Pediatric Left Bundle Branch Block Workup

Updated: May 25, 2018
  • Author: Bahram Kakavand, MD, FACC, FHRS, CEPS-PC; Chief Editor: Stuart Berger, MD  more...
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Approach Considerations

Laboratory studies

In left bundle branch block (LBBB), blood work is rarely necessary; however, assessing cardiac enzymes (troponins, creatine kinase [CK]) and the erythrocyte sedimentation rate (ESR) may be useful if myocarditis is suspected. When cardiomyopathy is considered, specific blood work to evaluate underlying causes may be helpful.

Imaging studies

Cardiac evaluation requires a thorough physical examination, repeat electrocardiography (ECG), and echocardiography.

Chest radiography may be helpful, depending on the clinical circumstances. Cardiac magnetic resonance imaging (cMRI) can be useful in demonstrating active myocardial inflammation, myocardial scars, or masses. A study by Jackson et al indicated that a U-shaped type II contraction pattern on cMRI in patients with strict LBBB who are guideline-appropriate for cardiac resynchronization therapy (CRT) appears to be predictive for reverse modeling and superresponse to CRT. [12] The investigators questioned whether strict LBBB criteria alone are enough to reliably predict a positive response to CRT.

A 24-hour ambulatory ECG recording can reveal other arrhythmias (eg, second-degree or third-degree heart block, atrial or ventricular extrasystoles, atrial or ventricular tachycardia). One study reported alternating right and left bundle branch block in a patient with atrial tachycardia. [1, 13]

Other investigational studies may be performed to evaluate for suspected associated abnormalities that may be the cause of LBBB.



The following diagnostic electrocardiographic (ECG) criteria for left bundle branch block (LBBB) have been established:

  • QRS duration of 120 milliseconds (ms) or more in adults, more than 100 ms in children aged 4-16 years, and more than 90 ms in children younger than 4 years

  • Broad notched or slurred R wave in leads I, aVL, V5, and V6 and an occasional RS pattern in V5 and V6 attributed to displaced transition of QRS complex

  • Absent q waves in leads I, V5, and V6: In the lead aVL, a narrow q wave may be present in the absence of myocardial pathology.

  • R peak time of more than 60 ms in leads V5 and V6 but normal peak time in leads V1, V2, and V3, when small initial r waves can be discerned in the above leads

  • ST and T waves usually opposite in direction to QRS

  • Possible normal positive T wave in leads with upright QRS (positive concordance)

  • Depressed ST segment and/or negative T wave in leads with negative QRS (negative concordance): This is abnormal and is discussed in part VI of this statement.

  • Changed mean QRS axis in the frontal plane to the right, to the left, or to a superior possible with left bundle branch block (in some cases in a rate-dependent manner)

ECG criteria necessary to confirm the diagnosis of left anterior hemiblock (LAH) in children include the following:

  • The duration of the QRS complex is normal for the patient's age or prolonged by less than 0.02 s.

  • The frontal-plane QRS axis is less than -30°.

  • A Q wave is present in lead I and a deep Q wave is present in lead aVL.

  • Major QRS forces in lead aVF are negative.

  • Slurred S waves are present in the left precordial leads.

  • A late R wave (delay, >0.045 s) is observed in lead aVR.

  • The terminal R wave in lead aVL is slurred.

Presence of LAH pattern in children usually reflects certain types of congenital heart defects, particularly endocardial cushion defects. Note the following:

  • In this group, the left anterior division of the left bundle is either congenitally absent or severely hypoplastic.

  • A superior frontal-plane QRS axis may occur in other congenital heart defects (double-outlet right ventricle, tricuspid atresia, single ventricle) with a normal anterior fascicle.

  • The literal diagnosis of LAH can be reserved for patients with previously normal ECG findings who develop left axis deviation after congenital heart surgery or other injury to the left anterior fascicle.

In left posterior hemiblock, ECG criteria necessary to confirm the diagnosis of left posterior hemiblock in children include the following:

  • The duration of the QRS axis is normal or only slightly prolonged for the patient's age.

  • A Q wave is present in leads II, III, and aVF.

  • The frontal plane QRS axis is +120° to +180°.

  • An S wave is present at the end of the QRS complex in leads I and aVF.

A study by Rivard et al indicated that in patients who develop new-onset LBBB after transcatheter aortic valve replacement (TAVR), the postoperative occurrence of an HV interval of 65 milliseconds or more is predictive of an atrioventricular (AV) block. [14] The study, which involved 75 pacemaker-free patients who underwent TAVR, included 30 who subsequently developed LBBB, eight of whom also developed AV block. The length of the HV interval was found to have a sensitivity and specificity of 83.3% and 81.6%, respectively, in predicting AV block in the patients with new-onset LBBB. [14]