'Flat-Line ECG' Indicates Poor Outcomes for Out-Of-Hospital Cardiac Arrest

Asystole, often referred to as a “flat-line” ECG, represents the most severe form of cardiac arrest in which the heart ceases all electrical activity. It is a global medical emergency with extremely poor survival rates, and outcomes remain dismal despite advances in emergency medicine. In many countries, emergency responders can terminate resuscitation efforts under specific conditions.

Little is known about the epidemiology of out-of-hospital cardiac arrest with asystole in countries where prehospital resuscitation is not withheld or terminated. For instance, in some regions, such as Japan, emergency medical services (EMS) must continue life support procedures, providing a unique opportunity to evaluate their real-world impact. Now, a large data study has revealed that 'flat-line ECG' indicates poor outcomes for out-of-hospital cardiac arrest.

Researchers from Hiroshima University (Hiroshima, Japan) conducted a large-scale study using national health data to assess whether pre-hospital life support interventions improve outcomes for patients experiencing asystole outside hospitals. The study, published in JAMA Network Open, analyzed detailed patient records and outcomes over a six-year period, offering one of the most comprehensive evaluations of emergency cardiac care in Japan.

The research included 60,349 adults who experienced out-of-hospital cardiac arrest between 2014 and 2020. Among them, 35,843 (≈59.4%) presented with asystole, and 93.9% received advanced life support (ALS) interventions such as airway management and intravenous epinephrine. Patients who received early defibrillation before emergency teams arrived or lacked ALS involvement were excluded to ensure uniformity of results.

The findings revealed that advanced airway management increased the odds of 30-day survival by 45%, while intravenous epinephrine improved it by 81%. However, neither intervention was associated with improved favorable neurological outcomes. Out of nearly 36,000 patients with asystole, only 497 survived beyond 30 days, and just 67 achieved a favorable neurological recovery. These data suggest that survival alone does not necessarily translate into meaningful recovery for most patients.

Further analysis showed that more than a third (35.5%) of these patients would have met the international criteria for termination of resuscitation, yet resuscitation continued under Japan’s emergency care system. Only 0.1% of these individuals demonstrated good neurological function at 30 days. These findings underscore the need to re-evaluate emergency response protocols and discuss the potential adoption of termination-of-resuscitation guidelines to better align resource use with patient outcomes.

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Hiroshima University