Editor's note: You can read additional research news on NIRS from December 12, 2014.

Disclosure: Dr. Artis reports no conflicts of interest regarding the content herein.

Dr. Andre Artis can be contacted at heart@netnitco.net.

What is NIRS?

In a single coronary pullback, the TVC Imaging System (Infraredx, Inc.) allows a physician to detect lipid core plaque which may be vulnerable to rupture and cause subsequent cardiovascular events. The TVC Imaging System improves on intravascular imaging by presenting an easy-to-read map of cholesterol throughout the vessel. This map is called a chemogram and it is made possible by near-infrared spectroscopy (NIRS). The NIRS chemogram enables a physician to quickly localize coronary plaque and immediately detect whether the plaque is lipid-rich and at an increased risk of causing an event, shown as yellow, or fibrotic and unlikely to trigger a sudden rupture, shown as red. The combination of NIRS with intravascular ultrasound (IVUS) in one catheter represents an exciting development in advancing the understanding of predicting and preventing cardiovascular events. 

Study introduction

The Methodist Hospitals of Gary and Merrillville (Indiana) are participating in the Lipid-Rich Plaque (LRP) Study, a prospective, global study designed to evaluate the relationship between coronary plaques containing lipid (or fat) and subsequent cardiovascular events over a two-year period, using intravascular NIRS. The LRP Study will use NIRS-IVUS to examine patients presenting with acute coronary syndrome and/or angiographically determined coronary artery disease. Following successful treatment of the culprit lesion, the investigator will employ the TVC Imaging System to perform NIRS-IVUS intracoronary imaging of the patient’s non-culprit epicardial vessels. For patients enrolled in the LRP Study, the investigator is blinded to the NIRS lipid core data for all non-culprit vessels imaged (the culprit vessel can undergo NIRS imaging during the procedure at the physician’s discretion, but it is not required as part of the LRP Study). The physician has access to all IVUS imaging data for enrolled patients. After the index treatment and NIRS imaging is performed, enrolled patients will be followed for 24 months to monitor the occurrence of subsequent coronary events. The following case of a patient enrolled in the LRP Study is an example of how NIRS imaging can be useful to assess a lesion before stenting and confirm successful results after the procedure. 

Case

A 57-year-old male presented to the emergency department (ED) with complaints of worsening chest pain, cough, and shortness of breath over the previous day. The patient was a former

smoker with a family history of coronary artery disease. His medical history included diabetes, hypertension, and asthma, with marked limitations in ordinary physical activity. 

At the ED, the patient was admitted with a diagnosis of unstable angina. Upon admission, the troponin levels were negative, and the lipid panel revealed normal results, including an HDL level of 60mg/dl. The electrocardiogram (ECG) showed normal sinus rhythm without ischemic changes.  The patient history included a negative stress test conducted two months prior.  

Cardiac angiography revealed an 80% stenosis in the mid right coronary artery (RCA) (Figure 1). The TVC Imaging System was used to evaluate the composition and structure of the RCA. With NIRS-IVUS imaging, a short (22.92mm) segment of the mid-RCA was determined to have two lipid core plaques located close together (Figure 2). The maximum lipid core burden index within a 4-millimeter segment (max4mmLCBI) provides a quantitative summary of the total lipid core plaque detected in a segment of interest. In this case, the two lipid core plaques measured had a max4mmLCBI of 288 and 277, respectively (for comparison, a large lipid core plaque is defined as a max4mmLCBI≥500). Another important characteristic of a lesion is the degree of stenosis calculated from the IVUS information. The tightest measured stenosis had a lumen area of 1.64mm² (Figure 3). The decision to intervene on the lesion was based on current treatment guidelines and findings from the PROSPECT study¹, which demonstrated that segments with a minimum lumen area of 4.0mm² or less were at increased risk of serious coronary events.

A 2.75 x 26mm bare metal stent was selected to cover the stenosis and both lipid segments, “stenting red to red” to ensure stent margins spanned healthy vessel to healthy vessel. Post procedure, measuring the stented artery revealed a lumen area of 6.88mm² with minimal remaining lipid (Figure 4). This procedure resulted in a 0% residual stenosis (Figure 5).

At the Methodist Hospitals, patients are screened to determine whether they meet the LRP Study inclusion and exclusion criteria. Qualifying patients are counseled on the study objectives, requirements and scope, and invited to participate. In the case of the patient described above, after treatment of the culprit lesion was performed, the TVC Imaging System was used to evaluate 89.7mm of the left anterior descending artery (LAD) and 59.95mm of the left circumflex artery (LCX). These additional NIRS scans were blinded as per the LRP study protocol and no subsequent intervention was indicated. A loading dose of aspirin and ticagrelor (Brilinta, AstraZeneca) was started, and no post-procedure complications were observed. 

Reference

1. Stone GW, Maehara A, Lansky AJ, de Bruyne B, Cristea E, Mintz GS, et al. A prospective natural-history study of coronary atherosclerosis. N Engl J Med. 2011 Jan 20; 364(3): 226-235. doi: 10.1056/NEJMoa1002358.

Use of NIRS with the TVC Imaging System at Methodist Hospitals of Gary and Merrillville in Indiana

Can you tell us about your practice and cath lab?

We have a Methodist system with two hospitals. We have six cath labs, two at one campus and four at the other campus. Our staff goes back and forth between the campuses. We have one electrophysiology (EP) room and five cath rooms where we do coronary, peripheral, and endovascular interventions. I have been in practice here for 25 years.

