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Ann Thorac Surg 1997;64:375-379
© 1997 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Intracoronary Ultrasound-Guided CABG in Patients With Angiographically Noncritical Lesions

Cardiovascular Surgery Associates, St. Thomas Hospital, Nashville, Tennessee

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Coronary angiography is used to determine the severity of coronary artery disease; however, in a small group of patients, clinically significant angina and physiologic tests indicative of myocardial ischemia do not correlate with angiographically demonstrable critical coronary artery disease. In these patients intracoronary ultrasound may demonstrate the true severity of lesions.

Methods. Eight patients with angina and positive stress testing but without angiographically critical left main or left anterior descending artery stenoses were retrospectively identified. After intracoronary ultrasonic demonstration of critical left main or left anterior descending artery lesions, coronary artery bypass grafting was performed. Follow-up evaluation of clinical status and repeat stress testing were carried out.

Results. Intracoronary ultrasound demonstrated critical left main (n = 4) or proximal left anterior descending artery (n = 7) stenoses in all patients. Severity of angiographic versus intracoronary ultrasound-documented stenoses was (mean ± standard error of the mean) 10% ± 10% versus 65% ± 10% for left main lesions and 30% ± 5% versus 75% ± 5% for left anterior descending artery lesions. After coronary artery bypass grafting all patients had decreased angina and normalization of stress testing.

Conclusions. In patients with clinical presentations indicative of significant coronary artery disease but with angiographically noncritical lesions, intracoronary ultrasound can accurately assess the severity of stenoses. Coronary artery bypass grafting guided by intracoronary ultrasonic findings successfully treats myocardial ischemia in these patients.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
See also page 379.

Coronary angiography has been accepted as the gold standard for the delineation of coronary artery stenoses. Despite the ability of angiography to accurately assess coronary lesions, it is well known that angiography may underestimate the severity of eccentric lesions as well as lesions in specific locations within the coronary circulation (eg, left main [LM] or proximal left anterior descending coronary artery [LAD]) [1, 2]. In addition, there remains a subpopulation of patients with both typical and atypical angina in whom coronary angiography fails to demonstrate either a single "culprit" lesion or a combination of coronary stenoses adequate to explain the clinical presentation [3]. Appropriate therapy for these patients is often further complicated by the demonstration of persistent myocardial ischemia by physiologic testing (eg, treadmill, thallium scintigraphy, stress echocardiography). In this group of patients alternative techniques for the visualization of coronary artery anatomy may be particularly useful.

Intracoronary ultrasound (ICUS) is a technique in which real-time 360-degree tomographic views of cross-sectional coronary artery anatomy can be rapidly obtained via introduction of a small catheter-mounted ultrasound probe into the coronary system. This alternative imaging technique can accurately evaluate all types of coronary lesions and can access virtually the entire epicardial coronary tree. These characteristics obviate some of the shortcomings of coronary angiography and make ICUS a powerful adjunct in the evaluation of coronary artery disease.

To demonstrate the efficacy of surgical revascularization guided by ICUS, coronary bypass grafting (CABG) must be performed based on ICUS results, postoperative resolution of angina must be documented, and preoperative indicators of myocardial ischemia must normalize. In this study we report the clinical results of ICUS-guided surgical revascularization in a group of patients with angina, positive physiologic tests for myocardial ischemia, and nondiagnostic coronary angiography.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
The patients reported in the study were retrospectively identified from all patients referred for CABG from January 1, 1995, to September 1, 1996. During that period patients were identified who met the following inclusion criteria: (1) disabling angina (Canadian angina class) and physiologic testing (treadmill, stress thallium scintigraphy, or stress echocardiography) documenting myocardial ischemia, (2) cardiac catheterization documenting noncritical LM or LAD stenoses (patients were included if circumflex or right coronary artery disease was demonstrated but was not extensive enough to warrant CABG in the absence of LM or LAD stenoses), (3) ICUS documenting critical LM or LAD lesions, (4) CABG based on the ICUS-delineated coronary lesions, and (5) follow-up evaluation including severity of residual angina and repeat physiologic testing documenting the presence or absence of residual myocardial ischemia.

Cardiac catheterization was performed using the Judkins technique with 6F diagnostic coronary catheters. A mean of 6.9 (range, 5 to 8) projections of the left coronary artery were obtained in each patient. The degree of stenosis was assessed by visual estimation of the diameter stenosis by two blinded, independent cardiologists. Angiographically critical lesions were defined as greater than 50% for LM lesions and greater than 70% for non-LM lesions.

