In light of randomized, controlled trials that clearly proved the benefits of second-generation stent retrieval devices to treat acute ischemic stroke, the American Heart Association and American Stroke Association just issued new guidelines recommending their use.
 |
| Stryker ProVue Retriever |
They will only add to the impetus to adopt the new devices, which are suddenly en vogue because the results of the randomized trials--in particular Swift Prime and Mr Clean--were so compelling that all other trials were halted, for it became unethical to randomize subsequent patients into the control group, members of which would not receive thrombectomy via the stent retrievers.
Previous studies did not find much evidence of benefit from devices to treat stroke due to the use of inferior first-generation stents, study design or suboptimal medical practices, such as letting too much time expire before surgery.
The guidelines call for use of a stent retriever (either Medtronic's ($MDT) Solitaire or Stryker's ($SYK) Trevo ProVue, at least in the U.S) to physically remove the clot if treatment can be initiated via groin puncture within 6 hours of symptom onset. Other conditions for stent retrieval use include possessing the occlusion in the brain that's appropriate for the devices, a patient age greater than 18, and meeting the criteria of various clinically assessed scores.
To determine if a patient has what's known as a large vessel occlusion, emergency CT imaging of the brain is recommended. Earlier studies of first-generation devices to treat stroke did not always use imaging as a means of patient selection, which generated poor results, Mark Paul, president of Stryker Neurovascular, told FierceMedicalDevices in an interview. He said the newer studies show that about 38% of patients who receive imaging will have an occlusion that makes them eligible for a stent retriever.
The guidelines also call for the development of regional systems of stroke care. Unlike drug therapy, stent retrievers are best deployed in comprehensive stroke centers, or units within hospitals dedicated specifically to treating stroke.
"Within the next two years we'll have close to 100 comprehensive stroke centers," Paul said.
The American Heart Association said that air medical transport and hospital bypass may be appropriate to get stroke patients to such centers as fast as possible so that the 6-hour deadline is met. Paul said that the Cleveland Clinic and Memorial Herman Hospital in Houston are deploying ambulances that house CT scanners so that the diagnosis of stroke patients can be made faster and patients can be taken straight to the comprehensive stroke center if necessary.
That's an example of the reconfigurations to the healthcare system that are occurring due to the new treatment paradigm, which should continue to include treatment using intravenous r-tPA medications, including among those for whom endovascular treatments are being considered, the guidelines say. This combination approach is known as "drip and ship," referring to the practice of sending some patients to the stroke center for surgery after they have received medication in the general hospital setting.
 |
| Solitaire FR Revascularization device--Screenshot courtesy of Medtronic |
In general, the recommendations in the new guidelines and changes to care standards are designed to get appropriate stroke patients to the operating table faster. In fact, an emphasis on speed was one of the major reasons Mr Clean and Swift Prime were successful studies. "As soon as patients were assigned to thrombectomy it was off to the races," said UCLA's Dr. Jeffrey Saver, lead investigator of the Swift Prime trial, in a previous interview with FierceMedicalDevices. The trial deployed Medtronic's (formerly Covidien's) Solitaire FR or Solitaire 2 in the treatment group.
Along with Stryker, Medtronic touted the new guidelines. "We helped to bring the five global trials to bear that have proven this device can be a gamechanger in the treatment of stroke, reducing functional disability in patients. The AHA/ASA guidelines have validated our commitment to and belief in this technology, and we will work hard to make it accessible to as many stroke patients as possible," said Brett Wall, president of Medtronic's neurovascular unit, in a statement.
Strykers' Trevo stent retriever was used to conduct the majority of the thrombectomies in the Mr Clean study.
Increasing evidence of the benefits of stent retrievers, and encouragement from the likes of the American Heart Association, means that Paul expects the devices to treat 60,000 patients in the U.S. by 2020, up from 18,000 patients in 2015. Meanwhile Medtronic says that the addressable market in the U.S. is 240,000 acute ischemic stroke victims per year.
Paul said improved devices also contributed to the strong study results, and believes the Trevo represents a clear improvement over its predecessor device, the Merci retriever, which the company obtained through its acquisition of Concentric Medical for $135 million in 2011. The Trevo was FDA-approved separately from the Merci; it is not another iteration of that device.
The Trevo traps the occlusion in a stent-like cage structure that's made out of nitinol before physically removing it, while the Merci uses a corkscrew action to try and pull the clot out, Paul said.
"The Trevo is unique because it's the only device that's fully visible during the entire procedure," he added, comparing the device to Medtronic's Solitaire.
The use of stent retrievers is expanding, but the American Heart Association guidelines list several areas for further research, indicating that the field is still evolving. Topics for further study include the effectiveness of other mechanical thrombectomy devices besides stent retrievers, use on patients below 18 and benefits of the retrievers more than 6 hours after the stroke has occurred.
Stryker is running a clinical trial to test the Trevo in strokes that occurred 6 to 24 hours in the past.
- download the guidelines
- here's Stryker's statement
- here's Medtronic's statement