What is “Intraventricular Conduction Delay” or “Incomplete Right Bundle Branch Block”?

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Families and physicians often wonder what the terms“intraventricular conduction delay” (IVCD) or “incomplete right bundle branch block” (IRBBB) or “rsR’” on an electrocardiogram mean and what to do with the information.  


Electrocardiograms (abbreviated as “ECG” or “EKG”) are routinely done and best suited to the evaluation of heart rhythm, but we can sometimes infer potential heart disease or issues such as chamber enlargement or heart malformations from looking at the electrocardiogram, but the problem with this is that there are many false positives (that is, the EKG is abnormal but the patient’s heart is actually normal).


In general, conduction delay refers to a slight widening of the QRS complex, especially in the right precordial leads (leads V1, V2, and V3); it is sometimes also called incomplete right bundle branch block.  The most common cause of this is just being a normal variant, in other words, there is nothing wrong with the heart.  There are, however, some patients who have enlargement of the right heart as a cause for this, such as having an atrial septal defect resulting in enlargement of the right ventricle or perhaps partial anomalous pulmonary venous drainage of some of the pulmonary veins return to the right side instead of the left side.  Sometimes medications can cause conduction delay because of indirect effects on the heart and generally that is considered safe.  Finally, there are some individuals where conduction delay may represent conduction system disease, but this is very uncommon.  


The difficulty for cardiologists reading an electrocardiogram with conduction delay without seeing the patient is that it is tempting to label it as normal since the vast majority of the patients with this, in fact, have a normal heart, but since there is a small proportion who do have some abnormality, a decision on whether or not the person should be evaluated further depends on the reasons for the electrocardiogram.  It is a decision which can only be made by the person who has ordered the electrocardiogram; the cardiologist does not have sufficient knowledge of the patient to make a recommendation. If the patient has no murmur and is completely asymptomatic from a cardiac point of view, that individual does not need further assessment.  On the other hand, if there is a murmur or problem with exercise tolerance or if there are other cardiovascular symptoms, then this situation would be best addressed by a pediatric cardiology consultation.

Marc D. Le Gras, B.Sc., M.D., C.M.

Pediatric Cardiology

Pediatric Electrophysiology and Pacing

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