Mechanical Thrombectomy – Faster than Ever

When caring for a patient with acute ischemic stroke, Professor Martin Bendszus and his team are racing against the clock. Using a combination of a CT scanner and mobile C-arm they cut the transfer time between stroke diagnosis and mechanical thrombectomy. The patient is diagnosed and treated in the same room on the same table, without transfer. Already in the first three patients, picture-to-puncture time was as little as 35 minutes.

Photo: Carsten Buell

The world of stroke has changed. For a long time, the only proven effective treatment for acute ischemic stroke was intravenously administered thrombolysis with recombinant tissue-type plasminogen activator (r-tPA). Now, mechanical thrombectomy has advanced to become an important option. Clinical studies with intriguing names such as MR CLEAN, ESCAPE, EXTEND-IA, SWIFT-PRIME, and REVASCAT have demonstrated that interventional clot retrieval improves the outcome for certain stroke patients.
The evidence was so convincing that the American Heart Association/American Stroke Association updated its guidelines back in June – giving the strongest recommendation possible for patients who meet certain criteria: class 1, level of evidence A.

Around 100 mechanical thrombectomies were performed last year in Heidelberg – this number was reached this year within the first six months. “Since the studies were published, we have received many more referrals from hospitals in the area and are doubling our numbers this year,” says Professor Martin Bendszus, MD, from Heidelberg University Hospital in Germany. Bendszus is Head of Neuroradiology. His department is a key component in the Heidelberg University Hospital stroke center, one of the leading stroke centers in Germany treating hundreds of stroke patients per year. With strict eligibility criteria, Bendszus estimates that around 15 percent of the 270,000 strokes per year in Germany could potentially be considered candidates for mechanical thrombectomy. With broader criteria, he estimates this number may increase to 20 percent.

In the case of a stroke, the decisive factor – in addition to the patient’s age and the National Institutes of Health Stroke Scale (NIHSS) – is the time it takes to restore perfusion. “In recent trials it was shown that if the blocked artery can be recanalized 20 minutes faster, this increases the chances of a better clinical outcome in the range of 10-15%,” says Bendszus. Unfortunately, in most hospitals critical time is lost while patients are transferred between emergency room, diagnostic imaging, and interventional suite, as well as with negotiations between parties preceding each transfer.

In Heidelberg, the CT and biplane angiography systems are located in adjacent rooms, yet it still takes fifteen to twenty minutes to move a patient. If the rooms are located further apart, as is the case in a number of hospitals, the move takes much longer. During the time the brain is not perfused approximately two million brain cells die every minute. This is why, when planning his second thrombectomy suite, Bendszus looked for a solution that avoided the need to move the patient, and with a better picture-to-puncture time. He wanted the diagnostic imaging and the mechanical opening of the artery to take place on one table and in one room. In a combined system, the technical personnel can begin preparing for the intervention directly after the patient has been scanned – the best way to minimize picture-to-puncture time.

Bendszus had three requirements for the new intervention suite: It had to be a solution that would not restrict normal CT operation. His department performs over 15,000 CT examinations per year, so the room had to be used for normal daily routine, too. In addition, everyone who would be performing a mechanical thrombectomy in the room should be immediately familiar with the system, with similarities to a standard angio system, and the system should provide sufficient image quality to perform the procedure safely. Finally, it was important for Bendszus to be able to switch from CT operation to the interventional procedure very quickly in the case of an acute indication for a thrombectomy. “We had a Formula One pit-stop approach in mind,” he says, “where everything is ready and available for use within a few minutes.”

How were his requirements met? The new suite is equipped with a SOMATOM Definition AS for diagnostic imaging. In the adjacent room, a mobile Cios Alpha C-arm with flat detector technology is available for the mechanical thrombectomy. It takes five minutes to set up. The CT table is placed at a distance of 95 cm from the gantry so that the C-arm can slot into this space during the intervention. The standard CT table is made of carbon and, using a commercially available extension, is longer than usual so that it is also suitable for the thrombectomy. The CT table, CT scanner, and C-arm can be controlled using remote controls mounted at the tableside, or on a trolley, similar to a standard angio system. The two monitors are mounted on the ceiling. A radiation protection wall was also installed. “What makes this CT and C-arm system so special is its simplicity,” explains Bendszus. “We’re using a 64-slice CT system and a mobile C-arm without any expensive reconstruction costs, and achieve a high level of flexibility and accessibility.”

