The heart functions as a pump, circulating blood to deliver oxygen and nutrients throughout the body. For the heart’s four chambers to work in coordination, a system must ensure blood flows in only one direction. This task is managed by four heart valves that act like one-way doors, opening to let blood pass to the next chamber or major blood vessel and then closing to prevent it from flowing backward. This mechanism allows the heart to build the necessary pressure to pump blood effectively to the lungs and then out to the rest of the body.
The Heart’s Two Atrioventricular Valves
The term “atrioventricular” (AV) describes the location of two of the heart’s four valves, positioned between an upper chamber (atrium) and a lower chamber (ventricle). These valves serve as gateways that control blood flow from the atria, which receive blood, into the ventricles, which pump blood out of the heart. There are two atrioventricular valves, distinguished by which side of the heart they occupy.
On the right side of the heart, the tricuspid valve is situated between the right atrium and the right ventricle. As its name implies, it is composed of three individual flaps, or leaflets, that open and close together. Their primary job is to allow oxygen-poor blood to move from the right atrium into the right ventricle without leaking backward.
On the left side, the mitral valve is located between the left atrium and the left ventricle. Unlike its counterpart on the right, the mitral valve is a bicuspid valve, meaning it has two leaflets. It performs a similar function, controlling the passage of oxygen-rich blood from the left atrium into the powerful left ventricle.
How Atrioventricular Valves Work
The function of the atrioventricular valves is tied to the cardiac cycle, the sequence of events that constitutes a single heartbeat. The cycle has two main phases: diastole (relaxation) and systole (contraction). During diastole, the ventricles relax, causing the pressure within them to drop below the pressure in the atria, prompting the tricuspid and mitral valves to open and allow blood to fill the ventricles.
When the ventricles are full, the systole phase begins as they contract to pump blood out to the lungs and the rest of the body. This contraction increases the pressure inside the ventricles, forcing the atrioventricular valves to snap shut. The closure of the AV valves produces the first heart sound (“lub”) of the heartbeat and prevents the regurgitation, or backward flow, of blood into the atria.
This process is supported by a subvalvular apparatus. Attached to the edges of the valve leaflets are strong, fibrous cords called chordae tendineae, often referred to as “heartstrings.” These cords are anchored to small mounds of muscle within the ventricles known as papillary muscles. When the ventricles contract, the papillary muscles also contract, creating tension on the chordae tendineae that prevents the valve leaflets from being pushed backward and prolapsing into the atria.
Conditions Affecting Atrioventricular Valves
When atrioventricular valves fail to function correctly, it can disrupt the heart’s ability to pump blood efficiently. These issues fall into two main categories: regurgitation and stenosis. Both conditions force the heart to work harder and can develop from congenital defects or damage acquired over a lifetime.
Regurgitation, also known as insufficiency, occurs when a valve does not close tightly, allowing blood to leak backward. This can happen if the valve leaflets are stretched or floppy, a condition known as prolapse, or if the valve structure is damaged. Mitral valve regurgitation is a common form of this problem.
Stenosis is where the valve leaflets become stiff, thickened, or fused together. This narrows the valve opening and obstructs the forward flow of blood from the atria into the ventricles. The heart must generate more force to push blood through the constricted opening. Common causes for both stenosis and regurgitation include age-related calcification, infections such as rheumatic fever, or damage from a previous heart attack.
Recognizing and Diagnosing Valve Problems
The symptoms of atrioventricular valve disease often develop because the heart is straining to compensate for the faulty valve. Common signs include:
- Shortness of breath, particularly with physical activity
- Persistent fatigue or weakness
- Dizziness
- Swelling in their ankles and feet
- Heart palpitations, which can feel like a fluttering or irregular heartbeat
A physician using a stethoscope to listen to the heart may detect a heart murmur, which is an unusual whooshing sound made by turbulent blood flow across a narrowed or leaky valve. While not all murmurs indicate disease, an abnormal sound often prompts further investigation.
The primary diagnostic tool to confirm a diagnosis is an echocardiogram. This non-invasive test uses sound waves to create detailed, moving images of the heart, allowing doctors to visualize the valve leaflets, assess their movement, and see the blood flowing through them. This imaging can identify issues like stenosis or regurgitation and helps guide treatment decisions.