The effect of heart rhythm on patient radiation dose with dual-source cardiac computed tomography

Background: To lower the radiation exposure associated with cardiac CT, it is essential to identify all factors that influence radiation dose. Objectives: We explored the effect of heart rhythm during scan acquisition on radiation dose with a 64-slice dual-source cardiac CT. Methods: Patient and scan data were collected prospectively in 302 consecutive patients referred for a clinical dual-source cardiac CT. Electrocardiograms recorded during acquisition were interpreted by a cardiologist and categorized as (1) normal sinus rhythm (NSR), (2) premature atrial contraction (PAC) or premature ventricular contraction (PVC), or (3) atrial fibrillation or flutter. Results: Of the 302 patients, 227 (75.2%) were in NSR and had no ectopy, 55 (18.2%) had PAC/PVC, and 20 (6.6%) had atrial fibrillation or flutter during the scan. Patients with irregular rhythm (PAC/PVC and atrial fibrillation or flutter) were older than patients with regular rhythm (61.0 vs 54.8 years; P = 0.006). Patients with NSR had the lowest estimated radiation dose, followed by PAC/PVC and atrial fibrillation/flutter (9.4, 14.5, 20.9 mSv; P < 0.001). The difference remained significant after adjustments for differences in examination type, tube current and voltage, scan length, pitch, and use of tube current modulation (9.8, 14.1, 17.9 mSv; P < 0.001). No significant association was observed between normal and abnormal heart rhythm and subjective image quality although scans with regular rhythm and no ectopy had higher signal-to-noise and contrast-to-noise ratios (P < 0.01). Conclusion: Compared with patients with NSR, patients with atrial fibrillation/flutter had the highest radiation exposure, followed by those with PAC/PVC. Even after adjustment for factors associated with radiation exposure, a significant difference in radiation dose persisted. These findings can be used to identify patients who are more likely to receive higher radiation dose when undergoing cardiac CT and to develop future more-efficient scanner algorithms for use in patients with arrhythmias.