What information about the patient’s state of health does the stress test give us?
The stress test, sometimes called a treadmill or exercise test on a mat, is used mainly as a non-invasive test in the diagnosis of coronary artery disease, but also, in the monitoring of the coronary artery disease after a heart incident e.g. after myocardial infarction or after percutaneous intervention (PCI), or after coronary artery bypass surgery (CABG). Besides the diagnosis of myocardial ischemia (ECG), the stress test provides important information on the functional capacity, exercise tolerance, the response of blood pressure to exercise, and the possible occurrence of arrhythmias caused by exercise. Alternatively, the stress test can be done by ergometric bicycle although the stress test on a mat is more common. The ergometric bicycle is particularly indicated for patients with severe obesity. It is also appropriate for children.
What are the basic stages of the stress test?
After pasting the special adhesive electrodes, the patient is connected to the continuous electrocardiographic (ECG) recording device of 12 leads and stands on the mat to start the test. There are many mat exercise protocols but the most common in clinical practice is the Bruce protocol, in which throughout the process the slope and speed of the pad changes automatically, every three minutes, via default software. The electrocardiogram is constantly supervised through the monitor screen and the blood pressure is measured every three minutes.
How long does the stress test last?
Besides the short time required for preparation, the duration of the test is determined primarily, by the patient’s resistance against the occurrence of muscle fatigue. From diagnostic point of view and regardless of the physical condition of the patient, the supervising cardiologist can stop the test when the heart rate (BPM) reaches the prescribed maximum according the age of the subject, which is approximately determined by the mathematic formula BPM/beats per minute = 220 – age. For example the BPM for a 40-year-old patient would be 220-40=180 beats per minute, while for a 65-year-old patient would be 220-65=155 BPM. A 35-50-year-old person with an average physical condition hold outs on the mat for 10 minutes, while people with good physical condition can exceed 12 minutes on the Bruce protocol. The supervising cardiologist can end the test even at a very early stage, if deemed necessary by the diagnostic findings.
What should the patient wear?
The most important is the appropriate footwear, so the person can walk easily and steadily on the mat without slipping. Sports shoes are recommended but they are not mandatory. It is also, suggested lightweight clothing, similar to the one that we would wear if we had to run. Body lotions are not recommended because they affect the recording quality of the electrocardiogram.
Does the patient have to be fasting?
Not necessarily, but it is recommended that a patient eats lightly at least 2-3 hours prior to the stress test. On the contrary, long fasting can significantly reduce the stamina due to exhaustion. We need fuel, but not an extremely full stomach.
Patients with diabetes, especially those treated with insulin should definitely eat something light after their anti-diabetic medication, to avoid hypoglycemia caused by the exercise.
Should the patient have received medical treatment?
This would be determined, in each case, by the physician who refers the patient to take the stress test. Many cardiologists want a 48-hour interruption of drugs, which are called beta-blockers, before the test, in order to reach a higher heart rate, while others want the patient to be examined without disturbing the regular medication. Caution should be taken when someone interrupts the antihypertensive drugs in hypertensive patients, because their disruption often leads to a rapid and significant increase in blood pressure, causing the imposed stop of the stress test at a non-diagnostic early stage.
How many types of stress tests exist?
Besides the simple exercise testing on mat with ECG recording, there is also, a cardiopulmonary stress test (Gas analyzer/Ergospirometry) where the individual is connected to an analysis mask of inhaled / exhaled respiratory gases and through a special software the doctor can determine the maximum oxygen consumption (VO2 in ml/kg/min) during the exercise. The value of the maximum oxygen consumption stands for to the aerobic capacity and the cardiopulmonary functional capacity. The Gas analyzer test (ergospirometry) is useful for determining the cardiopulmonary reserve in patients with heart failure. Indeed the result of Ergospirometry is a criterion for heart transplantation and it is required for pre-transplant evaluation. The Gas analyzer test is used to determine the aerobic capacity of athletes, particularly those involved in the championship.
Is the stress test safe?
It is a very safe test and the adverse incidents are very rare. Based on international clinical studies, the probability of death during the test is determined to less than 0.01% (i.e. 1 in 10,000 cases), while arrhythmias that are life-threatening, such as e.g. ventricular fibrillation, found with a probability of 0.05% (ie 5 in 10,000 cases). Moreover, in this case, the test is carried out in a safe hospital environment.
