Physiological and intravascular ultrasound assessment of an ambiguous left main coronary artery stenosis

Intravascular Imaging versus Physiological Assessment versus Biomechanics-Which Is a Better Guide for Coronary Revascularization

Today, coronary artery disease (CAD) continues to be a prominent cause of death worldwide. A reliable assessment of coronary stenosis represents a prerequisite for the appropriate management of CAD. Nevertheless, there are still major challenges pertaining to some limitations of current imaging and functional diagnostic modalities. The present review summarizes the current data on invasive functional and intracoronary imaging assessment using optical coherence tomography (OCT), and intravascular ultrasound (IVUS). Amongst the functional parameters-on top of fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR)-we point to novel angiography-based measures such as quantitative flow ratio (QFR), vessel fractional flow reserve (vFFR), angiography-derived fractional flow reserve (FFRangio), and computed tomography-derived flow fractional reserve (FFR-CT), as well as hybrid approaches focusing on optical flow ratio (OFR), computational fluid dynamics and attempts to quantify the forces exaggerated by blood on the coronary plaque and vessel wall.

Imaging during percutaneous coronary intervention for optimizing outcomes

Angiography is the current gold standard for imaging during percutaneous coronary interventions but has significant limitations. Catheter-based intravascular imaging techniques such as intravascular ultrasound and the more recent optical coherence tomography have the potential to overcome these limitations and thus optimize clinical outcomes. In this update, we discussed the current applications of the available imaging techniques, existing evidence, continuing unmet needs, and potential areas for further research.

Utility of intracoronary imaging in the cardiac catheterization laboratory: comprehensive evaluation with intravascular ultrasound and optical coherence tomography

BACKGROUND

Intracoronary imaging is an important tool for guiding decision making in the cardiac catheterization laboratory.

SOURCES OF DATA

We have reviewed the latest available evidence in the field to highlight the various potential benefits of intravascular imaging.

AREAS OF AGREEMENT

Coronary angiography has been considered the gold standard test to appropriately diagnose and manage patients with coronary artery disease, but it has the inherent limitation of being a 2-dimensional x-ray lumenogram of a complex 3-dimensional vascular structure.

AREAS OF CONTROVERSY

There is well-established inter- and intra-observer variability in reporting coronary angiograms leading to potential variability in various management strategies. Intracoronary imaging improves the diagnostic accuracy while optimizing the results of an intervention. Utilization of intracoronary imaging modalities in routine practice however remains low worldwide. Increased costs, resources, time and expertise have been cited as explanations for low incorporation of these techniques.

GROWING POINTS

Intracoronary imaging supplements and enhances an operator's decision-making ability based on detailed and objective lesion assessment rather than a subjective visual estimation. The benefits of intravascular imaging are becoming more profound as the complexity of cases suitable for revascularization increases.

AREAS TIMELY FOR DEVELOPING RESEARCH

While the clinical benefits of intravascular ultrasound have been well validated, optical coherence tomography in comparison is a newer technology, with robust clinical trials assessing its clinical benefit are underway.

Left main coronary artery stenosis: severity evaluation and implications for management

INTRODUCTION

The significant stenosis of the left main coronary artery is associated with poor outcomes and is considered a strong indication for revascularization. However, deciding whether the stenosis is significant can sometimes be challenging, especially when the degree of stenosis is intermediate, and can necessitate additional tests and imaging modalities. Areas covered: We did a literature search using keywords like 'left main', 'imaging', 'intravascular ultrasound', 'fractional flow reserve', 'computed tomographic angiography' and 'magnetic resonance imaging'. The most commonly used methods for better characterizing intermediate left main coronary stenoses are intravascular ultrasound and fractional flow reserve, while optical coherence tomography is the newer technique that provides better images, but for which not as much data is available. The noninvasive techniques are coronary computed tomographic angiography and, to a lesser degree, coronary magnetic resonance imaging. Expert commentary: Accurately determining the severity of left main coronary stenosis can mean the difference between a major intervention and conservative therapy. The reviewed newer imaging modalities give us greater confidence that patients with left main stenosis are assigned to the right treatment modality.

Long-term outcome of intravascular ultrasound application in patients with moderate coronary lesions and grey-zone fractional flow reserve

OBJECTIVE

This study aimed to assess the long-term outcome of intravascular ultrasound (IVUS) application in patients with a fractional flow reserve (FFR) of 0.75-0.80.

BACKGROUND

Scientifically evaluating anatomical structures is vital because structure influences both physiological function and decision-making in moderate coronary lesions, especially for those with an FFR of 0.75-0.80.

