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Synonyms: include exercise ECG testing, treadmill testing, exercise stress test
Chest pain is a common presentation to both general practitioners and A&E departments. Often one of the main differentials is cardiac chest pain and ruling this out in patients who might be otherwise well or only have one or two cardiac risk factors, can be difficult. Exercise tolerance testing (ETT) is one method which is used to determine the presence of significant coronary heart disease.
ETT has been quoted as having a sensitivity of 78% and a specificity of 70% in detecting coronary artery disease. Thus, a negative test may not necessarily be true and further testing or advice may be warranted. Diagnostic accuracy is also poor in women and this may relate to smaller heart size. For this reason, ETT is being superseded by cardiac imaging techniques, such as myocardial perfusion scans, in some centres. Even so, ETT can be valuable when performed in selected patients and the following criteria have been suggested:
- Ability to exercise.
- Normal baseline 12-lead ECG.
- No previous cardiac revascularisation.
Indications for exercise tolerance testing
- Diagnosis of coronary heart disease (keeping in mind the high number of false positives and false negatives).
- Assessment of 'fitness' in certain occupations and medical conditions, eg the police force and some cardiomyopathies.
- Arrhythmias - ETT can help to record arrhythmias which are provoked by exercise (but only in those with non-life-threatening arrhythmias).
What the exercise tolerance test involves
- ETT consists of exercising on a treadmill following a defined protocol, the Bruce protocol, over approximately 20 minutes. The test begins gently and gradually the level of intensity is increased through a combination of increased treadmill speed and incline.
- Intensity of exercise is measured in in METs where 1 MET (metabolic equivalent) is the amount of energy expended at rest or 3.5 ml oxygen per kilogram per minute.
- The test is divided into seven stages of three minutes and there is also a less strenuous version called the modified Bruce.
- ECG is recorded throughout and blood pressure measured intermittently.
- ETT might be prematurely stopped for any of the following: development of chest pain, presence of ST elevation, very deep ST depression, arrhythmias, hypotension or if the patient becomes tired and is unable to continue. In addition, elevation of blood pressure to dangerous levels such as >170/120 mm Hg should also lead to termination of the test.
- Beta-blockers and digoxin can interfere with the results so are usually stopped before the ETT.
Contra-indications to exercise tolerance testing
- Chest pain at rest or at night.
- Any condition where left ventricular output is reduced, eg aortic stenosis or hypertrophic obstructive cardiomyopathy (HOCM).
- Active systemic illness.
- Abnormal baseline ECG, eg bundle branch block patterns or left ventricular hypertrophy - these make interpretation of the ETT difficult.
- Suspected or confirmed life-threatening arrhythmias.
Interpreting the exercise tolerance test
- ST elevation - usually this will be picked up straightaway and dealt with.
- The patient is normally considered to have been adequately 'stressed' if they achieve 85% or more of their maximum heart rate (calculated as 220 - age in years for men and 210 - age for women). However, recent data suggest that using these criteria to terminate the test may lead to an underestimation of inducible ischaemia.
- At each stage each lead should be examined for:
- Planar ST depression (this can be difficult to delineate from depression of the J point, which is the point where the QRS complex meets the ST wave).
- 'Flipping' of the T waves.
- Examination of all leads should continue into the recovery stage after the exercise stage of the test has been completed.
These are rare but can be fatal, eg myocardial infarction, left ventricular rupture, ventricular fibrillation or ventricular tachycardia.
Following up an abnormal exercise tolerance test
- Referral to cardiologists if an adequate ETT was undertaken and is abnormal.
- If an inadequate test was performed, further non-invasive investigations may be indicated, such as myocardial perfusion scanning, cardiac MRI, or stress echocardiogram. These are usually requested by the cardiologists, so a referral or discussion may be needed.
Further reading & references
- Fitzgerald P, Goodacre SW, Cross E, et al; Cost-effectiveness of point-of-care biomarker assessment for suspected myocardial Acad Emerg Med. 2011 May;18(5):488-95. doi: 10.1111/j.1553-2712.2011.01068.x.
- Megnien JL, Simon A; Exercise tolerance test for predicting coronary heart disease in asymptomatic Atherosclerosis. 2009 Aug;205(2):579-83. Epub 2008 Dec 31.
- Hill J, Timmis A; Exercise tolerance testing. BMJ. 2002 May 4;324(7345):1084-7.
- Siegler JC, Rehman S, Bhumireddy GP, et al; The accuracy of the electrocardiogram during exercise stress test based on heart PLoS One. 2011;6(8):e23044. Epub 2011 Aug 17.
- Miller TD; Stress testing: the case for the standard treadmill test. Curr Opin Cardiol. 2011 Sep;26(5):363-9.
- Jain M, Nkonde C, Lin BA, et al; 85% of maximal age-predicted heart rate is not a valid endpoint for exercise J Nucl Cardiol. 2011 Dec;18(6):1026-35. Epub 2011 Sep 16.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
|Original Author: Dr Gurvinder Rull||Current Version: Dr Gurvinder Rull||Peer Reviewer: Prof Cathy Jackson|
|Last Checked: 14/03/2012||Document ID: 2122 Version: 25||© EMIS|