Catheterization of the Heart and Coronary Arteriography
A catheter is simply a long, thin, hollow tube of any kind. It’s possible to thread a catheter up a vein or an artery and into the heart. If a catheter is threaded up a vein it will move through the inferior or superior vena cava, and then into the right atrium, the right ventricle, and, if desired, into the pulmonary artery (Fig. 20-1).
If it is threaded up an artery it ends up in the left ventricle. It’s not practical to try to force a catheter backward across the mitral valve, so the left ventricle is as far as the catheter can go (Fig. 20-2).
 FIGURE 20-1 Catheterization of the right heart. A catheter is threaded up a vein in the arm, through the right atrium, and on into the right ventricle and pulmonary artery. It’s possible to measure pressures and oxygen levels at each level; for special tests, dye or radioisotopes can be injected. |
 FIGURE 20-2 Catheterization of the left heart. The catheter is threaded up an artery and into the left ventricle. By comparing pressures in the left ventricle and the aorta just outside the heart, it’s easy to determine if there is narrowing of the aortic valve. Special catheters can be directed into the openings of the coronary arteries so that dye can be injected into the vessels; x-ray movies can then be recorded. |
Once the catheter is inside the heart, we can measure the pressure in the different chambers. It’s also possible to detect stenosis of the aortic or pulmonic valves and evaluate the degree of narrowing. This is done by measuring the pressure above and below the valve. The pressure above a stenotic valve will be high and the pressure below the stenosis will be low.
By knowing the difference in pressure, the cardiologist can use a formula to calculate the actual size of the valve opening (see Fig. 9-8).
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