Stress Test
The exercise test or stress test or exercise electrocardiogram or ergometry is an examination consisting of an ECG recording during the course of a calibrated exercise. It can help in the diagnosis of coronary artery disease. It may be associated with the measurement and analysis of ventilatory volumes and flows. It is useful in assessing respiratory and metabolic diseases and also to assess the behavior of an individual athlete or not vis-a-vis the effort, which may allow refinement of the athletic training or retraining.
Materials
ECG
The electrodes may be standard. However, an ECG recording on a subject full exercise contains many artifacts, due to the mobilization of the patients, the high amplitude respiratory problems of adhesion of electrodes (sweating). The device Eletrocardiography is often provided with features to improve the electrical signal and its interpretation:
* Algorithm for the recovery of the isoelectric line (the boundary issue in "waves");
* Averaging over several successive complex, and to reduce noise, essentially random;
* Alarms serious events;
* Help define criteria for positivity.
The ECG is often but the digital recording format is proprietary, not allowing the playback on other systems.
The unit of effort
The ergometer allows a graduated effort that can quantify levels of power measured in watts. These may include:
* A treadmill and Tilt: The patient walks on it at a speed and a growing inclination defined according to different protocols, one of the most used being the so-called "Bruce". The effort is then relatively physiological. The joint constraints are weak (except for the back). The rise is faster in most cases. The patient is obliged to follow the movement of the belt which allows him to make a greater effort if it is unmotivated. In return, the patient monitoring (exercise tolerance) must be careful because he can not stop the effort itself (risk of falling).
* A cycle ergometer, the patient cycles at a constant speed but a progressive brake is applied, making the effort more and more important. The joint constraints are more important (knees, hips). The rise is low, thereby prolonging the test if the subject is sports. The maximum effort is lower in the patient not motivated.
Protocol
The patient is not fasting. He did not need to be hospitalized. He must be aware of the examination, his interest and risks of the latter (if it can be required to sign an acceptance form).
The examination is done in the presence of a physician and an assistant (medical electrophysiology technologist or respiratory therapist in Canada, nursing).
The patient is shirtless and ECG electrodes are put in place after preparation of the skin (shaving, trimming). The diversions are common but we prefer to have the electrodes in the standard back to the roots of members, rather than the latter.
The first recording of the electrocardiogram is done at rest. The patient then began his effort.
This is continued until the occurrence of one of the following criteria:
* Muscular exhaustion or breathlessness too large;
* Heart rate reaching the maximum frequency theoretical (= 220 - patient age);
* Development of a criterion of positivity: the most common is the appearance of a shift in ST segment horizontal or downward, beyond a certain voltage;
* Emergence of a serious heart rhythm disorder;
* Onset of malaise, a fall in blood pressure.
Cardiovascular indications
The exercise test can help diagnose coronary artery disease and target intensity (target heart rate) of rehabilitation training in case of optimal management of cardiac patient movement activities.
Like any diagnostic test, it has a sensitivity and specificity. They are both close to 60% for the stress test. According to the Bayes theorem we can calculate the positive predictive value and negative predictive value depend on the estimated frequency of coronary disease.
To summarize, there is practically no effort to test if it is almost certain diagnosis (or lack thereof), the probability of having the disease only changing slightly depending on whether the test is positive or negative. The stress test is especially useful if you have a belief through: if the test is positive, the probability that the patient is sick becomes significant (positive predictive value). If test is negative, we can eliminate the disease with a low probability of error (negative predictive value).
In case of positivity of the exercise test, the doctor may:
* Be dealing directly with drugs: anti-anginal and fight against the risk factors ...
* Is the diagnosis confirmed by angiography which allows for targeted treatment: for medicine, coronary angioplasty or bypass surgery.
Additional tests
* You can measure oxygen consumption during exercise testing and calculating and maximum oxygen consumption, called VO2max. This is done through a mask applied on the patient's face during exercise, enabling instant analysis of inspiratory and expiratory flow and expired gas composition test is interesting in the top sportsman level to adapt its training. It is also measured in cases of severe heart failure because it's an important indicator of prognosis (life expectancy).
* You can simultaneously perform echocardiography during stress testing. This is called an ultrasound effort, which allows for a more refined of coronary disease: improved sensitivity and specificity, topographical diagnosis of the diseased artery. Its realization, however, requires a special table, the heart is best viewed when the patient lies on the left side (left lateral position) and thus to make the effort in this position.
* You can pair the stress test with intravenous injection of radioactive material to produce a myocardial perfusion imaging or cavitary (display content = blood in the cavities) or muscle (direct visualization of the heart muscle) . The review allows for a more refined (better sensitivity, better specificity, topographical diagnosis of the diseased artery).
See also Heart
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