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Eletrical alternans: an ECG sign of pericardial effusion and cardiac tamponade
The pericardial space (cavity) always contains a small amount of serous fluid which acts as a lubricant that prevents friction during ventricular contraction and relaxation. Pericardial effusion is the presence of an abnormal amount of fluid in the pericardial space. It can be caused by numerous local and systemic disorders. Accumulation of fluid in the pericardial space may lead to increased intrapericardial pressure, which in turn affects ventricular relaxation (and thus ventricular filling). This may even lead to compression of the ventricles during diastole; cardiac tamponade occurs if excess pericardial fluid causes hemodynamic effects. Electrical alternans – i.e the beat-to-beat variation i electrical amplitude – is the ECG hallmark of cardiac tamponade.
Causes of pericardial effusion and cardiac tamponade
- The most common cause of pericardial effusion is infections, such as viral, bacterial, and tuberculous infections.
- Post-pericardiotomy syndrome.
- Acute transmural myocardial infarction.
- Rupture of the free ventricular wall.
- Neoplasms (particularly breast and lung cancer).
- Inflammatory conditions, such as rheumatoid arthritis, systemic lupus erythematosus, scleroderma, and rheumatic fever.
- Aortic dissection rupturing into the pericardium.
- Idiopathic pericardial effusion.
- Renal failure, hypothyroidism, and hypercholesterolemia.
- Dressler syndrome.
- Iatrogenic damage to the pericardium.
The most common cause of pericardial effusion is pericarditis. Because it is difficult to determine if there is also myocarditis (which is frequent), it is common to use the term perimyocarditis.
Hemodynamic effects of pericardial effusion and cardiac tamponade
Intrapericardial pressure increases as fluid accumulates in the pericardial space. Intrapericardial pressure may reach the point where the ventricles and atria can no longer relax normally, and the ventricles may even be compressed during diastole. This causes adverse hemodynamic effects, and the condition is classified as cardiac tamponade. The classical signs of cardiac tamponade are hypotension, muffled heart sounds and jugular venous distention. Other frequent symptoms are pulsus paradoxus, pericardial friction sounds, tachycardia, tachypnea, weakened peripheral pulses, edema, cyanosis. Cardiac tamponade is seen in Video 1.
ECG changes caused by pericardial effusion and cardiac tamponade
Small amounts of pericardial effusion may not cause any ECG changes. Significant pericardial effusion may bring about the following ECG changes.:
- Low voltage: large amounts of pericardial effusion will diminish the QRS amplitudes.
- Electrical alternans: The amplitude of the QRS complexes vary from one beat to another (in the same lead). This is due to the swinging back and forth of the heart in the pericardial space. Note that tachycardia, pulmonary embolism and ischemia may also cause electrical alternans.
- PQ segment depression.
- Sinus tachycardia.
Refer to Figure 1.