Bifascicular block I45.2

Synonyms

Intraventricular block; bundle branch block; bundle branch block; BFB;

RSB + LPH = classic right bundle branch block;

First author

Permanent pacing 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 x / d. The pacemaker had to be replaced after a few hours. 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 ripe old age of 86 (Detho 2009).

Programmable pacemakers have been classified since 1988 by the International Nomenclature of Pacing Systems, the so-called NBG- code (Bauch 2002).

The possibility of recording a long-term ECG was first presented 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

Bifascicular block (BFB) is a block below the His bundle (Herold 2022).

Affected can be:

- the right tawara thigh as a so-called right thigh block (RSH) and one half of the left tawara thigh, either the left anterior fascicle or the left posterior fascicle (Klinge 2015).

- Left bundle branch block (LSB), which is a block of both fascicles of the left tawara thigh (Pölz 2022).

Bifascicular block is one of the intraventricular infrahispheric blocks. Due to the trifascicular structure of the ventricular conduction system, one differentiates between the following blockages:

- unifascicular

- bifascicular

- trifascicular (Herold 2022)

Bifascicular block is differentiated between:

- 1. RSB + LAH

In this case, the right tawara limb and the left anterior fascicle are blocked. These are both supplied by the LAD (left anterior descending) and RIVA (Ramus interventricularis anteroir), respectively (Strödter 2008).

- 2. RSB + LPH

In this type, the right tawara limb and the left posterior fascicle are blocked (Strödter 2008).

- 3. LSB

Both fascicles of the left tawara limb are blocked (Vogler 2022).

As with all other conduction disorders, a distinction is made between 3 degrees of severity:

- I. incomplete

- II. intermittent

- III. permanent (Herold 2022)

Shabbir (2022) found BFB in 11.2% of a population of 580 adults who consulted their primary care physician for unexplained syncope.

Right bundle branch block and/or BFB occur clustered in the elderly and affect approximately 1% of the population (Erkapic 2020).

One most commonly finds the combination of right bundle branch block (RSB) plus left anterior hemiblock (LAH) = RSB + LAH. The combination right bundle branch block plus left posterior hemiblock = RSB + LPH occurs rarely (Klinge 2015).

In patients with bifascicular block and syncope, structural heart disease is found in 32%-71% (Ebert 2009).

• RSB + LAH can be caused by:

- CHD (most common cause).

In this case, RSB + LAH can be caused by a high occlusion of the left coronary artery or one of the proximal branches, since the right Tawara- limb and also the left anterior fascicle run close together in the anterior portion of the septum (Klinge 2015).

- Cardiomyopathy (Klinge 2015).

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

• RSB + LPH can be caused by:

- All structural heart diseases (Hamm 2014).

• Cause of complete left bundle branch block may be:

- CHD

- vitiation

- myocarditis

- cardiomyopathy

- arterial hypertension (Hamm 2014)

In RSB + LAH, excitation conduction starts from the AV node via the His bundle through the left posterior fascicle into the ventricles. This changes the PQ time (Klinge 2015).

The symptomatology depends on the disease triggering the bifascicular block (Krehan 2017). The following symptoms are frequently found:

- Vertigo

- Syncope (Klinge 2015)

In bifascicular block, there is no clinically detectable arrhythmia. The diagnosis is made on the basis of the ECG alone (Herold 2022).

ECG / Long-term ECG / Stress ECG

- RSB + LAH:

The ECG in V1 shows the typical right bundle branch block shape of the QRS complex with widening of the QRS complex to ≥ 0.12 s in complete block (Herold 2022) or between 0.10 - 0.11 s in 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- jag in lead III, which is usually always present in complete right bundle branch block, is absent in the frontal plane. The QRS axis shows an overrotated left type.

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

- RSB + LPH:

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

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

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

- in the chest wall leads changes of a RSB can be found

- 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 it does in RSB, but rather like a "sugar cone" found in V5 and V6 in LSB (Strödter 2008).

- In derivative III, a terminal vector directed to the right is also recognizable (Klinge 2015).

