TOOLS TO DIAGNOSE HEART DISEASE: CARDIAC CATHETER, RADIOISOTOPES AND ULTRASOUND
Cardiac catheter and contrast radiography
An essential diagnostic aid is the cardiac catheter - first developed by Werner Forssman, who conducted the dramatic experiments on himself. It is only because of the sophisticated development of this technique that surgery on the coronary arteries has become possible. The long, thin tube is inserted into a blood vessel in the arm and, under X-ray guidance, is gently pushed into the heart. The catheter can be fitted with a pressure-gauge, to measure the pressure in the chambers of the heart, and it is also used to collect blood samples from different areas so that their oxygen content can be measured. This information is used to diagnose the presence of septal defects and the size and direction of shunts. For example, if blood in the right atrium contains more oxygen than it should, this means that blood has shunted from the left atrium, probably through an atrial septal defect.
Another exploratory technique which uses a cardiac catheter is contrast radiography. The radiographer injects a harmless radio-opaque dye through the already positioned catheter. X-ray pictures are taken in quick succession to show the movement of the dye through the heart and blood vessels. By positioning the catheter in different areas before injecting the dye, the cardiologist gets a clear view of the blood vessels and heart chambers - their dimensions, any obstructions, the formation of their walls and so on - enabling accurate identification of shunts and obstructions.
Another way of gathering information is to inject radioactive materials (radioisotopes), such as thallium-200, into the bloodstream. A scanner records the progress of the isotope, and thereby the blood-flow, on its journey to the heart muscle, thus providing still more information on a person's heart and circulation.
Finally, there is an investigatory method which is both safe and totally noninvasive: the use of ultrasound, sound-waves of very high frequencies, far too high for us to hear. A bat beams out ultrasonic waves to bounce them off a likely prey, just as a warship can use ultrasound ('sonar') to detect an enemy submarine. Both bat and warship pick up the echoes, and from them can tell a great deal about the position, motion and shape of the target. In just the same way, we can bounce ultrasound off all parts of the heart, repeating this process from different positions until we have built up a picture of the shape and movement of the heart walls and valves. This technique is very similar to that used to monitor the embryo in the womb. In recent years cardiologists have been attracted to the safety and accuracy of 'ultrasound echocardiography', as it is termed in their own particular line of medical work.
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