Internal Medicine

0521779407-C01 CUNY1086/Karliner 0 521 77940 7 June 4, 2007 20:53

312 Chronic Bundle Branch Block

Chronic Bundle Branch Block and Hemi-blocks..............

EDMUND C. KEUNG, MD

history & physical

History

■Associated with high incidence of cardiac disease and sudden death

(from complete heart block and ventricular tachycardia or fibrilla-

tion), especially LBBB.

■RBBB: widely split second heart sound (delayed P2)

■LBBB: reversed splitting of second heart sound (P2 before A2)

Signs & Symptoms

■Rarely symptomatic but may develop syncope or near syncope

with progression to complete heart block or with ventricular tach-

yarrhythmias.

tests

■Basic Tests

➣12-lead ECG:

➣RBBB:

QRS≥120 ms. rsR’ (90%) or notched R (10%) in V1.

Deep and broad S wave in leads I and V6 (may be masked by

LAFB

Incomplete RBBB: waveforms similar to RBBB but QRS

<120 ms

➣LBBB:

QRS≥120 ms.

Absence of q in I and V6.

Monophasic and usually notched R wave in lead I and a dom-

inant S wave (rS, 67%; QS, 33%) in V1–2.

Incomplete LBBB: waveforms similar to LBBB but QRS

<120 ms. Often seen in LVH.

➣Intraventricular conduction delay (IVCD):

QRS≥120 ms but characteristic waveforms for LBBB or RBBB

not present (often seen in severe dilated cardiomyopathy).

➣Left anterior fascicular block (LAFB):

left QRS axis deviation (− 30 ◦to− 90 ◦) with rS or QS in leads

II, III and F, qR in lead aVL with onset of Q to peak of R

≥45 ms