Non-Calcified Coronary Artery Plaque on CT Angiograms: What It Is, How Common It Is, and Why It Matters for Your Heart

Table of Contents

• Key Points
• Understanding the Basics: Why This Research Matters
• What Is Non-Calcified Plaque?
• How This Review Was Conducted
• Key Findings: Non-Calcified Plaque in Patients with Symptoms
• Key Findings: Non-Calcified Plaque in People Without Symptoms
• What This Means for Patients
• Study Limitations
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• Non-calcified plaque is soft, fatty buildup that can rupture and cause heart attacks, even when calcium score is zero.
• CCTA with contrast dye detects non-calcified plaque, unlike standard calcium-scoring CT scans.
• In studies, patients with non-calcified plaque had hazard ratios from 1.6 to 151 for heart events.
• High-risk plaque features like positive remodeling and low-attenuation plaque greatly increase risk.
• Diabetic patients, even young ones with zero calcium scores, often have substantial non-calcified plaque.

Understanding the Basics: Why This Research Matters

Coronary artery disease is widely recognized as a leading cause of death in developed countries. For decades, doctors have used a simple measurement—the coronary artery calcium (CAC) score—to predict cardiovascular outcomes in people without symptoms. This test detects calcified (hardened) plaque on a non-contrast CT scan.

But there is a catch. Calcium is only visible once plaque has been present for a long time. Before plaque becomes calcified, it exists as "non-calcified plaque" (NCP)—a soft, fatty substance that is invisible to traditional calcium-scoring scans. This is where newer technology changes the picture.

Coronary computed tomography angiography (CCTA) is a special type of CT scan that uses intravenous contrast dye to visualize the coronary arteries in detail. Unlike a standard calcium scan, CCTA can distinguish between different types of plaque, including:

• Non-calcified plaque (NCP): Soft, fatty buildup that has not yet hardened
• Calcified plaque: Older, hardened plaque containing calcium
• Mixed plaque: A combination of both soft and calcified components

The most recent American College of Cardiology/American Heart Association (ACC/AHA) guidelines for chest pain assessment have highlighted coronary CTA as one of the first-line tests to evaluate obstructive coronary artery stenosis (narrowing of the arteries). Regardless of how severe the narrowing appears, the overall plaque burden has been linked to poor prognosis in multiple previous reports.

One of the most valuable features of CCTA is its ability to identify high-risk plaque (HRP)—features that suggest a plaque is vulnerable to rupturing. High-risk plaque features include:

• Positive remodeling (PR): The artery wall expands outward to accommodate plaque, which paradoxically makes the vessel look normal on the outside while harboring dangerous plaque inside
• Napkin-ring lesions: A ring-like pattern of higher density surrounding a low-density core, resembling a napkin ring
• Spotty calcification: Scattered small calcium deposits (less than 3 mm in all directions) within a partially calcified plaque
• Low-attenuation non-calcified plaque (LAP): Very soft plaque measuring less than 30 Hounsfield units (HU)—a measure of tissue density on CT scans

What Is Non-Calcified Plaque?

Non-calcified plaque (NCP) is the earliest visible form of coronary atherosclerosis—the disease process that leads to heart attacks. It consists of lipids (fats), inflammatory cells, and connective tissue that accumulate within the artery wall. Because it is soft and fragile, NCP is more prone to rupture than calcified plaque, and a ruptured plaque can trigger a blood clot that blocks blood flow, causing a heart attack (myocardial infarction).

The review's central conclusion is that NCP is the initial precursor of calcified plaque. In other words, every calcified plaque was once a non-calcified plaque. This makes NCP a prominent marker of early coronary atherosclerosis and a critical target for early detection and intervention.

For example, consider the data from the ROMICAT-II trial, one of the key studies analyzed in this review. Patients with significant coronary artery disease (defined as at least 50% stenosis, or narrowing, in a coronary artery) were 34 times more likely to experience an acute coronary syndrome (ACS)—a sudden reduction of blood flow to the heart—during their hospitalization compared to those without significant CAD. When specific high-risk plaque features were examined separately, the relative risks were striking:

• Positive remodeling: relative risk (RR) of 11.1
• Low HU plaque (napkin-ring sign): RR of 8.2
• Spotty calcification: RR of 37.2
• At least one high-risk plaque feature: RR of 32

These numbers mean that patients with these plaque characteristics are many times more likely to experience a cardiac event, independent of how narrow the artery appears on a traditional angiogram.

