Real-time dispatcher & app-guided compression coaching for out-of-hospital cardiac arrest (OHCA) — metronome, depth feedback, and AED integration
Out-of-hospital cardiac arrest (OHCA) kills faster than almost any other medical emergency: without intervention, survival falls by roughly 7–10% every minute. Yet OHCA is uniquely treatable in the field — bystanders equipped with nothing more than their hands, a phone, and a nearby AED can double a victim's odds of walking out of the hospital. This page summarizes the evidence base the simulator above is built on.
The American Heart Association frames OHCA response as a Chain of Survival: (1) early recognition of arrest and activation of emergency response, (2) immediate high-quality bystander CPR, (3) rapid defibrillation, (4) advanced EMS/ACLS care, and (5) integrated post-arrest and rehabilitative care. Each link depends on the one before it — a fast 911 call is worthless without someone willing to start compressions, and flawless compressions cannot restart a fibrillating heart without a shock. The chain is only as strong as its weakest link, and in most communities that weak link is bystander action in the first few minutes before EMS arrives.
Roughly 90% of OHCAs occur at home or in public, and in the vast majority a bystander is present. Every minute that passes before compressions begin costs measurable survival — brain and myocardial ischemia compound quickly once circulation stops.
Telephone-CPR (T-CPR), also called dispatcher-assisted CPR, is the practice of a 911/999/112 dispatcher recognizing a probable cardiac arrest from the caller's description, then talking the bystander through chest compressions in real time — "push hard, push fast, right here on the center of the chest" — using a simplified compression-only protocol, often synced to a metronome or cadence count the dispatcher speaks aloud.
Multiple US and international studies have found that structured T-CPR protocols roughly double bystander CPR rates compared with communities without them, and are associated with meaningfully higher survival to discharge and better neurological outcomes. T-CPR works because it removes the single biggest barrier to bystander action: not knowing what to do, or freezing under panic. It also compresses the time-to-first-compression interval, which is one of the strongest predictors of survival in the literature.
Modern smartphone CPR-guidance apps extend the same idea outside the 911 call: visual/audio metronomes paced to 100–120/min, phone-accelerometer depth estimation, and step-by-step voice prompts give real-time feedback on rate and depth quality — precisely the feedback loop the "T-CPR / App Feedback" toggle in the simulator models.
AHA/ILCOR guidelines specify a compression rate of 100–120 per minute and a depth of at least 5 cm but not more than 6 cm in an average adult, with full chest recoil allowed between compressions so the heart can passively refill. All three parameters matter independently:
• Too slow (<100/min): inadequate cardiac output and coronary flow between compressions. • Too fast (>120/min): compressions become shallow and incomplete because there isn't time for full recoil, and diastolic filling time shrinks. • Too shallow (<5 cm): insufficient intrathoracic pressure generation to produce forward flow. • Too deep (>6 cm): increases risk of rib fracture, sternal fracture, and cardiac/pulmonary injury without added hemodynamic benefit. • Incomplete recoil (leaning on the chest): raises intrathoracic pressure at rest, reducing venous return and coronary perfusion pressure — a subtle error that's invisible without feedback.
Chest Compression Fraction (CCF) — the percentage of resuscitation time that compressions are actually being delivered — is itself an outcome-linked metric; guidelines target CCF ≥ 60%, ideally > 80%. Every pause (rescue breaths, rhythm analysis, pulse checks) reduces coronary perfusion pressure, which takes many subsequent compressions to rebuild — this is why the simulator's 30:2 conventional mode visibly dips its CCF and CPP each time breaths are given.
Compression-only ("hands-only") CPR is recommended by the AHA for untrained bystanders and lay rescuers responding to a witnessed adult collapse: it is easier to perform correctly under stress, avoids hesitation around mouth-to-mouth contact, and studies show outcomes at least as good as conventional CPR for witnessed adult arrests of presumed cardiac origin.
Conventional CPR with rescue breaths (30 compressions : 2 breaths) remains recommended for: rescuers trained in CPR who are confident performing breaths, pediatric arrests, and asphyxial/hypoxic arrests such as drowning, drug overdose, and choking — situations where the primary problem is oxygenation rather than a purely electrical cardiac event, so ventilation matters more.
The 30:2 ratio trades a small compression-time cost for oxygen delivery. In a witnessed adult VF arrest, blood already contains usable oxygen for the first several minutes — which is exactly why hands-only CPR performs so well for that specific scenario, while asphyxial arrests deplete oxygen content first and benefit more from breaths.
For the most common shockable rhythms in early OHCA — ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT) — defibrillation is the only intervention that reliably converts the rhythm. Survival for shockable OHCA falls by an estimated 7–10% for every minute that passes without a shock when no bystander CPR is being performed; high-quality bystander CPR slows, but does not stop, that decline by sustaining some coronary and cerebral perfusion until a shock is available.
Public Access Defibrillation (PAD) programs place AEDs in airports, gyms, offices, and other public venues specifically to shrink the time-to-first-shock below the ~8–12 minute typical EMS response interval in many regions. AEDs are designed for untrained laypeople: they analyze the rhythm automatically and only permit a shock when a shockable rhythm is detected, with voice prompts guiding pad placement and compressions between shocks.
Community first-responder apps (in the spirit of PulsePoint) extend PAD further: when a 911 center receives an OHCA call, the app simultaneously alerts nearby CPR-trained citizen volunteers and shows them the location of the nearest registered AED, so a volunteer can arrive with a defibrillator before EMS — directly shortening the time-to-shock interval that dominates survival odds.
Witnessed VF arrest with an AED shock delivered within the first few minutes, combined with high-quality bystander CPR, is associated with survival to discharge in the 30–40%+ range in published series — several times the ~8–10% baseline for all-rhythm, unwitnessed OHCA treated by EMS alone.