Optimize This Query?

I have a nightly job that aggregates data into a summary table.  Each night, an additional item may or may not be added, so the table is cleared and repopulated.  I've got this working fine.  Now, I am being asked to track when an item first appears in the summary table.  Here is the code I am using to do this.  I realize it is very poor performance, but I don't know how to make it better.

MyTable Columns:
  id INT PK
  ,v1 VARCHAR(4)
  ,v2 VARCHAR(10
  ,v3 DECIMAL
  ,item1 BIT
  ,item2 BIT
  ,item3 BIT

MyTable2 Columns:
  v1 VARCHAR(4)
  ,v2 VARCHAR(10
  ,v3 DECIMAL
  ,item INT
  ,FirstKnownDate DATETIME

All columns are NOT NULL.1 DECLARE @iNextRowID INT
2 ,@iCurrentRowID INT
3 ,@iLoopControl INT
4 ,@v1 VARCHAR(4)
5 ,@v2 VARCHAR(10)
6 ,@v3 DECIMAL
7
8 /* This is a loop that executes for a dynamic number of items, eg item1=1, then item2=1, etc */
9 SET @iLoopControl=1
10 SELECT @iNextRowID=MIN(id) FROM MyTable WHERE item1=1
11
12 IF ISNULL(@iNextRowID,0) <> 0 BEGIN
13 SELECT @iCurrentRowID = id
14 ,@v1 = v1
15 ,@v2 = v2
16 ,@v3 = v3
17 FROM MyTable
18 WHERE id=@iNextRowID
19
20 WHILE @iLoopControl = 1 BEGIN
21 IF NOT EXISTS(SELECT * FROM MyTable2 WHERE v1=@v2 AND v2=@v2 AND v3=@v3 AND item=1) BEGIN
22 INSERT INTO MyTable2
23 /* COLUMN */ (v1,v2,v3,item,firstknowndate)
24 SELECT @v1, @v2, @v3, 1, GETDATE()
25 END
26
27 SELECT @iNextRowID = NULL
28 SELECT @iNextRowID = MIN(id) FROM MyTable WHERE id>@iCurrentRowID AND item1=1
29
30 IF ISNULL(@iNextRowID,0) = 0 BEGIN
31 BREAK
32 END
33
34 SELECT @iCurrentRowID = id
35 ,@v1 = v1
36 ,@v2 = v2
37 ,@v3 = v3
38 FROM MyTable
39 WHERE id=@iNextRowID
40 END
41 END
42 /* This is the end of the items loop */
This query takes 5 minutes to do straight inserts without the test for exists in the loop for 3 items.  MyTable has just under 96,000 rows in it. MyTable2 has 121,857 rows in it. It is not about 55 minutes and it is still running with the exists so that a row isn't inserted twice. Is there anything I can do to optimize this? EDIT: The query just finished running again with the test for exists on each row. It shouldn't have inserted any new rows, but it took 57 minutes and inserted another 114,115 rows. Not good. Anyone see what is wrong with the query?