How long have you been using near-infrared spectroscopy (NIRS)?

We started using the TVC Imaging System in 2013, about six months before we entered the Lipid-Rich Plaque (LRP) Study, which was in May of this year.

What do you like about using NIRS?

The TVC Imaging System uses NIRS and intravascular ultrasound to provide information that no other imaging modality can — it gives us the amount and location of lipid content in the vessel, adding a completely different dynamic to vessel imaging. With other imaging systems, you are able to see if there is plaque or calcium present, and then you try to determine whether it is soft or hard, but with NIRS, we are actually able to see the fat content, exactly where it is located, and how much of the vessel is involved. When looking at the angiogram, we often see what looks like a haziness or a defect in a vessel, even sometimes in an otherwise completely normal-looking vessel. Imaging that same vessel with NIRS shows us a whole new world. NIRS has been instructive for us, particularly in detecting vulnerable plaque — lipid-rich plaque, the rupture of which is believed to cause coronary events.^1-3 Patients may only have 50% lesions, but can still be at risk for developing acute coronary events in the short, mid, and long term. That is the new paradigm that has been opened up for us with the information from the TVC Imaging System.

How many patients have you enrolled into the LRP study so far? 

Thus far, 40 patients with acute coronary syndrome have been enrolled, and I would describe the study patients as very real world. 

Since enrolling in the study, have any patients returned for revascularization?

I have had two that have returned, and both of them have been in the past month. One of the patients was particularly interesting. After viewing the initial angiogram, we stented a segment of the vessel that was problematic. The segment distal to that had some irregularity, but it did not appear to have significant stenosis. We proceeded to place a stent in the stenotic region, the angiographic result looked good, and we took the patient into a holding room, where he began having chest pain within 30 minutes of the procedure being completed. We took him back to the cath lab, performed NIRS and saw that the stent edge had been placed right in the middle of a vulnerable plaque. That plaque had since ruptured and caused downstream thrombus in the same vessel. Imaging the vessel with NIRS allowed us to determine the extent of the plaque and ensure that we covered the entire segment of diseased vessel with another stent. This is a good example of the limitations of angiography — where the vessel segment with the vulnerable plaque had clear flow and did not appear severely stenotic, despite being problematic and leading to poor treatment outcomes.   

How did the use of NIRS influence the patient you describe in your case report, the 57-year-old male with an 80% stenosis in the right coronary artery?

In this case, we used NIRS prior to stenting, and this patient actually had two lipid-rich areas within close proximity in the right coronary. Even though one of the areas was not a significant stenosis by angiography, NIRS showed a pool of lipid-rich plaque. One lipid area was located in an area with a significant stenosis and one lipid area was not. Because NIRS revealed the plaques to be near each other, we chose to modify the stent we selected, in order to cover both lipid segments.

Are you limiting your use of NIRS-IVUS to only LRP Study patients?

No. The LRP Study excludes patients who have had bypass surgery and patients who have low ejection fractions. We have a number of patients in those populations with coronary disease where it is important to have lipid information. I use the TVC Imaging System for all my interventional patients, regardless of whether they are in the study or not. Sometimes I will image patients because it looks as if there may be a problematic vessel; for example, in severe cardiomyopathy patients, even though the vessels look like they are fairly normal, I will image them with NIRS. Our primary use of NIRS, however, is for interventional patients. We use NIRS prior to stenting for many of our LRP Study patients and I use it post-stenting in all my patients. The LRP Study does not require the use of NIRS before stenting in the culprit vessel; this study is collecting data only from non-culprit segments of the vessels in order to track the occurrence of future coronary events. The use of NIRS in the culprit vessel is left to the discretion of the operator.

Can you talk more about what happens when you stent a vulnerable plaque?

Imagine that if you land the stent itself in the middle of a lipid pool, as that stent puts pressure on the vessel, the plaque then is extruded from the edge of the stent downstream. However, if you are able to cover the entire area of vulnerable plaque, then you avoid rupturing the plaque and keep it from moving further downstream by trapping it. This process is also helped by the presence of anticoagulants during the procedure. The entire plaque volume is not sent downstream, as it is in a patient where the stent edge lands in the center of a lipid pool. We usually put a stent directly over the plaque and extend the stent past where we would expect the vulnerable plaque to be. We cover the plaque completely with the stent — not just to the edge of the plaque but also a short margin beyond, to avoid disrupting the plaque.

Any final thoughts?

NIRS has enhanced how we look at vessels when we do percutaneous coronary intervention. It allows us to consider more than just a particular stenotic segment as the only part of the vessel that is diseased. NIRS is the only imaging tool that allows us to visualize the entire vessel and its plaque composition, not just the focal area of stenosis that is visible by angiography. n

References

1. Virmani R, Burke AP, Farb A, Kolodgie FD. Pathology of the vulnerable plaque. J Am Coll Cardiol. 2006 Apr 18; 47(8 Suppl): C13–C18.
2. Madder RD, Goldstein JA, Madden SP, Puri R, Wolski K, Hendricks M, et al. Detection by near-infrared spectroscopy of large lipid core plaques at culprit sites in patients with acute ST-segment elevation myocardial infarction. JACC Cardiovasc Interv. 2013 Aug; 6(8): 838-846. 
3. Madder RD, Husaini M, Davis AT, et al. TCT-398: Identification of Vulnerable Patients by Intracoronary Near-infrared Spectroscopy. J Am Coll Cardiol. 2014;64(11_S).