ST. LOUIS (MD Consult) - The aortic dissection that killed actor John Ritter on September 11 is a rare but instantaneous occurrence that can defy early diagnosis because of its similarity to other life-threatening heart ailments.

"Aortic dissection has often been referred to as the great imitator because it can mimic so many different disease processes," said Dr. Marc Moon, associate professor of cardiac surgery at Washington University School of Medicine in St. Louis. "The first (and most common) diagnosis ... is the patient is having a heart attack or myocardial infarction. But it can mimic almost any disease based on what blood vessels it affects. However, the most common thing that needs to be ruled out first is a heart attack."

This compounds the problem doctors face in dealing with aortic dissection.

"It certainly is a matter of time with this problem. It needs to be addressed quickly and early," said Dr. Moon, who is also director of the Center For Diseases of the Thoracic Aorta, which is affiliated with Barnes-Jewish Hospital in St. Louis and Washington University.

Aortic dissection, a tear in the aorta, occurs in about 30 to 40 people per million, Dr. Moon said. In a city the size of St. Louis, for instance, it happens in about 40 to 50 people per year.

"It''s not common, however there are patients in whom there''s a higher risk of it occuring," he said.

People with hypertension or a family history of aortic aneurysms are more susceptible to aortic dissection and should be checked with a chest X-ray and a CT scan, Dr. Moon said. It''s also important for hypertensive patients to see a physician regularly to control the high blood pressure.

"It''s rare that someone has an aortic dissection who doesn''t have hypertension," he said. "However, it''s also rare for a patient with hypertension to have an aortic dissection. So, you''ve got to have bad luck in both directions.”

It''s also difficult to detect.

"An aortic dissection is an instantaneous thing," he said. "One minute before an aortic dissection occurs, the aorta is normal in its thickness. However, one minute later, it''s irreparably abnormal. There''s a slightly higher risk in patients with an aneurysm, and that''s essentially the only preventive measure we can take other than monitoring blood pressure."

Identifying patients with asymptomatic aneurysms is important, because the risk of an aneurysm becoming an aortic dissection increases as the aneurysm gets bigger, Dr. Moon said.

"In those patients, we can follow them with serial examinations, to see if their aneurysms are enlarging, which puts them at a higher risk of rupture," he said. "Those are the kind of patients who would benefit from an elective repair of an aneurysm, surgically."

The average age when an aortic dissection occurs is in the 50s or late 40s, Dr. Moon said. The aorta has three layers in it. In a dissection, the middle layer of the aorta splits in two. So instead of a cylinder, it becomes a cylinder within a cylinder, with both walls thinned out.

"What happens is the outer layer becomes quite thin, and that is at risk of bursting," he said. The rupture of the outer cylinder wall is "often the cause of death in the dissection," he added.

The tear can also extend from the base of the heart, all the way around the blood vessels that go up to the head, arms, spine, the legs and the kidneys.

"It can tear all the way around," Dr. Moon said. "What happens when it tears into one of those vessels is it can impair the blood flow into those vessels and cause what''s called ischemia, or diminished blood flow in those areas, which can kill those organs."

Aortic dissection most commonly causes a sharp, stabbing pain either in the chest or the back, depending on whether the dissection starts at the root of the aorta, which is near the heart, or in the back, another common origin. It can cause abdominal pain, weakness, sweating and fatigue.

"It''s generally quite severe and all of a sudden," Dr. Moon said.

The mortality rate for a tear at the base of the heart is 50 percent within 48 hours, up to 90 percent by three months.

"That''s because after 48 hours the aorta starts to solidify a little bit, but the problem is not fixed," Dr. Moon said. "The reasons people die after 48 hours are continued malperfusion or inadequate blood flow to the organ, late rupture of the aorta, or the aortic valve, which is down at the base of the heart and can oftentimes start to leak massively with this tear. Which can lead to stretching of the heart and failure after that period of time."

But there is hope.

The keys to survival with aortic dissection are early diagnosis and early transfer to a center that is experienced with surgical intervention in these problems," Dr. Moon said. "If it''s a tear in the root of the aorta, the only treatment is emergency surgery. In which case, what we do is replace that portion of the aorta with a tube made out of dacron so that we can restore normal blood flow to the rest of the body."

Survival depends on how sick the patient is, although even patients who need PR can survive, Dr. Moon said.

"It needs to be diagnosed and taken care of before one of those fatal complications occurs, such as a rupture," he said.

The operation generally takes six to eight hours and is "extensively involved," Dr. Moon said.

"It requires the heart-lung machine," he said. "Blood flow to the body has to be stopped for a short period of time. Blood flow to the brain has to be stopped for a short period of time, because the tear almost always involves the portion of the aorta where the blood vessels go to the head. So we have to stop circulation to the brain in order to repair that portion of the aorta. That involves packing the head in ice and cooling the patient to very low temperatures - sort of a suspended animation type situation."

Due to the time constraints, the possibility of an aortic dissection should always be considered.

"It''s certainly a diagnosis that every emergency room will see from time to time," he said. "However, again, it''s quite rare. If you think about it, say there are 40 to 50 patients in St. Louis that get an aortic dissection, there are probably 40 to 50 hospitals in St. Louis too, or somewhere in that range. So they''ll see two patients a year that have this diagnosis."

Reprinted from MDConsult.com from September 17, 2003 by Doug Kaufman