Age shock index and age-modified shock index are valuable bedside prognostic tools for postdischarge mortality in ST-elevation myocardial infarction patients

Figures & data

Table 1. Demographics and characteristics of STEMI patients.

Variable	Within 30 days (N = 3389)			From 30 days to 1 year (N = 3247)
	Survivor (N = 3347)	Non-survivor (N = 42)	p Value	Survivor (N = 3179)	Non-survivor (N = 68)	p Value
Demographic characteristic
Age (years), median (IQR)	62.0 (51.6, 69.4)	71.4 (61.8, 80.4)	<.001	61.6 (51.3, 69.0)	72.4 (65.8, 81.2)	<.001
≥75years, n (%)	434 (13.0)	16 (38.1)	<.001	385 (12.1)	30 (44.1)	<.001
Women, n (%)	742 (22.2)	17 (40.5)	.005	700 (22.0)	17 (25.0)	.558
Tertiary hospital, n (%)	1718 (51.3)	20 (47.6)	.633	1646 (51.8)	38 (55.9)	.503
Risk factors and medical history
Hypertension, n (%)	1483 (44.3)	21 (50.0)	.461	1403 (44.1)	35 (51.5)	.228
Dyslipidaemia, n (%)	1926 (57.5)	20 (47.6)	.196	1836 (57.8)	35 (51.5)	.299
Diabetes, n (%)	555 (16.6)	14 (33.3)	.004	527 (16.6)	18 (26.5)	.031
Current smoker, n (%)	1430 (42.7)	10 (23.8)	.014	1373 (43.2)	19 (27.9)	.012
Coronary heart disease, n (%)	218 (6.5)	3 (7.1)	1.000	203 (6.4)	8 (11.8)	.126
Stroke, n (%)	401 (12.0)	8 (19.1)	.162	381 (12.0)	15 (22.1)	.012
Clinical characteristic
Admission time
On-hour, n (%)	1452 (43.4)	17 (40.5)	.706	1370 (43.1)	29 (42.7)	.941
Off-hour, n (%)	1895 (56.6)	25 (59.5)		1809 (56.9)	39 (57.4)
Hospital approaching method
Self-transport, n (%)	2413 (72.1)	26 (61.9)	.144	2288 (72.0)	49 (72.1)	.987
By ambulance/transferred in, n (%)	934 (27.9)	16 (38.1)		891 (28.0)	19 (27.9)
MI symptoms, n (%)			.053			.079
Typical	2843 (84.9)	30 (71.4)		2710 (85.3)	53 (77.9)
Atypical	489 (14.6)	12 (28.6)		457 (14.4)	14 (20.6)
No symptom	15 (0.5)	0 (0.0)		12 (0.4)	1 (1.5)
Anterior MI, n (%)	1901 (56.8)	34 (81.0)	.002	1796 (56.5)	44 (64.7)
Killip class, n (%)			.002			<.001
I	2655 (79.3)	27 (64.3)		2536 (79.8)	41 (60.3)
II	521 (15.6)	8 (19.1)		489 (15.4)	16 (23.5)
III	171 (5.1)	7 (16.7)		154 (4.8)	11 (16.2)
Atrial fibrillation, n (%)	75 (2.4)	2 (4.8)	.247	72 (2.3)	2 (2.9)	1.000
SBP, mmHg, median (IQR)	130 (117, 149)	127 (108, 148)	.314	130 (117, 149)	130 (107, 148)	.331
DBP, mmHg, median (IQR)	80 (71, 92)	80 (70, 88)	.169	80 (71, 92)	80 (70, 88)	.167
HR, BPM, median (IQR)	76 (66, 86)	85 (74, 102)	<.001	76 (66, 86)	80 (74, 98)	.002
White blood cell
Normal, n (%)	1819 (54.4)	16 (38.1)	.036	1729 (54.39)	39 (57.35)	.627
Abnormal, n (%)	1528 (45.7)	26 (61.9)		1450 (45.61)	29 (42.65)
Reperfusion therapy, n (%)			.008			<.001
None	1300 (38.8)	26 (61.9)		1218 (38.3)	41 (60.3)
PCI	1114 (33.3)	7 (16.7)		1085 (34.1)	13 (19.1)
Fibrinolysis	933 (27.9)	9 (21.4)		876 (27.6)	14 (20.6)
Successful reperfusion, n (%)	1959 (58.5)	8 (19.1)	<.001	1876 (59.0)	25 (36.8)	.001
Onset-to-FMC, min, median (IQR)	205 (107, 570)	490 (130, 1430)	.031	203 (106, 551)	263 (112, 1402)	.204
Medicine used postdischarge
Aspirin, n (%)	3192 (95.4)	31 (73.8)	<.001	3030 (95.3)	63 (92.7)	.057
P2Y12 antagonists, n (%)	3193 (95.4)	32 (76.2)	<.001	3031 (95.3)	64 (94.1)	.854
Statin, n (%)	3094 (92.4)	29 (69.1)	<.001	2938 (92.4)	61 (89.7)	.405
Beta-blocker, n (%)	2330 (69.6)	20 (47.6)	.002	2216 (69.7)	50 (73.5)	.497
ACEI/ARB, n (%)	1727 (51.6)	13 (31.0)	.008	1650 (51.9)	29 (42.7)	.131
Hospital days, day, median (IQR)	10.9 (8.0, 13.9)	9.7 (1.7, 12.8)	.035	10.9 (8.0, 13.9)	10.6 (7.1, 15.3)	.737
Age SI, median (IQR)	34.1 (27.7, 41.9)	49.5 (35.7, 58.3)	<.001	34.0 (27.6, 41.7)	47.4 (36.7, 55.4)	<.001
Age MSI, median (IQR)	45.76 (36.8, 56.4)	60.2 (49.7, 83.0)	<.001	45.5 (36.7, 56.1)	63.7 (52.7, 73.9)	<.001
TIMI risk score, median (IQR)	3 (2, 5)	6 (5, 7)	<.001	3 (2, 5)	6 (4, 8)	<.001
GRACE score, median (IQR)	137 (119, 159)	162 (143, 186)	<.001	137 (118, 158)	173 (151, 186)	<.001

