Introduction Acute Pulmonary Embolism (PE) is a major cause of cardiovascular mortality with rate up to 24.5% in high-risk patients, despite evident progress in diagnosis and treatment. Early risk stratification for patients with acute PE remains essential in order to establish the appropriate treatment and management [1]. A basic 12 lead Electrocardiogram (ECG) is initial, most common non-invasive test that is quickly interpretable and performed in almost every patient with cardiac or respiratory symptoms in the emergency department. Numerous ECG abnormalities have been reported in PE. Certain constellations of ECG abnormalities (patterns) have been associated with Right Ventricular (RV) dysfunction in the context of PE. This is commonly known in the literature as a concept of ECG RV strain patterns. These ECG patterns are including changes in the rhythm, rate, conduction, axis of QRS complex and morphology of P wave, QRS complex, ST segment and T wave [1]. Many studies [3-13] that have been published are describing the association between various ECG RV strain patterns and: more extensive and complicated PE [2,3]; pulmonary arterial hypertension [4,5] and association with negative clinical outcome [6-13]. Current guidelines of the European Society of Cardiology (ESC) [1] are discussing ECG findings in PE, however the use of ECG as a prognostic tool is not listed in the recommended modalities. On the other side, there is growing evidence in the literature supporting the usefulness of ECG in predicting outcome in acute PE. Various ECG RV strain patterns related to clinical deterioration and mortality among patients with PE are shown in many clinical studies [6-13]. A recent meta-analysis [13] found several ECG patterns (atrial fibrillation, S1Q3T3 pattern, right bundle branch block, right axis deviation) and ischemic patterns (negative T waves, ST depression, ST elevation) to be significantly predictive of an adverse outcome in acute PE. As such, ECG could be an easily, widely available prognostic tool to help guide management in acute PE. Furthermore, the reported results in previous studies vary greatly and are showing inconsistent data regarding the prognostic value of different ECG RV strain patterns in PE. Currently, there is a paucity of data about the prognostic significance of the number of ECG RV strain patterns. We hypothesized that various ECG RV strain patterns at hospital admission, as well as the total number of these ECG patterns, could predict an adverse in-hospital outcome in patients with acute PE. Thus, the aim of this study was to evaluate and analyze various ECG RV strain patterns at hospital admission, their occurrence rate in patients with acute PE and their relation with in-hospital clinical outcome. In addition, we investigated the relationship between total number of ECG RV strain patterns and in-hospital clinical outcome in patients with acute PE.

Materials and Methods This was a retrospective study, that evaluated data from medical charts of 183 consecutive patients diagnosed with acute pulmonary embolism, who were hospitalized in one university hospital in Skopje (Clinic of Anesthesiology, Reanimation and Intensive Care) during a 7 year period ( (January 2013- September 2020). All patients included in the study had acute first time diagnosed PE, were hospitalized, had ECG done within the first 24 hours upon hospital admission and echocardiography within 72 h from admission. Patients whose medical documents were not complete, patients with recurrent PE, uninterpretable ECG (pacemaker leads, left bundle branch block) and those who were transferred to other centers for different reasons were excluded from the study. Pulmonary embolism was diagnosed by multislice Computed Tomographic (CT) scan of the pulmonary arteries presented as partial or complete filling defect within the pulmonary arteries or by echocardiographic visualization of the thrombus in the right heart or pulmonary arteries. In all patients we analyzed demographic data, clinical data, risk stratifications, admission ECG, admission echocardiography, laboratory and CT findings, and treatment and patient outcomes. Additionally all patients were stratified into one of the following 3 risk categories: high, intermediate and low risk group of patients, defined by the different levels of PE severity (according to latest ESC recommendations for the diagnosis and management of pulmonary embolism [1]. High-risk group of patients were defined as those haemodynamically unstable, suffering cardiac arrest or obstructive shock or persistent hypotension (systolic arterial blood pressure at presentation ≤ 90 mmHg or a pressure drops of ≥ 40 mmHg for more than 15 min (if not caused by hypovolaemia, sepsis or new onset arrhythmias). All those patients who were haemodynamically stable at admission were classified as not high risk patients. The criteria used to categorize not high risk patients into intermediate or low-risk groups were the presence or absence of RV dysfunction (strain) at echocardiography or presence or absence of myocardial injury as indicated by an elevated cardiac troponin level [1].