By Nicholas Borgert

The unexpected death last year of veteran actor John Ritter at 54 focused attention on an often-overlooked condition that threatens aging men more than any other population. Ritter was stricken by an aortic dissection while working on a television sound stage. Despite immediate surgery, he died a few hours later at the hospital.

John Ritter

Compared to other heart and artery conditions, aortic dissection is rare. Only about 2,000 cases are diagnosed worldwide each year. Aortic dissection symptoms are similar to those of other conditions. Sudden chest pain can appear to signal a heart attack. Others may feel a pain in the back and assume the cause is a pulled muscle; still other patients experience abdominal pain often associated with stomach flu.

Also known as dissecting aneurysm or dissecting hematoma, acute aortic dissection occurs when a weakened portion of the thoracic aorta begins to tear apart along its longitudinal axis. Men are three times more likely to be diagnosed with aortic dissection than women. About 75% of cases occur in those 40 and older. African Americans are more prone to the disease; Asians less prone.

Hypertension: A Common Culprit
Most patients with aortic dissection are predisposed to a weakened or torn aorta due to several factors. The most common culprit is high blood pressure, which is present in nearly 70% of patients diagnosed with aortic dissection. Other causes include hereditary connective-tissue disorders, such as Marfan’s and Ehlers-Danlos syndromes, chest trauma caused by a motor vehicle accident, Turner syndrome, polycystic kidney disease, syphilis, and homocystinuria. Crack cocaine users and pregnant women are also at increased risk of suffering from aortic dissection.

Some cases of aortic dissection can be traced to heart and blood vessel defects present at birth yet left undiagnosed for years. In rare occasions, AD results from faulty insertion of a catheter during heart or blood vessel surgery. Aortic tears near the heart usually require immediate surgery. When the dissection occurs lower in the aorta—and farther from the heart—medications have proven to be a successful alternative to surgery.

A dissection can result in a heart attack, which can mask the tearing. Early symptoms include fainting, changes in blood pressure, confusion, shortness of breath, and pain or numbness in the arms and legs. Still, in 10% of aortic dissections, patients feel no pain at all.

Aortic dissection patients often complain of pain from a tearing or ripping feeling originating in the chest and radiating to the back. As the tear progresses, it can block openings to arteries that branch off from the aorta and disrupt blood flow to the brain and other vital organs. The result can be stroke, heart attack, extreme pain, nerve damage, and lack of pulse in the arms and legs.

In some cases, a dissection moving in the direction of the heart generates a murmur detectable by a stethoscope. In the past, an initial step in diagnosing aortic dissection involved a chest x-ray. In 9 of 10 cases, the x-ray is effective at revealing a widened aorta; however, that condition is common to any number of disorders.

Testing is a key component for both initial diagnosis and the monitoring of patients after discharge. In addition to the chest x-ray, other tools have included intravascular ultrasound, aortic angiography, computed tomography (CT), magnetic resonance imaging (MRI), and transthoracic or transesophageal echocardiography (TTE/TEE).

Critical Role of Diagnostics
Rajendra H. Mehta, MD, is clinical assistant professor of internal medicine at the University of Michigan Cardiovascular Center and one of the coinvestigators for the world’s largest registry of acute aortic dissection—the International Registry of Acute Aortic Dissection (IRAD).

“Around the world, the most widely used test is the CT scan,” Dr Mehta says. “It is available at most sites and is noninvasive. One disadvantage: the patient has to be moved to the CT scanner, which can be a problem because patients are sick.”

Dr Mehta says the best diagnostic tool for aortic dissection is MRI; however, it is not available at many centers, and it is time consuming and requires a patient to be moved. Another frequently used test option is TEE. “A semi-invasive test, TEE does not require the patient to be moved and is as good as a CT scan,” Dr Mehta says. The least-used and most invasive diagnostic test, he says, is the aortography.

“As MRI gets faster, it may yet be another breakthrough in diagnosis,” Dr Mehta says. “Treatment has not advanced much and is fairly standard at most centers.”

International Database Valuable
The Michigan cardiovascular center houses IRAD and the most comprehensive collection of data on aortic dissection patients ever assembled. The IRAD database includes information from all aortic dissection patients—those treated with medications as well as those who underwent surgery. The accumulation of statistics and analysis of protocols from around the world in an accessible and central location is helping researchers develop new and improved approaches for diagnosing and treating aortic dissection.

A 30-Minute Biochemical Test?
Reports from Japan indicate work is continuing on development of the first biochemical diagnostic test for aortic dissection. Over a 3-year period, a rapid 30-minute assay was tested on a limited number of patients with cooperation from eight major cardiovascular centers in Japan. The study included 95 patients with aortic dissection, 48 patients with acute myocardial infarction, and 131 healthy volunteers.

The new assay is designed to measure levels of circulating smooth-muscle myosin heavy-chain proteins. These proteins are released from damaged smooth muscle during the early onset of aortic dissection. The study found the assay had high sensitivity and acceptable specificity in aortic dissection patients who presented themselves during the first 3 hours after symptoms appeared.

According to an abstract of the study, as outlined in Annals of Internal Medicine, the new assay would likely be most useful for the triaging of a patient in an emergency room or clinic. Compared with other diagnostic approaches that depend on imaging technologies, the new assay is similar to cardiac enzyme tests, such as myoglobin and troponin, and could be done at a fraction of the cost.

“The cost of a relatively inexpensive blood test is likely to outweigh the small risk for overlooking or failing to exclude the diagnosis of aortic dissection,” the study summary says. “The assay may be most effective in its negative predictive role, given the low prevalence of aortic dissection in patients with chest pain.” (Estimates are that aortic dissection is present in only 1% to 2% of patients who experience chest pain.)

The assay pioneers are not releasing much information about recent developments. “The assay is progressing toward clinical use,” says Toru Suzuki, MD, of the Department of Cardiovascular Medicine in the Graduate School of Medicine at the University of Tokyo.

Fairly Standard Treatment
A doctor usually admits a patient with aortic dissection to intensive care where vital signs can be closely monitored. Then drugs are administered to reduce heart rate and blood pressure to the lowest level for sustaining blood flow to vital organs such as the brain, heart, and kidneys. The physician must then decide whether to continue the drug therapy or perform surgery.

In most cases, the surgeon removes the largest area of the torn aorta, closes any gulfs between layers of the aorta’s wall, and may use a synthetic graft to rebuild the aorta. This surgery can last from 3 to 6 hours. Recovery in the hospital can last up to 2 weeks.

The usual drug protocol for patients is oral use of beta-blockers in combination with ACE inhibitors to keep blood pressure down and reduce stress on the aorta. Most patients will have to continue that drug regimen for the rest of their lives. Possible complications of the surgery include another dissection, aneurysms in a weakened aorta, and aortic valve leakage.

According to Dr Mehta, most patients are studied at 1-month, 3-month, and 6-month intervals after discharge, as recommended by the European Society of Cardiology Task Force on Aortic Dissection. Again, the CT is most commonly used in patient monitoring, followed by the TEE and MRI.

In spite of recent advances in testing and treatment, aortic dissection mortality rates have not changed much. One of every four patients will die without leaving the hospital. Left untreated, 75% of those with an aortic dissection will die within the first 2 weeks.

“The best strategy is prevention though aggressive blood-pressure control,” Dr Mehta says. “Marfan patients should have their family members screened.”

Nicholas Borgert is a contributing writer for Clinical Lab Products.