Is it right for someone to undergo a stress test without consulting a doctor?
This is a common mistake made by patients. This is because patients listen to a misguided informed surrounding recommending “a stress test after a certain age” without doctor’s order. Before a stress test, every patient should be examined by a cardiologist, who will determine the indication or even the contraindicate for a stress test based on the medical history, a physical examination, an electrocardiogram and any risk factors. The cardiologist, and not any other doctors of irrelevant specialties, is responsible for the issue of the medical referral. It is necessary to assess the ability of the patient to walk on the mat. We often see patients with orthopedic problems who are unable to complete the process.
What is the reliability and prognostic value of the test?
Regarding the diagnosis of coronary artery disease, the prognostic value of the test is greater in patients who either have symptoms (e.g. chest pain) or multiple risk factors for coronary artery disease (hypertension, high cholesterol, diabetes, smoking, coronary heart disease –CHD- family history). The test is of small prognostic value in asymptomatic patients or people who do not have risk factors. Nevertheless people who do not show any risk factor before testing the estimated probability of developing CHD is very low. Also, in women – particularly of reproductive age i.e. before menopause – there are more often obtained false positive results, during the test, compared to men of similar age.
The stress test is useful for monitoring patients after myocardial infarction, after coronary artery bypass surgery (CABG), and after percutaneous intervention (PCI) if there is a comparable stress test done before any operation. After such operations the stress test is recommended for monitoring patients at least annually and always in accordance with the recommendations of their therapists.
In patients with impaired left ventricular function and heart failure symptoms it is recommended the long term monitoring with Ergospirometry.
Recent major clinical studies indicate that in clinically healthy populations and particularly in patients who have already manifested coronary artery disease, to attain a good tolerance result at a stress test (>9 minutes on Bruce protocol) and a negative one regarding the detection of ischemia at the electrocardiogram is connected with good prognostics and reduced ultimate mortality.
What does the cardiologist answer to the patient’s question “Did I make it?” after the completion of the stress test?
There is no meaning in the expression “make it” because every patient has a different fitness level and what is important for the diagnosis is to achieve the maximum predicted heart rate (maximum heart beats) for a certain age (see beyond, how to estimate the maximum predicted heart rate). However, many patients stop earlier because they experience acute muscle fatigue (not good physical condition) or because they have symptoms of pain in the chest, or because they experience dangerous arrhythmias, or because the doctor detects signs of severe myocardial ischemia on ECG. In several cases, the test is interrupted by a sudden and significant increase in blood pressure or conversely sometimes due to a sharp and substantial drop in pressure during the test. In each case of interruption due to patient’s exhaustion, the test has prognostic value if it is generally achieved at least the 85% of the maximum predicted heart rate. Therefore, when a patient asks, “if I made it” the answer include a simplified explanation of all the parameters taken into account during a stress test.
Often patients, after the completion of the test, ask the doctor whether “it was a good test”.
The physician should explain to the patient the findings of the stress test and also, whether he or she needs to undergo more tests. In many cases, patients are confused about the result of the test e.g. a positive or a negative test. It should be clearly stated in its outcome that the test is positive for ischemia (i.e. there is a myocardial ischemia issue at the electrocardiogram) or that the test is negative of ischemia (i.e. there is no myocardial ischemia issue at the electrocardiogram). Patients are often confused with the terms “positive” and “negative”, but in general, a positive test for ischemia may need further examination and the negative test for ischemia would not. The attending cardiologist will determine the need for further examination after he or she is informed about the test result. It goes without saying that the occurrence or not of severe arrhythmias and also, the variation in the blood pressure during the test are reported in the findings.
Many patients come to take the stress because they are over 40 and heard that “you should do a stress test after 40”.
This is not exactly true, though indeed the possibility to develop some atheromatous disease in the arteries increases with age. As aforementioned if the patient is asymptomatic and if he or she does not have any of the known risk factors (high cholesterol, diabetes, hypertension, smoking, family history of CHD), the prognostic value of the test is very low. Consequently, the general saying “I grew up, let’s have a preventive stress test” does not apply.