The FDA has issued a warning following two deaths in the US connected to premature battery depletion in St Jude Medical Cardiac implantable electronic devices.

Patients with Medical Implantable Cardioverter Defibrillators (ICDs) and Cardiac Resynchronisation Therapy Defibrillators (CRT-Ds) produced by St Jude Medical have been warned that they are at risk of life threatening premature battery depletion.

The US Food and Drug Administration has warned that patients with affected devices should seek immediate medical attention as soon as they get a low battery alert from their monitoring devices, rather than the normal three months to allow for device replacement.

Some batteries in the heart devices have run out within 24 hours of the patient receiving an alert.

The FDA reports that two deaths have been associated with devices that were unable to provide the required pacing therapy because of battery depletion.

The problem has been identified in St Jude Medical ICDs and CRT-Ds manufactured before 23 May 2015. The affected devices are those in the Fortify, Fortify Assura, Unify, Unify Quadra, Unify Assura and Quadra Assura product ranges. Any unused devices are to be recalled.

398,740 affected devices have been sold worldwide, including in the UK. 349,852 of the affected devices have been implanted in patients.

If you think your device may have been affected, you can check by inputting the model and serial number on the St Jude Medical website.

ICDs deliver electrical shocks to restore a normal heart rhythm when necessary, using a battery powered pulse generator. CRT-Ds use electrical impulses to resynchronise heart contractions and terminate abnormally fast, life-threatening heart rhythms.

If the batteries are depleted, the devices are unable to deliver life-saving pacing and shocks.

The FDA has stated that people with a high requirement of life-saving shocks, and those who are pacemaker dependent, are most at risk.

Battery levels are measured using at-home monitoring, which sends information about a patient’s heart activities directly to their doctor’s clinic.

A vibratory alert directly from the device also alerts the patient that the battery is nearing the end of its life. Premature depletion is caused by the lithium deposits forming within the battery, known as lithium clusters, which create abnormal electrical connections which lead to rapid battery failure.

Concerns about battery life in cardiac implantable electronic devices such as ICDs and CRT-Ds have recently been raised in the British Medical Journal.

With each revision surgery to replace batteries there is an increased risk of life threatening infection, as well as the risk of complications inherent in any procedure.

ICD batteries tend to have a shorter life than those found in pacemakers, meaning patients are at greater exposure to these risks.