What is heart automatism? The answer to this question can be found in the article below. In addition, it contains information about human health disorders associated with this concept.
What is heart automatism?
Muscle fibers in the human body have the ability to respond to an irritating impulse by contraction and then sequentially transmit this contraction throughout the muscle structure. It is proved that isolated heart muscle is capable of independently generating excitement and making rhythmic contractions. This ability is called heart automatism.
Causes of Cardiac Automatism
To understand what is the automatism of the heart, you can from the following. The heart has a specific ability to generate an electrical impulse followed by its passage to muscle structures.
The sinoatrial node is an accumulation of pacemaker cells of the first type (it contains about 40% mitochondria, loosely located myofibrils, there is no T-system, it contains a large amount of free calcium, it has an underdeveloped sarcoplasmic reticulum), it is located in the right wall of the superior vena cava, at the place where it enters the right atrium .
The atrioventricular node is formed by transitional cells of the second type, which conduct an impulse from the sinoatrial node, but under special conditions they can independently generate an electric charge. Transitional cells contain less mitochondria (20-30%) and slightly more myofibrils than first-order cells. The atrioventricular node is located in the interatrial septum, along which excitation is transmitted to the bundle and legs of the bundle of His (contain 20-15% of mitochondria).
Purkinje fibers are the next step in the transmission of excitation. They depart approximately at the middle of the septum from each of the two legs of the bundle of His. Their cells contain about 10% mitochondria, in structure they are somewhat more similar to cardiac muscle fibers.
The spontaneous occurrence of an electrical impulse occurs in the pacemaker cells of the sinoatrial node, which potentiates an excitation wave that stimulates 60-80 contractions per minute. He is a first-order driver. Then, the resulting wave is transmitted to the conductive structures of the second and third level. They are capable of both conducting excitation waves and independently inducing contractions of a lower frequency. The driver of the second level after the sinus node is the atrioventricular node, which is able to independently create 40-50 discharges per minute in the absence of suppressive activity of the sinus node. Further, the excitation is transmitted to the structures of the His bundle, which reproduces 30-40 contractions per minute, then the electric charge flows to the legs of the His bundle (25-30 pulses per minute) and the Purkinje fiber system (20 pulses per minute) and enters the working muscle myocardial cells .
Usually, impulses from the sinoatrial node suppress the independent ability to electrical activity of underlying structures. If the functioning of the first-order driver is disrupted, then the lower-level links of the conductive system take over the work.
Chemical processes that ensure automatism of the heart
What is heart automatism in terms of chemistry? At the molecular level, the basis for the independent occurrence of an electric charge (action potential) on the membranes of pacemaker cells is the presence of a so-called impulse. His work (function of automatism of the heart) contains three stages.
Stages of the impulse:
- The 1st phase is preparatory (as a result of the interaction of superoxide oxygen with positively charged phospholipids on the surface of the membrane of the pacemaker cell, it acquires a negative charge, this violates the resting potential);
- 2nd phase of the active transport of potassium and sodium, during which the external charge of the cell becomes +30 mW;
- 3rd phase of the electrochemical jump - uses the energy arising from the disposal of reactive oxygen species (ionized oxygen and hydrogen peroxide) with the help of superoxide dismutase and catalase enzymes. The resulting energy quanta increase the biopotential of the pacemaker so that it causes an action potential.
The processes of pulse generation by cells - pacemakers necessarily occur in conditions of sufficient presence of molecular oxygen, which is delivered to them by red blood cells of the incoming blood.
A decrease in the level of work or a partial cessation of the functioning of one or several stages of the impulse system disrupts the coordinated operation of pacemaker cells, which causes arrhythmias. Blocking one of the processes of this system causes a sudden cardiac arrest. Having understood what the automatism of the heart is, one can also realize this process.
The impact of the autonomic nervous system on the work of the heart muscle
In addition to its own ability to generate electrical impulses, the work of the heart is controlled by signals from the sympathetic and parasympathetic nerve endings that innervate the muscle, in case of failure of which a violation of the automatism of the heart is possible.
The impact of the sympathetic department accelerates the work of the heart, has a stimulating effect. Sympathetic innervation has a positive chronotropic, inotropic, dromotropic effect.
Under the predominant action of the parasympathetic nervous system , the depolarization of pacemaker cells slows down (inhibitory effect), which means a decrease in heart rate (negative chronotropic effect), a decrease in cardiac conduction (negative dromotropic effect), a decrease in systolic contraction energy (negative inotropic effect), but the excitability of the heart increases (positive batmotropic effect). The latter is also taken as a violation of the function of automatism of the heart.
Causes of heart automatism disorders
- Myocardial ischemia.
- Inflammation.
- Intoxication.
- Imbalance in sodium, potassium, magnesium, calcium.
- Hormonal dysfunction.
- Violation of the impact of autonomous sympathetic and parasympathetic endings.
Types of rhythm disturbances due to impaired heart automatism
- Sinus tachy and bradycardia.
- Respiratory (youthful) arrhythmia.
- Extrasystolic arrhythmia (sinus, atrial, atrioventricular, ventricular).
- Paroxysmal tachycardia.
Arrhythmias are distinguished due to a violation of automatism and conduction with the formation of a circulation of an excitation wave (re-entry wave) in one or several parts of the heart, resulting in atrial fibrillation or flutter.
Ventricular fibrillation is one of the most life-threatening arrhythmias, resulting in sudden cardiac arrest and death. The most effective treatment is electrical defibrillation.
Conclusion
So, having examined what the automatism of the heart is, you can understand what kind of disturbances are possible in case of illness. This, in turn, makes it possible to fight the disease with more optimal and effective methods.