What electrocardiogram (ECG) changes are associated with acute pulmonary embolism?

EKG Changes Associated with Acute Pulmonary Embolism

Primary Role of EKG

The EKG cannot diagnose or exclude pulmonary embolism, but serves primarily to exclude alternative life-threatening diagnoses (acute MI, pericarditis) and to assess disease severity through detection of right ventricular strain patterns. 1, 2, 3

The EKG should be obtained immediately in every patient with suspected PE, but must always be interpreted in conjunction with validated clinical prediction scores (Wells or revised Geneva) rather than used in isolation. 2, 3

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Most Common EKG Abnormalities

Sinus Tachycardia

• Sinus tachycardia is the single most frequent finding, present in approximately 40% of PE cases, but is entirely non-specific. 2, 3
• In milder cases, sinus tachycardia may be the only detectable abnormality. 2
• Despite being non-specific, it remains independently associated with PE in multivariable analysis. 4

T-Wave Inversions (Most Clinically Significant)

• T-wave inversions in right precordial leads (V1-V4) are the most clinically significant finding, with the highest specificity (97.4%) for RV strain. 2, 3
• These inversions indicate right ventricular overload and are typically found in more severe cases of PE. 2, 3
• T-wave inversion is the most persistent ECG abnormality, often lasting beyond 2 weeks. 5
• Liberal RV strain criteria (inverted/flattened T-waves in ≥2 inferior + ≥2 anterior leads) yield a positive likelihood ratio of 4.75, making this the most useful ECG finding for increasing post-test probability. 4

S1Q3T3 Pattern

• The classic S1Q3T3 pattern is present in a minority of PE cases and has limited sensitivity. 2, 3
• When present, it yields a positive likelihood ratio of only 2.07, providing modest diagnostic value. 4
• This pattern is more common during hemodynamic instability (90%) compared to baseline (5%). 6

Right Bundle Branch Block

• Complete or incomplete RBBB occurs in 4.8-9% of PE cases and is associated with RV strain. 2, 3
• RBBB is one of the traditional manifestations of acute cor pulmonale, though present in only a minority of patients. 5

Atrial Arrhythmias

• Atrial fibrillation and other atrial dysrhythmias occur in 10-23.5% of PE patients. 2, 3
• Notably, atrial flutter and fibrillation were absent in patients without pre-existing cardiac disease in one large study. 5

Other Findings

• QR pattern in lead V1 suggests acute RV overload but is uncommon. 2, 3
• Right axis deviation occurs infrequently (only 7% in one study, equal to left axis deviation). 5
• Non-specific ST-T wave changes are very common (42% T-wave changes, 41% ST-segment abnormalities) but lack diagnostic specificity. 5
• Low voltage QRS complexes occur in approximately 6% of patients. 5

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Critical Diagnostic Limitations

Normal EKG Does Not Exclude PE

• The EKG is normal in 6% of massive PE cases and 23% of submassive PE cases. 5
• A negative EKG has a negative predictive value of only 40-50% and cannot exclude PE. 1

Poor Standalone Diagnostic Accuracy

• Traditional manifestations of acute cor pulmonale (S1Q3T3, RBBB, P pulmonale, right axis deviation) occur in only 26% of patients. 5
• Overall sensitivity is 50-60% and specificity is 80-90%, with no individual finding having sufficient accuracy for standalone diagnosis. 3, 4
• Classical ECG findings modestly increase post-test probability but lack sufficient standalone accuracy; the EKG should never be used in isolation to rule in or rule out PE. 4

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EKG Patterns During Hemodynamic Instability

When patients with acute PE deteriorate with hemodynamic instability, three distinct ischemic ECG patterns emerge:

• ST-segment elevation in lead aVR with concomitant ST-depression in leads I and V4-V6 6
• ST-segment elevation in leads V1-V3/V4 6
• ST-segment elevation in leads III and/or V1/V2 with concomitant ST-depression in leads V4/V5-V6 6

Ischemic ECG patterns combined with S1Q3 and/or abnormal QRS morphology in V1 are present in 90% of patients during hemodynamic instability, compared to only 5% at baseline. 6 This combination reflects myocardial ischemia superimposed on the right ventricular strain pattern. 6

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Clinical Algorithm for EKG Interpretation in Suspected PE

Step 1: Exclude Alternative Diagnoses

• First, use the EKG to exclude acute MI, pericarditis, and other cardiac emergencies. 2, 3
• This is the primary utility of the EKG in the PE diagnostic pathway. 1, 2

Step 2: Look for RV Strain Pattern

• Specifically assess for T-wave inversions in V1-V4, as this has the highest specificity (97.4%) and suggests more severe PE. 2, 3
• Check for the liberal RV strain pattern (inverted/flattened T-waves in ≥2 inferior + ≥2 anterior leads), which provides the best positive likelihood ratio (4.75). 4

Step 3: Integrate with Clinical Prediction Scores

• Never interpret EKG findings in isolation. 2, 3
• Integrate EKG findings with Wells or revised Geneva scores to determine pre-test probability. 2, 3
• The presence of ≥1 classic RV strain sign is associated with higher adverse event rates and worse prognosis. 2, 3

Step 4: Assess for Hemodynamic Instability

• If hemodynamic instability is present with RV strain on EKG, obtain urgent echocardiography to assess RV function and guide reperfusion therapy decisions. 2, 3
• Look for ischemic patterns (ST-elevation in aVR, ST-changes in precordial leads) combined with RV strain, which indicate severe PE with myocardial ischemia. 6

Step 5: Implement Continuous Monitoring

• Continuous EKG monitoring is strongly recommended during transport/transfer for suspected PE, as arrhythmias and ischemic patterns may develop acutely. 2, 3

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Prognostic Correlation

• EKG findings correlate with severity of pulmonary hypertension and RV dysfunction. 2, 3
• Patients with abnormal EKGs have significantly higher pulmonary arterial mean pressures and right ventricular end-diastolic pressures compared to those with normal EKGs. 5
• Larger perfusion defects on imaging occur in patients with EKG abnormalities compared to those with normal EKGs. 5
• The presence of RV strain patterns indicates more severe PE with greater hemodynamic compromise. 2, 3

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Common Pitfalls to Avoid

• Do not rely on traditional cor pulmonale signs alone (S1Q3T3, RBBB, P pulmonale, right axis deviation), as they occur in only 26% of cases. 5
• Do not use the EKG to exclude PE—a normal EKG is present in up to 23% of submassive PE cases. 5
• Do not interpret EKG findings without clinical context—always integrate with validated prediction scores. 2, 3
• Do not miss ischemic patterns during hemodynamic instability—ST-elevation in aVR with diffuse ST-depression suggests severe PE with myocardial ischemia requiring urgent intervention. 6
• Be aware that non-specific ST-T changes are the most common findings (>40% of cases) but provide minimal diagnostic value. 5