BIOABSORBABLE VASCULAR SCAFFOLD
The Bioresorbable Vascular Scaffold (BVS) is a non metallic mesh tube, similar to a stent designed to help open up a blocked artery in the heart and restore blood flow to the heart muscle. BVS gradually dissolves once the artery can stay open on its own, potentially allowing the blood vessel to function naturally again.
Bioresorbable Vascular Scaffold (BVS) system that elutes everolimus in a similar way to normal stents and then resorbs naturally into the body leaving no permanent scaffold (i.e.) the stent disappears in 3 years and get back to its normal nature
Dr G Sengottuvelu, senior Interventional Cardiologist, Apollo Hospitals, Chennai who was one of the first to implant the commercially available BVS in India shares his views on this important advance in treatment of blocks in heart blood vessels.
Bioresorbable Vascular Scaffold BVS is similar in appearance to a stent, but is a non-metallic,non-permanent, mesh implant which gets absorbed gradually, dissolves over time and allows the artery to function naturally again, similar to the way a cast supports a broken arm and is then removed. This new scaffold disappears over 12- 24 months and supports the vessel until it has the ability and strength to stay open on its own says Dr G.Sengottuvelu
Absorb scaffold , presently available BVS is made of a material commonly used in other medical devices,such as dissolving stitches. This material allowsthe BVS to break down into elements already found in your body: Water (H2O) and carbon dioxide (CO2 enabling the artery to return to a more natural state.
Bioresorsable Vascular Scaffold (BVS) is the latest advance in treating CAD.
Being treated with BVS means you do not have a permenant implant which allows your artery to resume a more natural function. BVS may benefit in the following ways.
• Eliminate the concern about receiving a permanent implant.
• Enable you to resume your everyday activities
• May positively impact your long-term heart health
• Help to reduce your chance of future CAD symptoms
Dr Sengottuvelu emphasises that powerful blood thinners need not be given for a long time, and as the stent disappears, the normal vasomotor function ( normal contraction and relaxation of the blood vessel) is restored. The vessel is brought back again to normal. It also helps in creating a normal vessel and if needed bypass grafts can be placed in that area in the future. Having an artery free of a permanent implant may mean more choices are available to find the best treatment in future if needed.
Receiving BVS also allows for more options during follow up care. Non invasive technique to check how your artery is doing, can be used.
Dr G Sengottuvelu, senior Interventional Cardiologist, further adds that this is considered as a 4th revolution in interventional cardiology after the introduction of metallic drug eluting stents. The new ABSORB bioresorbable vascular scaffolds are everolimus-eluting and provide transient vessel support with drug-delivery capability, without the long-term limitations of the metal, presently in drug-eluting stents.This novel technology also overcomes many safety concerns associated with metal stent and possibly also has more clinical benefits.
Newer Bioabsorbable technology
Dr Sengottuvelu is one of the investigator among the few centres studying the newer Indian bioabsorabable scaffold Meres 100 with 100 microns struts.
Advances in Catheters
The ClearWay™ RX – Rapid Exchange Therapeutic Perfusion Catheter helps save larger area of heart muscle in heart attacks.
The CrossBoss Catheter is the latest technology for treatment of chronic and 100% blocked arteries. A decade ago, most of the patients with 100% blocked arteries were either managed medically or sent for surgery .This catheter facilitates the crossing of the 100% block, either through the tough lesions or can travel behind the blocked segment and exit beyond the lesion. The StingRay Balloon is used to get back into the actual passage of the blood vessel, using specialised wires.
FRACTIONAL FLOW RESERVE (FFR)
Angiography forms the basis of most revascularization decisions. This approach is perfectly reasonable when the angiogram clearly demonstrates either a severely stenosed coronary artery or a normal one. However, angiography has well-known limitations and the significance of lesions of moderate severity is often difficult to determine based on just the angiogram. This uncertainty may result in inappropriate care with stenting of non flow limiting lesions or failure to revascularize significant ones. When confronted with an ambiguous angiogram, additional testing is required to make a confident decision. Myocardial Perfusion Imaging (MPI) could be used to determine the presence of ischemia in the vascular territory supplied by the suspect artery. Fractional flow reserve is physiologically based and describes the ratio of the maximum achievable flow in the presence of a stenosis to the theoretical maximum flow in the same vessel in the absence of a stenosis. It takes into consideration the multiple, complex variables influencing coronary flow including lesion severity, lesion length and collateral flow.
Fractional Flow Reserve (FFR) is used to determine if a cardiac patient really needs a stent or bypass surgery or can be kept only on medicines. FFR is determined by a carefully calibrated sensor that measures the blood pressure upstream and downstream (before and after the block) after the administration of medicine like adenosine to induce maximum flow.
FFR –involves inserting a coronary pressure guidewire into the artery instead of relying solely on the traditional coronary angiogram to determine which arteries should be stented for patients with coronary artery disease. It not only helps avoid unnecessary surgery but also saves cost. FFR has been extensively used and widely available.
