Carotid Artery Imaging: Why Measuring Plaque Beats Measuring Wall Thickness for Predicting Heart Attack and Stroke Risk

Table of Contents

• Key Points
• Understanding the Debate: Two Ways to Look at the Carotid Artery
• The Study That Sparked This Editorial
• What Is Carotid Intima-Media Thickness (cIMT)?
• Carotid Plaque Burden: A More Powerful Predictor
• Key Evidence From Major Studies
• Why the Way We Measure Matters
• The Power of 3D Ultrasound Technology
• Treating Arteries Instead of Risk Factors
• What the Official Guidelines Say
• What This Means for Patients
• Limitations to Keep in Mind
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• Carotid plaque burden is a stronger predictor of heart attack and stroke than cIMT, according to this editorial analyzing over 10,000 patients.
• Major studies, including Northern Manhattan and BioImage, found plaque burden predictive while cIMT often was not.
• Plaque changes can be measured within 3 months, enabling treatment adjustments, unlike cIMT which changes slowly.
• Guidelines from ACC/AHA and ESC/EAS no longer recommend cIMT and support carotid plaque detection for risk assessment.
• A 'treating arteries' approach, using plaque measurements, was tied to over 80% lower 2-year risk of stroke and heart attack in high-risk patients.

Understanding the Debate: Two Ways to Look at the Carotid Artery

The carotid arteries are the main blood vessels in your neck that carry oxygen-rich blood to your brain. When cholesterol, fat, and other substances build up inside these arteries, they form plaques that can narrow the vessels or break loose and cause strokes. For decades, doctors have used ultrasound to look for signs of early artery disease, and there are two main measurements they can take.

The first is called carotid intima-media thickness (cIMT). This measures how thick the two inner layers of the artery wall have become. The second is carotid plaque burden, which measures the actual amount of plaque buildup. The question of which one better predicts who will go on to have a heart attack or stroke has been a subject of intense scientific debate. This editorial, published in the journal Angiology, makes the case that plaque burden is the winner — and that continuing to rely on cIMT may be holding back better patient care.

The Study That Sparked This Editorial

The editorial was written in response to a study by Kolkenbeck-Ruh and colleagues, also published in Angiology. That study looked at 473 patients who had either critical limb ischemia (CLI, a severe blockage of blood flow to the legs that can cause pain, wounds, or gangrene) or stroke, and compared them with 479 healthy control participants.

The researchers found a number of important relationships:

• In older participants (over 50 years old), the presence of carotid plaque was independently linked to CLI, with statistical significance values ranging from P < .005 to P < .0001 (meaning there was less than a 0.5% to 0.01% chance the finding was due to random chance).
• In younger participants (under 50), this relationship was not significant (P > .38).
• In younger participants, carotid plaque was independently linked to stroke (P < .005 to < .0001), and cIMT was independently linked to CLI (P < .0001).

The investigators then asked whether adding cIMT measurements to plaque information improved the ability to detect arterial events. In older patients, it did not: the area under the receiver operating curve (AUC, a measure of how accurate a test is, where 0.5 means no better than a coin flip and 1.0 means perfect prediction) was 0.680 ± 0.020 with cIMT versus 0.664 ± 0.017 without, a difference that was not statistically significant (P = .27).

However, in younger patients, adding cIMT did improve detection significantly: the AUC increased from 0.631 ± 0.026 to 0.719 ± 0.023 (P < .0001). The authors of the original study concluded that cIMT complements plaque presence in younger — but not older — patients when it comes to predicting cardiovascular events.

What Is Carotid Intima-Media Thickness (cIMT)?

cIMT measurement was first developed and validated in the 1980s. Since then, it has been used in hundreds of research studies as a stand-in (surrogate) for atherosclerosis, the disease process that causes plaque to build up in arteries. It has been used to study risk factors, genetics, and even the effects of treatments such as cholesterol-lowering drugs.

