Checking quite a few texts I found that most describe IRBBB in sparse detail. Rather RBBB is described, and a definition of IRBBB is given as: “its RBBB with a QRS from greater than 100ms and less than 120ms. So then I guess true definition of RBBB is required. It seems there are four criteria to fill to truly diagnose RBBB, they are quoted in the AHA/ACCF/HRS recommendations for standardization and interpretation of the ECG part III (1) as:
“Complete RBBB
1. QRS duration greater than or equal to 120ms in adults, greater than 100ms in children ages 4 to 16 years, and greater than 90ms in children less than 4 years of age.
2. rsr’, rsR’ or rSR’ in leads V1 or V2, the R’ or r’ deflection is usually wider than the initial R wave. In a minority of patients, a wide and often notched R wave pattern may be seen in V1 and or V2.
3. S wave of greater duration than R wave or greater than 40ms in leads I and V6 in adults.
4. Normal R peak time in leads V5 and V6 but greater than 50ms in lead V1.
Of the above criteria, the first 3 should be present to make the diagnosis. When a pure dominant R wave with or without a notch is present in V1, criterion 4 should be satisfied.”
The
same AHA/ACCF/HRS recommendations describe all these features as being required
for IRBBB apart from the QRS complex width, which should between 110-120ms in
adults 90-100ms in children age 16-4 and 86-90ms in children less than 4.
So now
that IRBBB is defined, how does this criteria fit the ECG up for review.
Looking
at criteria 1. On eyeball the QRS complex appears to be 110ms but on closer
inspection the QRS is only 90ms wide.
This fails the first criteria for IRBBB
and indeed this rsR’ complex in V1 would now be considered a normal variant or
would it?
WHO
taskforce state (2) in relation to QRS complex width: “There is no minimal QRS
duration for incomplete right bundle branch block.”
Marriott (3) defines IRBBB QRS complex width as
between 90-100ms, whereas Chan et al (4) state 80 – 110ms
The
second criteria is met easily with an rsR’ in V1 with R’ wider than the initial
r wave. Figure
Criteria
3 is not met as there is no distinct s wave in either lead I or V6. Figure
Criteria
4 is met as the onset of the QRS to the peak of the R’ wave is about 60ms.
Figure
After
all this discussion, what conclusions can be made? I guess strictly speaking
this ECG can’t be called an IRBBB. I make this conclusion due to the lack of an
s wave in V6 and lead I. The width criteria I think is less clear-cut as many
respected authors differ in their definition. From here on in my own
interpretation will reflect the WHO (2) definition on IRBBB where the QRS width
in less than 120ms.
Areas to look at in future are:
What are the clinical ramifications of IRBBB and RBBB?
Does IRBBB have any prognostic value?
Analysis of bundle branch block ECGs to practice all the diagnostic criteria.
References:
1: Surawicz, B. Childers, R. Deal, B. J. Gettes, S. (2009) AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, Part III, Intraventtricular Conduction DIsturbances. A Scientific Statement from the American Heart Association Electrocardiography and Arrhythmias, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Journal of the American College of Cardiology Vol. 53, No. 11.
2: Willems, J.L. et al (1985) Criteria for Intraventricular Conduction Disturbancesand Pre-excitation WHO / International Society and Federation for Cardiology Task Force. JACC, Vol. 5, No. 6.
3: Marriott, H.J.L. Practical Electrocardiography 8th ed, Williams & Wilkins, Baltimore.
4: Chan, T.C. et al (2005) ECG in Emergency Medicine in Acute Care, Elservier Mosby, Philadelphia.
5: Surawicz, B. et al (2008) Chou's Electrocardiography in Clinical Practice 6th Ed, Saunders Elsevier, Philadelphia.
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