M.W. Luong, MD, FRCPC, M. Ignaszewski, MD, C.M. Taylor, MD, FRCPC Stress testing: A contribution from Dr Robert A. Bruce, father of exercise cardiology The exercise treadmill test known as the Bruce protocol continues to play an important role in diagnosing coronary artery disease in intermediate-risk patients. ABSTRACT: Recognizing the im- hour and a 22% grade. The aim of r Robert Arthur Bruce was portant physiological relationship testing is to detect the presence of born in Somerville, Massa- between the heart and exercise, coronary artery disease by looking D chusetts, on 20 November Dr Robert Arthur Bruce undertook for electro cardiogram changes dur- 1916. He graduated from Boston research that revolutionized the ing times of stress. The sensitivity Uni versity with a bachelor of science way physicians approach cardiac of exercise treadmill testing is esti- degree and went on to finish his medi- disease. His contributions to exer- mated to be 70% and the specific- cal studies at the University of Roch- cise physiology and cardiology have ity to be 80%. These values range ester School of Medicine in 1943. In shaped many concepts used today broadly depending on multiple fac- 1950, at the age of 34, Dr Bruce was in clinical practice. He is best known tors, including the definition of a appointed as the first chief of cardiol- for developing a protocol for the ex- positive test result. The strongest ogy at the University of Washington ercise treadmill test known as the predictor of survival found on ex- School of Medicine, where he served Bruce protocol. Because of its uni- ercise treadmill testing is exercise as director for 21 years and co-direc- versality, reproducibility, and prac- capacity. Treadmill testing can also tor for another 10 years.1,2 ticality, the protocol remains one of be combined with imaging modali- During his time at the University the most widely used methods for ties to further increase sensitivity of Washington, Dr Bruce contributed diagnosing ischemic heart disease. and specificity, making it one of the to the evolution of the exercise tread- Patients commonly start exercising first tests considered when coro- mill test (ETT) from a single-stage on a treadmill set at 1.7 miles per nary artery disease is suspected in cardiac stress test to a multistage hour and a 10% grade, and increase a patient. examination called the Bruce proto- to a maximum speed of 6.0 miles per col, which involved increasing both speed and incline while monitoring a patient’s cardiovascular response using electrodes. Before the devel- opment of the Bruce protocol, physi- cians had been using the Master two- Dr Luong is a cardiology resident in the Divi- sion of Cardiology at the University of Brit- ish Columbia. Dr Ignaszewski is a medical resident at the State University of New York Upstate Medical University. Dr Taylor is a staff cardiologist in the Division of Cardiol- This article has been peer reviewed. ogy at the University of British Columbia. 70 BC MEDICAL JOURNAL VOL. 58 NO. 2, MARCH 2016 bcmj.org Stress testing: A contribution from Dr Robert A. Bruce, father of exercise cardiology step exercise test, which involves the Association of University Cardi- gen demand is from skeletal muscle, obtaining an electrocardiogram ologists in 1969.2,6 where oxygen extraction increases by (ECG) after a patient has repeatedly As a believer in practising his up to threefold. As exercise intensity climbed up onto and down from a own medicine, Dr Bruce enjoyed a increases, the increase in cardiac out- small platform,3,4 a test that can be too healthy lifestyle and walked a mile put by up to sixfold is due mainly to an strenuous for some patients. along the waterfront with his wife increased heart rate as stroke volume In 1963, when Dr Bruce described almost daily until his passing. Every plateaus. In addition, total peripheral the stress test in print, he identi- bit the gentleman, he donned a sport resistance and diastolic blood pres- fied angina as the development of coat and tie at a celebration of his life sure (DBP) decreases, while systolic chest pain with exercise due to either and career with his closest family, blood pressure (SBP) and pulse pres- underlying coronary artery disease friends, and colleagues on 11 Febru- sure increases.10 (CAD), a previous myocardial infarc- ary 2004 in Seattle, Washington.2,6 The heart rate increase during ex- tion (MI), or a ventricular aneurysm.5 He passed away the next day at age ercise is due to decreased vagal tone The ETT remains a well-proven tool 87 after a 13-year battle with chronic followed by increased sympathetic for diagnosing underlying CAD and lymphocytic leukemia. His discover- tone. As people age, beta-receptor for determining a patient’s maximal ies in exercise physiology and cardi- responsiveness decreases, leading to functional aerobic capacity, a term ology have altered the way cardiolo- a lower maximum heart rate and car- that Dr Bruce himself coined. gy is practised. Dr Bruce’s name will diac output