OCT: Seeing the Artery in a New Light
The similarities between IVUS and OCT are numerous. However, the power of resolution and clarity provided by the latter is truly phenomenal. This has been somewhat hard for me to take because I have spent so much time and effort analyzing IVUS images. The realization that IVUS is fast becoming the aging “over-the-hill” tool for intra-vascular imaging has made me keen to get to grips with OCT ASAP. What is striking is how much information and detail you can actually get. It is like wiping the snow from your glasses and being sucked down a microscope. I suppose it is akin to watching something on an old black and white television versus a new HD 3D TV. The one thing I am struggling with is the lack of penetration depth (always hard for a man to come to terms with……!) I tend to rely on IVUS vessel measurements as a comfort blanket for stent sizing; it is not as obvious with OCT and I feel that this is an important limitation.
However, when it comes to procedure logistics, the OCT catheter is very easy to use and very deliverable. The automatic pullback on delivery of contrast is extremely fast (20mm/s), smooth and very accurate compared to the clumsy “stick and pop” routine from previous IVUS pullback devices. The sheer amount of detail available has created some problems though. What should we do with these “things” we have never seen before? Like a caveman being handed a smartphone, the interventional community is slowly coming to terms with the fact that “things are going on in there after PCI” It is no longer the simple Homo-Erectus scratch and grunt “ME MAKE TUBE BIGGER!” If you intend to start looking at your stent results with OCT, then be prepared to deal with a few home truths! You will probably see a lot of the following:
- Plaque prolapse
- Edge dissections
- Residual thrombus
- Strut malapposition
- Uncovered plaque, possibly TCFA
- Strut coverage thickness (longterm follow-up)
- Percentage of uncovered stent struts (longterm follow-up)
What should we do with all this new information? Although a lot of studies have been performed, we are lacking the high quality level of evidence to make informed judgments upon. For instance, what amount of malapposition can be safely left alone? Should you post-dilate plaque prolapse? Should you cover all edge tears or just the significant ones? What criteria do we have for a significant edge tear and how can this be defined? Should we aspirate any residual thrombus or just leave it to pharmacology? Will any of this make a difference to clinical outcomes over plain old angiography, or are we all being swept up in the hysteria? What if only 40% of stent struts are covered at one year and not by neo-intima??
My naiveté with this technology is clearly creating post-procedural anxiety. Ignorance used to be bliss, but now you can actually see what you have done; there is a slightly more pressing agenda to make sure you have fixed all the potential problems before the tea and medals arrive.
Seeing things clearly in a new light, almost a new dimension, was always going to create questions. However, I feel these questions hold the answers we need to perfect the science and art of coronary intervention. Let’s hope that time will tell.
Dr Scott Murray is a Specialist Registrar in Cardiology and a Clinical Research Fellow at Liverpool Heart and Chest Hospital, United Kingdom.
Pictures courtesy of St Jude medical C7-XR brochure.