Intracoronary ultrasound was performed with a 1.1-mm-diameter 30-MHz imaging catheter (Sonicath; Boston Scientific, Boston MA) and an ultrasound image acquisition system (Hewlett-Packard, Dallas TX). Images were obtained with a pullback technique (0.5 mm/second) from the distal coronary artery through the LM. Patients were fully anticoagulated with heparin, and 200 to 400 mg of intracoronary nitroglycerin was given to prevent coronary spasm. Probe positioning was achieved with an 8F percutaneous transluminal coronary angioplasty guiding catheter and a 0.014-inch coronary guidewire. The images were recorded on inch super-VHS videotape. Images were not used for analysis if significant nonuniform rotational distortion was noted. Intracoronary ultrasound was performed simultaneously with coronary angiography.

Coronary artery bypass grafting was performed with standard cardiopulmonary bypass and myocardial protection techniques. Standard protocols for postoperative care were employed. Results are reported as mean ± standard error of the mean.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Preoperative Characteristics
Eight patients were identified who satisfied inclusion criteria. Mean age was 54.1 years (range, 46 to 59 years). Seven patients were female. All patients had disabling angina preoperatively with a mean angina class of 3.4 (range, 2 to 4). Preoperative physiologic testing documented the presence of myocardial ischemia in all patients. One patient had a positive treadmill test, 6 patients had positive stress thallium scintigraphy, and 1 patient had positive stress echocardiography. Physiologic testing demonstrated apical ischemia in 2 patients, anterior ischemia in 3 patients, inferoseptal ischemia in 1 patient, and inferior ischemia in 1 patient; no regional localization was determined in the patient who underwent a treadmill test.

Coronary Artery Stenoses
By angiography single-vessel coronary artery disease (CAD) was present in 5 patients. Multivessel CAD was present in 3 patients. In no patients were significant LM or LAD lesions documented by angiography. Intracoronary ultrasound demonstrated critical coronary artery stenoses in LM or LAD coronary arteries in all patients. The mean stenosis of LM lesions (n = 4) was 10% ± 10% by angiography and 65% ± 10% by ICUS. The mean stenosis of LAD lesions (n = 7) was 30% ± 5% by angiography and 75% ± 5% by ICUS. The percent stenosis by angiography and ICUS for all lesions in all patients is shown in Table 1. Representative still frames from diagnostic angiography and ICUS for a single patient are shown in Figure 1.

View larger version (141K): [in this window] [in a new window]   Fig 1. . (A) Left anterior oblique view of left coronary system in 1 patient showing no significant left anterior descending artery lesion. (B) Right anterior oblique view of left coronary system in the same patient again demonstrating no significant left anterior descending artery lesion. (C) Intracoronary ultrasonic image obtained at the origin of the left anterior descending artery demonstrating high-grade eccentric lesion with 1.1-mm ultrasound catheter completely filling the coronary lumen. The echolucent area to the right of the catheter is the circumflex coronary artery as it courses away from the left main bifurcation. (D) Intracoronary ultrasonic image obtained of the mid-left anterior descending artery showing essentially normal vascular architecture and the absence of significant stenosis.

Postoperative Physiologic Testing
All patients were followed up at 1 month and the presence of persistent angina was determined. In all patients angina was reduced. Mean angina class was 0.4 (range, 0 to 2). Preoperative and postoperative angina classes for the study group are shown in Figure 2. Repeat physiologic testing was carried out in all patients within 13 months of discharge (range, 2 to 13 months). In all patients repeat physiologic testing demonstrated no residual myocardial ischemia.

View larger version (23K): [in this window] [in a new window]   Fig 2. . Preoperative (PRE) and postoperative (POST) Canadian angina classes for the 8 patients in this study.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

