After my CABG my echo report reveals that I have developed a grade I diastolic dysfunction. How?

Diastolidysfunction. Diastolic dysfunction is diagnosed by finding of reversal of e-a ratio on echo. Not sure whether there are any gradations. But it may be seen in long standing hypertension as well as elderly, and in congestive heart failure. If you do not have any symptoms of heart failure, I do not think you need to worry about this finding.