C Joon Choi

Eastern Virginia Medical School, Norfolk, Virginia, United States

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Publications (5)24.8 Total impact

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    ABSTRACT: We hypothesized that (1) a significant proportion of ischemic dysfunctional segments that do not improve function will demonstrate postrevascularization contractile reserve and (2) electromechanical mapping (EMM) can identify segments that improve function as well as those with postrevascularization contractile reserve, a potential indicator of delayed functional improvement. Eighteen patients with severe ischemic left ventricular dysfunction underwent EMM and dobutamine (D) cardiac magnetic resonance imaging (CMR) followed by revascularization. Four months after revascularization, all patients underwent a repeated D-CMR, and at 35 months, a subgroup (n=6) underwent a third CMR. Of 120 dysfunctional segments, 60 segments had improved rest function (IRF) and 60 did not. Twenty-eight of 60 segments (47%) that did not improve RF demonstrated postrevascularization contractile reserve (CR), and 32 of 60 segments (53%) that demonstrated neither IRF nor CR were persistently dysfunctional (PD). CR segments recovered significantly greater late function compared with IRF or PD: 14+/-12% vs 2+/-5% and 4+/-7%, respectively; P<0.05. EMM ratio, defined as the unipolar voltage divided by linear shortening, was significantly higher in IRF segments compared with segments that did not improve RF: 2.4+/-4.5 vs 0.7+/-3.5, P<0.05. Unipolar voltage was stepwise lower in normal, IRF, CR, and PD segments (10.5+/-4.7, 9.3+/-3.9, 8.8+/-3.2, and 7.4+/-2.3 mV, respectively; P<0.01 for trend). Almost half of dysfunctional myocardial segments in chronic ischemic heart disease that do not improve RF early after revascularization demonstrate early CR and delayed functional recovery. EMM parameters can identify segments that improve RF and retain CR early after revascularization.
    Circulation 11/2004; 110(16):2410-6. · 15.20 Impact Factor
  • Journal of The American College of Cardiology - J AMER COLL CARDIOL. 01/2004; 43(5).
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    ABSTRACT: Delayed contrast-enhanced cardiac magnetic resonance imaging (ceCMR) delineates infarct size. The presence of hypoenhancement consistent with microvascular obstruction (MO) signifies larger infarcts with a worse prognosis. We hypothesized that the size of the contrast defect (CD) on ceCMR in acutely infarcted myocardium may change during infarct healing and depend upon the presence of MO. Twenty-five patients underwent CMR on weeks 1 and 8 after reperfused myocardial infarction. After short-axis cine CMR was performed, gadolinium was infused and ceCMR images and matched tagged cine MR images were obtained in the three most dysfunctional short-axis slices on cine CMR. The area and transmural extent of hyperenhancement (HE) with or without MO representing total CD size were planimetered. Between week 1 and week 8, the CD area fell from 1729+/-970 mm2 at week 1 to 1270+/-706 mm2 (p<0.001), as did the transmural extent of infarction (71+/-22% to 63+/-24%, p<0.001). The decline in CD trended to be higher in patients with MO (840+/-807 mm2) than in HE (312+/-485 mm2, p<0.07). In the patient group as a whole, ejection fraction (EF) improved (56+/-9% to 60+/-10%, p=0.002) between weeks 1 and 8, but patients with MO showed no increase in EF. Segments with some HE demonstrated partial functional improvement whereas no improvement was seen in HE+MO segments. In patients 8 weeks after reperfused myocardial infarction (MI), the size of infarction by ceCMR decreases compared to week 1 post-MI, especially in those with microvascular obstruction in whom there is little improvement in regional or global function.
    Journal of Cardiovascular Magnetic Resonance 01/2004; 6(4):917-25. · 4.44 Impact Factor
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    ABSTRACT: This study was designed to evaluate several electromechanical mapping parameters for assessment of myocardial viability and inducible ischemia as defined by dipyridamole single-photon emission computed tomographic (SPECT) imaging at rest in patients with severe ischemic cardiomyopathy. Unipolar voltage, normalized unipolar voltage, bipolar voltage, and fragmentation were compared with tracer uptake at rest and reversibility on stress or rest quantitative technetium-99m sestamibi SPECT imaging in 32 patients with severe ischemic cardiomyopathy (left ventricular ejection fraction 0.24 +/- 0.08). In dysfunctional myocardial segments, logistic regression showed unipolar voltage, normalized unipolar voltage, and bipolar voltage to be predictive of viable myocardium (> or = 60% tracer uptake at rest) and was significantly higher in viable than in nonviable segments (p <0.01). A unipolar voltage of > or = 7.1 mV was the best predictor of viable myocardium. In dysfunctional viable segments, unipolar voltage was significantly higher in reversible than in fixed segments (p <0.001), and a unipolar voltage of > or = 8.5 mV had optimal power for identifying reversibility on dipyridamole SPECT imaging. We conclude that in patients with severe ischemic cardiomyopathy, unipolar voltage can identify viable from nonviable myocardium and reversible from fixed viable defects as defined by dipyridamole technetium-99m sestamibi SPECT imaging.
    The American Journal of Cardiology 04/2003; 91(7):807-11. · 3.21 Impact Factor
  • C Joon Choi, Christopher M Kramer
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    ABSTRACT: MRI is a powerful noninvasive imaging tool with high spatial resolution that continues to prove its value in determining atherosclerotic plaque size, volume, and tissue components. Multispectral MRI sequences have been validated to characterize atherosclerotic plaque components in animals; they have recently been applied to human aorta and carotid artery and are being used to identify the vulnerable plaque. The ability to measure wall thickness in human coronary artery wall has been realized. Future developments may allow plaque characterization in the coronary arteries with surface coil imaging, but intravascular MRI may play an important role in this regard. Novel contrast agents for identifying inflammation and thrombus within atherosclerotic plaque will aid in the identification of higher-risk atherosclerotic disease. Lastly, MRI has progressed to the point where it can be used in serial studies of atherosclerotic plaque progression and regression in the face of therapeutic intervention. MRI will continue to evolve an important role in imaging of atherosclerotic plaque.
    Radiologic Clinics of North America 08/2002; 40(4):887-98. · 1.95 Impact Factor