Causes of Heart Attacks

 

Unfortunately, there is no simple test which can be used to detect coronary disease in the way that the chest X-Ray can be used to detect lung cancer. To be effective, such a test would have to be simple, quick cheap, safe and very reliable.

A lot of effort is going into ways of devising a suitable method, but at the moment the only methods we have are the electrocardiogram, the exercise test, isotope techniques and arteriogram. The electrocardiogram measures the heart’s electricity but although it invariably becomes abnormal after a heart attack, it is often normal in patients who have angina, let alone those with no angina whose arteries may be narrowed. An improvement is stressed by physical activity, when some of the heart’s reserve is being used. This test it still a poor indicator of those with incipient trouble, however, and can even be misleading because in those with no symptoms the test is falsely positive more often than truly positive; in other words, it may suggest an abnormality where none exists, more often than suggesting an abnormality where there actually is one. This is because the flow of blood through the arteries may not be significantly reduced until the artery is narrowed to about 60 or 70% of its cross-sectional area, and because abnormal electrocardiograms can be caused by other types of abnormality.

Isotope techniques are more reliable but they are expensive and need complex equipment. Minute amounts of radio-active materials which localize in the heart are injected into the blood stream during exercise and the heart is then “imaged” with a gamma camera. Because of its expense and complexity it cannot be applied to routine screening for people without symptoms, and although better than the exercise electrocardiogram this is also not foolproof.

The final method is the coronary arteriogram in which the coronary arteries are visualized by injection of X-Ray opaque fluid during cine X-Ray filming. It is very reliable but it is an “invasive” test requiring the passage of a fine tube (catheter) from a blood vessel in the arm or leg into the heart.

It is an uncomfortable rather than a painful test and may carry a very small element of risk. In certain circumstances it is essential, but it can hardly be used as a screening method where the suspicion of coronary disease is not very high, not only because of the risk but also because it is time consuming and expensive. It is likely that in the future ways will be found of imaging the coronary arteries in similar fashion non-invasively without the passage of a catheter.