Ventricular Replacement Rhythm: Function, Role & Diseases

Ventricular replacement rhythm is the electrical self-excitation of the ventricular muscles. When ventricular replacement rhythm occurs, the patient has a serious cardiac arrhythmia due to failure of the two upstream excitation centers, the sinus node and AV node. The body tries to ensure survival through the ventricular replacement rhythm. The ventricular beating rate is then 20 to 40 beats per minute without support from the atria and requires emergency medical treatment.

What is ventricular replacement rhythm?

Ventricular replacement rhythm is the electrical self-excitation of the ventricular muscles. The cardiac muscles of the ventricles (chambers) have the capacity for spontaneous self-excitation, also known as self-depolarization. Because of the relatively long time required for the ventricular muscles to repolarize, the resulting replacement rhythm of the ventricles is only 20 to 40 beats per minute. In a healthy heart with a normal beating rhythm (sinus rhythm), the ability of the ventricular muscles to self-depolarize does not occur. Before it can occur, depolarization is already triggered by an electrical impulse transmitted from the sinus node in the right atrium to the cells of the ventricular muscles via the AV node, HIS bundle, and Purkinje fibers. The electrical excitation originating from the sinus node effectively precedes the ventricular replacement rhythm. A similar process occurs when the sinus node fails as a clock generator and the AV node steps in as the first safeguard with a replacement rhythm of about 40 to 60 beats per minute. Although the ventricular replacement 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 output of the heart. The low pumping capacity of the heart is further complicated by the low rate of beating and by the failure of the atrioventricular chambers, which beat or “fibrillate” completely uncontrollably in their own rhythm and frequently pump blood “in circles.”

Function and task

The ability of the cells of the ventricular muscles to self-depolarize, which can trigger coordinated contraction of the two ventricles, represents a life-sustaining evolutionary development and serves solely to maintain blood circulation in the body in the short term, albeit in an attenuated manner. The ventricular replacement rhythm thus assumes the role of an endogenous emergency program to ensure short-term survival when either the upstream pulse generators or the transmission of the electrical impulses are disturbed. The system is also independent of the nervous system, since excitation generation and excitation transmission of the heart rhythm are performed by specialized cardiac muscle cells. However, the heartbeat rate can be adapted to changing requirements or the respective stress level via the sympathetic and parasympathetic nervous systems by varying the beat frequency almost without delay via neurotransmitters. This means that the normal heart rhythm is subject to indirect influence. The particular advantage of the ventricular replacement rhythm is that it is largely autonomous and fail-safe because it is physiologically-anatomically integrated into the design of the cells of the ventricular musculature and therefore automatically goes into action if the Purkinje fibers do not provide an electrical impulse to depolarize the ventricular musculature within a certain period of time. Ventricular replacement rhythm, as ventricular replacement rhythm is also called, should not be confused with other cardiac rhythm defects, especially ventricular fibrillation. Ventricular fibrillation results from a disturbance in the conduction of excitation within the ventricles, so that uncoordinated and unregulated contractions occur, at a rate of 300 to 800 beats per minute. The heart’s pumping capacity approaches zero and circulatory arrest occurs. Ventricular replacement rhythm, along with junctional replacement rhythm, is the only cardiac arrhythmia with a positive, short-term life-sustaining, function.

Diseases and medical conditions

Ventricular replacement rhythm simultaneously represents a serious cardiac arrhythmia and an immediate life-saving bodily function. Ventricular replacement rhythm is always associated with dysfunction or outright failure of the upstream excitation centers of the heart rhythm.In the presence of a normal heart rhythm, which originates from the sinus node in the right atrium at the entrance to the superior vena cava and is clocked, a ventricular replacement rhythm cannot occur because the electrical impulses that stimulate the cells to depolarize come too briefly. The cells of the myocardium then do not have sufficient time to self-depolarize. Also, in the event of sinus node failure, the downstream AV node (atrioventricular node) normally steps in with its replacement rhythm. With a frequency of 40 to 60 beats per minute, even this rhythm is still too fast for any activation of the ventricular replacement rhythm. Only when the AV node also fails to generate electrical impulses or these cannot be properly transmitted to the myocardial cells via the Tawara legs and the Purkinje fibers does self-depolarization of the myocardial muscle cells at a frequency of 20 to 40 beats per minute automatically occur. Because the heart’s pumping capacity is severely restricted under the ventricular replacement rhythm, all the symptoms of circulatory weakness up to and including impaired consciousness and even loss of consciousness occur. Dizziness, shortness of breath, nausea, sweating and fear of death are characteristic symptoms. Numbness in the arms and legs and chest pain, comparable to angina pectoris, resulting from the lack of blood supply, are also frequently observed. The pulse is slowed and occasionally irregular. ECG (electrocardiogram) usually shows a widened ventricular complex and disordered atrial and ventricular excitations. The widened ventricular complex is evidenced by the negative Q-wave and the strong positive R-wave that follows it being more widely spaced than usual. If ventricular replacement rhythm is detected, the blood supply must be improved as soon as possible. Temporary use of a transcutaneous pacemaker is often necessary. These are external pacemakers that deliver their pulse through the skin and therefore use significantly more current than implanted pacemakers with more direct contact to the heart.