At @-month follow-up , primary venous patency was @ % in the ultrasound-assisted catheter-directed thrombolysis group and @ % in the conventional catheter-directed thrombolysis group ( P = @ ) , and there was no difference in the severity of the post-thrombotic syndrome ( mean Villalta score : @ @ -LSB- range @-@ -RSB- versus @ @ -LSB- range @-@ -RSB- ; P = @ ) , respectively .