MI: myocardial ischemia; SBP: systolic blood pressure; DBP: diastolic blood pressure; HR: heart rate; BPM: beat per minute; PCI: percutaneous coronary intervention; FMC: first medical contact; P2Y12: clopidogrel or ticagrelor; ACEI: angiotensin-converting enzyme inhibitor; ARB: angiotensin receptor blocker; SI: shock index; MSI: modified shock index; TIMI: thrombolysis in myocardial infarction; GRACE: Global Registry of Acute Coronary Events.

Values are presented as median (IQR) or n (%).

Figure 1. Receiver operating characteristic (ROC) curves of age SI, age MSI, TIMI risk score and GRACE score for STEMI patients. (A) ROC for postdischarge mortality within 30 days; (B) ROC for postdischarge mortality from 30 days to 1 year.

Table 2. Performance for the prognosis prediction of age SI, age MSI, TIMI risk score and GRACE score.

Endpoints	Discrimination					Calibration
	Cut-off point	AUC	95% CI	Sensitivity	Specificity	HL Chi-square	HL p Value	Nagelkerke-R^2	Brier score
Post-discharge mortality within 30 days
Age SI	51.07	0.753	0.677–0.829	0.500	0.898	9.690	.288	0.078	0.012
Age MSI	46.57	0.755	0.680–0.830	0.857	0.525	9.807	.279	0.085	0.012
TIMI risk score	6.00	0.779	0.706–0.851	0.714	0.812	15.046	.020	0.099	0.012
GRACE score	157.00	0.729	0.651–0.806	0.619	0.736	3.701	.883	0.077	0.012
Post-discharge mortality from 30 days to 1 year
Age SI	45.74	0.746	0.683–0.809	0.603	0.826	11.950	.154	0.076	0.020
Age MSI	52.58	0.755	0.694–0.816	0.765	0.689	10.033	.263	0.077	0.020
TIMI risk score	5.00	0.759	0.700–0.818	0.691	0.708	2.020	.918	0.102	0.020
GRACE score	151.00	0.754	0.690–0.819	0.750	0.685	10.093	.259	0.101	0.020

AUC: area under the curve; CI: confidence interval; HL: Hosmer–Lemeshow; SI: shock index; MSI: modified shock index; TIMI: thrombolysis in myocardial infarction; GRACE: Global Registry of Acute Coronary Events.

