To the Editor.—In the April Archives Alpert and Flaker1 gave a nice review of the literature on chronic fascicular block and the thinking on this descriptive entity. They noted varying rates of progression and I wonder if they would further discuss the possibility that this may be due to "fascicular block" being a far-from-homogeneous entity (not necessarily only in its cause but also, and particularly, in the actual lesions causing what appears on the ECG).
What we actually see on the ECG is axis deviation. For this, fascicular block is only one interpretation. For one thing, if a lesion in the anterolateral left ventricle slows conduction locally due to myocardial damage, the final vectors would be generated in that area and would necessarily produce a left-axis deviation without conduction system involvement. The old, so-called "peri-infarction" and "arborization" blocks exemplify this. On the other hand, the conduction system's "wires"
Spodick DH. Chronic Fascicular Block. Arch Intern Med. 1984;144(10):2095–2099. doi:10.1001/archinte.1984.04400010222045