The eligible study population included patients who were admitted to SGH and MSH. As shown in Fig. 1, we excluded 8 patients because of missing clinical information, including ECGs, admission notes, and laboratory exams. The study included a total of 46,017 patients, of which 1,548 and 639 patients underwent sepsis and septic shock, respectively. The DLM was developed using a development dataset of 73,727 ECGs of 18,142 patients from SGH. The internal validation of the performance of DLM was conducted using 7,774 ECGs of 7,774 patients from SGH. External validation of the DLM was conducted using 20,101 ECGs of 20,101 patients from MSH. The patients were divided into development, internal validation, and external validation, exclusively. In patients with sepsis, the ECG had a rightward P, R, and T-wave axis, prolonged QTc, and tachycardia (Table 1).
Table 1
Baseline characteristics table
Characteristics | Non-sepsis patients (n = 44,469) | Sepsis patients (n = 1,548) | p |
Age, yr, mean (SD) | 58.01 (19.83) | 61.83 (24.93) | < 0.001 |
Male, n (%) | 20,836 (46.9) | 810 (52.3) | < 0.001 |
Systolic blood pressure, mmHg, mean (SD) | 121.61 (33.43) | 101.05 (39.53) | < 0.001 |
Heart rate, bpm, mean (SD) | 76.92 (17.63) | 103.59 (23.65) | < 0.001 |
Respiratory rate, bpm, mean (SD) | 18.79 (4.34) | 26.29 (8.72) | < 0.001 |
Peripheral oxygen saturation, %, mean (SD) | 97.18 (16.97) | 92.81 (28.20) | < 0.001 |
Mental change, n (%) | 288 (0.6) | 753 (48.6) | < 0.001 |
C-reactive protein, mg/dL, mean (SD) | 13.30 (37.22) | 49.80 (74.46) | < 0.001 |
Lactate, mmol/L, mean (SD) | 1.87 (1.87) | 4.64 (5.03) | < 0.001 |
White blood cell count, per uL, mean (SD) | 8180 (4200) | 13090 (6190) | < 0.001 |
Total bilirubin, mg/dL, mean (SD) | 0.72 (0.83) | 1.39 (2.58) | < 0.001 |
Creatinine, mg/dL, mean (SD) | 0.98 (0.97) | 1.47 (1.53) | < 0.001 |
PR interval, ms, mean (SD) | 169.07 (31.53) | 161.47 (41.24) | < 0.001 |
QRS duration, ms, mean (SD) | 96.59 (18.91) | 96.96 (23.49) | 0.461 |
QT interval, ms, mean (SD) | 401.65 (47.90) | 372.11 (63.62) | < 0.001 |
QTc, ms, mean (SD) | 442.41 (37.66) | 469.16 (43.79) | < 0.001 |
P-wave axis, degree, mean (SD) | 43.42 (30.85) | 45.50 (38.72) | 0.033 |
R-wave axis, degree, mean (SD) | 38.40 (46.36) | 47.11 (61.76) | < 0.001 |
T-wave axis, degree, mean (SD) | 47.42 (53.10) | 66.09 (81.47) | < 0.001 |
Legend: SD denotes standard deviation. |
During the internal and external validation, the AUC of the DLM for detecting sepsis, the primary outcome, using a 12-lead ECG, was 0.901 (95% CI = 0.882–0.920) and 0.863 (95% CI = 0.846–0.879), respectively (Fig. 3). The AUC of the DLM for detecting septic shock using 12-lead ECGs during internal and external validations were 0.906 (95% CI = 0.877–0.936) and 0.899 (95% CI = 0.872–0.925), respectively. The AUC of the DLM for detecting sepsis using 6-lead and single-lead ECGs were 0.845–0.882, and the AUC of the DLM for detecting septic shock using 6-lead and single-lead ECGs were 0.881–0.906.
A sensitivity map showed that the QT interval and T wave were associated with sepsis, and the variable importance of deep learning confirmed that the prolonged QTc was associated with sepsis (Fig. 4). The logistic regression and random forest had different variable importance and showed that the prolonged QTc, T axis, and QRS duration were important variables (Table 2).
Table 2
Variable importance for detecting sepsis
Rank | Logistic regression (Deviance difference) | Random forest (Mean decrease Gini) | Deep learning (Relative importance) |
1 | QTc (4,640) | QTc (545.3) | QT interval (0.192) |
2 | QT interval (3,187) | QT interval (535.6) | QTc (0.145) |
3 | Age (243) | T wave axis (507.6) | PR interval (0.118) |
4 | QRS duration (204) | R wave axis (493.8) | Age (0.111) |
5 | T wave axis (152) | P wave axis (458.7) | QRS duration (0.104) |
6 | P wave axis (21) | Age (444.7) | T-wave axis (0.091) |
7 | R wave axis (14) | PR interval (433.2) | Sex (0.084) |
8 | PR interval (2) | QRS duration (424.4) | R wave axis (0.082) |
9 | Sex (-1) | Sex (0) | P wave axis (0.073) |
Legend: none |
Subgroup analysis was conducted using ECGs from 4,609 patients who admitted with infectious disease patients in validation dataset. There were 256 in-hospital mortality cases in subgroup study population. The AUC of the DLM using 12, 6, and single-lead ECG, SOFA, qSOFA, NEWS, MEWS, lactate, WBC, and CRP for predicting in-hospital mortality was 0.817 (0.793–0.840), 0.815 (0.794–0.836), 0.802 (0.780–0.825), 0.817 (0.786–0.847), 0.797 (0.767–0.828), 0.808 (0.777–0.839), 0.778 (0.747–0.808), 0.801 (0.758–0.844), 0.591 (0.552–0.630), and 0.541 (0.499–0.583) outperformed other predictive models (Fig. 5).
As shown in Fig. 6, there was a significant difference in the prediction score of DLM using ECG according to the presence of infection in the validation dataset (0.277 vs 0.574, p < 0.001). In patients with COVID-19, the same trend was also observed in prediction score of DLM using ECG before and after COVID-19 infection (0.260 vs 0.725, p = 0.018).