Table 3. Comparisons of the prognostic performance of age SI, age MSI versus TIMI risk score and GRACE score.

Endpoints	AUC difference (95% CI)	p for C-statistic	NRI	p for NRI	IDI	p for IDI
Post-discharge mortality within 30 days
Age SI vs. TIMI risk score	−0.026 (–0.080, 0.028)	.344	−0.001 (–0.010, 0.009)	.898	−0.292 (–0.596, 0.012)	.060
Age MSI vs. TIMI risk score	−0.024 (–0.074, 0.026)	.352	0.002 (–0.009, 0.013)	.678	−0.438 (–0.734, –0.142)	.005
Age SI vs. GRACE score	0.024 (–0.023, 0.071)	.317	0.0002 (–0.008, 0.009)	.961	−0.089 (–0.392, 0.214)	.566
Age MSI vs. GRACE score	0.026 (–0.011, 0.063)	.161	0.003 (–0.007, 0.013)	.530	−0.139 (–0.443, 0.165)	.371
Post-discharge mortality from 30 days to 1 year
Age SI vs. TIMI risk score	−0.014 (–0.075, 0.048)	.670	−0.002 (–0.021, 0.017)	.836	−0.380 (–0.618, –0.143)	.002
Age MSI vs. TIMI risk score	−0.004 (–0.061, 0.053)	.896	−0.005 (–0.020, 0.011)	.550	−0.309 (–0.548, –0.070)	.012
Age SI vs. GRACE score	−0.009 (–0.057, 0.039)	.722	−0.004 (–0.018, 0.011)	.627	−0.372 (–0.611, –0.133)	.002
Age MSI vs. GRACE score	0.001 (–0.046, 0.047)	.968	−0.006 (–0.018, 0.005)	.279	−0.367 (–0.606, –0.128)	.003

AUC: area under the curve; CI: confidence intervals; NRI: net reclassification improvement; IDI: integrated discrimination improvement; SI: shock index; MSI: modified shock index; TIMI: thrombolysis in myocardial infarction; GRACE: Global Registry of Acute Coronary Events.

Figure 2. Cumulative postdischarge mortality according to classified age SI and age MSI by cutoff points. (A) Age SI for postdischarge mortality within 30 days. (B) Age MSI for postdischarge mortality within 30 days. (C) Age SI for postdischarge mortality from 30 days to 1 year. (D) Age MSI for postdischarge mortality from 30 days to 1 year.

Figure 3. Effect of age SI and age MSI as continuous variable on postdischarge mortality. The baseline (red) line is hazard ratio, and the red shaded area represents the 95% CI. (A) Age SI for postdischarge mortality within 30 days. (B) Age MSI for postdischarge mortality within 30 days. (C) Age SI for postdischarge mortality from 30 days to 1 year. (D) Age MSI for postdischarge mortality from 30 days to 1 year.

Table 4. HR and corresponding 95% CI of categorized age SI and age MSI according to univariate and multivariate analyses based on Cox regression model.

Classifier	Model	Post-discharge mortality within 30 days		Post-discharge mortality from 30 days to 1 year
		HR (95% CI)	p Value	HR (95% CI)	p Value
Age SI	Model 1	1.05 (1.04–1.06)	<.001	1.05 (1.04–1.06)	<.001
	Model 2	7.92 (4.31–14.55)	<.001	6.55 (4.03–10.63)	<.001
	Model 3	6.52 (3.47–12.25)	<.001	6.21 (3.79–10.20)	<.001
	Model 4	5.72 (2.93–11.16)	<.001	5.40 (3.23–9.03)	<.001
	Model 5	5.44 (2.73–10.85)	<.001	5.34 (3.18–8.96)	<.001
Age MSI	Model 1	1.04 (1.03–1.05)	<.001	1.04 (1.03–1.05)	<.001
	Model 2	5.48 (2.43–12.33)	<.001	6.96 (3.97–12.20)	<.001
	Model 3	4.43 (1.94–10.12)	<.001	6.50 (3.67–11.51)	<.001
	Model 4	4.00 (1.73–9.25)	.001	5.80 (3.24–10.38)	<.001
	Model 5	4.17 (1.78–9.79)	.001	5.75 (3.20–10.31)	<.001

HR: hazard ratio; CI: confidence intervals.