How This Review Was Conducted

The research team performed a broad, comprehensive review of the current scientific literature pertaining to CCTA and non-calcified plaque in both symptomatic patients (those experiencing chest pain or other symptoms) and asymptomatic patients (those without symptoms). The review also included studies comparing plaque assessment on CT with intravascular ultrasound–virtual histology (IVUS-VH), an invasive imaging technique that uses sound waves to create detailed pictures of the artery wall from the inside.

Initial searches were conducted on the PubMed database using a combination of relevant Medical Subject Headings (MeSH) terms and keywords such as "non-calcified coronary artery plaque," "coronary CT angiogram," "prevalence," and "significance." The search aimed to identify studies published in English without imposing limitations on publication dates.

The inclusion criteria were carefully defined to encompass studies that specifically investigated non-calcified coronary artery plaques as detected by CTA and that provided insights into both their prevalence and clinical relevance. The following types of studies were excluded:

• Reviews (rather than original research)
• Case reports
• Conference abstracts
• Studies lacking essential data

Only peer-reviewed, full-text articles were incorporated to uphold the credibility of the review.

Key Findings: Non-Calcified Plaque in Patients with Symptoms

The review identified seven major studies examining NCP in symptomatic patients, yielding remarkably consistent conclusions about the importance of this plaque type.

Hausleiter and colleagues (2006) analyzed 161 patients and found non-calcified coronary plaques in 48 patients (29.8%). Among these:

• 38 patients (23.6%) also had coronary calcifications
• 10 patients (6.2%) had non-calcified plaques as the sole manifestation of coronary artery disease
• 53 patients (32.9%) had no coronary artery disease at all
• 60 patients (37.3%) had calcifications without non-calcified plaque

Patients with non-calcified plaques exhibited higher total cholesterol, LDL (low-density lipoprotein, or "bad" cholesterol), and C-reactive protein (CRP, a marker of inflammation) levels, along with a trend toward increased diabetes mellitus. Most non-calcified plaques resulted in lumen narrowing of less than 50%, meaning they weren't causing significant blockages—yet they were still present and detectable.

Nance Jr. and colleagues (2012) evaluated 458 patients at low-to-intermediate risk for coronary artery disease presenting with chest pain. During a 13-month median follow-up period, the presence of plaque was associated with higher adverse outcomes. The hazard ratios (HR)—a statistical measure of how much more likely an event is in one group compared to another, where 1.0 means no difference—for each plaque type were:

• Mixed plaque: HR 86.96
• Non-calcified plaque: HR 58.06
• Calcified plaque: HR 32.94

All of these findings were statistically significant (p-values below 0.05). Patients with isolated non-calcified plaque had a significantly higher likelihood of adverse cardiac events at 5% (hazard ratio 151.77, p < 0.01)—meaning their risk of events was drastically elevated compared to patients without plaque.

Liu and colleagues (2017) performed a subgroup analysis on 260 individuals from the ROMICAT-II trial, analyzing segmental coronary plaque on CTA. Among 888 segments with plaque, 391 segments (44%) showed the presence of high-risk plaque features. Segments associated with high-risk plaque had higher total plaque volume, higher low-attenuation plaque volume, higher total plaque burden, and a higher remodeling index. The odds ratio (OR)—the odds that a particular finding is associated with an outcome—associated with low-attenuation plaque was 1.12 (95% CI 1.04–1.21), meaning that each unit increase in low-attenuation plaque volume increased the odds of adverse outcomes by 12%.

Al-Muhaidb and colleagues (2021), in a retrospective study, explored the prevalence of non-calcified plaque in 299 patients with a coronary artery calcium score of zero (CACS = 0). The prevalence of NCP was found to be 6.4% (19 out of 299 patients). Among these patients:

• 52.6% had no stenosis (narrowing)
• 26.3% had less than 25% stenosis
• 21% had 25–50% stenosis
• None had greater than 50% stenosis

A strong association of NCP was noted with male sex, hypertension (high blood pressure), and smoking—with all p-values below 0.005.

