Exercise stress testing

Exercise stress testing (EST) using electrocardiography (ECG) is routinely performed to diagnose myocardial ischemia, estimate prognosis, evaluate the outcome of therapy, and assess cardiopulmonary reserve. Exercise is used as a physiological stress to detect cardiac abnormalities that are not present at rest. They are accomplished with a treadmill, bicycle ergometer, or rarely with an arm ergometer and may involve ventilatory gas analysis (the latter is called a cardiopulmonary stress test). Different protocols of progressive cardiovascular workload have been developed specifically for EST (e.g., Bruce, Cornell, Balke-Ware, Asymptomatic Cardiac Ischemia Pilot [ACIP], modified-ACIP [mACIP], Naughton, Weber). Bicycle ergometers are less expensive and smaller than treadmills and produce less motion of the upper body, but early fatigue of the lower extremities is a common problem that limits reaching maximal exercise capacity. As a result, treadmills are more commonly used in the United States for EST. Much of the reported data are based on the multistage Bruce Protocol, which is performed on a treadmill and has become the most commonly protocol used in clinical practice. ESTs may involve only ECG monitoring or may be combined with other imaging modalities (i.e., nuclear imaging, echocardiography).

Maximal EST or symptoms-limited EST is the preferred means to perform an EST and attempts to achieve the maximal exercise workload tolerated by the patient. It is terminated based on patient symptoms (e.g., fatigue, angina, shortness of breath), an abnormal ECG (e.g., significant ST depression or elevation, arrhythmias), or an abnormal hemodynamic response (e.g., abnormal blood pressure response). The goal of maximal EST is to achieve a heart rate response of at least 85% the maximal predicted heart rate (see Question 9).

Submaximal EST is performed when the goal is lower than the individual maximal exercise capacity. Reasonable targets are 70% of the maximal predicted heart rate, 120 beats per minute, or 5 to 6 metabolic equivalents (METs) of exercise capacity (see Question 12). Submaximal EST is used early after myocardial infarction (MI) (see Question 8).

Multiple studies have been reported comparing the accuracy of EST with coronary angiography. However, different criteria have been used to define a significant coronary stenosis, and this lack of standardization, in addition to a variable prevalence of coronary artery disease (CAD) in different populations, complicates the interpretation of the available data. A meta-analysis of 24,074 patients reported a mean sensitivity of 68% and a mean specificity of 77%. The sensitivity increases to 81% and the specificity decreases to 66% for multivessel disease, and to 86% and 53%, respectively, for left main disease or three-vessel CAD. The diagnostic accuracy of EST can be improved by combining other imaging techniques with EST such as echocardiography or myocardial perfusion imaging. The PROMISE trial randomized 10,003 symptomatic patients with suspected CAD to anatomic or functional noninvasive testing. Anatomic testing consisted of coronary computed tomography (CT) angiography (CCTA) and functional testing included EST (used in 10% of subjects), stress echocardiography (22%), or nuclear stress testing (68%). The study found no difference in composite of all-cause mortality, MI, hospitalization for unstable angina, and major complications from cardiovascular procedures between CTA and the various modalities of functional testing, thus supporting EST (which has the lowest cost and no radiation exposure) as the preferred testing strategy for the vast majority of patients with a moderate pretest likelihood of underlying CAD. The Scottish Computed Tomography of the HEART (SCOT-HEART) randomized 4146 patients to CCTA compared with standard care after EST among low- to intermediate-risk patients with chest pain suggestive of obstructive coronary disease, showing that the addition of CCTA was associated with a better prognosis after 5 years due to a reduction in nonfatal MI and improving the certainty in the diagnosis of angina due to coronary heart disease suggesting a complementary role of CCTA after EST.

When supervised by an adequately trained physician, the risks are very low. In the general population, the morbidity is less than 0.05% and the mortality is less than 0.01%, A survey of 151,944 patients 4 weeks after an MI showed slight increased mortality and morbidity of 0.03% and 0.09%, respectively. According to the national survey of EST facilities, MI and death can be expected in 1 per 2500 tests.

The most common indications for EST, according to the current American College of Cardiology (ACC) and American Heart Association (AHA) guidelines, are summarized in Box 5.1 . When ordering an EST, three fundamental variables need to be considered to achieve an optimal diagnostic test:

• Appropriate indication for EST.

• Normal baseline ECG ST-T segments.

• Ability to complete the planned exercise protocol.

In general, EST for asymptomatic patients is discouraged because the pretest probability of CAD in this population is low, leading to a significant number of false-positive results, requiring unnecessary follow-up tests and expenses without a well-documented benefit. There are no data from randomized studies that support the use of routine screening EST in asymptomatic patients to reduce the risk of cardiovascular events. Nevertheless, selected asymptomatic patients may be considered for EST under specific clinical circumstances if clinically appropriate (e.g., diabetic patients planning to enroll in a vigorous exercise program, certain high-risk occupations, positive calcium score, family history).

The contraindications and relative contraindications for EST according to the ACC/AHA guidelines are summarized in Box 5.2 .

During EST, three parameters are monitored and reported:

• The clinical response of the patient to exercise (e.g., shortness of breath, dizziness, chest pain, angina pectoris, Borg Scale score, functional capacity, etc.).

• The hemodynamic response (e.g., heart rate, blood pressure response, etc.).

• The ECG changes that occur during exercise and the recovery phase of EST.