The study population was derived from 413 patients with chest pain presenting to the ED for evaluation (See Figure 1). A total of 49 patients (11.9%) had a MACE: 31 patients (7.5%) underwent PCI, and 1 patient (0.2%) underwent CABG. There were 17 (4.1%) deaths. The baseline characteristics of the study cohort are shown in Table 2. The C statistic for the score in the whole study group was 0.83 (95% CI: 0.77 to 0.89). There was a progressive, significant pattern of increasing event rates as the score increased in the study cohort (P < 0.001 by χ2 for trend; Figure 2).
Table II: Baseline characteristics risk factors of the study cohort
Age, years
59.77 ± 16.92
Male
248 (60.1%)
History of Atherosclerotic disease
120 (29.1%)
Hypertension
222 (53.8%)
Hyperlipidemia
166 (40.2%)
Diabetes Mellitus
144 (34.9%)
Obesity (BMI>30)
0 (0.0%)
Smoking
60 (14.5%)
Positive Family History
20 (4.8%)
Ethnicity
Chinese
227 (55.0%)
Malay
109 (26.4%)
Indian
50 (12.1%)
Others
27 (6.5%)
* The rate of MACE in the three groups was different (P < 0.001 by χ2 test). CABG: coronary artery bypass graft; MACE: major adverse cardiac events; PCI: percutaneous coronary intervention. Data are mean ± SD or n (%).
To stratify chest pain patients in the ED, patients were classified into three groups (Table 3). The boundaries of low, intermediate, and high risk groups were defined as having a MACE rate of ≤ 2.5%, > 2.5% but ≤ 20%, and > 20% respectively. In the low risk group, there were 72 patients (17.4%) out of which 1 patient underwent PCI. The MACE rate in this group was 1.4%. In the intermediate risk group, there were 233 patients (56.4%) out of which there was 6 deaths and 6 PCIs. The MACE rate was 5.2% in this group. In the high risk group, there were 108 patients (26.2%) out of which there were 24 PCIs, 11 deaths and 1 CABG. The MACE rate in this group was 33.3%.(Table 3)
Table III: Classification of patients
Classification
Score
Patients,
n (%)
MACE (n)
Rate of MACE*
Low Risk
0-2
72 (17.4%)
PCI (1)
1.4%
Intermediate Risk
3-5
233(56.4%)
PCI (6), Death (6)
5.2%
High Risk
6-10
108 (26.2%)
CABG (1), PCI (24), Death (11)
33.3%
* The rate of MACE in the three groups was different (P < 0.001 by χ2 test). CABG: coronary artery bypass graft; MACE: major adverse cardiac events; PCI: percutaneous coronary intervention
The rationale for choosing classification of HEART Score 0-2 (Low-Risk), 3-5 (Intermediate Risk), and 6-10 (High Risk) is because there was significant difference in the trend of MACE between the three groups using this classification (Low-risk, Intermediate Risk and High Risk), P < 0.001 by χ2 test. The MACE rate rose to 2.6% with HEART score of 3, above the threshold of 2.5% which we would consider low risk. Between a HEART score of 5 and 6, the HEART score increased from 8.7% to 21.7% defining the boundary between intermediate and high risk. (See Figure 2) This risk group classification differs from the original HEART score but is somewhat similar to the validation study for the Modified HEART score by Chun-Peng MA et al. [7]
The numerical distribution of the score’s five components in the groups with or without MACE is shown in Table 4. Amongst the components of the HEART score that predict MACE; History, ECG, Risk Factors and Troponin reached statistical significance (P < 0.05 by χ2 for trend). In our study, the MACE rate was 3.1% (9/294) if the troponin was within the normal range (score 0 points for troponin component); the MACE rate was 22.7% (10/44) if the troponin score was one point; the MACE rate was 40.0% (30/75) if the troponin score was two points. There was a progressive, significant pattern of increasing event rates as the troponin score increased (P < 0.001 by χ2 for trend).
The mean HEART score was 6.65 ± 1.97 in the MACE group and 4.02 ± 1.87 in the non-MACE group (P < 0.001 by t-test).
Table IV: Number of patients in each component of the modified HEART score
No MACE, n= 364
MACE, n= 49
p-value for trend
0
1
2
0
1
2
History*
105 (28.8%)
149 (40.9%)
110 (30.2%)
7 (14.3%)
22 (44.9%)
20 (40.8%)
0.031
ECG**
255 (70.1%)
95 (26.1%)
14 (3.8%)
12 (24.5%)
15 (30.6%)
22 (44.9%)
<0.001
Age
77 (21.2%)
150 (41.2%)
137 (37.6%)
5 (10.2%)
24 (49.0%)
20 (40.8%)
0.209
Risk Factors*
85 (23.4%)
133 (36.5%)
146 (40.1%)
5 (10.2%)
17 (34.7%)
27 (55.1%)
0.017
Troponin**
285 (78.3%)
34 (9.3%)
45 (12.4%)
9 (18.4%)
10 (20.4%)
30 (61.2%)
<0.001
Data are n (%). **: p-value<0.01; *: p-value<0.05
HEART: History, ECG, Age, Risk factors and Troponin; MACE: major adverse cardiac events.
In our study, we found the number of risk factors had a significantly affect MACE (P=0.020). However, we found certain risk factors such as Diabetes Mellitus and Smoking increase MACE by 1.638 and 1.383 respectively but it is not statistically significant (Refer to Table 5).
Table V: Risk Assessment of risk factors that will result in MACE.
Risk Factors
Odds Ratio
P-value
95% Confidence Interval
History of Atherosclerotic Disease
0.439
0.060
0.186-1.035
Hypertension
0.401
0.027
0.178-0.902
Hyperlipidemia
0.360
0.008
0.169-0.765
Diabetes Mellitus*
1.638
0.236
0.724-3.708
Smoking*
1.383
0.485
0.556-3.435
Positive Family History
0.102
0.052
0.010-1.022
Age
0.402
0.037
0.171-0.945
Male
0.400
0.001
0.230-0.697
Intermediate HEART Score
0.219
<0.001
0.104-0.457
High HEART Score**
5.893
0.002
1.940-17.899
**: Significantly increase odds of MACE; p-value<0.05.
*: Increase odds of MACE but not significant.
MACE: major adverse cardiac events.