Arterial Plaque 101

What is arterial plaque

Plaque is the term used to describe the gradual build-up of fatty and inflammatory material within the walls of an artery over time. This process, known as atherosclerosis, is the underlying cause of angina and heart attacks when plaque narrows or blocks the arteries supplying the heart.

Although this resource focuses on atherosclerosis affecting the arteries of the heart, it is important to recognise that it is a disease of the arteries throughout the body. When plaque reduces blood flow to the legs, it can cause claudication (pain in the legs during walking). When it affects the arteries supplying the brain, it can lead to a stroke or transient ischaemic attack (TIA).

Atherosclerosis does not develop overnight. It progresses slowly over many years, often decades, but can develop more rapidly in people with diabetes, high blood pressure, high cholesterol, tobacco exposure (including smoking), chronic inflammatory diseases, or a family history of premature heart attack or stroke.

Over the last few decades our understanding of atherosclerosis, also known as atherosclerotic cardiovascular disease (ASCVD), has evolved. ASCVD of the heart arteries is called coronary artery disease (CAD). What was once viewed as a simple “cholesterol buildup problem” is now understood as a dynamic biological process involving inflammation, lipid biology, and time-dependent structural changes. We use ‘soft’ to describe plaque that is more actively inflamed and vulnerable to rupture. ‘Hard’ plaque is more fibrous or calcified and represents the body’s attempt to heal these inflamed areas. 

To be a bit more technical, in the earliest stages of ASCVD the inner lining of the arterial wall (endothelium) becomes damaged by exposure to excessive cholesterol esters (specifically, oxidized low-density lipoprotein / LDL), reactive oxygen species (as found in air pollution, cigarette smoke, and radiation) and inflammation. ASCVD begins as fatty streaks composed of macrophages (inflammatory cells) that have scavenged excess cholesterol from the body. As the body attempts to ‘heal’ the arterial wall, these streaks progress to more complex structures with a collagen, elastin and proteoglycan cap covering a ‘core’ of cholesterol, lipids and dead cells. Further progression of these lesions leads to calcium deposition which is where the term ‘hardening of the arteries’ comes from. 

Key ideas

Atherosclerosis (plaque in the arteries) is a buildup of:

• Cholesterol (especially ApoB-containing particles like LDL)

• Immune cells (inflammation)

• Fibrous tissue

• Calcium deposits (in later stages)

What’s the difference between asymptomatic and symptomatic ASCVD

This process of plaque formation occurs over decades. We consider diseases like diabetes, hyperlipidemia (high cholesterol), and hypertension (high blood pressure) as ‘silent killers’ because of their role in the development and acceleration of atherosclerotic plaque.

Asymptomatic screening:

In patients with borderline or moderate risk of developing ASCVD, we use methods to detect existing plaque to help drive decisions about when to start lipid lowering therapy (e.g., statins) or when to intensify therapy.

Symptomatic patients:

ASCVD can become symptomatic in one of two ways. 

1. Ischemia: If enough plaque builds up to impede the blood flow through an artery, the tissue supplied by that artery may not receive enough blood flow and become ischemic. Generally, ASCVD lesions do not limit blood flow until they create a narrowing >70%. In the heart this ‘ischemia’ typically becomes evident during exercise since the heart muscle demands more oxygen during physical activity. Symptomatic ischemia to the heart muscle (angina) typically presents as exertional chest tightness, pressure or pain. 

2. Infarction: A myocardial infarction (heart attack) typically occurs when a non-obstructing plaque ruptures and acutely occludes (obstructs) the flow of blood. A rupture event is often what triggers clot formation and suddenly blocks an artery causing a heart attack. This acute lack of blood flow deprives the muscle cells of oxygen and can cause permanent damage, which is why acute heart attack symptoms require emergent treatment to restore blood flow.

Key points

• Diabetes, high blood pressure, and high cholesterol lead to acceleration of plaque formation.

• ASCVD typically exists without symptoms for decades before it is recognized.

• If the plaque build up in an artery impedes blood flow (>70% narrowing), it can cause ischemia (angina).

