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Exercise electrocardiography
INVESTIGATIONS
Exercise electrocardiography
What’s new?
David Sprigings C
Matthew J Daniels
Exercise ECG is increasingly challenged by other tests that provide greater diagnostic accuracy or information that can more appropriately guide coronary revascularization procedures.
Abstract Exercise electrocardiography (exercise ECG) is the least expensive and most readily available functional test for atherosclerotic coronary artery disease (CAD). Its major weakness is limited accuracy, with a false negative rate of around 30% (sensitivity 70%), and a false positive rate of around 20% (specificity 80%). It provides diagnostic and prognostic information in patients presenting with suspected angina; when applied to those with known CAD it can stratify risk and guide management. Patients with resting ECG abnormalities (e.g., complete left bundle branch block) or with non-cardiac problems that limit their exercise tolerance, are better investigated by other tests. We describe how to perform an exercise ECG, the information yielded by the test and the integration of this information with clinical data. With greater access to more accurate tests, the future of exercise ECG as the workhorse for diagnosis of CAD is uncertain.
article focuses on performing the test and its interpretation, and the current place of the exercise ECG in the diagnosis of CAD.
Rationale and limitations of the exercise ECG In the presence of flow-limiting coronary disease, myocardial perfusion is typically normal at rest but insufficient during exercise, resulting in subendocardial ischaemia and abnormal ventricular repolarization, with ST segment depression on the surface ECG. The limitations of the exercise ECG can be summarized: not all patients with flow-limiting CAD manifest exerciseinduced ST depression; there is a false negative rate of around 30% (i.e., sensitivity of 70%)2; not all patients with exercise-induced ST depression have flow-limiting CAD; there is a false positive rate of around 20% (specificity 80%)2; the exercise ECG may be inconclusive if exercise tolerance is limited by non-cardiac factors; the exercise ECG cannot accurately identify the location of coronary stenoses or the extent of ischaemia associated with an individual stenosis (e.g., to guide percutaneous coronary intervention in multi-vessel CAD); the exercise ECG cannot provide direct information about left ventricular systolic function or myocardial viability.
Keywords Chest pain diagnosis; coronary artery disease; exercise ECG; exercise electrocardiography; exercise stress test
Introduction Many tests can be used to diagnose coronary artery disease (CAD) (Table 1); they are broadly divided into those that show the anatomy of epicardial coronary arteries, and those that reveal the functional effects of CAD. Invasive testing requires arterial cannulation, carries a higher risk and is costly. Non-invasive testing is therefore used first in most patients, particularly when the likelihood of CAD is considered to be moderate or low (i.e. <60%). Exercise ECG is the least expensive and most readily available non-invasive functional test, but is less accurate than the competition, and may not be feasible in certain groups of patients with a high prevalence of CAD e such as those with severe chronic obstructive pulmonary disease or peripheral arterial disease. When patients with major contraindications are excluded (Table 2), the exercise ECG is generally safe; the incidence of serious complications (e.g., ventricular fibrillation, acute coronary syndrome) is around one in 2500 tests.1 This
How to do an exercise ECG The exercise ECG is done using a motor-driven treadmill or stationary bicycle ergometer. Treadmill exercise is the more widely used method in the UK and USA. The exercise protocol (e.g., Bruce) specifies the speed and gradient of the treadmill, and the number and duration of exercise stages. Exercise stress testing can be safely done by cardiac physiologists or nursing staff: the minimum requirement is two trained personnel qualified in advanced life support. ECG electrodes are placed in the standard chest positions and at the base of the limbs (shoulders and hips). A 12-lead ECG is recorded before exercise. The ECG is monitored continuously, and further 12-lead ECGs are recorded at the end of each stage of exercise, at peak exercise, immediately on stopping, and during each min of recovery for at least 5 min and until any changes have resolved. A brief clinical assessment is made (Table 3), and the test is explained to the patient. The patient is asked to exercise for as long as possible and to report any symptoms. Exercise is then done until an end-point is reached (Table 4). The patient then rests on a chair for at least 5 min and until any symptoms have fully resolved. Blood pressure is measured before exercise with the patient standing, during the last min of each stage of exercise, and at peak exercise.
David Sprigings MA FRCP is Consultant Cardiologist at Northampton General Hospital, Northampton, UK. He qualified from the University of Oxford, and trained in general medicine and cardiology in Oxford and London. Competing interests: none. Matthew J Daniels BSc MA PhD MRCP is Clinical Lecturer in Cardiovascular Medicine in the University of Oxford and honorary specialist registrar in cardiology at the John Radcliffe Hospital, Oxford, UK. Competing interests: none.
MEDICINE 38:7
362
Ó 2010 Elsevier Ltd. All rights reserved.
