From the Guidelines
Incomplete right bundle branch block (IRBBB) typically does not require specific workup in asymptomatic patients with no underlying heart disease, as stated in the 2019 ACC/AHA/HRS guideline 1.
Definition and Diagnosis
IRBBB is defined by a QRS duration between 110 and 120 ms in adults, with the same QRS morphology criteria as complete RBBB, including an rsr', rsR, rSR, or rarely a qR pattern in leads V1 or V2 2. The diagnosis of IRBBB should be based on these specific electrocardiographic criteria, which distinguish it from other forms of intraventricular conduction delay.
Clinical Approach
If IRBBB is found incidentally on an ECG, no further evaluation is necessary unless there are concerning symptoms or other cardiac abnormalities. For patients with symptoms like syncope, palpitations, or shortness of breath, a more comprehensive evaluation is recommended, including:
- A complete history and physical examination
- Additional ECG monitoring
- An echocardiogram to assess cardiac structure and function In some cases, exercise stress testing may be appropriate to evaluate for ischemia or stress-induced conduction abnormalities 1.
Prognosis and Management
IRBBB represents a partial delay in electrical conduction through the right bundle branch of the heart's conduction system, causing the QRS complex to be slightly prolonged but not meeting full criteria for complete RBBB. This conduction delay is often a benign finding, especially in young, healthy individuals, and does not typically progress to complete RBBB or cause clinical consequences. However, in patients with underlying structural heart disease or those with concerning symptoms, IRBBB may warrant closer monitoring as part of overall cardiac care, as outlined in the 2009 AHA/ACCF/HRS recommendations 2.
Key Considerations
- The presence of IRBBB in asymptomatic patients without heart disease does not necessitate further workup.
- Symptomatic patients or those with underlying heart disease require a comprehensive evaluation.
- The management of IRBBB should focus on the underlying cause and associated symptoms rather than the conduction abnormality itself.
From the Research
Incomplete Right Bundle Branch Block Workup
- Incomplete right bundle branch block (IRBBB) is a common electrocardiogram (ECG) finding that can be benign or pathological 3
- IRBBB is defined by an rSr' pattern with a QRS width below 100 ms, and can be caused by various factors such as posterior apex deviation, subpulmonic area delay, or late crista supraventricularis activation 3
- The diagnosis of IRBBB can be challenging, and it is necessary to differentiate it from other pathological patterns such as type-2 Brugada ECG pattern, right ventricular enlargement, and arrhythmogenic right ventricular cardiomyopathy 3
Clinical Significance
- IRBBB is not always a benign condition, and clinicians need to be familiar with this ECG finding to identify potential underlying heart disease 3
- The presence of IRBBB has been associated with an increased risk of mortality in the general population and patients with heart disease 4
- However, the prognostic significance of IRBBB is inconsistent across studies, and its clinical utility in evaluating patients with suspected acute myocardial infarction is uncertain 5, 4
Diagnostic Criteria
- The diagnosis of IRBBB can be made based on ECG criteria, including an rSr' pattern with a QRS duration of less than 0.12 s in the right precordial leads 6
- Other ECG features that may help to distinguish IRBBB from normal variants 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 > or = 0.10 s 6