Cath Lab Digest

This interview took place at the VeithSymposium, held in New York City from November 14-18, 2012. For more information about the meeting, visit http://www.veithsymposium.com

How do you perform catheter-directed ultrasound thrombolysis?

We use a specially designed catheter, the EkoSonic Endovascular System (Ekos Corporation), composed of two components. The first component is a catheter that fits through a 6 French sheath, and usually placed in the femoral vein. It is passed over an .035” guide wire, up the inferior vena cava into the right atrium. It crosses the tricuspid valve into the right ventricle and goes up through the right ventricular outflow tract into the pulmonary arteries. The first portion of the catheter has multiple side holes that allow for the delivery of a thrombolytic agent, such as tPA. The second portion of the catheter is a central ultrasonic core wire. Each transducer is very small and is placed about 1 cm apart, and this portion sits inside the first catheter with the side holes. The ultrasonic core vibrates at 2 million cycles per second, or 2 megahertz. The resulting ultrasonic energy breaks up clot by exposing plasminogen receptor sites, making the clot more ‘porous’, so to speak, and allowing delivery of tPA drug into the clot. The ultrasonic waves drive the drug deeper inside the clot. It also allows us to use less tPA, meaning a lower risk of bleeding complications.

Bleeding complications are an issue with the traditional systemic dose of tPA in acute pulmonary embolism. 

Exactly. That is primarily why physicians have been very reluctant to use systemic tPA. There is the elevated incidence of intracranial bleed and major bleeding, which can be catastrophic. It only takes one patient to die of a catastrophic bleed to make a physician retreat from the use of tPA. Catheter-directed ultrasound thrombolysis allows us to give one-fifth of the dose and still get the same effect. 

Research has shown without a doubt that a systemic dose of tPA works. It will do the same thing that catheter-directed thrombolysis does with the Ekos catheter. The right ventricle get smaller, the right ventricular/left ventricular ratio decreases, and the patient does much better in the short term as well as the long term. But now, with the use of the Ekos catheter, only one-fifth of the dose of tPA is required. It should make physicians less reluctant to use tPA to treat these patients. 

The SEATTLE II trial (A Prospective, Single-arm, Multi-center Trial of EkoSonic Endovascular System and Activase for Treatment of Acute Pulmonary Embolism) is looking at submassive and massive pulmonary embolism patients. Can you tell us about the trial?

SEATTLE II began in June 2012 with the goal of 150 patients. Enrollment is going extremely well and over halfway at this point. The trial has two endpoints. First, efficacy: measuring the improvement in right ventricular/left ventricular ratio after use of the ultrasound-assisted thrombolysis catheter in submassive or massive pulmonary embolism (PE). Patients get a pre-treatment computed tomography angiography (CTA) of the chest, we perform the treatment, and then the patient undergoes a post treatment CTA of the chest 48 hours later. The second endpoint is safety: looking at the complications that may develop during treatment. 

The pretreatment CTA is also used for diagnosis?

Yes, the CTA is the most frequently used imaging study to diagnose pulmonary embolism. From the CTA, we can also measure the right ventricular/left ventricular ratio; this allows us to determine eligibility for the trial. 

Yet only a very small amount of PE patients are actually diagnosed. 

That is correct, and it is unfortunate, because there are 600,000 cases yearly in the United States, with over 200,000 deaths due to PE. It is the most preventable cause of death for in-hospital patients. PE is a very common disease, yet it is not recognized nearly enough, and I think it is misdiagnosed frequently. I can’t tell you the number of patients I eventually get called to take care of that have had multiple trips to various emergency rooms, complaining of chest pain and shortness of breath. A CTA was not done and these patients have been signed out with any number of different diagnoses.

Is there a particular group of patients at risk of a PE?

Any patient with a diagnosis of cancer or a patient who is immobilized for any period of time is at risk for pulmonary embolism. Unprovoked PE can often be the first manifestation of an underlying hypercoagulable disorder. What’s interesting about PE is that we are not talking about the elderly who have multiple medical problems. PE can strike the very young and the very healthy. We see it all the time, the 20- or 30-year-old athlete and the 42-year-old businessman who steps off of a plane after flying cross-country. It can strike anybody.

Yet I would say as many as 75% of all physicians don’t realize that PE should be separated into three categories and are not aware of the importance of the submassive category. The patient doesn’t know how sick they are and the doctor frequently doesn’t know the seriousness of the submassive category.