Cardiovascular disease is the most common cause of death in the United States resulting in almost 700,000 deaths per year. For this reason, a lot of resources have been focused on reducing this number. Progress has been made identifying risk factors for heart disease.  Diabetes, High Blood Pressure, Cholesterol, Smoking, Obesity, Sedentary Lifestyle and Excessive Alcohol consumption are all well-known modifiable risk factors. Age, Sex, and Family history also contribute to risk, but these are non-modifiable risk factors. We can't change them.

Beyond reducing our modifiable risk factors what else can we do to reduce the risk of heart attack? Compare our approach to a disease like cancer, where our approach has been to try and screen for disease in healthy patients before symptoms occur whenever possible. Can that approach work for heart disease? As with cancer we would need to understand the nature of the disease and then determine if we can identify an early stage and a method for preventing or reversing its progression. That would seem to be the logical approach, but heart disease is very different than cancer so a similar approach may not necessarily work. To understand how heart attacks occur read the post at the link below and then return to this page.

If you finished reading "How do Heart Attacks Happen" then you've understood that it's not always the biggest blockage that poses the biggest risk. For this reason it can be very difficult to find and treat the plaque that will actually cause a problem. There are a number of cardiac screening tests available but while these are all moderately successful at finding large plaques or blockages, they are incapable of distinguishing between plaques that are solid and stable vs those that are unstable and prone to rupture. I will go over some of those tests here and explain who should have the test, who shouldn't,  and why.

Exercise Stress Test 

There are several types of exercise stress tests. The standard test monitors your EKG while you exercise. A stress echo test does an echocardiogram before and after exercise, and a Thallium Stress test uses a radioactive tracer to see if parts of the heart are getting insufficient blood flow after exercise. While these tests have their differences, each with its own strengths and weaknesses, in the end they all attempt to measure the same thing. They are indirect ways of assessing blood flow to the heart muscle. I won't get into the differences here because they are not important for this discussion.

Stress tests are useful when a patient is having symptoms that could indicate that the heart isn't getting enough blood flow, Symptoms like chest pain or unexplained shortness of breath and decreased exercise tolerance are common examples. There are other less obvious symptoms like nausea with exertion.  All of these could be caused by insufficient blood flow. For these situations a stress test can be a good way to see if the symptoms are accompanied by evidence of reduced blood flow to some portion of the heart.

So, a stress test is a good way to evaluate a patient who is having possible signs or symptoms of reduced blood flow to the cardiac arteries. They are not very effective ways to search for an impending heart attack though. As mentioned in the linked story, heart attacks do not always occur in areas that contain the biggest plaques or narrowest arteries. So, while a stress test may discover an area with reduced blood flow, opening that area up with a stent may not prevent a heart attack. In addition, these tests, like all tests have some level of false positive results. They may indicate abnormal blood flow in someone who has normal blood flow. In fact, the majority of positive stress test results in patients who had no symptoms prior to testing will be a false positive. The concern here is that any positive result will then require further testing and that usually means an angiogram. Angiograms are described below but suffice to say these are invasive tests with significant associated risks.

Risks:

• Arrhythmias: During a stress test, especially in patients with underlying heart disease, there is a small risk of developing abnormal heart rhythms (arrhythmias), such as atrial fibrillation or ventricular tachycardia. Most of these arrhythmias are transient and resolve once the exercise stops but there is a small risk of a fatal arrhythmia.
• Chest Pain or Discomfort: The physical exertion involved in a stress test can sometimes cause chest pain or discomfort, particularly in patients with underlying heart disease or coronary artery blockages.
• Heart Attack: While rare, in patients with severe coronary artery disease and sometimes in patients with no known prior history of disease, the physical exertion during a stress test could potentially trigger a heart attack. This risk is generally low, 
• False positive tests that require follow up with more invasive and riskier tests like an angiogram.

SUMMARY:

• Who should have this test:  Patients who are having symptoms that suggest the possibility of inadequate blood flow to the heart. 

