3.3. Subgroup analysis
Subgroup analyses were also conducted based on the type of surgery, FET graft type, and the geographical location of the study center (Table 2 ). The pooled estimates of outcomes in subgroup analyses revealed that the heterogeneity for secondary endovascular treatment during follow-up post-FET period disappeared, as there was no heterogeneity among patients receiving the Cronus (I2 = 15.1%) or Frozenix (I2 = 1%) stent-grafts. In addition, amongst patients undergoing emergent surgery, the source of heterogeneity was non-significant (I2 = 8%). Based on the geographical location of study centers, there was least source of heterogeneity among Asian countries (I2 = 39.5%). On the other hand, with regards to the development of dSINE, there was no heterogeneity (I2 = 0%) amongst European studies, including those utilizing Thoraflex Hybrid and E-Vita stent-grafts. Moreover, the pooled estimates of postoperative endoleak were also without heterogeneity (I2 = 0%) in patients receiving Thoraflex Hybrid as well as those undergoing FET HP implantation in European centers. Other subgroup analyses and their effect on the pooled estimates of outcomes and the heterogeneities are summarized in Table 2 .