Accentual Trimeter
As with many of his Cantos, Pound decides not to worry too much about unstressed syllables in Canto XLV. The only syllables he counts out for each line are the stressed ones, which is a type of meter known as accentual verse. Pound would have known that this type of meter is closely associated with Old English poetry (we're talking maybe 1100 C.E., like Beowulf). Yeah, the guy knew a thing or two about the history of poetry.
It might be a tricky thing to get your head around, but Old English poetry uses a different kind of meter than the one you're probably used to, where you count the number of stressed and unstressed syllables. Old English poetry only cares about the number of stressed syllables per line, leaving the number of unstressed syllables totally random. This type of meter is called accentual verse, while the kind you're used to is called accentual-syllabic (because the number of syllables—both stressed and unstressed—matters).
Break it Down
Confused yet? Well here's a good example of this accentual trimeter, which means that each line has three stressed syllables and a totally random number of unstressed ones:
Usura rusteth the chisel
It rusteth the craft and the craftsman
It gnaweth the thread in the loom
None learneth to weave gold in her pattern (38-41)
As you can probably see, there's no real logic to the syllables that aren't stressed. The one consistent thing is that there are three stressed syllables per line, and that's all that matters for accentual trimeter.