Portal flow diversion based on portography is superior than puncture site in the prediction of overt hepatic encephalopathy after TIPS creation | BMC Gastroenterology

In this single-center, retrospective study with relatively large cohort of patients with cirrhosis submitted to TIPS, we found in approximately three quarters of cases the blood from SV and SMV were fully mixed in the intrahepatic portal system under portography, and these cases have comparable risk of postoperative overt HE regardless of the puncture site. For the remaining cases, approximately three quarters of them belong to type A (the right portal branch receives blood from SV and the left branch receives blood from SMV). Besides, portal flow diversion based on intraprocedural portography is an independent predictor of post-TIPS overt HE, in which the SMV superiority type is associated with increased risk of overt HE and ammonia elevation compared with the mixed type.

Hyperammonemia plays a central role in the pathogenesis of overt HE, especially after TIPS creation as this procedure diverts portal blood containing gut-derived neurotoxins into the systemic circulation [15, 16]. Thus, several studies concluded that puncture of the left portal branch might decrease the risk of post-TIPS overt HE based on the hypothesis that the left branch mainly receives blood from SV containing less neurotoxins [7, 11, 12]. However, this hypothesis was based on several animal studies [17, 18], and hemodynamic evidence from human studies (especially from patients with cirrhosis) were scarce. Contrary to previous views, our results showed that in 73.4% of patients with cirrhosis undergoing TIPS the blood from SV and SMV were fully mixed in the portal system, while the percentage of patients with the assumed blood distribution (type B) was only 5.6%. This discrepancy may be attribute to the fact that blood distribution depends on multiple factors including venous angles, blood velocity and length of the main PV. Thus, the previous hypothesis might not be applicable to all cirrhotic patients due to individual variation.

Based on these preliminary findings we subsequently combined blood distribution with puncture site to establish a new risk stratification approach based on portal flow diversion, and speculated that this approach is superior than using puncture site in the identification of patients at different risk of post-TIPS overt HE. In our cohort, patients presented with the SMV superiority type was associated with a significantly higher risk of the outcome, and the SV superiority type was related to a 43% decreased risk compared with the mixed type. Moreover, our hypothesis is supported by analyzing the change of serum ammonia level, in which the SMV group showed a substantially higher level within one month compared with the baseline level and the level of other two groups. Of note, we attempt to investigate the predictive value of flow diversion based on the portography after stent insertion, which might be more relevant to the outcome. However, portal flow was mostly diverted through TIPS shunt soon after stent placement and intrahepatic blood distribution was purely visual in some cases. Besides, the diversion degree in post-TIPS portography was affected by multiple factors (e.g. stent size and angle), making the results unreliable and reproduceable.

The cumulative rate of post-TIPS overt HE presented no difference between puncture of the left and right portal branch in the entire cohort as well as in subgroups of different flow diversion. This negative result could be explained on several grounds. First, most cases belonged to the mixed type which might not be affected by different puncture site. Second, previous studies suggested that puncture of the left branch has minimal impact on hepatic perfusion and less impairment on liver function since the left branch is smaller with fewer perfusion. However, atrophy of the right lobe and hypertrophy of the caudate and left lobe frequently occur in the presence of advanced cirrhosis [19,20,21]. Therefore, the effect of puncture site on post-TIPS overt HE is heterogeneous and flow diversion based on portography is a more reliable and accurate approach in the prediction of the outcome.

Our study is of clinical relevance as it reveals another independent risk factor for post-TIPS overt HE. For patients present with SMV superiority type under portography, under-dilated strategy to achieve a higher post-TIPS PPG may be an optimal choice [22, 23], and this subgroup of patients may benefit from pharmacological prophylaxis due to the positive results of the latest RCT [24]. Moreover, the incidence of overt HE in the SMV group was far beyond the reported ranges [4], and these patients were those with type A but were mis-punctured the left portal branch or type B but were mis-punctured the right branch. Since several modalities were developed to visualize the portal system which provides not only anatomical but hemodynamic information [25,26,27], novel techniques may aid clinicians to visualize blood distribution before procedure and select appropriate portal branch.

Potential limitations exist in the present study. First, patients in the SV group and SMV group were relatively small, limiting the ability to draw firm conclusions. Second, other outcomes such as shunt dysfunction and mortality were not assessed in our study, which were reported to have a correlation with different puncture site [9, 10, 13], though the results were controversial. Third, the reliability of identification of portal flow diversion may be confounded by different catheter position and different contrast dose, and standardized portography protocol should be generated. Forth, potential bias is inherent due to the retrospective nature and single-center design, and prospective studies are warranted to validate these results.

In conclusion, this study showed that in three quarters of patients submitted to TIPS the blood from SV and SMV were fully mixed in the intrahepatic portal system, and for patients with SMV superiority type the risk of post-TIPS overt HE increased significantly. Portal flow diversion based on portography is more reliable and accurate than puncture site in the stratification of patients at different risk of the outcome, which has the potential to affect decision-making by achieving preprocedural visualization of blood distribution.

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