Stress Testing



Stress Testing


Ian Brown

Donald Schreiber



BACKGROUND AND APPROACH

Stress testing is one diagnostic instrument currently available to medical professionals for the evaluation and risk stratification of patients with known or suspected coronary artery disease (CAD). Stress testing may be done with concurrent electrocardiogram (ECG) monitoring, nuclear scintigraphy, or echocardiography. Indeed, the different tests and the wide variety of patients tested have made stress testing an increasingly complex and challenging area for practitioners. This chapter is aimed at providing the reader with an enhanced understanding of the subject. The first portion of this chapter examines exercise stress testing, describing which patients would benefit from exercise stress tests, the appropriate timing for these tests, and test protocols. The next section details pharmacologic and imaging alternatives, reviewing the indications for each and comparing the different modalities. The final section gives guidelines on interpretation of stress test results.


INDICATIONS

Stress tests have two primary indications: to diagnose CAD and to riskstratify patients with known CAD.


Diagnosis of Obstructive CAD

For patients with symptoms of chest pain, or possible anginal equivalent, the medical provider reviews the history, physical, and ECG to help establish the likelihood that symptoms are due to CAD (Table 2-1). If the diagnosis is unclear, the physician can use a stress test to assist in the diagnosis of CAD.1

Stress tests are most useful in patients with intermediate pretest probability of CAD. If the patient has a high pretest probability of CAD, then the results of a stress test are not likely to change the management. If the patient has a low pretest probability, then the frequency of false positive tests may lead to overtreatment and/or unnecessary procedures. Note that inTable 2-1, a 40-year-old male with a clinical diagnosis of nonanginal chest pain is still considered intermediate pretest probability for CAD. This underscores the limitations of clinical evaluation for ruling out CAD. Table 2-2 lists indications for exercise stress testing.









TABLE 2-1 Pretest probability of CAD




































































Age

Gender

Typical/Definitive angina pectoris

Atypical/Probable angina pectoris

Nonanginal chest pain

Asymptomatic


30-39

Male

Intermediate

Intermediate

Low

Very Low

Female

Intermediate

Very Low

Very Low

Very Low


40-49

Male

High

Intermediate

Intermediate

Low

Female

Intermediate

Low

Very Low

Very Low


50-59

Male

High

Intermediate

Intermediate

Low

Female

Intermediate

Intermediate

Low

Very Low


60-69

Male

High

Intermediate

Intermediate

Low

Female

High

Intermediate

Intermediate

Low


From Gibbons RJ, Balady GJ, Timothy Bricker J, et al. ACC/AHA 2002 guideline update for exercise testing: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). 2002; and from Diamond G, Forrester J. Analysis of probability as an aid in the clinical diagnosis of coronary-artery disease. N Engl J Med. 1979;300:1350-1358.


Stress tests also play an important role in evaluating CAD in the context of preoperative risk evaluation. Stress testing is most useful in patients with intermediate clinical cardiac risk who either have poor functional capacity (<4 METS) or who have better functional capacity (≥4 METS) but are undergoing a high-risk surgical procedure. Stress testing is also useful in patients who are in a low clinical cardiac risk group but have poor functional capacity and are undergoing a high-risk surgical procedure. A stepwise approach to preoperative cardiac risk evaluation for non-cardiac surgery is explored elsewhere.4


Risk Assessment in Patients with Symptoms or History of CAD

In patients with suspected or confirmed CAD, stress tests may be used for risk assessment: to develop a prognosis, and to help guide treatment. Table 2-3 shows indications for stress tests in these patients.









TABLE 2-2 Indications for exercise testing to diagnose obstructive CAD














































Class I (Evidence and/or General Agreement that Procedure is Useful)


•

Patients with an intermediate pretest probability of CAD on basis of gender, age, and symptoms (Table 2-1)


Class IIa (Weight of Evidence/Opinion is in Favor of Usefulness)


•

Patients with vasospastic angina


Class IIb (Usefulness Less Well Established)


•

Patients with high pretest probability of CAD


•

Patients with low pretest probability of CAD


•

Patients with <1 mm of baseline ST depression taking digoxin


•

Patients with ECG criteria for LVH with <1mm of ST depression


Class III (Evidence/Opinion that Procedure is Not Useful and May be Harmful)


•

Patients with any of the following baseline ECG abnormalities:


•

Pre-excitation syndrome (e.g., WPW)


•

Electronically paced ventricular rhythm


•

>1 mm resting ST depression


•

Complete LBBB


ECG, electrocardiogram; LVH, left ventricular hypertrophy; WPW, Wolff-Parkinson-White; LBBB, left bundle branch block. From Gibbons RJ, Balady GJ, Timothy Bricker J, et al. ACC/AHA 2002 guideline update for exercise testing: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines).



Long-Term Risk Assessment

Stress tests are useful to help predict survival. Risk stratification is improved when the stress test augments the history of the patient and the description of the pain. There are many risk stratification schemes based on electrocardiographic, hemodynamic, symptomatic and imaging parameters. These are reviewed in more detail in the last section of this chapter. High-risk patients may benefit from angiography, angioplasty, or revascularization.


