Thank you for asking your query.
It's bit tricky to identify what exactly is causing this particular 'breathing problem', but I can give you some insights which might be valuable. PVCs are usually asymptomatic and if at all there are symptoms its the feeling of skipped beat or syncope. This shortness of breath rarely arises primarily due to PVC.
But, another mechanism can operate , in which you get PVC -> You get stresses/anxious -> Catecholamine release (a kind of chemical in the nerve endings) -> Asthma attack.
So this means your anxiety and asthma needs to be attended. Since you have been evaluated with a full battery of imaging and lab tests you need not be much worried about the PVCs. This 'sudden shortness of breath' needs to addresses as soon as possible and I recommend you to work closely with your Doctor. Its may need some trial and error methods and can take some time. But I am sure this can be fully taken care of.
Some suggestions would be :
1. Adopt strategies to reduce the anxiety levels, which ever works best for you. Meditation , music, recreational activities all can help.
2.Be aware that the PVCs are usually harmless and since you have been fully evaluated there is no need for worry.
2.You can discuss with your Physician regarding the option to have an alternative to metoprolol (Its a beta blocker which rarely can induce asthma symptoms)
3.Trying Asthma medications, like inhaled steroids at the time of attack.
4. Radiofrequency ablation if the above measures fail.
I am sure with some effort and patience this problem can be fully solved. Wishing you the very best.
Hope this helps.