Cardiovascular disease is the leading cause of death in men and women in the United States. Approximately 50% of acute myocardial infarction's occur in people without any history of coronary artery disease. Sudden cardiac death is often the first sign of coronary heart disease. Coronary atherosclerosis is a slow progressive disease that oftentimes goes unrecognized until the person develops symptoms. By the time symptoms start to occur coronary artery disease is usually in a relatively advanced stage requiring either percutaneous or surgical revascularization. The opportunity for disease prevention or aggressive risk factor modification is missed. What is needed is a way to identify asymptomatic people who are at high risk for cardiovascular events early in their disease process. Traditional cardiovascular risk factors are well established (elevated lipid levels, hypertension, smoking, obesity, lack of exercise, diabetes, family history heart disease) and helpful to predict future cardiovascular disease. Many people however suffer cardiovascular events in the absence of these established coronary artery disease risk factors.
Myocardial infarctions usually occur in patients who have a mild of moderate coronary artery stenosis that develops plaque rupture and leads to an acute thrombosis. These mild to moderate coronary lesions may not cause symptoms and / or may not cause enough ischemia to be picked up during a routine stress test.
During the early stages of coronary atherosclerosis calcium starts to accumulate within the plaque. As the atherosclerotic process progresses the amount of calcification increases. During the advanced stages of atherosclerosis a large amount of coronary calcification may be present.
Women have been reported to have less coronary artery calcification than men and the mean prevalence of calcification in women occurs about one decade later than in men, as does the incidence of cardiovascular events. The prevalence of calcium in adults 30 to 39 years of age is 21% for men and 11% for women, while in adults 40 to 49 years of age the prevalence is 44% in men and 23% in women. A recent study found coronary calcium scores were similar in African American and Caucasian women even though African American women had more risk factors. Diabetes mellitus and not exercising regularly was associated with increased Coronary Artery Calcium Scores in white women but not African American women. The overallvalence of calcium in women is about half that of men until age sixty. Another study in asymptomatic women found that smoking, elevated total cholesterol levels, and hypertension were all associated with higher Coronary Artery Calcium Scores. Calcium deposits have also been found to increase with age irrespective of gender. Patients with diabetes and patients with end stage renal disease requiring hemodialysis have a higher prevalence of calcium. The more cardiovascular risk factors a person has the higher the prevalence of calcium.
Atherosclerosis is the only disease process known to cause calcium to deposit in coronary artery walls. Calcification is not a degenerative disease, it is not a part of the "normal" aging process. Calcium is not found in normal coronary arteries.
Since calcium deposits start to develop during the early stages of atherosclerosis and if we are able to identify the presence of calcium we are able to identify preclinical coronary artery disease during the asymptomatic stage. This can allow for the implementation of early aggressive risk factor reduction.
The calcium score screening heart scan is a non-invasive test that detects calcium deposits in the coronary artery walls. The test is performed with an electron beam cat scanner (EBCT) that permits very rapid scanning. The images are triggered with the assistance of ECG monitoring during diastole and a few second breath hold to eliminate motion artifact. The actual scan only takes about thirty seconds and computer software then quantifies the calcium area and density.
The EBCT detects the presence, location and amount of calcium deposits in the coronary system. Separate calcium scores may be obtained for the left main artery, left anterior descending artery, left circumflex, and right coronary artery but the total calcium score is most important. The EBCT can detect minuscule calcium deposits which is what is usually present with early coronary artery disease. The presence of any coronary calcification signifies coronary artery disease. People with low total calcium scores are at a lower cardiovascular risk than high scores.
Calcium scores range from zero (no plaque) to several thousand (extensive plaque) and is a unitless measurement calculated for the entire coronary system. A calcium score of zero indicates the absence of any calcium and an extremely low likelihood of obstructive coronary artery disease. A calcium score greater than 400 signifies extensive calcification and a high likelihood of significant coronary artery disease. (See Average Calcium Score Chart) These people should undergo further evaluation with exercise stress test or nuclear stress test for myocardial ischemia. The higher the total score the greater the overall plaque burden. Asymptomatic people with an intermediate calcium score require a thorough risk assessment and individualized risk factor modification. A person's age and gender also need to be considered when evaluating the calcium score results. A calcium score of 175 may be average for a 65 year old male but grossly abnormal for a 55 year old female.
