Bioresorbable vascular scaffolds: The shape of things to come?

In the old days, the limitations of percutaneous transluminal coronary angioplasty (PTCA) were elastic recoil, dissection, and restenosis, problems which were immediately improved by the availability of bare metal stents (BMS). Although the benefits of BMS for elastic recoil and dissection were obvious by angiography, the mechanisms for decreasing the risk of restenosis were less apparent by angiography, but were ultimately elucidated by insights gained from intravascular ultrasound (IVUS). While many studies demonstrated that restenosis was caused by a combination of elastic recoil and intimal hyperplasia, careful IVUS studies revealed that BMS were actually associated with more intimal proliferation than PTCA. Later, IVUS studies clearly demonstrated that even though there was more intimal proliferation after BMS compared with PTCA, the immediate gain in lumen dimensions after BMS (from reduction in elastic recoil) was partially offset by the late loss in diameter due to intimal hyperplasia (which was, in fact, more than after PTCA), but the net gain was higher after BMS. These findings emphasized the need to eliminate elastic recoil and decrease intimal hyperplasia, to have a profound effect on restenosis. IVUS studies showed that angiography alone was insensitive to the adequacy of stent deployment; IVUS assessment of stent dimensions, eccentricity, and symmetry was recommended to ensure optimal stent deployment, and by doing so, particularly with high-pressure balloon inflations, improved the early and late results of BMS. Given this background, it is not surprising that the availability of drug eluting stents (DES) was truly revolutionary, since the benefits of eliminating the geometrical (elastic recoil) and biological (intimal hyperplasia) limitations of PTCA and BMS were combined into a single device. Of course, this is not the end of the story. While truly revolutionary, DES have led to a number of unanticipated consequences, many of which are clinically important. The drugs that inhibit intimal proliferation are intended to decrease the risk of restenosis, but also significantly delay stent endothelialization. This delay can expose the patient to the risk of stent thrombosis even years after stent deployment, and although this risk is small, the consequences include myocardial infarction and death. To reduce the risk of late stent thrombosis, patients often require extended periods of treatment with dual-antiplatelet therapy (DAPT), which increases the risk of bleeding and cost to the patient. The need for DAPT has led to the development of additional genetic and point-of-care assays to help guide the selection of (and the need for) specific antiplatelet agents, which may further complicate medical therapy. In addition, the combination of DAPT with antithrombotic agents for atrial fibrillation, mechanical heart valves, or venous thromboembolic diseases, can substantially increase the risk of bleeding. Finally, patients requiring DAPT may not be able to undergo elective surgery, and the need for urgent surgery could expose the patient to additional cardiovascular risks if DAPT must be interrupted. Fortunately, an entirely new technology appears to be emerging, that may allow us to improve the safety and outcome of DES. Bioresorbable stent technology seems to share some of the benefits and address some