Introduction to mechanical thrombectomy
The progress of clinical medicine lies within the purview of translational research, for if change is constant through time, then normalcy is backwardness. Dr. Y. Pierre Gobin of Weill Cornell Medical College understood this axiom in 1995 when he began developing the first mechanical thrombectomy device, now FDA-approved, for treatment of acute stroke.
The model for stroke treatment remains at the mercy of time. Acute stroke is a heart attack of the brain. Treatment options prior to 2004 were limited to clot-busting medications that could only be administered within three hours of symptom onset. Thus, many patients were ineligible for these treatments and patient mortality remained high. What’s more was that clot-busting drugs increased the risk of intracerebral hemorrhages making the drug particularly unsafe for patients with other underlying conditions. In addition, clot busting medications proved ineffective for clots in certain major arteries leading to the brain. One such artery is the internal carotid artery (ICA). A study showed that between 2 and 12% of patients experiencing an ICA occlusion will have a good recovery.
New treatment options were necessary. Something that could push the time window further and prove efficacious against clots unmanageable with thrombolytic treatments. Mechanical thrombectomy options were explored and in 2004 Dr. Pierre Gobin’s ideas came to fruition.
MERCI Device
The first Mechanical Embolus Removal for Cerebral Ischemia (MERCI) device was conceived by Drs. Pierre Gobin and Jeffrey Wensel. With scant success using clot-busters, Gobin was the Initiator driven to try something new. “Frustrated, I thought that we should have a device that would just remove the clot, that should be faster and have less risk of hemorrhage than thrombolytics,” said Gobin. Gobin was attempting to use a clot-busting medication termed urokinase which “could not reopen the occlusion despite a two-hour infusion.” Learning from past failures, he immediately went back to the drawing board and by 1996, animal trials were performed. Gobin’s artistic gift of design was finally coalescing with his magnificent knowledge of science.
The MERCI device consists of a wire and catheter with an inflatable balloon. The catheter begins in the femoral artery with a straight-shaped wire and is passed distal to the location of the clot. Once distal to the clot, the balloon inflates proximal to the clot to prevent anterograde flow and the wire adopts a helicoid shape to ensnare the clot. The clot is slowly pulled out and perfusion is restored.
Patent struggles apart, the first clinical trial in a human being came soon enough. In 2001, a team of neuroradiologists and neurosurgeons at UCLA performed the first successful MERCI procedure and the results were instantaneous. Dr. Gary Duckwiler, a professor of Radiology at UCLA, proclaimed that the “patient immediately went from hemiplegic to full strength…It became immediately obvious with our uncontrolled shouts of ‘YES’ and ‘WooHoo’!
The preliminary success planted the seed and results quickly germinated. The MERCI trials began and by 2004 the FDA approved the second form of treatment for acute stroke: the MERCI device.
The MERCI Trials
The purpose of the MERCI trials was to investigate the safety and efficacy of the MERCI device in a non-randomized, multi-center trial at 25 United States centers. The primary outcomes measured were recanalization (ability to restore blood flow in previously occluded vessel) in large cerebral vessels and safety.
These studies showed that in 48% of the patients receiving treatment from the MERCI device, recanalization occurred. This rate is significantly larger than the 18% observed in another study which tested the efficacy of recanalization using the clot-busting drug urokinase. Thus, these studies suggested that the device is highly effective in restoring flow compared to previous treatment modalities. The studies also mentioned that higher recanalization rates are associated with better clinical outcomes, although they do not directly assert that the MERCI device leads to better clinical outcomes.
However, symptomatic intracranial hemorrhage was also observed in 7.8% of the patients. Thus, the device is not without its complications. This is a small price to pay considering that patients receiving the MERCI procedure are not eligible for traditional clot-busting medications. Thus, they would need to rely on spontaneous recanalization to experience recovery. And that is a risky matter.
Modern day use of the MERCI device
The bottom line: the MERCI device may be a better alternative than traditional stroke treatments for patients who are outside the time window and are prone to hemorrhaging. The MERCI device can be administered within 8 hours of symptom onset.
The MERCI device is becoming an international phenomenon. More than 14,000 patients have been treated with this device in countries including the United States, Europe, Australia, Singapore and Canada. MERCI stories are also becoming a mainstay of hospitals.
Dr. Dougal DeOrchis of Miriam Hospital in Rhode Island successfully treated a patient who experienced 99 percent recovery by six weeks after the operation. This is a remarkable recovery considering some patients do not ever experience full rehabilitation. Dr. Vallabh Janadrhan, medical director of the stroke program at The Medical Center of Plano in Texas, also states that “I have seen stroke patients come in completely paralyzed, not able to speak… and after extracting the blood clots through our clot retrieval procedure, they were able to walk and talk again. Such cases are living testaments to how powerful this technology really is.
Although new technology is challenging the potential usage of the MERCI device, it was the first. And the first always decides what comes next.
Contributing Writer
Chicago Medical School
I enjoy writing in my free time; I have interest in emergency medicine, surgery and academic medicine.