The calcium scoring scan is not able to identify the location of a significant coronary artery lesion nor identify the percent stenosis. The quantity of coronary artery calcium predicts the total atherosclerotic plaque mass and likelihood of developing future cardiovascular events. Coronary calcium has been reported to be an independent predictor of stable angina, myocardial infarction, cardiovascular death, and need for coronary revascularization. A study in asymptomatic adults 20 to 69 years old found that at 18 month follow-up the myocardial infarction and cardiovascular death rate was 6.6% in people who had any calcium present on scan versus 0.9% in people without any calcium. There is a direct relationship between increasing calcium scores and the occurrence of adverse events. Asymptomatic people with very high calcium scores (> 1,000) have been found to have an approximately 25% risk per year of developing a myocardial infarction of cardiovascular disease. A recent study of asymptomatic adults over 45 years of age with at least one cardiovascular risk factor found a fourfold increase in cardiovascular risk in patients with coronary artery calcium scores greater than 300. A study performed on symptomatic patients found that coronary artery calcium score greater than 170 was associated with an increased likelihood of obstructive coronary artery disease regardless of the number of risk factors present.
A recent meta-analysis reported a 92.3% sensitivity and 51.2% specificity for the accuracy of the EBCT to diagnose obstructive coronary artery disease. This makes the overall predictive accuracy approximately 70%. One advantage of the scan is there are no "false positive" scans, calcium deposits are only found in the presence of plaque. Interscan reliability of calcium scores has been questioned and has been reported to vary more with lower score. One study reported a calcium score variability of 28% in women and 43% in men when repeat scans were performed on the same individual. This really needs to be evaluated further and may be dependent on the facility, equipment of physicist interpreting the results.
Non-calcified, soft plaques will not be detected by EBCT. Younger patients who are heavy smokers may not have calcium deposits present but are still at high cardiovascular risk and prone to spasm and thrombus formation. There has been some research to suggest that patients with unstable angina are sooner to have fewer calcified plaques than patients with stable angina. Younger patients may develop a significant stenosis in the absence of calcification. This may falsely reassure people who are at high risk. There is not enough data to support using the coronary calcium scans in symptomatic patients of patients already know to be at high risk.
The coronary calcium scan (EBCT) is most useful in asymptomatic patients with intermediate risk, to help determine the need for aggressive risk factor management. (See Coronary Artery Calcium Scans chart below)
Traditional non-invasive tests to evaluate coronary artery disease (exercise stress test, nuclear scans, stress echocardiography) only detect coronary lesions that are sufficient enough to limit blood flow and cause myocardial ischemia. People with very mild coronary artery disease or early atherosclerosis will not be identified. Coronary calcium screening is able to identify non-obstructive mild coronary artery lesions before symptoms develop. Asymptomatic people with high calcium scores are also more likely to have abnormal nuclear stress tests indicative of silent ischemia. In one study 46% of patients with coronary artery calcium scores greater than 400 had an abnormal nuclear scan while 0% of patients with coronary artery calcium scores less than 10 had an abnormal nuclear scan.
EBCT surveys may prove to be more beneficial for screening women. Many times women present with atypical symptoms and are more likely to have false positive exercise stress tests and / or nuclear scans. Calcium scoring scans have been reported to have a higher predictive value for significant coronary artery disease in women and less false positives than men. The negative predictive value in one study of symptomatic patients was 96% in women and 89% in men. Women with normal lipid levels are also more likely to experience angina / myocardial infarction than men. The standard lipid profile does not always adequately reflect a woman's cardiovascular risk. A study of asymptomatic women over 55 years of age with normal lipid levels found elevated coronary artery calcium score. This is an area that needs to be evaluated further but suggests that coronary artery calcium scores may prove to be very beneficial in assessing cardiovascular risk profiles in women.
Indications for Coronary Artery Calcium Scans:
1. Family history heart disease (especially premature heart disease)
2. History of smoking
5. Elevated lipid levels
7. Men over 40 years old or postmenopausal women
8. Young people with atypical symptoms
Contraindications for Coronary Artery Calcium Scans:
1. Known coronary artery disease
2. People over 70 years old (little clinical benefit)
3. Pregnant women
4. Arrhythmias (Chronic atrial fibrillation, resting tachycardia – heart rate greater than 90 bpm) will
compromise image quality
Average Calcium Scores:
74 years old 521
74 years old 149