Thigh blocks

Permanent stimulation of the heart has been possible since the 1950s (Kasper 2015). Earl Bakken, co-founder of Medtronic, developed the first wearable pacemaker in 1957. The device was worn with a chain around the neck and the electrodes were guided directly to the myocardium via a thoracotomy (Detho 2009).

In 1958, Senning implanted the first pacemaker. This was a simple chamber pacemaker with a fixed stimulation frequency (Gertsch 2008).

The patient, Arne Larsson, had a complete thigh block with Adam Stokes seizures, which caused him to lose consciousness up to 30 times per day. Although the device had to be replaced after a few hours and several times in the following weeks, Larsson was highly satisfied. He died of carcinoma at the advanced age of 86 (Detho 2009).

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

Since 1988, programmable pacemakers have been classified by the International Nomenclature of Pacemaker Systems, the so-called NBG code (Bauch 2002).

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).

A bundle branch block is a disturbance in the conduction of the heart from the AV node to the ventricular myocardium (Sagmeister 2019), whereby the conduction from the AV node to the ventricular myocardium is disturbed in the area of the Tawara legs (Christ 2019).

The bundle branch block is one of the intraventricular blockages (Herold 2022).

The excitation conduction of the heart normally originates from the sinus node, which is located in the upper right atrium (Meinertz 2018). After excitation of the atria, the excitation is transmitted to the ventricles. However, to ensure that the atria and ventricles are not excited at the same time, the excitation is briefly slowed down in the AV node (So 2004). The excitation is transmitted into the His bundle via the AV node and divides below the His bundle into a right bundle branch (RBB = right Tawara bundle branch) and a complex, dividing left bundle branch (LBB = left Tawara bundle branch) (Fisher 2018). More recent investigations suggest the suspicion of a further additional fascicle of the left bundle branch that supplies the septum (Fisher 2018).

A distinction is made between 3 degrees of severity of conduction disturbance:

- I. Incomplete block

- II: Intermittent block

- III. permanent block (Herold 2022)

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

I. Unifascicular block = hemiblock

The hemiblock itself is further subdivided according to the localization into a:

I. a. left anterior hemiblock = LAH

In this case, the ECG shows 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 changed, only the QRS axis is shifted (Kasper 2015).

I. b. Left posterior hemiblock = LPH (Schuster 2006)

The position type here is a right type or over-twisted right type. There are small Q-spikes in II, III, aVF. The R-spikes 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).

II Bifascicular block

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

- II. a. RSB + LAH:

The ECG in V1 shows the typical right bundle branch block form of the QRS complex with widening of the QRS complex to ≥ 0.12 s in a complete block (Herold 2022) or between 0.10 - 0.11 s in an incomplete block (Herold 2022) as well as a large R wave in V1 caused by a pronounced terminal vector to the right.

The wide R wave in lead III, which is usually present in a complete right bundle branch block, is missing in the frontal plane. The QRS axis shows an over-twisted left type.

The combination of an over-rotated left-typical cardiac axis with the missing terminal vector in lead III can only be explained by an additional left anterior hemiblock (Klinge 2015).

- II. b. RSB + LPH:

In this case, the ECG shows features of the right bundle branch block (RSB) and the right type (Strödter 2008).

- the QRS complex is widened to ≥ 0.12 s in the case of a complete block (Herold 2022) or between 0.10 - 0.11 s in the case of an incomplete block (Herold 2022)

- the cardiac axis can be determined despite the RSB: cardiac axis is typical right to over-rotated right

- changes of a RSB are found in the chest wall leads

- the terminal vector is directed to the right:

- in V1 there is a conspicuous plump positive ventricular complex whose vector is directed to the right over the entire excitation time (Klinge 2015). The widened QRS complex in V1 sometimes does not look "M-shaped", as is the case with RSB, but more like a "sugar cone", which is found in V5 and V6 in LSB (Strödter 2008).

