Chamber replacement rhythm

As Chamber replacement rhythm is an electrical self-excitation of the ventricular muscles. If the ventricular replacement rhythm occurs, the patient has a serious cardiac arrhythmia due to failure of the two upstream excitation centers, the sinus node and the AV node. The body tries to ensure survival through the chamber replacement rhythm. The beat frequency of the chambers is then 20 to 40 beats per minute without the support of the atria and requires emergency medical treatment.

What is the chamber replacement rhythm?

The cardiac muscles of the chambers (ventricles) have the ability to spontaneously excite themselves, which is also known as self-depolarization. Due to the relatively long time it takes for the ventricular muscles to repolarize, the resulting substitute rhythm of the ventricles is only 20 to 40 beats per minute.

In a healthy heart with a normal beat rhythm (sinus rhythm), the ability of the ventricular muscles to self-depolarize does not come into play. Before it can occur, the depolarization is triggered by an electrical impulse, which is passed on from the sinus node in the right atrium via AV nodes, HIS bundles and the Purkinje fibers to the cells of the ventricular muscles. The electrical excitation emanating from the sinus node virtually anticipates the ventricular replacement rhythm.

A comparable process occurs when the sinus node fails as a clock and the AV node steps in as the first safeguard with a substitute rhythm of around 40 to 60 beats per minute.

Although the ventricular substitute rhythm can ensure survival in the short term if both rhythm generators fail or if the transmission of electrical signals fails, it is still an immediately life-threatening cardiac arrhythmia due to the significantly reduced ejection capacity of the heart. The low pumping capacity of the heart is made even more difficult by the low beat frequency and by the failure of the atria, which beat in an uncontrolled manner in their own rhythm or “flicker” and often pump blood “in a circle”.

Function & task

The ability of the cells of the ventricular muscles to self-depolarize, which can trigger a coordinated contraction of the two ventricles, represents a life-securing development of evolution and serves solely to maintain the blood circulation in the body for a short time - albeit at a weakened level. The chamber replacement rhythm thus takes on the task of the body's own emergency program to ensure short-term survival if either the upstream pulse generator or the transmission of electrical impulses are disturbed.

The system is also independent of the nervous system, since the heart's rhythm is generated and passed on by specialized heart muscle cells. The heartbeat frequency can, however, be adjusted almost instantaneously via neurotransmitters via the sympathetic and parasympathetic nervous system to the changing requirements or the respective stress level by varying the beat frequency. This means that the normal heart rhythm is indirectly influenced.

The particular advantage of the ventricular replacement rhythm is that it is largely autonomous and fail-safe, as it is physiologically-anatomically integrated in the structure of the cells of the ventricular muscles and therefore automatically comes into action if the Purkinje fibers do not receive an electrical impulse within a certain period of time for depolarization of the ventricular muscles.

Of the ventricular reserve rhythmAs the ventricular substitute rhythm is also called, must not be confused with other cardiac arrhythmias, in particular not with ventricular fibrillation. Ventricular fibrillation is caused by a disturbance in the conduction of excitation within the chambers, so that uncoordinated and unregulated contractions take place at a frequency of 300 to 800 beats per minute. The pumping capacity of the heart goes to zero and it comes to a cardiac arrest.

In addition to the junctional substitute rhythm, the chamber replacement rhythm is the only cardiac arrhythmia with a positive, short-term life-sustaining function.

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Illnesses & ailments

The chamber replacement rhythm stands at the same time for a serious cardiac arrhythmia and for an immediate life-saving body function. The ventricular replacement rhythm is always to be seen in connection with functional disorders or complete failure of the upstream excitation centers of the heart rhythm. If the heart rhythm is normal, which starts from the sinus node in the right atrium at the entrance of the superior vena cava and is clocked, a ventricular substitute rhythm cannot occur, since the electrical impulses that stimulate the cells to depolarize are too short-term. The cells of the myocardium then do not have enough time to self-depolarize.

Even in the event of a failure of the sinus node, the downstream AV node (atrioventricular node) normally steps in with its substitute rhythm. With a frequency of 40 to 60 beats per minute, this rhythm is still too fast for a possible activation of the chamber replacement rhythm. Only when the AV node does not generate any electrical impulses or these cannot be properly passed on to the cardiac muscle cells via the tawara thighs and the Purkinje fibers does the self-depolarization of the myocardial muscle cells occur automatically with a frequency of 20 to 40 beats per Minute one.

Because the pumping capacity of the heart is severely restricted under the ventricular replacement rhythm, all symptoms of circulatory weakness up to impaired consciousness and even loss of consciousness occur. Dizziness, shortness of breath, nausea, sweats, and fear of death are characteristic symptoms. Also numbness in the arms and legs as well as chest pain, comparable to angina pectoris, which are the result of the insufficient blood supply, are often observed.

The pulse is slow and occasionally irregular. The ECG (electrocardiogram) usually shows a widened ventricular complex and disordered atrial and ventricular excitation. The widened chamber complex is reflected in the fact that the negative Q-wave and the strong positive R-wave that follows are drawn further apart than usual.

If the chamber replacement rhythm is determined, the blood supply must be improved as quickly as possible. Temporary use of a transcutaneous pacemaker is often necessary. These are external pacemakers that emit their impulse through the skin and therefore consume significantly more electricity than implanted pacemakers with more direct contact with the heart.