One in four patients with internal defibrillators has boost in heart function

30th July 2015

A quarter of people having an internal defibrillator (ICD) for declining heart function experience improvements making them no longer fit the criteria for having one of the devices, says a study.

The patients had a markedly lower risk of dying and were far less likely to suffer device shocks, suggesting their hearts were less prone to developing a dangerous heart rhythm, said the study from the Johns Hopkins University School of Medicine in America.

Internal defibrillator

Researchers looked at 1,200 people who were fitted with the devices because doctors thought they were at risk of a cardiac arrest. None of them had already had a cardiac arrest.

A report on the study, just published in the Journal of the American College of Cardiology, said researchers attributed the improvement mostly to heart drugs that help the heart’s ability to pump and, in a small portion of patients, the use of devices that include a biventricular pacemaker for synchronising the contraction of the heart’s chambers. The researchers said the real surprise was not the fact that patients got better, but rather how many did.

Because the number of device shocks never reached zero among those with improved heart function, the researchers said arrhythmia risk was not completely eliminated and patients may continue to get some protection from defibrillators even as their hearts become less susceptible to dangerous rhythms.

But because defibrillators can also cause serious complications, the risk-benefit ratio does shift substantially in people whose heart function improves dramatically, the researchers say. “Our results highlight an urgent need to refine the risk-benefit assessment in people repeatedly, over the course of their treatment, and not just at the time of device implantation,” says senior investigator Dr Alan Cheng, a cardiac electrophysiologist and an associate professor of medicine at the Johns Hopkins University School of Medicine.

“Determining if patients with defibrillators whose hearts get better over time may be better off without the device is just as important as determining who needs a defibrillator in the first place,” he says.

ICDs can also occasionally misfire, delivering unnecessary shocks. And because placing the device inside the chest is an invasive and complex procedure, there is risk of blood vessel damage and heart valve infections, said the researchers.

Predicting which patients are most at risk for a cardiac arrest and stand to benefit most from a defibrillator is often tricky and invariably involves some guesswork, researchers add. Those in the study were aged from 18 to 80 and received their ICDs at four heart centres in America between 2003 and 2013 and who were followed for an average of five years. A portion of the group, 538 (45 percent), underwent at least one heart function re-assessment after initial device placement.

In a quarter of patients, their ejection fraction (a measurement of how well the heart is pumping) increased above 35 per cent, the threshold that calls for defibrillator placement.

These patients had a 33 per cent lower risk of dying and a 30 per cent lower risk of appropriate device shocks, compared with patients whose heart function remained unchanged.

The investigators say the fact that fewer than half of all patients in the study had their heart function re-assessed prior to their regularly scheduled device replacement points to the need for better ongoing monitoring.