Carotid Artery Ultrasound and Longevity

The opposite of longevity is death. If longevity is what we seek we must obsess about death, and those things that increase the risk of us dying.

#1 Killer – Cardiovascular Disease

Cardiovascular disease is the biggest killer on the block claiming the lives of 1 in every 3 people worldwide. Almost 1 million people a year die from cardiovascular disease in the United States alone, often due to events like heart attacks and strokes. The main cause of cardiovascular disease is atherosclerosis.

Atherosclerosis

Thickening and hardening of the artery walls caused by the deposition of plaque (made of cholesterol, fats, other materials) into the blood vessel walls. Plaques can slowly grow causing occlusion of a blood vessel (stenosis). Plaques can also rupture, leading to blood clots (ischemic heart attacks, strokes, and other infarctions). Plaques can also break away from the walls, forming emboli (also causing ischemic heart attacks, strokes, and other infarctions).

Infarction: Obstruction of blood supply to an organ or region of tissue (usually from a blood clot or embolis)

Thickening of blood vessel walls, plaques, and restriction of blood flow can all be visualized using Carotid ultrasound. In the body, if blood vessel disease (e.g. atherosclerosis) is seen at one area, it is likely present in other areas as well. As such:

Carotid Ultrasound is a very important Longevity Metric. This non-invasive imaging modality gives us important information about a person risk for strokes, heart attacks, and death. Several studies have demonstrated an increased risk of death (mortality risk) if atherosclerosis, plaques, or impaired blood flow are present on carotid ultrasound exam.

Carotid Arteries

The carotid arteries are large blood vessels on both sides of the neck that supply blood to the brain (internal carotid) and face (external carotid). About 15% of the blood pumped from the heart go through these arteries. Essentially each side of the Artery forms a Y. The common carotid can be seen at the base of the neck. As you move up toward the neck, the carotid gets wider forming a bulb. This bulb then splits into the internal and external branch. Blood vessel, heart, and brain health are tightly linked to Carotid blood vessel health. Due to the proximetry of the Carotid blood vessels to the surface of the neck, they can be visualized with a high degree of resolution with ultrasound! If longevity is your goal, Carotid Ultrasound is something you are not going to want to miss.

Ultrasound

Imaging study that uses sound waves to recreate an image. This is possible because sound waves reflect at different intensities when they hit tissues made of different materials. So the probe sends out sound waves. Those sound waves get reflected and the probe picks up these sound reflections. An image is then created based on this. Ultrasound is based on the same principles used in echolocation (whales and bats) as well as sonar (mapping the surface of the ocean, looking for fish in the sea, and planes in the sky). That is, bouncing sound off objects and measuring what comes back. Additionally, due to something called the doppler effect, the velocity and flow of blood can also be measures using carotid duplex ultrasound. Pretty incredible! Ultrasound is the most dynamic imaging modality available. And, it does not require the use of any ionizing radiation.

What Is Seen/Can Be Measured on Carotid Duplex Ultrasound

Crisp/Clean Images of the Carotid Arteries

The Carotid blood vessels can be seen very clearly from the base of the neck (just above the clavicle) to the skull. As these blood vessels are so close to the surface, beautifully clear images can be obtained. The common carotid artery, bulb, internal, and external carotid arteries can all be clearly visualized.

Intima-Media Thickness

Blood vessels walls have 3 layers. The thickness of the middle (tunica media) and inner  (tunica intima) layers can be measured with ultrasound. This is typically done 1 cm before the bulb on the posterior (deepest) wall of the artery. A normal Intima-Media thickness depends a bit on age (gets thicker with age), but < 1mm is generally considered normal. In my practice I uses a cutoff of <0.8 for normal. However, for younger individuals, <0.6mm may be more ideal.

Resistance Index

The velocity of the flow of blood can be measured using ultrasound. This can be done in all 3 carotid vessels, but is most often performed in the common carotid artery as it is the easiest. Blood flow velocity increases when the heart beats and decreases when the heart relaxes. The difference in blood flow between peak systole (heart beating), and end-diastole (heart relaxing) can be used to calculate a resistance index based on the following equation.

Resistance Index = (Peak systolic velocity – End Diastolic Velocity)/Peak Systolic Velocity

Resistance index shows how much resistance there is to blood flow both distally (to the brain) and proximally (from the aorta). Increased resistance can be a sign of blood vessel disease and is associated with an increased risk of things like hypertension and stroke-risk). A normal resistance index is typically between 0.55 and 0.8. Some studies report and upper limit of normal of 0.7. Numbers > 0.7 show elevated resistance (hypertension, increased risk of stroke, harder to pump blood to the brain). Numbers <0.55 demonstrate a reduced resistance index (typically from arteriovenous malformation and increased blood volume).

