Atrioventricular block is a physiological violation of the transmission of nerve impulses through the conduction system of the heart from the ventricles to the atria. At first glance, the name is complicated from the Latin words atrium and ventriculus, which mean the atrium and ventricle, respectively.
About the heart, its structure and conductive system
The human heart, like many other living creatures related to mammals, consists of the right and left parts, each of which has an atrium and a ventricle. Blood from the entire body, namely from a large circle of blood circulation, enters first into the right atrium, and then into the right ventricle, then through the vessels to the lungs. Blood enriched with oxygen from the pulmonary circulation from the lungs flows into the left atrium, from which it enters the left ventricle, and from it passes through the aorta to organs and tissues.
The blood flow in the heart ensures the functioning of its conducting system. It is thanks to her that the correct heartbeat occurs - the timely reduction of the atria and ventricles and the flow of blood through them. If there is a violation in the transmission of nerve impulses between the atria and ventricles, the latter contract too slowly or untimely - after a long period of time after atrial contraction. As a result of this, the strength of the blood flow changes, it does not release into the blood vessels at the right time, there is a drop in pressure and other serious changes in the work of the cardiovascular system.
What is the danger of AV block?
The degree of danger of atrioventricular blockade depends on its severity. Mild forms of conduction disturbance can be asymptomatic, medium ones - require clarification of the causes and treatment to prevent heart failure. With complete blockade, instant death from cardiac arrest may occur. That is why a violation of nerve conduction in the heart cannot be ignored, even if at the moment there are no severe signs of the disease.
Classification by degree of AV block
AV blockade of the heart is of several types and subtypes. The severity is distinguished: AV blockade of the first degree, often not accompanied by any external violations and in many cases being the norm, blockade of the second degree, which, in turn, is divided into two subtypes: type 1 (Mobits 1, or Wenckebach block) and type 2 (Mobitz 2), and blockade of the third degree - a complete stop of the transmission of nerve impulses from the atria to the ventricles.
1st degree of AV blockade
Grade 1 AV block may be a normal physiological event in young patients. It is often diagnosed in regularly trained athletes, and they are also considered the norm. With such a blockade, a person usually does not have any noticeable symptoms indicating heart problems. Grade 1 AV block in the absence of signs of the disease, as a rule, does not require treatment, however, it may be necessary in the presence of other abnormalities in the work of the heart. Also in this case, the doctor may prescribe repeated ECG, daily ECG monitoring and additional studies, such as echocardiography (ultrasound of the heart). On an electrocardiogram, atrioventricular block 1 degree is manifested by an increase in the interval between the P and R teeth, while all P waves are normal, and they are always followed by QRS complexes.
2nd degree
AV block of the 2nd degree happens, as already described above, of the first and second type. During the course of the 1st option (Mobits 1), it may be asymptomatic and not requiring treatment. In this case, the physiological basis for the occurrence of the block is usually a problem in the atrioventricular node. Mobits 2 type II AV block is usually a consequence of pathology in the lower conducting system (His-Purkinje). As a rule, it proceeds with obvious symptoms and requires additional diagnosis and quick start of treatment to prevent the development of complete blockade with cardiac arrest.
AV blockages on the ECG (second degree of type 1) are characterized by a progressive increase in the PR interval, after which the QRS complex falls out and then restores a rhythm close to normal. Then everything repeats. This periodicity is called the Samoilov-Wenckebach periodical. The second type of AV block with a second degree on the ECG is characterized by a constant or spontaneous loss of the QRS complex, while the prolongation of the PR interval, as with Mobitz type 1, does not occur.
3rd degree
Grade 3 AV block is congenital and acquired. It is characterized by the complete absence of impulses passing from the atria to the ventricles, and therefore is called complete blockade. Since no pulses are transmitted through the atrioventricular heart node, second-order pacemakers are activated to urgently support the work of the heart, i.e., the ventricle works according to its own rhythm, not associated with the atrial rhythm. All this causes severe disturbances in the functioning of the heart and the work of the cardiovascular system. Blockade of the third degree requires a quick start of treatment, because it can lead to the death of the patient.
On the ECG, a 3rd degree blockade looks like this: there is completely no connection between the P waves and QRS complexes. They are recorded at an inappropriate time and with a different frequency, that is, two unrelated rhythms are detected, one is atrial, the other is ventricular.
The causes of AV blockade
The most common causes of such a disorder as AV blockade are an increased vagus nerve tone in athletes, sclerosis and fibrosis of the cardiac conduction system, heart valve pathology, myocarditis, myocardial infarction, electrolyte disturbances, and the use of certain medications, such as cardiac glycosides (Digoxin) , Korglikon, Strofantin), calcium channel blockers (Amlodipine, Verapamil, Diltiazem, Nifedipine, Cinnarizine), beta blockers (Bisoprolol, Atenolol, Carvedilol ) Complete blockade may be congenital. This pathology is often recorded in children whose mothers suffer from systemic lupus erythematosus. Another cause of third-degree blockade is Lyme disease, or borreliosis.
