Every year, firefighters across the country die or are taken out of work due to preventable medical conditions. Many of these conditions could have been identified in annual medical screenings and exams and treated before resulting in loss of life or injury time-off.
A Cardiac Stress Test may be a part of your fire department's routine physical exam or something your Primary Care Physician may suggest based on the nature of your work - but does just the thought of getting a "Treadmill" Stress Test give you chest pain you didn't have before?
Steve Vrieze (Volunteer Firefighter/EMT/Master Degree in Exercise Science) takes us into the University of Minnesota Medical Center in Cardiac Stress Testing to show us their facility and explains to us how this exam is administered and what to expect.
OVERVIEW OF A STRESS TEST
By Steve Vrieze, MS, NREMT-B
It’s quite likely that you know someone with heart disease. Heart disease has established itself as the No. 1 killer in the United States (1). According the American Heart Association (AHA) 375,000 lives are claimed each year and 735,000 people suffer a heart attack per year.
Similar to the rest of the American population, the fire service feels the effects of heart disease too. Sudden cardiac death (SCD) is the leading cause of on duty firefighter deaths (2). In most research SCD is an umbrella term that typically groups causes of abrupt loss of heart function together. In fact, 45% of all duty related deaths are due to heart disease. Furthermore for every SCD event, almost 17 non-fatal cardiovascular events occur (3). This means many fire departments, while not dealing with line of duty deaths, are still losing personnel to heart disease. With these findings the National Fire Protection Association suggests fire departments focus on detectable heart problems through annual medical exams and wellness programs.
One method for evaluating detectable heart problems is a cardiac stress test. If you mention to your department or personal physician that you have had any type of chest discomfort, shortness of breath, or palpitations, it is likely you will be scheduled to have a stress test. Elements such as age, risk factors, and previous heart history are considered when ordering a stress test. However, given the before mentioned statistics of heart disease and the fire service, it is likely a physician would order a stress test regardless of risk factors and medical history. There are a variety of stress tests available: exercise and non-exercise, as well as with and without heart imaging. Given the physical nature of firefighting, an exercise stress test is likely the type of test chosen for a firefighter. When looking at the diagnostic value of a stress test we often talk about specificity and sensitivity in clinical exercise testing. Specificity is the percent of those without heart disease that will have normal test results. In most cases the specificity of a stress test is 84%. Sensitivity is the percentage of those with heart disease that will have abnormal test results, which is typically 66% (4). In basic terms this means if you have disease and don’t know it, a majority of the time it will be discovered through a cardiac stress testing. If there this imaging added to the test these numbers can be increased.
Once a stress test is scheduled there are a number of things to expect. First, understand there is often a discrepancy between how your physician describes the test to you and how the actual test is performed. An exercise stress test can be performed using a variety of devices. While a treadmill remains the most common modality for testing, an upright bicycle is often used, or a supine bicycle is possible. Some places may even use a simple step in which the patient steps up and down to an audio cue. Secondly, you may have to have an I.V. placed prior to testing. For those with a phobia of needles this can often be a test taking deal-breaker if the patient isn’t prepared for it. The I.V. serves two purposes; first for safety and second for administration of an imaging solution. If any type of imaging is ordered with the stress test an I.V. is a given.
While the modality that a stress test is performed on may be different, the process often follows a common pattern: resting baseline, exercise, and recovery. During the rest phase, a patient has their blood pressure and electrocardiogram (ECG) assessed as well as reviewing cardiac history and risk factors. An ECG is an electrical recording of the heart. The ECG will consist of 10 sticky electrodes placed in various locations on the torso. For patients with chest hair, expect that the hair will be shaved for maximal adherence of the electrodes. With the skin prepped and electrodes applied, a resting ECG will be recorded as well as blood pressure measured. Blood pressure and ECG are recorded in a supine or lying position as well as in a standing position to assess for any abnormal postural change. Once the patient’s resting hemodynamic measurements and ECG is assessed, it’s time for the main event.
The exercise portion of a stress test follows incremental, pre-programmed stages from a well-established protocol. A stage can range from 2-3 minutes at a set speed and incline. Each stage increases in difficulty. A patient’s blood pressure, heart rate, and ECG are recorded and assessed during each stage of exercise. Standard exercise protocols, such as Bruce, Balke, or Naughton, are used because of the extensively researched blood pressure and heart rate responses for each stage. If blood pressure increases too rapidly that can be a sign of future hypertension as well as potentially being associated with coronary artery disease. A blood pressure that drops with exercise is suggestive of poor cardiac pumping function and possibly suggestive of heart disease. The ECG is assessed for changes during each stage. Electrical changes on the ECG can suggest inadequate blood flow through the arteries of the heart. ECG changes are the primary indicator of heart disease during a stress test. It is these changes a physician is most interested in.
Exercise testing is often a symptom limited procedure, meaning the patient exercises as long as possible, exerting a maximal effort and stopping only because of fatigue or the development of symptoms such as chest pain, or shortness of breath, etc. However, testing can be terminated for other reasons, such target heart rate achievement, exaggerated blood pressure response, or significant ECG changes. The typical exercise portion of a stress test can last approximately 6-12 minutes.
Once exercise has been terminated, the recovery phase begins. In some situations where cardiac imaging is involved the patient may completely stop moving so the imaging can be performed. However in most situations the intensity of the modality is decreased to allow the patient to gradually cool down. The patient’s heart rate, blood pressure and ECG are continually monitored as the patient’s hemodynamics return to pre-exercise levels. The ECG is monitored for any changes that may develop in recovery which could be indicative of heart disease. Once the patient’s heart rate and blood pressure as well as ECG have returned normal resting levels or the established levels of the testing center, testing is done. If stress testing is performed with a competent, experienced, and efficient staff, a stress test can be completed in about an hour.
The idea of a stress test can elicit anxiety in a person. When armed with knowledge of what to expect during testing, the event can be a little less stressful. Additionally the risk of an adverse event occurring with a stress test is very low, about 1 in 5,000. A stress test can provide information as to how the body responds to calculated and controlled exertion, which provides an understanding of how the body might react to the rigors of firefighting. If heart disease is detectable with a stress test, it could be deadly on the fireground if undetected. An ounce of prevention is worth a pound of cure.
Mozaffarian, D, E.J. Benjamin, A.S. Go. et al. Heart disease and stroke statistics – 2015 update: a report from American Heart Association. Circ. 131:e29-e322, 2015.
Fahy, R.F. U.S. firefighter fatalities due sudden cardiac death 1995-2004. Nat Fire Prot Assoc J. 99:44-47, 2005.
Smith, D.L., D.A. Barr, S.N. Kales. Extreme sacrifice: sudden cardiac death in the US fire service. Extreme Physiology and Medicine. 2:6-15, 2013.
Fletcher, G.F, G.J. Balady, E.A. Amsterdam, et al. Exercise standards for testing and training a statement for healthcare professionals from American Heart Association. Circulation. 104:1694-1740, 2001.