Two thousand four hundred and thirty-two articles were identified by titles and abstracts obtained from Medline/PubMed, EMBASE and the Cochrane library. An additional 16 articles were identified from the reference lists of suitable articles. After eliminating the duplicate studies, further articles were excluded since they were not relevant to the topic of this research. Forty-four full-text articles were assessed for eligibility. Another 32 articles were excluded for the following reasons: data for patients with NITDM could not be retrieved, data were not usable or the studies were published before the year 2006. Finally, 12 articles [5–16] were selected for this meta-analysis. The flow chart showing study selection has been illustrated in Fig. 1.
Table 1 shows the clinical outcomes reported in each of the 12 studies included.
General features of the studies included in this analysis
Table 2 represents the general features including the total number of patients in the NITDM and the NDM groups respectively, the type of study, and the follow-up periods of each of the studies included in this analysis.
As shown in Table 2, this meta-analysis included a total number of 52,451 patients among which, 14,863 were NITDM patients, whereas 37,588 patients were NDM.
Data reporting the mean age of the patients in years, the percentage of patients with male gender, with co-morbidities such as hypertension, dyslipidemia and the percentage of patients who were current smokers were listed in Table 3. According to Table 3, no significant differences were observed in the baseline characteristics between these two groups of patients (NITDM and NDM).
Results of this meta-analysis
A total number of 4163 patients were analyzed for MACEs and MI respectively and 17,015 patients were analyzed for mortality during the short-term follow-up period.
This analysis showed a significantly higher rate of MACEs and MI in the NITDM group with OR: 1.63, 95% CI (1.17, 2.27); P = 0.04 and OR: 1.82, 95% CI (1.08, 3.06); P = 0.02 when compared to NDM respectively during the short term follow up period following PCI. Compared to NDM, the mortality rate was also significantly higher in the NITDM group with OR: 1.71, 95% CI (1.40, 2.10), P < 0.00001. Results representing the short-term outcomes were illustrated in Fig. 2. Table 4 summarized the result for the short-term follow up period.
For the long-term follow up period, a total number of 21,465 patients were analyzed for MACEs, 37,756 patients were analyzed for mortality, 31,964 patients were analyzed for MI, 30,388 patients were analyzed for TLR, 14,320 patients were analyzed for TVR and 36,900 patients were analyzed for ST.
This current long-term analysis showed a significantly higher MACEs and mortality in the NITDM group with OR: 1.25, 95% CI (1.12, 1.40), P = 0.0001 and OR: 1.32, 95% CI (1.19, 1.47), P < 0.00001 respectively, and a significantly higher rate of TLR and TVR with OR: 1.32, 95% CI (1.10, 1.59), P = 0.003 and OR: 1.36, 95% CI (1.18, 1.56), P < 0.0001 respectively when compared to NDM. MI was similarly manifested with OR: 1.03, 95% CI (0.89, 1.21); P = 0.67. However, compared to NDM, even if the long-term ST was higher in the NITDM group, the result was not statistically significant with OR: 1.13, 95% CI (0.91, 1.40), P = 0.28. Results for the long-term follow up period were illustrated in Figs. 3, 4 and 5. Table 5 summarized the results for this long-term follow up period.
A separate analysis was conducted (excluding observational studies) involving only randomized trials. The results showed long term MACEs and TVR to be significantly higher in the NITDM group with OR: 1.19, 95% CI (1.03, 1.36); P = 0.02 and OR: 1.47, 95% CI (1.23, 1.74); P < 0.0001 respectively when compared to NDM. However, even if mortality was higher in the NITDM group with OR: 1.20, 95% CI (0.96–1.50); P = 0.10, the result was not statistically significant. These results have been shown in Fig. 6. In addition, long term MI and ST were also not significantly different between these 2 groups with OR: 1.04, 95% CI (0.85, 1.28); P = 0.68 and OR: 1.05, 95% CI (0.77, 1.43); P = 0.75 respectively. These results have been shown in Fig. 7.
For the included studies, publication bias was visual estimated through funnel plots. Little evidence of publication bias was observed for the included studies that assessed all clinical endpoints (Fig. 8a–c).