Sir
We would like to reply to the letter from Dawson et al. The limit of 30 days was selected to allow a relatively close range of duration of occlusions; this then provides efficient lysis in comparable patients. We fully agree that lesions of longer duration can be treated, albeit with a longer duration of lysis, and hence a tendency to a higher haemorrhagic complication risk. As experience with new agents such as r-TPA increases, more mature lesions will undoubtedly be accepted for lysis.
Peripheral arterial graft thromboses can be lysed even in the early postoperative period, the fresh intraluminal thrombus being more susceptible to lysis than the 'mature' (cross-linked) anastomotic and wound thrombus/fibrin. However, the longer the infusion continues, the higher the risk of this also being lysed and hence causing haemorrhage. In the periphery, this risk can be monitored, and if necessary controlled by pressure whilst other specific measures are introduced. However, following intra-abdominal, intrathoracic, or intracerebral surgery this presents an unacceptable risk.
Postlysis anticoagulation rather than low-dose platelets was chosen following the occurrence of early rethromboses on patients only given aspirin in earlier work. These patients were successfully relysed and their patency has been maintained on warfarin. All patients are anticoagulated for 3 months and then transferred to low-dose aspirin.