But the authors of this editorial argue that a widespread misconception has taken hold: that an increased cIMT represents "preclinical atherosclerosis." In other words, many doctors assume that if the artery wall is thicker, the patient must be developing artery disease. The editorial authors strongly dispute this, pointing out that cIMT is biologically and genetically distinct from plaque burden. Having a thick artery wall is not the same as having plaque buildup.

Part of the confusion comes from the fact that there are two different ways to measure cIMT. According to the Mannheim Consensus, cIMT should be measured in the far wall of the distal common carotid artery, at a location where there is no plaque. The other approach includes plaque thickness in the measurement of IMT. Since some patients have plaque and others do not, combining these two approaches as if they were the same thing is, in the authors' words, "invalid."

Carotid Plaque Burden: A More Powerful Predictor

Carotid total plaque area (TPA) is a measurement of the total surface area of all plaques in the carotid arteries. It was first measured in London, Ontario, Canada, in 1986, and has been used routinely in vascular prevention clinics there since 1995. The method was first described in a 1997 article examining the effects of blood pressure elevation during mental stress on atherosclerosis.

In a landmark 2002 study, Spence and colleagues followed 1,686 patients from the Premature Atherosclerosis Clinic and the Stroke Prevention Clinic at the London Health Sciences Center in Canada. They found that the 5-year risk of stroke, heart attack, or vascular death increased steadily with each quartile (fourth) of plaque area:

1. First quartile (least plaque): 5.6% risk of a major cardiovascular event within 5 years
2. Second quartile: 10.7% risk
3. Third quartile: 13.9% risk
4. Fourth quartile (most plaque): 19.5% risk

These numbers were adjusted for age, sex, systolic blood pressure, cholesterol levels, homocysteine, diabetes, and treatment of blood pressure and cholesterol — meaning the association between plaque area and risk held up even after accounting for other major risk factors.

Another study combined risk scores with various ultrasound measurements (average, minimum, and maximum cIMT, cIMT variability, and TPA) to see what added the most predictive value. The greatest improvement came from adding TPA to a risk score based on coronary risk factors alone. This led to the development of the AtheroEdge Composite Risk Score, which significantly increased the area under the curve in receiver–operating characteristic analysis of cardiovascular risk prediction.

Key Evidence From Major Studies

The editorial draws on several large, well-known studies to make its case that plaque burden outperforms cIMT.

The Northern Manhattan Study

This study followed 2,189 participants for a mean of 6.9 years. Individuals whose maximum carotid plaque thickness was greater than 1.9 mm had a 2.8-fold increased risk of combined vascular events compared to patients without carotid plaque (hazard ratio [HR] = 2.80; 95% confidence interval [CI]: 2.04–3.84). A hazard ratio of 2.80 means those with thick plaques were nearly three times as likely to experience an event.

The High Risk Plaque BioImage Study

This study followed 5,808 participants for a median of 2.7 years. It compared three measures — cIMT, carotid plaque burden, and maximum carotid plaque thickness. Both carotid plaque burden and carotid plaque thickness were predictive of future cardiovascular events (P < .001), while cIMT was not (P = .372). In fact, carotid plaque burden was just as predictive as a coronary calcium score, a well-established test that measures calcium deposits in the heart's arteries.

The Tromsø Study (Norway)

The authors describe the Tromsø Study as one of the most important studies demonstrating the superiority of plaque burden over cIMT. It was a prospective, population-based study of over 6,000 healthy participants. Both cIMT and TPA were measured by ultrasound at the start of the study.

After a mean follow-up of 9.6 years (median: 10.8 years), a first-ever stroke had occurred in 7.3% of men (n = 235) and 4.8% of women (n = 162). After adjusting for age, total cholesterol, HDL (good) cholesterol, systolic blood pressure, use of blood pressure-lowering drugs, current smoking, diabetes, and coronary heart disease, the results were striking:

• TPA was significantly associated with ischemic stroke in both sexes. In men, the hazard ratio was 1.23 (95% CI: 1.09–1.38; P = .0009). In women, it was 1.19 (95% CI: 1.01–1.41; P = .04).
• Participants in the highest quartile of TPA had dramatically higher stroke risk compared to those without plaque: men had a hazard ratio of 1.73 (95% CI: 1.19–2.52; P = .002), and women had a hazard ratio of 1.62 (95% CI: 1.04–2.53; P = .03).
• By contrast, cIMT predicted stroke only in women, and only when the measurement included plaque thickness. Common carotid artery IMT measured in the far wall was not associated with future ischemic stroke after adjusting for other cardiovascular risk factors.