Soft and Calcified Plaques

When enough deposit (of fat, cholesterol, and other materials from atherosclerosis) builds up in the artery of the wall, it starts to protrude into the blood vessel tube (lumen). This can be visualized and measured on ultrasound as a plaque. Plaques can be soft or hard. Hard plaques have been stabilized with calcium. Hard plaques can be visualized well with xray technologies. Ultrasound can see both hard and soft plaques very well. The number of plaques, particularly soft plaques, I am seeing in 20 and 30 years olds at Longetrics is alarming (almost everyone). Prevalence for plaques has been estimated at 21% of people aged 30-79 in large meta-analyses. I suspect that plaque prevalence is skyrocketing and now much higher than this, largely driven by the epidemic of poor metabolic health. Because of the blood flow dynamics present around the carotid artery bulb, plaques in this area are perhaps the most common. Thinking about a river helps me understand this. The parts of the river with the most turbulent water flow, experience the most erosion (damage).

Stenosis (blockage of the artery)

As the blood vessel wall thickens and plaques grow, they can start to literally take over the entire lumen (opening) of the blood vessel and cause restriction of blood flow (stenosis). This can be seen visually on ultrasound. As stenosis gets worse, velocity of blood flow around it goes up. Just think about how a narrowing in a river can increase the velocity of water flow to increase causing a local rapid (white water). So blood flow velocity around a stenotic plaque lesion can be measured. If no flow is present, the blood vessel is completely blocked. As blood flow velocity increases, it demonstrates worsening of stenosis, until complete occlusion occurs and velocity goes to 0.

Common Sense Perspective

The idea that a carotid artery ultrasound would be an important marker of longevity makes a lot of sense. Cardiovascular disease is the number 1 cause of death worldwide. We all have experienced this with our deceased loved ones. The ultrasound study allows for the direct visualization of a major blood vessel and the ability to see if vascular disease is present. If blood vessel disease is seen in the Carotid, it is likely present in other blood vessels as well. If you see cockroaches in the kitchen, it’s a safe bet that they are also in the walls, garage, and other areas of the house.

Clinical Perspective

Heart attacks and strokes are very common serious adverse clinical events and causes of death. I see them in the hospital and in the clinic all the time. We know things like hypertension, elevated atherogenic levels of cholesterol (ApoB, LDLc), and metabolic disease are major risk factors for serious adverse cardiovascular events. The reason these problems lead to heart attacks and strokes is due to blood vessel damage. This blood vessel damage can be directly visualized using Ultrasound. So Carotid ultrasound allows us to directly see how much damage has been done to the blood vessel. Therefore, from a clinical persective, Carotid Artery Ultrasound seems very important. In fact, evaluated the carotid arteries with imaging is part of the stroke workup standard of care. We know putting hairs down the drain, increases the risk of a drain pipe getting blocked. But the only way to see how much damage/blockage is present, is to take a camera and visualize the inside of the pipes directly. US gives us that direct visualization.

Research Perspective

More than 1000 clinical research trials, looking at well over 1 million patients combined have investigated carotid ultrasound findings and mortality. These include a variety of study designs including cohort studies (many prospective), observational trials, and meta-analyses in multiple different countries. The finding are clear, consistent, and graded. The below findings on carotid ultrasound have demonstrated and increased cardiovascular mortality and all-cause mortality :

-              Increased intima-media thickness

-              The presence of plaque

-              Narrowing and dilation of the carotid arteries

Wow! And as thickness, plaque burden, and stenosis so does mortality (risk of dying). Let's look at these individually.

Increased intima-media thickness (IMT)

Earliest sign of atherosclerosis and plaque formation. As such the link with all-cause mortality not as strong as the other findings listed above. But the increased risk is present even after adjusting for other findings linked to cardiovascular disease (e.g. increased blood pressure). Lorenz et al (2007 – Circulation) is one of many studies demonstrating and increased risk of heart attacks, strokes, cardiovascular mortality, and all cause mortality. This study showed that for each 0.1mm increase in IMT the relative risk of heart attack and stroke, increased by 1.26 and 1.32 respectively. So it predicted stroke the best.

