Micra TPS
A pacemaker the size of a vitamin is changing the cardiac game at Vanderbilt Heart and Vascular Institute. Last September, cardiologist Christopher Ellis, MD, director of clinical arrhythmia research, implanted the first Medtronic Micra Transcatheter Pacing System (TPS) in a 59-year old Johnson City patient.
The VHVI arrhythmia team has implanted 10 more since that first procedure, participating in a global clinical trial to test the safety and efficacy of the world’s smallest pacemaker.
How it Works
The Micra TPS is recommended in patients requiring a pacemaker for intermittent, or permanent pacing of the right ventricle only (VVI or VVIR), and in those with no existing transvenous defibrillation or pacemaker devices in place. The minimally-invasive procedure lasts approximately a half-hour with the device placed through a catheter running from the femoral vein into the heart. Ellis said the Micra TPS is a welcome change from traditional wire pacemakers, which require a much bigger surgery.
“You can walk out the door same day and be sure it’s going to work,” said Ellis, lead investigator for the Micra TPS clinical trial. Traditional single wire pacemakers require surgical incision, a device pocket created above the muscle, a transvenous lead and a lot more hardware, said Ellis. Wire pacemakers also carry greater risk of complications including device infection, air leakage around the lungs and fractured leads under the collarbone. While traditional pacemakers are necessary for certain diagnoses, Ellis expects the wireless, miniature technology to completely revolutionize cardiac care over the next decade. Patients don’t require antibiotics following implantation, and no surgical pocket means no wound checks. A tenth the size of a traditional pacemaker, the Micra TPS can last 12 to 14 years for intermittent pacing and six to 10 years when used for full-time pacing. The device also is MRI compatible and capable of rate responsive pacing. “The watch-like battery is a very novel design, and the MICRA is pulled into the muscle nicely by tiny hooks which keep the pacing threshold very low,” Ellis explained. “You can also steer it right to where you want it, so there’s no hunting for healthy tissue like with traditional surgeries.”
Once positioned, the pacemaker is securely attached to the heart wall and can be repositioned or retrieved if needed. The pacemaker delivers electrical impulses that pace the heart through an electrode at the end of the device. Vanderbilt is one of only 50 hospitals worldwide to use the investigational device, and the only trial site in Middle Tennessee.
Surgical Treatment of Pulmonary Hypertension
VHVI also is among an elite list of referral centers offering surgical treatment for chronic thromboembolic pulmonary hypertension (CTEPH). Patients with this life-threatening condition often have a history of acute pulmonary embolism, or blood clots in the lung.
“We don’t know why some patients get blood clots in the lung and don’t resolve it,” said VHVI cardiologist Ivan Robbins, MD, professor of medicine. “While most people resolve the problem with or without coagulation, clots turn into scar tissue for some.”
For that small percentage of patients, scar tissue causes obstruction in the pulmonary arteries, putting strain on the right heart and causing potential heart failure.
“Cardiologists and pulmonologists need to keep in mind that there will always be a percentage of patients who don’t resolve clots, and we suggest they get follow-up imaging and care,” Robbins said. Diagnosing the problem is difficult and is confirmed by pulmonary angiography. Initial, nondescript symptoms often include shortness of breath, on oxygen and able to walk for only short distances without having to rest.
Big Surgery, Big Results
For the 400-plus CTEPH patients who undergo surgery annually, pulmonary thromboendarterectomy (PTE) offers a second chance at life.
Robins said the surgery is sometimes confused with embolectomy. However, PTE is a high-risk, complex operation reserved for a specific type of patient. Patients are placed on the heart-lung machine, and the body temperature is cooled to 64.4 degrees Fahrenheit. The chest is opened via median sternotomy, and the surgeon removes scar tissue from the lungs, operating on each side in 20-minute intervals.
Robins said results are immediate and extremely gratifying, as pulmonary pressure returns immediately to a safe level. One of fewer than 10 sites nationwide to offer PTE, Vanderbilt has performed 40-plus surgeries since their first operation more than five years ago, with patient outcomes equal to those of the most prominent referral centers.
While physicians often know about treatment facilities in San Diego or North Carolina, Robbins said many are still unaware about options in Middle Tennessee. “People are starting to realize there’s surgical treatment for this,” he said of the life-threatening diagnosis. “It’s the only form of pulmonary hypertension that can be treated surgically and markedly improved, and many patients go on to live normal lives.”
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