Symptoms of AV blockade
Atrioventricular block of the 1st degree, as well as block of the 2nd degree in the first type, is usually not accompanied by any symptoms. However, with a blockade of the Moritz 1 type, in some cases dizziness and fainting are observed. The second type of the second degree is manifested by the same signs, as well as clouding of consciousness, pain in the heart and a feeling of stopping it, prolonged fainting conditions. Symptoms of complete atrioventricular blockade are a decrease in heart rate, severe weakness, dizziness, darkening of the eyes, cramps, loss of consciousness. There may also be a complete halt in the activity of the heart with a fatal outcome.
Diagnosis of AV blockade
Diagnosis of atrioventricular block is carried out using electrocardiography. Often, AV block of the 2nd degree (as well as the 1st) is detected by chance during an ECG without complaints during a preventive medical examination. In other cases, the diagnosis is carried out in the presence of any symptoms that may be associated with problems in the nerve impulse conduction system of the heart, for example, with dizziness, weakness, darkening in the eyes, or fainting.
If a patient is diagnosed with an ECG blockade by ECG, and there are indications for further examination, the cardiologist usually recommends daily ECG monitoring. It is carried out using the Holter monitor, therefore it is also often referred to as Holter monitoring. Within 24 hours there is a continuous continuous recording of the ECG, while a person leads a familiar and characteristic way of life - moves, takes food, sleeps. The study is non-invasive and does not cause almost any discomfort.
After the recording of the electrocardiogram, the data from the monitor is analyzed with the issuance of the appropriate conclusion. The advantage of this diagnostic method, in comparison with the usual short ECG recording, is that it is possible to find out with what frequency blockages occur, in which period of the day they are most often recorded and at what level of patient activity.
Treatment
Not always atrioventricular block of the first degree, as well as the second, requires medical intervention. With the first in therapeutic measures, as a rule, there is no need. Also, with the second type (Moritz 1), therapy is usually not carried out, although additional studies to identify concomitant heart problems may be recommended.
Treatment of AV blockade is necessary for the second degree of Moritz type 2, as well as for partial or complete blockade of the third degree, since such a significant violation of conduction can lead to sudden death. The main method for correcting malfunctioning of the heart is to install a patient's pacemaker (EX), temporary or permanent. Specific drug therapy is also prescribed - Atropine and other drugs. Medications are not able to cure a person with this disease and are usually used in the period before implantation of EX.
Preparing for the installation of EX
Preparation for implantation of a pacemaker includes, in addition to electrocardiography, conducting echocardiography - an ultrasound examination of the heart. Echocardiography allows you to visualize the wall, cavities and septa of the heart and detect any primary diseases that could be the cause of AV blockages, for example, valve pathology. If a cardiologist during an ultrasound scan found heart problems, concomitant therapy is carried out in parallel with the treatment of atrioventricular block. This is especially important in those cases when it is these pathologies that are the cause of conduction disturbance. Standard clinical trials are also prescribed - blood and urine tests. If the patient has diseases of other organs and systems, in the preoperative period, appropriate diagnostic measures may be recommended to him.
EX implantation
The installation of a pacemaker with a diagnosis such as AV block is a planned surgical intervention. It can be carried out both under general anesthesia and under local anesthesia. The surgeon passes through the subclavian vein through the vessels towards the heart electrodes, which are fixed there. The device itself is sewn under the skin using a special technique. Stitches are placed on the wound.
EX is an artificial substitute for a pacemaker, conducting impulses from the atria to the ventricles and normalizing the heartbeat. Due to periodic or constant stimulation, the chambers contract in the correct order and at the right interval, the heart fully fulfills its pumping function. In the circulatory system, congestion and sudden changes in pressure do not occur, and the risk of symptoms such as dizziness, loss of consciousness, and others usually occurring in patients diagnosed with AV block, is significantly reduced, as is the risk of sudden death from a stop cardiac activity.
After operation
The postoperative period, if there are no other health problems complicating its course, is usually not accompanied by any serious restrictions. The patient’s home is released for 1-7 days, after conducting some research. Wound care in the area of the implanted body of the device is carried out according to the recommendations of a doctor. Removing sutures is necessary if they are sutured by material that does not absorb on its own. If during the installation of EX, the wound was closed with a cosmetic suture, it is not necessary to remove it.
The first weeks after the implantation of a pacemaker, it is recommended to avoid physical exertion, as well as to protect the seam area (sports, if there are no contraindications, you can start after a few months, be sure to consult with your doctor). 1 month after the procedure, a control consultation with a cardiologist is appointed. Then the check is carried out after six months and again after a year from the day of implantation, and then - annually.
The operating time of EX-depends on many factors. On average, this period is 7-10 years, and in children it is usually much less, which is associated, inter alia, with the growth of the child's body. The control of the stimulator, as well as its programming for a particular patient, is carried out by the doctor. Checking the performance of the device must be carried out in a timely manner. Also, if necessary, the program is also adjusted - the specified functioning parameters. This may be necessary if the pacemaker does not fulfill the tasks assigned to him: the heart rate is too low or high and / or the patient is not feeling well. Also, other settings can be set by the doctor when changing a person’s lifestyle and insufficient stimulation, for example, with active sports.
The main reason for the failure of the EX is a decrease in battery capacity - its discharge. In such cases, the device must be replaced with a new one, and a consultation with a cardiologist is required. The electrodes located in the cavity of the heart usually remain for life and during proper operation do not require replacement, giving the person the opportunity to live fully, despite heart problems.