Williams and colleagues (2020) conducted a post-hoc analysis of 1,769 patients with stable chest pain from the SCOT-HEART cohort, examining the presence of adverse plaque (positive remodeling and low-attenuation plaque) and its association with outcomes at 5 years. The findings were particularly compelling:

• Primary events (fatal and non-fatal myocardial infarction, or heart attack) were higher in the presence of low-attenuation plaque compared to other plaque types (HR: 1.6, 95% CI: 1.1–2.34, p = 0.014)
• More events were noted in patients with adverse plaque despite having a calcium score below 100 Agatston units, with an HR of 3.38 (CI 1.13 to 10.08, p = 0.03)
• The 41 patients who experienced fatal or nonfatal heart attacks at follow-up had significantly higher low-attenuation plaque burden: 7.5% (interquartile range 4.8–9.2) versus 4.1% (0–6.8) in patients without events (HR of 1.6; 95% CI = 1.1–2.3, p < 0.001)
• The overall presence of a low-attenuation plaque burden greater than 4% increased the likelihood of major adverse cardiovascular events (MACE) by five times in this population (HR, 4.65; 95% CI, 2.06–10.5; p < 0.001)

Osborne-Grinter and colleagues (2022) analyzed the same SCOT-HEART cohort and focused specifically on patients with a calcium score of zero, which was seen in 36% of patients (529 out of 1,769). Among these zero-calcium patients:

• 14% had non-obstructive coronary artery disease
• 2% had obstructive coronary artery disease
• 2% had visually apparent adverse plaque
• 13% had a low-attenuation plaque burden greater than 4%

At follow-up, 10% of the total reported heart attacks (4 out of 41) were found solely in the zero-calcium-score group. This is a crucial finding: a calcium score of zero provided false reassurance for these patients who subsequently had heart attacks.

Villines and colleagues (2011) evaluated 10,037 symptomatic patients without known coronary artery disease from the CONFIRM registry and identified 51% of patients (5,128) with a calcium score of zero. In this group:

• 84% had no underlying coronary artery disease
• 13% were diagnosed with non-obstructive non-calcified plaque
• 3.5% had luminal stenosis greater than 50%
• 1.4% had luminal stenosis greater than 70%

In patients diagnosed with non-calcified plaque, when more than 50% stenosis was identified (which occurred in 3.9% of cases), the risk of adverse events was significantly higher, with a hazard ratio of 5.7 (confidence interval: 2.5–13.1, p < 0.001). This means these patients were nearly six times more likely to experience adverse events compared to those without obstructive plaque.

Notably, a receiver–operator characteristic (ROC) curve analysis demonstrated that there was no significant additional prognostic value in incorporating the coronary artery calcium score when compared to assessing the extent of non-calcified plaque on CCTA for predicting composite endpoints. In other words, the CCTA findings alone were just as predictive as combining them with calcium scoring.

Key Findings: Non-Calcified Plaque in People Without Symptoms

The review also examined multiple studies observing NCP prevalence in asymptomatic patients—individuals with no chest pain or other warning signs of heart disease.

Rodriguez and colleagues (2015) examined 202 asymptomatic patients over 55 years old who were eligible for statin therapy. The study found that male sex was associated with a significantly higher total plaque index compared to women (42.06 mm² ± 9.22 versus 34.33 mm² ± 8.35; p < 0.001). The non-calcified plaque index was positively correlated with several risk factors:

• Elevated LDL levels: an increase of 0.04 mm² per mg/dL (p = 0.02)
• Elevated systolic blood pressure: an increase of 0.80 mm² per 10 mmHg (p = 0.03)
• Diabetes mellitus: an increase of 4.47 mm² (p = 0.03)

Nezarat and colleagues (2017) studied patients younger than 40 years old, comparing those with type II diabetes (86 patients) to age- and gender-matched non-diabetic controls (95 patients). Both calcified plaque and non-calcified plaque were elevated in diabetic patients compared to non-diabetics (19% vs. 58%; p < 0.001). Despite having a calcium score of zero, patients with diabetes had a higher prevalence of non-calcified plaque (46%, p < 0.0001). On quantitative plaque assessment, all volumes in the non-calcified plaque type were threefold higher in the presence of diabetes. This demonstrates that even young diabetic patients with no detectable calcium can have substantial soft plaque burden.

