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An Inner View of IVUS

By allowing a cross-sectional view of arteries of the heart and looking at their walls, IVUS helps interventional cardiologists to do complex angioplasties and reduces angioplasty failures. Despite its multiple merits, Rita Dutta finds out why only a handful of hospitals are using it

It would be no exaggeration to say that Intravascular Ultrasound (IVUS) has expanded the frontiers of coronary interventions invasively. IVUS has definitely emerged as the new gold standard for atherosclerosis imaging as it provides a cross-sectional view of any major artery of the heart, aiding interventional cardiologists to perform complex angioplasties. With detailed visualisation information and analysis, IVUS empowers cardiologists for better deployment of intra-coronary-artery-stents and allows study and assessment of previously deployed stents. This state-of-the-art imaging system also ensures reduced angioplasty failures in the cath-lab.

Advantage IVUS

A catheter-based system, IVUS allows physicians to acquire images of diseased vessels from inside the artery. IVUS provides detailed and accurate measurements of lumen and vessel size, plaque area and volume, and the location of key anatomical landmarks in three dimensions and in real time. Says Dr Upendra Kaul, Executive Director and Dean of Cardiology at Escorts Hospital and Fortis Hospital, Vasant Kunj, New Delhi, who has been using the technology for the last 15 years, “IVUS has significantly improved our knowledge of the interiors of arteries, especially the coronary arteries and has revolutionised percutaneous interventions (PCI). It has taught us several important lessons which have perfected the art of angioplasty.”

With IVUS, users are able to visualise the internal structure and cross-sectional view of any major artery of the heart that was earlier not possible. IVUS aids by revealing the composition of fatty deposits / calcium / cholesterol / plaque etc. that cause blockages and reduce blood flow into arteries. In addition to the heart, the IVUS can also be used for visualisation of various other major arteries in the body.

"IVUS has significantly improved our knowledge of the interiors of
arteries, especially coronary arteries"

- Dr Upendra Kaul
Dean of Cardiology
Escorts Hospital and Fortis Hospital
Vasant Kunj, New Delhi

"IVUS is able to provide a cross sectional view of the coronary artery along its entire length"



- Dr Debdutta Bhattacharya

Senior Consultant Cardiologist
RTIICS
Kolkata

"Twenty-five Indian hospitals are using iLab and 20 more installations are in the pipeline"



- Riyaz Desai

Business Manager
Boston Scientific
India

It allows users to retrieve useful information on possible tears, damage or dissections in the wall of the artery. It provides accurate information on the thickness of the artery, the internal diameter, the reduced diameter due to the blockage, cross-section area, the exact length of the critical region, and enables users to take important decisions in evaluating the correct action to be taken during complex cases. “IVUS has improved our knowledge of the vessel wall which cannot be seen well by contrast angiography,” adds Dr Kaul.

Says Dr A Sreenivas Kumar, Director, Cardiac Catheterisation Laboratory and Director and Head, Clinical Research Department, Care Hospital, Hyderabad, “It is definitely a useful modality in evaluating coronary artery disease patients in the cath-lab, especially useful in managing more and more complicated cases in the lab.”

It’s to be noted that IVUS comes in-built with angioplasty. This concept is developing, as the major limitation of angioplasty is acute re-blockage or restenosis that can happen when stents are not properly deployed during angioplasty. An IVUS catheter on an angioplasty balloon will guide in proper deployment and optimise the results of angioplasty.

IVUS Vs Angiography

When compared with the conventional diagnostic tool, angiography, IVUS scores in multiple ways. Dr Nagendra Singh Chouhan, who is a Consultant Interventional Cardiologist & Electrophysiologist, Medanta Heart Institute, Gurgaon, and has been using IVUS for the last 15 years, opines, “Angiography is 2-dimensional imaging and is subjective and thus does not give details of stenotic plaque. IVUS can be especially useful in situations in which angiographic imaging is considered unreliable; such as for the lumen of ostial lesions or where angiographic images do not visualise lumen segments adequately, such as regions with multiple overlapping arterial segments. IVUS enables accurately visualising not only the lumen of the coronary arteries, but also the atheroma (membrane/cholesterol loaded white blood cells) ‘hidden’ within the wall.”