Short-Term Risk Assessment

For patients presenting with symptoms of acute coronary syndrome (ACS)—that is, with unstable angina (UA) or myocardial infarct (MI)—stress tests are useful to predict short-term risk.









TABLE 2-3 Risk assessment in patients with symptoms or history of CAD




















































Class I (Evidence and/or General Agreement that Procedure is Useful)


•

Patients undergoing initial evaluation with suspected or known CAD


•

Patients with suspected or known CAD who present with significant change in status


•

Low-risk UA patients, 8-12 hours after presentation, who have been free of active ischemic or heart failure symptoms


•

Intermediate-risk UA patients, 2-3 days after presentation, who have been free of active ischemic or heart failure symptoms


Class IIa (Weight of Evidence/Opinion is in Favor of Usefulness)


•

Intermediate-risk UA patients who have initial normal cardiac markers, repeat ECG without significant change, normal cardiac markers 6-12 hours after the onset of symptoms, and no other evidence of ischemia during observation


Class IIb (Usefulness Less Well Established)


•

Patients with any of the following baseline ECG abnormalities:


•

Pre-excitation syndrome (e.g., WPW)


•

Electronically paced ventricular rhythm


•

>1 mm resting ST depression


•

Complete LBBB or any IVCD with QRS >120


•

Patients with stable clinical course who undergo periodic monitoring to guide treatment


Class III (Evidence/Opinion that Procedure is Not Useful and May be Harmful)


•

Patients with severe comorbidity likely to limit life expectancy and/or candidacy for revascularization


•

High-risk UA patients


CAD, Coronary artery disease; UA, unstable angina; ECG, electrocardiogram; WPW, Wolff-Parkinson-White; LBBB, left bundle branch block; IVCD, interventricular conduction defect. From Gibbons RJ, Balady GJ, Timothy Bricker J, et al. ACC/AHA 2002 guideline update for exercise testing: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). 2002.


The ability to rule out imminent ischemia is based on the test’s negative predictive value. The negative predictive value of a stress test is dependent upon the specific test used; however, for low to moderate risk patients who rule out by enzymes and have an adequate negative exercise stress test, the short-term event rate is generally very low. Gibler et al. showed that only 1 of 1010 patients in a chest pain unit who ruled out for acute myocardial infarction and had a negative stress test died (cause unknown) within 30 days.6 In
another study, 0 of 374 patients had a combined endpoint of death or acute MI at 150 days.7


CONTRAINDICATIONS

Stress tests are generally safe procedures.8 In a large national survey of exercise stress test facilities, encompassing both inpatient and outpatients, Stuard et al. enumerated complications including arrhythmias (<0.05%), infarcts (<0.04%), and death (<0.01%).9 Looking at a higher risk group—632 hospitalized subjects evaluated for unstable angina symptoms—Stein et al. reported the combined incidence of MI and death within 24 hours of exercise testing as 0.5%.10 Complications can be reduced by a careful history and physical, reviewing an ECG, and a pretest chest radiograph. Contraindications for exercise stress tests are shown in Table 2-4. Most of these contraindications are also applicable to pharmacologic stress tests.








TABLE 2-4 Contraindications to exercise stress tests

























































Absolute


•

Acute myocardial infarction (within 2 d)


•

High-risk unstable angina


•

Symptomatic or unstable arrhythmia


•

Symptomatic severe aortic stenosis


•

Uncontrolled symptomatic heart failure


•

Acute pulmonary embolus or pulmonary infarction


•

Acute myocarditis or pericarditis


•

Acute aortic dissection


Relative


•

Left main coronary stenosis


•

Moderate stenotic valvular heart disease


•

Electrolyte abnormalities


•

Severe hypertension (>200 mm Hg/100 mm Hg)


•

Tachyarrhythmias or bradyarrhythmias


•

Hypertrophic cardiomyopathy or other outflow tract obstruction


•

Mental or physical impairment leading to inability to exercise adequately


•

High-degree atrioventricular block


From Gibbons RJ, Balady GJ, Timothy Bricker J, et al. ACC/AHA 2002 guideline update for exercise testing: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). 2002.




TIMING OF STRESS TESTS

Stress tests should not be performed until the patient is clinically stable. Low-risk outpatients being evaluated for ACS symptoms should have a stress test within 72 hours.1 The majority of low-risk patients admitted to the hospital can safely obtain their stress tests as outpatients. Current guidelines recommend that the stress test be obtained within 72 hours of discharge.5 In general, outpatient stress tests for patients presenting via the emergency department (ED) with symptoms should be reserved for patients who are either at low risk for having ACS or low risk for short-term death or MI.11,12 Outpatient stress tests are appropriate only for adherent patients.

Observation or chest pain units are increasingly common and provide a middle ground between inpatient and outpatient testing. Patient selection and management are based on accelerated rule-out protocols that ideally include stress testing.5, 6, and 7,10,13 These units have been shown to decrease unnecessary admissions, reduce the rate of missed MIs, reduce costs, and increase patient satisfaction.

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Jul 16, 2016 | Posted by in CARDIOLOGY | Comments Off on Stress Testing

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