Advances in
Intracoronary Diagnostics and Therapeutics
The field of
cardiology has experienced impressive progress over the past decades, in part
due to improvements in intracoronary diagnostic and therapeutic techniques.
However, despite these advances, cardiovascular disease remains the leading
cause of death in the developed world. Today’s Forum will focus on emerging
intracoronary technologies that may substantially improve management of
cardiovascular disease. The first talk will feature a discussion of the
problems associated with current stent designs, and strategies to improve
them. The second talk will examine the limitation of traditional
intracoronary diagnostic methods, and will describe novel approaches that may
shift the diagnostic paradigm.
Moderator:
Thomas J. Brady, MD, Co-Program Leader, Cardiovascular Disease,
Co-Director, Office of Education and Senior Consultant, CIMIT; Director,
Cardiovascular Imaging and Intervention and Vice Chairman, Director of
Radiology Research, Massachusetts General Hospital; L.L Robbins Professor of
Radiology, Harvard Medical School,
4:00PM Introduction: Ahmed Tawakol, MD,
Co-Leader: CIMIT Cardiovascular Disease Program; Co-Director, Cardiac MR-PET-CT
Program and Associate Director, Nuclear Cardiology, Massachusetts General
Hospital, atawakol@partners.org
4:10PM Drug
Eluting Stents: Lessons in Biocompatibility
Sahil A. Parikh, MD, Interventional
Cardiology Fellow, Brigham and Women’s Hospital; Clinical and Research Fellow,
The
purpose of placing a stent in an artery is to prevent restenosis (re-narrowing
of the artery) without causing thrombosis (the formation of a clot), for both
restenosis and thrombosis can lead to heart attacks. Drug-eluting stents, which limit restenosis,
were regarded as a major medical advance when they first appeared, but new
evidence suggests that they also confer long-term risks. In a significant number of cases,
particularly in patients who stop taking anti-clotting drugs, the stents have
caused fatal thromboses years after their placement in an artery. To make drug-eluting stents as safe and
effective as possible, researchers are seeking to improve the stents’
biocompatibility.
A
stent is a foreign object in the body, and the body responds to the stent’s
presence in a variety of ways. Amongst
other responses, macrophages accumulate around the stent, and nearby smooth
muscle cells proliferate. These
physiological changes, which can cause restenosis, can be limited by drugs
released by the stent, but these drugs also limit re-endothelialization. This lack of healing can make the stent an
exposed surface on which a life-threatening clot can form.
The
safety and effectiveness of a drug-eluting stent depends on its design and on
its materials. The structure of a
stent’s metal backbone, for example, has a significant effect on the amount of
endothelial denudation that the stent causes.
When comparing drug-eluting stents to bare-metal stents, one should
remember that drug-eluting stents are only beginning to adopt the sophisticated
structures that are commonly used in state-of-the-art bare-metal stents. The properties of the drug used in a drug-eluting
stent are also extremely important.
Hydrophobic drugs are more likely to be retained in the arterial wall
than hydrophilic drugs, and for all drugs, the concentration varies with wall
depth. Finally, the polymer coating of a
drug-eluting stent influences the stent’s tendency to cause a clot.
In the future,
researchers hope to create stents, or at least polymer coatings, that will
degrade in the body over time. This
project will require expertise in both materials science and medicine.
4:30PM Advances in Intra-coronary Diagnostic Methods
as a means of Matching Type of Therapy with the Type of Plaque Present
James E. Muller, MD , CEO,
InfraReDx, Inc., jmuller@infraredx.com
Coronary
heart disease is the leading cause of death in the
Myocardial
infarctions often occur when a lipid-rich plaque ruptures and causes an
artery-clogging clot to form.
Unfortunately, current diagnostic methods are largely incapable of
identifying lipid-rich plaques before they rupture. With this problem in mind, researchers are
exploring new ways to identify lipid-rich plaques. Intravascular magnetic resonance imaging
(MRI), which uses a magnetic coil small enough to fit inside an artery,
presents one possibility; and optical coherence tomography (OCT) provides
another. At the moment, however, both of
these techniques are hampered by blood, so both require arterial
occlusion. In contrast, near-infrared
(NIR) spectroscopy, which characterizes a chemical mixture based on its
absorption of NIR light, works even if the spectroscopic catheter is surrounded
by blood. NIR spectroscopy can
differentiate between the fat in plaques and the fat in surrounding tissue, and
early results indicate that the technique can be used to effectively identify
lipid-rich plaques.
Doctors
may soon be able to make treatment decisions, such as whether to use a
bare-metal stent or a drug-eluting stent in a given patient, based on the type
of plaque that the patient has.
Hopefully, “personalized stenting” based on tissue type will be the
method of the future. Non-invasive
molecular imaging techniques will also hopefully be developed to help doctors
make informed diagnostic decisions.
5:00PM Panel discussion – View
this video