RV and LV Size Assessment in Critical Care Echocardiography

RV and LV Size Assessment in Critical Care Echocardiography

Chamber size immediately narrows the differential diagnosis of shock and guides fluid, vasopressor, thrombolysis, or mechanical support decisions. Current CCE competency statements recommend that every intensivist be able to assess global LV size and global RV size, initially by visual estimation and, when necessary, by quantitative measurements.

Table of Contents

Which Views are Used?

Echo View	LV Assessment	RV Assessment	Best Use
Parasternal Long Axis (PLAX)	Excellent	Limited	LV size, wall thickness
Parasternal Short Axis (PSAX)	Excellent	Good	Septal shape, RV pressure overload
Apical 4 Chamber (A4C)	Excellent	Excellent	Compare RV vs LV
RV-focused A4C	Moderate	Best	RV dimensions
Subcostal 4 Chamber	Good	Good	ICU patients, mechanically ventilated

Practical CCE “Eyeball” Algorithm (10 seconds)

Obtain A4C or RV-focused A4C.
Compare RV and LV at end-diastole:
- RV < ⅔ LV → Normal.
- RV ⅔–1× LV → Mild–moderate dilation.
- RV = LV → Significant dilation.
- RV > LV → Severe dilation; consider acute RV failure (e.g., massive PE, severe pulmonary hypertension).

Assess the interventricular septum:

- Round LV → Normal.
- D-shaped LV → RV pressure overload.

Look for supporting findings:

- Reduced TAPSE (<16–17 mm), reduced RV S′ velocity, dilated IVC, elevated TR velocity, or McConnell sign increase confidence in RV dysfunction.

Quantitative RV Dimensions

Measured in RV-focused A4C.The RV has an irregular crescent shape that wraps around the LV.

Because of this:

One diameter cannot represent RV size.
The RV may dilate only at the base or only in the outflow tract.
Therefore ASE/EACVI guidelines recommend measuring three dimensions.

Measurement	Normal	Abnormal
Basal diameter	25–41 mm	>41 mm
Mid cavity diameter	20–35 mm	>35 mm
Longitudinal length	56–86 mm	>86 mm

An RV basal diameter >41 mm is abnormal.

RV Enlargement Severity

Grade	RV compared with LV
Normal	<60% of LV
Mild	60–90%
Moderate	Equal to LV
Severe	Larger than LV

Acute vs Chronic RV Enlargement

Feature	Acute	Chronic
RV wall	Normal thickness	Thick
RA	Mild enlargement	Large
Pulmonary artery	Normal	Enlarged
Septum	Acute flattening	Chronic flattening
TAPSE	Often reduced	Variable
RV free wall	Thin	Hypertrophied

Quantitative LV Dimensions

The LV is much more symmetrical. Instead of measuring three diameters, guidelines use:

1. Linear dimensions (most common)

Measured in PLAX.

Measurement	Men	Women
LVIDd	42–58 mm	38–52 mm
LVIDs	25–40 mm	22–35 mm

These measurements are taken perpendicular to the long axis at the level of the mitral valve leaflet tips.

2. LV Volumes (more accurate)

Measured by the biplane Simpson’s method from apical 4- and 2-chamber views.

Measurement	Men	Women
LVEDV	62–150 mL	46–106 mL
LVESV	21–61 mL	14–42 mL

Volumes are preferred because they account for the LV’s three-dimensional shape and are more accurate than a single diameter.

RV : LV Ratio

Measure both ventricles at end-diastole in A4C.RV should normally be less than two-thirds (⅔) of LV size.

RV/LV Ratio	Interpretation
<0.6	Normal
0.6–0.9	Mild RV enlargement
0.9–1.0	Moderate enlargement
>1.0	Severe RV enlargement
RV > LV	Massive RV dilation (acute RV failure until proven otherwise)

An RV/LV end-diastolic ratio >0.9 is considered abnormal on echocardiography and is used as one marker of RV dysfunction.

Common Pitfalls

Pitfall	Effect
Foreshortened A4C	Underestimates RV size
Non-RV-focused A4C	RV appears falsely small
Off-axis imaging	Incorrect RV/LV ratio
Measuring in systole	Underestimates chamber size
Mechanical ventilation	Alters chamber filling
Tachycardia	Difficult end-diastolic frame selection

Pathologies

Finding	Detailed Causes and Mechanism
Small Left Ventricle (LV)	Hypovolemia (most common) Distributive (early septic) shock Cardiac tamponade Massive pulmonary embolism (PE) Tension pneumothorax: Positive-pressure ventilation/high PEEP: Reduces venous return and LV preload, especially in hypovolemic patients. Severe tachycardia Constrictive pericarditis/restrictive physiology
Large Left Ventricle (LV)	Dilated cardiomyopathy (ischemic or non-ischemic) Acute myocarditis Septic cardiomyopathy (late sepsis) Chronic mitral regurgitation (MR) Chronic aortic regurgitation (AR) Long-standing hypertension: Post-myocardial infarction remodeling: Chronic high-output states: Severe anemia, AV fistula, thyrotoxicosis, pregnancy (physiological), chronic volume overload may produce LV enlargement. End-stage valvular heart disease
Small Right Ventricle (RV)	Hypovolemia Distributive shock (early sepsis) High intrathoracic pressure/PEEP: Reduced systemic venous return decreases RV preload. Cardiac tamponade Severe tricuspid stenosis (rare) Congenital RV hypoplasia (rare)
Large Right Ventricle (RV)	Massive pulmonary embolism (most important acute ICU cause): Pulmonary hypertension (Group 1–5): Acute respiratory distress syndrome (ARDS): Chronic lung disease (COPD/interstitial lung disease): Right ventricular myocardial infarction: Severe tricuspid regurgitation (TR): Atrial septal defect (ASD): Pulmonary regurgitation: Congenital heart disease: Ebstein anomaly, repaired tetralogy of Fallot, partial anomalous pulmonary venous return, and other lesions causing chronic RV volume or pressure overload. Mechanical ventilation with severe pulmonary hypertension: High PEEP, hypercapnia, and hypoxemia increase RV afterload, causing acute RV dilation in susceptible patients.