Hello. You did not inform the poem to which this question refers, which makes it impossible for me to give you an exact answer. However, I will try to help you in the best possible way.
In a poem, the rhythm is responsible for creating the tone, that is, the feeling that the poem will promote to the reader. If the lines you are quoting above create a sense of suspense, it means that they have a fast rhythm, which is capable of stimulating the reader's anxiety and causing him to be apprehensive and with the sensation of suspense.