Each year, more than 300,000 people in the United States suffer sudden cardiac death, with some estimates placing this number as high as 460,000. The prognosis after a cardiac arrest is extremely poor; only 18 percent with an in-hospital arrest and less than 10 percent of patients with an out-of-hospital arrest survive to discharge. Unfortunately, poor outcomes continue to dog the few survivors of cardiac arrest, with many of these patients suffering from post-arrest anoxic brain injury, leading to further disability and death.
Landmark Studies
In 2002, two landmark studies assessing the use of therapeutic hypothermia in cardiac arrest patients changed the course of post cardiac arrest management. The first was an Australian study that randomized 77 patients with out-of-hospital ventricular fibrillation (VF) cardiac arrest with return of spontaneous circulation (ROSC) to therapeutic hypothermia vs. normothermia. The therapeutic hypothermia treatment group was cooled to a target body temperature of 33 degrees Celsius within two hours of ROSC. They were ultimately found to have significantly higher rates of neurologically intact survival (49 percent) compared with the normothermia control group (26 percent). The number needed to treat for this effect was 5 percent.
The Hypothermia after Cardiac Arrest (HACA) trial was a multicentered, randomized trial in Europe that compared therapeutic hypothermia to normothermia in 176 patients with a witnessed VF cardiac arrest with ROSC. The study showed cooling this population to a target temperature of 32-34 degrees Celsius led to a significant mortality benefit (41 percent compared with 55 percent in the control group) as well as significant meaningful neurologic recovery (55 percent compared with 39 percent in the control group). Therapeutic hypothermia is therefore now a class IIa recommendation for out-of-hospital VF cardiac arrest, and a class IIb recommendation for in-hospital arrest and non-VF arrest patients.
Hypothermia in the Cath Lab
The most common cause of cardiac arrest is cardiovascular disease and myocardial ischemia. Several post-mortem studies in cardiac arrest patients have shown that more than 80 percent have high-grade coronary artery stenosis, and up to 29 percent of patients have evidence of plaque rupture or thrombus formation. Immediate angiography in cardiac arrest survivors have demonstrated acute total coronary occlusions in 48 percent and irregular type II lesions suggestive of plaque rupture in 18 percent.
Initiating therapeutic hypothermia while performing primary percutaneous coronary intervention (PCI) in this situation may lead to better outcomes, but the evidence supporting this statement is far from conclusive, as the vast majority of patients in the landmark trials did not receive any revascularization therapies. One observational study showed that rates of meaningful neurological recovery and survival in patients with ST-elevated myocardial infarction (STEMI) and ROSC who remain comatose at the time of PCI are 51 percent. In patients who regain consciousness at the time of PCI, the survival rates were 100 percent and rivaled that of STEMI patients without cardiac arrest. Another observational study in Europe also showed similar rates of survival – 54 percent at six months – using a strategy of therapeutic hypothermia and early revascularization in STEMI patients with cardiac arrest and ROSC.
Initiating hypothermia protocols were not associated with delays to reperfusion in the cath lab. Despite being predominantly observational, the data supports therapeutic hypothermia and early revascularization in cardiac arrest patients with electrocardiogram (ECG) evidence of STEMI. Revascularization strategies in VF patients without ST elevation is less clear and data on non-arrest patients with STEMI have been disappointing with the COOL-MI trial. That study demonstrated a trend towards an increase in adverse events in non-arrest STEMI patients undergoing cooling compared to the normothermia group and the early termination of the COOL-MI II trial without publication of trial results.
First-Hand Experience
Anecdotally, in our own experience, we have witnessed several cases of out-of-hospital arrest and in-hospital arrest that have recovered full neurologic function and walked out of the hospital that we would have otherwise thought to be impossible.
One patient collapsed at home and was found to be in V-fib arrest by paramedics who arrived 30 minutes after the patient was found. The patient was defibrillated five times on the way into the hospital for recurrent V-fib and coded twice more in the emergency department before undergoing emergent PCI of the left anterior descending (LAD) and right coronary artery (RCA). Neurologic exam prior to being taken to the cath lab demonstrated fixed pupils, absent gag and decerebrate posturing. Our institutional cooling protocol was implemented after successful PCI and to my amazement, the patient started recovering neurologic function on day three post-arrest. They were able to walk out of the hospital a week later.
Two other cases involving a 91-year-old patient with V-fib arrest during vein graft PCI and another out-of-hospital arrest in a patient down for at least 30 minutes demonstrated similar miraculous recoveries.
Hypothermia for out-of-hospital and in hospital cardiac arrest has been demonstrated to have significant survival and neurologic benefits. While the data supporting its use in the cardiac cath lab is limited and the number of patients where this protocol would be potentially useful is small – STEMI patients surviving cardiac arrest with persistent comatose state after ROSC – the potential benefit to our patients is extremely high and in our opinion well worth the effort.
Editor’s note: Jane Luu, M.D., MPH, was recently a third-year cardiology fellow at Virginia Commonweath University Hospital in Richmond, Va., and is now an interventional fellow at Scripps Clinic in La Jolla, Calif. John Kao, M.D., FACC, is director of cardiovascular services at Kapiolani Medical Center and is a member of the DAIC Editorial Board. The medical center uses the Alsius Cool Guard device and the Alsius Icy heat exchange catheter for induction of hypothermia.