INVESTIGATIONS
Tests for coronary artery disease
Anatomical
Invasive Selective coronary angiography
Non-invasive CT coronary calcium scoring CT coronary angiography
Functional
Intravascular ultrasound Coronary catheterization with pressure wire to measure fractional flow reserve (FFR)
Exercise ECG Stress echocardiography (using exercise or pharmacological stress) Myocardial perfusion imaging (using exercise or pharmacological stress) Cardiac magnetic resonance imaging (using pharmacological stress)
Table 1
Information derived from the exercise ECG
leads for at least three consecutive beats (with baseline stability), is the most reliable ECG sign of myocardial ischaemia. The following points should be remembered: ST depression may occur in subjects without heart disease, more commonly in women than in men. Cardiac causes of ST depression other than flow-limiting CAD include bundle branch block, left ventricular hypertrophy, pre-excitation and treatment with digoxin. The greater the degree of ST depression, the more likely is CAD. Down-sloping ST depression is a stronger predictor of CAD than horizontal ST depression, and both are more predictive than up-sloping ST depression. ST depression caused by CAD is most often seen in lead V5. ST depression confined to the inferior leads is seldom indicative of CAD. The location of ST depression is a poor predictor of the site of coronary stenoses.
Exercise duration Prognosis is closely related to the duration of exercise. As a ‘rule of thumb’, patients who can exercise into stage 4 of the Bruce protocol (or into stage 3 without ST segment change) are in a good prognostic group. Symptoms Angina during exercise is predictive of CAD, particularly when associated with ST depression. Haemodynamic response A decrease in systolic blood pressure during exercise below that obtained while standing at rest is a poor prognostic sign when caused by myocardial ischaemia.
ST segment response
Other information
ST segment elevation Exercise-induced ST elevation is relatively common in leads with Q waves from previous MI. ST elevation (other than in aVR or V1) in patients with a normal resting ECG represents transmural ischaemia and localizes the affected coronary artery. If this is seen, the test should be stopped and the patient admitted for stabilization.
Ventricular arrhythmia Ventricular tachycardia or fibrillation may be seen in patients with critical CAD. Frequent ventricular ectopy in the recovery period is associated with increased mortality. Heart rate recovery Delayed heart rate recovery after exercise is also associated with increased mortality.
ST segment depression Down-sloping or horizontal ST depression of 1 mm or more, measured 80 ms after the inflection point between the QRS complex and the ST segment (J point), in at least two contiguous
Combining data to predict prognosis The Duke treadmill score combines duration of exercise, maximum degree of ST segment shift, and the presence and
Contraindications to exercise testing Checklist before starting an exercise stress test C C C C C C C C C C
Acute coronary syndrome (within 2 days) Uncontrolled cardiac arrhythmia Symptomatic severe aortic stenosis Uncontrolled heart failure Acute pulmonary embolism Acute myocarditis or pericarditis Acute aortic dissection Acute systemic illness Resting blood pressure > 200/120 mmHg Significant risk of falling because of neurological or musculoskeletal disorder
C
C C
C C C C C
Table 3
Table 2
MEDICINE 38:7
Check equipment works (ECG monitoring, treadmill, resuscitation equipment) What is the indication for the test? Check the patient has no contraindications to exercise stress testing (Table 2) Has the patient’s clinical condition changed since the referral? What medications are being taken? Check blood pressure Check resting ECG e has it changed since the referral? Explain the test to the patient and obtain verbal/written consent
363
Ó 2010 Elsevier Ltd. All rights reserved.
INVESTIGATIONS
End-points of exercise ECG Absolute Relative C Patient expresses a wish to stop C Decrease in systolic blood pressure (BP) of >10 mmHg from C Moderate-to-severe angina standing BP at rest, without other evidence of myocardial ischaemia C Decrease in systolic blood pressure (BP) of >10 mmHg from C ST depression > 2 mm horizontal or down-sloping C Arrhythmia other than sustained ventricular tachycardia standing BP at rest, with other evidence of myocardial ischaemia C Signs of low cardiac output C Development of bundle branch block that cannot be distinguished C Sustained ventricular tachycardia from ventricular tachycardia C ST elevation > 1 mm in leads without diagnostic C Increasing chest pain C Fatigue, shortness of breath, leg pain Q waves (other than V1 or aVR) C Increasing neurological symptoms (e.g., ataxia, dizziness, presyncope) C Hypertensive response to exercise with systolic C Technical difficulties in monitoring ECG or BP BP > 250 mmHg/diastolic BP > 115 mmHg Table 4
severity of angina during the test, to yield a score that divides patients into groups at low risk (mortality < 1% per year), intermediate risk and high risk (mortality > 5% per year) (Figure 1).3 This score also correlates with the angiographic severity of coronary disease; patients with high-risk scores are likely to have three-vessel or left main-stem coronary disease. Other more recent nomograms incorporate additional clinical and exercise ECG data, and may have better discrimination than the Duke treadmill score.4
12 min of Bruce protocol. Achieved target heart rate. No chest pain. At peak exercise 2 mm plane ST depression. Comment: the likelihood of CAD in a woman of this age with non-specific chest pain is very low, and testing for CAD should not have been done. The probability of CAD remains low (<10%) despite the abnormal ST segment response to exercise. If further testing is required because of concern on the part of the patient (or cardiologist), stress echocardiography would be the preferred test, to avoid radiation exposure.
