year of the approval of Cypher, over 80 percent of coronary angioplasty procedures employed drug-eluting stents.  Cardiologists began to use these devices more broadly.  Drug-eluting stents were increasingly used to treat coronary blood clots associated with heart attacks.  They were placed in coronary bypass grafts.  Multiple overlapping stents were used to treat long segments of plaque.  Many patients who previously would have been referred for major bypass surgery were now being referred for angioplasty of multiple coronaries with drug-eluting stents.

PROBABLY the most significant advance in treating coronary blockages was the introduction of stents in the 1990’s.

As more and more patients received drug-eluting stents, reports of stent clotting, or thrombosis, emerged.  While restenosis of stents is usually associated with the gradual progression of symptoms (usually chest pain) stent thrombosis often presents dramatically – as a heart attack.  These heart attacks from drug-eluting stent thrombosis have lead to death in up to 15 percent of patients.

The occurrence of stent thrombosis was recognized during the early days of coronary stents.    As foreign bodies within the circulation, the metal struts of the stent stimulate the formation of blood clot and could lead to complete occlusion of the stent causing a heart attack.  The risk of thrombosis continues until the stent is covered by endothelium, the natural “Teflon” lining of blood vessels.

The use of potent agents to inhibit platelet function and vessel clotting, such as Clopidogrel (or Plavix) was found to reduce the risk of thrombosis to less than 1 percent.  Bare metal stents are completely lined with endothelium by 3 months.  Initially, Plavix therapy was recommended for only three months.

The drugs found on drug-eluting stents seem to slow the growth of this protective endothelial lining around the stent struts.  However, concern mounted that patients with drug-eluting stents could be at risk for stent thrombosis over a longer period of time than those with bare metal stents.  In 2006, a European study showed higher rates of heart attack and death in patients receiving drug-eluting stents as compared to bare metal stents.  This prompted a flurry of news reports and a re-evaluation of these devices by the FDA.

Plavix Therapy
These studies all emphasize the importance of anti-platelet therapy with Plavix in preventing stent complications.  Indeed, recommendations for the duration of Plavix therapy after drug-eluted stenting have gradually increased from three months to 12 months or even longer.  Premature discontinuation of Plavix was the primary risk factor in predicting a heart attack or death after stenting.  Patients should not be taken off of Plavix for minor procedures which could be postponed.  If major surgery is anticipated within the next year, then drug-eluted stent should not be used.   In cases where unexpected surgery or bleeding problems require the discontinuation of Plavix, patients should be watched carefully, and Plavix resumed as soon as possible.

The introduction of coronary stents has dramatically altered the treatment of coronary artery disease during the past ten years.  The development of platelet inhibitors liked Plavix and the ability to bind drugs directly to stents have contributed greatly to the widespread adoption of coronary stents. As stenting became easier and more effective, cardiologists were able to help millions of patients without major heart surgery.

Inevitably, as we applied the technique too liberally, we discovered the limitations of our technology.  Now, the pendulum has swung back from unbridled enthusiasm to a more realistic utilization of these devices.  Drug-eluting stents continue to be an important option for treating patients with heart disease.  The future will no doubt bring further refinements in our techniques allowing cardiologists to improve the success of our therapies and avoid unfortunate complications.

Dr. Karas is a native of New York.  After completing his undergraduate education at Columbia University, Dr. Karas attended medical school at Duke University.  He did a residency in Internal Medicine and a fellowship in Cardiology at Georgetown University.   He then spent two years in advanced training in Interventional Cardiology at the Andreas Gruentzig Cardiovascular Center at Emory University. Dr. Karas has been in practice in Melbourne, Florida for 16 years, most recently with the MIMA group. His professional interests include Interventional Cardiology, Nuclear Cardiology and Cardiovascular Research. Dr. Karas lives with his wife Valerie and four children in Indialantic.

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