The coronary angiogram is often referred to as a road map of the heart. As such, it serves the cardiologist and cardiac surgeon well. It shows where the coronary arteries are, how they intersect, the angles of the branches, etc. There are diagrams of these anatomical features in many textbooks, but the reality is that these characteristics can vary from individual to individual, so it’s necessary to get a road map for each individual in whom an intervention is being contemplated. Then, of course, there’s the issue of narrowings in the coronary arteries. Should these receive stents? Should they be bypassed? Should they be left alone and treated with medical therapy?
What has become clearer in the past few years is that seeing is not believing. The angiogram may show a narrowing, but that narrowing may not be causing a reduced flow of blood to the heart, a.k.a. “ischemia.” Stenting or bypassing such a “non-ischemic” narrowing may not be of much benefit to the patient, but it will add a small risk factor of stent restenosis or perhaps a surgical complication. This was the conclusion of the FAME trial, in which the use of physiologic measurement, in the form of a pressure wire to measure blood flow across a narrowing, resulted in one-third less stents being used, and interestingly, one-third less MACE (Major Adverse Cardiac Events).
So, to bring the analogy home, think of using Google Maps to see how to get from where you are to where you want to be. If, for example, you were driving into Brooklyn, you might want to call up a road map. And this is what you’d see.
Okay. I can see the Long Island Expressway intersecting the Brooklyn-Queens Expressway. “X” marks the spot, My road map shows me the way to go. The main traffic arteries tell me that I should just cruise along the LIE and merge onto the Brooklyn-Queens Expressway.
But what if you clicked the option to add “traffic” to the road map? Well, here’s what you’d see. The main wide traffic arteries that looked like the right way to go in the first road map are now being shown as red, blocked up, bumper-to-bumper. In coronary terms, “ischemic.” You’d be much better taking the side roads or the northern route. Physiologic monitoring, like FFR or iFR, is like having a road map “with traffic.”
The point is that the coronary angiogram only shows part of the picture. It shows the lay of the land. But physiologic measurement, using FFR (Fractional Flow Reserve) or iFR (Instant wave-Free Ratio) shows how well traffic is moving. And when you’re deciding whether or not to stent or bypass an artery, or perhaps to just leave it alone and treat it with medications, you need to know how well the traffic is moving.
For more information on these modalities, visit our Intravascular Guidance Center.
And for even further information, check out this album from the San Francisco Bay Area punk pop band, “This Time Next Year,” titled “Road Maps and Heart Attacks.”