A test that puts patients into cardiac arrest to find out if their new heart device is working is redundant and even harmful, new research out of McMaster University suggests. 

Patients with implantable cardioverter-defibrillators (ICDs), a device that paces fast heart rates with a electrical shock, are routinely sedated and put into cardiac arrest to ensure the new device has the power to bring the patient back to life. 

Known as defibrillator testing (DT), the test has been around for 30 years for the some 300,000 ICDs inserted worldwide every year. But noticing that some physicians, particularly in Canada, had stopped performing the potentially harmful test, McMaster associate professor of medicine Jeff Healey decided to look into if modern technology has made the routine redundant. 

"We don't see any value [anymore]," Healey said by phone from San Francisco, Calif., where he presented his study to the Heart Rhythm Society Thursday. "We're going to advocate from moving away from [testing]."

ICDs are similar to pacemakers in that they aid the heart in regulating a steady beat. 

"In broad strokes," explained Healey, "pacemakers are put in patients with slow heart rates, and ICDs are put in patients with fast heart rates, which are associated with cardiac arrests."

The battery-powered devices are implanted in the upper left chest and shock patients back into a steady rhythm. Healey said the device works along the same lines at the "paddles" on T.V.

In Hamilton, only about 10 per cent of ICDs were tested with a DT after implementation. The study looked at a cohort of 2,500 patients, many of whom were from Hamilton. It did not include replacement ICDs or more complex ICDs, like those on the right side of the body which is further away from the heart.

In the U.S., the practice is more widely used with 150,000 ICDs implanted every year. Healey said complications run at rate of 4.5 per cent and that fatalities are rare. 

"The ICD has matured over the last 20 to 30 years," Healey said. 

He estimated roughly 80,000 patients in the U.S. would go through DT testing when the device is implanted. Eliminating those tests would make for "80,000 fewer general anaesthetics a year. There's a lot of cost and potential complication savings."