Auriculo-ventricular Block

A auriculo-ventricular block (BAV) is a defect of transmission of the electric impulse (deceleration or interruption) between the auricles and the ventricles of the heart.

It belongs to the Troubles of cardiac conduction.

It can appear by a slow heart (Bradycardie), being able to be responsible for a faintness, even for a syncope.

Mechanism

Anatomy

The synchronization of the contractions auricle-ventricles is under electric drive. The electric phenomenon is secondary with a depolarization of the cells (inversion of the electric polarity between the interior and the outside of the cell by migration of ions through the wall). The macroscopic translation of this phenomenon constitutes ECG. This depolarization is led gradually to the whole of the heart but can take preferential ways which are the ways of conduction. The principal structures in causes are:

the sinusal Node (also called node of Keith and Flack): located in the right auricle. It is where begins the rhythmic electric activation from the heart which is transmitted gradually until the
ventricular node auriculo (also called node of Aschoff-Tawara), located at the auriculo-ventricular junction. It is about a specialized fabric allowing the transmission and the filtering of the auricular electric activity (of the auricle) the ventricles. Thanks to him, a too fast auricular stimulation only is partially transmitted, thus avoiding the racing of the ventricular frequency.
It is connected to the Faisceau of His (with the high part of the septum inter ventricular) which is divided into two branches, going towards the ventricles right and left.

The auriculo-ventricular block consists of a lesion of the auriculo-ventricular node (one speaks about nodal block or block supra-hissien) or on the level of the Faisceau of His (one speaks about block tronculaire when the " blocage" has place with the emergence of the trunk of the beam of His, and block infra-hissien, when it low located on the beam).

Blocks supra and infra-hissiens

Each cardiac cell, including on the level of conductive fabrics, has a certain automation allowing a " rate/rhythm of échappement" : it contracts spontaneously with more or less regular intervals. More the cell is " haut-situé" (i.e., near to the auricles), plus the spontaneous frequency of contraction is fast and relatively stable. On the contrary, the ventricular cells have an extremely low and particularly unstable spontaneous frequency, being able to cause prolonged pauses. A block supra hissien thus makes it possible spontaneous depolarizations of the auriculo-ventricular node to lead to the ventricles at an acceptable frequency: the heart is only moderately slowed down and risks it of syncope is reduced. On the contrary, these last are blocked during a block tronculaire or will infra hissien. The rate/rhythm of exhaust can thus come only from the beam of His or the ventricles. It is then slow and unstable, with a high risk of syncope.

Degree of the block

The auriculo-ventricular block can be complete: no passage of the electric impulse is thus possible between the auricles and the ventricles, only the rate/rhythm of exhaust, more or less slow according to the topographic level of the block, making it possible to ensure the contraction of the ventricles. One also speaks in this case about auriculo-ventricular dissociation or auriculo-ventricular block about the third degree.

If the lesion is partial, the block can be only incomplete and be translated, either by a simple deceleration of conduction between the auricles and the ventricles, the latter remainder controlled by the first ( auriculo-ventricular block of the first degree), or by a blocking of certain numbers of auricular depolarization (wave P on ECG), remaining ventricular depolarizations being however from the auricles ( auriculo-ventricular block of the second degree).

Private clinic

Circumstances of discovery

Symptomatology depends primarily on the minimal heart rate and its adaptation according to the needs for the organization. The signs can be acute or chronic according to the paroxystic or permanent character of the block. The subject can be thus completely asymptomatic, i.e., that he does not complain about nothing. It can feel faintnesses (Lipothymie S), a weakness, a feeling of Malaise, breathlessness which can go to a table of Cardiac failure (due to the absence of acceleration of the heart in the circumstances requiring it). In the worst case, it appears by syncopes called in this case syncopes of Adams-Stokes (or Stokes-Adams ), characterized by a brutal and short loss of consciousness, without sign heralding.

Clinical examination

The auriculo-ventricular blocks of the first degree do not have clinical translation, not having a consequence on the heart rate.

In the blocks of higher degree, the clinical examination can highlight a heart rate decreased (Bradycardie) with a sometimes irregular rate/rhythm (cardiac pause). The examination can highlight a widening of the blood Pressure differential (increase in the systolic pressure with diastolic pressure decrease). Seldom a dissociation jugulo-carotidienne can be objectified (the jugular Veine beats in a synchronous way to the auricles and the Artère synchronous carotid of manner to the ventricles).

Complementary examinations

The auriculo-ventricular block can be paroxystic or permanent. In the first case, the electrocardiogram is sometimes completely normal.

The block is characterized:

by its degree;
not its topography (supra or hissienne will infra);

Electrocardiogram

It comprises anomaly only if the block or permanent or if one with the chance to make a layout at the time of a paroxystic block. It primarily makes it possible to determine the degree of the block. The level of the block (will infra or supra-hissien) is more difficult to evaluate on a simple electrocardiogram.