• A heart attack occurs when a plaque ruptures and a clot forms in the artery and suddenly blocks flow.

Soft plaque (non-calcified plaque)

What it is

Soft plaque, also called non-calcified plaque, is the earlier, more biologically active form of atherosclerosis.

It contains:

• Lipid-rich “fatty” material

• Macrophages (inflammatory immune cells)

• A fibrous cap (composed of collagen and other proteins)

Key ideas

• Soft plaque tends to be more biologically active and less stable than hard plaque.

• It is associated with acute events like heart attacks when it ruptures.

• In asymptomatic patients, soft plaque quantification hasn’t shown benefit. 

• What matters most is managing the underlying drivers, such as high-blood pressure, lipids (e.g., ApoB, LDL), toxin exposure (e.g., stop smoking) and inflammation.

• In general, the thinner the fibrous cap, the greater the risk that a plaque will rupture. Statins and other cholesterol-lowering therapies help stabilize plaque by reducing its lipid-rich core and strengthening the fibrous cap. While plaque is not "scrubbed away," treatment can shrink softer plaques and make them less likely to rupture, reducing the risk of heart attack.

Hard plaque (calcified plaque)

What it is

Hard plaque is plaque that has undergone calcification, meaning calcium has been deposited into the lesion over time. This is what shows up on a coronary artery calcium (CAC) scan. Arteries with no calcified plaque will have a CAC of 0. 

Key ideas

• Hard (calcified) plaque is not harmless; it is a marker of long-term cumulative exposure to risk factors. It’s often thought of as the 'scar tissue' of atherosclerosis.

• While hard plaque is less acutely dangerous than soft plaque because the ‘hard’ fibrous cap is less likely to rupture, its presence is a marker of the extent of ASCVD or CAD. 

• Since hard and soft plaque exist together, the amount of hard plaque is an excellent gauge for the risk of a heart attack.

The evolving medical view: from “cholesterol clogging pipes” to a dynamic disease

Old model (mid-20th century)

Doctors once viewed atherosclerosis as cholesterol slowly clogging arteries like rust in a pipe.

Focus was mostly on:

• Total cholesterol

• Surgical (bypass) or percutaneous (stent) intervention when blockage was severe.

Modern understanding (1990s–today)

While we still use bypass and stents when blockage is severe, the view has shifted dramatically. Atherosclerosis is now seen as a chronic inflammatory and lipid-driven process where plaques evolve over time from soft, lipid-rich lesions into more fibrotic and calcified structures.

Key additions to this model:

• LDL particles (especially ApoB-containing particles) enter artery walls

• Immune system reacts, leading to inflammation

• Elevated lipoprotein a / Lp(a) levels are now recognized as an independent risk marker

• Plaques form and evolve

• Some become calcified (generally more stable), others remain soft (generally more risky).

Measuring plaque

The most widely used test for detection of asymptomatic ASCVD is cardiac CT scan to measure coronary artery calcium (CAC) score.

This is:

• Fast

• Low radiation

• Inexpensive (though not usually covered by insurance)

• Widely available

• Predictive of long-term cardiovascular risk and overall plaque burden

• Validated in large population studies and incorporated into major international cardiovascular prevention guidelines to help diagnose coronary artery disease and guide treatment decisions.

It measures:

• ONLY calcified (hard) plaque

• A CAC of 0 does not indicate absolute freedom from ASCVD

• Patients with a CAC of 0 still need to manage their cardiovascular risks to prevent onset or progression of disease.

A CAC score of:

• 0: no detectable calcified plaque

• 1–99: low plaque burden

• 100-299: moderate plaque burden

• 300-999: increasing plaque burden

• 1,000+: high plaque burden.

Once a patient has a coronary artery calcium (CAC) score greater than 0, the diagnosis of coronary artery disease (CAD) is established. This finding is used to guide treatment, including starting or intensifying LDL cholesterol-lowering therapy.

