DEAR DR. DONOHUE: Please explain what happened to the actor John Ritter. Reporters used the expression “undiagnosed heart disease.” How could a star and wealthy person not have gotten the best medical care? Did his doctor miss this? – A.M.

ANSWER: John Ritter had an aortic dissection. The aorta is the body’s main artery. It receives the blood pumped from the heart and delivers it to all the artery branches in the body. An aortic dissection is a tear between the layers of the aorta’s wall. Blood seeps into the tear and can split great lengths of the aorta. When the split begins at the aorta’s origin, the situation is grim.

If an aortic dissection is not treated quickly, the mortality rate is high. At least 24 percent of aortic dissection patients will die within 24 hours unless they get prompt treatment. If no treatment has been given for two weeks, 75 percent of these patients die. If treated quickly, the mortality is reduced but not eliminated.

Mr. Ritter’s doctor is not at fault. An aortic dissection cannot be detected until it happens. When it does, people complain of a ripping or tearing pain in their chests and often believe they are having a heart attack.

If the tear occurs in the first segments of the aorta, emergency surgery is the only thing that can sometimes save the patient’s life. If the tear is lower in the aorta, then it can often be managed with medicines and without surgery.

A newer approach to treatment involves putting a stent inside the aorta. Stents are used for clogged heart arteries. They expand when they reach a narrowed segment of artery, and here they expand when they reach the point of the tear.

Reporters should not say “undetected heart disease.” They should say “a sudden vascular calamity.”

DEAR DR. DONOHUE: I read an article you wrote a while back that dealt with sleep eating. Would you repeat the article? I would like to give the information to my doctor, since he hadn’t heard of it. – S.L.

ANSWER: The night eating syndrome is peculiar. People with it eat close to 60 percent of their total daily calories between the hours of 8 p.m. and 6 a.m. Part of the picture is insomnia and waking from sleep to eat. A few have little recollection the next day of eating during the night. No night eater has an appetite for breakfast. The syndrome afflicts about 1.5 percent of the general population and up to 26 percent of the obese.

Hormones might figure into this disorder. Melatonin, the sleep-maintenance hormone; leptin, the appetite-suppressant hormone; and hormones coming from the adrenal gland are not produced in normal amounts. Emotional stress is another ingredient that figures into the syndrome’s genesis.

The antidepressant Zoloft has been suggested as a treatment.

There’s a short summary of the syndrome in the Sept. 17, 2003, issue of the Journal of the American Medical Association and a longer article in the Aug. 18, 1999, edition of the same journal.

DEAR DR. DONOHUE: I was in the hospital for 30 days due to a heart-lung problem and am now wearing a portable defibrillator. I am supposed to have surgery to place a defibrillator inside my body. Is this internal defibrillator better than a portable one, and is it worth the risk? – R.S.

ANSWER: Readers, a defibrillator is a device that delivers an electric shock to a heart beating so erratically that it is not pumping blood. Unless a normal heart rhythm is quickly restored, death is the outcome.

Having a defibrillator implanted is not traumatic. It’s about the size of a pacemaker, and wires that connect it to the heart are threaded through blood vessels that serve the heart. It is no more risky than implanting a pacemaker.

Yes, the internal defibrillator is better than an external one. It is better-protected from being banged, and it lessens the risk of infection.

DEAR DR. DONOHUE: My friend has tested positive for the AIDS virus. She is not on any treatment. Now she’s pregnant. She refuses to see a doctor because she doesn’t want her positive AIDS test to be on any medical record. I tell her that she might be putting her baby at risk of coming down with AIDS unless she seeks treatment. She says she doesn’t need treatment until she starts feeling sick. Who is right? – N.A.

ANSWER: When there were few medicines that could keep the AIDS virus from rapidly destroying the body’s immune system, a pregnant woman had a 30 percent chance of passing the infection to the fetus.

With today’s drugs, the chances of transmitting the virus to the fetus are slight. Your friend ought to seek medical treatment right now. She has an obligation to do so for her baby.