Variation of heart rate and electrocardiograph trigger interval during ultrafast computed tomography.

Objectives: Electrocardiographic (ECG) trigger records obtained during cardiac ultrafast computed tomography (UFCT) scanning were analyzed to estimate the variability in heart rate and ECG trigger interval to develop a protocol that would allow the development of better ECG triggering software.

Methods: One-hundred-eighteen patients underwent cardiac UFCT imaging for diagnostic purposes. All subjects were divided into three groups according to the heart rate and ECG trigger condition. Thirty slices were obtained in the high-resolution volume mode for each patient.

Results: A decrease in heart rate and ECG trigger interval was found during image acquisition of the first four slices in all three groups. The nadir of the heart rate occurred during acquisition of the 4th slice, 5.3, 3.5, and 5.6 beats per minute less than the initial heart rate in groups 1, 2, and 3 respectively, with a 6.9%, 2.8%, and 5.0% shorter ECG trigger interval (p < .001, p = .08, p < .05, respectively). From the 4th to the 30th slices, heart rate and ECG trigger interval progressively increased, but less variability was found in the last 20 slices in all three groups.

Conclusions: Significant variation in heart rate and ECG trigger interval was seen during 30-level cardiac UFCT imaging, especially during image acquisition of the first four slices (approximately 1-6 seconds after breatholding). This can result in scanning during the suboptimal phase of the cardiac cycle by the current UFCT triggering software. A delay in the initiation of scanning to approximately 6 to 10 seconds after breatholding would result in imaging during a time when the heart rate is relatively stable, and a smaller variability in ECG trigger interval occurs. Recalculation of the required delay before each heart beat may improve the precision of ECG triggering.