SELECT
DeadlockGraph,
LastStart = DeadlockGraph.value(N'(deadlock/process-list/process[1]/@lasttranstarted)[1]', N'datetime')
FROM
(
SELECT DeadlockGraph = XEvent.query(N'(event/data/value/deadlock)[1]')
FROM
(
SELECT XEvent = CAST(event_data AS XML)
FROM sys.fn_xe_file_target_read_file(N'system_health*.xel', NULL, NULL, NULL)
WHERE [object_name] = N'xml_deadlock_report'
) AS x
) AS y;