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Heart Scans...Should You Get One?
Article Submitted by:
Medical Author: Daniel Lee Kulick M.D.
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
What are heart scans?
So-called "heart scans" are specialized CT scans that measure calcium in the coronary arteries. Atherosclerosis (hardening of the arteries) is a process that develops over many years and represents the deposit of plaques in the walls of the arteries. These plaques may obstruct blood flow, and, as their size increases, they may obstruct blood flow enough to cause angina pectoris (chest pain) or myocardial infarction (heart attack). These plaques consist of cholesterol, calcium, muscle cells, and connective tissue. There is a fairly good correlation between the amount of calcium in an artery and the degree of plaque in the same artery.
Commercially available heart scans quantitate (measure) the amount of calcium in the wall of an artery and yield a calcium score. This score is used to provide a rough estimate of the risk of future cardiac events (defined as nonfatal heart attack or sudden cardiac death). By using comparative studies with patients who undergo coronary angiograms (a test in which dye is injected into the coronary arteries to assess the number and severity of coronary artery plaques), the calcium score has been demonstrated to give a rough estimate of the severity of coronary artery blockages that are present. It should be realized, however, that the calcium score does not give an exact quantification (measure) of the severity of an individual blockage. For instance, multiple minor plaques in close proximity in an artery may yield a similar calcium score as a severe plaque. However, the implications and management of the two situations may be very different.
What is coronary risk?
In order to assess the implications of your calcium score, it is important to understand your risk profile for the development of coronary artery disease (CAD). There are several specific and predictive risk factors for the development of CAD, including: (1) cigarette smoking; (2) abnormal blood lipid profile, including an elevated LDL cholesterol and/or a low HDL cholesterol; (3) a strong family history of CAD at relatively young ages; (4) the presence of high blood pressure (hypertension); and (5) the presence of diabetes mellitus. In addition, with advancing age, the likelihood of developing CAD increases, particularly past the age of 65. Finally, if the patient is having symptoms consistent with CAD (e.g., chest pain), has already survived a heart attack, or has had coronary artery angioplasty and/or bypass surgery, there is already evidence of significant underlying CAD. If these factors are present, there is no need for a screening test such as a heart scan for underlying calcium. In these patients, who already have symptoms suggestive of CAD or who have already had documented CAD, doctors perform physiologic tests, such as exercise stress tests. These tests assess whether there is a severe blockage that may place the patient at significant risk for cardiac events. The results of these physiologic tests may indicate the need for further, more aggressive evaluation and treatment. The important point is that the heart scan is a screening test and is designed for use in patients without known CAD but who are at risk. In patients already known to have CAD, such a test is unnecessary and will not affect appropriate management.
The following are examples of helpful and non-helpful uses of heart scans:
Heart Scan Helpful
1. A 38 year old male goes to the doctor (presents) with no history of chest pain, smokes one pack of cigarettes a day, has an abnormal cholesterol profile, and has a father who had a heart attack at age 42. His scan revealed a very high calcium score in one artery. His doctor performed a treadmill test that was abnormal, and his angiogram revealed a 90% blockage, which was successfully treated with a coronary stent. In this young high-risk patient, the heart scan led to the detection of early coronary disease before any adverse events occurred.
2. A 54 year old female presents with a history of recurrent chest pain while jogging, but has no known risk factors for CAD. She had two exercise stress tests that were both normal over a 6 month period. Her heart scan revealed a calcium score of zero, making the presence of significant CAD unlikely. She was subsequently discovered to have a form of asthma. In this patient, who was at low risk for CAD, the normal heart scan provided reassurance as to the absence of significant CAD.
3. A 28 year old male presents with no history of chest pain or other symptoms, but with a low HDL cholesterol and a very strong family history of early CAD in multiple male relatives. His heart scan revealed a moderate level of calcium and his exercise test was entirely normal. In this instance, the scan accurately depicted the early beginnings of CAD. This suggested the need for aggressive lifestyle modifications and therapy to optimize the blood cholesterol profile, which may prevent the occurrence of adverse cardiac events one or two decades later.
Heart Scan Not Helpful
1. A 78 year old male presents with a very high blood cholesterol level and high blood pressure (hypertension), but no history of chest pain or other cardiac symptoms. His calcium score was very high. Despite a normal exercise treadmill test and reassurance from his doctor that no further testing was indicated, he requested an angiogram, which revealed multiple 20 to 40% blockages in his coronary arteries. These blockages did not require specific intervention other than management of his cholesterol and blood pressure. In this instance, a patient who is at very high risk for CAD (elderly with multiple coronary risk factors), will likely have an elevated calcium score. In such high risk patients who have no history of cardiac symptoms, a physiologic test, such as an exercise stress test, is a much more appropriate form of screening than a heart scan.
2. A 40 year old male presents with high cholesterol levels, a family history of early CAD, and diabetes mellitus. He also has a three month history of chest pain during physical exertion. His exercise test was abnormal, suggesting the presence of severe coronary artery narrowing, and an angiogram was strongly recommended by his doctor. The patient was reluctant and opted for a heart scan. The scan revealed a fairly low calcium score and the patient assumed the angiogram was unnecessary. His chest pain became progressively more severe and occurred with minimal exertion. He ultimately had an angiogram, which revealed multiple severe coronary artery narrowings, and he underwent successful coronary artery bypass surgery. In this instance, the calcium score was relatively low because the patient was fairly young and had "soft plaques," which contain less calcium. In a patient with a very high likelihood of severe CAD (as in this patient who had multiple coronary risk factors, severe symptoms suggestive of CAD, and an abnormal treadmill test), there is little if any role for a heart scan. You see, the scan will generally be abnormal in these patients. Not only does the scan not add new information, it may at times reveal a misleadingly low calcium score. Consequently, this may lead to a delay in appropriate diagnosis and treatment, with potentially adverse outcomes.
Summary
The availability of heart scans for the detection of coronary artery calcium represents an important advance in the noninvasive detection and management of CAD. As a general rule, the presence of an abnormal scan in a patient who has no symptoms but significant risk factors for the development of CAD, suggests the need for a physiologic test for the presence of severe coronary narrowings (e.g., exercise stress test, with or without adjunctive (supplemental) nuclear or echocardiographic imaging). If this heart scan is normal, the patient should undergo aggressive risk factor modification, including smoking cessation, optimization of blood cholesterol levels, correction of underlying elevated blood pressure (hypertension), and any other recommendations by the doctor.
As can be seen from the above examples, however, there are instances in which the scan may be misleading or unnecessary. For this reason, the decision to undergo a heart scan should be discussed in advance with your personal doctor. The results of the scan should also be carefully reviewed with your doctor in order to place the information from the scan in proper perspective and decide if any further testing is indicated
