The surprising results of a recent study on heart attack therapy were recently released at the Transcatheter Cardiovascular Therapeutics Conference in Washington, DC. Dr. William O'Neill, Chief of Cardiology at the William Beaumont Hospitals in Royal Oak, MI, presented the results of a study showing that internally cooling the heart may significantly reduce the loss of heart muscle in certain types of heart attacks. Specifically, internal cooling was shown to reduce by 49% the area of damaged heart muscle for attacks centered in the anterior, or front, part of the heart. While cooling has shown no overall reduction in infarct size (that is, the amount of tissue destroyed by blocked blood flow) in other types of heart attacks to date, further studies in this area continue.
The COOL Study (Cooling as an Adjunctive Therapy to Percutaneous Intervention in Patients with Acute Myocardial Infarction) led by Dr. O'Neill involved 421 patients. The purpose of the study was to evaluate the safety and effectiveness of endovascular cooling (the term for cooling delivered internally via the blood vessels) to protect heart muscle and thus preserve heart function.
"Endovascular cooling is safe and well-tolerated in awake patients," said Dr. O'Neill. "With advances in technology to speed the rate of cooling, this therapy may be a first-line approach in the emergency room for patients with anterior heart attacks."
This cooling treatment is most applicable for anterior heart attacks, because the anterior portion of the heart has only one source of alternative, or collateral, blood flow in the event that a main vessel is blocked. Other areas of the heart have two or more alternative sources of blood flow, which both act to make the cooling technique less effective and help to limit the size of the damaged area of heart muscle from the outset.
Cardiologists say that emergency room physicians, and even first responders such as EMR personnel, can easily distinguish an anterior heart attack from other types; care providers would consequently be able to decide early on whether endovascular cooling would be beneficial for a heart attack patient.
Currently, methods of cooling the heart muscle involve threading a catheter into the inferior vena cava via an access point in the patient's femoral leg vein (doctors have found this an advantageous method, because other treatment techniques such as angioplasty would likely use the same femoral access point). Next, cool, sterile saline solution is circulated through the catheter, lowering blood temperature without actually mixing with the blood. Dr. O'Neill stated that a range of 35 to 33 degrees C (95-91.4F) is safe for this therapy. While this temperature may sound warm, it is cold enough that the chilled heart muscle's need for oxygen drops significantly enough to protect areas that would otherwise be at risk of destruction; additionally, with lower internal temperatures there is a risk of life-threatening heart arrhythmia.
One important area of research is centered around attempts to accelerate the rate of cooling. It currently takes about 30 minutes to lower the blood temperature to 35 degrees C. If that rate can be doubled, it will take only 15 minutes to get a patient's heart temperature down to a clinically beneficial temperature, helping doctors to intervene more efficiently and possibly win the race against heart tissue destruction.
Dr. O'Neill speculates that once this rate of cooling can be reached, endovascular cooling will become standard procedure in the emergency room for certain heart attack patients, enabling the maximum amount of heart muscle to be protected prior to the blockage in the heart being cleared, and ultimately making the restoration of normal blood flow (reperfusion) possible.
Dr. O'Neill and his colleagues are working closely with the developer of the cooling system, Radiant Medical (Redwood City, CA) to perfect the technology. Additional clinical studies of the technique are planned, as well.
