Compensatory Dilation

This concept, now accepted by most experts, is extremely important in understanding the insidious nature of atherosclerosis. Plaque can grow to a large degree before any symptoms become manifest.

Heart attacks are caused by a sudden rupture of a plaque. Rupture is more likely to occur is the early unstable plaque that does not cause any significant chronic obstruction and therefore no angina.

In 50% of cases the first manifestation of plaque in coronary arteries is sudden death or a heart attack; there is no warning.

Intravascular ultrasound has shown how deceptive the traditional angiogam can be. On the left is the standard angiogram showing what appears to be a normal coronary artery. On the right are two cross sections of the artery at A (yellow) and B (blue) only a few millimeters along the same artery. At A there is a huge plaque shown by the blue arrows. At B the artery is normal. The red curves outline the internal elastic lamina which denotes the inside boundary of the muscle layer. In keeping with the theory of compensatory dilation, the section of artery at A with the big plaque has dilated to keep the lumen at its normal size. So, while the artery looks normal on the angiogram, the plaque at A could rupture at any time and cause a heart attack. This is why procedures like angioplasty and coronary bypass which deal only with visbly narrowed lumens, that may cause chronic angina, but do nothing for the huge amount of hidden plaque do not prevent heart attacks or prolong life. Procedures treat only the "tip of the iceberg."