Heart Attack (cont.)
Not infrequently, however, advanced atherosclerosis is found in the coronary arteries of people with no known added risk factor. Given the absence of a obvious culprit, scientists are examining some new suspects. One of these is infection.
The concept is that certain chronic (long-term) infections may trigger atherosclerosis -- or they may at the least aggravate it -- and lead to heart attacks. In this regard, Drs. Sandeep Gupta and John Camm from St George's Hospital Medical School in London have weighed the available scientific data associating infections with the development of atherosclerosis and coronary heart disease. Their comprehensive review was published in the periodical Clinical Cardiology (vol. 20, pages 829-836,1997).
In the laboratory, for example, chickens infected with a strain of herpes virus were discovered to have aggressive atherosclerosis in their coronary arteries. Prior vaccination against the virus protected against much of the coronary atherosclerosis.
From epidemiology, it is known that there is a higher incidence of heart attacks in the winter and spring than in the summer and autumn, possibly related to the seasonal increase of the common cold and influenza infections.
On a clinical level, in some cases, common cold or flu-like symptoms are known to have preceded the heart attack. However, common colds are by definition common and flu-like symptoms are quite common, too. Such circumstantial evidence hardly constitutes concrete proof that infections cause coronary atherosclerosis and heart attacks.
One of the more provocative clues pointing to infection as a factor in the development of coronary atherosclerosis and heart disease involves a small bacteria, Chlamydia pneumoniae (C. pneumoniae). As its name suggests, C. pneumoniae causes respiratory tract infections and, in fact, it does so very commonly. About half of middle-aged adults have had C. pneumoniae. Most initial infections with C. pneumoniae cause no symptoms or just mild flu-like symptoms. Many people with C. pneumoniae are unaware they have it.