4 | DISCUSSION
Although a large number of studies has been published on variations of the PVs ostia, their results are often contradictory and precise prevalence of each variation has not been established yet. Therefore, the aim of this meta-analysis was to provide a detailed, more precise and up-to-date anatomical knowledge base. An accurate understanding of the anatomy is important for clinicians as it may greatly increase a chance of successful therapy. Gathering and analyzing data published in the literature before, allowed us to establish more precise and statistically significant prevalence for each variation type (Figure 2).
Moreover, homogeneity between the general group and the patients with AF was established. P-value for classical type was 0.92 and for other than classical types was 0.90. Hence, it may be concluded that there are no statistically significant differences between the general group and patients with AF. Additionally, a comparison between patients with and without AF was made. All obtained p-values (Table 3) are higher than 0.05, except for types 5 (other arrangements) and 10 (LCPV and RCPV). Therefore, it may be assumed that, in a great majority, there are no statistically significant differences in PV anatomy between patients with and without AF. However, it must be noted that abundance and I2 of those two groups are strongly different. Hence, those results are burdened with a potential bias, which can be eliminated in further papers, where a larger group of patients with AF will be studied, and if the results will have been showing greater heterogeneity. Furthermore, maximal diameter and ostial area of PVs also indicate substantial variability. The mean maximal diameters range from 10.9 mm to 27.7 mm for RSPV, from 7.5 mm to 23 mm for RIPV, from 10.0 mm to 25.0 mm for LSPV, from 8.0 mm to 21.5 mm for LIPV, from 6.9 mm to 17.0 mm for RMPV and from 18.7 mm to 38.2 mm for LCPV. Regarding ostial area of each PV, the values range from 132.2 mm2 to 377.0 mm2 for RSPV, from 142.6 mm2to 298.0 mm2 for RIPV, from 106.5 mm2 to 317.3 mm2 for LSPV, from 98.0 mm2 to 248.2 mm2 for LIPV, from 36.2 mm2 to 123.6 mm2 for RMPV and from 308.2 mm2 to 694.0 mm2 for LCPV.
AF is the most common cardiac rhythm disturbance and is responsible for substantial morbidity and mortality in general population . PVs play a crucial role in AF development . Catheter ablation is a standard treatment for patients with AF, which primarily focuses on electrical isolation of the pulmonary veins . It is a very promising procedure, as it shows a great efficacy rate; however, a detailed knowledge and awareness of patients’ PV arrangement and their morphological parameters are essential for safe and successful performance . Collecting and analyzing the data gathered in the literature allowed us to establish the most accurate values of the ostial area and its diameter. Narrower PVs pose a greater challenge when performing a catheter ablation. Therefore, the results from this meta-analysis may be a helpful tool for surgeons performing this procedure. Detailed and accurate anatomical knowledge combined with an appropriate pre-procedural imagining may strongly increase chances of successful therapy.
A detailed and precise anatomical knowledge is also essential when performing other cardiothoracic procedures. The PVs are often overlooked structures in chest imaging, and can become directly or indirectly involved in a wide array of pathological and nonpathological processes ranging from malignant involvement to surgical changes to differences in anatomic arrangement . Although PV variations are frequently asymptomatic, the knowledge of these variations is important while planning cardiothoracic surgeries, as it may prevent potential complications . Therefore, physicians, especially radiologists, should be aware of them, as appropriate pre-procedural imagining may increase the chances of successful therapy.
Choosing an appropriate method to establish patients’ individual internal anatomy may also play a significant role in clinical practice. In included studies, most frequently used ways of imaging PV anatomical variations were computed tomography scans, magnetic resonance imaging, magnetic resonance angiography and echocardiography. However, there are no statistically significant differences in imaging method of the observed PV anatomical variations (all p > 0.05). The most frequently used method of establishing the maximal diameter of each PV were angiography, computed tomography, magnetic resonance imaging, magnetic resonance angiography and echocardiography. Comparison of the groups showed statistically significant difference between echocardiography and the rest of the methods (all p < 0.05), with echocardiography reporting the smallest values (Table 5). Therefore, it may concluded that the values of maximal PV diameter obtained using echocardiography differ from the results obtained by other methods (as they are underestimated). Consequently, echocardiography should not be recommended for establishing PV diameter. The most frequently used method of establishing the ostial area were computed tomography, magnetic resonance imaging and magnetic resonance angiography. Comparison of the groups showed no statistically significant differences between results obtained by those methods (all p > 0.05) (Table 7).
Human anatomy can potentially vary in different regions of the world (geographical and ethnical differences). The results obtained in different continents were compared in order to establish the potential heterogeneity among them. With regards to the PV ostia anatomical variations, maximal PV ostia diameter and PV ostial area, there were no statistically significant differences between continents, as all the p-values were significantly higher than 0.05 (Table 2, 5 and 7).
This study has several limitations. First of all, all limitations in the current study are the reflection of many flaws of individual studies included in the meta-analyses. The majority of our results were determined by the rate of significant heterogeneity. Although many subgroup analyses were conducted, the potential sources of heterogeneity could not be indicated. The measurement site and the method of collecting the PV ostium maximal diameter and ostial area may also significantly differ between individual studies. Furthermore, the RCPV ostial diameter and ostial area were not established due to limited and inconsistent amount of data in the literature. Due to insufficient number of studies, we were not able to perform subgroups analyses targeting other disease entities than AF. Furthermore, the studies investigating variations, diameter and ostial area of the PVs were mostly carried out in Asia, Europe and North America. This can be a potential source of bias as our results reflect Asian, European and Northern American people rather than the global population. Further anatomical studies should be conducted to investigate these features in a larger and more ethnically diverse group of patients.
In conclusion, this is the most comprehensive and up-to-date study regarding PV ostia variability and their size. Several types of the PV ostia arrangement may be observed with the classical type being the most popular (70%), followed by the type with common ostium for left-sided PVs (17%), type with common ostium for right-sided PVs (9%) and type with additional middle PV on the right side (8%). Significant differences in PV ostia variations are observed in AF patients with more prevalent types with either additional middle PV ostium on the left or right or both sides. A significant variability in PV ostia is observed. Left-sided PVs have smaller ostia than corresponding right-sided PVs, and the inferior PVs ostia are smaller than superior. The size of the LCPV ostium is the largest among all analyzed veins, while the ostium of RMPV is the smallest. It is hoped that the results from this meta-analysis will help clinicians in planning and performing procedures that involve pulmonary and cardiac area.