The Tromsø Study also showed that after 7 years of follow-up, TPA strongly predicted coronary risk, whereas only cIMT measured in the carotid bulb (a widened area near the base of the skull) was predictive. A subsequent meta-analysis confirmed these findings: IMT that included plaque thickness in the bulb was a stronger predictor of coronary artery disease and future heart attacks than IMT measured in the common carotid artery, where plaque is less common. Importantly, the meta-analysis found that carotid plaque burden was more predictive than either IMT phenotype.

Why the Way We Measure Matters

The editorial highlights a common statistical error that appears in research studies, including the Kolkenbeck-Ruh study and others. It occurs when researchers compare the presence or absence of carotid plaque (a categorical variable — plaque is either there or it is not) with the quantity of IMT (a continuous variable — measured on a continuous scale).

This matters because continuous variables are about 3 times more powerful for statistical purposes than categorical variables. Comparing them directly is like comparing apples to oranges. Adding plaque thickness into an IMT measurement makes IMT more predictive of events, but the authors point out that this approach mixes together patients with and without plaque as if they were the same group — an invalid comparison.

This distinction is not just an academic technicality. It has real consequences for how doctors interpret risk and how researchers design studies.

The Power of 3D Ultrasound Technology

One of the biggest advantages of measuring carotid plaque burden — especially with modern three-dimensional (3D) ultrasound — is that plaque changes can be detected in a clinically useful time frame. The spatial resolution of carotid ultrasound is about 0.3 mm, and on average, cIMT changes by only about 0.15 mm per year. This makes it virtually impossible to reliably measure a change in cIMT within a single individual over the course of a year.

This is why studies that use cIMT as an outcome typically need 200 to 300 patients per group, followed for 2 years, to detect a treatment effect. Coronary intravascular ultrasound studies face a similar limitation, requiring about 200 patients per group followed for 2 years, because plaque is present throughout the length of the artery being examined, reducing the measurement to a single dimension (average thickness).

Carotid plaques, in contrast, are focal — meaning they occur in specific spots — and they can change in 3 dimensions: thickness, length, and circumferential extent. Carotid plaques grow in the direction of blood flow, and plaque length changes 2.4 times faster than thickness. Plaque volume and area can change measurably within just 3 months, making them highly effective ways to assess whether preventive therapy is working and to guide treatment decisions.

Compared to cIMT, measuring carotid plaque volume using 3D ultrasound reduces the sample size and duration of treatment needed to evaluate new therapies by 2 orders of magnitude (that is, by a factor of 100). Unlike cIMT, carotid plaque burden measured by 3D ultrasound is highly correlated with coronary calcium scores and is predictive of major adverse cardiac events (cardiovascular death, heart attack, and stroke).

Treating Arteries Instead of Risk Factors

Because plaque progression and regression can be measured in real time, a new approach to cardiovascular prevention emerged in 2003, described by the authors as "treating arteries instead of treating risk factors." Instead of simply lowering cholesterol numbers and blood pressure readings on paper, doctors using this approach directly measure whether the plaque inside the arteries is shrinking, stabilizing, or growing — and they adjust treatment accordingly.

This strategy was associated with a more than 80% reduction in the 2-year risk of stroke and heart attack among high-risk patients with asymptomatic carotid stenosis (narrowing of the carotid artery that has not yet caused symptoms). The editorial ends this section with a memorable analogy: "Treating atherosclerosis without measuring plaque would be like treating hypertension without measuring blood pressure."