- In derivation III, a terminal vector pointing to the right is also recognizable (Klinge 2015)

III Trifascicular block

This is characterized by the blockage of all 3 fascicles. If the block is complete, it is referred to as a total AV block (Klinge 2002). If the blockage in one of the fascicles is incomplete, the excitation can be transmitted from the atria to the ventricular muscles, albeit with a delay. In this case, one speaks of an AV block of I or II degree. In this case, the ventricular complexes appear on the ECG as in a bifascicular block (Klinge 2002).

Left bundle branch block (LSB)

There are currently at least 3 different definitions of LSB: AHA / ACC / HRS criteria, Strauss definition and the ESC criteria (Herold 2022).

An LSB can be complete, i.e. the QRS duration is prolonged to ≥ 0.12 sec. or incomplete with a QRS time of 0.10 - 0.11 sec (Herold 2022).

In LSB, the main vector is directed to the left and posteriorly (Kasper 2015).

In an LSB, a distinction is made between a:

- Unifascicular bundle branch block of the left Tawara leg before branching

- Bifascicular block of the left Tawara bundle branch after branching (Herold 2022)

The ECG typically shows:

- deep S-waves in V1 and V2

- in V5 / V6 split ventricular complex (the so-called "broken off sugar loaf")

- Discordance of the chamber end part to the chamber complex

- delayed onset of the final negativity movement

- there is no Q-spike in I and aVL

- in I and aVL a clumsy, fragmented R-wave (Herold 2022)

Right bundle branch block (RSB)

An RSB is caused by blockage of the right Tawara limb (Herold 2022). Here, too, a distinction is made between a complete RSB with a prolonged QRS duration of ≥ 0.12 sec and an incomplete RSB with a QRS time of 0.10 - 0.11 sec (Herold 2022).

In RSB, the terminal QRS vector is directed to the right and anteriorly (Kasper 2015).

The ECG typically shows the following changes:

- S wave splintered in I (Herold 2022)

- Narrow, small R in I

- In V1, the QRS complex is splintered in an M-shape

- In V1 and V2 there are:

- St depression

- Negative T

- Final negativity movement delayed (So 2004)

- Discordance of the ventricular end part to the ventricular complex (Herold 2022)

LSB occurs in < than 1 % of the population and RSB is found in approx. 0.3 - 2.5 %. Both bundle branch block patterns increase significantly with age. For example, 15 - 20 % of > 80-year-olds have a bundle branch block (Meinertz 2018).

An LSB is often the result of serious heart disease (Striebel 2015).

There are many causes of a bundle branch block. They can occur, for example, in the context of the following diseases:

- CHD

- vitia

- myocarditis

- Cardiomyopathy

- Arterial hypertension

- Atrial septal defect of the ostium primum type (Hamm 2014)

- Myocardial infarction

- Valve defects (especially tricuspid and aortic valve defects)

- Ventricular septal defects (Elizari 2021)

- Septum primum defect (Weber 2022)

- Left ventricular hypertrophy (e.g. this is the most common cause of LSB)

- Idiopathic fibrotic degeneration of the conduction system as can occur, for example, in the context of Lev's and Lenègre's disease

- Right heart strain due to e.g. congenital vitia or pulmonary embolism (Herold 2022)

The diagnosis is made by resting ECG, long-term ECG, ergometry and echocardiography (Herold 2022). Sometimes, e.g. to differentiate a trifascicular block or an AV block, a His bundle ECG may also be necessary (Klinge 2002).

Treatment of bundle branch blocks initially consists of treating the underlying disease (Herold 2022).

In the case of alternating bundle branch blocks and trifascicular block, a class I indication for a pacemaker exists (Herold 2022).

In the case of a bifascicular block and simultaneous cardiac syncope, a class IIa indication for a pacemaker exists after exclusion of other causes for the disease (Herold 2022).

Since thigh blocks are not independent diseases, the prognosis depends on the underlying disease (Meinertz 2018).

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