Interpretation of the exercise ECG
The exercise ECG and licensing of vocational drivers with arterial disease
The exercise ECG cannot give a yes/no answer to the question: does this patient have CAD? The probability of CAD is strongly influenced by the age, sex, risk factor profile and symptoms of the patient. The information from the exercise ECG can be combined with clinical data, to yield a revised estimate of the probability of CAD and the prognosis of the patient.5 The following examples illustrate some common clinical situations: Case 1: a 54-year-old man with a 3-month history of typical angina. Cigarette smoker. Normal examination and resting ECG. Exercised for 6 min of Bruce protocol, limited by knee arthritis. No chest pain or ST segment shift. Comment: the probability of CAD is very high (>90%), based on clinical characteristics. The exercise ECG does not demonstrate myocardial ischaemia, but is limited by non-cardiac factors. The probability of CAD remains high (>70%). Invasive coronary angiography is advised. Case 2: a 63-year-old woman with a 6-month history of atypical angina. Diet-controlled type 2 diabetes, non-smoker. Normal examination and resting ECG. Exercised for 10 min of Bruce protocol, limited by fatigue. No chest pain or ST segment shift. Comment: the pre-test probability of CAD is around 50%. This normal test result reduces the probability to <30%. The exercise duration, and absence of chest pain or ST segment shift place her in a group with a good prognosis (average annual mortality < 1.5% by Duke treadmill score). The patient was content not to take investigation further. If further testing was needed, CT coronary calcium scoring/coronary angiography or a functional imaging study could be done. Case 3: a 35-year-old woman with non-specific chest pain. No risk factors. Normal examination and resting ECG. Exercised for
MEDICINE 38:7
The Driver and Vehicle Licensing Agency (DVLA) requires drivers who hold a Group 2 licence (larger goods vehicles/ passenger carrying vehicles), and have a history of previously symptomatic CAD or other arterial disease, to undertake an exercise ECG every 3 years.6 To maintain the licence, the driver (off anti-anginal therapy for 48 h) must be able to complete 9 min of the Bruce protocol, without symptoms or horizontal/downsloping ST depression > 2 mm (equivalent to a Duke treadmill score predicted annual mortality of <2%).
The exercise ECG in screening for CAD As exercise ECG has limited accuracy in the detection of flowlimiting coronary stenoses, and cannot reveal non-flow-limiting coronary atheroma (which may be the substrate for acute coronary syndromes and sudden cardiac death), its usefulness in screening for CAD is predictably low. Some observational studies have shown an association between ST depression during exercise and the risk of sudden cardiac death in asymptomatic patients with coronary risk factors. However, no randomized controlled trials have shown that screening asymptomatic adults for CAD leads to improved outcomes. The exercise ECG is therefore not advised as a screening test for CAD in the absence of symptoms.
Other applications of the exercise ECG The exercise ECG has applications beyond the assessment of patients with suspected or known stable CAD: It can be safely extended to patients presenting with chest pain to the emergency department, provided ECG/troponin
364
Ó 2010 Elsevier Ltd. All rights reserved.
INVESTIGATIONS
Derivation of prognostic score from the exercise test ST-segment deviation during exercise
Ischaemia-reading line
Angina during exercise
0 mm
Prognosis 5-year survival 0.99
None
Non-limiting 1 mm
Exercise-limiting
Duration of exercise
Average annual mortality
0.98
0.2% 0.4%
0.95
1.0%
0.93 0.90
1.5% 2.0%
0.85 0.80 0.75 0.70
3.0% 4.0% 5.0% 6.0%
0.55
9.0%
MET
Minutes
20
18
17
15
13
12
10
9
7
6
5
3
0
0
2 mm
3 mm
4 mm
• The observed exercise-induced ST-segment deviation (the largest elevation or depression after resting changes have been subtracted) is marked on the first line. • The observed degree of angina during exercise is marked on the third line. • The marks for ST-deviation and degree of angina are connected with a straight edge. The point at which this line intersects the ischaemiareading line is noted. • The total number of minutes of exercise in treadmill testing according to the Bruce protocol (or the equivalent in multiples of resting oxygen consumption, METs, from an alternative protocol) is marked on the fifth line. • The mark for ischaemia is connected with that for duration of exercise. The point at which this line intersects the prognosis line indicates the 5-year survival and average annual mortality in patients with these characteristics. Source: Mark D B, Shaw L, Harrell F E Jr et al. N Engl J Med 1991; 325: 849–53.
