3 The procedure
3.1 Ultrasound‑enhanced, catheter‑directed thrombolysis is an endovascular technique that uses high‑frequency, low‑energy ultrasound waves in combination with infusion of a thrombolytic drug, with the aim of accelerating plasmin‑mediated thrombolysis. It aims to reduce treatment time, the dose of thrombolytic drug delivered and thrombolysis‑related complications, compared with catheter-directed thrombolysis alone.
3.2 The procedure is usually done using local anaesthesia, with imaging guidance by fluoroscopy. Therapeutic doses of heparin are administered through a peripheral catheter before and during the procedure.
3.3 With the patient in the supine position, an angiographic catheter is inserted from the femoral vein into the main pulmonary artery. The position of the pulmonary embolic occlusion is identified using angiography. A guide wire is passed into the embolus and the angiographic catheter is removed. A multi‑lumen infusion catheter is passed over the guide wire into the embolus and the guide wire is replaced with an ultrasound wire. This wire has multiple small transducers that deliver ultrasound waves along the entire treatment zone. A thrombolytic drug is infused directly into the embolus through holes in the side of the catheter, using an infusion pump, along with a flow of saline to serve as a coolant while the ultrasound wire is activated. An electronic device controls the ultrasound power output. The patient is continuously monitored from the start of treatment. Treatment typically lasts for 12–24 hours.
3.4 Follow‑up angiographic and echocardiographic assessment is performed at regular intervals after the start of the procedure. Once the embolus has cleared, or there is no further progress, the treatment is stopped and the patient starts standard anticoagulation therapy.