Low-Voltage QRS Made Simple in 60 Seconds (Impedance Issue vs. Impulse Generation Issue)

Hi! I’m Prerak Juthani, MD/MBA, a Hospitalist at Stanford University. Through my clinical training and passion for medical education, I create videos that break down complex medical concepts into clear, high-yield explanations for medical students, residents, and anyone curious about health.

Low voltage on an EKG is a common finding that can provide critical diagnostic clues. It is defined as:
- QRS amplitude less than 1 large box in the limb leads
- QRS amplitude less than 2 large boxes in the precordial (chest) leads

When encountering low voltage, think in two main categories: Impedance issues – something is blocking or dampening the electrical signal before it reaches the electrodes. Pericardial effusion – fluid around the heart absorbs the signal. COPD or hyperinflated lungs as increased lung volume distances electrodes from the heart. Obesity – increased tissue reduces voltage.

There can also be impulse generation issues – the heart itself generates a weaker signal:
• Cardiac amyloidosis – infiltrative disease reduces conduction
• Post-myocardial infarction – scar tissue lowers electrical activity

Clinical pearl: Low voltage is not a diagnosis but a clue. Recognizing whether it is due to impedance or poor myocardial conduction guides further workup and management.
Disclaimer: This video is for educational purposes only and does not constitute medical advice.

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