Bifascicular block is characterized by an irregular electrical conduction pattern in the heart, because of a blockage in two of the three fascicles of the His/Purkinje system.
Bifascicular block often is asymptomatic. Possible symptoms include syncopal episodes, dizziness, thoracic pain and shortened breath. Abnormalities in the heartbeats may also be experienced, alongside a slightly decreased heart rate. The symptomatology is attributed to the hearts inability to produce a contraction forceful enough to distribute the adequate volume of blood throughout the body. Additional symptoms may be present, depending on the cause of BFB, such as symptoms related to heart failure, hypertension of a myocardial infarction.
A bifascicular block is diagnosed via an electrocardiogram, carried out due to BFB suspicion or for other suspected diseases. An echocardiogram will help to illustrate cardiac functionality, once the ECG findings reveal signs compatible with a BFB.
An electrophysiological study can also corroborate the findings of the aforementioned procedures. His bundle electrograms [H] are used in order to track the duration of conduction intervals and atrial incremental pacing is also applied. The latter usually leads to the detection of AV nodal Wenckebach periodicity, which could lead to an atrioventricular block and sudden cardiac death.
- Wide QRS Complex
An AV block at the level of the bundle branches will result in an idioventricular escape rhythm – wide QRS complexes with very slow rates – which is a low-output rhythm. [ecgguru.com]
Mont L. et al: A new approach to the differential diagnosis of a regular tachycardia with a wide QRS complex. Circulation 83:1649, 1991. [books.google.de]
The QRS complexes are wide both due to preexcitation and due to right bundle branch block, which persists during preexcitation. [the-medical-dictionary.com]
The association of structural heart disease, renal failure and a wide QRS complex with an increased incidence of complete AV block is interesting, while not completely surprising. [revespcardiol.org]
Most patients do not require any type of treatment for BFB and frequent monitoring suffices to track the progression of the condition. Lifestyle adaptations can help an individual cope better and include dietary changes, physical exercise, smoking cessation and weight loss. The underlying conditions that have led to the occurrence of BFB should, however, be treated with a variety of medications targeting each disease. Drugs used against hypercholesterolemia, anti-hypertensive medications, drugs to prevent blood clotting and angioplasty are all potential treatments used to manage the underlying disease. Patients who have a medical history of syncopal episodes may need a pacemaker in order to restore the normal heart rate.
A 2006 study  evaluated 100 individuals with an average age of 68 years old and affected by bifascicular block: 50% had previously experienced a syncopal episode and patients categorized under the NYHA 4 category were not included in the study. The follow-up procedure lasted for 7 years and comprised electrocardiographic tests, Holter monitoring and electrophysiological assessment. Statistical analysis revealed that the only independent factor that could predict sudden cardiac death was the underlying congestive heart failure. The severity of congestive heart failure is therefore deemed as an unfavorable prognostic marker amongst people who are diagnosed with BFB.
Bifascicular block tends to more frequently affect people as their age increases; its prevalence has been estimated at approximately 0,1% amongst individuals aged < 35 years old and 1% amongst patients older than 35 years old  . It has been detected in around 8% of the patients hospitalized for a syncopal episode  and is frequently accompanied by various coexistent disorders such as coronary heart disease and hypertension. Mortality rates are high amongst these patient sub-categories and are estimated to amount to up to 12%  . A study  that monitored 260 patients with BFB calculated that the most prevalent comorbidity amongst them was hypertension, followed by structural heart disease, diabetes and dyslipidemia. Average survival was estimated to be approximately 5 years and 20% of them eventually succumbed (7% due to heart dysfunction). It is believed that heart failure corresponding to the NYHA ≥2 category and accompanied by renal insufficiency constitute bad prognostic markers for people with a BFB.
In order to comprehend the pathophysiological mechanisms of a bifascicular block, it is important to briefly outline the route of the electric cardiac signal. An impulse is normally generated in a specific location of the right atrium, the sinoatrial node (SA) and proceeds further below to the atrioventricular node (AV), which is found in-between the left and right atria. A slight delay of transmission occurs in the AV node and the impulse is then transferred to the bundle of His, which consists of a single right bundle branch and two left bundle branches (anterior and posterior). Finally, the Purkinje fibers receive the electrical transmission and are responsible for a coordinated contraction which involves the entire ventricles.
