Exercise stress testing and other tests conducted in the evaluation of chest pain in the emergency department
5 million patients present to U.S. emergency departments each year complaining of chest pain. The vast minority of these patients will be diagnosed with a heart attack and undergo the appropriate immediate treatment, either clot dissolving medicines (fibrinolytics) or procedures that use balloons to open heart vessels (angioplasty). The difficult job of the emergency room doctor is to sort out the rest of the patients who do not have as clear of a diagnosis. Many of these patients have an unrelated problem and can safely be sent home, but for other patients their chest pain may be evidence of cardiac ischemia (decreased blood to the heart without the heart tissue dying) and they may be at risk of a future heart attack.
The dilemma lies in determining which patients need to stay at the hospital for further testing, and who can be sent home and make an appointment with their regular doctor. Approximately 60% of patients with chest pain stay in the hospital for further testing, although only 15% prove to have a heart attack. Also, 4-5% of patients sent home are later determined to have had a heart attack! This means many patient with chest pain unnecessarily stay in the hospital in order to be sure they are not having a heart attack, wasting both money and the patient’s time. Many patients actually having a heart attack, or at risk to have one in the near future, are not correctly diagnosed and are inappropriately sent home.
Patients may think that all the blood tests and EKG’s done to them should make the diagnoses obvious, but these test often give unclear results. A little understanding of the events that lead to a heart attach will help clarify why these test results are often ambiguous. A heart attack occurs when a blood vessel that supplies blood to the heart muscle becomes blocked. The area served by that muscle will die releasing chemicals into the patient’s blood. The now dead tissue will also conduct electricity differently, which can be seen on an EKG 90% of the time. Some patients with chest pain do not have dead heart muscle, but have a partial blockage of a blood vessel that serves the heart. This event referred to as cardiac ischemia means the heart is getting blood, but not as much as it needs. These patients usually have some complaints of pain, but the pain worsens with exercise, called angina. The pain becomes worst because the heart is already getting too little blood, and exercise increases the heart’s need for blood.
Many of the tests used in the evaluation of chest pain check the blood for chemicals released from dead heart muscle. Despite having chest pain, many of these chemicals do not reach high enough blood levels for many hours, or even days. Patients are often admitted to the hospital and have blood levels of these chemicals tested every couple of hours to see if they become positive. If a patient has a partial blockage of a blood vessel (ischemia), these chemicals may never show up in the blood. These patients may inadvertently be sent home, despite risk of a future heart attack.
Limitations of the EKG and need for stress testing
EKG’s test the flow of electricity through the heart and it normally shows a characteristic pattern. Dead or dying heart muscle usually conducts electricity in different patterns. But a patient who has a full heart attack will only have EKG changes 90 % of the time, which is one of the reasons why some heart attacks are not correctly diagnosed. Some patients also have abnormal EKG’s all of the time, despite having a normal heart. Because of this scenario, doctors like to compare old EKG’s, to see if there are any changes, but in the ER they rarely have access to a patient’s old EKG. Patients with decreased blood flow may show subtle changes in their EKG, but these changes are also normal in many patients. These subtle changes may not be present when the patient is at rest, but may be present when the patient is having pain with exercise. This is the reason why doctors often use an exercise stress test in patients with chest pain. As discussed earlier, when a patient’s blood vessels to the heart has a narrowing, with exercise the heart’s demand for blood increases but the supply cannot be increased. This produces both chest pain (angina) and EKG changes. The idea is to have the patient exercise on a treadmill while connected to an EKG. If the patient develops chest pain while on the treadmill or typical EKG changes, it becomes clear there may be a narrowing of the heart’s vessels and more tests need to be conducted. Cardiologists have historically done this test, but it is now being evaluated for use in the emergency department. A normal exercise test in patients at low risk for a heart attack can more safely be sent home rather than unnecessarily staying in the hospital. On the other hand, a low risk patient with a normal EKG at rest and an abnormal EKG on the treadmill can be admitted to the hospital rather than incorrectly being sent home. Despite these advantages to exercise stress testing in the emergency room, many patients are unable to perform the necessary exercise (such as a patient with knee problems) and some patients with heart disease still have a normal stress test or ambiguous changes on their EKG. This test is still not performed in most emergency rooms because it is still considered experimental and there is not great evidence to support its use in patients in the ER, despite sounding helpful.
Supervised Exercise Stress Test
Positive ECG/EKG Changes Indicating Cardiac Ischemia: A Positive Stress Test
The serious consequences of heart disease make it a diagnosis that doctors must make. The full evaluation in order to diagnose it or rule it out is both time consuming and expensive. Doctors over test and observe many patients without heart disease in order to ensure that a patient who does have heart disease is not missed. Much research is being conducted in order to discover new tests that diagnose all patients with heart disease without incorrectly diagnosing other patients. These tests, such as the exercise stress test in the emergency department, will save the lives of many patients with heart disease while also helping correctly diagnose patients with chest pain but who do not have heart disease.
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