Stroke Prevention Research
Dr. J. David Spence
&
Dr. Daniel Hackam

We measure plaque in the carotid arteries for three purposes: patient management, genetic research and evaluation of new therapies.

Management of patients:

Beginning in 1990, we developed a new paradigm for management of patients with atherosclerosis, using plaque measurements in the carotid arteries to determine whether therapy has been successful. To us, trying to manage arteries without knowing how they are doing is like trying to manage hypertension without measuring blood pressure, or hyperlipidemia without measuring serum cholesterol.

In the past, we measured the total plaque area, taking the sum of the cross-sectional area of all plaques seen in both common, internal and external carotid arteries. As discussed below, we are now, in collaboration with Dr. Aaron Fenster of the Robarts Imaging Research Laboratory, measuring plaque volume by 3-D ultrasound. The figure below shows measurement of a long plaque in the right common carotid artery.

(From Spence JD, Eliasziw M, DiCicco M, Hackam DG, Galil R, Lohmann T. Carotid Plaque Area: A Tool for Targeting and Evaluating Vascular Preventive TherapyStroke. 2002;33:2916-2922. )

Plaque increases steeply with age; at any age women have less plaque than men.

( from Iemolo F, Martiniuk A, Steinman DA, Spence JD. Sex differences in carotid plaque and stenosis. Stroke 2004 Feb;35(2):477-81 )

We have published evidence that the amount of plaque is a very strong predictor of outcomes: after adjustment for all the traditional risk factors and some new risk factors (age, sex, blood pressure, cholesterol, smoking, diabetes, homocysteine and treatment of blood pressure and cholesterol), patients in the top quartile of plaque area at baseline have 3.5 times the risk of stroke, death or heart attack (MI) compared to patients in the bottom quartile of plaque area ( Spence JD, Eliasziw M, DiCicco M, Hackam DG, Galil R, Lohmann T. Carotid Plaque Area: A Tool for Targeting and Evaluating Vascular Preventive Therapy. Stroke. 2002;33:2916-2922.)

The graph below, copied from that paper, shows the survival free of stroke, death or MI by quartile of baseline plaque area.

We also found that plaque progression was a strong predictor of outcome: patients with plaque progression in the first year had twice the risk of those with stable plaque or regression, as shown in the figure below:

(From Spence JD, Eliasziw M, DiCicco M, Hackam DG, Galil R, Lohmann T. Carotid Plaque Area: A Tool for Targeting and Evaluating Vascular Preventive TherapyStroke. 2002;33:2916-2922. )

This knowledge allows us to use plaque progression or regression in management of patients. If the patient has had plaque regression for successive years, this means that we have not missed anything, the treatment is working, and things are on track. Thus the patient can continue with the family physician, and does not need to return annually to clinic; usually we book a followup in 3-5 years depending on the age, risk level, and other factors.

If the plaque is progressing because known risk factors are not yet well controlled, then efforts are intensified to control known risk factors, and we look for new risk factors. Efforts at smoking cessation, a Mediterranean diet, exercise, target levels of cholesterol, HDL, and control of diabetes on are intensified.

New risk factors that are looked for include hypothyroidism, elevated homocysteine (including deficiency of vitamin B12), Lipoprotein (a) [Lp(a)].

If the plaque is progressing despite good control of all traditional and new putative risk factors, then we have to consider genetic testing in the family, if the family is large enough.