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How cutting-edge technologies like Fractional Flow Reserve, Optical Coherence Tomography and Intravascular UltraSound are helping cardiologist diagnose accurately, and effectively.

Looking into your heart and listening to what it tells for your welfareOptical Coherence Tomography
Wednesday, November 01, 2017 - 15:58

 

Medical science and medical technology has advanced to an extent we would not have imagined possible 15 years ago. Nowhere is this more readily felt than in the Cathlab of Cardiology in a some of the hospitals in India.

The stethoscope, invented by Rene Laennec, and refined by many other physicians since - our current familiar version was designed and perfected by George Phillip Cannman - is sometimes called the most important medical invention. For the first time, it allowed a doctor to “look” into a patient’s body without having to cut them open. The stethoscope helped doctors hear the sounds made by the heart and lung of a patient, and use that as a guide to diagnose diseases. Which meant that diseases now were seen not as a collection of symptoms, but as a root cause, producing a certain number of symptoms.

The goal, for much of medical science and technology, since then, has been to refine this process: accurately identify the root of the problem, and determine the best course of treating it.

The developments in heart based medical technology, then, is on par with that of the stethoscope. The Cathlab - Catheterisation Laboratory - is a highly specialized, high-tech division within departments of Cardiology, in big hospitals. It is here that doctors bring patients, to see into, and hear closely, what the heart says.

Dr. Sengottuvelu, a senior Interventional Cardiologist at Apollo Hospitals, Chennai, swears by the Cathlab. He says it has allowed him to “understand, and transform the way we treat”.

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Here, technologies such as Fractional Flow Reserve, Intra-vascular Ultra Sound, and Optical Coherence Tomography, among others, allows Dr. Sengottuvelu to “visualise” the arteries, and determine the location, duration, and extent of stenosis - the blockages caused due to deposits, and the thickening of the artery wall. This then lets the cardiologist to prescribe the most effective course of action.

When precision counts

Fractional Flow Reserve, or FFR, is the difference between the maximum flow of blood in a normal artery, vs. the maximum flow in a stenotic (blocked) artery. The FFR is expressed as a ratio, or a fraction.

During an FFR procedure, the cardiologist guides a pressure sensitive wire into the arteries closest to the heart, and measures the flow of blood, and its pressure. Cardiologists take two measurements of this pressure: one “above” the block, and one “below” it. The difference in the pressure between these two points will tell the doctor the scope and extent of the block, and help them determine if the stenosis needs to be immediately cleared using procedures such as angioplasty, or if it is not critical yet and can be cured using medication.

Traditional methods of determining a block - such as an angiogram - were not accurate enough. An angiogram may show a block in the artery, but it will not show its effect on blood flow. Further, the quality of image that an angiogram produces is sometimes inconsistent, and this prevents a doctor from making an accurate diagnosis.

It is here that FFR excels.

Tests have proven that FFR technique is more successful and more accurate in determining stenosis of the arteries, in more than 90% of the cases. Further, these tests also concluded that FFR decreased the chances of adverse events when angioplasty was combined with FFR.

Additional studies looked at the age of patients, and compared those who received Percutaneous Coronary Intervention (PCI) guided by FFR, and PCI based on Angiography.

FFR based PCI reduced the chances of repeat hospitalisation, or death, than Angiogram-based PCI. Further, the study also proved that stenosis in older people was less critical, although they may look serious in an angiogram.

Dr. Sengottuvelu says, “When you have a block, which we have been measuring it visually till recently. I say 50%, someone else says 60% or 70%. When the block is 90%, clearly, no one has any doubts. But with a block that is only 50-70%, we were saying - above 70 it should be stented, below 50, we can leave it to medication. Ultimately, what really matters to the heart muscle is when the blood flow to the heart is reduced. As long as the blood is flowing, it can be managed without permanent damage to heart muscle. Even though the block is 50% or 70%, these blood vessels can modify and give more blood.”

FFR therefore is even more advantageous to a patient. If a doctor, based on FFR results, can determine that the stenosis is not critical enough, and there is adequate blood flow, can advise the patient to avoid expensive surgeries and hospitalisation.

Dr. Sengottuvelu uses the FFR technique extensively at Apollo Hospitals, and began using it much ahead of other hospitals in India. But he realised early that while the technique has its great advantage, there was very little data on FFR for Indian patients. He therefore specifically set out to research this, and has published his study in the Catheterization and Cardiovascular Intervention Journal, published by the Society for Cardiovascular Angiography and Interventions. His study concluded that when only angiograms are used for decision making, there is a 40% higher chance of deciding that a non-critical stenosis needed intervention. That is, more than 40% of patients were adviced to go for surgery, when medication would have sufficed. When FFR is added to diagnostic process, the study found that fewer stents were required. Dr. Sengottuvelu’s study also showed that using FFR also had a cost-benefit. It resulted in a total savings of over Rs. 8 Lakhs for his group of patients.