MATERIALS AND METHODS

Patients (n=128) were divided into three groups based on treatment: the drug control group (n=40), the IVUS-percutaneous coronary intervention (PCI) group (n=40) and the IVUS-drug group (n=48). A PCI was performed when a patient had a minimum lumen area less than 4 mm(2) and a plaque burden of 70% or greater. Major adverse clinical events were defined as cardiac death, nonfatal myocardial infarction, target vessel revascularization, including PCI or coronary artery bypass grafting, and unstable angina, all of which were also evaluated during follow-up.

RESULTS

Kaplan-Meier curves indicated that the incidence of major adverse clinical events did not differ between the IVUS-PCI and IVUS-drug groups (5 vs. 6.3%, P=0.810), but the levels in both of these groups significantly decreased compared with the drug control group (5 vs. 22.5%, P=0.024, and 6.5 vs. 22.5%, P=0.026, respectively).

CONCLUSION

The long-term outcome of the application of IVUS in patients with a grey-zone FFR of 0.75-0.80 was superior to that of patients who were treated only with drugs without IVUS measurement. Patients with a grey-zone FFR should receive an individualized treatment strategy according to their IVUS parameters. Patients with the same FFR values may require different treatment strategies.

Percutaneous revascularization of left main: role of imaging, techniques, and adjunct pharmacology

Refinement of interventional techniques, adjunctive pharmacological therapy, and the introduction of drug-eluting stents have fostered new interest for the percutaneous treatment of unprotected left main coronary artery (ULMCA) stenosis. Several observational registries, some randomized trials and several meta-analyses have consistently shown no difference in mortality and myocardial infarction between percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG) surgery in patients with ULMCA stenosis, but a higher rate of target vessel revascularization in patients treated with PCI. As a consequence, PCI of ULMCA stenosis has been upgraded to class IIa or IIb indication in the current European or American practice guidelines. However, several critical issues should be properly addressed when pursuing a percutaneous strategy for the treatment of ULMCA stenosis, such as the use of IVUS for procedural guidance, assessment of disease location, optimal technique for distal ULMCA stenosis, risk of stent thrombosis, optimal duration of dual antiplatelet therapy, and the most appropriate strategy for post-procedure follow up. Multidisciplinary team approach remains essential to provide a balanced information to the patient and to offer the beast treatment option.

Intravascular Ultrasound Classification of Plaque Distribution in Left Main Coronary Artery Bifurcations

Background— Angiographic classifications of the location and severity of disease in the main vessel and side branch of coronary artery bifurcations have been proposed and applied to distal left main coronary artery (LMCA) bifurcation.

Methods and Results— We reviewed 140 angiograms of distal LMCA and ostial left anterior descending (LAD) and left circumflex (LCX) artery lesions with preintervention intravascular ultrasound (IVUS) of both the LAD and LCX arteries as well as the LMCA. Of 140 patients, 92.9% had at least 1 cross section with ≥40% IVUS plaque burden versus 57.2% of patients with an angiographic diameter stenosis ≥50%. Contrary to angiographic classifications, IVUS showed that bifurcation disease was rarely focal and that both sides of the flow divider were always disease-free. Continuous plaque from the LMCA into the proximal LAD artery was seen in 90%, from the LMCA into the LCX artery in 66.4%, and from the LMCA into both the LAD and LCX arteries in 62%. Plaque localized to either the LAD or LCX ostium and not involving the distal LMCA was seen in only 9.3% of LAD arteries and 17.1% of LCX arteries. Plaque distribution was not influenced by the LAD/LCX angiographic angle, lesion severity, LMCA length, or remodeling. We proposed an IVUS classification for bifurcation lesions illustrating longitudinal and circumferential spatial plaque distribution.

Conclusions— Angiographic classification of LMCA bifurcation lesions is rarely accurate. IVUS shows that the carina is always spared and that the disease is diffuse rather than focal.

Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00180466.