What the Official Guidelines Say

The editorial notes that official medical guidelines have been moving away from cIMT for some time. The 2013 American College of Cardiology/American Heart Association (ACC/AHA) Guidelines no longer recommend cIMT measurement for cardiovascular risk assessment. The 2016 European Guidelines on cardiovascular disease prevention in clinical practice also dropped cIMT from their recommendations.

Most recently, the 2019 European Society of Cardiology/European Atherosclerosis Society (ESC/EAS) Guidelines for the management of dyslipidemias (abnormal blood fats) explicitly state that cIMT measurement is inferior to coronary artery calcium scoring and carotid plaque detection. These guidelines support the use of ultrasound to assess carotid or femoral (leg) plaque burden as a predictor of cardiovascular events.

For patients who have no plaque at all, the authors suggest that a better alternative to cIMT — and even to coronary calcium scoring — is measurement of 3D vessel wall volume, an advanced ultrasound technique that measures the volume of the artery wall itself.

What This Means for Patients

For patients, this editorial carries several clear takeaways. If you undergo a carotid ultrasound for cardiovascular risk assessment, the presence and quantity of plaque is more meaningful than the thickness of the artery wall. Knowing whether you have plaque — and how much — tells your doctor far more about your future risk of heart attack and stroke than a cIMT number alone.

This is particularly true for older adults, where the editorial's data show that adding cIMT to plaque information does not improve risk detection. For younger patients, cIMT may still offer some added value, but plaque assessment remains the cornerstone.

The ability to measure plaque changes over time also means that treatment can be personalized. If your plaque is shrinking or staying stable on a given treatment, that is a strong signal that the therapy is working. If plaque is growing, your doctor may recommend more aggressive treatment — such as intensifying cholesterol-lowering medication, improving blood pressure control, or emphasizing lifestyle changes like diet, exercise, and smoking cessation.

It is worth asking your doctor whether your carotid ultrasound report includes plaque burden information, such as total plaque area or 3D plaque volume, rather than a cIMT measurement alone. Not all laboratories currently offer advanced 3D plaque assessment, but the authors note that automated methods are coming soon and will make this feasible in any laboratory with modern ultrasound equipment.

Limitations to Keep in Mind

This article is an editorial, not a new research study. It represents the opinions and interpretation of the authors based on their review of existing evidence. Editorials are important in medicine because they synthesize research and guide clinical practice, but they do not provide new patient data.

The authors also have financial relationships with industry. One author (J.D.S.) is a consultant to Amgen and Orphan Technologies, an officer of Vascularis Inc., and has received lecture fees from Pfizer and Bristol-Myers Squibb. Another (H.H.S.) is a consultant to Bayer, Novo Nordisk, and Philips Ultrasound, and has received research grants from Cook Medical and Philips Ultrasound. One author (T.R.) is supported by grants from the National Institutes of Health (NIH) and the Evelyn F. McKnight Brain Institute. These relationships are disclosed in the article so readers can weigh potential conflicts of interest.

Additionally, the primary study that prompted this editorial (Kolkenbeck-Ruh et al.) was a single study with a moderate sample size (473 patients and 479 controls), and its findings — particularly the age-related differences in the value of cIMT — would benefit from replication in larger, diverse populations.

Recommendations for Patients

Based on the evidence presented in this editorial, here is what patients may want to discuss with their healthcare providers:

1. Ask about plaque measurement. If you are having a carotid ultrasound, ask whether the report will include plaque assessment (plaque area, plaque thickness, or 3D plaque volume) in addition to any cIMT measurement.
2. Know your plaque status. If you have been told you have carotid plaque, ask how much and where it is located. A maximum plaque thickness greater than 1.9 mm was associated with a 2.8-fold increased risk of vascular events in the Northern Manhattan Study.
3. Understand that risk is not destiny. Even a high plaque burden does not guarantee a future heart attack or stroke — it is a signal to take prevention seriously.
4. Expect follow-up imaging. Because plaque can change within 3 months, your doctor may recommend repeat ultrasound to see whether treatment is working. This is a feature, not a flaw, of modern care.
5. Focus on proven prevention. The >80% risk reduction seen in the "treating arteries" approach came from intensive medical therapy — including aggressive risk factor management — so continue taking prescribed medications and addressing lifestyle factors.
6. Stay informed about guideline updates. Major guidelines have dropped cIMT from routine risk assessment. If your doctor still orders cIMT alone, a conversation about newer approaches may be worthwhile.

