LBBB with First Degree AV Block
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Left bundle branch block (LBBB) with first degree AV Block is a type of trifascicular block, since the PR interval prolongation could indicate that the conduction in the right bundle is also affected. Rarely it could be due to a co-existent conduction delay in the AV node, rather than in the infra Hisean conduction system. LBBB with first degree AV block may be considered as a fore runner of complete AV block. First degree AV block in this ECG is manifest as the prolonged PR interval of 280 milliseconds. LBBB is manifest as broad notched QRS complexes in lead I and aVL. The poor progression of R waves and wide QS complexes in anterior leads are also consistent with LBBB. But V6 is not showing a wide notched predominantly positive QRS complex. This disparity between V6 and lead I are often seen when the QRS axis is leftward in LBBB. Inferior and anterior leads are showing a pseudoinfarction pattern, which is common with LBBB. QRS duration of more than 120 milliseconds with LBBB pattern in a person with refractory heart failure will be an indication for cardiac resynchronization therapy (CRT, biventricular pacing, heart failure device). It is often associated with mechanical dyssynchrony and wasted systolic effort of the left ventricle. CRT produces a narrowing of the QRS complexes as the right ventricle and posterolateral left ventricle are paced in synchrony, to produce a better left ventricular output.