CT coronary angiography in atrial fibrillation: a comparison of radiation dose and diagnostic confidence with retrospective gating vs prospective gating with systolic acquisition

Abstract

Objective: To compare unmodulated, retrospective electrocardiographic (ECG) gating to prospective ECG gating with systolic acquisition for CT coronary angiography (CTCA) in patients with atrial fibrillation (AF), considering the radiation dose and the diagnostic confidence achieved with each technique.

Methods: A retrospective service evaluation was conducted before and after prospective gating with systolic acquisition replaced retrospectively gated imaging for patients with AF undergoing CTCA at our institution. 25 consecutive patients were examined in each group. The scan parameters and radiation dose information had been collected in a prospective fashion. The image sets were read by blinded, expert readers who rated their diagnostic confidence using a 5-point Likert scale.

Results: The radiation dose received by patients was significantly greater in the retrospectively gated group than those being scanned using prospective gating (21 vs 5.9 mSv, p < 0.01). The prospective gating technique was also associated with greater diagnostic confidence (mean, per-patient score 3.09 vs 3.78, p = 0.02).

Conclusion: Prospective gating with systolic acquisition appears to improve diagnostic confidence at a significantly reduced radiation dose compared with retrospective gating in patients with AF.

Advances in knowledge: The use of prospective gating with systolic triggering significantly reduces the radiation exposure to patients in AF undergoing CTCA. The same protocol also appears to improve diagnostic confidence.

Figure 1.

Illustrative comparison of prospective and retrospective gating in atrial fibrillation. Both right coronary artery images were assessed as good examples with only mild artefact. (a) A prospectively gated study undertaken with a dose–length product of 83 mGy cm⁻¹ (body mass index 24 kg m⁻², acquisition heart rate 63–74 bpm, 10 mg IV metoprolol)—there is a small step artefact in line with the arrow, which also highlights a contrast boundary due to the axial acquisition. (b) A retrospectively gated study undertaken with a dose–length product of 367 mGy cm⁻¹ (body mass index 27 kg m⁻², acquisition heart rate 68–87 bpm, 15 mg IV metoprolol)—there is a slightly larger area of motion blur in the proximal artery (arrowheads).

Figure 2.

Prospective gating methods in atrial fibrillation. (a) Arrows represent predicted mid diastole (70–75% R–R interval) based on the preceding R–R interval; if this is used to time image acquisition, subsequent R waves may occur before or during acquisition, impacting on cardiac motion and therefore image quality. (b) Arrows represent predicted end systole (40% R–R interval) based on the preceding R–R interval; this method is less likely to be affected by subsequent R waves. (c) Arrows represent end systole based on time from R wave; this is likely to be the most consistent method.