Diagnosing asymptomatic partial atrioventricular canal?

Hello there! I have heard that partial atrioventricular canal is often asymptomatic. Still, I think that it is important that partial atrioventricular canal is diagnosed because of its long term consequences. So can anyone enlighten me? Just how is asymptomatic partial atrioventricular canal diagnosed? How do they know to screen for partial atrioventricular canal? Thanks for your help.