Left Bundle Branch Block ECG Findings, Lead ii, Characteristics, Criteria - Right vs Left Bundle Branch Block ECG

Content:

• What is Left bundle Branch Block?
• Left bundle Branch Block ECG 
• Left bundle Branch Block Findings
• Left bundle Branch Block Lead ii
• Left bundle Branch Block Characteristics
• Left bundle Branch Block Criteria 
• Right vs. Left Bundle Branch Block ECG

What is Left bundle Branch Block?

Left Bundle Branch Block (LBBB) is a condition where there's a delay or blockage in the electrical conduction pathway of the left bundle branch of the heart's conduction system. This disruption affects the heart's ability to coordinate the contraction of the left ventricle properly, potentially leading to inefficient heart pumping. LBBB may result from underlying heart conditions such as hypertension, coronary artery disease, cardiomyopathy, or it can be congenital.

Symptoms of LBBB can vary. Some individuals remain asymptomatic, while others may experience dizziness, fatigue, palpitations, or shortness of breath. Diagnosis is typically made through an electrocardiogram (ECG), where characteristic changes in the QRS complex are observed. Treatment depends on the underlying cause, and severe cases may require a pacemaker.

Left Bundle Branch Block ECG

An ECG is the primary diagnostic tool for identifying LBBB. In LBBB, the typical findings include a widened QRS complex (greater than 120 ms) and a 'notched' or slurred R wave in leads I, aVL, V5, and V6. The absence of Q waves in the left-sided leads and a prolonged R wave peak time are also indicative. The ST segment and T-wave changes in opposite directions to the QRS complex may be present.

LBBB can make it challenging to diagnose other cardiac conditions like myocardial infarction through an ECG, as the altered conduction masks typical patterns. Therefore, a thorough clinical assessment and possibly additional imaging are crucial when LBBB is identified.

Left Bundle Branch Block Findings

The hallmark findings of LBBB on an ECG include a widened QRS complex greater than 120 milliseconds, broad or notched R waves in leads I, V5, and V6, and the absence of Q waves in these leads. There is typically a delayed intrinsic deflection in the left precordial leads. The T waves may show discordant changes relative to the QRS complex.

These findings help differentiate LBBB from other conduction abnormalities and provide insight into potential underlying cardiac conditions. The presence of new LBBB in symptomatic patients often suggests an acute cardiac event, necessitating further evaluation.

Left Bundle Branch Block Lead ii

Lead II in an ECG primarily shows the inferior view of the heart. In LBBB, Lead II may demonstrate a widened, slurred QRS complex and potentially discordant T wave changes. However, Lead II alone is not sufficient for a complete diagnosis of LBBB; it should be assessed alongside other leads, especially leads I, V5, and V6.

Since LBBB alters the heart's normal conduction, it may obscure the typical ECG patterns used to diagnose acute myocardial infarction. As such, the interpretation of Lead II should be considered within the context of the entire ECG.

Left Bundle Branch Block Characteristics

LBBB is characterized by a QRS duration greater than 120 ms, a delayed and widened R wave in leads I, V5, and V6, and the absence of Q waves in these leads. Additionally, discordant ST-T changes are common, with ST segments and T waves oriented opposite to the direction of the QRS complexes.

The development of LBBB is associated with underlying cardiovascular conditions, and new-onset LBBB often warrants prompt evaluation for ischemic heart disease, especially if accompanied by symptoms like chest pain.

Left Bundle Branch Block Criteria

To diagnose LBBB, the following ECG criteria are used:

• QRS duration greater than 120 milliseconds.
• Broad, notched, or slurred R waves in leads I, V5, and V6.
• Absence of Q waves in leads I, V5, and V6.
• ST-T changes that are discordant with the QRS complex.

Additional criteria include a delayed R-wave peak time greater than 60 ms in leads V5 or V6. Meeting these criteria helps accurately diagnose LBBB and guide appropriate clinical management.

Right vs. Left Bundle Branch Block ECG

Right Bundle Branch Block (RBBB) and Left Bundle Branch Block (LBBB) both result in delayed ventricular depolarization but differ in their ECG presentations. RBBB typically shows an 'rSR’ pattern in lead V1, while LBBB shows a wide, slurred R wave in leads I, V5, and V6. In RBBB, the QRS complex is greater than 120 ms, but the terminal force is directed rightward, whereas in LBBB, it is leftward.

Clinically, LBBB is more often associated with significant underlying heart disease and may indicate a higher risk of adverse cardiac events. RBBB may occur in healthy individuals or those with conditions like pulmonary embolism or right ventricular hypertrophy. Identifying the differences between RBBB and LBBB on an ECG is essential for accurate diagnosis and management.