Alternans on ECG: What It Means and Why It Matters

Introduction

Alternans on an electrocardiogram (ECG) is a phenomenon where the amplitude of certain waveforms, such as the T-wave or QRS complex, alternates with each heartbeat. This finding can indicate electrical instability in the heart and is often associated with an increased risk of arrhythmias.

Types of Alternans

1. T-Wave Alternans (TWA): This is the most clinically significant type. It refers to a beat-to-beat variation in the T-wave amplitude and can be a marker of increased risk for ventricular arrhythmias and sudden cardiac death.
2. Electrical Alternans: A more generalized form, often seen in cases of pericardial effusion, where the entire QRS complex alternates in amplitude due to the swinging motion of the heart in the pericardial fluid.
3. Mechanical Alternans: This refers to alternating stroke volume and is usually associated with severe heart failure.

Causes of ECG Alternans

• T-wave alternans:
  • Ischemic heart disease
  • Long QT syndrome
  • Cardiomyopathy
  • Electrolyte imbalances (e.g., hypokalemia, hypocalcemia)
  • Digitalis toxicity
• Electrical alternans:
  • Large pericardial effusions
  • Cardiac tamponade

Clinical Significance

• T-wave alternans is a predictor of malignant ventricular arrhythmias, such as ventricular fibrillation or ventricular tachycardia.
• Electrical alternans is crucial in diagnosing pericardial effusion and impending cardiac tamponade, which can be life-threatening.

Diagnosis and Management

• Diagnosis: Standard 12-lead ECG, Holter monitoring, or stress testing can help detect alternans.
• Management:
  • Treat underlying heart disease (e.g., ischemia, electrolyte disturbances, heart failure)
  • Consider implantable cardioverter-defibrillator (ICD) for high-risk patients with T-wave alternans
  • Perform pericardiocentesis for large pericardial effusions.

Conclusion

ECG alternans is an important marker of cardiac instability. Recognizing and addressing the underlying cause can help prevent life-threatening arrhythmias or cardiac complications.

Source recommendations

1. European Society of Cardiology Guidelines on Sudden Cardiac Death

1. https://academic.oup.com/eurheartj/article/43/40/3997/6675633
2. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death
3. https://pubmed.ncbi.nlm.nih.gov/29191938/
4. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000549
5. https://pubmed.ncbi.nlm.nih.gov/36017572/

2. American Heart Association Guidelines for Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000549
2. https://pubmed.ncbi.nlm.nih.gov/29097320/
3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000548
4. https://pubmed.ncbi.nlm.nih.gov/16949478/
5. https://professional.heart.org/en/science-news/2017-guideline-for-management-of-patients-with-ventricular-arrhythmias-and-the-prevention-of-scd