Table 1. Characteristics of the 11 studies included in a systematic review and diagnostic accuracy meta-analysis.

Study ID	Study setting	Study location	Study scene	Mean age (years)	Sample size (n)	Patients’ characteristics	US views	US operators’ experience	The time US was performed
Aichinger 2012	Unknown	Austria	Pre-hospital	70.3	11	Non-traumatic	Subxiphoid	A 2-h course in echocardiography	During a rhythm and pulse check
Blaivas 2001	Single	USA	In-hospital	71	38	Non-traumatic	Subxiphoid; if unable to obtain, use parasternal views	Ultrasound trained and credentialed	The duration of the pulse check
Breitkreutz 2010	Single	Germany	Pre-hospital	65±15	51	Both	One of three views	Having undergone the standard FEER training program	During an ALS-conformed interruption of CPR
Flato 2015	Single	Brazil	In-hospital	59.75±18.11	32	Both	Various views	Had a 60-min lecture on ALS-conformed-TTE	During the intervals for rhythm check for 10s
Chardoli 2012	Multicenter	Iran	In-hospital	58±6.1	50	Both	Subxiphoid	Attended a teaching course to performing echocardiography	Just in the first NFI
Salen 2001	Multicenter	USA	In-hospital	Unknown	55	Non-traumatic	Subxiphoid view; the apical view as an adjunct in obese patients	Received a 4-h trauma sonography course	During the pulse check pause of the ALS
Salen 2005	Multicenter	USA	Pre-hospital/in-hospital	16–94	34	Non-traumatic	Subxiphoid or parasternal	Physician sonographers	Examinations during the pulse check
Tayal 2003	Single	USA	In-hospital	57±15	20	Non-traumatic	Various views	Trained with a 20-h ultrasound course	During CPR
Gaspari 2016	Multicenter	USA and Canada	In-hospital	64.2±17.4	414	Non-traumatic	Subxyphoid or parasternal long axis views	Emergency physician’s credentialed in bedside ultrasound by their individual hospitals	During pauses in resuscitation
Kim 2016	Single	Korea	Pre-hospital	63.9±14.5	8	Non-traumatic	Subcostal or parasternal window	The senior emergency resident or emergency specialist who had≥3 years’experience in emergency echocardiography	During pulse checks
Tomruk 2012	Single	Turkey	In-hospital	61.6±17.9	64	Both	Subxiphoid cardiac approach	Theoretical and hands-on training in cardiac ultrasonography	During the initial assessment

PEA, pulseless electrical activity; ROSC, restoration of spontaneous circulation which was defined as a return of spontaneous circulation for ≥20 mins or ROSC upon hospital admission; US, ultrasound; ALS, advanced life support; NFI, no flow interval; TTE, transthoracic echocardiography; in-hospital indicates that bedside ultrasound was not used until arrival at hospital; pre-hospital indicates that ultrasound was used at the scene; Unknown, the data was unable to be obtained; FEER, focused echocardiographic evaluation in resuscitation; CPR, cardiopulmonary resuscitation.