ICD Software Upgrade Could Cut Risk of Shocks

A downloadable software upgrade designed to reduce inappropriate shocks enhances nominally functioning, previously implanted cardioverter defibrillators (ICDs), according to a new study.

Researchers at the Cedars Sinai Heart Institute (CSHI; Los Angeles, USA) conducted a prospective study to determine whether a lead-integrity alert (LIA) ICD software upgrade could reduce inappropriate shocks in patients that had ICD lead fractures, confirmed by analysis of explanted leads. The LIA group included the first 213 patients who met the inclusion criteria and had downloaded the LIA software upgrade; the control group included the first 213 patients who did not have the LIA downloaded. The patients were monitored by daily impedance measurements, which respond with a daily alert.

The results showed that the LIA group had a 46% relative reduction in the percentage of patients with more than one inappropriate shock, and a 50% relative reduction in the percentage of patients with five or more inappropriate shocks. The LIA group also had a higher percentage of patients who either did not receive a shock, or had more than 3 days of warning before the shock. The researchers concluded that the LIA software download that upgrades previously implanted ICDs without surgical revision reduces inappropriate shocks caused by lead fractures. The study was published in the October 12, 2010, issue of Circulation.

"Hundreds of patients have been saved from unnecessary shocks by software that is safe and can be painlessly downloaded in one minute during a standard defibrillator check,” said lead author Charles Swerdlow, M.D., a cardiac electrophysiologist at the CSHI. "One year after LIA was released for download by physicians into patients' ICDs, 30% of patients undergoing remote monitoring had not had the software downloaded. If your doctor hasn't done it yet, it can still be downloaded safely and painlessly.”

ICDs monitor the heart's electrical activity and deliver a shock to reset the heart to a normal rhythm if the pulse becomes too rapid and unable to sustain life. If the lead wires that connect the device to the heart muscle break, the ICD may interpret the rapid electrical signals caused by the fracture as coming from the heart, delivering one or more unnecessary and often painful shocks. The LIA upgrade is triggered by high impedance or rapid oversensing, responding by delaying detection of ventricular fibrillation and initiating a patient alert every 4 hours.

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Cedars Sinai Heart Institute