ECG 4: Bundle Branch Blocks

Question 1

Complete left bundle branch block

Answer 1

The following should be present:

QRS duration ≥120 ms in adults
broad notched or slurred R wave in leads I, aVL V5, and V6, and an occasinoal RS pattern in V5 and V6

Absent Q waves in leads I, V5, and V6, but in the lead aVL, a narrow Q wave may be present in the absence of myocardial pathology
R peak time > 60 ms in leads V5 and V6 but normal in V1-V3, where small initial R waves can be discerned in the precordial leads followed by deep S waves

ST and T waves usually opposite in direction to QRS (i.e., discordant to QRS)

Question 2

Incomplete LBBB

Answer 2

LBBB but QRS duration is between 110 and 119 ms in adults

Question 3

Complete RBBB

Answer 3

The ff should be present:

QRS duration ≥120 ms in adults
rsr’, rsR’, or rSR’ in leads V1 or V2
S wave of greater duration than R wave or >40 ms in I and V6 in adults
Normal R peak time in V5 and V6 but >50 ms in V1

first 3 should be present
4th should be present if there’s a pure dominant R wave with or without a notch in V1

Question 4

incomplete RBBB

Answer 4

RBBB but QRS duration is between 110 and 119 ms in adults

Question 5

Clinical significance of LBBB

Answer 5

Higher-than-normal risk of mortality and morbidity from infarction, heart failure, and arrhythmias and high-grade AV block

Question 6

clinical significance of RBBB

Answer 6

Often found as an incidental finding in the absence of any demonstrable heart disease

a small but significant increase in all-cause mortality and an increase in cardiac death

frequent detection in athletes