Echoes Dr Debdutta Bhattacharya, Senior Consultant Cardiologist, Rabindranath Tagore International Institute of Cardiac Sciences (RTIICS), Kolkata, which introduced the technology in eastern India six months back, “IVUS is able to provide a cross-sectional view of the coronary artery along its entire length unlike coronary angiography, which is able to show only the profile of the artery. As a result, blockages which are sometimes missed or under by correctional angiography, can be detected by IVUS.”

IVUS, however, is not considered an alternate to angiography. IVUS is always done along with angiography, when an angioplasty is planned. It adds to angiographic information, standalone it has no value in diagnosis. “Angiography and IVUS are complementary diagnostic tools. It is invariably combined with the procedure of PCI. The lessons learnt from IVUS have been incorporated during routine angioplasty procedures. All over the world the use of IVUS in routine angioplasty procedures is rare,” says Dr Kaul.

However some question the superiority of IVUS over angiography. Says Dr Anil Bhat, Director, Senior Consultant and Head, Department of Adult Cardiology from Manipal Heart Institute, “Coronary angiography when indicated is the gold standard for patients with coronary artery disease (CAD), whereas IVUS is not used for diagnosing CAD. It is used in some instances to optimise stent implantation.”

When is IVUS Useful?


iLab from Boston Scientific

For what kind of patients is IVUS useful? “Current clinical uses of IVUS technology include checking how to treat complex lesions before angioplasty and checking how well an intracoronary stent has been deployed within a coronary artery after angioplasty. If a stent is not expanded flush against the wall of the vessel, turbulent flow may occur between the stent and the wall of the vessel. Some fear this might create a nidus for acute thrombosis of the artery,” says Dr Chouhan. He adds that IVUS is a must in patients with left main artery angioplasty and in cases where on angiography, the blockage is between 50-70 per cent and there is difference of opinion about further management by angioplast or drug therapy. Interventional cardiologists opine that it is an important investigation for managing left main coronary stenting, treating in-stent restenosis, angioplasty of very small calibre vessels, and calcified lesions to choose the right device as well as assessing the post stent deployment result.

So, how are hospitals managing to do complex angioplasties without IVUS? According to Dr Shailender Singh, Interventional Cardiologist, Global Hospital, Hyderabad, which is using IVUS from the last year, “Hospitals without IVUS can continue doing PTCAs, but in high-risk patients and complex interventions, there is clarity of end result and outcome in IVUS operator’s cases.” To this Dr Bhattacharya adds, “Any centre performing complex interventions like left main stem angioplasty, rotablation and stenting etc. should have IVUS guidance to achieve optimum results.”

However, Dr Bhat is not convinced. Explaining why Manipal is not using IVUS, he says, “Data is lacking on whether IVUS-guided angioplasty is better than routine angioplasty. Angioplasty (done at time of heart attack) has a proven role in reducing death from MI. IVUS does not reduce mortality in patients with stable disease. IVUS at present has no role during angioplasty for acute MI. IVUS’s only use is in optimal stent placement (under some circumstances) and an evolving indication is diagnosing coronary artery disease in patients having undergone cardiac transplant.”

How is IVUS Conducted?
To visualise an artery or vein, angiographic techniques are used and the physician positions the tip of a guidewire, usually 0.36 mm (0.014") diameter with a very soft and pliable tip and about 200 cm long. The physician steers the guidewire from outside the body, through angiography catheters and into the blood vessel branch to be imaged.

