Low Voltage QRS Complex on ECG
Low Voltage QRS Complex on ECG
Q1. What is the diagnostic cut-off for low voltage QRS in limb leads?
Q2. Low voltage QRS in all precordial leads is defined as amplitude < ?
Q3. Which of the following is a common extracardiac cause of low voltage QRS?
Q4. Which condition is classically associated with low voltage + electrical alternans?
Q5. Which infiltrative disease can lead to low voltage QRS?
Q6. Severe hypothyroidism (myxedema) is a cause of:
Q7. Why can COPD cause low voltage QRS?
Q8. Which statement is TRUE regarding low voltage QRS?
Q9. Which ECG finding is a red-flag combination for tamponade?
Q10. Which of the following is NOT a cause of low voltage QRS?
Definition
- Low Voltage QRS = Amplitude of QRS complexes is reduced below standard thresholds.
- Diagnostic cut-offs:
- Limb leads: QRS amplitude < 5 mm in all leads.
- Precordial leads: QRS amplitude < 10 mm in all leads.
⚡ Mechanisms
Low voltage occurs when the electrical potentials generated by the heart are dampened before reaching the recording electrodes.
✅ Common Causes
1. Increased distance between heart and electrodes
- Obesity
- Pericardial effusion
- Pleural effusion
- Emphysema (COPD with hyperinflation)
2. Loss of viable myocardium (weak electrical source)
- Extensive myocardial infarction
- Infiltrative cardiomyopathies (amyloidosis, sarcoidosis, hemochromatosis)
- Dilated cardiomyopathy
- Severe hypothyroidism (myxedema heart)
3. Other causes
- Constrictive pericarditis
- Severe cachexia
- End-stage renal or liver disease
🔍 Clinical Relevance
- Pericardial effusion + low voltage + electrical alternans = cardiac tamponade (classic triad).
- Important diagnostic clue in systemic diseases (amyloidosis, hypothyroidism, COPD).
- Helps in risk stratification of cardiomyopathy.
🧾 Key Exam Pearls
- Check both limb and chest leads before labeling.
- Always correlate with clinical context + echocardiography.
- Voltage criteria for LVH cannot be applied reliably in low-voltage ECGs.
Low Voltage QRS Complex
- Definition: QRS amplitude < 5 mm in all limb leads OR < 10 mm in all precordial leads.
- Measured in: Peak-to-peak height of QRS complexes.
- Primary mechanism: Attenuation of cardiac electrical potentials before reaching body surface electrodes.
- Cause group 1 – Increased distance: Obesity, pericardial effusion, pleural effusion, emphysema.
- Cause group 2 – Weak source: Extensive myocardial infarction, dilated cardiomyopathy.
- Cause group 3 – Infiltrative disease: Amyloidosis, sarcoidosis, hemochromatosis.
- Cause group 4 – Endocrine/metabolic: Severe hypothyroidism (myxedema heart).
- Cause group 5 – Other: Constrictive pericarditis, cachexia, end-stage organ failure.
- ECG hallmark: Low QRS amplitude across multiple leads, not just one.
- Classic triad in tamponade: Low voltage + electrical alternans + tachycardia.
- COPD: Hyperinflated lungs increase thoracic impedance → low voltage.
- Pericardial effusion: Fluid insulates the heart, dampening voltages.
- Obesity: Excess fat tissue increases electrode–myocardium distance.
- Myxedema: Glycosaminoglycan deposition weakens myocardial contractility.
- Infarction/cardiomyopathy: Loss of muscle mass = reduced electrical force.
- Infiltrative diseases: Protein/fibrosis infiltration reduces conduction.
- Clinical clue: Suggests systemic disease if diffuse.
- Diagnostic step: Always confirm with echocardiography or imaging.
- Pitfall: Voltage criteria for LVH/RVH unreliable if low voltage present.
- Prognostic note: Associated with poor outcomes in cardiomyopathy and amyloidosis.
🔹 Short Q&A Block: Low Voltage QRS Complex
Q1. What is the definition of low voltage QRS in limb leads?
A1. QRS amplitude < 5 mm in all limb leads.
Q2. What is the definition of low voltage QRS in precordial leads?
A2. QRS amplitude < 10 mm in all precordial leads.
Q3. What are the two main mechanisms for low voltage QRS?
A3. (1) Increased distance between heart and electrodes, (2) Reduced myocardial electrical activity.
Q4. Name 2 conditions where increased distance causes low voltage.
A4. Obesity, pericardial effusion, pleural effusion, emphysema.
Q5. Name 2 conditions where myocardial electrical activity is reduced.
A5. Extensive myocardial infarction, dilated cardiomyopathy.
Q6. What infiltrative diseases can cause low voltage?
A6. Amyloidosis, sarcoidosis, hemochromatosis.
Q7. What endocrine disorder is classically associated with low voltage QRS?
A7. Severe hypothyroidism (myxedema heart).
Q8. What ECG finding along with low voltage suggests cardiac tamponade?
A8. Electrical alternans with sinus tachycardia.
Q9. Why is COPD associated with low voltage?
A9. Hyperinflated lungs increase impedance and reduce voltage transmission.
Q10. What is the prognostic significance of low voltage in cardiomyopathy?
A10. It indicates advanced disease and poor prognosis.