Kral and colleagues (2014) evaluated healthy patients with a family history of premature coronary artery disease using dual-source CT. A higher total plaque burden was identified in men versus women (57.8% vs. 35.8%, p < 0.0001). The non-calcified plaque volume constituted most of the total plaque volume—accounting for more than 70% of plaque in men and more than 80% of plaque in women. The study also found that NCP volume increased with age (p < 0.001) and was higher in men than women (p < 0.001), but as a percentage of total plaque, NCP was inversely related to age (p < 0.01)—meaning that younger patients' plaques are relatively softer and more vulnerable.

Cho and colleagues (2013) evaluated 4,491 asymptomatic patients with zero calcium scores who underwent CCTA as part of a general health evaluation. Non-calcified plaque was found in 7% of these patients (313 patients). The study revealed that age, male gender, diabetes mellitus, hypertension, and dyslipidemia (abnormal blood fats) were significantly associated with the presence of NCP (all p-values < 0.05). However, during follow-up of the 313 patients with NCP matched with patients without NCP, no difference in all-cause death or composite outcomes (cardiac death, heart attack, unstable angina requiring hospitalization, and revascularization) occurred after 90 days from the index CCTA in either group. This suggests that the short-term prognosis for these patients was reassuring.

Lee and colleagues (2013) assessed a cohort of 8,668 asymptomatic patients, including 6,531 with zero calcium scores, and identified non-calcified plaque in 6.75% (441 patients). During a mean follow-up of 26.4 ± 14.4 months, all cardiac events (death, acute coronary syndrome, or subsequent revascularization)—which occurred in only 0.18% of patients (12 patients)—occurred in patients with NCP who also had lower mean CT attenuation values (softer plaque) and a higher remodeling index. In other words, among all the asymptomatic patients with zero calcium scores, the few who experienced cardiac events were those whose non-calcified plaque had particularly dangerous characteristics.

Yang and colleagues conducted a retrospective, long-term follow-up study aimed at assessing the progression of coronary plaque and its influence on cardiac events among asymptomatic individuals with diabetes mellitus. In a cohort of 197 patients, with an average age of 63.1 years and 60% being male, and a median follow-up duration of 41.8 months, the study observed that:

• Patients with a calcium score greater than 10 exhibited an increase in the volume of densely calcified coronary calcium
• Patients with a calcium score of 10 or lower showed a more significant increase in the volume of low-attenuation ("lipid-rich") plaque components between successive CCTA scans
• The presence of a calcium score greater than 10 was an independent predictor of cardiac events
• The extent of plaque volume increase was associated with subsequent cardiac events
• Interestingly, the level of coronary calcification appeared to have an inverse relationship with outcomes in asymptomatic diabetic patients—meaning less calcification was paradoxically associated with worse outcomes, likely because softer plaque is more prone to rupture

Jin and colleagues evaluated the characteristics and predictors of subclinical coronary atherosclerosis and cardiac events in 914 asymptomatic young adults. Non-calcified plaque was the most common type of plaque in these young adults and was identified in 6.9% of the population. Among the 46 subjects (5.3% of the cohort) who had subclinical coronary atherosclerosis:

• 29 subjects had a calcium score of 0
• 17 subjects (42.5%) had a calcium score greater than 0

Multivariate analysis revealed a hazard ratio of 2.2 for subclinical coronary atherosclerosis, and non-calcified plaque accounted for 49.17% of cases. This confirms that even in young people, NCP is the predominant form of early heart disease.

Yoo and colleagues evaluated the presence of plaque, plaque characteristics, and calcium scores in 7,515 asymptomatic subjects. When comparing individuals with a calcium score of 0 to those with a low calcium score, the study observed:

• Notably higher prevalence of non-calcified plaque in the low-calcium-score group: 31.5% versus 6.9% (p < 0.001)
• Independent factors predictive of significant NCP in the low-calcium-score group included diabetes mellitus, hypertension, and elevated LDL levels (all p-values < 0.05)
• Over a median follow-up period of 42 months, individuals in the low-calcium-score group experienced a significantly higher rate of cardiac events compared to those in the zero-calcium-score group: 2.6% versus 0.27% (p < 0.001)

This demonstrates that even "low" calcium scores carry meaningful risk when accompanied by non-calcified plaque.