FFR is a guide wire-based procedure that can accurately measure blood pressure and flow through a specific part of the coronary artery. FFR is done through a standard diagnostic catheter at the time of a coronary angiogram. The measurement of Fractional Flow Reserve has been shown useful in assessing whether or not to perform angioplasty or stenting on “intermediate” blockages.
The FFR is defined as the ratio between distal coronary pressure and aortic pressure, both measured simultaneously at maximal hyperemia. Distal coronary pressure is measured with a coronary pressure guide wire. Maximal hyperaemia is usually induced by intravenous adenosine, administered at 140g/kg/min via a central vein or by intracoronary bolus dose. In diffuse or tandem lesions, hyperemic pullback recordings are performed. The unequivocal normal value of 1.0 is well accepted and has been firmly established in humans; Although the initial validation studies determined that an FFR of 0.75 most strongly correlated with ischemia, coronary stenoses with FFR between 0.75 and 0.80 have been considered “borderline” and may, in fact, be significant; currently, most clinicians and investigators consider an FFR of 0.80 as “ischemic”. Importantly, revascularization of lesions with nonischemic FFR can safely be deferred, thereby establishing FFR as a valuable tool and important adjunct to angiography in clinical decision making. The FAME 2 trial recently published in NEJM, indicates that angioplasty and stenting along with the best available medications result in better outcomes than medications alone for patients who have significant blockages in their heart arteries, as measured by Fractional Flow Reserve (FFR).
It is common practice for physicians to make revascularization decisions in the cath lab after a cursory review of the angiogram. It is frightening to think how many patients undergo unnecessary revascularization procedures or whose symptoms are dismissed as noncardiac because their physician “guessed” the significance of an ambiguous lesion. It is now easy to perform FFR at the time of the procedure, and, unlike conventional SPECT MPI, it is not influenced by disease in other vessels. With FFR we can be confident that a lesion requires revascularization. Also the deferral of revascularization based on a nonischemic FFR is safe. We have been regularly using FFR and it is simple ready to use and readily available in the cathlab and has tremendous utility with lots of scientific evidence backing its routine use.
Coronary angiogram showing borderline lesion in the left main coronary artery and FFR done with bolus adenosine showing physiological insignificance (FFR value -0.90)
Dr G Sengottuvelu study shows “Supplementing angiograms with other probe called FFR saves money as well as lives”. To arrive at this above quote, a detailed study was conducted at Apollo Hospitals on 59 patients over a period of two years and follow up of this study was done for more than a year on these patients.
A new interventional heart technology that can help patients avoid needless stenting operations by providing in-depth measurements of blood flow in the vessels to the heart has now been found to also save money as well as lives. “This is one of those rare situations in which a new technology not only improves outcomes but also saves resources,” said Dr G Sengottuvelu.
The technology is known as “fractional flow reserve,” or FFR. It involves inserting a coronary pressure guidewire into the artery instead of relying solely on the traditional coronary angiogram to determine which arteries should be stented for patients with coronary artery disease. Dr Sengottuvelu said “In spite of the advantages of FFR there is paucity of data in Indian population who have frequent diffuse, small and multivessel disease where it would probably be more beneficial in terms of cost and outcome. Our methodology of using both FFR and angiographic data was compared with that of a reviewing cardiologist decision based on a retrospective analysis of angiogram alone. The results were that Eighty-one vessels with intermediate lesions in 59 patients required 26 stents lesser when FFR data was added to the angiogram. The concordance of management decision was about 58% which means that more than 40% of intermediate lesions would be misclassified as significant based on angiography alone. There were no major events at a mean follow up of over a year. The net cost benefit in favor of FFR based management was INR 8,57,600 (USD 15,600) in our centre. The study conclusion was that Indians with more severe form of CAD benefit from a FFR based management plan for intermediate lesions, both clinically and economically.
“What we found was a combination of savings first at the initial procedure as a result of fewer stents and then further savings due to fewer events during follow-up — fewer heart attacks, fewer blood clots, fewer repeat surgeries,” Dr Sengottuvelu said.
Dr G Sengottuvelu further said “Fractional Flow Reserve (FFR) a golden technology is now frequently used to determine if a cardiac patient really needs a stent or bypass surgery or can be kept only on medicines avoiding any procedure. This scientific and evidence based procedure is beneficial to the patient as FFR technology not only saves lives while avoiding unnecessary surgery but also helps patients to save cost.” “Fractional flow reserve – guided stent implantation has been established to be economically attractive in cost-effectiveness analysis,” he said.
Patients with heart disease have blockages in the blood vessels (arteries) of their heart. When these blockages limit the amount of blood able to flow through the artery, they are “hemodynamically significant” or “ serious blocks.” These “serious or tight” blockages often cause frightening symptoms such as chest discomfort or shortness of breath and cause heart attack. Blockages in blood vessels are identified during diagnostic coronary angiogram which forms the basis of most decisions whether the particular patient needs a stent or bypass or only medicines. This approach is perfectly reasonable when the angiogram clearly demonstrates either a severely blocked blood vessel or a normal one. However, angiography has well-known limitations and the significance of lesions of moderate severity is often difficult to determine based on just the angiogram.
