What ECG findings correlate with a pulmonary embolism (PE) being dangerously imminent?

From the Guidelines

ECG findings that correlate with a pulmonary embolism (PE) being dangerously imminent include the S1Q3T3 pattern, right bundle branch block (RBBB), right axis deviation, sinus tachycardia, and T wave inversions in the right precordial leads (V1-V4), as these changes reflect right heart strain and increased pulmonary pressures. These ECG changes are associated with right ventricular overload, which is a sign of a more severe PE, as noted in the 2020 study by the Acute Cardiovascular Care Association (1). The presence of these ECG findings should prompt immediate further evaluation with imaging studies like CT pulmonary angiography, especially when accompanied by clinical symptoms such as sudden dyspnea, chest pain, or hypoxemia. Some key points to consider when evaluating a patient for a suspected PE include:

• Clinical probability is usually high in patients presenting with shock or hypotension, and the differential diagnosis includes cardiogenic shock, acute valvular dysfunction, tamponade, and aortic dissection (1)
• The use of clinical prediction scores, such as the Wells criteria and the Geneva score, can help determine the likelihood of PE (1)
• Bedside transthoracic echocardiography can yield evidence of acute pulmonary hypertension and RV dysfunction if acute PE is the cause of the patient’s haemodynamic decompensation (1)
• CT pulmonary angiography (CTPA) is commonly performed in patients with a high pretest probability for PE or in those with a positive D-dimer without a high-risk clinical score (1) It's essential to note that ECG findings can be normal in up to 30% of confirmed PE cases, so the absence of these patterns doesn't rule out a PE. A practical approach to diagnosing PE, as suggested by the British Thoracic Society (1), emphasizes the importance of considering clinical symptoms, imaging evidence, and laboratory results to make an accurate diagnosis and provide appropriate treatment.

From the Research

ECG Findings Correlating with Imminent Pulmonary Embolism

To identify a pulmonary embolism (PE) that is dangerously imminent using ECG findings, several key patterns and changes can be considered:

• S1Q3T3 pattern: This is a classic but not highly sensitive or specific sign of PE 2, 3, 4.
• Atrial tachyarrhythmias: These can occur in the context of PE due to right ventricular strain 2.
• Incomplete right bundle-branch block: This is another ECG change that may be seen in patients with PE 2, 3.
• Negative T wave over right and midprecordial leads: T-wave inversions, particularly in leads V1-V4, can indicate right ventricular strain 3.
• ST elevation: Although rare, ST elevation, especially in anterolateral leads, can be associated with PE and may represent reciprocal changes of myocardial strain in the interventricular septum or right ventricle lateral wall 2.
• Right ventricular strain pattern: This is significantly more common in patients with PE, especially those with a large clot load, and includes signs such as T-wave inversions in the right precordial leads, suggesting right ventricular dysfunction 5.
• QTc prolongation with ST-T changes: These can occur during episodes of PE and may be associated with myocardial ischemia or acute right ventricular overload 4.
• S-wave notch in lead V1 with clockwise rotation: This is an uncommon finding that may be associated with PE, possibly due to acute right ventricular overload or vagal reflex 4.
• Atrioventricular junctional rhythm with sinus arrest: Transient arrhythmias can occur in the setting of massive PE, possibly due to acute right ventricular dilatation and strain 4.

Diagnostic Utility and Limitations

While these ECG findings can suggest the presence of a PE, especially when considered in the clinical context, their sensitivity and specificity vary:

• Many patients with PE have normal ECGs or nonspecific changes 5.
• The presence of right ventricular strain pattern on ECG is highly suggestive of PE, particularly in patients with large clot loads 5.
• Echocardiography can play a crucial role in diagnosing PE, especially when ECG findings are confusing or nonspecific, by demonstrating right ventricular dilatation and dysfunction 2, 6.

Clinical Application

In clinical practice, the diagnosis of PE should be considered in patients presenting with symptoms such as chest pain and dyspnea, and ECG should be interpreted in the context of these symptoms and other diagnostic findings:

• A high index of suspicion for PE should be maintained, especially in patients with risk factors for thromboembolism 3.
• ECG changes, when present, can support the diagnosis but are not definitive on their own 5.
• Further diagnostic testing, including echocardiography and computed tomographic pulmonary angiography, is often necessary to confirm the diagnosis of PE 2, 6.