Assessment of intermediate severity coronary lesions in the catheterization laboratory

The management of intermediate coronary lesions, defined by a diameter stenosis of 40% to 70%, continues to be a therapeutic dilemma for cardiologists. The 2-dimensional representation of the arterial lesion provided by angiography is limited in distinguishing intermediate lesions that require stenting from those that simply need appropriate medical therapy. In the era of drug-eluting stents, some might propose that stenting all intermediate coronary lesions is an appropriate solution. However, the possibility of procedural complications such as coronary dissection, no reflow phenomenon, in-stent restenosis, and stent thrombosis requires accurate stratification of patients with intermediate coronary lesions to appropriate therapy. Intravascular ultrasound (IVUS) and fractional flow reserve index (FFR) provide anatomic and functional information that can be used in the catheterization laboratory to designate patients to the most appropriate therapy. The purpose of this review is to discuss the critical information obtained from IVUS and FFR in guiding treatment of patients with intermediate coronary lesions. In addition, the importance of IVUS and FFR in the management of patients with serial stenosis, bifurcation lesions, left main disease, saphenous vein graft disease, and acute coronary syndrome will be discussed.

Characterizing momentum change and viscous loss of a hemodynamic endpoint in assessment of coronary lesions

Myocardial fractional flow reserve (FFR(myo)) and coronary flow reserve (CFR), measured with guidewire, and quantitative angiography (QA) are widely used in combination to distinguish ischemic from non-ischemic coronary stenoses. Recent studies have shown that simultaneous measurements of FFR(myo) and CFR are recommended to dissociate conduit epicardial coronary stenoses from distal resistance microvascular disease. In this study, a more comprehensive diagnostic parameter, named as lesion flow coefficient, c, is proposed. The coefficient, c, which accounts for mean pressure drop, Delta p, mean coronary flow, Q, and percentage area stenosis, can be used to assess the hemodynamic severity of a coronary artery stenoses. Importantly, the contribution of viscous loss and loss due to momentum change for several lesion sizes can be distinguished using c. FFR(myo), CFR and c were calculated for pre-angioplasty, intermediate and post-angioplasty epicardial lesions, without microvascular disease. While hyperemic c decreased from 0.65 for pre-angioplasty to 0.48 for post-angioplasty lesion with guidewire of size 0.35 mm, FFR(myo) increased from 0.52 to 0.87, and CFR increased from 1.72 to 3.45, respectively. Thus, reduced loss produced by momentum change due to lower percentage area stenosis decreased c. For post-angioplasty lesion, c decreased from 0.55 to 0.48 with the insertion of guidewire. Hence, increased viscous loss due to the presence of guidewire decreased c compared with a lesion without guidewire. Further, c showed a linear relationship with FFR(myo), CFR and percentage area stenosis for pre-angioplasty, intermediate and post-angioplasty lesion. These baseline values of c were developed from fluid dynamics fundamentals for focal lesions, and provided a single hemodynamic endpoint to evaluate coronary stenosis severity.

Long-Term Outcome After Surgical Left Main Coronary Angioplasty

BACKGROUND

Direct surgical angioplasty of the left main coronary artery is aimed to restore a more physiologic flow of the left coronary artery compared with conventional coronary artery bypass graft surgery and allows subsequent percutaneous coronary interventions of more distal coronary lesions if necessary. Relatively little data are known about long-term outcome in these patients.

METHODS

In 1996 and 1997, in 31 patients in our hospital, surgical angioplasty of the left main coronary artery was attempted. The left main coronary artery was approached in the anterior way. Follow-up was performed during 8 years and concluded by invasive anatomic and functional evaluation of the left main coronary artery.

RESULTS

In 4 of these patients, the procedure was converted to conventional coronary artery bypass graft surgery owing to calcification of the left main coronary artery. Of the remaining 27 patients, 3 patients died in the perioperative period and 4 other patients died during follow-up. In 18 of the 20 survivors, coronary angiography was performed after 8 years, and the left main coronary artery was also evaluated by intravascular ultrasound and coronary pressure-based fractional flow reserve measurement. At angiography and intravascular ultrasound, a dilated funnel-shaped left main coronary artery was seen in all of these patients. In 1 patient, a hemodynamically significant left main coronary artery stenosis was present (fractional flow reserve < 0.75), and in this patient coronary artery bypass graft surgery was performed.

CONCLUSIONS

Although the total mortality of 23% was somewhat disappointing, the majority of the survivors had an excellent anatomic and physiologic result after direct surgical angioplasty of the left main coronary artery. Therefore, this technique deserves a place in the surgical armamentarium.