The blockages are often assessed visually and the narrowing described as 50 % or 90% depending on the visual severity of narrowing . Most of the bocks above 70 % are treated by stents or bypass surgery. But very often we come across blockages around 60 or 70% where the decision to treat by surgery or medicine is not clear. This uncertainty may result in inappropriate care with stenting of non flow limiting lesions (non – serious) or failure to treat significant or serious blocks which can cause a heart attack.
Now with advances and availability of scientific data, Fractional Flow Reserve (FFR) procedure is done to measure how “tight or serious” a blockage is? The FFR is defined as the ratio between distal heart blood vessel pressure and aortic pressure, both measured simultaneously at maximal flow using a tiny coronary pressure guide wire. FFR is determined by a carefully calibrated sensor that measures the blood pressure upstream and downstream (before and after the block) after the administration of medicine like adenosine to induce maximum flow.
Fractional flow reserve is physiologically based and describes the ratio of the maximum achievable flow in the presence of a stenosis to the theoretical maximum flow in the same vessel in the absence of a stenosis. It takes into consideration the multiple, complex variables influencing coronary flow including lesion severity, lesion length and collateral flow.
Dr. G. Sengottuvelu, senior consultant interventional cardiologist, one of the high volume operators of Fractional Flow Reserve technology says,” I have been using FFR for the past 2 years and found it extremely useful. It is simple ready to us, readily available in the cathlab and has tremendous utility with lots of scientific evidence backing its routine use. Nowadays almost every alternate PCI is FFR guided in my practice as the procedure is quick and easy to perform”.
He further said that performing fractional flow reserve takes only a few minutes, but it provides physiological significance of a block, ie objective evidence of ischemia. We may find a block in one of the heart blood vessels which may be borderline, whether it is causing a problem or not – this technology will give us the answer. “We have ample proof that fractional flow reserve correlates with outcomes,” Dr Sengottuvelu said. “It can guide management of multiple blocks ie, identify which are the blocks that are serious and plan stenting for only the serious ones and leave the rest with medicines. It can help determine whether stent is required and also how many stents to be placed in a procedure there by avoiding unnecessary stents. I call this ischemia-guidance for multi-vessel stenting.”
Initial validation studies determined that an FFR of 0.75 most strongly correlated with ischemia, currently however, most clinicians consider an FFR of less than 0.80 as “ischemic”. Importantly, those patients with blocks showing FFR more than 0.8, surgery or stent can safely be avoided, thereby establishing FFR as a valuable tool and important adjunct to angiography in clinical decision making.
The FAME 2 trial recently published in New England Journal of Medicine, indicates FFR guided decision making results in better outcomes for patients who have blockages in their heart arteries. FAME 2 is an important clinical trial in part because it enrolled consecutive patients with stable coronary artery disease, a patient group whose treatment strategy has been the subject of active debate since the 2007 presentation of COURAGE, which ultimately randomized less than 10 percent of eligible patients. In FAME 2, FFR was performed on every patient to confirm that “hemodynamically significant” (or “tight”) blockages in their coronary arteries were limiting blood flow. The patients with hemodynamically significant blockages were then randomized to PCI plus the best medications available or medications alone. The results of FAME 2 have been anticipated, when it was announced that an independent safety monitoring board halted the trial early, essentially deeming it unsafe to deny angioplasty and stenting to any study patients whose coronary blockages were found to be significant according to FFR.
The findings from FAME 2 are now the best data currently available to inform treatment decisions for patients with stable coronary artery disease. These data clearly demonstrate that the benefit of FFR guidance for PCI ( angioplasty & stenting).
Intravascular imaging is being done more often as these tests during angioplasty procedure helps to achieve best and optimal stenting results. Intra blood vessel imaging gives many useful information, for instance they provide an accurate measurement of vessel size and length of block, which helps to choose appropriate stent size especially in complex angioplasty.
Intravascular imaging has revolutionized the precision of angioplasty . One type of imaging is the Intravascular Ultrasound , where a miniature probe is used to study the nature of the plaque . Where regular angiography shows only a two-dimensional silhouette of the interior of the coronary arteries, IVUS visualizes the coronary artery from inside-out. This unique point-of-view picture, generated in real time, yieldsvaluable information.
Yet another innovative method of intravascular imaging is Optical Coherence Tomography [OCT] . This produces high resolution intracoronary images using infrared light.
The new imaging technologies give crucial information whether the plaque blocking the vessel is hard or soft , is made up of lipids or calcium etc . They can also give accurate detail about the size of stent that may be needed, and assess post stenting status of the vessel as well.
OPTICAL COHERENCE TOMOGRAPHY (OCT)
Optical coherence tomography (OCT) technique uses near-infrared light to create images of the inside of your blood vessels. It can obtain images of the blood vessels that are about the same as if they were looking under a microscope. OCT is a recently-developed, catheter-based intravascular imaging technology that provides micron-scale resolution. It is the laser light equivalent of ultrasound imaging, measuring the intensity of backscattered infrared light rather than sound waves, and translates to these optical echoes into a high-resolution, 2D tomographic image. It is available only in very few centres in the country.