Despite considerable progress in treating patients who suffer an out-of-hospital cardiac arrest, survival and—especially—neurologic outcomes remain relatively poor. Two areas in which more progress can be made are improved resuscitative measures, including the use of an automatic support pump, and better ventilation control. A third area that is slowly gaining traction is hypothermia therapy, according to Timothy D. Henry, an interventional cardiologist and director of research at the Minneapolis Heart Institute at Abbott Northwestern Hospital in Minnesota.
The Minneapolis Heart Institute already has an established regional STEMI door-to-balloon system that encompasses patient transfers to its cath lab for PCI from as far away as 210 miles. Building upon that STEMI system, the Heart Institute developed a standardized “Cool It” program for patients with out-of-hospital cardiac arrest (OOHCA) and STEMI. EMS personnel apply ice packs to patients at referring hospitals and cooling is continued en route. At the Heart Institute cath lab, cooling is continued with the Arctic Sun device (Medivance) and the target core temperature of 91.4°F is maintained for 24 hours.
In 2002, the Hypothermia after Cardiac Arrest (HACA) study found that therapeutic hypothermia (started in-hospital) significantly improved survival and neurologic outcomes compared with normothermia (N Engl J Med 2002;346:549-556). Inclusion criteria for the HACA study was OOHCA due to ventricular fibrillation (VF) or ventricular tachycardia (VT). In a study by Henry and colleagues, inclusion was much broader. Out of 103 patients, 52 had VF/VT (HACA criteria), while the remaining patients had either pulseless electrical activity (PEA) or asystole (non-HACA criteria). In addition, 50 percent of patients had STEMI and 40 percent had cardiogenic shock. Medical student Leah Swanson presented the study at the 2009 American College of Cardiology meeting in March.
Researchers found a 73 percent survival rate for patients with HACA criteria and a 39 percent survival rate for higher-risk non-HACA criteria patients. The Cool It protocol had a significantly higher rate of favorable neurological outcomes than the HACA study, while the HACA study had a significantly higher rate of unfavorable neurological outcomes.
The average time for STEMI patients from the return of spontaneous circulation (ROSC) to hypothermia therapy in the cath lab was 139 minutes, compared with 148 minutes for non-STEMI patients. It took an average 157 minutes to reach the target temperature in STEMI patients versus 173 minutes in non-STEMI patients. The differences were significant. Researchers found that for each hour that therapeutic hypothermia was delayed, the relative risk of death increased by 25 percent.
“While STEMI is frequently associated with OOHCA, these patients are not routinely receiving therapeutic hypothermia,” says Henry. “Given these outcomes, a therapeutic hypothermia protocol should serve as a neuroprotective adjunct to regional STEMI programs that function as tertiary centers.”
In another study at the ACC meeting, Vinod S. Kudagi, MD, and colleagues at Hartford Hospital in Connecticut studied 42 consecutive patients who were resuscitated from cardiac arrest and underwent endovascular therapeutic hypothermia (CoolGard 3000, Alsius). In this cohort, 33 patients received 2 liters of ice-cold saline prior to endovascular cooling. Patients included those with both shockable (VF/VT) and non-shockable rhythms (PEA and asystole).
Complete neurologic recovery in patients with a shockable rhythm was much higher (67 percent) compared to those in a non-shockable rhythm (33 percent). Researchers also found a five-fold increase in the odds of survival if a patient had shockable rhythm undergoing therapeutic hypothermia.
“Therapeutic hypothermia is safe, effective and can be implemented with relative ease in the ICU,” Kudagi concludes.