“The ultrasound catheter tip is slid in over the guidewire and positioned using angiography techniques so that the tip is at the farthest away position to be imaged. The sound waves are emitted from the catheter tip, usually in the 10-20 MHz range, and the catheter also receives and conducts the return echo information out to the external computerised ultrasound equipment which constructs and displays a real time ultrasound image of a thin section of the blood vessel currently surrounding the catheter tip, usually displayed at 30 frames/second image,” says Dr Chouhan.

The guide wire is kept stationary and the ultrasound catheter tip is slid backwards, usually under motorised control at a pullback speed of 0.5 mm/s. (The motorized pullback tends to be smoother than hand movement by the physician.)

“The blood vessel wall inner lining, atheromatous disease within the wall and connective tissues covering the outer surface of the blood vessel are echogenic, i.e. they return echoes making them visible on the ultrasound display,” adds Dr Chouhan.

The procedure takes about 15-20 minutes. The technique is not demanding, technically. However, it needs to be conducted by a person who performs angioplasty procedures regularly. It involves instrumenting coronary arteries, carefully. “The procedure is not meant for non-invasive cardiologists or occasional angiographers,” cautions Dr Kaul.

An Emerging Market


present in the slide

The market for IVUS in India, pegged at $ 2.5 -3 million, has picked up in the last few years as interventional cardiologists started doing more complex cases, previously sent for CABG. Also, with increasing numbers of left main artery angioplasties, IVUS is catching up in India. An estimated 45 hospitals in India are using IVUS, while there are around 500 cath labs in the country. IVUS is more popular in the US, Japan and South Korea. According to a global report, the penetration of IVUS in a region is directly proportional to reimbursement systems. Experts point out that the penetration rate of IVUS is as high as 90 per cent in Japan, because of its well-established reimbursement system and also the fact that interventional cardiologists there dare to do angioplasties even in more complex cases.

The vendors of IVUS are Boston Scientific Corporation and Volcano Corp. Only in Japan, a third player-Terumo Corporation is present. A standalone IVUS system is sold by Boston Scientific, which has tied up with Trivitron for sales and marketing in India. Says Riyaz Desai, Business Manager, Boston Scientific, India, “Twenty-five Indian hospitals are using iLab (our IVUS product) and 20 more installations are in the pipeline.”

On the other hand, Volcano Corporation has made an exclusive agreement with GE Healthcare in 2005, by which Volcano’s IVUS is integrated with GE Innova cathlab systems. Says V S Raghavendra Rao, Business Manager, Surgery, GE Healthcare India, “We have installed 20 units and 20 more are in the pipeline. Due to integration, the IVUS images are saved as part of DICOM images, in the same image folders and can be retrieved or queried easily.  The system is controlled by Innova control panels during a patient operation.”

Only two versions of IVUS are available in the market, one with mechanical rotatory catheter and another with static electronic catheter. The latter has virtual histology--IVUS technology helps differentiate the four plaque types: fibrous, fibro-fatty, necrotic core and dense calcium. The first version of IVUS in India was introduced around 1995 by Hewlett Packard. That model is now obsolete. Several modifications have occurred since its introduction. “There has been continuous introduction of improved quality of image, tissue characterisation tool and user-friendly software. iLab is the third generation platform in BSC IVUS business and we are working on the next generation catheter as well,” says Desai.  

Now, the IVUS catheters are easier to introduce even in complex situations like totally blocked arteries to evaluate the lesion characteristics and the true lumen etc. “The systems are much more user-friendly, and smaller; on line calculations with good imaging are possible,” says Dr Kaul. A major change was when Siemens Medical combined the algorithms combining the monitors for angiogram, IVUS and pressure.

