Sean Javaheri, DO, FACP, FACC, FSCAI
In the early years of treating narrowing of the coronary arteries, the only option was balloon angioplasty, during which a balloon was inflated across a coronary stenosis to widen the opening of the blood vessel. While successful, complications of dissection and residual stenosis limited its long-term usefulness. The advent of bare metal stents (BMS) allowed for the successful treatment of complications associated with balloon angioplasty and prevented the need for emergency cardiac surgery in many patients. Unfortunately, BMS were prone to develop scar tissue inside of them (restenosis), hampering the long-term success of the procedure.
After BMS, a new type of stent was developed, which dramatically reduced the rate of restenosis. These stents are called drug-eluting stents (DES) and are coated with a medication to prevent scar tissue formation. DES revolutionized the field of interventional cardiology by dramatically reducing the rate of restenosis and allowed for the treatment of more complex lesions. Because of the success of DES, many patients who previously would have been referred for coronary artery bypass surgery were now able to undergo DES placement. Unfortunately, there remained a population of patients who, despite DES placement, continued to suffer from restenosis. These patients often have significant limitations in the quality of their lives, suffering from chest pain, difficulty breathing, fatigue and other symptoms of coronary artery disease. Many of these patients have had two or more stents placed to treat re-narrowing and have limited options to treat stent restenosis.
Because the stent is a permanent scaffold inside the blood vessel, repeated stenting can crowd the blood vessel and limits lumen size. While application of radiation therapy inside a stent (brachytherapy) is a treatment option for many of these patients at Augusta University Heart and Cardiovascular Services, a new generation of device has recently been approved by the U.S. Food and Drug Administration for the treatment of coronary stenosis.
This new device is a dissolvable stent, called a scaffold. It opens the blood vessel, then, over time, the scaffold dissolves and eventually leaves the blood vessel back to its normal state without a permanent implant. The first generation of this device is called the Absorb GT1 and was approved for use in the United States in July 2016. The Absorb GT1 scaffold is made up of polylactic acid (commonly used in medical devices) and provides a scaffold to treat a coronary stenosis. A potential advantage to this kind of stent includes dissolving over time, allowing for normal vasomotion of the coronary artery. Because it is not a permanent scaffold, it allows for future intervention or surgery, if needed, without a permanent stent. The device is also radiolucent and allows for the stent to be evaluated with a cardiac CT scan. It is not made of a metal or metal alloy, so X-ray imaging allows stent visualization without the metal inferring. This potentially prevents the need for a repeat cardiac catheterization in many patients.
There are some limitations to this new technology, which requires experienced and skilled physicians to perform the intervention. First, the scaffold is not a stent and requires careful preparation of the vessel prior to deployment in a way that differs from standard stent deployment. Second, the scaffold is nearly twice the thickness of a regular stent, which limits its use in small blood vessels.
There are three steps that the implanting physician must perform to assure adequate scaffold deployment. The interventional cardiologists at Augusta University Heart and Cardiovascular Services have a unique level of experience, making them well-equipped to provide this new therapy. The steps are as follows:
- Lesion preparation: This means that anything that will interfere with the optimal scaffold expansion must be treated. This is often calcification and often involves the use of an atherectomy technique. The use of atherectomy requires experience and a unique skill set to perform safely.
- Accurate vessel sizing: It has been shown that visual estimation of the vessel size is often inaccurate and intravascular imaging techniques are superior for accurate vessel sizing.
- Aggressive post-dilation of the scaffold to assure it is maximally apposed to the vessel wall with full expansion: We are excited about this new technology and feel our experience with intravascular imaging (used on 89 percent of our percutaneous coronary intervention cases), along with our experience with atherectomy (used in 11 percent of our cases), places us in a prime position to effectively utilize this new scaffold technology for the treatment of our patients with advanced and complex atherosclerotic coronary artery disease.