Study: Better data needed to decipher variability in out-of-hospital cardiac arrest

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The incidence and outcomes of out-of-hospital cardiac arrest (OHCA) vary greatly around the world and researchers call for a better understanding of this variability to help improve OHCA prevention and resuscitation. However, to reach that understanding, researchers examining OHCA need to adopt standardized reporting techniques, according to a study in press in Resuscitation.

Jocelyn Berdowski, MSc, from the University of Amsterdam in the Netherlands, and colleagues identified a total of 67 studies: 30 from Europe, 24 from North America, seven from Asia and six from Australia— 20 with only adults, 47 with both children and adults.

Overall, there were 178,440 OHCAs in a source population of more than 100 million people.

Researchers noted that the variability in incidence and survival rates could be related to the definition of OHCA used in studies. "The definition of an OHCA could be all patients who die outside of a hospital, only patients who die suddenly, only those attended by EMS personnel, only those for whom resuscitation efforts were attempted, only those with a presumed cardiac cause, only those with witnessed arrests, or only those with witnessed ventricular fibrillation [VF]," they wrote.

Similarly, populations in studies may include all people in a region, only adults or only children. Berdowski and colleagues used various weighting techniques and analytic models to compare the data.

They specifically focused on four OHCA patient groups: EMS attended OHCAs, OHCA treated by EMS personnel, EMS treated OHCAs of cardiac etiology and EMS treated OHCAs with VF.

Researchers found substantially different incidences among the studies, with a 10-fold variability in incidences of OHCA. The global average incidence was 55 adult OHCAs of presumed cardiac cause per 100,000 person-years. Of all OHCAs, 27 percent had VF as the initial rhythm. The average survival following adult OHCA was 7 percent.

The researchers did not find a significant difference in survival to discharge rates or VF survival to discharge rates among studies.

The incidence of resuscitations with presumed cardiac cause was the highest in North America. Asia had the lowest percentages of VF (11 percent) and survival to discharge rate (2 percent) compared with in Europe (35 and 9 percent, respectively), North America (28 and 6 percent, respectively), or Australia (40 and 11 percent, respectively). The differences in both categories were significant.

The incidence of treated OHCAs was higher in North America (54.6 per 100,000 person-years) than in Europe (35.0), Asia (28.3) and Australia (44.0). The difference was significant.

"The striking variability in survival across studies underscores potential opportunities to make improvements," they wrote, noting that a main factor influencing survival was whether the patient was in VF.

Shortening the time to defibrillation could increase survival, as does bystander CPR, which slows down VF deterioration.

Berdowski and colleagues noted that some of their findings differ from previously published data and that these differences could be attributed to the various definitions used for OHCA, as well as the differing populations.

"The results of this review underscore the importance of being explicit with regard to reporting the study population, those attended by EMS, those treated by EMS, those treated by EMS due to cardiac etiology and those treated by EMS with VF," Berdowski and colleagues wrote. "Only when this information is reported in a clear and concise manner can we fully understand the potential reasons for differences in incidence and outcome."