Some Leading Hospitals Using IVUS
  • Lilavati Hospital, Mumbai
  • AIIMS, New Delhi
  • RNR, New Delhi
  • Escorts Heart Institute, New Delhi
  • Fortis Hospital, Vasant Kunj, New Delhi
  • Medanta, Gurgaon
  • Rabindranath Tagore International Institute of Cardiac Sciences, Kolkata
  • Care Hospital, Hyderabad
  • Global Hospital, Hyderabad
  • Amrita Institute of Medical Sciences, Kochi

Impact of IVUS


IVUS reveals stent under expansion in ISR

Because the vessel, plaque and stents are visible, IVUS guidance clarifies previous PCI results, and frequently discovers under expanded stents

IVUS has greatly helped interventional cardiologists in management of calcified coronary arteries. “It helps to choose the device (balloon, cutting balloon or a rotablator). It has taught us how to deploy stents properly. In the initial days of coronary stenting, in the early 1990s, acute and subacute stent occlusions used to occur in three to four per cent patients, but IVUS showed how high pressure deployment helps in adequate expansion of stent leading to reduction in this rate to less than one per cent in the present era. Research has also made us aware of how to differentiate between an injured artery and a spasm or a pseudo lesion,” says Dr Chouhan.

How Much Research?

IVUS has been increasingly used in research to better understand the behaviour of the atherosclerosis process in living people. IVUS is also useful to understand mechanism or re-stenosis problem after angioplasty leading to the recognition that most of the re-stenosis is due to inadequate stent implantation.

Some of the studies where it was used for stent studies are Abbott's Bioabsorbable Everolimus Eluting Stent and Taxus II Trial. In India, in 2002, the Co-star study in 2004 used IVUS for around 100 patients who had put Co-star stents. “IVUS was used to do follow-ups of 78 per cent of the patients,” says Dr Kaul, Principal Investigator for the study.

Experts also refer to the clinical research trials completed in the United States in the late 1990s, using combined angiography and IVUS examination, to study which coronary lesions most commonly result in a myocardial infarction. “The study revealed that most myocardial infarctions occur in areas with extensive atheroma within the artery wall, however very little stenosis of the artery opening,” says Dr Chouhan.

The six-month TULIP study is often cited by proponents of IVUS. The study demonstrated an improved angiographic and clinical outcome after stent placement after long coronary stenosis guided by IVUS compared with angiographic guidance only.

A study in Korea suggests that using IVUS during left main PCI with DES can improve chances of survival by almost 10 per cent over three years. Another study points to reductions in one-year MACE and definite stent thrombosis among DES-implanted patients who also underwent IVUS imaging to optimise stent placement. American Heart Association in 2004, after going through various studies involving IVUS, concluded, “These studies indicate that serial ultrasound studies have the potential to assess progression and regression in relatively small numbers of patients and over a relatively short time period -- certainly compared with angiography, which typically shows no change, and compared with clinical endpoints, which typically require large numbers of patients followed for long periods of time.”

However, another study which analysed the clinical impact of IVUS on stent deployment, using bare-metal stents, indicated the contrary. These investigators retrospectively evaluated the clinical outcomes of 50 stent cases where IVUS was used, and compared the subsequent clinical events with 50 randomly selected cases wherein IVUS was not employed. Clinical outcomes tended to favour the group not receiving intravascular ultrasound guidance. This led the authors to conclude that the added expense of intravascular ultrasound does not appear to be warranted.“This is a conclusion many will accept at face-value, as it is consistent with perhaps the most-commonly prevailing attitude towards the use of IVUS,” points out The Journal of Invasive Cardiology in June 2004 issue.

Another article, ‘Clinical Outcomes Following IVUS-Guided Stent Deployment in a Community Hospital’, which appeared in the same journal in the same issue, states, “IVUS-guided stent deployment does not appear to reduce the need for clinically-driven repeat TVR at six months or MACE. The added expense of IVUS does not appear to be warranted.”

