A vulnerable plaque is an atheromatous plaque, an unstable collection of white blood cells (primarily macrophages) and lipids (including cholesterol) in the wall of an artery which is particularly prone to produce sudden major problems, such as a heart attack or stroke.
In many cases, a vulnerable plaque has a thin fibrous cap and a large and soft lipid pool underlying the cap. These characteristics together with the usual hemodynamic pulsating expansion during systole and elastic recoil contraction during diastole contribute to a high mechanical stress zone on the fibrous cap of the atheroma, making it prone to rupture. Increased hemodynamic stress correlates with increased rates of major cardiovascular events associated with exercise, especially exercise beyond levels the individual does routinely.
Researchers now think that vulnerable plaque, see atherosclerosis is formed in the following way:
When this inflammation is combined with other stresses, such as high blood pressure (increased mechanical stretching and contraction of the arteries with each heart beat), it can cause the thin covering over the plaque to split, spilling the contents of the vulnerable plaque into the bloodstream. The sticky cytokines on the artery wall capture blood cells (mainly platelets) that accumulate at the site of injury. When these cells clump together, they form a clot, sometimes large enough to block the artery.
The most frequent cause of a cardiac event following rupture of a vulnerable plaque is blood clotting on top of the site of the ruptured plaque that blocks the lumen of the artery, thereby stopping blood flow to the tissues the artery supplies.
Upon rupture, atheroma tissue debris may spill into the blood stream; this debris is often too large (over 5 micrometers) to pass on through the capillaries downstream. In this, the usual situation, the debris obstruct smaller downstream branches of the artery resulting in temporary to permanent end artery/capillary closure with loss of blood supply to, and death of the previously supplied tissues. A severe case of this can be seen during angioplasty in the slow clearance of injected contrast down the artery lumen. This situation is often termed non-reflow.
Additionally, atheroma rupture may allow bleeding from the lumen into the inner tissue of the atheroma making the atheroma size suddenly increase and protrude into the lumen of the artery producing lumen narrowing or even total obstruction.
The tests most commonly performed clinically with the goal of testing susceptibility to future heart attack include several medical research efforts, starting in the early to mid-1990s, using intravascular ultrasound IVUS), thermography,(near-infrared spectroscopy) careful clinical follow-up and other methods, to predict these lesions and the individuals most prone to future heart attacks. These efforts remain largely research with no useful clinical methods to date (2006).
Another approach to detecting and understanding plaque behavior, used in research and by a few clinicians, is to use ultrasound to non-invasively measure wall thickness (usually abbreviated IMT) in portions of larger arteries closest to the skin, such as the carotid or femoral arteries. While stability vs. vulnerability cannot be readily distinguished in this way, quantitative baseline measurements of the thickest portions of the arterial wall (locations with the most plaque accumulation). Documenting the IMT, location of each measurement and plaque size, a basis for tracking and partially verifying the effects of medical treatments on the progression, stability or potential regression of plaque, within a given individual over time, may be achieved.
Patent No. 7,734,330 Issued on June 8, Assigned to Meridian Medical Systems for Vulnerable Plaques Detection, Treatment Method, Apparatus (Maine Inventor)
Jun 09, 2010; ALEXANDRIA, Va., June 15 -- Kenneth L. Carr, Woolwich, Maine, has developed a method and apparatus for detecting and treating...
Guidant (Indianapolis) disclosed plans to conduct a study designed to increase clinical understanding of vulnerable plaques--lipid-rich coronary lesions that suddenly rupture--that may cause most heart attacks.(TCT notebook)
Nov 01, 2004; * Guidant (Indianapolis) disclosed plans to conduct a study designed to increase clinical understanding of vulnerable...