Presence of Plaque

The presence of plaque is a later stage finding of atherosclerosis than IMT. Studies indicate it is a better and more accurate predictor of cardiac, stroke, and all-cause mortality than IMT. In various studies, hazard ratios for all cause mortality were between 1.6 and 2.8 (60 to 180% risk increase of death). The higher the plaque burden the greater the risk of badness

Narrowing and Dilation of the Carotid Artery

Same story. Strong predictor of stroke. Predictor of heart attack and all cause mortality as well. See studies below in the references.

Increased Resistance Index

There no robust data demonstrating increased all-cause mortality with increasing RI. But the link between increased RI, other cardiac risk factors, end organ damage from vascular disease, and increased risk of cardiovascular death is well established. See the Quiles et al. study cited below.

Conclusions

-              Cardiovascular disease is the leading cause of death

-              Findings on carotid artery US including increased IMT, plaque burden, stenosis, and dilation are strongly associated with increased risk of stroke, heart attack, and death.

-              Carotid artery ultrasound is relatively easy to perform, non-invasive, and provides important information about a persons future longevity, above and beyond standard cardiovascular risk factors like hypertension and elevated levels of atherogenic cholesterol (ApoB)

-              Carotid Artery Ultrasound is a very important Longevity Metric.

-              The amount of young people I am seeing with plaques in the carotid artery are much much higher than previously reported prevalence of 21% (more like 90%).

-              If longevity is important to you, strongly consider a carotid artery ultrasound. In my opinion as early in adult life as possible.

References

-       Song P, Fang Z, Wang H, Cai Y, Rahimi K, Zhu Y, Fowkes FGR, Fowkes FJI, Rudan I. Global and regional prevalence, burden, and risk factors for carotid atherosclerosis: a systematic review, meta-analysis, and modelling study. Lancet Glob Health. 2020 May;8(5):e721-e729. doi: 10.1016/S2214-109X(20)30117-0. PMID: 32353319.

-       Lorenz MW, Markus HS, Bots ML, Rosvall M, Sitzer M. Prediction of clinical cardiovascular events with carotid intima-media thickness: a systematic review and meta-analysis. Circulation. 2007 Jan 30;115(4):459-67. doi: 10.1161/CIRCULATIONAHA.106.628875. Epub 2007 Jan 22. PMID: 17242284.

-       Inaba Y, Chen JA, Bergmann SR. Carotid plaque, compared with carotid intima-media thickness, more accurately predicts coronary artery disease events: a meta-analysis. Atherosclerosis. 2012 Jan;220(1):128-33. doi: 10.1016/j.atherosclerosis.2011.06.044. Epub 2011 Jun 30. PMID: 21764060.

-       Ihle-Hansen H, Vigen T, Berge T, Walle-Hansen MM, Hagberg G, Ihle-Hansen H, Thommessen B, Ariansen I, Røsjø H, Rønning OM, Tveit A, Lyngbakken M. Carotid Plaque Score for Stroke and Cardiovascular Risk Prediction in a Middle-Aged Cohort From the General Population. J Am Heart Assoc. 2023 Sep 5;12(17):e030739. doi: 10.1161/JAHA.123.030739. Epub 2023 Aug 23. PMID: 37609981; PMCID: PMC10547315.

-       Yin Z, Guo J, Li R, Zhou H, Zhang X, Guan S, Tian Y, Jing L, Sun Q, Li G, Xing L, Liu S. Common carotid artery diameter and the risk of cardiovascular disease mortality: a prospective cohort study in northeast China. BMC Public Health. 2024 Jan 22;24(1):251. doi: 10.1186/s12889-024-17749-x. PMID: 38254061; PMCID: PMC10801967.

-       Giannopoulos A, Kakkos S, Abbott A, Naylor AR, Richards T, Mikhailidis DP, Geroulakos G, Nicolaides AN. Long-term Mortality in Patients with Asymptomatic Carotid Stenosis: Implications for Statin Therapy. Eur J Vasc Endovasc Surg. 2015 Nov;50(5):573-82. doi: 10.1016/j.ejvs.2015.06.115. Epub 2015 Aug 20. PMID: 26299982.

-       Morillas P, Quiles J, Mateo I, Bertomeu-González V, Castillo J, de Andrade H, Roldán J, Miralles B, Masiá MD, Carrillo P, Bertomeu-Martínez V. Carotid resistive index in treated hypertensive patients: relationship with target organ damage. Blood Press. 2012 Dec;21(6):360-6. doi: 10.3109/08037051.2012.694181. Epub 2012 Jul 3. PMID: 22747334.