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[[Image:Stress_test.jpg|thumb|300px|'''Figure 10.''' Cardiac stress test making use of a walking treadmill. Source: Wikimedia public domain.]]
[[Image:Stress_test.jpg|thumb|300px|'''Figure 10.''' Cardiac stress test making use of a walking treadmill. Source: Wikimedia public domain.]]


Cardiac stress testing is a test used to measure the heart’s ability to respond to external stress in a controlled environment. The stress response of the heart in the test is induced by exercise, such as treadmill walking or biking, or by mimicked by drugs, such as adenosine, dipyridamole or dobutamine. Exercise is the preferred modality for inducing cardiac stress and increasing myocardial oxygen demand. Two main reasons for a pharmalogical induced stress test are; the patient's inability to exercise adequately because of physical or psychologic limitations; or the chosen test does not go along with exercise (i.e., PET scanning). Methods used in stress testing are:
'''Cardiac stress test''' (or '''Cardiac diagnostic test''') is a test used in medicine and cardiology to measure the heart's ability to respond to external stress in a controlled clinical environment.
*Electrocardiography
*Echocardiography
*Myocardial perfusion imaging
*Positron-emission tomography
*Myocardial resonance imaging
The induced cardiac stress is most widely used to compare the coronary circulation during exercise with the circulation in rest. An imbalance between myocardial oxygen supply and demand due to coronary disease can be revealed as a result of the increased oxygen demand during stress conditions. By this means stress testing can reveal myocardial ischemia during exercise, while no symptoms are present at rest. Furthermore, stress testing can also be used to determine cardiac reserve in patients with valvular and myocardial disease. Deterioration of left ventricular performance during the test suggests a decline in cardiac reserve that could have therapeutic and prognostic implications.  


The focus of the stress test is on the assessment of the function of the myocardium. However, there should be also close attention to physical symptoms before, during and after the stress test. Symptoms such as angina pectoris, extreme dyspnoea, light-headedness or syncope can be equally important in evaluating patients. New physical findings during the test could also have diagnostic and prognostic value.  
The stress response is induced by exercise or drug stimulation. Cardiac stress tests compare the coronary circulation while the patient is at rest with the same patient's circulation observed during maximum physical exertion, showing any abnormal blood flow to the heart's muscle tissue (the myocardium). The results can be interpreted as a reflection on the general physical condition of the test patient. This test can be used to diagnose ischemic heart disease, and for patient prognosis after a heart attack (myocardial infarction).


Continuous electrocardiographic monitoring is the most common evaluation technique used during stress testing. In fact, during every type of stress testing also simultaneously a continuous ECG recording is assess the heart rate and look for any new arrhythmias. If patients are have complaints of angina with a normal resting ECGs, the development of ST segment depression or elevation is highly sensitive and specific for the existence of stress induced myocardial ischemia due to coronary artery disease. Stress electrocardiography is an easy and safe tool to investigate the existence of coronary artery disease in people with a normal resting ECG and the ability to exercise.  
The cardiac stress test is done with heart stimulation, either by exercise on a treadmill, pedalling a stationary exercise bicycle ergometer [1] or with intravenous pharmacological stimulation, with the patient connected to an electrocardiogram (or ECG). People who cannot use their legs may exercise with a bicycle-like crank that they turn with their arms.[2]


In case there is an abnormal resting ECG or the main focus of the test is in the area of hymodynamic changes or quantification of myocardial dysfunction, other myocardial imaging modalities can be added. In general additional imaging techniques add to the specificity and sensitivity of ischemic testing, although still not perfect.
The level of mechanical stress is progressively increased by adjusting the difficulty (steepness of the slope) and speed. The test administrator or attending physician examines the symptoms and blood pressure response. With use of ECG, the test is most commonly called a cardiac stress test, but is known by other names, such as exercise testing, stress testing treadmills, exercise tolerance test, stress test or stress test ECG.


Additional myocardial imaging modalities are chosen based on the scope of the researcher (i.e. hemodynamic or ischemic abnormalities), the quality in relation to the costs, and their availability.
==Stress echocardiography==
A stress test may be accompanied by echocardiography.[1] The echocardiography is performed both before and after the exercise so that structural differences can be compared.
 
==Nuclear stress test==
The best known example is myocardial perfusion imaging. Typically, a radiotracer (Tc-99 sestamibi, Myoview or Thallous Chloride 201) may be injected during the test. After a suitable waiting period to ensure proper distribution of the radiotracer, photos are taken with a gamma camera to capture images of the blood flow. Photos taken before and after exercise are examined to assess the state of the coronary arteries of the patient.
 
Showing the relative amounts of radioisotope within the heart muscle, the nuclear stress tests more accurately identify regional areas of reduced blood flow.
 
