Duplex of the Hepatic Artery Post-Liver Transplant: Tardus-Parvus, RI, and AT
Direct and Indirect Criteria for Hepatic Artery Stenosis
In Doppler evaluation of a liver transplant, direct (at the hepatic artery anastomosis) and indirect (in intrahepatic arteries) signs of stenosis are distinguished. According to Diagnostic Ultrasound: Vascular (2nd Ed., 2025), hepatic artery stenosis (HA stenosis) is characterized by the following parameters.
| Sign | Criterion |
|---|---|
| Direct: PSV at the anastomosis | >200–250 cm/s |
| Indirect: waveform in intrahepatic arteries | parvus-tardus (delayed systolic rise, reduced peak velocity) |
| Acceleration Time (AT) | >0.08 s |
| Resistive Index (RI) | <0.5 |
Tardus-Parvus Phenomenon
The tardus-parvus waveform in intrahepatic arteries reflects flow dampening distal to a hemodynamically significant proximal stenosis: the systolic rise is delayed (tardus), and the peak velocity is reduced (parvus). A similar mechanism is described for intrarenal arteries, where a very low RI on the affected side is considered an indirect sign of significant proximal stenosis (flow dampening).
Assessment of RI and AT
The resistive index is calculated as (PSV − EDV)/PSV. In hepatic artery stenosis, the RI in intrahepatic branches decreases (<0.5), which, along with prolonged AT (>0.08 s) and the parvus-tardus waveform, forms an indirect picture. It is important to note that for renal transplants, acceleration indices and acceleration time are less specific than PSV of the main artery and should not be used in isolation; sensitivity and specificity depend on the combination of criteria. Similarly, indirect signs in a hepatic transplant should also be interpreted in conjunction with direct criteria.
Hepatic Artery Occlusion
In hepatic artery occlusion, blood flow in the artery is not detected on color and spectral Doppler. Collateral transformation is possible: tortuous collaterals at the liver hilum and parvus-tardus waves in intrahepatic arteries. In CEUS, the portal vein enhances before the arterial tree.
Additional Findings
A hepatic artery pseudoaneurysm appears as a round, well-defined structure with swirling flow and a yin-yang sign on color Doppler.
Frequently asked questions
What PSV threshold at the anastomosis indicates hepatic artery stenosis?
An increase in PSV at the anastomosis zone >200–250 cm/s (Diagnostic Ultrasound: Vascular, 2025).
What AT and RI values are characteristic of stenosis?
Acceleration time (AT) >0.08 s and resistive index (RI) <0.5 in intrahepatic arteries.
What does the parvus-tardus wave mean?
Delayed systolic rise and reduced peak velocity in intrahepatic arteries are indirect signs of significant proximal stenosis due to flow dampening.
How does hepatic artery occlusion appear on Doppler?
Absence of blood flow on color and spectral Doppler; possible tortuous collaterals at the liver hilum and parvus-tardus in intrahepatic branches. In CEUS, the portal vein enhances before the arterial tree.
Can a diagnosis be made based solely on indirect signs?
No. For renal transplants, AT and acceleration index are less specific than PSV of the main artery and are not used in isolation; criteria are assessed collectively.