A Shocking Improvement in Cardiology

s-icd-2Implantable pacemakers and defibrillators have been a staple of cardiology for decades. Offering round-the-clock protection against heart attacks and other issues, it’s not hyperbole to say that the devices have been a lifesaver for hundreds of thousands of people. But the majority of these implantable devices are still placed predominantly in older patients with heart conditions, with the average age of recipients consistently in the high 60’s in clinical trials. Because of the finite lifetime of an internal cardoverter defibrillator (ICD) or pacemaker and the difficulties associated with removing or replacing those devices, many doctors prefer to avoid those options in younger patients.

“That’s crazy,” said Martin Burke, director of the heart rhythm center at the University of Chicago Medical Center. “You have more to gain from a defibrillator if it saves your life when you’re 50 rather than when you’re 80.”

But some of the concerns over implantable defibrillators are legit. Classic ICDs and pacemakers require the electrical leads that deliver the shock to be placed inside the heart, where any infection can be a serious complication. The sensory system that tells the defibrillator to fire sometimes overreacts to benign changes in heart rhythm, causing unnecessary shocks. Flexible materials must also be used due to the hostile environment inside the heart – “It’s a 98.6 degree, dynamic environment that pumps like a piston 60 to 100 times a minute; it’s a miracle they last 15-20 years in my mind,” said Burke, who is a specialist at removing ICDs as well as implanting them.

So Burke has been part of a lengthy effort to improve the technology of ICDs, with a new device – the subcutaneous-ICD, or S-ICD – that finally reached the clinical trial stage this year. Last month, Burke performed the first S-ICD implantation in the United States upon 38-year-old Brooke Bergeron, who suffered a heart attack last year while giving birth to her fourth child.

The subcutaneous ICD changes the location of the leads from inside the heart to just beneath the skin over the sternum. If an infection should occur in that location, it would be less dangerous, and removing the leads would be a less difficult process. While the added distance from the heart means a more powerful shock is delivered by the S-ICD (about 2.5 times stronger than traditional ICDs), the power is still well within a safe range, Burke said. And patients should experience fewer of those shocks, thanks to an improved monitor system that measures more complex heart rhythm characteristics to separate out dangerous cardiac events from false positives.

“We’ve been shocking people like this for 40 years, that’s no different. The big change is the position of the electrodes under the skin and the sensor,” Burke said.

“One issue is the ability to adequately and appropriately sense and distinguish sinus rhythm from any arrhythmia, and the way that we’ve developed so far is to start to create a rhythm classification model as opposed to just a beat detector,” Burke said. “Where the rubber hits the road is when the device doesn’t shock you inappropriately.”


The S-ICD device (picture from Cameron Health)

So far, in the five patients who have been implanted with S-ICDs by Burke, there have been no “spurious shocks,” he said. That’s been a blessing for Bergeron, who as the mother of four children doesn’t have time for false alarms. After the frightening ordeal of her heart attack – where she underwent a C-section procedure and double-bypass surgery only hours apart – Bergeron was initially reluctant to be the first to receive a new, experimental medical device.

“I wasn’t sure if I wanted to be a test dummy,” Bergeron said. “It’s like the iPad – do you want to get it right away or do you want to wait until they get the kinks out?”

But reassured by Burke that the device had already passed initial tests in Europe, and eager to be free from worries about the potential for another serious heart attack, Bergeron agreed to be first. The first couple weeks of recovery were difficult, she said – “It’s tricky having a 10-pound weight limit for lifting when you have a 7-month-old baby.” But only a month after the procedure, Bergeron was on a jet ski on the Gulf of Mexico during a vacation with her family.

“I didn’t want to have the current technology and then in ten years go back and have to do this again with a new device, it just didn’t make sense,” Bergeron said. “I wanted to get moving with my life; I wanted to go on spring break and swim with my kids.”

Burke was encouraged by the early results from Bergeron and other patients in the first month of the trial, and is optimistic than the long-term results will continue to show that the S-ICD is an improvement over its predecessor. While there will still be a role for transvenous ICDs that place leads inside the heart, Burke hopes that the new subcutaneous device will act as a “bridge” to the older model for younger patients who may need an internal defibrillator for decades.

“Every beat that goes by in these people in the last month, it’s gold. It’s working like a charm and not shocking them,” Burke said. “Each day is testimony to its effectiveness.”

About Rob Mitchum (525 Articles)
Rob Mitchum is communications manager at the Computation Institute, a joint initiative between The University of Chicago and Argonne National Laboratory.
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