Questions about how MVCC dealing with multiple rows

Question

I am currently studying the transaction processing in database systems. I understand that MVCC prevents blocking readers by allowing reader to read an old version of the row. I wonder how MVCC deals with a transaction updating multiple rows. For example, a read-write transaction Txn1 updates rowA and rowB by creating two new versions, but another concurrent read-only transaction may read the old version of rowA and the new version of rowB, which violates the atomicity guarantess. I wonder if this case would occur and how to deal with it?