- Left bundle branch block:

Here, the QRS- complex is also broadened to ≥ 0.12 s in complete block (Herold 2022) or between 0.10 - 0.11 s in incomplete block (Herold 2022). In leads I, aVL, V5, V6, the QRS complex is deformed like a sugar loaf (Strödter 2008).

Electrophysiological examination = EPU

If there are still doubts after the ECG findings, further clarification by an electrophysiological examination is recommended (Ebert 2009), as there is always a risk of impending high-grade AV block inpatients with BFB (Brignole 2018).

In patients with Z. n. myocardial infarction and new-onset syncope, there is even a recommendation grade I for this examination (Brignole 2018).

However, in a 2019 paper, Roca- Luque et al. demonstrated that if the electrophysiological study (EPS) result was negative, advanced AV block occurred in approximately 25% of patients during a 25-month follow-up period. For this reason, in case of a negative result of the electrophysiological examination, an additional examination with a loop recorder is recommended (Shabbir 2022).

However, if the syncope was preceded by an arrhythmia, this cannot be detected with the electrophysiological examination (Brignole 2018). This is the case in approximately 50% of patients with negative EPS (Glikson 2021).

Interestingly, the proportion of patients tested negative is lower when the EPS was with flecainide rather than procainamide (Rivera- Lopez 2020).

Loop recorder

If electrophysiology testing is negative, implantation of a loop recorder = ILR may be recommended (Shabbir 2022).

Indications for early implantation of a loop recorder are:

- recurrent syncope and lack of evidence of relevant structural heart disease

- ECG- changes such as bifascicular block, long QT syndrome, epsilon wave, preexcitation (Schuchert 2018).

Glikson (2021) recommends empiric pacing in elderly, frail patients with bifascicular block and syncope when electrophysiologic testing is negative because of the risk of traumatic recurrence.

- Development of trifascicular block in approximately <3%/a (Krehan 2017).

- Development of a higher-grade AV block

- Occurrence of complete block of the conduction system (Shabbir 2022).

The primary focus should be on treatment of the underlying condition (Herold 2022).

In patients with bifascicular block and symptoms - especially syncope - implantation of a permanent pacemaker is additionally required (Kasper 2015).

Especially in old age, implantation often becomes necessary (Fumagalli 2022).

Pacemaker implantation

According to the European Society of Cardiology (ESC), an indication with recommendation grade I for implantation of a permanent pacemaker (PPM) exists in fascicular block with positive electrophysiological study (EPU) or positive result of loop recorder study (ILR) if:

- the baseline HV interval is ≥ 70 ms

- there is a high-grade AV block (Shabbir 2022)

- occurrence of a His- Purkinje- block of II. or III. degree after pharmacological provocation

- occurrence of a symptomatic pause of > 3 s

- On the occurrence of an asymptomatic pause of > 6 s (Brignole 2018).

In elderly, frail patients with bifascicular block and syncope, Glikson (2021) recommends empiric pacing if the electrophysiologic study is negative because of the risk of traumatic recurrence.

If electrophysiological study (EPU) or loop recorder study (ILR) were not performed or were negative, there is a recommendation grade IIb after empirical pacing (Brignole 2018).

For asymptomatic patients with BFB, pacemaker implantation is not recommended (Glikson 2021).

The prognosis of bifascicular block depends on the underlying disease (Krehan 2017).

Left bundle branch block is considered more severe than right bundle branch block because both fascicles fail in the former (Strödter 2008).

Since bifascicular block RSB + LPH is usually based on a serious disease, the prognosis is also rather poor in this case (Ebert 2009).

The occurrence of BFB in patients with acute myocardial infarction carries a high risk of complete AV interruption of conduction (Kasper 2015).

An analysis of 554 patients with bifascicular block/leg block and syncope showed the following results over 42.4 + / - 8.5 months:

- mortality was 29%.

Patients died predominantly from myocardial infarction or malignant tachycardia. Risks for increased mortality are CHD and heart failure (Ebert 2009).

- sudden cardiac death in 12

- occurrence of complete AV block in3 % of patients

- Syncope occurred before or during follow-up in 17% (Ebert 2009).

There is a high recurrence rate in patients with unclear syncope and simultaneous evidence of a thigh block in the ECG (Ebert 2009).

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