Frequently Asked Questions

What is the difference between carotid intima-media thickness (cIMT) and carotid plaque burden?

cIMT measures the thickness of the two inner layers of the carotid artery wall. Carotid plaque burden measures the actual amount of plaque buildup inside the artery. The editorial concludes that plaque burden is a substantially stronger predictor of heart attack and stroke than cIMT, based on data from over 10,000 patients.

Which is a better predictor of heart attack or stroke: cIMT or plaque burden?

According to the editorial, carotid plaque burden is a substantially stronger predictor of cardiovascular events than cIMT. Evidence from the Northern Manhattan Study, High Risk Plaque BioImage Study, and Tromsø Study supports plaque burden as more predictive, while cIMT was not predictive in some major studies.

Why is measuring carotid plaque burden better than measuring cIMT?

Plaque burden measures actual plaque buildup, while cIMT only indicates wall thickness, which is biologically distinct from plaque. Plaque grows in three dimensions and can change within 3 months, making it easier to track treatment response. cIMT changes only about 0.15 mm per year, making change hard to detect.

What does a carotid plaque thickness greater than 1.9 mm mean for my risk?

In the Northern Manhattan Study, individuals with maximum carotid plaque thickness greater than 1.9 mm had a 2.8-fold increased risk of combined vascular events compared to those without carotid plaque. This means they were nearly three times as likely to experience a heart attack, stroke, or related event.

Can carotid plaque shrink or stabilize with treatment?

Yes, plaque volume and area can change measurably within just 3 months, allowing doctors to see if therapy is working. A 'treating arteries' approach, which adjusts treatment based on plaque changes, was associated with more than an 80% reduction in the 2-year risk of stroke and heart attack in high-risk patients.

Should I ask my doctor for a carotid plaque measurement instead of cIMT?

Yes, ask whether your carotid ultrasound report includes plaque assessment, such as total plaque area or 3D plaque volume. The article notes that guidelines no longer recommend cIMT alone, and plaque burden is more meaningful. Not all labs offer 3D assessment yet, but automated methods are coming.

Does cIMT have any value in younger patients?

The study that prompted the editorial found that in younger patients under 50, adding cIMT significantly improved detection of arterial events (AUC increased from 0.631 to 0.719, P < .0001). However, in older patients over 50, adding cIMT did not improve prediction. Plaque assessment remains the cornerstone for all ages.

Source Information

This patient-friendly article is based on the following peer-reviewed editorial:

• Original title: "Carotid Intima–Media Thickness Versus Carotid Plaque Burden for Predicting Cardiovascular Risk"
• Authors: Kosmas I. Paraskevas, MD, PhD; Henrik H. Sillesen, MD, DMSc; Tatjana Rundek, MD, PhD, FANA; Ellisiv B. Mathiesen, MD, PhD; and J. David Spence, MD, FRCPC
• Journal: Angiology, 2020, Vol. 71(2), pages 108–111
• Publication date: Published online 2019 (DOI: 10.1177/0003319719878582)

The editorial was written in response to: Kolkenbeck-Ruh A, Woodiwiss AJ, Monareng T, et al. "Complementary impact of carotid intima-media thickness with plaque in associations with noncardiac arterial vascular events." Angiology. 2019;71(2):122–130. DOI: 10.1177/0003319719862681.

This patient-friendly article is based on peer-reviewed research. It is intended for educational purposes and should not replace advice from a qualified healthcare professional. Always discuss your individual cardiovascular risk and treatment options with your doctor.