in the elderly. A common Dr Bruce was also one of the remain synonymous with one of the and simplified method of estimating founders of the Seattle Heart Watch most extensively used screening and a person’s maximum heart rate is 220 program in 1971, which led to the diagnostic tools for detecting signs of minus age. To take into account indi- development of a database including CAD, and he will forever be known vidual variability, it is common prac- results from more than 10 000 indi- as the father of exercise cardiology tice to conclude that patients reach viduals who completed his treadmill because of this. their target heart rate at 85% of this test over a 10-year span. Using ambu- calculated maximum value.11 After latory cardiac patients and healthy Exercise treadmill testing exercise, the increased vagal tone will individuals as test subjects, the pro- Exercise treadmill testing to identify rapidly reduce the heart rate in the gram proved that the Bruce protocol CAD is now a widely available and first 30 seconds, followed by a more was both a reproducible and verifiable relatively low-cost examination that gradual decline back to baseline. method for diagnosing underlying has been used for more than 60 years.7 Another value that can be obtained heart disease. It is with this very data- The use of the ETT has expanded to from an ETT is a patient’s myocardi- base that Dr Bruce created the stan- include testing for functional capac- al oxygen uptake. This value is esti- dards we use when assessing today’s ity, chronotropic incompetence, car- mated by the product of heart rate patients.1,4 diac rehabilitation, valvular heart dis- and SBP. This rate-pressure product Publishing well over 300 articles, ease, hypertrophic cardiomyopathy, is important since myocardial oxy- Dr Bruce was an innovator above all, arrhythmias, and pacemaker evalua- gen uptake and coronary perfusion and was one of the first physicians tion.8-10 In addition, exercise testing are directly correlated. Since coro- to contemplate the benefit of throm- has been combined with other modal- nary flow can increase by up to five- bolysis in acute coronary syndrome. ities such as radionuclide imaging fold above baseline with exercise, a Moreover, his merging of cardiology and echocardiography to elicit infor- patient who has obstructed coronary with technology inspired him to suc- mation that may be required in select arteries cannot meet this increased cessfully measure QRS and ST seg- patients. demand and ischemia results. In gen- ments during exercise.1 The ETT can reveal cardiovas- eral, a rate-pressure product 25 000 Dr Bruce is truly a giant of car- cular abnormalities that are not seen or higher indicates that a patient has diovascular medicine, whose inquisi- at rest by taking measurements that achieved an adequate workload.10 The tive nature led him to research that unmask these during aerobic exer- rate-pressure product can also be used advanced the field. He held many cise, when the heart responds to the to estimate when ischemia occurs and leadership positions throughout his body’s demand for more oxygen by is a better predictor of when ischemia illustrious career, including founding increasing heart rate, stroke volume, will develop than the exercise testing and serving as the second president of and cardiac output. Much of this oxy- stage.12 BC MEDICAL JOURNAL VOL. 58 NO. 2, MARCH 2016 bcmj.org 71 Stress testing: A contribution from Dr Robert A. Bruce, father of exercise cardiology Maximal oxygen uptake (VO2 Table 1. Absolute contraindications for exercise testing.10 max) is an additional accurate repre- sentation of a person’s cardiovascu- Acute myocardial infarction, within 2 days lar fitness and exercise capacity, and Ongoing unstable angina is estimated from the peak workload Uncontrolled cardiac arrhythmia with hemodynamic compromise achieved on an ETT. This is usually Active endocarditis expressed in terms of a metabolic Symptomatic severe aortic stenosis equivalent task (MET), where 1 MET Decompensated heart failure is equal to 3.5 mL O2 per kg per min. The VO2 max value is affected by Acute pulmonary embolism, pulmonary infarction, or deep vein thrombosis age, gender, baseline exercise capac- Acute myocarditis or pericarditis ity and genetics.10 Metabolic equiva- Acute aortic dissection lent tasks (METs) can be estimated Physical disability that precludes safe and adequate testing based on the protocol used for an ETT. Table 2. Relative contraindications for exercise testing.10 Patient selection Exercise stress testing to diagnose Known obstructive left main coronary artery stenosis CAD is considered appropriate in an Moderate to severe aortic stenosis with uncertain relation to symptoms adult patient who is able to exercise Tachyarrhythmias with uncontrolled ventricular rates and who has an intermediate pretest Acquired advanced or complete heart block probability of CAD with an interpre- Hypertrophic obstructive cardiomyopathy with severe resting gradient table ECG.