What This Means for Patients

The findings of this comprehensive review carry several important messages for patients.

A calcium score of zero does not mean your arteries are clear. Across multiple studies, between 4% and 7% of patients with zero calcium scores were found to have non-calcified plaque on CCTA. In the SCOT-HEART cohort, 10% of all heart attacks occurred in patients with zero calcium scores. This means that relying solely on a calcium score may give false reassurance, particularly in patients with symptoms or with risk factors such as diabetes.

Non-calcified plaque is dangerous precisely because it is soft. The studies consistently showed that low-attenuation (very soft) plaque and positive remodeling—both features of non-calcified or mixed plaque—were the strongest predictors of future heart attacks. As the ROMICAT-II data showed, spotty calcification carried a relative risk of 37.2, and having any high-risk plaque feature carried a relative risk of 32. This is because soft, lipid-rich plaque is more likely to rupture than hard, calcified plaque.

CCTA provides actionable information that calcium scoring alone cannot. The Villines study found that the extent of non-calcified plaque on CCTA had equivalent predictive value to combining it with calcium scoring. This supports the growing role of CCTA as a first-line imaging test for evaluating chest pain and, increasingly, for assessing cardiovascular risk in select asymptomatic patients.

A "low-risk" calcium score may still warrant attention. The Yoo study found that even patients with low (not zero) calcium scores had a cardiac event rate of 2.6% during a median of 42 months, compared to 0.27% in the zero-calcium group. And the Williams study found that patients with adverse plaque features and calcium scores below 100 still had a hazard ratio of 3.38 for future events.

Diabetes is a particularly important risk factor for NCP. The Nezarat study found that diabetic patients younger than 40 had a 46% prevalence of non-calcified plaque even with zero calcium scores, with all plaque volumes threefold higher than non-diabetics. The Yang study showed that diabetic patients with lower calcium scores had more dangerous lipid-rich plaque progression than those with higher scores.

Study Limitations

Several limitations of this review and the underlying studies should be acknowledged.

First, this is a systematic review of existing literature rather than a single prospective trial. The individual studies varied in their patient populations, imaging protocols, definitions of non-calcified plaque, and lengths of follow-up, which makes direct comparisons between studies challenging.

Second, many of the studies were retrospective in design, including the Al-Muhaidb, Cho, Lee, and Yang studies. Retrospective studies can have selection bias and unmeasured confounding factors.

Third, the review included studies with relatively short follow-up durations in some cases. For example, the Cho study followed patients for only 90 days after their index CCTA, which may not be long enough to capture cardiac events that take years to develop.

Fourth, the review excluded non-English-language studies, case reports, conference abstracts, and gray literature, which could introduce publication bias.

Fifth, CCTA itself has limitations. It involves radiation exposure and intravenous contrast dye, which carries risks including allergic reactions and kidney injury in susceptible patients. Additionally, while modern CCTA has high accuracy, it can still miss very small plaques or provide suboptimal image quality in patients with fast heart rates or irregular rhythms.

Finally, while the presence of non-calcified plaque strongly predicts cardiovascular risk, the review cannot establish that screening for NCP in asymptomatic patients improves long-term outcomes. Randomized controlled trials of CCTA-guided management strategies are needed to confirm this benefit.

Recommendations for Patients

Based on the findings of this review and current guidelines, here are actionable recommendations for patients:

1. If you have chest pain or other cardiac symptoms, ask about CCTA. The ACC/AHA guidelines now recommend coronary CTA as a first-line test for evaluating obstructive coronary artery disease in patients with chest pain. CCTA can detect both narrowings and plaque characteristics that predict risk.
2. Do not assume a calcium score of zero means no heart disease. If you have symptoms, multiple risk factors, or a strong family history of premature heart disease, ask your doctor whether a CCTA would provide additional information beyond a calcium score.
3. If you have diabetes, be especially vigilant. The data show that diabetic patients, even young ones with zero calcium scores, can harbor substantial non-calcified plaque. Aggressive risk factor management is critical.
4. Address modifiable risk factors identified in these studies. The studies consistently linked high LDL cholesterol, high blood pressure, smoking, and diabetes to the presence and progression of non-calcified plaque. Work with your doctor to control these factors through lifestyle changes and medications such as statins.
5. Understand the concept of "vulnerable plaque." Not all plaque is created equal. If your CCTA report mentions high-risk features such as positive remodeling, low-attenuation plaque, napkin-ring lesions, or spotty calcification, these findings warrant serious attention and aggressive medical therapy—even if the blockages themselves are not severe.
6. Static imaging is a snapshot, not a final verdict. Plaque is dynamic. With appropriate treatment—particularly statin therapy, blood pressure control, and lifestyle modification—plaque can stabilize or even regress. Early detection of non-calcified plaque creates an opportunity to alter the disease's evolutionary course, potentially preventing future heart attacks.