Figure 1
results indicate a low probability of acute coronary syndrome, and other high-risk causes of chest pain (e.g., aortic dissection; Table 2) have been excluded.7 It can be used to investigate exertional symptoms (e.g., palpitation, syncope) which may reflect an exercise-induced arrhythmia. In hypertrophic cardiomyopathy, assessment of the risk of sudden death includes exercise ECG.8 An abnormal blood pressure response to exercise is associated with an increased risk of sudden death, especially in patients under age 40. In asymptomatic patients with severe aortic stenosis, an exercise ECG may be indicated to assess their objective exercise tolerance and blood pressure response to exercise, which will influence the decision regarding valve replacement.9 Exercise testing should not be done in symptomatic patients with severe aortic stenosis.
guideline is out for consultation and, if approved, will be ratified in 2010. Surprisingly, the exercise ECG is not recommended as the preferred first test for any group of patients. The exercise ECG is regarded as an acceptable alternative to non-invasive functional testing in patients with chest pain who have confirmed CAD (e.g., previous myocardial infarction or coronary revascularization). CT coronary calcium scoring is advised as the first test in patients with chest pain whose clinical characteristics give a probability of CAD of <30%, with further investigation dependent on the calcium score. It remains to be seen whether consultation will lead to a modification of this guideline, which in its current form will be difficult for most UK hospitals to implement.
Summary The exercise ECG cannot match the accuracy of other noninvasive tests for CAD, but is inexpensive and readily available (and does not expose the patient to radiation). It can provide diagnostic and prognostic information to guide further management. For these reasons, most UK cardiologists still use it as the first-line test in patients with suspected CAD who have a normal resting ECG and who are able to exercise. A
The future of the exercise ECG In 2009, the National Institute for Health and Clinical Excellence (NICE) published a guideline on the assessment and investigation of recent onset chest pain of suspected cardiac origin.10 This
MEDICINE 38:7
365
Ó 2010 Elsevier Ltd. All rights reserved.
INVESTIGATIONS
REFERENCES 1 Gibbons RJ, Balady GJ, Bricker JT, 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 on Exercise Testing). Circulation 2002; 106: 1883e92. 2 Gianrossi R, Detrano R, Mulvihill D, et al. Exercise-induced ST depression in the diagnosis of coronary artery disease: a metaanalysis. Circulation 1989; 80: 87e98. 3 Mark DB, Shaw L, Harrell Jr FE, et al. Prognostic value of a treadmill exercise score in outpatients with suspected coronary artery disease. N Engl J Med 1991; 325: 849e53. 4 Lauer MS, Pothier CE, Magid DJ, Smith SS, Kattan MW. An externally validated model for predicting long-term survival after exercise treadmill testing in patients with suspected coronary artery disease and a normal electrocardiogram. Ann Intern Med 2007; 147: 821e8. Software application available free at: http://clinicriskcalculators.org. 5 Diamond GA, Forrester JS. Analysis of probability as an aid in the clinical diagnosis of coronary-artery disease. N Engl J Med 1979; 300: 1350e8. 6 Driver and Vehicle Licensing Agency. At a glance guide to the current medical standards of fitness to drive. Available for download at: http://www.dft.gov.uk/dvla/medical/ataglance.aspx; September 2009. 7 Stein RA, Chaitman BR, Balady GJ, et al. Safety and utility of exercise testing in emergency room chest pain centers. An advisory from the Committee on Exercise, Rehabilitation, and Prevention, Council on Clinical Cardiology, American Heart Association. Circulation 2000; 102: 1463e7. 8 Elliott PM, Poloniecki J, Dickie S, et al. Sudden death in hypertrophic cardiomyopathy: identification of high risk patients. J Am Coll Cardiol 2000; 36: 2212e8.
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9 The Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology. Guidelines on the management of valvular heart disease. Eur Heart J 2007; 28: 230e68. 10 National Clinical Guidelines Centre for Acute and Chronic Conditions. Chest pain of recent onset: assessment and investigation of recent onset chest pain or discomfort of suspected cardiac origin: sections 1 and 2. Full guideline e consultation version. Available for download at: http://www.nice.org.uk/guidance/index. jsp?action¼folder&o¼44316; May 2009.
Practice points C
C
C
C
366
In patients with suspected or known coronary artery disease, exercise ECG provides diagnostic and prognostic information additional to that obtained from clinical assessment and the resting ECG. Patients with resting ECG abnormalities or with non-cardiac problems that limit their exercise tolerance are better investigated by other tests. The exercise ECG remains the standard test used by the DVLA to assess the cardiac fitness of vocational drivers with a history of ischaemic heart disease. Exercise duration is the single most important variable derived from the exercise ECG and is a powerful predictor of prognosis.
