← Section III · Chamber Size and Function

III.I

Inferior and Superior Vena Cava

7 cards

Notes

IVC assessment

Best imaged in the subcostal view.
Measure ~1–2 cm from the RA-IVC junction, before the hepatic veins.
Diameter measured at end-expiration (or in average tidal breathing).

RA pressure estimation from IVC

IVC diameter	Inspiratory collapse	Estimated RA pressure
≤ 2.1 cm	> 50 %	~3 mmHg (0–5)
≤ 2.1 cm	< 50 %	~8 mmHg
> 2.1 cm	> 50 %	~8 mmHg
> 2.1 cm	< 50 %	~15 mmHg

"Sniff" test: brief forceful inspiration accentuates IVC collapse.
Ventilated patients or athletes may have unreliable IVC estimation.

IVC-plethora and RA inversion

Plethora = dilated non-collapsing IVC - sensitive for elevated RA pressure.
Combined with RA inversion for > 1/3 of the cardiac cycle → sensitive for tamponade.
RV diastolic collapse → most specific for tamponade.

Persistent left SVC

Most common thoracic venous anomaly (~0.3% of general population, higher in CHD).
Drains into the coronary sinus → dilated CS.
May coexist with or without the right SVC.
Diagnosis: agitated saline injection into the LEFT arm opacifies the CS before the RA.

Absent IVC / azygous continuation

Rare congenital anomaly.
IVC is interrupted below the hepatic segment; blood returns via a dilated azygous vein to the SVC.
Echo: absent IVC-RA junction; dilated azygous vein visible posterior to the aorta on subcostal short-axis.
Associated with polysplenia (left isomerism).

Cards

basicIII.I-001
Where is the IVC measured for RA pressure estimation?
→ Subcostal view, ~1–2 cm from the RA-IVC junction (before the hepatic vein confluence), at end-expiration or during average tidal breathing.
basicIII.I-002
IVC parameters for a NORMAL RA pressure of ~3 mmHg?
→ IVC diameter ≤ 2.1 cm AND > 50% collapse with sniff.
basicIII.I-003
IVC parameters for an ELEVATED RA pressure of ~15 mmHg?
→ IVC diameter > 2.1 cm AND < 50% collapse with sniff.
basicIII.I-004
When is IVC-based RA pressure estimation unreliable?
→ Mechanically ventilated patients (positive-pressure ventilation reverses normal respiratory dynamics) and highly trained athletes (baseline vena caval dilation).
basicIII.I-005
IVC plethora and RA inversion — sensitivity/specificity for tamponade?
→ IVC plethora is SENSITIVE (present in nearly all significant tamponade). RA inversion > 1/3 of the cardiac cycle is more sensitive but less specific than RV diastolic collapse, which is highly SPECIFIC for tamponade.
basicIII.I-006
Describe azygous continuation of an interrupted IVC.
→ Congenital absence of the intrahepatic IVC — venous return continues through a dilated azygous vein (posterior to the aorta) to the SVC. Associated with polysplenia (left isomerism / heterotaxy).
basicIII.I-007
Where does a persistent left SVC drain and how is it diagnosed on echo?
→ Drains into the coronary sinus → produces a dilated CS. Diagnosed by injecting agitated saline into the LEFT arm — bubbles appear in the CS before the RA.