Blackouts

Q:  I have had two incidents that have me worried. About two weeks ago I was picking some tomatoes in my garden, and a while later, I found myself on my knees. I was not on my knees when I began picking the tomatoes. Could this be a blackout?

The first incident occurred about 13 months ago while driving a car. Before I knew it, I hit a post (I shudder when I think of this). When I told my doctor about this, he put me on aspirin. I was given a CAT scan and was told it was a small stroke. I did have a mild stroke 4 years ago, and fully recovered from it.

Since the stroke, I did get some ischemic attacks (TIAs) which passed quickly. I just feel that there must be more help for what happened to me. I have been going to this doctor for almost 10 years and I don't know if I should change. I have not driven a car since the first incident, although he told me I could drive again. I am too scared to drive!

A:  A blackout or sudden loss of consciousness can be due to several causes, and it is not always easy to determine the exact cause in a particular case. A simple faint would probably be the least serious cause. Fainting can occur for many reasons, such as standing in one position for a long time, being dehydrated, severe fright (e.g., at the sight of blood), or other emotional stress. Prior to fainting, some people may experience warning symptoms such as sweating, light-headedness, weak knees, or queasiness of the stomach.

A variety of heart problems can cause a blackout. Some people may have very low blood pressure or a sudden drop in their blood pressure when they stand up. Irregularities of heart rhythm may produce a sudden loss of consciousness without any warning signs. The heart may stop beating for a while or throw in extra beats or beat very fast, all of which result in reduced blood flow to the brain.

A seizure is another reason for loss of consciousness. With a seizure, the person may have jerking movements of the arms and legs and lose bowel or bladder control.

The transient ischemic attack (TIA), which your doctor mentioned as the cause in your case, is really a "mini stroke" that lasts less than 24 hours and leaves a person with no permanent damage. Usually a small blood clot will flip off from an artery in the neck and travel to part of the brain, causing blockage of blood flow. Depending on which part of the brain, a person may also have numbness and weakness of the hand or foot, or difficulty speaking or drooping of the face, but not necessarily.

Up to 40% of the time, no explanation is found for a sudden loss of consciousness. Why don't you ask your doctor if he has investigated the other possibilities I have mentioned, particularly checking for any heart abnormalities. Since your two incidents occurred without any warning, I think you're wise to be hesitant to drive anywhere alone.

"Dear Doctor" is a compilation of patient questions answered by doctors from the Medical College of Wisconsin.