Quicker use of defibrillator improves survival rate in some cardiac arrest cases

By Russell Rian / October 2011

Paramedics who deliver defibrillator shocks within three minutes of arriving at the scene of a cardiac arrest can boost survival in some cases, a new study involving UT Southwestern emergency physicians reveals.

People with a potentially fatal abnormal heart rhythm called ventricular fibrillation have higher survival rates when paramedics perform cardiopulmonary resuscitation (CPR) while setting up defibrillator machines, then deliver electrical shocks within three minutes of arrival. The findings are reported in a closer analysis of smaller groups in a study that appears in the Sept. 1 edition of the New England Journal of Medicine.

Dr. Ahamed Idris
Dr. Ahamed Idris

“Survival definitely declines for those who get their shock after three minutes, so one emergency medical services worker can continue CPR while the other EMS worker is getting the defibrillator out and attached. That generally takes about a minute to a minute and a half,” said Dr. Ahamed Idris, Professor of Emergency Medicine who heads the Dallas-Fort Worth arm of the Resuscitation Outcomes Consortium (ROC), funded by the National Institutes of Health. “If they can give the shock in about two minutes of arrival, they’ll be maximizing survival.”

The consortium is a $120 million joint U.S.-Canadian series of clinical trials aimed at identifying the best on-scene practices for traumas and cardiac arrest cases. The Dallas-Fort Worth arm has the highest enrollment in the U.S., with about 4,500 people enrolled annually.

Dr. Idris, a pioneer in resuscitation research, directs the Dallas-Fort Worth Center for Resuscitation Research, which has revolutionized the list of critical steps that paramedics should take within a few minutes.

Between 2006 and 2009, survival rates in Dallas-area cities improved by 50 percent. Irving’s have improved by nearly 60 percent, Mesquite doubled its survival rate and Carrollton has quadrupled its survival rates. The Dallas-Fort Worth ROC has focused its efforts on training area firefighters and paramedics to administer the best possible basic life support CPR.

“Performing CPR well is like a highly coordinated dance. You have to get the steps down,” Dr. Idris said.

Before 2006, paramedics worked on airway passages and rushed to get the patient into the ambulance so they could race to the hospital. But research has shown it is better to keep the patient at the scene, start CPR and then deliver shocks if needed before focusing on airways.

Other factors that can improve survival include spending at least 60 percent of each minute of CPR doing chest compressions and reducing the intervals between the last compression and the initial defibrillator shock to less than 10 seconds.

Also involved in the investigation was Dr. Ray Fowler, Professor of Emergency Medicine and of Emergency Medicine Education in the UT Southwestern School of Health Professions, and Co-Chief of the Section on EMS, Disaster Medicine, and Homeland Security at UT Southwestern.

In an accompanying study in the journal that involved Drs. Idris and Paul Pepe, Chairman of Emergency Medicine, researchers found no advantage to using an impedance threshold device. The device is designed to help generate negative pressure similar to breathing, to improve blood flow to the heart.