Why can't wedge hepatic vein pressure (WHVP) be used as a direct measure of portal pressure in patients with liver disease, particularly those with portal hypertension?

Why Wedged Hepatic Vein Pressure Cannot Always Represent Portal Pressure

Wedged hepatic vein pressure (WHVP) accurately reflects portal pressure only in sinusoidal portal hypertension (the most common type in cirrhosis), but fails to measure portal pressure in pre-hepatic and presinusoidal causes because the balloon catheter only captures sinusoidal pressure, not the pressure upstream in the portal venous system. 1, 2

Understanding the Anatomic Limitation

The fundamental issue is anatomic: WHVP measures pressure at the sinusoidal level within the liver parenchyma, not in the portal vein itself. 1, 2

Portal Hypertension Classification by Site

Portal hypertension is classified by where the resistance to blood flow occurs: 2

• Pre-hepatic (e.g., portal vein thrombosis): The obstruction is before blood enters the liver
• Intrahepatic presinusoidal (e.g., schistosomiasis, idiopathic portal hypertension, cholestatic cirrhosis): Resistance occurs before the sinusoids
• Intrahepatic sinusoidal (e.g., alcohol-related cirrhosis, hepatitis C cirrhosis, NASH): Resistance at the sinusoidal level—this is the most common type 2
• Intrahepatic postsinusoidal (e.g., sinusoidal obstruction syndrome): Resistance after the sinusoids
• Post-hepatic (e.g., right heart failure): Obstruction is after blood leaves the liver 2

When WHVP Accurately Reflects Portal Pressure

WHVP only provides useful data in sinusoidal portal hypertension, where the increased resistance occurs at the level being measured. 1, 3 In these cases:

• The wedged pressure is elevated
• The free hepatic vein pressure remains normal
• The hepatic venous pressure gradient (HVPG = WHVP - free pressure) is elevated and accurately reflects the portal pressure gradient 1, 2

This is why HVPG is considered the gold standard for assessing portal hypertension in cirrhosis from alcohol, hepatitis C, hepatitis B, and NASH—all sinusoidal causes. 2, 3

When WHVP Fails to Reflect Portal Pressure

Pre-hepatic Portal Hypertension

In portal vein thrombosis, the obstruction is upstream from the liver sinusoids. 2 The measurement shows:

• Normal WHVP (sinusoidal pressure is unaffected)
• Normal free hepatic vein pressure
• Normal HVPG—despite severely elevated actual portal vein pressure 1, 2

The wedged catheter cannot "see" the obstruction because it only measures pressure downstream from the blockage.

Presinusoidal Portal Hypertension

In conditions like schistosomiasis or idiopathic portal hypertension, resistance occurs before the sinusoids. 2 Early in disease:

• WHVP remains normal (sinusoids are not yet affected)
• HVPG is normal
• Actual portal pressure is elevated 1

Important caveat: In advanced presinusoidal disease, secondary sinusoidal changes can develop, causing WHVP and HVPG to eventually rise—but this is a late finding. 1

One study comparing direct transhepatic portal vein pressure measurement to WHVP found that in chronic active hepatitis, portal vein pressure tended to be higher than WHVP, indicating a presinusoidal component that the wedged pressure could not detect. 4

Post-hepatic Portal Hypertension

In right heart failure, both the wedged and free hepatic vein pressures are equally elevated due to backward transmission of pressure. 2 The result:

• Elevated WHVP
• Elevated free hepatic vein pressure
• Normal HVPG (both pressures rise together, so the gradient is unchanged) 1, 2

The HVPG fails to reflect the true portal hypertension because the measurement technique subtracts out the elevated downstream pressure.

Clinical Implications

The anatomic classification is critical because HVPG measurement only accurately reflects sinusoidal pressure and does not provide useful data in pre-hepatic or presinusoidal portal hypertension. 2, 3

When evaluating a patient with suspected portal hypertension: 1, 2

• If HVPG is elevated: Confirms sinusoidal or mixed portal hypertension
• If HVPG is normal but clinical signs of portal hypertension exist: Consider pre-hepatic (portal vein thrombosis) or presinusoidal causes
• If both wedged and free pressures are elevated with normal gradient: Consider post-hepatic causes like right heart failure

Direct transhepatic portal vein pressure measurement with a thin needle can be performed when WHVP measurements are discordant with clinical findings, though this technique requires specific expertise and carries higher risk. 4

Despite HVPG being the gold standard for most cirrhosis cases, invasive measurement remains valuable for diagnosis and monitoring, especially when combined with transjugular liver biopsy to clarify the underlying pathology. 5