What is the relationship between aberrancy and Left Bundle Branch Block (LBBB) on an Electrocardiogram (ECG)?

From the Guidelines

Aberrancy and Left Bundle Branch Block (LBBB) on an Electrocardiogram (ECG) are related as they both represent abnormal ventricular conduction patterns, but they occur in different contexts and have distinct clinical implications. Aberrancy refers to temporary abnormal ventricular conduction typically occurring with premature beats or rapid heart rates, while LBBB is a fixed conduction defect in the left bundle branch. On ECG, both conditions show wide QRS complexes with similar morphology - typically a dominant R wave in lead V6, slurred S waves in V1, and a QRS duration ≥120 ms. The key distinction is that aberrancy is rate-dependent and transient, often following a premature atrial contraction with a short coupling interval (Ashman's phenomenon), whereas LBBB is consistently present regardless of heart rate.

According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1, the presence of bundle branch block on ECG is a predictor for abnormal conduction properties identified at EPS. Additionally, the guideline highlights that LBBB can be associated with increased risk of death and cardiac events, particularly when it is exercise-induced 1.

Some key points to consider when evaluating wide complex rhythms include:

• Aberrancy represents functional delay in an otherwise intact conduction system during stress
• LBBB indicates structural damage to the left bundle branch that permanently alters ventricular activation sequence
• Distinguishing between these patterns helps determine whether the abnormal conduction is a temporary phenomenon or represents underlying cardiac pathology
• The presence of LBBB can make it more difficult to interpret ischemic electrocardiographic changes, and an imaging component may be necessary 1

In clinical practice, it is essential to distinguish between aberrancy and LBBB on ECG, as this distinction can significantly impact patient management and outcomes. By understanding the differences between these two conditions, clinicians can better evaluate and manage patients with wide complex rhythms, ultimately reducing morbidity, mortality, and improving quality of life.

From the Research

Relationship between Aberrancy and Left Bundle Branch Block (LBBB) on an Electrocardiogram (ECG)

• The relationship between aberrancy and LBBB on an ECG is complex, with studies suggesting that LBBB can lead to aberrant ventricular conduction, or wide QRS complex tachycardia (Ashman beats) during episodes of atrial fibrillation 2.
• Aberrant cardiac conduction due to LBBB can be inhibited by pharmacologic cardiac resynchronization therapy, which can effectively slow heart rate, reduce symptoms of heart failure, and improve left ventricular ejection fraction (LVEF) 2.
• The presence of LBBB on an ECG can make it difficult to diagnose acute myocardial infarction (AMI), as traditional ECG indicators of ischemia, such as ST-segment elevation, are common in LBBB and may not indicate acute ischemia 3, 4.
• However, certain ECG criteria, such as the Sgarbosa criteria, can be used to diagnose AMI in patients with LBBB, and elevated biochemical markers of myocardial necrosis can confirm the diagnosis 4.
• The presence of LBBB on an ECG can also impact the triage and outcome of patients with suspected acute coronary syndrome, with patients with LBBB being older and more likely to have a history of cardiac or related diseases 5.
• Studies have also demonstrated a relationship between electrical activation by ECG and mechanical contraction by echocardiography in LBBB, which can help identify candidates for cardiac resynchronization therapy (CRT) 6.

ECG Criteria for LBBB

• New strict criteria for LBBB based on ECG include QRS duration ≥140 ms (men) or 130 ms (women), QS or rS in leads V1 and V2, and mid-QRS notching or slurring in ≥2 of leads V1, V2, V5, V6, I, and aVL 6.
• These criteria can help identify patients with LBBB who may benefit from CRT, with a sensitivity of 90% and specificity of 65% for predicting response to CRT 6.

Clinical Implications

• The presence of LBBB on an ECG should be carefully evaluated in patients with suspected acute coronary syndrome, as it can impact diagnosis and treatment 3, 4, 5.
• Patients with LBBB may benefit from pharmacologic cardiac resynchronization therapy to inhibit aberrant cardiac conduction and improve LVEF 2.
• The relationship between electrical activation by ECG and mechanical contraction by echocardiography in LBBB can help identify candidates for CRT 6.