  When IVUS? Why IVUS?
Pre PCI Decide PCI Strategy and Sizing Basic Image Interpretation :Vessel reference and % stenosisLength of the lesionPlaque composition
Angiographically intermediate lesions To evaluate if a stenosis is significant - MLA <4 mm2 (6 mm2 in Left Main)
Left Main disease To objectively quantify the stenosis and ensure appropriate stent apposition
Bifurcation To evaluate access to a branch and the need for branch protection based on bifurcation morphology
Unusual lesion morphology To clarify angiographic ambiguity (complex plaque, calcium)
Advanced Technologies To assess and quantify plaque composition within arterial wall
Post PCI Re-intervention
ISR
Stent Results Evaluation
To accurately assess previous treatment Stent and restenotic tissue assessment
To verify final lumen, expansion,

Costs & Benefits

IVUS Volulmetric Analysis

The complications associated with IVUS evaluation are the same as for diagnostic angiography. Experts say that a carefully performed procedure is safe and should not have a morbidity of more than 0.5 per cent. “There should be no mortality associated with it,” says Dr Kaul.

The cost to the patient for IVUS may range from Rs 15,000 to Rs 20,000 per procedure in RTIICS to Rs 30,000 to Rs 50,000 in the rest of the country. The cost is usually added to the cost of the angioplasty charges. The IVUS machine which records and stores and interprets the images costs anything from Rs 60 lakh to Rs 90 lakh. The cost of the disposable IVUS catheter is around Rs 20,000 to Rs 50,000 per piece. It is usually a single-use catheter.

Despite its multiple merits and the fact that it was introduced 15 years back, its acceptance has not been too high. Experts point out that even hospitals having IVUS use it sparingly on 20 to 25 per cent of patients who truly require it. Factors such as additional cost to hospital and patient, lack of reimbursement by insurance companies and absence of training and exposure to interpretation of IVUS images are the deterrents to its popularity. “It adds to the procedure time and leads to use of multiple stents sometimes as we are able to see much more in the artery,” says an expert.

“It is an expensive equipment which adds to the cost of angioplasty. There is always a hesitation in using a procedure, which is not an absolute must and adds to the cost and time. It is more often used during live demonstration courses and in some multi centric research protocols than as a regular procedure by most hospitals,” says Dr Kaul.

Lack of sufficient data on whether IVUS-guided angioplasty is better than routine angioplasty and also the fact that only 10 to 15 per cent of angioplasty patients require IVUS have deterred hospitals from purchasing IVUS. But are patients given an option to choose it as insurance companies don’t reimburse it? “Patients will be advised by treating cardiologists regarding the requirement of it, depending upon angio findings. We don't base our decisions on whether insurance companies or someone else would reimburse it or not. We do it only if required for the patient,” says Dr Kumar.

A Threat from OCT?

Analysts opine that the future of this technology is definitely bright, especially the combination of IVUS with pressure wire. About the combination, Dr Kaul says, “This combines detailed anatomic visualisation combined with flow determinations across the blocks to calculate the fractional flow reserve (FFR) and makes decision making more scientific. Combining anatomy and physiology during the study is an ideal combination.” However, others counter that only in some patients may both modalities be used, not in all. According to Dr Bhat, coronary flow reserve will possibly increase IVUS usage as coronary flow reserve is more important than IVUS.

But the big question is whether IVUS will be used as a regular imaging tool in India for patients who require it or will it continue to be an essential tool for research, especially for the evolution of newer generation coronary stents and for the evaluation of the effect of various lipid lowering drugs on coronary blockages? Opinion is divided.

The future of IVUS is thwarted by another emerging competitive technology called Optical Computed Tomography (OCT), which is expected to arrive in India in the next six months. “OCT gives better picture, better delineation of thrombus than IVUS,” says Dr Singh. “Time will tell us which technology is going to stay between OCT and IVUS. At present, IVUS is much more acceptable,” says Dr Kaul. But Dr Kumar counters this saying, “OCT is useful to image only superficial-endothelial structures and can't image deeper within arterial wall structures and contents.”

Definitely more scientific data, reduction of cost, expertise in interpreting IVUS images and reimbursement by insurance companies would make the benefits of IVUS reach more patients, until something better comes up.

rita.dutta@expressindia.com

 

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