Once calcium is present, repeating the CAC score is generally not clinically useful. As plaque responds to treatment, it often becomes more stable through a healing process that includes calcium deposition. As a result, the CAC score may increase over time even as the risk of plaque rupture decreases. An increasing CAC score therefore does not necessarily indicate worsening disease or treatment failure.

Soft plaque is harder to measure and requires more detailed imaging:

1. Coronary CT angiography (CCTA)

   • Visualizes both calcified and non-calcified plaque

   • Can detect narrowing and plaque composition

   • Newer AI-powered plaque analysis (e.g., Cleerly, Heartflow) can quantify soft plaque with a thin cap. In patients with chest pain this analysis is used to drive intensification of therapy. 

   • In a small subset of patients with markedly elevated Lp(a) and a CAC of 0, detection of soft plaque may be beneficial to drive more intensive lipid lowering therapy.

2. Intravascular ultrasound (IVUS)

   • Very detailed

   • Invasive (catheter-based)

   • Used in specialized clinical cases to assist in decision to place stents

3. Optical coherence tomography (OCT)

   • Extremely high resolution

   • Also invasive

   • Also useful to determine when and where to place a stent

Key ideas

• Coronary artery calcium (CAC) score is useful to detect ASCVD in asymptomatic patients.

• Hard plaque (as detected by CAC >0) predicts risk of heart attack because hard and soft plaque co-exist within the same arteries.

• A CAC over 0 indicates coronary artery disease (CAD) and warrants lipid lowering therapy and lifestyle modification to prevent heart attack and stroke.

• Serial measurement of CAC is generally not clinically useful.

• In selected patients at moderate risk of ASCVD who have a CAC of 0, CCTA may be useful to detect soft plaque.

Understanding your personal risk of ASCVD

For Asymptomatic Patients, Measuring Soft Plaque Usually Doesn't Change Treatment

For most asymptomatic people, the difference between a high soft plaque burden and a high calcium score has little impact on treatment. The presence of plaque, whether calcified or soft, indicates atherosclerosis, and the focus remains on reducing overall cardiovascular risk with lifestyle changes and appropriate medical therapy.

As of 2026, non-invasive measurement of soft plaque has primarily been shown to help guide treatment decisions in patients with symptoms or known coronary artery disease. It has not yet been shown to improve heart attack risk prediction beyond established clinical risk assessment in asymptomatic individuals.

To estimate an individual's risk of heart attack or stroke, clinicians use validated risk calculators such as the American Heart Association's PREVENT™ risk calculator, together with clinical judgment. These tools incorporate factors including:

• Age

• Diabetes

• Gender

• Hyperlipidemia (cholesterol level)

• Hypertension (blood pressure) 

• Kidney function

• Smoking status

• Obesity

Clinicians may also consider additional prediction-enhancing factors that are not fully captured by risk calculators, including:

• Elevated high-sensitivity C-reactive protein (hsCRP)

• Elevated lipoprotein(a) / Lp(a)

• Family history of premature cardiovascular disease

• Presence of chronic inflammatory diseases (such as HIV, lupus, rheumatoid arthritis, , psoriasis, or HIV)

• South Asian ancestry

• Other conditions associated with increased cardiovascular risk

Bottom line

• Soft plaque is earlier, more biologically active, and more likely to trigger acute events.

• Hard plaque is generally more stable but reflects accumulated long-term disease.

• Both soft and hard plaque are part of a single evolving disease process, not separate conditions.

• Because soft plaque and hard plaque occur together, hard plaque is an excellent marker of risk for acute events. 

• At present, quantification of soft-plaque is not clinically useful in asymptomatic patients.

• For prevention of heart attacks and strokes, risk factor modification (such as eating a healthy diet, maintaining a healthy weight, managing blood pressure & blood sugar, regular cardiovascular exercise, and smoking cessation) remains the key.

• For patients at intermediate or high risk (or those with known ASCVD), lipid lowering therapy is the cornerstone to stabilize soft plaque to prevent rupture and acute coronary events. 

This content is for general informational purposes only and is not medical advice. Talk with your healthcare provider before making any decisions about your health.