IVC filter and Pulmonary embolism- make it make sense!

Hi all,

Would really appreciate someone explaining this one to me. For patients that have an established pulmonary embolism that have a contraindication to anticoagulation how do IVC filters actually help?

My understanding is that the embolism is now sitting in the lungs and so has passed the IVC filter. Or am I just being a simpleton?

Thanks in advance!