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High in the upper part of the left atrium is a muscular ear-shaped pouch – the left atrial appendage (LAA) (lat: auricula atrii sinistra), which has a tubular trabeculated structure. [9] LAA anatomy as seen in a CT scan is characterized as being in one of four groups: chicken wing (48%), cactus (30%), windsock (19%), and cauliflower(3%).
Atrium (heart), an anatomical structure of the heart; Atrium, the genital structure next to the genital aperture in the reproductive system of gastropods; Atrium of the ventricular system of the brain; Pulmonary alveolus (also known as atrium alveolus), microscopic air sac in the lungs
The atrioventricular node delays impulses by approximately 0.09s. This delay in the cardiac pulse is extremely important: It ensures that the atria have ejected their blood into the ventricles first before the ventricles contract. [9] This also protects the ventricles from excessively fast rate response to atrial arrhythmias (see below). [10]
The heart has four valves, which separate its chambers. One valve lies between each atrium and ventricle, and one valve rests at the exit of each ventricle. [8] The valves between the atria and ventricles are called the atrioventricular valves. Between the right atrium and the right ventricle is the tricuspid valve.
The anchored and electrically inert collagen framework of the four valves allows normal anatomy to house the atrioventricular node (AV node) in its center. The AV node is the only electrical conduit from the atria to the ventricles through the cardiac skeleton, which is why atrial fibrillation can never degrade into ventricular fibrillation.
When the ventricles of the heart contract in ventricular systole, the increased blood pressures in both chambers push the AV valves to close simultaneously, preventing the backflow of blood into the atria. Since the blood pressure in the atria is much lower than that in the ventricles, the flaps attempt to evert to the low pressure regions.
The atrioventricular septum is a septum of the heart between the right atrium (RA) and the left ventricle (LV). [1] [2]Although the name "atrioventricular septum" implies any septum between an atrium and a ventricle, in practice the divisions from RA to RV and from LA to LV are mediated by valves, not by septa.
There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously (see cycle diagram at right margin). [1]