Coronary Calcium Score 

Coronary calcium scoring is a relatively new test that uses a CT scan to grade the amount of calcium in coronary arteries. This test was developed when it was noticed that there is some correlation between calcium content and plaque formation. For that reason it can be helpful to some extent in evaluating the overall risk of a future myocardial infarction (heart attack).  A high coronary calcium score might indicate a greater likelihood of significant coronary artery disease.

The only true indication for this test is to help your doctor determine if you should be treated with cholesterol lowering medications . if you are someone who’s cholesterol numbers and other risk factors puts you on the fence a high or low calcium score may help make the decision.

Calcium scoring should not be used just to screen for heart disease. This is a very common misconception and unfortunately some health care facilities are inappropriately marketing it for this reason, Some physicians are also incorrectly using it for this purpose. There are good reasons not to do this test in someone who is otherwise asymptomatic especially if they are otherwise low risk or are already being treated with cholesterol lowering drugs.

Risks:

• Radiation exposure – A single Coronary Calcium Score scan exposes the patient to 10 - 50 times as much radiation as a typical chest xray. While this is similar to the amount of background radiation the average person gets in a year, radiation is cumulative and additive, so this radiation is in addition to your other yearly exposures.
• Additional testing – A high calcium score may sometimes trigger additional testing such as an angiogram (see below). During this test a physician threads a catheter into the heart and then injects dye into the blood vessels. On average about 1 to 10 out of every 1,000 people who have an angiogram will die during the procedure. It's a reasonable risk in a patient who is symptomatic and needs this done to restore circulation to their heart, but it may not be reasonable in patients who were perfectly healthy or symptom free when this screening began.
• False positive and false negative scores are not uncommon - Patients with very high calcium scores sometimes have perfectly normal angiograms and vice versa which can lead to unnecessary invasive procedures or a false sense of security.
• Lack of evidence of benefit – There is no evidence currently to support the idea that this test will result in fewer heart attacks, fewer deaths, or better outcomes of any kind.

While it may seem like common sense that screening for heart disease would lower the risk of death and disease, our bodies are far more complicated than most people realize. This may seem counterintuitive but if you read the "How do Heart Attacks Happen" article I linked to above then you know that heart attacks don’t always occur by way of the gradual occlusion of an artery. In fact, many heart attacks occur in places where there was no significant restriction in blood flow moments before the heart attack. Many heart attacks occur from relatively small plaques that often won't set off alarms on these tests. These plaques may sometimes be unstable leading to rupture and the formation of a clot which suddenly occludes the artery. Unfortunately, there is no test that can reliably distinguish between unstable plaques and stable plaques.

The greatest risk from a coronary calcium score when done for the wrong reasons, as in an asymptomatic low risk patient, is that the patient may then be subjected to an angiogram during which a narrowing is discovered and a stent is placed, and some complication develops from the procedure, but no real benefit was obtained. In other words, all risk with no proven benefit. So, in general until studies are done showing that this test provides more benefit than risk or unless there is a question about starting cholesterol medication there is no role for coronary calcium scores in patients.

SUMMARY:

• Who should have this test:  Patients who have borderline cholesterol levels or a borderline cardiac risk calculation where additional information would be helpful before deciding whether to start cholesterol medications.

CT Angiogram 

A CT angiogram is a procedure in which dye is injected into a vein. The dye then circulates through the body to the heart where it can be used to image the arteries in the heart. This test will not show as much detail as a standard angiogram (see below) but it is non-invasive and low risk.

Risks:

• Radiation: 5-20 mSv (equivalent to 50-100 chest xrays)
• Dye injury - angiogram dye can cause injury to the kidneys. This is usually temporary and resolves on its own in most cases but sometimes it can lead to permanent kidney injury.

SUMMARY:

• Who should have this test:  This test can be used to look for blockages in blood vessels. It is generally used when someone has a normal stress test in a setting where their symptoms are highly suggestive of coronary artery disease.