Model 1, age SI or age MSI was included as continuous variable. Model 2, age SI and age MSI were divided into binary categorical variable according to the cutoff point and included in the model. Model 3, on model 2 basis, adjusted for gender (women or man), and risk factors and medical history (hypertension, diabetes, dyslipidaemia, current smoker and stroke). Model 4, on model 3 basis, adjusted for clinical characteristic (anterior myocardial infarction, Killip class (II or III vs. I) at admission), reperfusion therapy (fibrinolysis or PCI vs. none), onset-to-FMC time and hospital days. Model 5, on model 4 basis, adjusted for medicine used at discharge (aspirin, P2Y12 antagonists, statin, β-blocker and ACEI)/ARB).

Figure 4. Decision curve analysis (DCA) of age SI, age MSI, TIMI risk score and GRACE score for postdischarge mortality. (A) DCA for postdischarge mortality within 30 days; (B) DCA for postdischarge mortality from 30 days to 1 year. The x-axis indicates the threshold probability; the y-axis indicates the net benefit; the grey line displays the net benefit of the strategy of treating all patients; the black line illustrates the net benefit of the strategy of treating no patients.

Table 5. Performance of age SI and age MSI for post-discharge mortality within 30 days in subgroups.

Subgroup	Event rate (95% CI), %	Age SI			Age MSI
		AUC (95% CI)	HR (95% CI)	p Value	AUC (95% CI)	HR (95% CI)	p Value
Age
<75 years	0.88 (0.55–1.22)	0.709 (0.609–0.810)	5.22 (1.89–14.37)	.001	0.704 (0.605–0.802)	3.30 (1.28–8.50)	.014
≥75 years	3.56 (1.84–5.27)	0.709 (0.579–0.840)	7.68 (1.70–34.84)	.008	0.718 (0.596–0.839)	2.78 (0.79–9.78)	.112
Gender
Female	2.24 (1.19–3.29)	0.744 (0.637–0.851)	6.12 (2.02–18.55)	.001	0.743 (0.631–0.854)	3.49 (1.18–10.34)	.024
Male	0.95 (0.58–1.32)	0.728 (0.618–0.837)	4.65 (1.96–11.04)	<.001	0.733 (0.627–0.839)	3.40 (1.39–8.29)	.007
Reperfusion therapy
None	1.96 (1.21–2.71)	0.776 (0.682–0.870)	6.92 (2.87–16.67)	<.001	0.788 (0.698–0.877)	5.90 (2.43–14.32)	<.001
PCI	0.62 (0.16–1.09)	0.719 (0.473–0.966)	4.77 (0.94–24.23)	.059	0.717 (0.475–0.960)	8.91 (0.98–80.71)	.052
Fibrinolysis	0.96 (0.33–1.58)	0.678 (0.557–0.799)	3.37 (0.60–18.92)	.168	0.658 (0.535–0.781)	2.98 (0.48–18.48)	.242
