Saturday, April 29, 2006

Screening for CAD: Part 2

This is part two of a two part series. The first part can be found here.

Perhaps the best test now to identify vulnerable plaques, is the use of the intravascular ultrasound (IVUS). The current generation of IVUS is so good that we can colour code the plaque density once we have imaged the plaque from inside the coronary artery. Soft vulnerable plaques tend to contain a large lipid core and a thin fibrous cap. Should it have a thrombus, that is also soft. Coding tissue density is indeed a very clever way to separate tisues in the atheroma, by their tissue density and colour code them Calcium is the hardest (colour white and green), and lipid pool and thrombus is the softest (yellow and red).

The downside to this method is that it is invasive. It requires a coronary angiogram to introduce a catheter to the index coronary artery, and the introduction of a guide-wire and IVUS catheter into the coronary artery, to get those nice pictures. This obviously carries a small risk and are only indicated in patients with important, significant CAD. Once a coronary angiogram is indicated by the the presence of reverisible ischemia and the need for re-vascularisation, be it symptomatic or assymptomatic, then the IVUS is also indicated. In that sense, the IVUS is not available as a general screening tool. Therefore in those patients with significant CAD, then spotting the vulnerable plaque has become possible. This may allow us to better target our angioplasty strategy. Also as a result of IVUS, more clinical drug studies on secondary prevention, is using IVUS as one of their endpoints.

In summary, screening of individuals (males above 40yrs and females above 50yrs) is an important strategy to identify the presence of CAD. There are many test available. However, it may be important to identify vulnerable plaques to try and help those in immediate danger. The intravascular ultrasound is an important accurate tool in that direction, but unfortunately, it is an invasive technique, and so has limited application.

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