FAQ on Carotid Intima Media Thickness
What is Carotid IMT?
Carotid IMT stands for Carotid intima media thickness and refers to the thickness of the inner layers of the artery.
What does the thickness of the vascular lining indicate?
Genetics and environmental factors (including diet, exposure to carcinogens such as cigarette smoke, and exercise – or the lack of exercise, etc) combine over time to cause inflammation of the inner layers of the artery and the formation of plaque on the inner lining of the arterial wall. This thickening can be measured using ultrasound and sophisticated edge-detection software to quantify the amount of disease present. The measurement of the thickness of the intima and media layers of the common carotid artery is predictive of future events (i.e. stroke, myocardial infarction, and heart attack).
What is an IMT test?
It is a painless noninvasive test utilizing digital ultrasound technology and digital sophisticated edge detection software. The test can be performed easily in the physician’s office.
The Carotid IMT scan is brief (approximately 10 minutes), does not require the patient to disrobe, is noninvasive (no needles), and does not expose the patient to radiation. It is relatively inexpensive and provides valuable information about an individual’s risk of experiencing a heart attract, stroke, or MI.
What information does the Carotid IMT test provide?
Multiple studies indicate that Carotid IMT measurement detects the presence or absence of atherosclerotic disease and also allows for assessment of the degree of atherosclerotic burden better than other noninvasive cardiovascular tests available. It is recommended by both the American Heart Association and the American College of Cardiology. The procedure:
- Can predict future cardiac and cerebrovascular events.
- Allows earlier detection and intervention
- Allows more accurate risk stratification in asymptomatic patients than do traditional risk factors
- Can distinguish between different types of plaque providing further information about stable (hard) and unstable (soft) plaque
How long has Carotid IMT testing been used in clinical practice?
Carotid IMT testing has been used in research for over 20 years. It has only been available in clinical settings since 2002. Carotid IMT testing has been validated in many published studies in the most reputable journals. Carotid IMT has been used in large epidemiologic trials as well as large outcome studies as a surrogate end point for clinical events. Carotid IMT is probably the most studied methodology used to assess large numbers of patients in epidemiologic studies to determine either the correlation of Carotid Intima Media Thickening to clinical events or the correlation of CIMT to other known risk factors. There is a high correlation between the disease found in this procedure and the disease found through pathology samples. The amount of disease found in the common carotid artery correlates highly to the amount of disease found elsewhere in the body.
Does this test also detect and predict disease in women?
This test is felt to be as predictive in women as it is in men and helps to eliminate the dilemma clinicians have experienced in diagnosing and treating women for heart disease.
How accepted is this test in clinical practice.?
In 2006, cardiologists in the Screening for Heart Attack Prevention and Education (SHAPE) task force recommended this test for all patients over 45 years of age, and younger if the patient has multiple risk factors (Family History, Hyperlipidemia, Dyslipidemia, Hypertension, Metabolic Syndrome etc). Patients that are believed to be at intermediate risk for heart disease and stroke are ideal candidates for this procedure.
At its annual Prevention Conference V, the American Heart Association concluded that “Carotid artery B-mode ultrasound imaging is a safe, noninvasive, and relatively inexpensive means of assessing subclinical atherosclerosis. The technique is a valid and reliable means of measuring IMT, an operational measure of atherosclerosis. The severity of Carotid IMT is an independent predictor of transient cerebral ischemia, stroke, and coronary events such as MI . . . in asymptomatic persons > 45 years old, carefully performed carotid ultrasound examination with Carotid IMT measurement can add incremental information to traditional risk factor assessment.”
In July of 2003, Dr. Pam Douglass, President of the American College of Cardiology recommended IMT as an effective screening tool. This stems from the fact that:
- It is highly predictive for presence of coronary and cerebral disease.
- It is highly predictive for the development of stroke, TIA and heart attack.
- The relationship of carotid disease to disease of the coronaries is the same as one coronary to another.
- Carotid IMT has the most data as a diagnostic tool for arteriosclerosis. (Transcript ACCEL interview – July 2003)
The test has been cleared by the Food and Drug Administration (FDA).
Leading physicians across the country have added IMT to their primary prevention as an initial risk assessment tool and as a secondary prevention tool to monitor the affect of prescribed treatment over time. Carotid IMT testing has been shown to provide incremental additional data to risk prediction and is the only imaging test which has been recommended by the American heart Association for that purpose.
Can Carotid IMT testing also be employed to monitor progression or regression of disease?
Testing over time can shed light on the efficacy of treatment by tracking thickening or thinning of the intima media as well as tracking the degree of involvement by plaque indicating change in size, number of plaques and plaque characteristics.
How long does it take to complete Carotid IMT testing of one patient?
The test has two parts. Ultrasound images are taken and digital samples of the images are then sent to the HeartSmart IMTplus Technical Center where they are measured or read by a Registered Vascular Technician (RVT). In general it will take about 15 minutes of the patient’s time to complete the test. The patient is not required to disrobe and the procedure is well tolerated.
Are there any special requirements for a patient prior to the test?
There are no special requirements.
Why is this testing important?
Cardiovascular disease is the #1 killer in our population. It kills more people than the next five leading causes combined, including cancer.
Estimates indicate that with the increasing incidence of Metabolic Syndrome and Diabetes, morbidity and mortality may increase over the next 20 years.
For many, the first indication that they have heart disease is a heart attack; and 25% of first time heart attacks are fatal!
As many as 50% of those who died from heart attacks or strokes had no previous signs or symptoms. This test allows early intervention and prevention of disease which has the potential to catch more of these patients so they can be treated before they experience an event.
More than 60% of those who died from heart attacks or strokes had normal “lipid” profiles. Carotid IMT will catch more people with disease who may have been shown to be normal on other tests like stress echo, standard lipid panels, and other blood/urine screens.
It is a cost effective diagnostic tool which provides health value and saves lives.
How accurate is Carotid IMT as a predictive tool?
Carotid IMT is more accurate in predicting disease than any other risk factor alone. Carotid IMT measurement is an independent risk factor even in the absence of any other identifiable risk factors.
In 2009, a direct comparison of CIMT versus coronary artery calcium scoring by high speed CT scan was made at the Mayo Clinic. CIMT was found to be the superior technology: “Subclinical atherosclerotic vascular disease can be detected by CIMT evaluation in young to middle-aged patients with a low Framingham Risk Score and a Coronary Artery Calcium Score (CACS) of zero.”
A 2007 article in the journal Circulation confirmed that carotid IMT “is a reliable and strong predictor of future stroke and myocardial infarction [heart attack]”.
Progression of disease over time is another independent risk factor. Studies have shown a very high correlation between the disease found in the common carotid and the disease found elsewhere in the body. There is a very high correlation between the thickness of the intima media and other risk factors. Perhaps most important is Carotid IMT’s correlation and ability to predict coronary and cerebral events. Carotid IMT was more accurate at predicting CAD than was an Angiogram.