Japanese large-data study reveals that 'flat-line ECG' indicates poor outcomes for out-of-hospital cardiac arrest

Asystole is the most serious form of cardiac arrest. It happens when the heart stops beating and there is no more electrical activity. It is sometimes called “flat-line” or “flat-lining” because the lines on an electrocardiogram become flat when electrical activity ceases. Management of asystole cardiac arrest by emergency medical services (EMS) outside of a hospital setting varies from country to country. In Japan, EMS are required to continue resuscitative efforts in most cases, providing a unique opportunity to measure the effect of pre-hospital life support procedures on asystole outcomes. 

The results of the large cohort study of cardiac arrest patients in Japan found that pre-hospital life support procedures did not meaningfully improve outcomes for patients with asystole. The results were published in JAMA Network Open on 18 November.

“Out-of-hospital cardiac arrest is a major public health problem across the world, and outcomes remain poor despite the recent accumulation of scientific knowledge. In particular, little is known about the epidemiology of out-of-hospital cardiac arrest with asystole in countries where prehospital resuscitation is not withheld or terminated. We hoped to understand if pre-hospital advanced life support procedures were associated with favorable outcomes,” said Junki Ishii, an assistant professor at Hiroshima University's Graduate School of Biomedical and Health Sciences in Hiroshima, Japan.

In many places, EMS personnel can stop resuscitative efforts on patients experiencing asystole. EMS personnel follow set guidelines to determine if resuscitation should be stopped. They may consider, for example, if the patient did or did not receive a shock with a defibrillator or if CPR was performed by bystanders. Studies out of North America and Australia where prehospital resuscitation efforts can be withheld or terminated, have shown that between 58.3% and 75% of patients with asystole did not receive resuscitative attempts or the resuscitative attempts were stopped in the field.

In contrast, Japanese EMS personnel are expected to continue resuscitative efforts in most cases. This difference in approach provided an opportunity for scientists to conduct a study to reveal whether continuing resuscitative efforts and advanced life support on these patients with asystole really contributed to improved outcomes. Examples of advanced life support include advanced airway management and intravenous epinephrine administration, in addition to basic life support including chest compression.

The study analyzed the outcomes for 60,349 adult patients who had an out-of-hospital cardiac arrest in Japan between June 1, 2014 and December 31, 2020. Patients who received defibrillation with an automated external defibrillator before EMS personnel arrived and those without involvement of ALS providers in the prehospital resuscitation were excluded. There were 35,843 patients (59.4%) who presented with asystole, with a median age of 77 years. Of these, 33,674 (93.9%) underwent advanced life support procedures.

Out of 35,843 patients with asystole, 497 survived after 30 days, but only 67 achieved a favorable neurological outcome. The two advanced life support procedures that were studied, advanced airway management and intravenous epinephrine, were not associated with favorite neurological outcomes. However, they did improve the odds of survival after 30 days. Advanced airway management increased the odds of survival after 30 days by 45% and intravenous epinephrine increased the odds of survival after 30 days by 81%.

“In this cohort study of patients with out-of-hospital cardiac arrest presenting with asystole, the proportion with a favorable neurological outcome at 30 days was substantially low, and no pre-hospital advanced life support procedure was associated with a favorable neurological outcome,” said Ishii.

Among the patients in this study with asystole, 35.5% would have been eligible for termination of resuscitation based on specific guidelines. Only 0.1% of these patients had a favorable neurological outcome at 30 days. “These findings suggest that discussions regarding implementation of a termination of resuscitation rule for these patients are warranted,” said Ishii.

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Other contributors include Mitsuaki Nishikimi, Kazuya Kikutani, Kohei Ota, Shinichiro Ohshimo, and Nobuaki Shime of Hiroshima University; Shingo Ohki of Shonan Kamakura General Hospital; Tatsuhiko Anzai and Kunihiko Takahashi of Tokyo Medical and Dental University; Masashi Okubo of University of Pittsburgh School of Medicine; and Taku Iwami of Kyoto University. 

This paper received funding from Hiroshima University to cover open access fees.

About Hiroshima University

Since its foundation in 1949, Hiroshima University has striven to become one of the most prominent and comprehensive universities in Japan for the promotion and development of scholarship and education. Consisting of 12 schools for undergraduate level and 5 graduate schools, ranging from natural sciences to humanities and social sciences, the university has grown into one of the most distinguished comprehensive research universities in Japan. English website: https://www.hiroshima-u.ac.jp/en