eGFR, mL/min/1.73 m^2
≥90	0.64 (0.33–0.96)	0.676 (0.527–0.826)	4.58 (1.48–14.11)	.008	0.681 (0.535–0.827)	3.73 (1.26–11.02)	.017
<90	2.89 (1.79–3.98)	0.725 (0.636–0.814)	3.81 (1.58–9.17)	.003	0.723 (0.630–0.817)	4.40 (1.78–10.85)	.001
Onset-to-FMC within 12 h
Yes	0.95 (0.58–1.32)	0.726 (0.628–0.825)	5.62 (1.86–17.03)	.002	0.726 (0.625–0.826)	4.10 (1.62–10.35)	.002
No	2.25 (1.19–3.31)	0.776 (0.653–0.900)	7.67 (2.46–23.90)	<.001	0.779 (0.657–0.900)	8.94 (2.77–28.90)	<.001
Killip class
I	1.01 (0.63–1.38)	0.761 (0.666–0.857)	4.89 (1.80–13.28)	.002	0.756 (0.659–0.852)	5.64 (2.05–15.52)	<.001
II	1.51 (0.47–2.55)	0.598 (0.388–0.809)	1.60 (0.28–9.04)	.598	0.628 (0.419–0.837)	9.89 (1.05–93.19)	.045
III	3.93 (1.08–6.79)	0.788 (0.627–0.949)	16.74 (0.17–1627.09)	.228	0.790 (0.648–0.933)	13.73 (0.23–832.71)	.211
Anterior myocardial infarction
Yes	1.76 (1.17–2.34)	0.755 (0.676–0.834)	8.83 (2.606–29.881)	<.001	0.751 (0.670–0.831)	5.00 (1.96–12.77)	<.001
No	0.55 (0.17–0.93)	0.692 (0.456–0.927)	8.99 (1.80–44.99)	.008	0.734 (0.512–0.956)	33.08 (5.63–194.42)	<.001
Admission time
On-hour	1.16 (0.61, 1.70)	0.757 (0.665, 0.849)	6.68 (1.27, 35.08)	.025	0.742 (0.641, 0.842)	7.72 (1.27, 46.74)	.026
Off-hour	1.30 (0.80, 1.81)	0.748 (0.635, 0.861)	5.04 (1.94, 13.13)	<.001	0.762 (0.654, 0.870)	6.17 (2.29, 16.63)	<.001
Hospital approaching method
Self-transport	1.07 (0.66, 1.47)	0.708 (0.603, 0.813)	3.66 (1.31, 10.22)	.013	0.714 (0.613, 0.816)	3.60 (1.27, 10.23)	.016
By ambulance/transferred in	1.68 (0.87, 2.50)	0.819 (0.724, 0.914)	5.41 (1.65, 17.76)	.005	0.818 (0.716, 0.920)	13.90 (2.84, 67.95)	.001
White blood cell
Normal	0.87 (0.45, 1.30)	0.721 (0.571, 0.870)	4.35 (1.44, 13.14)	.009	0.715 (0.565, 0.865)	4.70 (1.56, 14.15)	.006
Abnormal	1.67 (1.04, 2.31)	0.771 (0.688, 0.854)	11.13 (2.47, 50.22)	.002	0.781 (0.701, 0.860)	6.24 (1.74, 22.40)	.005

AUC: area under the curve; HR: hazard ratio; CI: confidence intervals; SI: shock index; MSI: modified shock index; eGFR: estimated glomerular rate filtration; FMC: first medical contact.

Table 6. Performance of age SI and age MSI for post-discharge mortality from 30 days to 1 year in subgroups.