Ó 2010 Elsevier Ltd. All rights reserved.
Exercise electrocardiography
What’s new?
David Sprigings C
Matthew J Daniels
Exercise ECG is increasingly challenged by other tests that provide greater diagnostic accuracy or information that can more appropriately guide coronary revascularization procedures.
Abstract Exercise electrocardiography (exercise ECG) is the least expensive and most readily available functional test for atherosclerotic coronary artery disease (CAD). Its major weakness is limited accuracy, with a false negative rate of around 30% (sensitivity 70%), and a false positive rate of around 20% (specificity 80%). It provides diagnostic and prognostic information in patients presenting with suspected angina; when applied to those with known CAD it can stratify risk and guide management. Patients with resting ECG abnormalities (e.g., complete left bundle branch block) or with non-cardiac problems that limit their exercise tolerance, are better investigated by other tests. We describe how to perform an exercise ECG, the information yielded by the test and the integration of this information with clinical data. With greater access to more accurate tests, the future of exercise ECG as the workhorse for diagnosis of CAD is uncertain.
article focuses on performing the test and its interpretation, and the current place of the exercise ECG in the diagnosis of CAD.
Rationale and limitations of the exercise ECG In the presence of flow-limiting coronary disease, myocardial perfusion is typically normal at rest but insufficient during exercise, resulting in subendocardial ischaemia and abnormal ventricular repolarization, with ST segment depression on the surface ECG. The limitations of the exercise ECG can be summarized: not all patients with flow-limiting CAD manifest exerciseinduced ST depression; there is a false negative rate of around 30% (i.e., sensitivity of 70%)2; not all patients with exercise-induced ST depression have flow-limiting CAD; there is a false positive rate of around 20% (specificity 80%)2; the exercise ECG may be inconclusive if exercise tolerance is limited by non-cardiac factors; the exercise ECG cannot accurately identify the location of coronary stenoses or the extent of ischaemia associated with an individual stenosis (e.g., to guide percutaneous coronary intervention in multi-vessel CAD); the exercise ECG cannot provide direct information about left ventricular systolic function or myocardial viability.
Keywords Chest pain diagnosis; coronary artery disease; exercise ECG; exercise electrocardiography; exercise stress test
Introduction Many tests can be used to diagnose coronary artery disease (CAD) (Table 1); they are broadly divided into those that show the anatomy of epicardial coronary arteries, and those that reveal the functional effects of CAD. Invasive testing requires arterial cannulation, carries a higher risk and is costly. Non-invasive testing is therefore used first in most patients, particularly when the likelihood of CAD is considered to be moderate or low (i.e. <60%). Exercise ECG is the least expensive and most readily available non-invasive functional test, but is less accurate than the competition, and may not be feasible in certain groups of patients with a high prevalence of CAD e such as those with severe chronic obstructive pulmonary disease or peripheral arterial disease. When patients with major contraindications are excluded (Table 2), the exercise ECG is generally safe; the incidence of serious complications (e.g., ventricular fibrillation, acute coronary syndrome) is around one in 2500 tests.1 This
How to do an exercise ECG The exercise ECG is done using a motor-driven treadmill or stationary bicycle ergometer. Treadmill exercise is the more widely used method in the UK and USA. The exercise protocol (e.g., Bruce) specifies the speed and gradient of the treadmill, and the number and duration of exercise stages. Exercise stress testing can be safely done by cardiac physiologists or nursing staff: the minimum requirement is two trained personnel qualified in advanced life support. ECG electrodes are placed in the standard chest positions and at the base of the limbs (shoulders and hips). A 12-lead ECG is recorded before exercise. The ECG is monitored continuously, and further 12-lead ECGs are recorded at the end of each stage of exercise, at peak exercise, immediately on stopping, and during each min of recovery for at least 5 min and until any changes have resolved. A brief clinical assessment is made (Table 3), and the test is explained to the patient. The patient is asked to exercise for as long as possible and to report any symptoms. Exercise is then done until an end-point is reached (Table 4). The patient then rests on a chair for at least 5 min and until any symptoms have fully resolved. Blood pressure is measured before exercise with the patient standing, during the last min of each stage of exercise, and at peak exercise.
David Sprigings MA FRCP is Consultant Cardiologist at Northampton General Hospital, Northampton, UK. He qualified from the University of Oxford, and trained in general medicine and cardiology in Oxford and London. Competing interests: none. Matthew J Daniels BSc MA PhD MRCP is Clinical Lecturer in Cardiovascular Medicine in the University of Oxford and honorary specialist registrar in cardiology at the John Radcliffe Hospital, Oxford, UK. Competing interests: none.
MEDICINE 38:7
362
Ó 2010 Elsevier Ltd. All rights reserved.
