The ECG in chamber hypertrophy and low-voltage states
- Measurement
- Exam priority: medium
More heart muscle makes bigger ECG waves; fluid, air, fat or scar between heart and skin makes them smaller.
Also called: LVH voltage criteria, Right ventricular hypertrophy, Low QRS voltage, Electrical alternans
See it in 3D: Left ventricle · Right ventricle · Left atrium · Right atrium · Pericardium
What it is
QRS voltage depends on how much muscle depolarizes and how well the current reaches the skin. A thick ventricle raises voltage and pulls the axis toward itself; a dilated or thick ventricle also takes longer to activate, widening the QRS slightly. Low voltage appears when muscle is lost or when tissue or fluid around the heart damps the signal.
How it works, step by step
- Pressure overload (hypertension, aortic stenosis) adds sarcomeres in parallel: the wall thickens and more muscle depolarizes at once.
- A bigger muscle mass makes a longer vector toward that side: tall R over the hypertrophied ventricle, deep S on the opposite side.
- The thick wall takes longer to activate from endocardium to epicardium, so the QRS widens a little (usually < 0.12 s).
- Repolarization of the thick wall changes order (and the subendocardium may be underperfused), giving ST–T opposite to the QRS: 'strain'.
- The right ventricle is normally hidden by the larger left; it must become very thick before its vector pulls the axis right and makes V1 positive.
- Fluid around the heart short-circuits current; air in the lungs and fat insulate it; both lower the voltage reaching the skin.
- Scar from old infarcts, infiltration (amyloid) or myxedema replaces or swells tissue that no longer generates current, so QRS voltage falls.
- In a large effusion the heart swings within the fluid; every other beat its axis changes, so QRS size alternates.
Electrocardiogram: a normal beat in lead II
HR 75 /minRR 0.80 sPR 0.16 sQRS 0.09 sQT 0.37 sQTc 0.41 s
Tap a wave (P, QRS, T, U), an interval (PR, ST, QT) or the RR.
- ECG trace (lead II)
- Small box: 0.04 s · 0.1 mV
- Big box: 0.20 s · 0.5 mV
- Selected part
ECG thresholds (adult, standard calibration 10 mm/mV)
| Parameter | Value | Note |
|---|---|---|
| Sokolow–Lyon LVH | S V1 + R V5/V6 ≥ 3.5 mV | less specific under ≈ 40 years |
| Cornell LVH | R aVL + S V3 > 2.8 mV (men), > 2.0 mV (women) | |
| Right atrial P (lead II) | ≥ 0.25 mV tall | |
| Left atrial P (lead II) | ≥ 0.12 s wide, notched | |
| Low voltage, limb leads | QRS < 0.5 mV in all | |
| Low voltage, chest leads | QRS < 1.0 mV in all | |
| Normal QRS duration | ≈ 0.06–0.10 s |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Patterns of high and low voltage
| Pattern | Key ECG features | Typical causes |
|---|---|---|
| Left ventricular hypertrophy | Tall lateral R, deep S V1–V2, left axis, lateral strain | Hypertension, aortic stenosis, hypertrophic cardiomyopathy |
| Right ventricular hypertrophy | Right axis, tall R V1, deep S V6, right strain | Pulmonary hypertension, mitral stenosis, chronic lung disease |
| Low voltage | Small QRS in all limb or all chest leads | Effusion, emphysema, obesity, hypothyroidism, amyloid, old infarcts |
| Electrical alternans | Beat-to-beat change in QRS height | Large pericardial effusion; partial intraventricular block at fast rates |
Clinical notes
- Voltage criteria are specific but insensitive: a normal ECG does not exclude LVH; echocardiography measures wall thickness directly.
- Young, thin people often exceed voltage criteria without hypertrophy because the heart lies close to the chest wall.
- A falling QRS voltage over days in a patient with pericarditis suggests the effusion is growing.
Test yourself
Think of the answer, then tap the question to see it.
A hypertensive patient has S in V1 of 1.6 mV and R in V5 of 2.2 mV with lateral ST depression. What does this suggest?
Left ventricular hypertrophy with strain: the Sokolow–Lyon sum is 3.8 mV (≥ 3.5 mV), and the lateral ST–T changes oppose the tall R.
Why does right ventricular hypertrophy change the ECG later than left ventricular hypertrophy?
The normal left ventricle is much thicker and dominates the QRS vector. The right ventricle must thicken a lot before its vector outweighs the left and moves the axis right.
A patient with dyspnea has sinus tachycardia, low QRS voltage and QRS height alternating beat to beat. What is the likely cause?
A large pericardial effusion, likely with tamponade: fluid damps the voltage and the heart swinging in the fluid makes the alternans.
Which three causes of low QRS voltage do not involve the heart muscle itself?
Pericardial effusion, emphysema (air in hyperinflated lungs), obesity; pleural effusion and poor electrode contact also lower voltage.
Connections
See it in 3D5
The structures of Durgical's 3D anatomy where it happens.
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: Hypertensive Heart Disease (StatPearls (NCBI Bookshelf), 2025); Cardiac Tamponade (StatPearls (NCBI Bookshelf), 2025); Chronic Obstructive Pulmonary Disease (COPD) (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.