Beam of His

The beam of His is a beam of cardiac muscular cells specialized in electric conduction. It transmits the electric impulses of the auricles to the cells of the ventricles, inducing the contraction of the cardiac muscles of the ventricles. It is also called auriculo-ventricular node .

These specialized muscle fibers of the heart owe their name with the Cardiologue Suisse Wilhelm His Jr., which them discovered in 1893, helped by work of Walter Gaskell.

By extension, the His indicates:

the beam itself;
electric translation of its activity (wave H);
the electrophysiological Exploration intended to find the latter ( to make His ).

The adjective being referred is hissien to it: beam hissien, conduction hissienne, block hissien…

Anatomy

The part separating the auricles from the ventricles is a fibrous ring, not letting pass the electric impulse: it is of the mitral ring on the left and the ring tricuspidien on the right. Electric conduction can thus be done only on the level of the septum inter ventricular via the beam of His. This structure remains indistinguishable by the simple sight, of the cardiac muscle.

The beam begins in top by a trunk which separates quickly in connects right and connects left moving each one towards its ventricle. These branches end in the fibers of Purkinje.

Physiology

The contraction of the muscular cell is caused by an electric depolarization (inversion of the electric polarity of the cellular membrane by a system of opening and closing of channels allowing the entry and the exit of certain ions). This depolarization is born from the sinusal Nœud, is propagated gradually in the auricles before arriving at the beam of His which makes it possible to transmit the electric impulse to the ventricles.

The beam of His has a role of conduction, but also of filter, preventing the complete propagation of an auricular depolarization (of the auricles) too fast to the ventricles like in the case of a auricular Fibrillation. The transmitted maximum frequency corresponds to approximately 220 - age of the subject (for example, it is of 180/mn for a 40 year old patient).

Exploration

The depolarization of His is of too low amplitude to be detected by a ECG. Its detection requires to mount a probe directly to its contact during a electrophysiological Exploration: a puncture of a gross Veine (generally femoral Vein) under Local anesthesia makes it possible to mount a probe under radiographic control and to position its end on the level of the opening tricuspidien, between right auricle and ventricle right. The recording then shows the presence of a wave H located between the wave has depolarization of the auricles and the wave V of the depolarization of the ventricles. One can then measure time AH (wave has with the wave H) and HV (of the wave H to the wave V).

Pathology

See also article Turbid cardiac conduction.

A lesion of the beam of His can result in a auriculo-ventricular Bloc more or less complete: the heart is slow (Bradycardie) and the patient can make a Lipothymie (simple faintness) or a syncope (brutal loss of consciousness). It can also appear by a tiredness, breathlessness with the effort. The block can be permanent or paroxystic. The ECG is characteristic in the first case but can be normal in the second case. One supplements exploration by a cardiac Holter (recording of the ECG during 24:00), and if need be by a electrophysiological Exploration. The latter makes it possible to distinguish the block supra hissien with a normal HV and an increased AH, by high lesion of the beam of His. This type of block is not very dangerous because the heart never slows down much. On the contrary, in the event of block will infra hissien (prolonged HV), the heart can make great pauses leading to syncopes.

In certain cases, there exist other ways of ventricular conduction inter auriculo: beam of Kent , beam of Maheim , leading to accesses of Tachycardia S (too fast heart) and whose evaluation must be made in a dedicated service.

See too

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