Fascicles?

BelgianRN · Jun 10, 2012

The fascicles are another division for your conduction system. The right bundle branch consists of just that a right bundle or right fascicle. But the left bundle branch can be further divided into two fascicles (anterior and posterior). A blockage of either the anterior or posterior can be identified on a 12-lead ECG by using the various indicators and is called a fascicular block or hemiblock. If both anterior and posterior are blocked at the same time the net result is a LBBB.

Alarm signs on an ECG are combinations of these blocks (bifascicular and trifascicular blocks). Since with every block the conduction to the ventricles is dependant on the remaining functioning fascicles. E.g. with posterior left fascicle and right bundle blocked all signals to the ventricles must go through the anterior fascicle of the left bundle. If this gets blocked as well (e.g. in the process of ongoing ischemia) you are dealing with a complete block and could have disastrous results.

Be especially vigilant with a (incomplete) trifascicular block which is the appearance of a first degree AV-block combined with RBBB and a fascicular block (either anterior or posterior or switching between the two). It warrants close monitoring and/or pacemaker since the entire conduction of the ventricular system is dependant on the remaining bundle. So diagnostic studies must be undertaken to determine the likelihood of this block evolving into complete heart block (also called complete trifascicular block, but is indistinguishable from third degree AVB).

Check ECGpedia.org for additional information on 12 lead ECGs.

Esme12, ASN, BSN, RN · Jun 15, 2012

Belgian....Love the ECGpedia. I can't believe I missed that one.