Subgroup	Event rate (95% CI), %	Age SI			Age MSI
		AUC (95% CI)	HR (95% CI)	p Value	AUC (95% CI)	HR (95% CI)	p Value
Age
<75 years	1.34 (0.92–1.77)	0.710 (0.617–0.802)	3.63 (1.75–7.54)	<.001	0.714 (0.621–0.807)	4.09 (2.08–8.05)	<.001
≥75 years	7.23 (4.74–9.72)	0.611 (0.510–0.712)	2.99 (1.22–7.31)	.017	0.594 (0.500–0.689)	2.68 (0.98–7.33)	.054
Gender
Female	2.37 (1.26–3.48)	0.768 (0.660–0.877)	13.29 (3.72–47.52)	<.001	0.765 (0.661–0.868)	11.96 (2.60–54.96)	.001
Male	2.02 (1.47–2.56)	0.739 (0.664–0.813)	3.53 (1.83–6.81)	<.001	0.753 (0.680–0.825)	4.27 (2.28–8.00)	<.001
Reperfusion therapy
None	3.26 (2.28–4.24)	0.764 (0.698–0.830)	5.41 (2.75–10.66)	<.001	0.779 (0.720–0.837)	7.60 (3.13–18.48)	<.001
PCI	1.18 (0.54–1.82)	0.830 (0.709–0.952)	18.46 (4.82–70.63)	<.001	0.823 (0.698–0.948)	18.11 (3.80–86.40)	<.001
Fibrinolysis	1.57 (0.76–2.39)	0.545 (0.364–0.726)	1.88 (0.62–5.74)	.268	0.551 (0.373–0.729)	2.69 (0.87–8.36)	.087
eGFR, mL/min/1.73 m^2
≥90	1.33 (0.87–1.79)	0.747 (0.652–0.841)	5.20 (2.27–11.94)	<.001	0.753 (0.661–0.845)	7.26 (3.29–16.03)	<.001
<90	4.28 (2.91–5.65)	0.687 (0.595–0.779)	2.89 (1.38–6.02)	.005	0.696 (0.606–0.785)	3.05 (1.43–6.53)	.004
Onset-to-FMC within 12 h
Yes	1.89 (1.36–2.42)	0.757 (0.678–0.835)	7.75 (4.13–14.55)	<.001	0.756 (0.679–0.834)	6.53 (3.30–12.89)	<.001
No	2.82 (1.6–4.04)	0.689 (0.576–0.802)	3.09 (0.998–9.56)	.050	0.726 (0.627–0.825)	4.02 (1.55–10.46)	.004
Killip class
I	1.59 (1.11–2.07)	0.753 (0.675–0.830)	5.30 (2.48–11.33)	<.001	0.757 (0.680–0.833)	5.55 (2.77–11.15)	<.001
II	3.17 (1.64–4.7)	0.699 (0.547–0.850)	5.17 (1.65–16.22)	.005	0.721 (0.579–0.863)	10.44 (2.21–49.41)	.003
III	6.67 (2.86–10.47)	0.684 (0.506–0.863)	20.06 (2.60–155.15)	.004	0.687 (0.522–0.852)	5.10 (1.04–25.05)	.045
Anterior myocardial infarction
Yes	2.39 (1.69–3.09)	0.702 (0.615–0.790)	4.48 (2.35–8.52)	<.001	0.711 (0.626–0.796)	3.94 (2.04–7.58)	<.001
No	1.71 (1.03–2.38)	0.818 (0.743–0.894)	6.98 (2.49–19.58)	<.001	0.831 (0.761–0.900)	11.45 (3.73–35.14)	<.001
Admission time
On-hour	2.07 (1.33, 2.82)	0.739 (0.649, 0.829)	6.10 (2.63, 14.15)	<.001	0.752 (0.662, 0.842)	5.29 (2.14, 13.09)	<.001
Off-hour	2.11 (1.46, 2.77)	0.748 (0.659, 0.837)	6.03 (2.97, 12.27)	<.001	0.756 (0.672, 0.840)	7.28 (3.29, 16.10)	<.001
Hospital approaching method
Self-transport	2.10 (1.52, 2.68)	0.728 (0.651, 0.805)	4.54 (2.47, 8.34)	<.001	0.741 (0.667, 0.815)	4.48 (2.30, 8.71)	<.001
By ambulance/transferred in	2.09 (1.16, 3.02)	0.791 (0.682, 0.901)	8.21 (2.70, 24.94)	<.001	0.793 (0.688, 0.898)	11.28 (3.02, 42.16)	<.001
White blood cell
Normal	2.21 (1.52, 2.89)	0.729 (0.644, 0.814)	5.94 (3.04, 11.61)	<.001	0.742 (0.662, 0.823)	5.06 (2.52, 10.17)	<.001
Abnormal	1.96 (1.25, 2.67)	0.767 (0.670, 0.863)	7.09 (2.60, 19.31)	<.001	0.771 (0.675, 0.867)	6.96 (2.70, 17.90)	<.001

AUC: area under the curve; HR: hazard ratio; CI: confidence intervals; SI: shock index; MSI: modified shock index; eGFR: estimated glomerular rate filtration; FMC: first medical contact.

Data availability statement

The identified participant data are not publicly available. All data generated or analysed during this study are included in this published article.