Right Bundle Branch Block on ECG as a Predictor of Sudden Cardiac Arrest Due to Pulmonary Embolism

BACKGROUND High-risk pulmonary embolism (PE) refers to a subset of massive PE that can lead to sudden cardiac arrest (SCA) or hemodynamic collapse. It is crucial to identify the clues that might precede high-risk PE in resuscitated SCA. The presence of right bundle branch block (RBBB) with a QR pattern in V1 on the electrocardiogram (ECG) has a high positive predictive value for diagnosing cardiac arrest caused by high-risk PE. Therefore, we present a case study of SCA caused by high-risk PE. CASE REPORT A 44-year-old woman with no medical history presented to the emergency room due to SCA. The first ECG showed sinus tachycardia and RBBB with a QR pattern in V1. The clinical manifestations, particularly the abnormal ECG findings, led to the consideration of high-risk PE. Urgent thrombolytic therapy was administered before confirmation with computed tomographic pulmonary angiogram (CTPA). The patient was eventually diagnosed with antiphospholipid antibody syndrome and treated with warfarin. CONCLUSIONS RBBB with a QR pattern in V1 on ECG has a high positive predictive value for the diagnosis of cardiac arrest caused by high-risk PE. Furthermore, the presence of a QR pattern in V1 performs as an independent predictor for high-risk PE patients who may require advanced treatments, including systemic thrombolysis or invasive embolectomy. It is worth further exploring the prioritization of thrombolysis for high-risk PE patients before confirmation with CTPA, when ECG findings strongly suggest the diagnosis.