Technology Offers Less Invasive Alternative For Those At Risk Of Sudden Cardiac Arrest
Research and Innovations Innovations in implantable defibrillator technology can save lives with fewer drawbacks than traditional implantable defibrillator systems.
n 2009, ex-professional basketball player Brian Brunson was halfway through a game when he started to feel dizzy. The next thing he remembers is waking up to a sea of concerned faces.
Unbeknownst to him, Brunson, who was newly married and had a baby on the way, had suffered a sudden cardiac arrest — collapsing while playing. He would have died on the court that day had it not been for the presence of an automated external defibrillator (AED). With the aid of the AED, Brunson was brought back within two and a half minutes.
“There’s a 95 percent mortality rate and within that 5 percent that survive, only 2 percent survive without any brain damage,” says Brunson. “I was pretty lucky.”
Brunson subsequently had a device implanted into his body that could detect and correct any future problems with dangerous heart rhythms, the root cause of the cardiac arrest. This device, known as a transvenous implantable cardioverter defibrillator (ICD), has wires that weave through the veins and into the heart. An implantable defibrillator acts like an insurance policy against future occurrences of sudden cardiac arrest.
Transvenous ICDs have saved countless lives but they have drawbacks. The wires are under tremendous physical stress related to lead movement in the hostile environment of the beating heart. In the worst case scenario, transvenous leads will fail to properly function at a rate of about two percent per year. This fail rate means patients will need to undergo further procedures and face the risks associated with such interventions.
In Brunson’s case, his device’s battery reached its expected lifespan and he underwent a replacement procedure. Two weeks after the replacement, Dr. Glen L. Sumner, Clinical Assistant Professor of Medicine at University of Calgary’s Libin Cardiovascular Institute of Alberta, identified a potentially life-threatening infection which required hospitalization and removal of both the wires inside the heart using a surgical laser, as well as removing the new generator. After careful review of the options, the cardiac device physicians at the Libin Institute decided to implant a newer kind of defibrillator.
Innovations in technology
The subcutaneous implantable cardioverter defibrillator (S-ICD) is similar to the transvenous ICD in that it is implanted in the body and can detect a dangerous heart rhythm and use an electrical shock to reset the heart rate, but there are some major differences between the two.
The subcutaneous device — literally meaning under the skin — is implanted beneath the skin of the chest wall. The S-ICD can, like its transvenous counterpart, act as an insurance policy against sudden cardiac arrest but there’s likely a significantly lower risk ofserious bloodstream infections or damage to the veins or heart that may occur with the transvenous ICD. The lower complication rate is because the S-ICD wire is not inside the veins and heart but instead underneath the skin. The device is also easier to implant meaning a potentially lower risk procedure. In addition, the subcutaneous lead is not subject to the same hostile environment and movement as the transvenous leads and therefore may have significantly less chance of failure over the long-term.
Although it’s too early to say, early findings seem to suggest subcutaneous systems will require significantly less system revisions than transvenous systems — for example, addressing damaged wires.
The future is promising
“We believe the S-ICD may have a lower complication rate,” says Dr. Sumner. “We don’t have enough data to know exactly how long the wires will be effective for but we suspect that they’ll be a lot more robust. This will ultimately be determined by long-term outcome studies and device registries but right now it looks very promising.”
Brunson had an S-ICD device implanted just over a month ago. “It was hard after the procedure because I couldn’t pick up my one-year-old son,” he says. “I’m 6’9” and my wife’s almost six foot so the baby is huge! But, I’m in good health and good spirits and I like the fact that I don’t have any wires in my heart anymore. If this got infected, they could just take it out, treat it and put it in again. And, with the traditional ICD those wires decay but with this S-ICD, one wire could potentially stay in your whole lifetime.”
Brunson, who lives in Calgary with his wife and three children, is recovering well and has just been cleared for heavy lifting.