Auricle (anatomy)

A auricle is a cardiac cavity which receives blood. Two, they allow the passage of the Sang Veine S towards the ventricles.

The adjective referring to the auricles is either atriale , or auricular .

Anatomy

They are cavities filled with blood whose wall consists of cardiac muscle. One distinguishes the right auricle from the left auricle, both being separated by the inter-auricular septum .

Right auricle

From ovoidal form with vertical main roads, it receives blood, in top, of the higher Vena cava, bellow of the lower Vena cava. It is separated from the ventricle right by the valve tricuspide, preventing the backward flow of the blood of the ventricle towards the auricle. It also receives, bellow, the principal coronary vein (called coronary Sinus).

In its high part (close to the meeting of the higher vena cava) the sinusal Nœud is located, structure microscopic from where share the electric impulse which ensures the contraction of the heart.

Left auricle

From also ovoidal form with rather horizontal main roads, it receives blood by four pulmonary veins, two on the right and two on the left. It is separated from the left ventricle by the mitral valve, preventing the backward flow of the blood of the ventricle towards the auricle.

There exists in its side part a small pocket forming cul-de-sac and called auricule .

Physiology

The Sang low in oxygen is brought to the right auricle by the venas cava. Oxygenated blood is brought Poumon S to the left auricle by the pulmonary veins.

The filling of the ventricles is done normally in two times:

a passive time, at the beginning of the ventricular Diastole (relaxation of the ventricular cardiac muscle), the running out blood of upstream downstream, in the direction of the gradient of pressure;
an active time, at the end of the diastole. The pressures between auricles and ventricles being about equalized and the finished passive flow, the auricles contract (auricular Systole), allowing an optimization of the filling of the ventricles.

Synchronization between the contractions of the four cavities is ensured by the conduction of the electric impulse coming from the sinusal Nœud, being gradually propagated in the two auricles and transmitted to the ventricle by the auriculo-ventricular Nœud and the Faisceau of His.

Exploration

Imagery

the thoracic Radiographie makes it possible to visualize only the shade of the auricles, its contours merging with the flat rim of the heart.
the echocardiography makes it possible to appreciate the form and the size of it. That remains the simplest examination. The auricles are however relatively major structures and a echography trans-oesophagienne is sometimes necessary for good to visualize them.
the Angiographie, by injection of a product of contrast iodized directly in the cardiac cavities, is used little.
the scanner and the Imagerie by magnetic resonance can be also used.

Pressure

The analysis of the pressures in the auricles makes it possible to know the quality of the filling of the ventricles (pressure of filling) and to guide the treatment of certain diseases. It can be made in an invasive way (by introduction of a Cathéter directly into the cavity studied) or indirectly by echocardiography.

Invasive method

The measurement of the pressures in the auricles requires the installation of a Cathéter (fine pipe) in the cavities to be studied.

The access of the right auricle hardly poses problem: the catheter is assembled through a large vein (femoral Veine, Veine humérale, Veine subclavian or jugular Veine until this one.

The access of the left auricle is much more complex: it cannot be approached by retrograde left way (by going up the flow of the blood current), the opening of the mitral valve being with close to 180° of the opening of the aortic valve. One is generally satisfied to measure the pressure on the level of the pulmonary capillary, the catheter being pushed by right way in the right auricle, the ventricle right, then in the pulmonary artery until his distality. The pressure obtained is then superposable with the pressure of the left auricle.

Noninvasive method

The estimate of the pressures of filling is made in an indirect way by echocardiography.

the size increased of the lower Vena cava or the veins know-hepatic S, the disappearance of the variations of the diameter of these veins according to the respiratory cycle (normally are crushed at the time of the inspiration) are indices of the increase in the pressures in the right auricle.
the presence of a wave has on the Doppler measured on the level of the opening of the mitral valve or tricuspide, testifies to a contraction of the auricles.
the increase in the size of the left auricle (apart from a disorder of the chronic rate/rhythm) generally testifies to an increase in the pressure in the latter.
a reduction the speed of the mitral ring (measured by tissue Doppler), brought back at the speed of blood flow at the beginning of the diastole with the level of the mitral valve, is a good witness of a pressure of left filling high.

Electric activity

On the electrocardiogram, the electric activity of the auricles is visualized in the form of P. wave.

Sometimes a finer analysis of the electric activity requires to position an electrode directly in contact with the auricles:

the right auricle can be analyzed thus while mounting an electrode in contact with its wall (while passing by a large vein and by positioning the end of the latter under radioscopy by x-rays) during a electrophysiological Exploration.
the left auricle can be in analyzed while making swallow an electrode, the end being in the esophagus, in contact with the posterior wall of the left auricle (trans-oesophagien recording). In a more complex way, an electrode can be thorough in the coronary Sinus whose meeting is located in the low part of the right auricle: it is then also in contact with the wall of the left auricle.

Diseases

The auricles can generate Troubles cardiac rhythm: auricular Fibrillation, auricular Flutter…

They can be the place of formation of Caillot S (thrombus) which can migrate secondarily while causing the occlusion of an artery (Cerebral vascular accident, acute Ischémie of the lower extremity…).

They can dilate because of the disorders of the rate/rhythm previously quoted but also of a disease of the cardiac valves (valvulopathy) or of a Cardiac failure.

More rarely, they can be the place of Tumeur of which most frequent is the benign Myxome.

References

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