All patients underwent CABG because of significant stenosis of the LM, proximal LAD, or both that were not appreciated angiographically. All of the lesions were identified by ICUS and shown to be highly eccentric. It has been recognized that angiography can underestimate the extent and severity of CAD. Specifically, angiography does not accurately assess eccentric lesions [6]. Figure 3 demonstrates that the angiographically apparent percent stenosis of an eccentric lesion is dependent on the angle of incidence of the x-ray beam. For lesions located in the LM or proximal LAD it may be difficult to achieve the appropriate "camera angle," and this may lead to an underestimation of the lesion severity. This limitation is particularly significant in that it has been estimated that 75% of coronary lesions may be eccentric [6]. Intracoronary ultrasound was developed because of the recognized limitations of angiography. By virtue of the tomographic cross-sectional nature of ICUS images the true severity of eccentric lesions may be more accurately measured and, when ICUS is combined with pull-back techniques, the extent of disease may be assessed. A potential limitation of ICUS is the artifactual enhancement of eccentricity occurring when the ultrasound probe is not orthogonal to the true cross-section of the vessel, resulting in an oblique tomographic image. This situation has been demonstrated not to occur in coronary vessels less than 6 mm in diameter [7]. In addition, should the probe become nonorthogonal with relation to the vessel cross-section, the development of nonuniform rotational distortion occurs; the absence of such distortion allows selection of appropriate images for analysis. Since the introduction of ICUS numerous reports have noted the marked discrepancy between the assessment of CAD by angiography and ICUS, with ICUS consistently demonstrated a greater extent and severity of CAD [7, 8].

View larger version (24K): [in this window] [in a new window]   Fig 3. . Effect of incident x-ray beam direction ( broad arrow) on the apparent percent stenosis during coronary angiography of concentric lesions (A) and eccentric lesions (B).

It is possible that this group of patients could have experienced coronary vasospasm as a cause of myocardial ischemia. Although "pure" coronary vasospasm without significant CAD is a possibility, the results of ICUS demonstrate that each patient had a severe obstructive lesion. In addition, no angiographic coronary artery spasm was noted at the time of ICUS examination, perhaps by virtue of the routine use of intracoronary nitroglycerin before instrumentation.

In conclusion, this report demonstrates that ICUS-guided CABG can provide excellent relief of angina and resolution of myocardial ischemia in appropriately selected patients. We recommend consideration of ICUS imaging of the coronary arteries in patients with angina and objective evidence of myocardial ischemia if standard angiography fails to explain the clinical presentation of the patient.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Presented at the Forty-third Annual Meeting of the Southern Thoracic Surgical Association, Cancun, Mexico, November 7–9, 1996.

Address reprint requests to Dr Pirolo, Cardiovascular Surgery Associates, St. Thomas Hospital, 4230 Harding Rd, Suite 501, Nashville, TN 37205.

^* William C. Alford, MD, Stephen K. Ball, MD, George R. Burrus, MD, William H. Coltharp, MD, David M. Glassford, Jr, MD, Steven J. Hoff, MD, John W. Lea IV, MD, Michael R. Petracek, MD, Thomas D. Starkey, MD, and William S. Stoney, MD.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

1. Waller BF. Anatomy, histology, and pathology of the major epicardial coronary arteries relevant to echocardiographic imaging techniques. J Am Soc Echocardiogr 1989;2:232–52.[Medline]
2. Isner JM, Donaldsen RF. Coronary angiographic and morphologic correlation. In: Waller BF, ed. Cardiac morphology. Philadelphia: Saunders, 1984:571–92.
3. Schwartz JN, Kong Y, Hackel DB, Bartel AG. Comparison of angiographic and postmortem findings in patients with coronary artery disease. Am J Cardiol 1975;36:174–8.[Medline]
4. Ehrlich S, Honye J, Mahon D, Bernstein R, Tobis J. Unrecognized stenosis by angiography documented by intravascular ultrasound imaging. Cathet Cardiovasc Diagn 1991;23(3):198–201.[Medline]
5. White CJ, Ramee SR, Collins TJ, Jain A, Mesa JE. Ambiguous coronary angiography: clinical utility of intravascular ultrasound. Cathet Cardiovasc Diagn 1992;26(3):200–3.[Medline]
6. Waller BF. The eccentric coronary atherosclerotic plaque: morphologic observations and clinical relevance. Clin Cardiol 1989;12(1):14–20.[Medline]
7. Nissen SE, Gurley JC, Booth DC, DeMaria AN. Intravascular ultrasound of the coronary arteries: current applications and future directions. Am J Cardiol 1992;69:18H–29H.[Medline]
8. Nissen SE, Gurley JC, Grines CL, Booth DC, Fischer C, DeMaria AN. Coronary atherosclerosis is frequently present at angiographically normal sites: evidence from intravascular ultrasound in man. Circulation 1990;82(Suppl 3):459.

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): John S. Pirolo Todd A. Shuman Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Pirolo, J. S. Articles by Shuman, T. A. Search for Related Content PubMed PubMed Citation Articles by Pirolo, J. S. Articles by Shuman, T. A. Related Collections Related Article