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Introduction   

Bundle branch blocks (BBB) are disruptions in the normal electrical conduction system of the heart. The heart’s electrical conduction system coordinates the contraction of the heart muscle, ensuring that it beats rhythmically and effectively pumps blood throughout the body. 

The sinoatrial node acts as the heart’s pacemaker in a normal, healthy heart. Electrical impulses start at the top of the heart in the right atria near its junction with the superior vena cava. These electrical impulses then work their way down to the bottom of the heart to the left and right ventricles. For the ventricles to receive the signals after passing through the AV node, the electrical impulse must move through a bundle of fibers called Bundle of His, much like an electrical wire inside the heart that then splits into a right and left side. These are the right and left bundle branches.  

Bundle branch blocks occur when there are disruptions in the heart’s electrical conduction system, affecting the transmission of signals. The BBB causes the electrical impulse to take a different pathway through the ventricle. When there is a blocked electrical pathway in the heart, the right and left sides don’t beat in unison and one ventricle will contract a split second slower. This uneven timing causes an arrhythmia [1].  

Abnormalities in the heart’s regular conduction system resulting in an arrhythmia can cause the heart to beat too fast, too slow, or irregularly. Many arrhythmias are undisruptive; however, some can be critical or potentially life-threatening. These changes in conduction affect the heart’s ability to pump blood appropriately, causing decreased oxygenation to the body. This lack of oxygen can be responsible for various symptoms that will be discussed in the following sections.  

Types of Bundle Branch Blocks and their Etiology 

Right BBB (RBBB) 

RBBBs are often benign and diagnosed during routine EKGs. An RBBB causes the left ventricle to contract before the right ventricle. Many people living with RBBB are asymptomatic and have no complications from the condition. If a patient has an asymptomatic RBBB with no other cardiac conditions or complications, patients rarely need ongoing cardiac evaluation. Some RBBBs can be attributed to damage to the myocardium. 

RBBBs that occur immediately after a myocardial infarction can be an indicator of increased mortality [2]. Furthermore, patients hospitalized for acute heart failure in conjunction with RBBB have poorer prognoses. 

Etiology of RBBB 

RBBB can be caused by disease processes that affect the myocardium through which the right bundle travels. RBBB can result from myocarditis, myocardial infarction, or right intraventricular pressure from pulmonary embolism that damages the right bundle branch and blocks electrical impulses [2]. RBBB is also found to be a degenerative disease of the right ventricle that slowly progresses with age [5]. 

Left BBB (LBBB) 

If a patient presents with LBBB, the bundle branch that carries electrical impulses to the left ventricle is either partially or fully blocked. This causes the right ventricle to contract before the left, resulting in cardiac pump inefficiency [3]. LBBB is often seen in tandem with heart failure. A patient with LBBB may be asymptomatic or experience syncope, chest pain, dizziness, or dyspnea during strenuous activity [3]. 

In rare cases, LBBB can be accompanied by chest pain. Because it’s rare, it often goes undiagnosed or is thought to be angina. “The mechanism of chest pain is not well understood. Still, it is postulated that sudden loss of the ventricular contraction synchrony, which happens in LBBB, will induce a different perception of heartbeat in the brain with possible translation to chest pain. [11]” 

Painful LBBB syndrome causes intermittent episodes of debilitating chest pain. To properly diagnose LBBB syndrome, coronary artery disease which restricts blood flow, and cardiac ischemia must be ruled out. One critical diagnostic marker for Painful LBBB syndrome includes rate-related (over 100 beats per minute) LBBB changes seen on the EKG.  

Etiology of LBBB 

Dilated cardiomyopathy (enlarged, weakened or stiffened heart muscle) or left ventricle enlargement causes strain and separation of the Purkinje fibers resulting in an LBBB. Many different, common cardiac diseases lead to LBBB including: 

• Heart Failure 

• Myocardial Infarction 

• Hypertension 

• Coronary Artery Disease 

• Congenital Heart Defects 

There are times when LBBB has no underlying cause and can be found in people with no other cardiac history.  

Epidemiology 

RBBB is more widespread than LBBB. It affects 0.8% of 50-year-old Americans, and this number increases to 11.3% for people 80 years old. Approximately 0.06% to 0.1% of the general U.S. population has an LBBB. Among heart failure patients, roughly 33% have LBBB [4].  