Auriculo-ventricular block of the 1st degree

It is a constant deceleration of conduction on the level of the auriculo-ventricular node. On ECG, there is thus a constant lengthening of space PR (higher than 200 ms) and a wave P always followed by a complex QRS.

Auriculo-ventricular block of the 2nd degree

Certain waves P are not followed by a complex QRS. There are two types:

Möbitz 1 (or of Luciani-Weckenbach type) comprising a progressive lengthening of space PR until a wave P is not followed of a complex QRS (wave P blocked).
Mobitz 2: complete and unexpected blocking of a wave P without lengthening of PR, being able to occur in a random or regular way (a complex on 2,1 out of 3…).

Auriculo-ventricular block of the 3rd degree

Also called complete auriculo-ventricular block, it corresponds to a complete and permanent blocking of auriculo-ventricular conduction. One thus witnesses a dissociation between the activity of the auricle S and the Ventricule S: all the waves P are blocked and the complexes QRS come from a hearth ectopic.

Level of the block

A ventricular block auriculo of Luciani-Weckenbach type is in secondary rule with a block supra-hissien (thus less serious). A complete auriculo-ventricular block with fine complexes of exhaust and without excessive bradycardia is in favor also of a block supra-hissien.

The association of a Bloc of branch with a lengthening of PR is in favor of a possible block infra-hissien but it is not always true.

Holter

The cardiac Holter consists of the recording of the electrocardiogram over one day or more. It makes it possible to naturally detect episodes of auriculo-ventricular blocks paroxystic, even if the patient is asymptomatic (complaining about nothing), in condition that the latter are sufficiently frequent. It also makes it possible to detect other cardiac causes of faintnesses (sino-auricular Bloc or ventricular Tachycardie for example). If the holter is normal, one can according to the cases, to repeat the examination so as to have a recording of several days. In certain cases, one can have to establish a small recording case under the skin which makes it possible to analyze the electrocardiogram during several months.

It should be noted that a ventricular block auriculo of Luciani-Weckenbach type is banal during the phases of sleep and is not abnormal.

Endo-cavitary study of the beam of His

This study will make it possible to specify the topography and the degree of the block. It consists in introducing electrodes directly in contact of various parts of the heart (right auricle, ventricle right, auriculo-ventricular junction where the beam of His is) generally by the femoral vein, under local anesthesia and X-ray control.

The electric activity of the beam of His (wave H) is detected thus directly and its place report/ratio with the electric activity of the ventricle right (wave V) can be analyzed. A significant lengthening of time HV signs nature infra-hissienne block. Exploration can be sensitized by the injection of certain drugs exploiting the auriculo-ventricular node like the Ajmaline.

Causes

Myocardial infarction: if the infarction is of lower topography, the block is in rule supra-hissien, therefore not very serious. If it is former, the block is then infra-hissien, potentially more serious

medicamentous causes: Digitalique S, Quinidiniques, Beat-blocking S, Imipraminique S…
rare causes: aortic Contracting, Cardiomyopathie nonobstructive, congenital forms , surgical lesions, endocarditis of Osler, Sarcoidosis, Spondylarthrite ankylosante, Hémochromatose, other infectious causes (Diphteria, Disease of Lyme)…

In the absence of found cause, it is generally about a degenerative block, dependant on the age, sometimes permanent from the start, sometimes paroxystic at its beginnings.

Treatment

A auriculo-ventricular block, some it is, requires an evaluation specialized to determine its gravity and its evolution of it.

Its treatment depends on its tolerance and the evolutionary risk: a nonsymptomatic block supra-hissien does not require for example any treatment.

The treatment of the cause must be made if the latter is given (stop of a responsible drug for example).

treatment into acute of the bradycardia

A hospitalization is in theory necessary. The installation of a venous access (perfusion) as well as the monitoring continues electrocardiogram is imperative (risk of prolonged cardiac pauses which can lead to a cardio-circulatory Arrêt. The Atropine is the drug of first intention. If the latter is ineffective, one must discuss according to the cases and the local possibilities:

the setting under Isoprenaline in continuous perfusion;
installation of a temporary external drive electrosystolic: two large electrodes are laid out on the thorax stripped of the patient and connected to a scope having the function of drive (often coupled with a semi-automatic Défibrillateur). Short electric impulses are then sent, causing the contraction of any muscle, of which the heart, located between the two electrodes. This method is very effective but very uncomfortable. It however makes it possible to reach a service equipped in all peace.
installation of a drive electrosystolic provisional intern: under X-ray control, an electrode is introduced into a large vein (Veine femoral for example) and pushed through the Vena cava, the right auricle to the point of the ventricle right. It is connected to a generator of electric impulses in the form of small case. The discharge being directly at the level of the cardiac muscle, it does not have there consequently stimulation of the other muscles.