Exercise ECG Testing

Synonyms include exercise tolerance testing, treadmill testing, ETT.

The evaluation of chest pain can be very difficult. It is possible to have a normal resting ECG with considerable narrowing of the coronary arteries. Exercise testing was developed in the 1950s with the Bruce protocol published in 1963. It is now a well established technique.

Exercise ECG testing can be used in the following circumstances:¹

• Assessing a clinical diagnosis of angina
• Risk stratification after myocardial infarction
• Risk stratification in patients with hypertrophic cardiomyopathy
• Evaluation of revascularisation procedures or drug treatment
• Evaluation of exercise tolerance and cardiac function
• Assessment of cardiopulmonary function in patients with dilated cardiomyopathy or heart failure
• Assessment of treatment for arrhythmia
• Assessment of asymptomatic people in high risk occupations like airline pilots

• Exercise testing has been quoted as having a sensitivity of 78% and a specificity of 70% in detecting coronary artery disease.¹ Thus a negative test may not necessarily be true and further testing or advice may be warranted. There is a suggestion that not enough women and the elderly are being tested.² Atypical chest pain is more common in women and risk factors that apply to men are not directly applicable.³
• Prognostic testing can be useful. A positive test at a low workload is a poor prognostic sign and it indicates the need for urgent treatment.

• The Bruce protocol is very widely used and has been extensively validated. There are 7 stages of 3 minutes each so that a complete test takes 21 minutes.
• The level of exercise is estimated in METs where 1 MET (metabolic equivalent) is the amount of energy expended at rest or 3.5 ml oxygen per kilogram per minute.
• In the first stage the patient walks at a set incline and then gradually the incline is increased as is the speed. Some patients will walk through the whole test and others may run towards the higher levels of intensity. The duration and MET level will be decided upon an individual basis. The information from an ETT can be used to advise the patient on what activities and exercise levels are reasonable.
• A modified Bruce protocol is used for exercise testing within one week of myocardial infarction and for those who are old and frail or expected to have poor exercise tolerance for other reasons. It starts at a lower work level and so takes longer to achieve the required heart rate.
• An adequate test is performed if the patient can achieve 85% of their maximum heart rate (calculated as 220-age in years for men and 210-age for women).¹
• Beta blockers are usually stopped the day before if possible as they can prevent an adequate heart rate being achieved. Digoxin will also need to be stopped a week before as the effect on the ST segment (reverse tick appearance) can make interpretation difficult.

• The patient is connected to the exercise ECG machine and a resting ECG is performed as is a baseline blood pressure measurement.
• Baseline ECG whilst standing and during hyperventilation may also be taken (T wave changes can occur on standing).¹ These can help in the analysis later.
• Before starting, patients will be informed about how to stop the treadmill and to inform staff if they have chest pain or any other symptoms. They will also have a blood pressure cuff around one arm and need to be informed to let their arm hang lose every time blood pressure needs to be recorded.
• Blood pressure is measured before starting and at the end of each stage of exercise. During the test it is common for systolic blood pressure to rise and diastolic blood pressure to fall slightly (normal response to exercise). But if systolic blood pressure falls during the exercise this indicates serious cardiac dysfunction and the patient may be having an acute MI. The test must be instantly terminated and help sought.
• The test can continue for approximately 20 minutes - but in most will be terminated at 12 minutes if no changes or problems have occurred.
• ECG recording and blood pressure measurements will continue in the rest period which can last up to 15 minutes. Adverse changes can occur during the recovery period and indicate the same risks as changes in the exercise period e.g. arrhythmias, ST depression.

The incidence of serious complications including death or acute myocardial infarction is low if patients are adequately selected.

• Death or myocardial infarction occurs in about 1 in 10,000 tests or 0.01%.¹
• Ventricular tachycardia or ventricular fibrillation may occur in about 1 in 5,000.¹

Full CPR equipment must be present and test supervisors must be able to provide CPR if needed.

The following are contraindications to performing the test:

• Acute myocardial infarction in the previous 4 to 6 days
• Unstable angina with rest pain in the previous 48 hours
• Uncontrolled heart failure
• Acute myocarditis or pericarditis
• Acute systemic infection
• Deep vein thrombosis is likely to shift and cause pulmonary embolism
• Uncontrolled hypertension with a systolic blood pressure >220mmHg or diastolic >120mmHg
• Severe aortic stenosis can cause sudden death on exercise
• Severe hypertrophic obstructive cardiomyopathy
• Untreated life threatening arrhythmia
• Dissecting aneurysm
• Recent aortic surgery

In asymptomatic aortic stenosis, a limited ETT may be of value to reassure the patient that a certain degree of exercise can be tolerated but it cannot be used to assess coronary artery disease.⁴

• An abnormal ST segment response is when there is horizontal (planar) or down-sloping depression of >1mm. Some people take 0.5mm or 2mm as their endpoint.
• T wave elevation of >1mm in leads without Q waves is also abnormal. It suggests severe coronary artery disease and poor prognosis.
• T wave changes such as inversion and pseudo-normalisation when an inverted T wave becomes upright are non-specific changes.
• A highly specific sign of ischaemia is inversion of the U wave but U waves are often difficult to identify when present, especially at high heart rates and so this finding is not sensitive.
• Extrasystoles induced by exercise are of no significance for coronary artery disease.