Stress and potential cardiac damage from exercise during the test is a problem in patients with ECG abnormalities at rest or in patients with severe motor disability. Pharmacological stimulation from vasodilators such as dipyridamole or adenosine, or positive chronotropic agents such as dobutamine can be used. Testing personnel can include a cardiac radiologist, a nuclear medicine physician,a nuclear medicine technologist, a cardiology technologist, a cardiologist, and/or a nurse.
 
==Function==
[[Image:StressECG STDepression.jpg|thumb|right|300px|Stress-ECG of a patient with coronary heart disease: ST-segment depression (arrow) at 100 watts of exercise. A: at rest, B: at 75 watts, C: at 100 watts, D: at 125 watts.]]
 
The American Heart Association recommends ECG treadmill testing as the first choice for patients with medium risk of coronary heart disease according to risk factors of smoking, family history of coronary artery stenosis, hypertension, diabetes and high cholesterol.
 
*Perfusion stress test (or sestamibi) is appropriate for select patients, especially those with an abnormal resting electrocardiogram.
*Intracoronary ultrasound or angiogram can provide more information at the risk of complications associated with cardiac catheterization.
 
==Diagnostic value==
The common approach for stress testing by American College of Cardiology and American Heart Association indicates the following:[2]
 
*'''Treadmill test:''' sensitivity 73-90%, specificity 50-74% (Modified Bruce Protocol)
*'''Nuclear test:''' sensitivity 81%, specificity 85-95%
 
(Sensitivity is the percentage of sick people who are correctly identified as having the condition. Specificity indicates the percentage of healthy people who are correctly identified as not having the condition.)
 
The value of stress tests has always been recognized as limited in assessing heart disease such as atherosclerosis, a condition which mainly produces wall thickening and enlargement of the arteries. This is because the stress test compares the patient's coronary flow status before and after exercise and is suitable to detecting specific areas of ischemia and lumen narrowing, not a generalized arterial thickening.
 
According to American Heart Association data,[citation needed] about 65% of men and 47% of women have as their first symptom of cardiovascular disease a heart attack or sudden cardiac arrest. Stress tests, carried out shortly before these events, are not relevant to the prediction of infarction in the majority of individuals tested.[dubious – discuss] Over the past two decades, better methods[citation needed] have been developed to identify atherosclerotic disease before it becomes symptomatic.
 
These detection methods have included either ''anatomical'' or ''physiological.''
 
*'''Examples of anatomical methods include'''
**CT coronary calcium score
**Intima-media thickness (IMT)
**Intravascular ultrasound (IVUS)
 
*'''Examples of physiological methods include'''
**Lipoprotein analysis
**HbA1c
**Hs-CRP
**Homocysteine
 
The anatomic methods directly measure some aspects of the actual process of atherosclerosis itself and therefore offer the possibility of early diagnosis, but are often more expensive and may be invasive (in the case of IVUS, for example). The physiological methods are often less expensive and more secure, but are not able to quantify the current status of the disease or directly track progression.
 
==Contraindications==
Stress cardiac imaging is not recommended for asymptomatic, low-risk patients as part of their routine care.[3] Some estimates show that such screening accounts for 45% of cardiac stress imaging, and evidence does not show that this results in better outcomes for patients.[3] Unless high-risk markers are present, such as diabetes in patients aged over 40, peripheral arterial disease; or a risk of coronary heart disease greater than 2 percent yearly, most health societies do not recommend the test as a routine procedure.[3][4][5][6]
 
Absolute contraindications to cardiac stress test include:
 
*Acute myocardial infarction within 48 hours
*Unstable angina not yet stabilized with medical therapy
*Uncontrolled cardiac arrhythmia, which may have significant hemodynamic responses (e.g. ventricular tachycardia)
*Severe symptomatic aortic stenosis, aortic dissection, pulmonary embolism, and pericarditis
*Multivessel coronary artery diseases that have a high risk of producing an acute myocardial infarction
*Decompensated or inadequately controlled congestive heart failure[7]
*Uncontrolled hypertension (blood pressure>200/110mm Hg)[7]
*Severe pulmonary hypertension[7]
*Acute aortic dissection[7]
*Acutely ill for any reason[7]
 
==Adverse effects==
Side effects from cardiac stress testing may include
 
*Palpitations, chest pain, myocardial infarction, shortness of breath, headache, nausea or fatigue.
*Adenosine and dipyridamole can cause mild hypotension.
*As the tracers used for this test are carcinogenic, frequent use of these tests carries a small risk of cancer.
 
==Pharmacological agents==
The choice of pharmacologic stress agents used in the test depends on factors such as potential drug interactions with other treatments and concomitant diseases.
 
Pharmacologic agents such as Adenosine, Lexiscan (Regadenoson), or dipyridamole is generally used when a patient cannot achieve adequate work level with treadmill exercise, or has poorly controlled hypertension or left bundle branch block. However, an exercise stress test may provide more information about exercise tolerance than a pharmacologic stress test.[8]
 
Commonly used agents include:
*Vasodilators acting as adenosine receptor agonists, such as Adenosine itself, and Dipyridamole (brand name "Persantine"),[9] which acts indirectly at the receptor.
*Regadenoson (brand name "Lexiscan"), which acts specifically at the Adenosine A2A receptor, thus affecting the heart more than the lung.
*Dobutamine. The effects of beta-agonists such as dobutamine can be reversed by administering beta-blockers such as propranolol.
 