INVESTIGATIONS
Tests for coronary artery disease
Anatomical
Invasive Selective coronary angiography
Non-invasive CT coronary calcium scoring CT coronary angiography
Functional
Intravascular ultrasound Coronary catheterization with pressure wire to measure fractional flow reserve (FFR)
Exercise ECG Stress echocardiography (using exercise or pharmacological stress) Myocardial perfusion imaging (using exercise or pharmacological stress) Cardiac magnetic resonance imaging (using pharmacological stress)
Table 1
Information derived from the exercise ECG
leads for at least three consecutive beats (with baseline stability), is the most reliable ECG sign of myocardial ischaemia. The following points should be remembered: ST depression may occur in subjects without heart disease, more commonly in women than in men. Cardiac causes of ST depression other than flow-limiting CAD include bundle branch block, left ventricular hypertrophy, pre-excitation and treatment with digoxin. The greater the degree of ST depression, the more likely is CAD. Down-sloping ST depression is a stronger predictor of CAD than horizontal ST depression, and both are more predictive than up-sloping ST depression. ST depression caused by CAD is most often seen in lead V5. ST depression confined to the inferior leads is seldom indicative of CAD. The location of ST depression is a poor predictor of the site of coronary stenoses.
Exercise duration Prognosis is closely related to the duration of exercise. As a ‘rule of thumb’, patients who can exercise into stage 4 of the Bruce protocol (or into stage 3 without ST segment change) are in a good prognostic group. Symptoms Angina during exercise is predictive of CAD, particularly when associated with ST depression. Haemodynamic response A decrease in systolic blood pressure during exercise below that obtained while standing at rest is a poor prognostic sign when caused by myocardial ischaemia.
ST segment response
Other information
ST segment elevation Exercise-induced ST elevation is relatively common in leads with Q waves from previous MI. ST elevation (other than in aVR or V1) in patients with a normal resting ECG represents transmural ischaemia and localizes the affected coronary artery. If this is seen, the test should be stopped and the patient admitted for stabilization.
Ventricular arrhythmia Ventricular tachycardia or fibrillation may be seen in patients with critical CAD. Frequent ventricular ectopy in the recovery period is associated with increased mortality. Heart rate recovery Delayed heart rate recovery after exercise is also associated with increased mortality.
ST segment depression Down-sloping or horizontal ST depression of 1 mm or more, measured 80 ms after the inflection point between the QRS complex and the ST segment (J point), in at least two contiguous
Combining data to predict prognosis The Duke treadmill score combines duration of exercise, maximum degree of ST segment shift, and the presence and
Contraindications to exercise testing Checklist before starting an exercise stress test C C C C C C C C C C
Acute coronary syndrome (within 2 days) Uncontrolled cardiac arrhythmia Symptomatic severe aortic stenosis Uncontrolled heart failure Acute pulmonary embolism Acute myocarditis or pericarditis Acute aortic dissection Acute systemic illness Resting blood pressure > 200/120 mmHg Significant risk of falling because of neurological or musculoskeletal disorder
C
C C
C C C C C
Table 3
Table 2
MEDICINE 38:7
Check equipment works (ECG monitoring, treadmill, resuscitation equipment) What is the indication for the test? Check the patient has no contraindications to exercise stress testing (Table 2) Has the patient’s clinical condition changed since the referral? What medications are being taken? Check blood pressure Check resting ECG e has it changed since the referral? Explain the test to the patient and obtain verbal/written consent
363
Ó 2010 Elsevier Ltd. All rights reserved.
INVESTIGATIONS
End-points of exercise ECG Absolute Relative C Patient expresses a wish to stop C Decrease in systolic blood pressure (BP) of >10 mmHg from C Moderate-to-severe angina standing BP at rest, without other evidence of myocardial ischaemia C Decrease in systolic blood pressure (BP) of >10 mmHg from C ST depression > 2 mm horizontal or down-sloping C Arrhythmia other than sustained ventricular tachycardia standing BP at rest, with other evidence of myocardial ischaemia C Signs of low cardiac output C Development of bundle branch block that cannot be distinguished C Sustained ventricular tachycardia from ventricular tachycardia C ST elevation > 1 mm in leads without diagnostic C Increasing chest pain C Fatigue, shortness of breath, leg pain Q waves (other than V1 or aVR) C Increasing neurological symptoms (e.g., ataxia, dizziness, presyncope) C Hypertensive response to exercise with systolic C Technical difficulties in monitoring ECG or BP BP > 250 mmHg/diastolic BP > 115 mmHg Table 4
severity of angina during the test, to yield a score that divides patients into groups at low risk (mortality < 1% per year), intermediate risk and high risk (mortality > 5% per year) (Figure 1).3 This score also correlates with the angiographic severity of coronary disease; patients with high-risk scores are likely to have three-vessel or left main-stem coronary disease. Other more recent nomograms incorporate additional clinical and exercise ECG data, and may have better discrimination than the Duke treadmill score.4
12 min of Bruce protocol. Achieved target heart rate. No chest pain. At peak exercise 2 mm plane ST depression. Comment: the likelihood of CAD in a woman of this age with non-specific chest pain is very low, and testing for CAD should not have been done. The probability of CAD remains low (<10%) despite the abnormal ST segment response to exercise. If further testing is required because of concern on the part of the patient (or cardiologist), stress echocardiography would be the preferred test, to avoid radiation exposure.
