ECG in patients after out-of-hospital cardiac arrest

Introduction: ECG is a simple method accessible in prehospital care and is commonly used in the management of out-of-hospital cardiac arrest (OHCA). Previous studies were focused mainly on ST elevation. The informative value of ECG after restitution of spontaneous circulation (ROSC) may be influenced by hemodynamic instability, acid-base changes, and hyposaturation after resuscitation.

Aim: To establish the incidence of different pathologies on ECG after ROSC, to determine its sensitivity and specificity for acute coronary syndromes (ACS), and to compare their validity immediately after ROSC and after hospital admission.

Methods: An observational retrospective study from a prospective OHCA registry of a cardiac arrest center (CAC). Different pathologies and their frequencies were described immediately after ROSC and after hospital admission, and their relation to coronary angiography findings and the definitive diagnosis. The sensitivity and specificity of the tests were established.

Results: A total of 146 patients after OHCA with (ROSC) were included. Their ECG was obtained both after OHCA and after admission to hospital. ST elevation was present in 52 % of patients after ROSC, and STEMI diagnosis was confirmed in 65.8 % of patients (sensitivity 66 %, specificity 96 % for STEMI). ACS was confirmed in 68.4 % of patients and significant coronary artery disease (CAD) in 91.7 %. Percutaneous coronary intervention (PCI) was performed in 73.3 % of the patients who underwent coronary angiography. ST elevation was present in 36 % of patients after admission, the diagnosis of STEMI was confirmed in 75.5 % (sensitivity 75 %, specificity 89 % for STEMI), ACS was confirmed in 75.5 %, significant CAD in 93.2 %, and PCI was performed in 77.3 % of patients. Between ROSC and admission ECGs, there was a significant difference in the incidence of ST elevation (p = 0.009) and QRS latitude (p = 0.003). We observed no significant differences between both groups in the incidence of ACS or significant CAD, PCI, and systolic blood pressure. The median interval between both curves was 60 mins (IQR 25-75), 45-90 mins. A change in ST elevation between ROSC and admission was present in 30.3 % of patients; compared to the group without differences, we observed no significant changes in systolic blood pressure, QRS latitude, and shockable rhythm. Left bundle branch block (LBBB) was present in 9.6% of patients after ROSC and in 11.6 % after admission, and had a low sensitivity and specificity for STEMI and ACS. The incidence of STEMI was 7.14 % after ROSC and 11.8 % after admission. ACS was present in 21.4 % after ROSC and in 17.6 % after admission; significant CAD occurred in 62.5 % and 75 %, respectively. ST depression was present in 24.8% of patients after ROSC and 27.8 % after admission, and had a low sensitivity and specificity for ACS (ACS in 36.1 % after ROSC and 45.7% after admission, significant CAD in 79,2 % after ROSC and 80.6 % after admission, and PCI was performed in 52.4 % and 51.6 %, respectively). A normal ECG was seen in 5.5 % after ROSC and 6.85 % after admission. ACS was confirmed in 50 % of patients after ROSC and 0 % after admission (sensitivity for ACS exclusion 100 %, specificity 56 % after admission). Significant CAD was present in 100% after ROSC (if coronary angiography was performed) and in 12.5 % after admission. PCI was performed in 100 % and 20 %, respectively.

Conclusions: ST elevations have a non-significantly higher sensitivity for the diagnosis of STEMI if they persist after admission, and both ST elevation groups have a high incidence of significant CAD and PCI. ST elevations after ROSC have a high specificity for STEMI. A normal ECG after ROSC is rare and not suitable for ACS exclusion; normal ECG after admission has a very high sensitivity for ACS exclusion. LBBB and ST depression have a low sensitivity and specificity for ACS and CAD.

Keywords: ECG, out-of-hospital cardiac arrest, acute coronary syndrome.