No more unwitnessed out-of-hospital cardiac arrests in the future thanks to technology?

Scquizzato T, Semeraro F. No more unwitnessed out-of-hospital cardiac arrests in the future thanks to technology. Resuscitation. 2021 Nov 22;170:79-81. doi: 10.1016/j.resuscitation.2021.11.010 READ

Nearly half of out-of-hospital cardiac arrest (OHCA) are unwitnessed. Most of these patients die because the chain of survival is not activated, and cardiopulmonary resuscitation (CPR) is not promptly initiated.

Early recognition, the first link of the chain of survival, is critical to enable rapid emergency medical services (EMS) activation, prompt CPR initiation, and early defibrillation. Technology is being increasingly used in OHCA. Apps to alert first responders effectively shorten the time to CPR initiation and improve outcomes. However, their efficacy is limited if the first link of the chain of survival is broken.

We describe four technologies, including mobile devices, wearables, and artificial intelligence, to aid the recognition of unwitnessed OHCA and facilitate rapid intervention. Such innovative technologies can measure biometrics signals, including heart rate, electrocardiogram, respiratory rate, motion, and activity and could be potentially implemented in the chain of survival in the short future.

Wearable devices to alert EMS

The first possibility is to use wearable devices to alert EMS automatically in case of unwitnessed OHCA. Some smartwatches can detect falls and monitor heart rate. When the smartwatch wearer falls and remains motionless, with or without detecting the absence of heart rate, the smartwatch automatically alerts EMS unless the wearer manually stops the process within seconds.

Surveillance cameras

Second, surveillance cameras installed worldwide are increasing and could be leveraged to detect OHCA automatically. When an OHCA occurs in remote or uncrowded places, such as parking lots and quiet streets during off-peak hours, OHCA recognition is delayed. Real-time advanced video analysis techniques allow detecting a sudden fall and absence of movement. Therefore, it is potentially possible to detect a cardiac arrest and trigger an alert.


Third, agonal breathing is common after cardiac arrest. Using smartphones and smart speakers for contactless, passive detection of abnormal breathing represents an innovative way to identify cardiac arrest. Considering that many unwitnessed OHCAs occurs at home where smart speakers are increasingly present, the adoption of these systems could be of significant impact.

Cardiac arrest prevention

Fourth, cardiac arrest prevention is another crucial but complex aspect. Patients may show signs of physiological deterioration before cardiac arrest. Wearable devices continuously monitoring biometrics signals may alert patients, hours or minutes in advance, of an impending life-threatening cardiac event. This will allow to recognize patients at risk of cardiac arrest and to alert EMS on time in the hope of preventing cardiac arrest.

An additional benefit could be obtained if these systems are integrated into a network of first responders allowing the simultaneous activation of EMS and nearby first responders.

Unwitnessed OHCA remains an unsolved problem

We imagined a future where unwitnessed OHCA will be survivable, and technology will likely play a central role. Research is needed to determine the feasibility and effectiveness of mobile and wearable technology to detect unwitnessed OHCA, facilitate early intervention, and improve chances of survival.

We invite clinicians and researchers worldwide to act now so that no one will die in 2050 due to an unwitnessed OHCA.

Tommaso Scquizzato
Tommaso Scquizzato

Tommaso Scquizzato is a researcher in the fields of cardiac arrest and resuscitation science at the Center for Intensive Care and Anesthesiology of San Raffaele Hospital in Milan, Italy. He is the Social Media Editor of Resuscitation, member of the Social Media Working Group of ILCOR, and member of the ERC BLS Science and Education Committee.

Articles: 35