From the Guidelines
Incomplete bundle branch block is a cardiac conduction abnormality that typically doesn't require specific treatment if the patient is asymptomatic, but regular cardiac follow-up is recommended to monitor for progression to a complete bundle branch block. This condition is often discovered incidentally on an electrocardiogram (ECG) and is characterized by a partial impairment of electrical impulse transmission through either the right or left bundle branch of the heart's conduction system 1. Unlike complete bundle branch blocks, the delay in conduction is not severe enough to meet the full diagnostic criteria. The significance of this finding varies depending on associated cardiac conditions - it may be benign in healthy individuals but could indicate underlying heart disease in others.
According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay, incomplete right bundle branch block (RBBB) is defined as a QRS duration between 110 and 119 ms in adults, with the same QRS morphology criteria as complete RBBB 1. Incomplete left bundle branch block (LBBB) is defined as a QRS duration between 110 and 119 ms in adults, with the presence of left ventricular hypertrophy pattern, R peak time >60 ms in leads V4, V5, and V6, and absence of Q wave in leads I, V5, and V6 1.
For patients with underlying heart disease, management focuses on treating the primary condition rather than the incomplete bundle branch block itself. Physiologically, this partial delay occurs because some fibers of the bundle branch are still functioning normally while others are damaged or conducting more slowly, allowing the electrical impulse to still reach the ventricle but with slight delay. If you have been diagnosed with an incomplete bundle branch block, maintaining heart health through regular exercise, healthy diet, and management of cardiovascular risk factors is advisable. The European Society of Cardiology guidelines also suggest that patients with bundle branch block and syncope should undergo a systematic diagnostic approach, including carotid sinus massage, electrophysiological study, and implantable loop recorder, to determine the cause of syncope 1.
Some key points to consider in the management of incomplete bundle branch block include:
- Regular cardiac follow-up to monitor for progression to a complete bundle branch block
- Treatment of underlying heart disease, if present
- Maintenance of heart health through regular exercise, healthy diet, and management of cardiovascular risk factors
- Consideration of further diagnostic testing, such as carotid sinus massage, electrophysiological study, and implantable loop recorder, in patients with syncope.
From the Research
Incomplete Bundle Branch Block
- Incomplete right bundle branch block (IRBBB) is characterized by an rSr' pattern with QRS duration of less than 0.12 s in the right precordial leads 2
- IRBBB may progress to complete right bundle branch block, and certain ECG features can help distinguish between IRBBB and a normal electrophysiological variant 2
- These features include diminution of the S wave depth, inversion of the ratio of the S wave depth to SV1 > SV2, slurring of the downstroke or upstroke of the S wave, and prolongation of the QRS duration to ≥ 0.10 s 2
Prognostic Implications
- Bundle branch block is associated with a higher risk of cardiovascular outcomes, including heart failure and cardiovascular death 3, 4
- Left bundle branch block (LBBB) is a strong predictor of mortality, independent of degree of heart failure, extent of coronary disease, and other variables 3
- Right bundle branch block (RBBB) is also associated with an increased risk of cardiovascular outcomes, including pacemaker implantation and heart failure 3, 4
Epidemiology
- IRBBB is found in approximately 6.8% of men aged 40-56 years without initial apparent heart disease 5
- The incidence rate of IRBBB is approximately 13.6% over 11 years of follow-up 5
- IRBBB is not uncommon in a healthy school-age population and is observed to have high inter-reader variability 6
Clinical Implications
- Opportunistic findings of bundle branch block subtypes in primary care patients without major cardiovascular disease should be considered warnings of future heart failure and pacemaker implantation 4
- The relationship between electrocardiographic bundle branch block subtypes and the risk of cardiovascular outcomes is an important consideration in primary care 4