Had echo done to rule out any adverse reason for rbbb. came back as 'normal study'. there was trivial mitral valve regurgitation. common? at risk?

Common, low risk: Isolated right bundle branch block is a very common conduction system issue that traditionally has not been associated with adverse outcome, in the absence of structural heart disease. Your physician is trying to verify that you have a structurally normal heart by getting an echo. Trivial mitral (and tricuspid) regurgitation are within normal limits and of no concern.