There are some ways to assist in identifying true CHF in the prehospital space. A combination and understanding of these tips will aid your practice and benefit your patients.
1. Pre hospital ultrasound and B-Lines. While ultrasound in the EMS space is nascent, its definitely coming. This website is a great resource for learning about Ultrasound.
2. S3 Heart sound. Sounds intimidating doesn't it? Heart sounds have always been something to avoid in EMS. But the S3 sound is the easiest to learn and will help you in not only Dx your patient, but help you better understand what's going on. It will also give you some serious credibility in the ED when you say "Patient has audible S3 on auscultation that supports the Hx of CHF"
This site is a nice place to start:
Then jump to these two sites to read up a bit more: