Cardiovascular test of effort

The test of effort , or test of effort is a consistent cardiologic examination in the recording of a ECG during the course of a gauged physical exercise. It makes it possible to help with the diagnosis of a disease of the coronary arteries.

History

Robert Bruce described a system of recording of the ECG to the effort on travelator in 1963.

Materials

ECG

The electrocardiograph can be standard. But the recording of a ECG on a subject in full physical exercise contains many artefacts, due to the mobilization of the patient, the great respiratory amplitude and problems of adherence of the electrodes (sweats). The apparatus eletrocardiographic is thus often provided with functionalities allowing the improvement of the electrical signal and with its interpretation:

• algorithm allowing the rectification of the isoelectric line (limit the aspect in “waves”);
• average on some successive complexes, allowing to decrease thus the noise, essentially random;
• serious alarms of events;
• assistance with the definition of the criteria of positivity.

The electrocardiograph is often numerical but the format of recording remains owner, not allowing the second reading on other systems.

The apparatus of effort

It allows a graduated effort which one can quantify on the levels or of many Watts. It can be a question:

• of a Travelator and tilting: the patient goes on this last at a definite speed and an increasing slope according to various protocols. The effort is then relatively physiological. The articular constraints are low except for the back). Rise to power is fast in the majority of the cases. The patient follows the movement of the carpet what enables him to carry out a main effort if it is justified little. N the other hand, the monitoring of the patient (tolerance to the effort) must be rigorous because it cannot stop its effort of itself (risk of fall).
• of an cyclo-ergometer: the patient pedals at a constant speed but a progressive brake is applied, making the effort increasingly important. The articular constraints are more important (knees, hips). Rise to power remains weak, which prolongs the test if the subject is sportsman. The maximum effort is less at the patient not motivated.

A system of measurement of the blood Pressure

It can be manual or automated.

An emergency carriage

It must comprise the whole of the hardware requirement to a cardiopulmonary Réanimation.

Protocol

The patient is not with jeun. He does not need to be hospitalized. He must be informed examination, of his interest and risks of this last (if necessary, he can have to sign a form of acceptance).

The examination is done in the presence of a Médecin as well as assistant (Inhalothérapeute with the Canada, Infirmier).

The patient is put barechested and the electrodes of the ECG are installed after preparation of the skin (shaving, degreasing). Derivations are usual (cf article ECG) but one prefers to lay out the electrodes standards in the back, with the root of the members, rather than on the latter.

A first recording of the electrocardiogram is made at rest. The patient begins his effort then.

This last is continued until occurred of the one of the following criteria:

• muscular exhaustion or too important breathlessness;
• heart rate reaching the theoretical maximum frequency (=220 - age of the patient);
• appearance of a criterion of positivity : most common is the appearance of under shift of the segment ST, horizontal or descendant, exceeding a certain voltage;
• appearance of a disorder of the serious cardiac rhythm;
• appearance of a Malayan, a fall of the Blood-pressure.

Indications

The test of effort makes it possible to help with the diagnosis of the diseases of the coronary arteries and to target the intensity (cradiaque frequency target) of réentraînement with the optimal effort in the event of assumption of responsibility of the heart case by the adapted Physical-activities.

Like any diagnostic test, it comprises a sensitivity and a specificity. They are both close relations of 60% for the test of effort. According to the Théorème of Bayes one can calculate his positive predictive Valeur and his negative predictive Valeur which depends on the estimated frequency of the coronary disease.

To summarize, it is not practically used for nothing to make a test of effort if one is quasi certain diagnosis (or of its absence), the probability of having the disease changing only little according to whether the test is positive or negative. The test of effort is especially interesting if there is an intermediate conviction: if the test is positive, the probability so that the patient is sick becomes significant (positive predictive value). If the test is negative, one can eliminate the disease with a weak probability of being mistaken (negative predictive value).

In the event of positivity of the test of effort, the doctor can:

• is to treat directly by drugs: anti-angineux and to fight against the risk factors…
• is to confirm the diagnosis by a Coronarographie what makes it possible to make a targeted treatment: by drug, coronary Angioplastie or aorto-coronary Bridging.
• to prescribe réentraînement with the effort.

Metabolic test of effort

Definition

The metabolic test of effort , consists of measurement and analyzes ventilatory volumes and flows during a gauged physical exercise, in order to determine the energy metabolisms concerned at each intensity (concept of the point of cross-country race-over). It makes it possible to target the intensity of assumption of responsibility by the adapted Physical-activities of the patients diabetics (standard 2) in situation of Obésité.

Unfolding

On cyclo-ergometer or travelator.

Objective and principles

The analysis of the respiratory quotiens makes it possible to determine, by the concept of the point of cross-country race-over, the point " Lipoxmax".

Lipoxmax corresponds àl' individual intensity of exercise for which the lipidic metabolism is mainly requested. Its value is to be recomputed regularly, because answers the drive. The corresponding intensity is under-maximum, and is in lower part of that which corresponds to the first threshold.

Counter-indications

They are defined by the doctor:

• impossibility of practicing an effort;
• unstable Angina pectoris;
• recent Myocardial infarction;
• instability of the blood Pressure.
• cardiac valvulopathies serious.

In practice, the test of effort is a not very dangerous examination if the counter-indications are respected. Serious accidents can however occur in an extremely rare way, which explains the presence of a carriage of reanimation.

Goscinny is deceased during a test of effort.

Complementary tests

• One can measure consumption in Oxygène during the test of effort and to thus calculate the maximum consumption oxygenates of it, called VO2max . This measurement is interesting in the high level sportsman in order to adapt his drive. It is also measured in the event of serious Cardiac failure because it is an important index of the forecast (life expectancy).

• One can simultaneously carry out a cardiac echography during the test of effort. It is then about a echography of effort , which makes it possible to make a finer diagnosis of the disease of the coronary ones: better sensitivity and specificity, topographic diagnosis of the sick artery.
• One can couple the test of effort with the injection into intravenous of a radioactive product making it possible to carry out a Scintigraphie cardiac, either cavitary (visualization of the contents = blood in the cavities), or muscular (direct visualization of the cardiac muscle). The examination makes it possible to make a finer diagnosis (better sensitivity, better specificity, topographic diagnosis of the sick artery).

Alternative tests

In the event of impossibility of carrying out a test of effort, one can make:

• a echography-dobutamine : the injection of dobutamine, a Catecholamine, involves an acceleration of the heart rate and force of contraction of the cardiac muscle which is visualized by echography. The appearance of a wall which contracts less better during this test is strongly in favor of a Ischémie of the latter, in connection with the attack of a coronary artery.
• a scintiscanning myocardique-dipyridamole . The injection of this last product involves a dilation of the healthy coronary arteries. If an artery is sick, the absence of vasodilatation involves a relative ischaemia detected by the examination scintigraphic.