A bifascicular block essentially involves a failure of the signal to be transmitted through the right fascicle and one of the two left fascicles; alternatively, the impulse may fail to travel down through both of the left fascicles. Either way, when signal transmission is blocked in two of the three fascicles, the phenomenon is termed a bifascicular block. If a BFB occurs after a myocardial infarction, it is an indicator of severe myocardial damage.
Blockages can generally occur in a single fascicle as well. A failure for the signal to be transmitted through the anterior or posterior fascicle of the left bundle branch leads to a left anterior or posterior hemiblock respectively.
Bifascicular block cannot be prevented. Appropriate management, however, of the underlying cause may help to minimize its occurrence.
The electrical impulse of each heartbeat is generated in the sinoatrial node of the right atrium. It is then transmitted to the atrioventricular node and, finally, through the bundle of His (left and right), it reaches the Purkinje fibers throughout the myocardium, which are responsible for a contraction. The bundle of His is divided into the right bundle branch (one fascicle) and the left bundle branch (anterior and posterior bundle branch). A bifascicular block (BFB) involves a signal blockage in the right bundle branch and in either the anterior or posterior left bundle branch, according to the American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) . European guidelines frequently use the term left bundle branch block (LBBB) in order to define a bifascicular block, since it is believed to encompass a blockage in both its fascicles  . Another sub-type involves a bifascicular block with a prolonged PR interval, many times mistakenly referred to as a "trifascicular block". Although American guidelines generally advise against the use of the terms bifascicular and trifascicular block , they are still frequently used today by many physicians. In general, a bifascicular block is any conduction failure affecting any two of the three bundle branches of the His bundle.
In rare occasions, a bifascicular block or its counterpart which involves a prolonged PR interval as well, can progress to a complete cardiac block; the possibility of this happening is rather scarce, as outlines by a study that documented 1 patient out of the 550 monitored eventually developed a complete heart block  .
BFB frequently remains unsymptomatic and is detected incidentally. In some patients it might produce symptoms, such as dizziness, fainting, chest pain and arrhythmias. Heart rate is usually decreased.
Bifascicular block may remain untreated and monitoring is adequate for the patient follow-up. Lifestyle changes and medication used to control the underlying cause can be applied as supportive measures. Pacemakers are used only in cases of individuals who experience frequent fainting.
What is a bifascicular block (BFB)?
The heart functions like an electrical pump. Each beat starts as an electrical impulse in one of the top chambers of the heart, travels to the area located in the middle of the organ and is then transmitted to the ventricles, the cavities that contract, through 3 passages called fascicles. These are the right bundle branch and the two left bundle branches; all together, they form the His bundle. The His bundle is a vital electrical path which carries the impulse from the location where it is generated to the rest of the heart so that a beat can be produced and the blood can be pumped throughout the body. A bifascicular block involves a blockage of the signal in two of the three branches of the His bundle.
What causes bifascicular block?
People can be born with a bifascicular block, due to congenital abnormalities of the conduction passages in the heart. Most often, however, BFB occurs as a complication of another disease, such as hypertension, heart attack, congestive heart failure, heart surgery or as a side effect of some medications.
What are the symptoms of bifascicular block?
It is very common for a bifascicular block to produce no symptoms at all. However, since two of the three fascicles do not conduct the signal to some parts of the heart, so that they can contract, the heartbeats can be irregular. Dizziness, fainting, chest pain and shortness of breath may also be experienced. The heart rate can be slower than normal and a severe complication of BFB is sudden cardiac death: instant death that is a result of a heart condition. People with severe congestive heart failure are in greater risk of dying from sudden cardiac death.
How is bifascicular block diagnosed and treated?
Bifascicular block can be diagnosed via an electrocardiogram and an echocardiogram. Both are non-invasive procedures and can accurately diagnose the condition. In most of the cases it does not need to be treated. Patients may receive treatment for the BGB itself if it causes fainting. Medications and other procedures are used to treat the underlying causes that led to BFB.
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