Analysis of heart rate and heart rate variation during cardiac CT examinations

RATIONALE AND OBJECTIVES: We sought to examine heart rate and heart rate variability during cardiac computed tomography (CT). MATERIALS AND METHODS: Ninety patients (59.0 +/- 13.5 years) underwent coronary CT angiography (CTA), with 52 patients also undergoing coronary artery calcium scanning (CAC). Forty-two patients with heart rate greater than 70 bpm were pretreated with oral beta-blockers (in five patients, use of beta-blocker was not known). Sixty-four patients were given sublingual nitroglycerin. Mean heart rate and percentage of beats outside a +/-5 bpm region about the mean were compared between baseline (free breathing), prescan hyperventilation, and scan acquisition (breath-hold). RESULTS: Mean scan acquisition time was 13.1 +/- 1.5 seconds for CAC scanning and 14.2 +/- 2.9 seconds for coronary CTA. Mean heart rate during scan acquisition was significantly lower than at baseline (CAC 58.2 +/- 8.5 bpm; CTA 59.2 +/- 8.8 bpm; baseline 62.8 +/- 8.9 bpm; P < .001). The percentage of beats outside a +/-5 bpm about the mean were not different between baseline and CTA scanning (3.5% versus 3.3%, P = .87). The injection of contrast had no significant effect on heart rate (58.2 bpm versus 59.2 bpm, P = .24) or percentage of beats outside a +/-5 bpm about the mean (3.0% versus 3.3%, P = .64). No significant difference was found between gender and age groups (P > .05). CONCLUSIONS: Breath-holding during cardiac CT scan acquisition significantly lowers the mean heart rate by approximately 4 bpm, but heart rate variability is the same or less compared with normal breathing.