In a feasibility study supported by Siemens, Bendszus and his colleagues have shown that diagnosing and treating stroke patients with the combined system is feasible. “The combination is equally suited for this procedure, compared to conventional angiography systems,” says Johannes Pfaff, MD, the physician in charge of the study. “The excellent performance and large field-of- view of the Cios Alpha deliver an image quality that is more than adequate to safely maneuver the instruments. The system has all the essential elements for angiography,” Pfaff explains. The feasibility study was published in May 2015 in the Journal of Neurointerventional Surgery (doi:10.1136/neurintsurg-2015-011744).

Pfaff and Bendszus treated three patients as part of the feasibility study: An 84-year-old with an occlusion in the M1 segment of the left-middle cerebral artery; a 51-year-old with an occlusion in the basilar artery following a wake-up stroke; and an 83-year-old with an occlusion in the M2 segment of the left-middle cerebral artery. “The average time between the diagnostic scan and puncture of the femoral artery was 35 minutes,” says Pfaff. “The time needed from high-quality CT stroke imaging to groin puncture could become as low as 28 min. None of us has ever been this fast. And we are pushing even further.” Time was saved crucially by keeping the patient in one place. If a patient has to be moved from the CT room into the neighboring angio suite, the picture-to-puncture time was 57 minutes in previous studies, and the picture-to-recanalization time was 250 minutes. In Heidelberg, all emergencies are now treated in the new suite. That is, unless two emergencies have to be treated concurrently. “We now have the problem that we’re so fast that the logistics have to be adjusted,” says Bendszus. “The anesthetist should theoretically already be in the room for the diagnostic CT scan.” Following the feasibility study, a larger study will now be conducted with fifty patients in order to confirm the incredibly impressive times. “We already included 34 patients,” says Pfaff. “We hope to publish the results next year.”

Who is eligible for mechanical thrombectomy? “We decide on the basis of the infarct core and the size of penumbra, not only on the basis of the time elapsed after symptom onset,” says Bendszus. The infarct core is the amount of irreversibly damaged tissue. The penumbra is malperfused tissue that may still be saved through fast recanalization. Core and penumbra are both measured using CT perfusion imaging.
In studies that have been published, mechanical thrombectomy was performed within twelve hours following the onset of symptoms. “If the infarct core is small and the penumbra is large, the time elapsed is less relevant,” says Bendszus. “Since the studies showed that mechanical thrombectomy is a safe and effective treatment for acute ischemic strokes, without an increased risk of complication, we no longer ask why we should perform one, but rather why we shouldn’t.” Bendszus also considers a wider range of indications. The published studies report on the treatment of patients with occlusions in the internal carotid artery and the proximal middle cerebral artery. In Heidelberg, also more distally located thrombi are removed using stent retrievers. The primary risk is that part of the thrombus is lost during its retrieval, causing a new embolization in another place. “We can perform a diagnostic CT scan at any point during the intervention, which allows us to react immediately to any complications,” says Pfaff. “This is a significant safety factor.”

Which hospitals should offer mechanical thrombectomy? “Maximum care hospitals with a Department of Neurology have to offer this procedure,” says Bendszus. “However, proper training is essential for the intervention. You have to understand the approach and learn how to probe the vessels. You also have to understand the diagnostic images.” This is why Bendszus calls for structured training, emphasizing that it is now up to professional medical associations to ensure that high-quality care is available across Germany in the near future.

Bendszus also envisages a new trauma room concept. Following the diagnostic CT scan, various vascular interventions can be performed on the same table. The effectiveness of the treatment can then be checked as required during the intervention using CT imaging. “The amazing thing is that it’s so easy to implement without needing any additional construction work,” says Bendszus. “Here, the technology is driving forward the clinical applications.”

Hildegard Kaulen, PhD is a molecular biologist. After stints at the Rockefeller University in New York and the Harvard Medical School in Boston, she moved to the field of freelance science journalism in the mid-1990’s and contributes to numerous reputable daily newspapers and scientific journals.