Atrioventricular blockade: causes, symptoms, diagnosis, treatment

Atrioventricular blockade is the partial or complete cessation of the impulse from the atria to the ventricles. The most common cause is idiopathic fibrosis and sclerosis of the conduction system. Diagnose pathology according to the ECG. Symptomatics and treatment depend on the degree of blockade, but therapy, if necessary, usually involves the use of ECS.

AV-blockade is the consequence of idiopathic fibrosis and sclerosis of the conduction system in approximately 50% of patients, and in 40% - the result of ischemic heart disease. The remaining cases fall on the intake of medications (for example, beta-blockers, calcium channel blockers, digoxin, amiodarone), increased vagal tone, valvulopathy, congenital pathology, genetic and other abnormalities.

[1], [2], [3], [4]

Atrioventricular block of degree I

All normal teeth are accompanied by complexes RR, but PR intervals are longer than normal (> 0.2 s). AV blockade I degree can be physiological in young patients with excessive influence of the vagus nerve and in well-trained athletes. Atrioventricular blockade of the first degree is always asymptomatic and does not require treatment, however, if it is combined with another pathology of the heart, further examination of the patient is shown, since it can be associated with the use of medications.

[5], [6], [7], [8], [9]

Atrioventricular block of degree II

Some normal teeth are accompanied by ventricular complexes, but some are not. There are three types of this pathology.

In the Mobitz type I atrioventricular blockade of the 2nd degree, the PR interval elongates progressively after each contraction until the atrial pulse is stopped at all, and the complex falls out (the Wenckebach phenomenon). Conducting through the AV node is restored to the next reduction, and the situation is repeated. Type Mobitz I atrioventricular blockade II degree may be physiological in young patients and many athletes. The blockade appears in the AV-connection in 75% of representatives with narrow QRS complexes and in the lower sites (the bundle of the Gys, the bundle bundle legs, the Purkinje fiber) from the rest. If the blockade becomes complete, a slipping nodal rhythm usually appears. The need for treatment is absent until the blockade leads to a bradycardia with clinical symptoms. It is also necessary to exclude temporary or removable causes. The treatment consists in the implantation of ECS, which can also be successful in patients without clinical manifestations with the type Mobitz I atrioventricular blockade of the II degree at the subunit level, revealed during the electrophysiological study performed on another occasion.

At type Mobitz II atrioventricular blockade of II degree the interval PR is identical. Impulses are not carried out immediately, and the QRS complex falls out, usually with repeated cycles of the tooth - every third cycle (1: 3 block) or the fourth (1: 4 block). Type Mobitz II atrioventricular blockade II degree is always pathological. In 20% of patients it occurs at the level of the bundle of the Hyis, in the branches of this bundle - in the rest. Patients may not have clinical manifestations or experience mild dizziness, presyncope and syncope, depending on the ratio of conducted and unmuted impulses. Patients have the risk of developing a high-grade clinical blockage or complete blockade, in which the slipping rhythm is likely to be ventricular, and therefore rare and incapable of providing a systemic blood supply. Therefore, IWR is shown.

Blockade II degree of high gradation is characterized by loss of every second or more often ventricular complex. To distinguish the blockade of Mobitz I and Mobitz II is difficult, because two prongs never appear on the contour line. The risk of developing a complete atrioventricular block is difficult to predict, therefore, IAD is prescribed.

Patients with any type of atrioventricular blockade of degree II who have a structural pathology of the heart should be considered candidates for permanent pacing, with the exception of transient and reversible causes.

[10], [11], [12]

Atrioventricular block of III degree

Atrioventricular blockade is complete: there is no electrical connection between the atria and ventricles and, accordingly, the connection between the teeth and QRS complexes (AB dissociation). Cardiac activity is supported by the slipping impulses of the pacemaker from the AV node or ventricle. The rhythm formed above the bundle bundle bifurcation gives narrow ventricular complexes of relatively high frequency (> 40 per minute), a relatively significant heart rate and a minor symptomatology (for example, weakness, postural dizziness, intolerance to physical exertion). The rhythm formed below the bifurcation gives wide QRS complexes , a small heart rate and more severe clinical manifestations (presyncopal and syncopal states, heart failure). Symptoms include signs of AB-dissociation, such as cannon a-waves, variability of blood pressure and changes in the sonority of tone I. The risk of syncope in connection with asystole, as well as sudden death, is higher with insufficient pulse generation by the pacemaker.

Most patients need IV. If the blockade occurs due to the use of antiarrhythmic drugs, the abolition of medicines can be an effective method of treatment, although temporary cardiac stimulation is sometimes necessary. In the case of a blockade with acute lower MI, there are usually signs of dysfunction of the AV node that are sensitive to atropine or can be resolved on their own in a few days. The blockade that develops in the anterior myocardial infarction usually indicates extensive necrosis zones involving the His-Purkinje system and requires immediate transvenous implantation of a pacemaker with temporary external cardiac stimulation, if necessary. Spontaneous resolution is possible, but it is necessary to study the state of the AV node and the underlying structures (for example, electrophysiological study, exercise test, 24-hour ECG monitoring).

The majority of patients with congenital atrioventricular blockade of the third degree have a nodal slipping rhythm that maintains a sufficiently adequate rhythm, however they need implantation of a permanent ECS before reaching middle age. Less often patients with congenital atrioventricular blockade of the third degree have a rare slipping rhythm, which necessitates the implantation of ECS in childhood, possibly even during early childhood.

[13], [14], [15]