Coronary Imaging and Physiology

I often get asked by my patient, “Did you fix everything? Doctor, what are you going to do about the 60% blockage in my other artery?”. Most cardiologists will agree on the management when looking at a normal angiogram or a very tight blockage in the arteries. It is usually the grey zone of those intermediate narrowing that divides the opinion. This is where coronary physiology in the form of a pressure wire study can be very helpful in giving some objective guidance. Following an angiogram, a miniaturized pressure sensor is placed beyond the blockage and the blood pressure before and after this lesion can be compared easily.

Coronary physiology does not look at the percentage of blood vessel narrowing, what it does is to measure the pressure drop before and after the blockage. Simple logic would dictate that if there is no significant drop in pressure across the narrowed segment of the artery, then it is not limiting blood flow to the heart muscle. Opening up such blockage may not make any difference to patients’ well-being. Think of this analogy, if one or two lanes of the expressway were closed off but yet the traffic was still flowing smoothly, there is no urgency to re-open those lanes. In fact, the road work involved to open up those closed lanes may itself lead to traffic jam.

This is exactly what the scientific data are showing. For borderline coronary blockage without significant pressure gradient, patients are better off treated with medication than with angioplasty.

Intra-coronary Imaging

Once the decision is made to treat a coronary blockage with angioplasty, the use of intra coronary imaging such as intravascular ultrasound (IVUS) or optical coherence tomography (OCT) can improve the final result of the angioplasty tremendously. Interpretation of these imaging data by cardiologists with expertise in these advanced technology is essential. This is especially the case in more complex procedures where the precise sizing and placement of device can make an enormous difference to patients’ long term outcome.