Fewer than 1 in 10 people who suffer an out-of-hospital cardiac arrest (OHCA) in the UK survive to leave hospital. That single figure is often quoted, but it hides an enormous range: for the small share of patients who receive a bystander shock within minutes, survival can be five times higher. Understanding why the range is so wide — and what closes it — is central to why this review treats bystander response as decisive, not incidental.
How Low Is "Low"? The National Picture
Recent data drawn from English ambulance services puts 30-day survival after an out-of-hospital cardiac arrest at around 7.8%. Resuscitation Council UK also reports a higher figure — survival to hospital discharge of 25.8% — for the subset of cases where survival is tracked across all presenting heart rhythms combined. The gap between these two numbers is not a contradiction; it reflects how differently OHCA outcomes are measured depending on which population is counted, from every attempted resuscitation through to only those who reach hospital alive. Either way, the honest summary is the same: most people who go into cardiac arrest outside a hospital do not survive it, and the margin between survival and death is frequently measured in single minutes.
Why the Range Is So Wide: Rhythm, Time and Who Is Nearby
Clinicians distinguish between "shockable" and "non-shockable" presenting rhythms, because a defibrillator can only restart a heart that is in a rhythm it can treat. That distinction, combined with whether the arrest was witnessed and how quickly it was treated, explains most of the variation in outcome. It also explains why survival statistics for out-of-hospital cardiac arrest cannot be reduced to one number: a patient who collapses in a crowded London street with a witness nearby is in a fundamentally different situation to one who arrests alone, unseen, with no one able to start the clock on treatment at all.
The Clock Nobody Can Pause
The chances of survival fall by roughly 10% for every minute that passes without defibrillation. Bystander CPR on its own has been shown to increase survival two- to four-fold by keeping oxygenated blood moving to the brain and heart until a defibrillator or ambulance crew arrives. The British Heart Foundation puts it more simply: early CPR combined with early defibrillation can double a person’s chance of surviving an out-of-hospital cardiac arrest. Neither intervention works well alone at scale — CPR buys time, but a shockable rhythm still needs a shock, and the sooner that happens, the better the odds.
London’s Own Evidence: What Happens When a Bystander Acts
National averages describe England as a whole, but London Ambulance Service has published a figure specific to the capital that makes the case starkly. In cases where a bystander used a public access defibrillator and delivered at least one shock before paramedics arrived, the survival rate reached 57.1% — more than five times higher than the baseline. Bystander CPR itself is delivered in a majority of witnessed OHCA cases in England, with figures around 72.6% reported nationally (against notably lower rates elsewhere in the UK, illustrating how much regional variation in bystander response still exists). Yet the use of a public access defibrillator by a bystander remains rare, occurring in fewer than 1 in 10 UK cardiac arrest cases overall. The gap between how often bystanders attempt CPR and how rarely they reach for a nearby defibrillator is one of the clearest single levers available for improving survival — not because the equipment is scarce everywhere, but because too few of the people standing next to it in the critical minute know it is there or feel able to use it.
| Bystander response | Reported survival outcome |
|---|---|
| Ambulance-only response, no bystander CPR | Consistent with the low national baseline (well under 1 in 10 to hospital discharge) |
| Bystander CPR provided | Two- to four-fold increase in survival |
| Bystander CPR plus early defibrillation | Chance of survival roughly doubled, per British Heart Foundation guidance |
| Bystander used a public access defibrillator and delivered a shock (London data) | 57.1% survival to discharge — over five times the baseline |
What This Follows From, for London’s Health System
The scale of the gap between "CPR only" and "CPR plus a fast shock" is why bystander response sits at the centre of how this review reads cardiac arrest outcomes, rather than treating it as one factor among many. It also reframes what "access" to emergency cardiac care actually means in a city the size of London: proximity to a defibrillator is only useful if the person standing beside it in the moment knows it exists, knows roughly what to do, and is willing to act before the ambulance arrives. That is a public-awareness and training question as much as an infrastructure one, and it sits squarely within the wider prevention and community-resilience agenda this review traces back to the Commission’s original brief for a health system built around what happens before, not just inside, a hospital.
Conclusion
Out-of-hospital cardiac arrest survival in the UK remains low by international standards, but it is not fixed. The London Ambulance Service figures show what is achievable when a bystander recognises an arrest, starts CPR, and reaches a defibrillator within minutes rather than waiting. The evidence here does not point to more equipment as the whole answer — it points to closing the gap between the equipment that already exists and the number of bystanders confident enough to use it.