you can try like
Set myfolder = Application.GetNamespace("MAPI").GetDefaultFolder(olFolderSentMail)
Set g = myfolder.Items.Restrict("[subject] > 'test'") '   change this to match your subject
Do While g.Count > 0
    g.Remove 1
Loop
test carefully, i am not sure if read receipts are linked to the sent mail, if they are it would probably be better to use that than the subject