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DOI:10.2214/AJR.07.0151
AJR 2007; 189:W50-W51
© American Roentgen Ray Society

Optimizing Coronary Artery Imaging in Patients with Atrial Fibrillation with ECG-Gated 64-MDCT

William M. Strub, Achala Vagal and Cristopher Meyer

University of Cincinnati Cincinnati, OH



 
WEB—This is a Web exclusive article.

We have been able to achieve diagnostic-quality images of the coronary arteries by using fixed temporal delay for reconstructions, postprocessing ECG editing, and limited dose modulation. In our experience in patients with atrial fibrillation, the 30–40% R-R interval, located in end systole–early diastole, provides the maximum information with the least cardiac motion. In general, the relative delay or absolute reverse method is most often used for reconstruction. Reconstructed images, although apparently acquired in the same time window during the R-R interval, may differ in actual cardiac phase because of the patients' atrial fibrillation; the result of this disjuncture is an apparent stepladderlike contour of the heart (Figs. 1A and 1B). As the heart rate increases, the duration of the end diastolic interval decreases. Moreover, when the heart rate is a variable, such as in atrial fibrillation in which it is episodically irregular, the durations of the diastole and the R-R interval are the most variable whereas the duration of systole is more constant.


Figure 1
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  		Fig. 1A —65-year-old man in atrial fibrillation. ECG tracing obtained during end diastole in which data acquisition is indicated by rectangles. Note that images obtained during this phase of cardiac cycle are susceptible to beat variability leading to data acquisition during different points during cardiac cycle with respect to the QRS complex (arrow).

 

Figure 2
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  		Fig. 1B —65-year-old man in atrial fibrillation. Corresponding curved reformat image obtained during end diastole shows degradation of coronary artery by stairstep artifact.

 
We found that an absolute temporal delay of 150–250 milliseconds resulted in marked improvement in the image quality compared with using a fixed percentage delay (Figs. 1C and 1D). Our results are consistent with and extend the work of Sato et al. [1] who, in a small group of patients with atrial fibrillation, noted improved continuity of reconstructed images obtained at end systole with a fixed temporal delay of 350 milliseconds for the R wave in each patient.


Figure 3
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  		Fig. 1C —65-year-old man in atrial fibrillation. ECG tracing obtained using fixed temporal delay technique. Note regularity of data acquisition with respect to QRS complex.

 

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  		Fig. 1D —65-year-old man in atrial fibrillation. Curved reformat image obtained using fixed temporal delay shows diagnostic quality image of coronary artery.

 
Artifacts resulting from irregular cardiac rhythm can also be addressed via ECG editing software because in patients with arrhythmias there may be a stairstep artifact due to cardiac motion. This is particularly important in those cases of premature ventricular contractions or early premature atrial contractions in which one or two outlying ectopic beats may be observed. This postprocessing ECG editing can improve the quality of the study; however, such editing is limited because greater manipulation will lead to gaps in the data [2]. When image slices with artifact are identified, we review the source images along with the ECG tracing on the scanner. If required, the corresponding reconstruction bar on the ECG tracing can be disabled. The ECG tracing is reviewed to ensure that the images being reconstructed are positioned in diastole or end systole. In our group of patients with atrial fibrillation, the combination of tachycardia and arrhythmias particularly limits the regular use of dose modulation. Thus, the different phases of the R-R interval must be used to visualize the coronary arteries. Although the major limitation is substantially increased radiation dose, the trade-off, a nondiagnostic examination, would mean futile irradiation. Hopefully, future work in this area will show reliable image reconstruction in atrial fibrillation at a specified fixed temporal delay, thereby allowing dose modulation in end systole.

Patients with atrial fibrillation are a challenging subgroup for cardiac MDCT. However, by altering a few technical parameters, it is possible to obtain excellent image quality despite the tachycardia and atrial fibrillation.


References
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 References
 

  1. Sato T, Anno H, Kondo T, et al. Applicability of ECG-gated multislice helical CT to patients with atrial fibrillation. Circ J 2005; 69:1068 -1073[CrossRef][Medline]
  2. Lawler LP, Pannu H, Fishman EK. MDCT evawluation of the coronary arteries, 2004: how we do it—data acquisition, postprocessing, display, and interpretation. AJR 2005;184 : 1402-1412[Abstract/Free Full Text]

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This article has been cited by other articles:


Home page
 Am. J. Roentgenol.Home page
H. Matsumoto, T. Kondo, S. Watanabe, R. Kikumoto, T. Shimada, Y. Hiraoka, and K. Ueda
ECG-Edited Middiastolic Phase Reconstruction Improves Image Quality at 64-MDCT Coronary Angiography of Patients with Atrial Fibrillation
Am. J. Roentgenol., December 1, 2008; 191(6): 1659 - 1666.
[Abstract] [Full Text] [PDF]

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