Interpretation of the exercise ECG
The exercise ECG and licensing of vocational drivers with arterial disease
The exercise ECG cannot give a yes/no answer to the question: does this patient have CAD? The probability of CAD is strongly influenced by the age, sex, risk factor profile and symptoms of the patient. The information from the exercise ECG can be combined with clinical data, to yield a revised estimate of the probability of CAD and the prognosis of the patient.5 The following examples illustrate some common clinical situations: Case 1: a 54-year-old man with a 3-month history of typical angina. Cigarette smoker. Normal examination and resting ECG. Exercised for 6 min of Bruce protocol, limited by knee arthritis. No chest pain or ST segment shift. Comment: the probability of CAD is very high (>90%), based on clinical characteristics. The exercise ECG does not demonstrate myocardial ischaemia, but is limited by non-cardiac factors. The probability of CAD remains high (>70%). Invasive coronary angiography is advised. Case 2: a 63-year-old woman with a 6-month history of atypical angina. Diet-controlled type 2 diabetes, non-smoker. Normal examination and resting ECG. Exercised for 10 min of Bruce protocol, limited by fatigue. No chest pain or ST segment shift. Comment: the pre-test probability of CAD is around 50%. This normal test result reduces the probability to <30%. The exercise duration, and absence of chest pain or ST segment shift place her in a group with a good prognosis (average annual mortality < 1.5% by Duke treadmill score). The patient was content not to take investigation further. If further testing was needed, CT coronary calcium scoring/coronary angiography or a functional imaging study could be done. Case 3: a 35-year-old woman with non-specific chest pain. No risk factors. Normal examination and resting ECG. Exercised for
MEDICINE 38:7
The Driver and Vehicle Licensing Agency (DVLA) requires drivers who hold a Group 2 licence (larger goods vehicles/ passenger carrying vehicles), and have a history of previously symptomatic CAD or other arterial disease, to undertake an exercise ECG every 3 years.6 To maintain the licence, the driver (off anti-anginal therapy for 48 h) must be able to complete 9 min of the Bruce protocol, without symptoms or horizontal/downsloping ST depression > 2 mm (equivalent to a Duke treadmill score predicted annual mortality of <2%).
The exercise ECG in screening for CAD As exercise ECG has limited accuracy in the detection of flowlimiting coronary stenoses, and cannot reveal non-flow-limiting coronary atheroma (which may be the substrate for acute coronary syndromes and sudden cardiac death), its usefulness in screening for CAD is predictably low. Some observational studies have shown an association between ST depression during exercise and the risk of sudden cardiac death in asymptomatic patients with coronary risk factors. However, no randomized controlled trials have shown that screening asymptomatic adults for CAD leads to improved outcomes. The exercise ECG is therefore not advised as a screening test for CAD in the absence of symptoms.
Other applications of the exercise ECG The exercise ECG has applications beyond the assessment of patients with suspected or known stable CAD: It can be safely extended to patients presenting with chest pain to the emergency department, provided ECG/troponin
364
Ó 2010 Elsevier Ltd. All rights reserved.
INVESTIGATIONS
Derivation of prognostic score from the exercise test ST-segment deviation during exercise
Ischaemia-reading line
Angina during exercise
0 mm
Prognosis 5-year survival 0.99
None
Non-limiting 1 mm
Exercise-limiting
Duration of exercise
Average annual mortality
0.98
0.2% 0.4%
0.95
1.0%
0.93 0.90
1.5% 2.0%
0.85 0.80 0.75 0.70
3.0% 4.0% 5.0% 6.0%
0.55
9.0%
MET
Minutes
20
18
17
15
13
12
10
9
7
6
5
3
0
0
2 mm
3 mm
4 mm
• The observed exercise-induced ST-segment deviation (the largest elevation or depression after resting changes have been subtracted) is marked on the first line. • The observed degree of angina during exercise is marked on the third line. • The marks for ST-deviation and degree of angina are connected with a straight edge. The point at which this line intersects the ischaemiareading line is noted. • The total number of minutes of exercise in treadmill testing according to the Bruce protocol (or the equivalent in multiples of resting oxygen consumption, METs, from an alternative protocol) is marked on the fifth line. • The mark for ischaemia is connected with that for duration of exercise. The point at which this line intersects the prognosis line indicates the 5-year survival and average annual mortality in patients with these characteristics. Source: Mark D B, Shaw L, Harrell F E Jr et al. N Engl J Med 1991; 325: 849–53.
