I got a ct scan and a sonogram a year ago for my arteries to heart and carotid arteries; both of them came clear. could arteries have blockage one year later?

Mildly: There can't be mild blockage one year later but certainly not full blockage or even major blockage.

Anything possible: Although somewhat unusual to occur this quickly it is not clear what your genetic background, dietary intake and other comorbidities have been. If you have this with more recent testing it is also possible that one of the two scans was in error.

In the world of: Probabilities and medical statistics the answer is most probably no. If you review the pathophysiology of plague formation takes longer. Do not smoke, control your bp, exercise, control weight and stay away from saturated fats.

Possible: Small plaques can suddenly ulcerate and develop localized hemorrhage which can result in dramatic enlargement of the plaque and acute obstruction.