Identification of RBBB and LBBB 

Electrocardiograms are the most common tool used for identifying bundle branch blocks. According to the American College of Cardiology and American Heart Association, diagnostic criteria for a Right Bundle Branch Block include the following: 

1. QRS duration is greater than or equal to 120 milliseconds 
2. In lead V1 and V2, there is an RSR` in leads V1 and V2 
3. In Leads 1 and V6, the S wave is of greater duration than the R wave, or the S wave is greater than 40 milliseconds 
4. In Leads V5 and V6, there is a normal R wave peak time 
5. In Lead V1, the R wave peak time is greater than 50 milliseconds 

According to the American College of Cardiology and American Heart Association, diagnostic criteria for a Left Bundle Branch Block include the following: 

1. Rhythm must be of super-ventricular origin (EG: ventricular activation coming from atrial or AV nodal activation) 
2. QRS Duration greater than 120 ms 
3. Lead V1 should have either a QS or a small r wave with a large S wave 
4. Lead V6 should have a notched R wave and no Q wave  

Echocardiograms are another diagnostic tool used to identify BBBs. Echos are noninvasive and use ultrasound to visualize cardiac anatomy. It allows practitioners to view the ventricles and left and right atrium which is critical in diagnosing BBBs. Although they aren’t the primary method used to identify bundle branch blocks, echocardiograms are extremely helpful in assessing cardiac function and providing supporting evidence that a bundle branch block may be present. They provide visualization for certain conditions such as cardiac dilation or ventricular hypertrophy that exist in conjunction with bundle branch blocks. [9].  

Treatments for BBB 

If a patient is experiencing symptoms from a BBB, treatment options must be examined. When a patient experiences symptoms such as presyncope, syncope, or dizziness, their physician may recommend cardiac resynchronization therapy or an LBBB pacemaker (LBBP). Treatments for BBB vary based on several factors and are unique to the patient. Patients with asymptomatic BBB may not need intervention. However, those with underlying cardiac conditions may need treatment for comorbidities such as hypertension and heart failure.  

If a patient has LBBB in conjunction with decreased cardiac output, cardiac resynchronization therapy (CRT) is indicated. CRT has been a successful approach in reducing the number of hospitalizations and increasing the quality of life for patients with LBBB and heart failure [8]. Unlike other pacemakers, CRT or a biventricular pacemaker has 3 wires instead of 2. Two leads are connected to the ventricles, and the third to the right atrium. In the presence of dysrhythmia, an electrical impulse is sent, triggering the right and left sides of the heart to work collectively. 

CRT does have limitations, including procedure failure in nearly 40% of patients, failure to capture, and inadvertent phrenic nerve stimulation (affecting respiration). Due to the shortcomings of CRT, left bundle branch pacing (LBBP) is now being recognized as a promising approach to the management of LBBB, where poor cardiac conduction and heart failure are a concern. Left bundle branch pacing (LBBP) can reduce QRS intervals and improve left ventricular ejection fraction [6].  

“As an innovative technique, left bundle branch pacing (LBBP) has emerged to be an alternative method by pacing the left bundle branch bypassing the block region, resulting in physiological pacing and achieving electrical synchrony of the left ventricle [7].” The pacemaker will supply the heart with the necessary electrical impulses to pace the heart regularly, hopefully alleviating discomfort and oxygenation issues caused by the LBBB. 

Nursing Consideration of the Patient with Bundle Branch Blocks 

Management of bundle branch blocks involves identifying and treating underlying causes, such as heart disease or electrolyte imbalances. Patients may require close monitoring for any signs of worsening heart function or arrhythmias. Nurses should educate patients about their condition, medications, and the importance of regular follow-up with their healthcare provider.  

Regular monitoring of the patient’s heart rhythm and overall cardiac function is also crucial. 

Nurses who are treating patients with LBBB and heart failure need to weigh patients daily and monitor any EKG changes.  

Nurses caring for patients who have received a pacemaker to address a bundle branch block should educate their patients accordingly. Provide patients with a pacemaker with a card that includes their specific unit’s type, serial number, and battery life. Continually assess the patient’s cardiovascular status, including rate and rhythm, hemodynamic stability, and EKG changes. It’s important to monitor respiratory effort, oxygen saturation, and breathing patterns [12].  

Nurses should provide clear instructions to their patients on what emergent symptoms might arise that warrant immediate care. If patients experience shortness of breath, chest pain, pre-syncope, syncope, or dizziness, immediate medical care is advised.  

Conclusion

In conclusion, bundle branch blocks can be significant electrocardiographic findings that require careful evaluation and management. This course has provided a comprehensive overview of bundle branch blocks, including their pathophysiology, clinical manifestations, diagnostic criteria, management strategies, and prognostic considerations. By enhancing your understanding of bundle branch blocks, you can contribute to improved patient outcomes and quality of care in cardiovascular medicine. 

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