Lexiscan (Regadenoson) or Dobutamine is often used in patients with severe reactive airway disease (Asthma or COPD) as adenosine and dipyridamole can cause acute exacerbation of these conditions. If the patient's Asthma is treated with an inhaler then it should be used as a pre-treatment prior to the injection of the pharmacologic stress agent. In addition, if the patient is actively wheezing then the physician should determine the benefits versus the risk to the patient of performing a stress test especially outside of a hospital setting.
 
Aminophylline may be used to attenuate severe and/or persistent adverse reactions to Adenosine and Lexiscan.
 
==Limitations==
The stress test does not detect:
*Atheroma
*Vulnerable plaques
 
The test has relatively high rates of false positives and false negatives compared with other clinical tests.
 
==Results==
Once the stress test is completed, the patient generally is advised to not suddenly stop activity, but to slowly decrease the intensity of the exercise over the course of several minutes.
 
*Increased spatial resolution allows a more sensitive detection of ischemia.
*Stress testing, even if made in time, is not able to guarantee the prevention of symptoms, fainting, or death. Stress testing, although more effective than a resting ECG at detecting heart function, is only able to detect certain cardiac properties.
*The detection of high-grade coronary artery stenosis by a cardiac stress test was the key to recognizing people who have heart attacks since 1980. From 1960 to 1990, despite the success of stress testing to identify many who were at high risk of heart attack, the inability of this test to correctly identify many others is discussed in medical circles but unexplained.
*High degrees of coronary artery stenosis, which are detected by stress testing methods are often, though not always, responsible for recurrent symptoms of angina.
*Unstable atheroma produces "vulnerable plaques" hidden within the walls of coronary arteries which go undetected by this test.
*Limitation in blood flow to the left ventricle can lead to recurrent angina pectoris.
 
==References==
 
^ Rimmerman, Curtis (2009-05-05). The Cleveland Clinic Guide to Heart Attacks. Kaplan Publishing. pp. 113–. ISBN 978-1-4277-9968-5. Retrieved 25 September 2011.
^ Gibbons, R., Balady, G.; Timothybricker, J., Chaitman, B., Fletcher, G., Froelicher, V., Mark, D., McCallister, B. et al. (2002). "ACC / AHA 2002 guideline update for exercise testing: summary article A report of the American College of Cardiology / American Heart Association Task Force on Practice Guidelines,Journal of the American College of Cardiology
^ a b c American College of Cardiology, "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation (American College of Cardiology), retrieved August 17 2012
^ Taylor, A. J.; Cerqueira, M.; Hodgson, J. M. .; Mark, D.; Min, J.; O'Gara, P.; Rubin, G. D.; American College of Cardiology Foundation Appropriate Use Criteria Task Force et al. (2010). "ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac Computed Tomography". Journal of the American College of Cardiology 56 (22): 1864–1894. doi:10.1016/j.jacc.2010.07.005. PMID 21087721. edit
^ Douglas, P. S.; Garcia, M. J.; Haines, D. E.; Lai, W. W.; Manning, W. J.; Patel, A. R.; Picard, M. H.; Polk, D. M. et al. (2011). "ACCF/ASE/AHA/ASNC/HFSA/HRS/SCAI/SCCM/SCCT/SCMR 2011 Appropriate Use Criteria for Echocardiography". Journal of the American College of Cardiology 57 (9): 1126–1166. doi:10.1016/j.jacc.2010.11.002. PMID 21349406.  edit
^ Hendel, R. C.; Abbott, B. G.; Bateman, T. M.; Blankstein, R.; Calnon, D. A.; Leppo, J. A.; Maddahi, J.; Schumaecker, M. M. et al. (2010). "The role of radionuclide myocardial perfusion imaging for asymptomatic individuals". Journal of Nuclear Cardiology 18 (1): 3–15. doi:10.1007/s12350-010-9320-5. PMID 21181519.  edit
^ a b c d e Henzlova, Milena; Cerqueira, Hansen, Taillefer, Yao (2009). "Stress Protocols and Tracers". Journal of Nuclear Cardiology. doi:10.1007/s12350-009-9062-4.
^ Weissman, Neil J.; Adelmann, Gabriel A. (2004). Cardiac imaging secrets. Elsevier Health Sciences. pp. 126–. ISBN 978-1-56053-515-7. Retrieved 25 September 2011.
^ Nicholls, Stephen J.; Worthley, Stephen (2011-01). Cardiovascular Imaging for Clinical Practice. Jones & Bartlett Learning. pp. 198–. ISBN 978-0-7637-5622-2. Retrieved 25 September 2011.
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