Hemiblock I44.6

Rosenbaum et al. were the first to describe the various forms of hemiblock in 1968 (Schmidt-Voigt 1982).

The possibility of recording a long-term ECG was first introduced by the American physicist Norman J Holter in 1961 (Apitz 2002).

The first loop recorder was the "Reveal", which has been on the market in the Netherlands since 1998 (Pezawas 2004).

Hemiblock is the blockage of conduction below the His bundle (Herold 2022) in the left Tawara bundle (Abdulla 2021). This is an intraventricular conduction disturbance (Schuster 2005).

The left Tawara bundle is divided into an anterior bundle (the so-called left anterior fascicle) and a posterior bundle (the so-called left posterior fascicle). If there is a blockage in one of these fascicles, this is referred to as a (mono-) fascicular block. In such a case, the left conduction pathway is not completely blocked, as is the case with a complete left bundle branch block, for example, but only partially and is therefore referred to as a hemiblock (Schuster 2005).

Below the His bundle, the conduction of the heart is divided into a right bundle branch (RBB = right Tawara bundle branch) and a complex, dividing left bundle branch (LBB = left Tawara bundle branch) (Fisher 2018).

Due to the trifascicular structure of the ventricular conduction system, a distinction is made between the following blockages:

- unifascicular block = hemiblock

- bifascicular block

- trifascicular block (Herold 2023)

The hemiblock affects only parts of the LBB (Weber 2022) and is subdivided according to localization into a:

- left anterior hemiblock (LAH)

- left posterior hemiblock (LPH)

If both LAH and LPH occur together, this is referred to as a complete left bundle branch block or a bifascicular (left) bundle branch block (Schuster 2005).

More recent investigations suggest the suspicion of a further additional fascicle of the left bundle branch. This supplies the septum (Fisher 2018).

Left anterior hemiblock was found as an incidental finding in 2 - 5 % of people over 40 years of age (Hombach 2001).

LAH is more common than LPH because the left anterior fascicle is narrower and smaller (Schuster 2005). LAH is the most common form of intraventricular blockage (Herold 2022).

In acute coronary syndrome (ACS ), LAH occurs in around 5 % of patients and LPH in just 0.5 % (Trappe 2016).

Numerous diseases can cause a hemiblock. These include:

- Arterial hypertension

- CHD

- Myocardial infarction

- Valve defects (especially tricuspid and aortic valve defects)

- Ventricular septal defects

- Cardiomyopathy (Elizari 2021)

- Septum primum defect (Weber 2022)

Hemiblock rarely causes clinical symptoms. It is usually an incidental finding (Weber 2022).

The diagnosis of a hemiblock is made by a resting ECG, long-term ECG, exercise ECG, echocardiography (Herold 2022).

The following should be excluded:

- CHD

- cardiomyopathy

- Arterial hypertension

- Storage diseases (Weber 2022).

12-lead ECG

- Left anterior hemiblock (LAH):

This is an over-twisted left type with deep S-waves in the chest wall leads V5 - V6 and only slowly rising R-waves. In leads I and aVL there is a small Q wave (Schuster 2005). However, the QRS duration is not significantly altered, only the QRS axis is shifted (Kasper 2015).

LAH is often associated with a right bundle branch block (RSB). This results in a bilateral bundle branch block (also known as "Bailey block"). These patients tend to develop a complete heart block, the so-called trifascicular block, in about 10 % of cases (Abdulla 2021).

- Left posterior hemiblock (LPH):

The position type here is a right type or over-rotated right type. There are small Q-spikes in II, III, aVF. The R-peaks in the chest wall leads only show a sluggish rise (Schuster 2005). Here, too, the QRS duration is not significantly altered, only the QRS axis is shifted (Kasper 2015).

The diagnosis of LPH is sometimes difficult to make. LPH is said to occur when the position type of a previously existing left type changes to a right type or an over-rotated right type (Abdulla 2021).

LPH

An LPH must be differentiated in the ECG in particular from a right heart strain or a right type due to a myocardial infarction in the area of the lateral wall (Schuster 2005).

In the case of a hemiblock, the disease causing the block is treated (Weber 2022). An isolated left anterior hemiblock does not require treatment (Krehan 2017).

The prognosis depends on the underlying disease, but in most cases the prognosis is good (Weber 2022).

Patients with proven hemiblock are still allowed to drive a vehicle according to road traffic regulations (Madea 2012).

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