Sunday, 21 September 2014
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Defibrillator garment detects and corrects abnormal heartbeat

Johns Hopkins biomedical engineering students have designed a lightweight, easy-to-conceal shirt-like garment to deliver life-saving shocks to patients experiencing serious heart problems.

The students said their design improves upon a wearable defibrillator system that is already in use. The students further claim in a statement that their design could help persuade patients at risk of sudden cardiac arrest to wear the system for extended periods.

‘In two studies, up to 20 per cent of patients who received the defibrillator garment that’s already available did not keep it on all the time because of comfort and appearance issues, problems sleeping in it, and frequent ‘maintenance alarms,’ which occur when the device does not get a good signal from sensors on the patient’s skin,’ said Sandya Subramanian, a Johns Hopkins junior who led the undergraduate team that built the new prototype. ‘We set out to address these issues.’

Wearable defibrillators, resting against the skin, are designed to detect arrhythmia, an irregular heart rhythm that can cause death in minutes if it is not stopped by controlled jolts of electricity. People who face this higher risk of sudden cardiac arrest include patients who have undergone open-heart surgery and those who have recently survived a heart attack.

The long-term treatment for such patients is to surgically implant a small defibrillator in the chest, similar to a pacemaker. The students said such operations cost roughly $150,000 and it generally takes three months of testing and insurance review to get approval for the costly procedure.

During this waiting period, insurance providers usually pay for the rental of an external defibrillator garment to protect the patient. More than 100,000 of these devices have been prescribed in the United States during the eight years or so that the device has been available.

The Johns Hopkins student team was assigned last year to develop a system that would lead to greater compliance among these patients.

In particular, the students replaced the existing chest harness-style garment with a more comfortable vest-like design made of thin, breathable and stretchable fabric, which also is waterproof for easy cleaning.

The shirt can be worn unobtrusively beneath the patient’s clothing. Its electrical components, capable of delivering a 200-joule shock to stop an arrhythmia, are encased in thin pockets on the sides of the garment.

The students also replaced a bulky control box hanging from the patient’s waist with a smaller wireless system worn like a watch on the patient’s wrist. This controller gives the wearer a 30-second warning to stop an impending shock if the system has been activated by a false alarm.

‘We did not change any of the science involving how a wearable defibrillator works,’ said team member Melinda Chen. ‘We just changed the form of the device. We pursued a ‘slip-on and forget’ approach to minimise the user’s need to maintain and interact with the device.’

The students’ have completed preliminary testing at the Johns Hopkins Hospital Simulation Center, using manikins wired to mimic heart patients. The team has obtained a provisional patent covering some of their innovations and team members will continue to refine the prototype and to confer with medical device makers about advancing the project.


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