From the Research
Electrical alternans, low voltage QRS, and sinus tachycardia have limited diagnostic value as individual ECG findings for detecting pericardial effusion, with the most recent and highest quality study suggesting that no ECG variable is sensitive for the detection of pericardial effusion 1.
ECG Findings in Pericardial Effusion
- Electrical alternans has high specificity (70-95%) but poor sensitivity (20-60%), making it useful when present but unreliable when absent, as it typically indicates a large effusion with cardiac swinging 2.
- Low voltage QRS complexes show moderate sensitivity (40-60%) and specificity (60-80%), occurring when fluid dampens electrical signals, but the correlation between QRS voltage and effusion size is weak (r = 0.296) 1.
- Sinus tachycardia has the highest sensitivity (50-80%) but lowest specificity (20-40%) as it occurs in many conditions beyond pericardial effusion 1.
Diagnostic Value of ECG Findings
- These ECG findings become more reliable when occurring together, particularly electrical alternans with low voltage QRS, but are still not sufficient for diagnosis 1.
- Echocardiography remains the gold standard for diagnosing pericardial effusion with sensitivity and specificity exceeding 90% 1.
Underlying Mechanism
- The underlying mechanism for these ECG changes relates to the insulating effect of pericardial fluid and the heart's movement within the fluid-filled space, altering electrical signal transmission to the body surface 2.
Clinical Implications
- The presence of electrical alternans, low voltage QRS, and sinus tachycardia should prompt further evaluation with echocardiography to confirm the diagnosis of pericardial effusion 1.