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Control/Tracking Number : 04-237-SCMR
Activity :Abstract
Current Date/Time : 9/12/2003 3:59:30 PM

Low Dose Dobutamine Stress 3D Tagged and First-Pass Contrast-enhanced Magnetic Resonance Imaging for Regional Detection of Stunned Myocardium

Izlem Izbudak, MD¹, Walter G. O'Dell, PhD², Luciano Amado, MD¹, Raymond C. Boston, PhD³, Dara L. Kraitchman, VMD, PhD¹.
¹Radiology, Johns Hopkins University, Baltimore, MD, USA, ²Radiology, University of Rochester, Rochester, NY, USA, ³University of Pennsylvania, Kennett Square, PA, USA.

Introduction: The differentiation of reversibly injured, i.e., stunned, myocardium from irreversibly injured myocardium is important for driving clinical therapy.

Purpose: A canine model of transient ischemia was used to investigate the role of low dose dobutamine stress (LDDS) tagged and perfusion MRI for the detection of stunned myocardium and recovery at 1 week.

Methods: Five mongrel dogs underwent a 20 minute coronary artery balloon occlusion followed by reperfusion to create myocardial stunning. Three-dimensional tagged MRI (fast, breath-hold, segmented k-space, ECG-gated gradient echo acquisition) was performed at rest and during 5 ug/kg/min dobutamine stress at one week before (baseline), ~1hr after, and one week after transient ischemia (recovery) on a 1.5T MR scanner. Short-axis and rotating long-axis tagged images were obtained spanning the left ventricle. The tag lines detection and tracking and 3D circumferential strain in the midwall were calculated in 12 circumferential segments at 8 anatomic levels using custom software. Myocardial tissue at risk of stunning (S) was identified based on <0.1 ml/g/min microsphere blood flow during occlusion and compared to remote (R) tissue. Early after reperfusion, 248 S segments and 424 R segments were identified for statistical analysis. A linear regression analysis of strain versus time yielded systolic strain rate (SSR) comparing the same S and R segments at baseline and recovery. First-pass CE MRI (saturation recovery fast gradient echo EPI hybrid sequence) was performed in the 4-6 short-axis planes after a 0.05 mmol/kg iv bolus of Gd-DTPA. TTC staining was performed post-mortem.

Results: TTC staining demonstrated 100% viable myocardium at euthanasia. Signal intensity time curves of CE MRI were similar between stunned (S) and non-stunned remote (R) tissue (P=NS). SSR was reduced in stunned tissue in the first hours after ischemia relative to remote at rest (-0.15 � 0.12 S vs. -0.32 � 0.10 R, P<0.05). LDDS in the first hours of reperfusion showed improved function in stunned tissue (-0.30 � 0.16 LDDS vs -0.15 � 0.12 rest, P<0.05) as well as remote ( -0.45 � 0.23 LLDS vs 0.32 � 0.10 rest, P<0.05 ). Moreover, S regions showed complete recovery of function at 1 week at rest (-0.53 � 0.23 S vs -0.44 � 0.20 R, P=NS ). There was no significant change in SSR at rest in R regions from baseline to reperfusion and recovery. LDDS caused significant increase in SSR in all regions at each time point of MR imaging.

Conclusion: LDDS MRI with 3D myocardial tagging can non-invasively identify dysfunctional myocardium that can be recruited, which is the hallmark of stunned tissue. CE-MRI did not demonstrate any differences between stunned and non-stunned tissue. Thus, tagged serial MRI exams may be sufficient to demonstrate stunned tissue and recovery at 1 week.

Category (Complete): Experimental MRI
Additional Information (Complete):
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Status: Complete

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