ECG Case #13 - Question #2 Answer

A bifascicular block occurs when there is a combination of a right bundle branch block and a left anterior fascicular block. If there is also a 1st degree AV block, then a trifascicular block is present as in case #13 (the AV node is sometimes considered the 3rd fascicle).

A trifascicular block is a precursor to complete heart block. While a trifascicular block itself does not require any treatment, high doses of AV blocking agents likely should be avoided. Some series report a 50% lifetime need for a permanent pacemaker in the setting of a trifascicular block.