Table 2 Comparison of characteristics between matched and unmatched patients using strategy 1, and between unmatched patients using all 4 strategies

Strategy 1 Matched patients (n = 1242) Unmatched patients (n = 41) p-value
Age (mean, sd) 63.5 (12.7) 53.6 (15.1)  < 0.001a
Male sex (%, n) 77.3 (960) 80.5 (33) 0.63e
Risk of death % (median, IQR) 1.08 (0.67–2.10) 7.50 (1.33–14.5)  < 0.001c
Urgent/emergent procedure (%, n) 22.0 (273) 58.5 (24)  < 0.001e
Procedure type (%, n)
CABG 56.6 (703) 26.8 (11)  < 0.001e
Valve repair/replacement 15.1 (187) 17.1 (7)
Combined CABG/Valve 7.49 (93) 4.9 (2)
Other 20.1 (259) 51.2 (21)
Unmatched patients: Strategy 1 (n = 41) Strategy 2 (n = 132) Strategy 3 (n = 72) Strategy 4 (n = 81) p-value
Age (mean, sd) 53.6 (15.1) 59.7 (14.7) 57.2 (15.7) 57.7 (16.2) 0.15b
Male sex (%, n) 80.5 (33) 80.3 (106) 81.9 (59) 80.3 (65) 0.99e
Risk of death % (median, IQR) 7.50 (1.33–14.5) 2.36 (1.2–7.6) 4.26 (1.29–13.2) 1.62 (0.82–8.78) 0.02d
Urgent/emergent procedure (%, n) 58.5 (24) 43.2 (57) 55.6 (40) 35.8 (29) 0.02e
Procedure type (%, n)
CABG 26.8 (11) 29.6 (39) 29.2 (21) 39.5 (32) 0.76e
Valve repair/replacement 17.1 (7) 19.7 (26) 16.7 (12) 13.6 (11)
Combined CABG/Valve 4.9 (2) 5.3 (7) 5.6 (4) 8.6 (7)
Other 51.2 (21) 45.5 (60) 48.6 (35) 38.3 (31)
1. Unmatched patient p-values refer to a comparison between all 4 groups. Comparison uses total available patients in database as denominator (n = 1283)
2. Tests used as follows:
3. aStudent’s t-test
4. bAnalysis of variance (ANOVA)
5. cWilcoxon rank-sum
6. dKruskall-Wallis
7. eChi-square