Hi and sorry you have had these problems. We are not doctors on here but I am a microbiologist and can try to give you some advice. Did you ever have strep throat? Since your ASO was also negative I doubt you had rheumatic fever unless you remember having strep throat and not being treated for it or treated very late for it. Other ways you can get endocarditis or infection of the heart values are through a blood infection, or if you had a procedure such as a catheter implanted or other device where bacteria can enter the blood stream and then get into the heart. You would know by the high fever. They call this Infective endocarditis.
Infective endocarditis (which is really rare) can also come from having a genetic disorder in the heart value and you don't necessarily know it. Then you get an infection and it gets into the heart value and causes an infection there.
There are other ways to get damage to the heart valve disease , genetic (at birth), from some diet pills such as fenfluramine and phentermine “fen-phen" , radiation treatments and very high cholesterol (rare not usual),
and autoimmune disorders.
So, most likely it is a genetic disorder you didn't know you had and that perhaps the flu or virus made it worse. I would talk to your cardiologist to see how serious it is and if you need any corrective procedure.
if you didn't have strep or any of the procedures I mentioned I doubt you got it via a bacterial infection.
Also, the ASO test antibodies peak at about 3 to 5 weeks after the illness and then tapers off but may remain detectable for several months after the strep infection has resolved. So you could have had antibodies after but they also could have tapered off. You would know if you had strep throat. It is a high fever, usually pus in the throat and very painful throat with no other symptoms (no cough, no sneezing etc.).
Yes it doesn't sound like from your overall symptoms that you had strep throat and thus got rheumatic fever from that. It sounds like a virus you had. Generally yes one of your markers for inflammation would have been up but you would have had to take your blood test at the right time. These markers are very non specific. Yes it is good to see another cardiologist to verify that the structural abonrmalities are not that bad. They sound so far, on the mild side and causing low symptoms. I have a benign arrhythmia that causes symptoms something like yours too. They found mine by accident because I felt a fluttering feeling and a skipping heart beat sometimes and was getting biofeedback at the time and she could see something abnormal then. So my echo was normal and they found it with a 24 hour monitor. You could get that done as well to see if you have any problem with the heart beat. Also, you could ask if you need to follow up in a year or two or keep tract of whether there will be any progression with the degree of damage or problems with the heart over time.
Glad to help. Hope it gives you some direction. Yes doctors only give you 5 minutes these days. LOL.
Have a good day.