Main findings
The statistical methods used in this study involved models that considered several factors, which makes it the most extensive study of normal PVs to date. This study reveals that the PVs ostia size is variable during cardiac cycles for normal person. All the maximum values of the four PVs’ size were observed in 45% of cardiac phases, while the maximum values of the RSPV angles and RIPV coronal-section angles, were observed in 5%. In addition, the maximum values of the LSPV angles, LIPV cross-sectional angles, and RIPV cross-sectional angles were observed in 45%; however, the maximum values of the LIPV coronal-section angles were observed in 55%.
Size of PVs
In our study, the maximum PVs size was in 45% of cardiac phase, while the minimum PVs size was in the 5% or 95% phases. However, Choi et al.[9] argued that the maximum size of the RIPV was in 35%, while the minimum size of the RIPV was in 85% phase; thus, they measured the RSPV, LSPV, and LIPV in these two phases. The subject of Choi et al’s study is AF and non-AF populations, while our study subject is only normal population. At the same time, Hauser et al.[17] find the timing of the PVs maximum size varied but generally occurred in ventricular diastole, and the timing of minimum PVs size also varied but generally occurred in ventricular systole, but they didn't provid specific cardiac timing points. Therefore, we believe that AF can affect the cardiac phase which the maximum and minimum of PVs is in. In normal population, Manghat NE et al.[10] directly measured the PVs size by MR cine in the end-systolic and end-diastolic stages of the ventricle, and found that the maximum size of the four PVs were all located in the ventricular end-systolic. Therefore, we can think that the ventricular end-systolic is equivalent to 45% phase of cardiac cycle in the CT reconstruction. According to Deng Wen et al's[18] physiological phases of the cardiac cycle, 40% phase corresponds to the ventricular isovolumic relaxation phase, while 50–90% corresponds to the filling phase, during which the atrial volume is larger in the early stage but later decreases. Some studies have demonstrated that during cardiac cycle, changes in the PVs ostia size are consistent with the changes in the atrial volume, and the atrial volume expansion could lead to an increase in the PVs ostia.[8, 19] In addition, the minimum size of the four PVs ostia was observed in 5% or 95%, which is equivalent to the systolic period of the cardiac phases (the atrioventricular valve is closing); at this point, the blood flow in the atrium enters the ventricle totally, and the LA volume is the smallest. Thus, the change of the PVs ostia size corroborates the behavior of the atrial volume, and any disease that causes abnormalities in the LA, such as mitral valve disease, would change the PVs’ size.
Dong et al.[20] measured the maximum diameter of the four PVs in AF patients. Compared with our study, RSPV (19.91 ± 3.26 mm) VS (17.79 ± 4.30 mm), RIPV (17.04 ± 2.46 mm) VS 15.92 ± 3.19 mm), LSPV (18.93 ± 2.78 mm) VS (18.54 ± 3.44 mm), and LIPV (16.52 ± 2.55 mm) VS (15.56 ± 3.25mm), we can find that the diameter of the four PVs in normal person is higher than that in AF patients. Hence, it is obvious that AF could lead to a reduction of the PVs’ size; however, Dong et al.[20] did not provide the phase of the maximum value of the PVs ostia.
The correlation between traditional risk factors and PVs
Regarding the correlation between gender and PV size, we found that the RSPV, RIPV, and LSPV differed between males and females. At the initial phase of the cardiac cycle, the average level of the three PVs size between individuals of different genders was different, and the size of these three PVs was larger in males than that in females. At different phases of the cardiac cycle, changes in the three PVs (RSPV, RIPV, and LSPV) were different, and the rate of change was also different. Notably, blood pressure and smoking affected the RSPV size. The diameter of the RSPV in hypertensive patients and smoker was small. We observed no effect of age, blood fat, blood sugar, BMI, and drinking on the PVs’ size.
Spatial angle of PVs
The changing trend of the RSPV, RIPV, and LSPV cross-sectional and coronal-section angles was a straight line. For the LIPV, however, the maximum and minimum values of cross-sectional angles were observed in 45% and 5% of cardiac phases, while the maximum and minimum values on coronal-section angles were observed in 55% and 85%, respectively.
Wang et al.[12] measured the angle of the PVs at a certain phase and reported that the angle is a real and stable imaging anatomical feature, which has nothing to do with gender or image features (magnetic resonance or CT).[12] In our study, we measured the spatial angles (cross-sectional and coronal-section angles) of the four PVs in 10 cardiac phases and revealed that in the initial phase of the cardiac cycle, the average value of the LIPV cross-sectional angles among individuals with different ages was different; with increasing age, the angle also increases. In different cardiac phases, individuals with different ages revealed different changes in the LIPV cross-sectional angles, and individuals with different ages had a different speed of LIPV cross-sectional angle changes. However, the cross-sectional and coronal-section angles of the RSPV, RIPV, and LSPV, as well as coronal-section angle of the LIPV, did not change considerably with the cardiac cycle change. Moreover, we found no effect of gender, blood lipid, blood glucose, BMI, drinking, and smoking on the spatial angle of these PVs. Thus, if intervening on the RSPV, RIPV, or LSPV, we concur with Wang et al.[12]; it is recommended to adjust the angle of the central X-ray based on the average value of the central X-ray angle. If intervening on the LIPV, we recommend that the pre- and postoperative image assessment should be performed at the same cardiac phase, and during the operation, the surgeon(s) must closely observe the changes in LIPV angles.