Coronary pressure measurement to determine treatment strategy for equivocal left main coronary artery lesions

It is often hard to select a treatment strategy for equivocal left main coronary artery (LMCA) disease. We investigated the usefulness of coronary pressure (CP) measurement for determining the treatment strategy in intermediate LMCA disease. We measured CP in 15 consecutive patients with equivocal LMCA disease (age 67.6 +/- 7.5 years, 14 males). Myocardial fractional flow reserve (FFRmyo) was obtained as the ratio of CP distal to the lesion/aortic pressure under maximal coronary dilation. Patients with FFRmyo > or = 0.75 and <0.75 received medical therapy and coronary artery bypass grafting (CABG), respectively, and were followed up for 32.5 +/- 9.7 (20-47) months. Eight patients received medical therapy and 7 patients underwent CABG in accordance with the FFRmyo criteria noted above. FFRmyo of the LMCA was 0.91 +/- 0.01 and 0.61 +/- 0.03 in patients who received medical and surgical therapy, respectively. Neither reference vessel diameter, minimal lumen diameter, nor percent diameter stenosis was significantly different between patients who received medical and surgical therapy. During the follow-up period, no patients with medical therapy showed symptoms due to the LMCA lesion. Similarly, 5 of 7 patients with CABG showed improvement of symptoms and the remaining 2 patients were hospitalized with congestive heart failure. No cardiac death was recorded in the patients with medical or surgical therapy. In conclusion, the present results clearly demonstrated that CP is clinically useful for determining the treatment strategy for equivocal LMCA lesions but coronary angiography is not.

Physiologic assessment of jailed side branch lesions using fractional flow reserve

OBJECTIVES

This study was performed to evaluate the feasibility of the physiologic assessment of jailed side branches using fractional flow reserve (FFR) and to compare the measured FFR with the stenosis severity assessed by quantitative coronary angiography (QCA).

BACKGROUND

It is not well-known which side branches should be treated after stent implantation at main branches and how to assess the functional significance of these lesions.

METHODS

Ninety-seven jailed side branch lesions (vessel size > 2.0 mm, percent stenosis > 50% by visual estimation) after stent implantation at main branches were consecutively enrolled. The FFR was measured using a pressure wire at 5 mm distal and proximal to the ostial lesion of the jailed side branch.

RESULTS

The FFR measurement was successful in 94 lesions. Mean FFRs were 0.94 +/- 0.04 and 0.85 +/- 0.11 at the main branches and jailed side branches, respectively. There was a negative correlation between the percent stenosis and FFR (r = -0.41, p < 0.001). However, no lesion with < 75% stenosis had FFR < 0.75. Among 73 lesions with > or = 75% stenosis, only 20 lesions were functionally significant.

CONCLUSIONS

The FFR measurement in jailed side branch lesions is both safe and feasible. Quantitative coronary angiography is unreliable in the assessment of the functional severity of jailed side branch lesions, and measurement of FFR suggests that most of these lesions do not have functional significance.

Intravascular ultrasound-guided treatment for angiographically indeterminate left main coronary artery disease: a long-term follow-up study

OBJECTIVES

The purpose of this study was to evaluate the efficacy of an intravascular ultrasound (IVUS)-guided strategy for patients with angiographically indeterminate left main coronary artery (LMCA) disease.

BACKGROUND

The assessment of LMCA lesions using coronary angiography is often challenging; IVUS provides useful information for assessment of coronary disease.

METHODS

Intravascular ultrasound was performed on 121 patients with angiographically normal LMCAs to determine the lower range of normal minimum lumen area (MLA), defined as the mean - 2 SD. We conducted IVUS studies on 214 patients with angiographically indeterminate LMCA lesions, and deferral of revascularization was recommended when the MLA was larger than this predetermined value.

RESULTS

The lower range of normal LMCA MLA was 7.5 mm(2). Of the patients with angiographically indeterminate LMCAs, 83 (38.8%) had an MLA <7.5 mm(2), and 131 (61.2%) an MLA > or =7.5 mm(2). Left main coronary artery revascularization was performed in 85.5% (71 of 83) of patients with an MLA <7.5 mm(2) and deferred in 86.9% (114 of 131) of patients with an MLA > or =7.5 mm(2). Long-term follow-up (mean 3.3 +/- 2.0 years) showed no significant difference in major adverse cardiac events (target vessel revascularization, acute myocardial infarction, and death) between patients with an MLA <7.5 mm(2) who underwent revascularization and those with an MLA > or =7.5 mm(2) deferred for revascularization (p = 0.28). Based on outcome, the best cut-off MLA by receiver operating characteristic was 9.6 mm(2). Multivariate predictors of cardiac events were age, smoking, and number of non-LMCA vessels diseased.

CONCLUSIONS

Intravascular ultrasound is an accurate method to assess angiographically indeterminate lesions of the LMCA. Furthermore, deferring revascularization for patients with a minimum lumen area > or =7.5 mm(2) appears to be safe.