ISET Feature: Ultrasound-assisted thrombolysis for PE shows promise
Transesophageal echocardiography showing thromboemboli in right pulmonary artery. Image source: Cardiovasc Ultrasound 2010;8:50.
A catheter device that can simultaneously deliver ultrasonic energy and thrombolytic drugs was able to dissolve massive pulmonary embolisms (PEs) faster than traditional anticoagulation therapy, while reducing thrombolytic dosage and overall hospital stays, according to a presentation at the annual International Symposium on Endovascular Therapy (ISET) in Miami Beach, Fla.

Tod C. Engelhardt, MD, chairman of the cardiovascular and thoracic surgery division at East Jefferson General Hospital in Metairie, La., and colleagues treated 27 patients with significant PEs using ultrasound-assisted thrombolysis. All patients survived and each benefitted from a significant reduction in right-heart chamber size.

On average, the size of each clot was reduced by more than half. Four patients suffered from major bleeding and two from minor bleeding. There were no bleeding complications in patients who received a lower dose of thrombolytics.

In traditional therapy, thrombolytic drugs are delivered to the blockage, but the method can take many hours or even days. In the ultrasound method, the device (EkoSonic System, Ekos) is advanced through the femoral artery to the clot, where it emits sound waves that loosen the clot, allowing the thrombolytic drugs to dissolve it faster. The system has received a CE mark and FDA approval for treatment of peripheral arterial disease, and recently received a CE mark for use in PEs.

Engelhardt has since treated an additional three patients and "the results are even better than the first 27," he told Cardiovascular Business News. "I have seen greater resolution of thrombus and an equal amount of benefit in the right ventricular size."

In patients with sudden massive PEs, physicians want to reverse the right ventricular/left ventricular (RV/LV) ratio. "It should be less than 0.9, and anything above that threshold indicates the RV is enlarged because of the PE," he said.

Initially, Engelhardt and colleagues didn't have a protocol for the amount of tPA they'd administer to the patient. They gave varying amounts, sometimes as much as 40 mg, depending on the patient's ability to tolerate the drug without bleeding and the surgeon's ability and the cath lab's availability to bring the patient back.

They have found, however, that 20 mg of tPA is the magic number. "Since we cut it back to 20 mg, we have seen a good response in terms of right ventricular size and dissolution of thrombus, as well as no bleeding complications," Engelhardt said.

The team at East Jefferson General Hospital relies on CT angiography (CTA) to assess the location of the PE, clot burden and ventricular size. After 12 hours of treatment (20 mg of tPA), a follow-up CTA is performed and the pre- and post-treatment CTAs are compared.

While Engelhardt does not have hard cost-effectiveness data, he noted with the ultrasound-assisted thrombolysis, patients with massive and submassive PEs stay in the ICU for one day, with a total hospitalization of about five days compared with three to five days in the ICU and 10 to 12 days of total hospitalization with traditional treatment. "And it's better for the patient if the clot is gone and right heart failure reverses within 12 hours," he said.

The standard of care for patients with sudden massive PEs who are stable is to treat with heparin and convert to warfarin over a period of seven to 10 days in the hospital. The patients are discharged with the hope that the body's own defenses will lyse the clot in the next several months, Engelhardt said.

"The problem is that up to 20 percent of these patients can develop pulmonary hypertension and right heart failure because the clot is not fully dissolved," he said.

In patients with massive PE who are dying, the treatment is systemic tPA, which carries a significant risk of bleeding, particularly intracranial hemorrhage.

"If we can direct the tPA in very low doses where it has to be, into the clot itself, complications should be lower and there should be less bleeding," Engelhardt said.

He noted that the ultrasound-assisted thrombolysis works best with acute clots, while chronic clots, those perhaps less than three months old, are more difficult to break down.

Engelhardt said he has used the system with success in the peripheral arteries (bypass grafts and native arteries) and veins, and has found success with the device in thrombosed vena cava filters.