The review's authors emphasize that by detecting non-calcified plaque during early stages, several medical measures can be implemented that can alter the trajectory of the underlying disease. This can potentially lead to a lower incidence of major adverse cardiovascular events.

If you have concerns about your heart disease risk, particularly if you have symptoms, diabetes, or a family history of early heart disease, ask your healthcare provider whether a CCTA might provide a more complete picture of your cardiovascular health than a calcium score alone.

Frequently Asked Questions

What is non-calcified plaque?

Non-calcified plaque is soft, fatty buildup inside coronary artery walls. It is the earliest visible form of atherosclerosis and can rupture, triggering heart attacks. Unlike calcified plaque, it is invisible on standard calcium-scoring CT scans, but coronary CT angiography with contrast dye can detect it.

What is CCTA and how is it different from a calcium score?

CCTA is a CT scan using intravenous contrast dye to see coronary arteries in detail. It can distinguish non-calcified, calcified, and mixed plaque. A standard calcium score only detects calcified plaque, which appears later. CCTA can show soft, dangerous plaque that calcium scoring misses.

If my calcium score is zero, does that mean I have no heart disease?

No. Studies show between 4% and 7% of patients with zero calcium scores still have non-calcified plaque on CCTA. In one large study, 10% of all heart attacks occurred in patients with zero calcium scores. A zero calcium score can give false reassurance, especially with symptoms or diabetes.

What are high-risk plaque features on CCTA?

High-risk plaque features include positive remodeling (artery wall expands outward), napkin-ring lesions, spotty calcification, and low-attenuation non-calcified plaque. These features make plaque vulnerable to rupturing. In one trial, having any high-risk feature carried a relative risk of 32 for acute coronary syndrome.

How much more likely are heart attacks with non-calcified plaque?

Risk varies by plaque characteristics. In studies, hazard ratios ranged from 1.6 to over 151. For example, in one study, patients with non-calcified plaque had a hazard ratio of 58 for adverse events, while those with high-risk features had relative risks up to 37 for spotty calcification.

I have diabetes. Should I be especially concerned about non-calcified plaque?

Yes. One study found diabetic patients under 40 had 46% prevalence of non-calcified plaque even with zero calcium scores, with plaque volumes threefold higher than non-diabetics. Another study showed diabetic patients with low calcium scores had more dangerous lipid-rich plaque progression. Diabetes is a major risk factor for soft plaque.

What should I do if I have chest pain or high risk factors?

Ask your doctor about CCTA. Current guidelines recommend it as a first-line test for chest pain evaluation. If you have diabetes, multiple risk factors, or a family history of early heart disease, CCTA may provide more information than a calcium score alone. Address LDL, blood pressure, smoking, and diabetes with your healthcare team.

Source Information

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

Original Title: Non-Calcified Coronary Artery Plaque on Coronary Computed Tomography Angiogram: Prevalence and Significance

Authors: Bandar Alyami, Matthew Santer, Karthik Seetharam, Dhivya Velu, Eswar Gadde, Bansari Patel, and Yasmin S. Hamirani

Journal: Tomography, 2023, Volume 9, Pages 1755–1771

DOI: 10.3390/tomography9050140

Publication Date: September 20, 2023

Type of Article: Systematic review

This article was published under the Creative Commons Attribution (CC BY) license and may be freely shared and adapted with appropriate citation. The patient-friendly summary above maintains all numerical data, statistical findings, and conclusions from the original source while translating technical terminology into accessible language for patients and their families.