Angiogram 

Unlike the CT Angiogram discussed above, a regular Angiogram is a procedure in which a small, flexible tube called a catheter is inserted into a blood vessel in the groin or arm. The doctor threads the catheter through the blood vessel and advances it toward the heart using X-ray guidance. Once the catheter is in place, a contrast dye is injected through it into the coronary arteries. This dye helps to make the blood vessels visible on X-ray images. As the contrast dye flows through the coronary arteries, X-ray images are taken. These images can show any blockages or narrowing that might exist in the blood vessels.

If a blockage or narrowing is found in an artery the catheter can also be used to place a stent that can open the narrowed area and improve blood flow. While there is no good evidence that stents can prevent a heart attack, they can reduce symptoms that may be due to reduced blood flow through a narrowed artery.

Risks:

• Radiation: 5-20 mSv (equivalent to 50-100 chest xrays)
• Dye injury - angiogram dye can cause injury to the kidneys. This is usually temporary and resolves on its own in most cases.
• Death - The mortality rate for an angiogram can be as high as 1 out of every 100 patients although in healthy individuals its closer to 1 in 1,000.

SUMMARY:

• Who should have this test:  This test can be used to look for blockages in blood vessels. It is generally used after someone has had an abnormal stress test to confirm or rule out any significant blockages in the coronary arteries, or it may be done if someone has symptoms so worrisome that a stress test is not necessary or advisable. In that case the doctor may go straight to an angiogram.

Echocardiogram

An echocardiogram uses sound waves to take pictures of the heart. This is similar to the device used to take images of the baby when a woman is pregnant. An echocardiogram can see the muscular walls of the heart as well as the valves and can even track blood flow through the heart chambers, but it cannot see blood flow in the blood vessels that provide the heart muscle with oxygenated blood.

Risks: There are no significant risks associated with this procedure

SUMMARY:

• Who should have this test:  This test can be used to look for heart valve defects such as leaky or stiff valves. It can also help doctors see if there has been damage to the heart muscle perhaps from a prior heart attack. In addition, it can be used to see if the heart is still pumping effectively.

Who should or shouldn't get a screening test and why

As you have probably already guessed from the discussions above, none of these tests are recommended as effective ways to screen for or prevent heart attacks in otherwise healthy individuals without symptoms suggestive of heart disease. That's because they are unable to identify the issue that leads to most heart attacks, which is inflamed unstable plaques that are at risk of rupture. Until we have such a test, screening is not advisable in patients who have no symptoms because it exposes the patients to risk but provides no proven benefit. This will come as a surprise to lots of people who have friends or family who have been told something different and may have even undergone some of these tests. This is mostly due to the counterintuitive nature of this situation.  If you think of our arteries like pipes in your house then of course it makes sense to look for clogs and clean them when you find them, but our arteries are really very different from pipes as I pointed out in the "How do Heart Attacks Happen" article.  

Physicians are human and as prone to making analogies with things they are familiar with ( like the pipe analogy ) as anyone else sometimes. As physicians we also want to be proactive and save lives so it's natural to want to test for something in the hope of preventing a poor outcome, but as discussed above all of these tests have varying degrees of risks, either by themselves or in the more invasive tests that may follow. If there is no proven benefit, then we may actually be doing more harm than good by ordering these tests. Physicians are also acutely aware of patient expectations. Often times patients think that a doctor who orders more tests is being more thorough and conversely a doctor who orders less tests is being less thorough or even careless. This is a false assumption. The best doctor is the one who orders the right tests, or no tests at all, not necessarily the one who orders more tests. The best doctor is the one who has taken the time to think about the problem and do only what's necessary to find the answers that they and their patients need.

The message I want to convey in this article is that although we don't currently have an effective way to screen for the kinds of problems in our arteries that may lead to a heart attack in otherwise healthy individuals, that doesn't mean that there is nothing you can do to prevent a heart attack. In fact, there is a lot one can do. The most powerful tools we have to prevent heart attacks is to identify modifiable risk factors and do our best to improve them. We can't change our genetics or our age, but we can control things like cholesterol and sugar levels as well as high blood pressure, smoking, obesity, exercise, and alcohol intake. That's where the focus should be. See your doctor regularly to have these things checked. Work on your diet and exercise, and when necessary, use medications to reduce the risk of heart disease as well as stroke.