Which one of the following patient characteristics is ideal for performance of a good quality coronary CT angiogram?a. Atrial fibrillation with a low ventricular response
Many patient characteristics have an effect on the quality of a CT coronary angiogram. A slow (<65 bpm) regular heart rate is optimal for cardiac CT as a slow rate increases the length of diastole and thus increases the time when the heart is relatively still in which image acquisition can be performed. A regular heart rate with low respiratory variation is also important to minimize reconstruction or ‘step’ artefacts caused by ectopic or irregular beats. Thus, even with a slow ventricular rate, atrial fibrillation may significantly degrade image quality. In view of the need for a slow heart rate, a contraindication to beta-blockers is not ideal, as this is the main pharmacological technique employed in cardiac CT for heart rate control; calcium-channel antagonists with a negatively chronotropic effect may be used as an alternative. Recent work on the use of sinus node blockers is under investigation. Depending on the exact specification of the CT scanner and the field of view of image acquisition, the breath-hold time is 5–10 seconds. Thus if a patient can only breath-hold for 2 seconds, there is likely to be motion (respiratory artefact) which will degrade the image quality.
A cardiac CT is performed with the patient’s arms extended above the head to ensure that there is no ‘beam-hardening’ artefact from the arms which reduces image quality.