Pulmonary embolism (PE) is a common and potentially life-threatening medical condition. It is estimated that thrombo-embolism affects over 1,000,000 people in the United States each year and results in over 25,000 deaths annually. ¹

Risk stratification is important in determining the likelihood of poor outcomes for patients with acute PE. It dictates the attitude towards patients with PE from early discharge to urgent care in intensive care units. Thus, recent risk stratification algorithms rely on various clinical, laboratory, and imaging factors to estimate the risk of complications and guide treatment decisions. ² A major area of uncertainty in the risk stratification of acute PE is the potential role of electrocardiography (ECG) abnormalities in predicting the risk of complications as several ECG abnormalities have been identified in patients with acute PE, including right ventricular strain and S1Q3T3 type pattern. ^{3 – 5} These changes are primarily related to right ventricular (RV) overload and reflect right ventricular dysfunction (RVD), injury and enlargement in patients with acute PE. ^{6 – 9} Furthermore, ECG abnormalities associated with acute PE are more likely to be present in patients with a confirmed diagnosis of PE. ^{2 , 10} Despite their potential prognostic value, none of these ECG changes are included in the current guidelines for PE risk stratification due to the lack of specificity. ^{2 , 11} Encouraging evidence has emerged showing the relationship between the right bundle branch block (RBBB) and SIQIII patterns in acute PE events with poor outcomes. ^{10 , 12 , 13} In addition, more research is needed to clarify the potential role of ECG abnormalities in the risk stratification of acute PE. By addressing these gaps in the literature, we can improve our ability to manage patients with this common and potentially life-threatening condition. ^{12 , 14}

A total of 255 patients were included in the analysis. All of the medical reports for these patients included a usable ECG from the time of their acute PE episode. Patients were divided into two groups: i) Group I (n=122, 47.8%) included patients with PE without RBBB nor SIQIII patterns; and ii) group II (n=133, 52.2%) included patients with RBBB and/or SIQIII type patterns. Patients in both groups did not differ by age nor sex. The proportion of diabetes mellitus (DM), hypertension (HTN) and dyslipidemia were homogeneous between the two groups ( Table 1). ²⁵

Group II patients had an active cancer (17.3% vs. 12.3%) more frequently but this difference did not reach statistical significance (p=0.29). Patients presenting with SIQIII pattern and/or RBBB were also significantly more likely to have history of systolic or diastolic heart failure (13.5% vs. 4.9%, p=0.03).

We analyzed the association between the presence of RBBB and/or SIQIII type pattern with PE severity and patient outcome.

Patients in group II presented more frequently with acute right heart symptoms (45.1 vs. 18%, p<0.001), more often showed cardiogenic shock (31.6 vs. 4.1%, p<0.001) and had lower systolic blood pressure (SBP) (110.3 vs. 122.8 mmHg, p<0.001) and diastolic blood pressure (DBP) (67.5 vs. 73.9 mmHg, p<0.001) at admission. The difference was statistically significant for all these parameters. Syncope occurred more frequently in Group II patients but the difference did not reach statistical significance (14.3 vs. 9%, p=0.24) ( Table 1).

Patients in group I had a significantly lower likelihood of positive Cardiac troponin I (cTnI) or high-sensitivity cardiac troponin (hs-cTn) levels (26.9 vs. 51.1%, p<0.001).

Echocardiographic parameters indicating a right heart injury also occurred more frequently in group II patients: SPAP >40 mmHg (63.2 vs. 28.3%, p<0.001), paradoxical interventricular septum (51.6 vs. 26.5%, p<0.001), tricuspid annular plane systolic excursion (TAPSE) <17 mm (55.6 vs. 4.2%, p<0.001), the presence of a thrombus in the right heart (25 vs. 4.2%, p<0.001). Thus, RVD was significantly more frequent in Group II patients by univariate analysis (p<0.001).

A total of 101 patients (39.6%) had RBBB, 66 (26%) had SIQIII type patterns, and 34 patients (13.4%) had both SIQIII pattern and RBBB.

Negative T waves in leads V1-V3 were significantly more frequently associated with Group II patients in univariate analysis (p=0.01) ( Table 1).

There were slightly more patients with atrial fibrillation (AF) in Group I patients, but this was not statistically significance (10.6 vs. 7.6%, p=0.4).

Groupe II patients were significantly associated with in-hospital mortality (22.6 vs. 6.1%, p=0.002) and MACEs during hospitalization by univariate analysis (43.3 vs. 13.7%, p<0.001) ( Table 1).

