Mechanics of the valvular apparatus
The graphical display of valve function demonstrates a clear alternation of phases. To understand intracardiac hemodynamics, the function of key structures in the left heart is traditionally considered:
- IV. Mitral valve. Two diametrically opposed positions are distinguished in its cycle. The “C” state means that the valve is completely closed, isolating the left ventricular cavity from the left atrium. The “O” state indicates that the valve is open, and ventricular filling is taking place.
- V. Aortic valve. Similar to the mitral valve, its mechanics are described by the alternation of “C” (closed) and “O” (open) states, which regulate blood ejection into the systemic circulation.
Functional anatomy of the aortic valve
When analyzing the cross-section of the aortic root, strictly two states of the valve can be identified that determine hemodynamics in this area. No third or intermediate functional states are distinguished in this context.
- State “C” (Closed). In this phase, all aortic valve leaflets close tightly right in the center of the vessel. As a result, the aortic lumen is completely blocked, which prevents retrograde blood flow back into the ventricle.
- State “O” (Open). During blood ejection, the leaflets part and press as tightly as possible against the inner walls of the aorta. This ensures an absolutely free, laminar blood flow directed along the main vessel (traditionally indicated on diagrams by a vector or arrow).
Physiology of myocardial repolarization
The proper functioning of the valvular apparatus, especially the atrioventricular valves, directly depends on electrical processes in the myocardium—specifically, on repolarization (the process of excitation fading away). This process does not occur all at once, but in a strict physiological sequence:
- First of all, excitation fades in the area of the interventricular septum.
- Then repolarization encompasses the lateral walls of the ventricles.
- Last of all, excitation disappears in the papillary muscles and trabeculae.
The complete extinction of electrical activity in all heart structures graphically corresponds to the TP segment. At this moment, a complete absence of excitation is observed in the heart.
Role of papillary muscles and trabeculae
The delayed repolarization in the structures that anchor the valves is of paramount physiological importance.
Since the papillary muscles and trabeculae recover from excitation last, their contraction lasts longer than the contraction of the free ventricular walls. This prolonged, continuous tension is necessary to securely hold the leaflets of the atrioventricular (including mitral) valves at the very end of ventricular systole. This mechanism prevents the pathological inversion (opening) of the leaflets toward the atrial cavities under the influence of high intraventricular pressure.
Briefly: answers to topical questions
Which heart valves belong to the group of atrioventricular valves?
Two heart valves belong to the group of atrioventricular valves.
- Tricuspid valve — located at the border of the right atrium and right ventricle, consists of three leaflets.
- Bicuspid valve (or mitral valve) — located at the border of the left atrium and left ventricle, consists of two leaflets.
How many leaflets does a normal aortic valve consist of?
Normally, the aortic valve consists of three leaflets.
- Left coronary cusp (left coronary cusp) — one of the anatomical landmarks of the valve.
- Right coronary cusp (right coronary cusp) — the second leaflet in the structure.
- Non-coronary cusp (non-coronary cusp) — the third leaflet of the aortic valve.
What mechanisms create the pressure gradient required to open the aortic valve?
The pressure gradient for opening the aortic valve is formed during the period of ventricular myocardial tension. Because all valves are closed and blood is incompressible, the chamber volume remains constant. Synchronous isometric contraction of cardiomyocytes occurs (the total length of the myocardium does not decrease), which leads to a sharp increase in intraventricular pressure. After reaching a threshold pressure value of 80 mmHg in the left ventricle, the semilunar aortic valve opens.
What phases and periods are distinguished in the structure of ventricular systole?
The structure of ventricular systole comprises two consecutive periods, each including two phases:
- Period of tension — consists of the phase of asynchronous contraction and the phase of isometric contraction.
- Period of blood ejection — consists of the phase of rapid ejection and the phase of reduced ejection of blood.
How does intracardiac hemodynamics change in mitral valve prolapse?
Intracardiac hemodynamics in mitral valve prolapse is associated with the bulging of mitral valve leaflets into the left atrial cavity during left ventricular systole. This can lead to the development of mitral regurgitation and the regurgitation of a portion of blood from the left ventricle into the left atrium. Regurgitation is not an obligatory component; its degree varies. When mitral regurgitation develops, volume overload of the left atrium occurs.
To remember the order of excitation disappearance (repolarization), use the “Center to Anchors” rule: first the septum (center), then the walls (periphery), and finally the papillary muscles (valve anchors).
Class and exam questions
What does the aortic valve look like in the closed state on cross-section?
Its leaflets close completely in the center of the aortic lumen, hermetically blocking blood flow.
Why is prolonged contraction of the papillary muscles necessary?
This is necessary so that at the end of ventricular systole, the leaflets of the atrioventricular valves are not inverted back into the atria under blood pressure.
What does the TP segment indicate?
The TP segment is recorded during the complete physiological absence of excitation in all heart structures.
What else to study on this topic
- Hemodynamic parameters in the “O” and “C” phases of the mitral valve
- Detailed analysis of valve function graphs
- The relationship of the TP segment to mechanical diastole of the heart
- The effect of pressure on pressing the aortic valve leaflets against the walls
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