Some of you may know that I have always had a special interest in cardiology. For the longest time, I have found EKGs (electrocardiograms–tracings of the electrical rhythms of the heart) fascinating. While I was in residency, this fascination lead me to take a month-long elective course in cardiac stress testing. For the past 3 years, I have worked in the cardiac stress testing lab a few days every month. This has been an especially rewarding part of my practice that developed into my niche in medicine.

Cardiac stress testing is incredibly important and profoundly misunderstood all at the same time. The capabilities and limitations of stress testing are often unknown to patients and physicians alike. I want Wise Patients to know when to get a stress test, what to expect when you have one done, and what limitations come with testing.

What is Stress Testing?

A cardiac stress test is a procedure in which we temporarily increase the workload on your heart and measure its response. We do this to get a lot of information, but the primary reason is to determine if you have any blocked arteries around your heart, also called coronary artery disease (CAD).

When Should You Have One Done?

CAD can present with a variety of symptoms, such as chest pain, shortness of breath, neck and left arm pain. The most common unifying factor among CAD symptoms is this: they will typically get worse with exertion and get better at rest. If you are having any of these symptoms, then you should talk with your doctor about getting a stress done.

We can also use stress testing to evaluate for arrhythmias, which are abnormal heart rhythms. If you get palpitations, irregular heart beats that you can feel, then we can do a stress test to try to catch the abnormal rhythm on the monitor during exercise.

Sometimes your doctor will recommend a stress test to screen for CAD even when you don’t have symptoms. For example, all patients on the kidney and liver transplant list have to have a stress test prior to receiving the transplant. If you have been diagnosed with CAD in the past, then your cardiologist may want you to complete a stress test periodically to monitor for progression of disease or to evaluate the effectiveness of your medical therapy.

How Do We Do It?

The best way to stress your heart, is to have you walk on a treadmill and monitor your blood pressure, EKG and oxygen level while you exercise. We will have you go as long as you can while we intermittently increase the speed and incline of the treadmill. We do not consider a stress test valid until you have reached a target heart rate. This target heart rate is equal to (220 – your age) x 0.85. Reaching the target heart rate ensures that the heart has been under enough stress to reveal an abnormality.

The easiest way to monitor your heart’s response to stress is with an EKG. There are certain changes on your EKG, called ST-segment depressions, which indicate that you may have blockages in the arteries around your heart.

Another easy way to measure your heart’s response is by measuring blood pressure. Your blood pressure is supposed to continue to rise as you exercise. If your blood pressure drops at peak exercise, then that is a sign that something is keeping your heart from pumping enough blood to compensate for the increased demand. Usually the cause is CAD.

The third way to monitor your heart’s response is to evaluate your symptoms. If you develop classic central chest pressure that gets worse with exercise and gets better at rest, then we consider this a positive test as well. Or if you develop neck or left shoulder pain with exertion, then that could be a positive result too.

Nuclear Stress Testing

If we cannot interpret your EKG for various reasons, or if you have had a positive test for any of the reasons mentioned above, then we will likely recommend that you do a treadmill stress test with nuclear imaging. Nuclear imaging is more sensitive and specific than ECG tracings for CAD. In order to determine if you have blocked arteries, we will inject a nuclear tracer into your IV. The tracer is picked up by your heart muscle and it essentially stains the area of heart muscle that was getting blood flow at the time. The stain remains in place for the next 30 minutes at which time we will take a picture of your heart with a nuclear camera to determine where you are getting blood flow in your heart.

After we have an initial “resting” picture of your heart, then we will have you perform an exercise treadmill test and inject the same nuclear tracer into your IV while you are at the peak of your exertion. This tracer will stain the areas of your heart that are getting blood while your heart is under stress. Now we can compare your “resting” picture to your “exercise” picture to determine if an artery is blocked and which artery is blocked.

Chemical Stress Testing

If you are unable to reach your target heart rate or if you have other issues that prevent you from walking, then we can perform a chemical stress test. A chemical stress test artificially stresses your heart without you having to exercise. We can inject you with a medication called regadenoson, which dilates all of the blood vessels in your body. If you have a blocked coronary artery, then this artery will not be able to dilate and the temporary lack of blood flow puts stress on your heart. The effects of the medication only last 1-2 minutes so no damage is done.

With a chemical stress test, we cannot interpret the EKG to determine if you have a blocked artery so we have to use nuclear imaging to make that assessment.

Why Don’t We Test Everyone?

Some may ask why we don’t just test everyone to make sure they don’t have CAD. Couldn’t we prevent heart attacks and cardiac death if we did this? The answer is no. I will just give you a personal example: last year my uncle had a heart attack 2 days after having a negative stress test. He’s doing fine now but a negative test didn’t rule out the possibility of a heart attack. The answer goes back to the question of sensitivity and specificity again. These tests are not sensitive enough to prevent future heart attacks. The blockages that typically cause heart attacks are small and suddenly rupture to obstruct the entire artery. These blockages are often too small to be detected by stress testing.

The other issue with testing everyone is the risk of false positive testing. Some patients who have no CAD at all will get ST-segment depressions on their EKG or will get positive symptoms during a test. This leads to further nuclear testing which can be expensive and can expose patients to unnecessary nuclear radiation.

The Importance of Fitness

Stress testing is a complicated subject, but I hope this is helpful. This guide is not all inclusive so please ask your doctor if you have concerns or further questions.

After doing this for 3 years I have seen an important trend: patients who are more physically fit have fewer heart attacks and less mortality. We have data showing the longer you are able to exercise on our treadmill protocol, the less likely you are to die from any cause. I have seen the value in physical fitness and I want you to understand it as well. I want to encourage you all to make fitness a priority in order to live longer and healthier lives.

Check out the patient resources page for fitness options. If you want to learn more about weight loss check out my article Staying Trim Around the Holidays and Part 2. If you would like to learn more about cardiac stress testing from the American Heart Association, click here.

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Need more wellness? Check out my previous article: Top 7 Conditions That Put You At Risk For COVID-19.