Multivariate logistic regression analysis demonstrated five independent predictors of MACE: SIQIII and/or RBBB (OR=2.4; 95% CI: 1.04, 5.9; p=0.039), renal failure (OR=2.5; 95% CI: 1.08, 5.8; p=0.031), positive troponin levels (OR=5.4; 95% CI: 2.34, 12.6; p<0.001), RVD (OR=7.9; 95% CI: 2.16, 28.8; p=0.002) and right heart failure symptoms during initial presentation (OR=2.5; 95% CI: 1.1, 5.8; p=0.025) ( Table 2). Using these models, SIQIII pattern (OR=4.8; 95% CI: 1.9, 12.2; p=0.001), RVD (OR=15.2; 95% CI: 1.9, 12.4; p=0.01) and cardiogenic shock at admission (OR=2.7; 95% CI: 1, 6.9; p=0.034) were independently associated with in-hospital mortality, on the other hand, no association was found between in-hospital mortality and group II patients ( Table 3).

A medium or long term follow-up was done for 83% of the cohort. The Kaplan–Meier survival analysis also demonstrated SIQIII patterns as a predictor of overall mortality (p<0.001) ( Figure 1). The Kaplan–Meier analysis also identified the presence of SIQIII and/or RBBB patterns as a predictive factor for overall mortality (p<0.001) ( Figure 2).

Early and risk-oriented diagnosis and management of patients with acute PE are key for a better prognosis. ² In our study, RBBB and SIQIII-type patterns at admission were found to be associated with worsening clinical, echographic and biological profiles and with a poor clinical outcome.

Meta-analyses by Shopp et al., reported different ECG patterns, such as inverted T wave in leads V1-V4, a QR pattern in lead V1, SIQIII, complete or incomplete RBBB and ST elevation in lead aVR as being associated with increasing severity and poor outcomes. ⁴

ECG scoring by Daniel et al., was notable for providing an applicable and reliable prognostic tool. ⁵ However, recent studies indicate that there are several ECG abnormalities that can provide valuable prognostic information, but are not currently included in these scores. ⁹ These ECG findings were also associated with early clinical deterioration. ²⁰ Despite these findings, ECG abnormalities were not included nor recommended in the latest guidelines for risk stratification of acute PE. ² This is probably due to the lack of specificity as these changes can be encountered in acute and chronic cor pulmonale. ²¹

The SIQIII pattern was found to be a strong independent predictor of in-hospital mortality, contrary to RBBB. Acute onset of SIQIII patterns mirror a longitudinal dextrorotation of the RV and appears to be more associated with poor hemodynamic outcomes than RBBB. RBBB alone was not found to be independently associated with in-hospital mortality The findings concerning RBBB were interpreted as follows: this characteristic can be observed in both acute pulmonary embolism (PE) and different conditions affecting the right ventricle (RV). Consequently, distinguishing between a new onset RBBB and a preexisting chronic RBBB is challenging. Furthermore, this challenge may be attributed to the limited sample size in various studies exploring the correlation between ECG abnormalities and risk assessment in acute PE.

New onset SIQIII and/or RBBB is likely to increase right heart failure, cardiogenic shock and intra-hospital mortality. These ECG changes seem to profoundly impact the overall survival as patients with SIQIII and/or RBBB patterns, and especially those with SIQIII, have significantly lower survival rates with curves diverging in less than a year. Parallel to the Pulmonary Embolism Severity Index (PESI) and to the simplified Pulmonary Embolism Severity Index (SPESI) scores, these findings suggest the importance of the RBBB and SIQIII patterns as important criteria in risk stratification of PE. ¹² The recent onset of these patterns may improve its specificity especially if other causes of acute cor pulmonale are ruled out.

Given the predictive value of these parameters, it would be beneficial to integrate them into new and more accurate risk stratification scores for future guidelines. This would probably outperform guideline-backed risk scores. ²²

Furthermore, our study suggests that ECG alone is a useful tool in determining the outcome of PE, particularly in limited resources environments where advanced diagnostic tools are not available. ^{23 , 24}

Risk stratification is key for the management of patients with acute PE. New-onset RBBB and/or SIQIII and especially SIQIII patterns are likely to worsen patient outcomes. Our study suggests important and independent prognostic values of RBBB and SIQIII patterns and their usefulness in determining the outcome of acute PE patients.