Cardiac Chamber Dimensions

POCUS-first practical categories are listed first. Formal echo reference values are included where useful.

2.1 Left ventricle

LVIDd

  • Less than 3.6 cm: small or underfilled.

  • 3.6–5.6 cm: normal practical range.

  • Greater than 5.6 cm: dilated.

  • Formal echo reference: approximately 3.9–5.3 cm in women and 4.2–5.9 cm in men.

LVIDs

  • 2.2–4.0 cm: normal practical range.

  • Greater than 4.0 cm: suggests impaired systolic emptying.

IVSd / LVPWd

  • 0.7–1.1 cm: normal.

  • 1.2 cm or greater: thickened.

  • 1.5 cm or greater: severely thickened, HCM range.

LVEF qualitative

  • Good, moderate, or poor.

LVEF quantitative

  • 55% or greater: preserved.

  • 50–54%: low-normal.

  • 40–49%: mildly reduced.

  • 30–39%: moderately reduced.

  • Less than 30%: severely reduced.

  • Formal echo reference: approximately 52–72%.

Fractional shortening

  • 25% or greater: normal.

  • Less than 25%: reduced.

  • Formal echo reference: approximately 25–45%.

LV volumes indexed

  • LV EDV indexed: men 40–80 mL/m²; women 30–70 mL/m².

  • LV ESV indexed: men 20–45 mL/m²; women 15–35 mL/m².

2.2 Left atrium

LA anteroposterior dimension

  • 4.0 cm or less: normal.

  • 4.1–4.5 cm: mildly enlarged.

  • Greater than 4.5 cm: enlarged.

  • Formal echo reference: approximately 3.0–4.1 cm.

LA area

  • 14–22 cm²: normal practical range.

LA volume index

  • 34 mL/m² or less: normal.

  • Greater than 34 mL/m²: enlarged; supports chronic elevated left atrial pressure.

2.3 Right atrium

RA A dimension

  • 6.0 cm or less: normal.

  • Greater than 6.0 cm: enlarged.

RA B dimension

  • 6.0 cm or less: normal.

  • Greater than 6.0 cm: enlarged.

  • Formal echo reference: approximately 4.0–6.0 cm.

2.4 Right ventricle

RVOT basal dimension

  • 3.2 cm or less: normal.

  • Greater than 3.2 cm: dilated.

  • Formal echo reference: approximately 1.7–3.2 cm.

RV free-wall thickness

  • 3–5 mm: normal.

  • Greater than 5 mm: thickened.

RV end-diastolic area

  • Men: 19–32 cm².

  • Women: 16–27 cm².

TAPSE

  • 17 mm or greater: normal.

  • Less than 17 mm: impaired.

  • Less than 14 mm: severely impaired.

  • Formal echo reference: approximately 17–26 mm.

RVFAC

  • 35% or greater: normal.

  • Less than 35%: impaired.

RV/LV diameter ratio

  • Less than 1: normal.

  • 1 or greater: RV dilation or acute strain.

RV/LV area ratio

  • Less than 0.6: normal.

  • 0.6–1.0: mild.

  • 1.0 or greater: marked.

RV S′ lateral tissue Doppler

  • Approximately 9.5–10 cm/s or greater: normal practical range.

2.5 Inferior vena cava

IVC diameter

  • Less than 1.5 cm: collapsed or small; possible hypovolaemia.

  • 1.5–2.5 cm: normal or intermediate; correlate clinically.

  • Greater than 2.1 cm with inspiratory collapse less than 50%: formal elevated RAP estimate; standard formal echo RAP approximately 15–20 mmHg.

  • Greater than 2.5 cm with poor collapse: plethoric or marked POCUS finding; avoid empiric fluids.

  • Greater than 3.0 cm with minimal collapse: markedly plethoric; late warning.

  • Greater than 3.5 cm: marked plethora in some protocols; not a universal formal RAP cutoff; interpret as protocol-specific late warning.

Collapsibility in spontaneous breathing

  • Greater than 50%: low CVP.

  • 20–50%: indeterminate.

  • Less than 20%: high CVP.

  • Formula: collapsibility index = (Dmax − Dmin) / Dmax × 100.

Distensibility in mechanical ventilation

  • Dmin-based distensibility: (Dmax − Dmin) / Dmin × 100.

  • Common general controlled-ventilation threshold: 15% or greater.

  • Validation-specific range: approximately 12–21%.

  • A 18% threshold remains appropriate in selected fully ventilated septic shock protocols; it is a validation-specific operating point, not the only standard.

  • Mean-based variability: (Dmax − Dmin) / [(Dmax + Dmin) / 2] × 100.

  • Common mean-based threshold: 12%.

  • Do not interchange collapsibility, Dmin-based distensibility, and mean-based variability.

POCUS safety rule

IVC greater than 2.5 cm with poor collapse is plethoric; avoid empiric fluids. IVC greater than 3.0 cm with minimal collapse is markedly plethoric and is a late warning. IVC greater than 3.5 cm is not a universal formal RAP cutoff; it is a protocol-specific marker of marked plethora.

Technique

Measure from the subcostal long-axis view, approximately 1–2 cm from the RA–IVC junction, perpendicular to the IVC long axis. Assess diameter and respiratory variation. In adults, use a low-frequency phased-array or curvilinear probe. Do not use sustained maximal inspiratory strain or Valsalva-like effort for collapsibility. In fully mechanically ventilated patients without spontaneous breathing activity, use distensibility or mean-based variability instead of collapsibility.

2.6 Aortic root

  • Less than 40 mm: normal.

  • 40 mm or greater: dilated.

  • 50 mm or greater: aneurysmal.

Aortic root measurement should be integrated with aortic valve assessment, pericardial effusion, aortic regurgitation, and clinical suspicion for acute aortic syndrome.