Out-of-hospital cardiac arrest (OHCA) is a life-threatening emergency where early cardiopulmonary resuscitation (CPR) by bystanders can significantly improve survival. Emergency dispatchers often guide bystanders to perform CPR over the phone, a method known as dispatcher-assisted CPR (DA-CPR). While this approach has increased bystander CPR rates worldwide, it relies on voice communication only, which may limit the dispatcher's ability to assess the situation and guide CPR effectively.

With advances in telecommunication technology, video-based communication has become more widely available. Telemedicine-assisted CPR (TA-CPR) allows dispatchers or emergency medical providers to see the patient and the rescuer through a live video call, potentially improving CPR performance by providing real-time visual feedback. However, evidence on whether this approach improves outcomes in real-world emergency medical service (EMS) systems is still limited.

This study aims to compare the effectiveness of TA-CPR with conventional DA-CPR in adult patients with suspected non-traumatic OHCA. The study is designed as a pragmatic cluster-randomized controlled trial conducted within a hospital-based EMS system in Bangkok, Thailand. Instead of randomizing individual patients, the CPR instruction protocol is assigned by month (cluster randomization). During each month, all eligible patients receive either the TA-CPR protocol or the DA-CPR protocol.

In both groups, CPR instructions are first provided through voice communication to avoid delaying the start of chest compressions. In the TA-CPR group, responders may switch to video communication if it is feasible, depending on factors such as the caller's device capability and the availability of another person to hold the camera. In the DA-CPR group, only voice communication is used throughout.

The study includes adult patients (aged 18 years or older) with suspected non-traumatic cardiac arrest who are managed by the participating EMS unit. Patients are excluded if resuscitation is declined, if the location is unsafe, if the cardiac arrest is witnessed by EMS personnel, or if communication barriers prevent CPR instructions.

The primary outcome of the study is the proportion of patients who receive bystander CPR before EMS arrival. Secondary outcomes include whether bystanders continue chest compressions until EMS arrives, how well responders follow the assigned protocol, and selected patient outcomes such as return of spontaneous circulation and survival.

Data are collected from an EMS cardiac arrest registry and hospital medical records. Audio recordings of dispatcher and responder communications are reviewed to assess adherence to the study protocols. The results of this study will help determine whether adding video communication to dispatcher-assisted CPR provides additional benefit in real-world EMS settings and inform future implementation of telemedicine in emergency care systems.

Inclusion Criteria:

• Adult patients aged ≥18 years
• Suspected non-traumatic out-of-hospital cardiac arrest
• Managed by the participating advanced life support (ALS) EMS unit

Exclusion Criteria:

• Resuscitation declined by patient's relatives
• Cardiac arrest occurring in unsafe or inappropriate locations for EMS intervention
• EMS-witnessed cardiac arrest
• Inability of bystander to communicate in Thai
• Cases where ALS unit is not directly dispatched to the scene

De-identified individual participant data (IPD) underlying the results reported in this study, including demographic characteristics, prehospital variables, and clinical outcomes, will be made available to qualified researchers upon reasonable request. Data will be shared after removal of all personally identifiable information in accordance with applicable data protection regulations.

Data will be available beginning 6 months after publication of the primary results and will remain available for up to 5 years.

Data available upon reasonable request and subject to approval by the study investigators and institutional review board, with a formal data use agreement.