His study is the only Indian study to be published in a peer-reviewed, international journal.

Dr. Sengottuvelu wonders why, with such conclusive evidence from around the world, and with such great benefit, the technology has not spread widely to other hospitals. “It takes a 5-10 –minutes to do the test, and gives fantastic results,” he says.

At Apollo, where FFR is now a routine part of examination, patients trust the doctor’s expertise and judgement, and know that they always have the best interests at heart.

When Seeing is Believing

FFR is just one of the tools in the cardiologist’s kit. The other big tool is Intra Coronary Imaging. “It is like taking a photograph inside the blood vessels.”

There are two types of Imaging. One is based on sound, and is called Intravascular Ultrasound, and the other is based on light - called Optical Coherence Tomography.

“Angiogram is not a true representation. It is just a luminogram. It only shows the areas the dye passes through, but doesn’t show the accurate dimensions of the arteries,” says Dr. Sengottuvelu.

IVUS has been around for 30 years, and there is a lot of research into, and evidence for its effectiveness. In this process, a miniaturised probe is placed inside the artery, and a scan is made. The probe emits high-frequency sound waves which are then measured by a specialised computer system that calculates the depth and thickness of the inner wall of the artery, the thickness of any plaque, and therefore the lumen - or available space for blood to flow.

IVUS’s big advantage over traditional angiogram is that it tells the doctor not just that a block exists, but also how thick it is, and whether it is causing the artery to weaken. Further, an angiogram may show a block in one section of the blood vessel, but if the entire vessel has significant plaque build-up over a large section, it becomes invisible. In such a situation, IVUS is of extreme importance.

“For a physician IVUS has longer learning curve. But it gives extremely useful information to understand the true dimensions of the blood vessel,” says Dr. Sengottuvelu.

It has been found that plaque build-up in the artery will significantly impact the thickness and strength of the artery wall. Identifying heavy build-up of calcium deposits will allow a cardiologist to identify and isolate weaker arteries - especially those that may not open with conventional balloon techniques, and could potentially burst open. IVUS therefore is critical to study the quality and health of the coronary arteries and treat them properly, preventing any potentially fatal problems early.

The other imaging technology, Optical Coherence Tomography, is even more advanced. It generates high-resolution image of the artery.

The OCT probe emits an infrared light to generate a high-resolution image. The technique was first developed for ophthalmology, and quickly adapted for interventional cardiology. It magnifies the image produced without losing detail. “It is like an electron microscope inside the blood vessel,” says Dr. Sengottuvelu.

Compared to IVUS, OCT has 10-time greater resolution - which allows the cardiologist to differentiate between various kinds of tissues and substances. So while an IVUS may tell you that an artery has various plaque deposits, OCT will more accurately tell whether it is fibrous, or calcified, or lipid-rich - that is, cholesterol heavy.

This knowledge is of great importance to a doctor in deciding the course of action. A lipid-rich plaque is easier to “crush” using a balloon, during a minimally invasive PCI procedure. A calcified deposit - which is harder - will take more effort to remove, and may require the use of a high-speed motor that scrapes away the deposit - a procedure known as rotablation.

The other great advantage with OCT is to accurately place the stent during an angioplasty. Using the high-resolution images, cardiologist can determine if the stent is placed well (I’ve struck this through because regular readers may not understand ‘opposed well to walls of blood vessel.) inside the blood vessel, and supports the walls of the artery effectively, enabling blood to flow freely. “OCT allows us to see if the stent is undersized, or still hanging - not attached to the blood vessel properly, or sometimes the stent is oversized, and could cause damage to the edge of the artery” says Dr. Sengottuvelu. OCT allows the cardiologists to take precise measurements of the blood vessels for placing the stents, which means that long-term risks due to angioplasty can be avoided.

Both IVUS and OCT is fast becoming indispensable tools for cardiologists to ensure that patients undergo effective, safe stenting procedures, and experience excellent results. In short, IVUS and OCT, and FFR procedures ensure that patients are able to live a better, healthy longer life.

Dr. Sengottuvelu says, “Ultimately by doing this, we are ensuring we get a perfect result, which means long-term safety.”

 

This article has been produced by TNM Marquee in association with Apollo Hospitals.