Significance of PQ interval in acquisition of coronary multidetector row computed tomography

Background: Since image quality obtained in the mid-diastolic [or slow filling (SF)] phase is generally superior to end-systolic image in coronary multidetector row computed tomography (MDCT), low heart rate (HR) comprises the most important factor for acquisition of high-quality images. However, despite HR <70 and optimum breath-hold, sometimes high quality images cannot be obtained in SF. We assessed the significance of PQ interval in acquisition of coronary MDCT. Methods and results: Of 541 consecutive patients who underwent coronary MDCT, 7 patients with incomplete breath-hold, 62 HR ≥70, and 70 arrhythmias were excluded. The remaining 402 patients (M: 222, 66 ± 11 years), including 38 with first-degree atrioventricular block (1°AVB, PQ >200 ms) were evaluated. RR and PQ were measured on electrocardiogram and systolic and SF phase with 4-chamber cine cardiac computed tomography. SF significantly (p < 0.0001) correlated with RR (SF = -471 + 0.720RR, r = 0.887) in all subjects. The SF of without 1°AVB (292 ± 97 ms) was significantly (p < 0.0147) longer than that of with 1°AVB (251 ± 121 ms), although RR was not significantly different between the two groups. The SF/RR of without 1°AVB (27.2 ± 6.1%) was also significantly (p < 0.0001) higher than that of with 1°AVB (22.7 ± 8.0%). The coefficient of correlation between (RR - PQ) and SF [r = 0.915, p < 0.0001, SF = -362 + 0.742(RR - PQ)] was significantly (p < 0.034) higher than that of correlation between RR and SF in all subjects. The SF of rank A image quality was significantly longer than that of rank B (p < 0.0001) or rank C (p = 0.0042). In critical HR (60-69 bpm), the optimum phase was ES in 7/139 patients without 1°AVB, and SF in 3/13 patients with 1°AVB (χ², p < 0.0416). Conclusion: Since SF depends on (RR - PQ), if PQ is long in critical HR, it might be difficult to reconstruct high quality images in the SF phase.