Although pericardiocentesis is still officially part of ATLS protocol, our trauma directors have discouraged the use of it in acute trauma situations, and say that its use is currently under review.
Pericardiocentesis an effective procedure in the extraction of thin, serous or serosanguinous pericardial fluids, as in the case of pericardia effusions. Frank, clotting blood, usually from the ventricle in a trauma situation, is poorly evacuated, and the underlying source for fluid accumulation is not addressed.
Basically, you either have a patient who is stable enough to undergo pericardial window, or you have an arresting patient, in which case you have one shot at finding and correcting the problem. ED thoracotomy allows for cross clamp of aorta, hilar clamping, temporizing repair of cardiac laceration, any of which might be life saving in the witnessed arrest of a penetrating chest wound.
That's our local teachings on the subject, anyway.
We're lucky to have extremely bright, capable EMTs here. They've been reliable in their determination of life signs at the scene and on arrival, so we don't get into situations of unindicated resuscitative efforts too often.
I've never had an ED thoracotomy ultimately survive. I have, however, had 2 of the 3 bedside thoracotomies I've done while on call survive. These were all performed in patients who were s/p CABG, with witnessed arrest and PEA unresponsive to ACLS protocol. One had a blown ventricle (the death); the other two had dehiscience of the suture line of a graft (one patient) and breakdown of the aortotomy closure - they both survived.