| PURPOSE:To investigate the effect of high heart rate on image quality at256-slicecoronary CT angiography and the diagnostic accuracy for detecting coronaryartery stenosis of50%or more.MATERIALS AND METHODS:The study protocol was approved by our local hospital InstitutionalReview Board. Thirty one patients (17men,14women) who had both coronaryCT angiography and invasive coronary angiography done within30days, wereselected. The enrolled patients were divided into2groups according to themean heart rate during the coronary CT angiography: Group A (mean HR <75bpm:5men,8women; mean age56.6±10.3years), and Group B (mean HR≥75bpm:12men,6women; mean age57.6±9.8years). All patients underwent256-slice coronary CT angiography using the retrospective ECG-gatingtechnique. Two radiologists evaluated the image quality of each coronarysegment with at least1mm diameter after optimal selection of R-Rreconstruction phases (1=no motion artefacts,5=not evaluative). Objectiveanalysis of the image quality included measuring CT image attenuation value inHU and image noise in ascending aorta at the level of the origin of LM on axialimages. Invasive coronary angiograms were evaluated by an interventionalcardiologist considering lesions with a stenosis50%or more in diameter.Pearson correlation analysis was performed to compare the image quality scorefor all segments and separate arteries (RCA, LAD, and LCX) with the meanheart rate and heart rate variability. Diagnostic accuracy of coronary CT angiography compared to that of invasive coronary angiography wasdetermined on a per-segment and per-vessel basis.RESULTS:Mean heart rate in group A was63.7±9.0bpm and82.9±5.8bpm in groupB. Thirty nine (7.4%) segments (19(6.2%) in group A and20(9%) in group B)were excluded from analysis because of variations of coronary anatomy (n=32)or small vessel diameter (n=7). Mean image quality for all included segmentswas1.38±0.26in group A and1.35±0.29in group B. There was no statisticallysignificant difference in image quality of segments in group A (<75bpm) andgroup B (≥75bpm)(p=0.761). Number of segments with image quality score of1was259(90.2%) in group A and158(78.6%) in group B. Seventeen (6.0%)segments in group A and18(9.0%) segments in group B had a score of2.Score of3was given to4(1.4%) segments in group A and13(6.5%) in groupB. No segments received an image quality score of above3. Interobserveragreement for image quality rating was strong (weighted κ index=0.84with p<0.001). There was no significant correlation between the mean heart rate andthe mean image quality scores for all coronary segments in each patients (r=0.176; P=0.344). No significant correlation was also seen between the meanheart rate and the image quality score for the RCA (r=0.122; P=0.513), theLCA (r=0.123; P=0.510) and the LCX artery (r=0.157; P=0.398). Meanheart rate variability in group A was4.9±2.2bpm and5.1±2.4bpm in group B.There was no significant difference in mean heart rate variability in both groups(P=0.729) and no significant correlation between the heart rate variability andimage quality score for all coronary segments (r=-0.74; P=0.691) is seen. Forobjective analysis of image quality, mean CT image attenuation value inascending aorta was362.2±72.8HU in group A and354.1±68.6HU in groupB and mean image noise was22.2±4.9in group A and21.3±4.6in group B.No significant differences were seen in the mean CT attenuation and noise measurements in both groups (P=0.755and0.620respectively). Stenoses≥50%were detected with accuracy, sensitivity, and specificity, respectively of97.1%(297of306) in group A and95.0%(210of221) in group B,94.0%(47of50) in group A and89.7%(26of29) in group B,97.7%(250of256) ingroup A and96.8%(184of190) in group B on a per-segment basis and92.6%(50of54) in group A and94.9%(37of39) in group B,96.4%(27of28) ingroup A and95.2%(20of21) in group B, and88.5%(23of26) in group Aand83.5%(15of18) in group B on a per-vessel basis.CONCLUSION:Retrospective ECG-gated coronary CT angiography using a wide-coverage256-slice multidetector CT scanner being less dependent on heart rateand heart rate variability, can yield diagnostic image quality in patients withhigh heart rates. This can be diagnostically helpful in contingent of patientspresenting with high heart rate but have contraindications or resistance to β-blockers. |
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