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CLINICAL RESEARCH: CARDIAC IMAGING

Prevalence of American Heart Association Type VI Carotid Atherosclerotic Lesions Identified by Magnetic Resonance Imaging for Different Levels of Stenosis as Measured by Duplex Ultrasound

Tobias Saam, MD^_*,, Hunter R. Underhill, MD, Baocheng Chu, MD, PhD, Norihide Takaya, MD, PhD, Jianming Cai, MD, PhD, Nayak L. Polissar, PhD, Chun Yuan, PhD and Thomas S. Hatsukami, MD^,_*

^_* Department of Clinical Radiology, University of Munich, Grosshadern Campus, Munich, Germany
Department of Radiology, University of Washington, Seattle, Washington
The Mountain-Whisper-Light Statistical Consulting, Seattle, Washington
VA Puget Sound Health Care System and Department of Surgery, University of Washington, Seattle, Washington.

Manuscript received July 5, 2007; revised manuscript received August 30, 2007, accepted October 15, 2007.

^_* Reprint requests and correspondence: Dr. Thomas S. Hatsukami, VA Puget Sound Health Care System, Surgery and Perioperative Care (112), 1660 South Columbian Way, Seattle, Washington 98108. (Email: tomhat{at}u.washington.edu).

Objectives: Via magnetic resonance imaging (MRI), we sought to determine the prevalence of atherosclerotic American Heart Association type VI lesions (AHA-LT6) (lesions with luminal surface defect, hemorrhage/thrombus, or calcified nodule) in carotid arteries that represented all categories of stenosis as measured by duplex ultrasound.

Background: Arterial stenosis alone has been shown to be a poor predictor of cardiovascular events. Autopsy studies suggest that features associated with AHA-LT6 lesions, rather than the degree of luminal narrowing, characterize the high-risk plaque.

Methods: A total of 192 subjects underwent bilateral carotid artery magnetic resonance imaging (MRI) scans at 1.5T after evaluation with ultrasound to determine stenosis. After excluding arteries with a previous endarterectomy, poor image quality, or missing ultrasound data, there were 175 patients with 260 arteries available for analysis. The AHA lesion type was determined by the consensus opinion of 2 experienced carotid MRI reviewers.

Results: In total, 96 of 260 (37.0%) arteries had 1 location with AHA-LT6. Of the arteries with AHA-LT6, 84.4% had hemorrhage, 45.8% had a ruptured fibrous cap, and 14.6% showed other type of complications. Prevalence of AHA-LT6 was an increasing sequence of 8.1% in the 37 arteries with 1% to 15% stenosis, 21.7% in the 60 arteries with 16% to 49% stenosis, 36.8% in the 114 arteries with 50% to 79% stenosis, and 77.6% in the 49 arteries with 80% to 99% stenosis.

Conclusions: Complicated AHA-LT6 are frequently found in arteries with 50% stenosis. These findings indicate that complex lesions develop in a substantial number of arteries in the absence of high-grade stenosis. Ongoing prospective studies will determine the predictive value of vulnerable plaque features, as visualized by MRI, for risk of subsequent ischemic events.

Abbreviations and Acronyms   3D = 3-dimensional   AHA = American Heart Association   ImQ = image quality   LT = lesion type   MRI = magnetic resonance imaging   NWI = normalized wall index   PD = proton-density   TOF = time-of-flight