The test may be stopped for the following reasons:

ECG criteria¹

• Severe ST depression of >3mm
• ST elevation >1mm in non-Q wave lead
• Frequent ventricular extrasystoles unless the test is to assess a ventricular arrhythmia
• Onset of ventricular tachycardia
• New atrial fibrillation or supraventricular tachycardia
• Development of new bundle branch block
• Progression of heart block to second or third degree
• Cardiac arrest

Symptoms and signs¹

• Patient too exhausted to continue
• Severe chest pain, dyspnoea, or dizziness
• Fall in systolic blood pressure beyond 20mmHg
• Rise in blood pressure above systolic of 300mmHg or diastolic of 130mmHg
• Unsteadiness
• The most common reason for stopping a test is fatigue and breathlessness as a result of the unaccustomed exercise

Normal changes that are not a reason to stop the test include¹

• P wave increases in height
• R wave decreases in height
• J point becomes depressed (the J point is an isoelectric point between the T wave and the next P)
• ST segment becomes sharply up-sloping
• Q-T interval shortens
• T wave decreases in height

This is a non-invasive screening test rather than a "gold standard".

The following findings suggest high probability of coronary artery disease

• Horizontal ST segment depression of <2mm
• Down-sloping ST segment depression
• Early positive findings within 6 minutes
• Persistence of ST depression for more than 6 minutes after stopping
• ST segment depression in 5 or more leads
• Hypotension with exercise

Limitations

• 20% of normal people have ST depression on ambulatory ECG monitoring.¹
• An abnormal resting ECG e.g. LVH, BBB makes interpretation of ETT more difficult - it is probably better to opt for a different investigation e.g. myocardial perfusion scanning.

Diagnostic testing¹

• ST depression indicates the possibility of coronary artery disease. The greater the depression the greater the probability of coronary artery disease.
• ST depression which occurs at low levels of intensity or are associated with symptoms/signs indicates more severe or extensive disease.
• False positive results are common in women and younger patients.

Prognostic testing¹

• Exercise testing in patients who have just had a myocardial infarction is indicated only if a revascularisation procedure is contemplated. The modified Bruce protocol is used in which the level of intensity is lower than that usually used. Indicators of poor prognosis include exercise induced hypotension and asymptomatic ST depression.
• Drivers of LGVs and PCVs have to achieve test results clearly specified by the DVLA before they are considered fit to resume driving.

Screening¹

• Testing asymptomatic patients (regardless of risk score) is controversial because of the high false positive rate and presence of angina should be used as an indication for the investigation. However, asymptomatic testing does take place in high risk occupations e.g. airline pilots.
• Part of the Framingham study involved exercise testing of asymptomatic men and women.⁵ Among asymptomatic men, ST-segment depression, failure to reach target heart rate and exercise capacity during ETT provided prognostic information over and above the Framingham risk score, particularly among those at highest risk. The evaluation of the results in women was limited by the sample size and the few CHD events in women.
• The testing of asymptomatic adults without high risk scores is controversial at best. An expert American group concluded that a wealth of data indicate that exercise testing can be used to assess and refine prognosis, particularly when emphasis is placed on measures other than ECG such as exercise capacity, chronotropic response, heart rate recovery, and ventricular ectopics.⁶

• Referral to cardiologists who are most likely to proceed with coronary angiography with or without intervention. Some of these patients may actually need to go on and have coronary artery bypass grafting.
• If an inadequate test was performed this may be followed by further cardiac investigations, most likely myocardial perfusion scanning. This can be very useful in the elderly⁷ where COPD or arthritis may prevent adequate exercise ability. In the elderly⁸ thallium scanning can produce slightly more reliable results than ETT.
• Stress echocardiography⁹ is also used at times.

There are three newer techniques that may be more widely used in the future.¹⁰ One is cardiac computerised tomography (CCT) but this provides an even higher dose of radiation than plain x-rays. Another is single photon emission computer tomography (SPECT) that gives a functional rather than an anatomical picture. The third and possibly the most important is cardiac MRI scanning. The advantage of MRI is that it gives a far more detailed 3-dimensional picture than x-rays and without the hazards of exposure to radiation.