Figure 1
results indicate a low probability of acute coronary syndrome, and other high-risk causes of chest pain (e.g., aortic dissection; Table 2) have been excluded.7 It can be used to investigate exertional symptoms (e.g., palpitation, syncope) which may reflect an exercise-induced arrhythmia. In hypertrophic cardiomyopathy, assessment of the risk of sudden death includes exercise ECG.8 An abnormal blood pressure response to exercise is associated with an increased risk of sudden death, especially in patients under age 40. In asymptomatic patients with severe aortic stenosis, an exercise ECG may be indicated to assess their objective exercise tolerance and blood pressure response to exercise, which will influence the decision regarding valve replacement.9 Exercise testing should not be done in symptomatic patients with severe aortic stenosis.
guideline is out for consultation and, if approved, will be ratified in 2010. Surprisingly, the exercise ECG is not recommended as the preferred first test for any group of patients. The exercise ECG is regarded as an acceptable alternative to non-invasive functional testing in patients with chest pain who have confirmed CAD (e.g., previous myocardial infarction or coronary revascularization). CT coronary calcium scoring is advised as the first test in patients with chest pain whose clinical characteristics give a probability of CAD of <30%, with further investigation dependent on the calcium score. It remains to be seen whether consultation will lead to a modification of this guideline, which in its current form will be difficult for most UK hospitals to implement.
Summary The exercise ECG cannot match the accuracy of other noninvasive tests for CAD, but is inexpensive and readily available (and does not expose the patient to radiation). It can provide diagnostic and prognostic information to guide further management. For these reasons, most UK cardiologists still use it as the first-line test in patients with suspected CAD who have a normal resting ECG and who are able to exercise. A
The future of the exercise ECG In 2009, the National Institute for Health and Clinical Excellence (NICE) published a guideline on the assessment and investigation of recent onset chest pain of suspected cardiac origin.10 This
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INVESTIGATIONS
REFERENCES 1 Gibbons RJ, Balady GJ, Bricker JT, 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 on Exercise Testing). Circulation 2002; 106: 1883e92. 2 Gianrossi R, Detrano R, Mulvihill D, et al. Exercise-induced ST depression in the diagnosis of coronary artery disease: a metaanalysis. Circulation 1989; 80: 87e98. 3 Mark DB, Shaw L, Harrell Jr FE, et al. Prognostic value of a treadmill exercise score in outpatients with suspected coronary artery disease. N Engl J Med 1991; 325: 849e53. 4 Lauer MS, Pothier CE, Magid DJ, Smith SS, Kattan MW. An externally validated model for predicting long-term survival after exercise treadmill testing in patients with suspected coronary artery disease and a normal electrocardiogram. Ann Intern Med 2007; 147: 821e8. Software application available free at: http://clinicriskcalculators.org. 5 Diamond GA, Forrester JS. Analysis of probability as an aid in the clinical diagnosis of coronary-artery disease. N Engl J Med 1979; 300: 1350e8. 6 Driver and Vehicle Licensing Agency. At a glance guide to the current medical standards of fitness to drive. Available for download at: http://www.dft.gov.uk/dvla/medical/ataglance.aspx; September 2009. 7 Stein RA, Chaitman BR, Balady GJ, et al. Safety and utility of exercise testing in emergency room chest pain centers. An advisory from the Committee on Exercise, Rehabilitation, and Prevention, Council on Clinical Cardiology, American Heart Association. Circulation 2000; 102: 1463e7. 8 Elliott PM, Poloniecki J, Dickie S, et al. Sudden death in hypertrophic cardiomyopathy: identification of high risk patients. J Am Coll Cardiol 2000; 36: 2212e8.
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9 The Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology. Guidelines on the management of valvular heart disease. Eur Heart J 2007; 28: 230e68. 10 National Clinical Guidelines Centre for Acute and Chronic Conditions. Chest pain of recent onset: assessment and investigation of recent onset chest pain or discomfort of suspected cardiac origin: sections 1 and 2. Full guideline e consultation version. Available for download at: http://www.nice.org.uk/guidance/index. jsp?action¼folder&o¼44316; May 2009.
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In patients with suspected or known coronary artery disease, exercise ECG provides diagnostic and prognostic information additional to that obtained from clinical assessment and the resting ECG. Patients with resting ECG abnormalities or with non-cardiac problems that limit their exercise tolerance are better investigated by other tests. The exercise ECG remains the standard test used by the DVLA to assess the cardiac fitness of vocational drivers with a history of ischaemic heart disease. Exercise duration is the single most important variable derived from the exercise ECG and is a powerful predictor of prognosis.
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