NEW YORK (Reuters Health) – Inappropriate shocks from implanted defibrillators don’t seem to cause long-term harm, new data suggest.
Instead, researchers say, prognosis is linked to the underlying arrhythmia, not the inappropriate shock itself.
“The ALTITUDE study is one of the first to be large enough to provide insight into the much debated topic of whether or not inappropriate shocks from implantable cardioverter defibrillators (ICDs) are harmful,” said Dr. Brian D. Powell from Sanger Heart & Vascular Institute, Charlotte, North Carolina, in email to Reuters Health.
“We found that ICD shocks do not appear to decrease a patient’s long-term survival, but instead the underlying rhythm at the time of the ICD shock was associated with long-term survival,” he added.
“We were surprised at how clear the results showed that patients who were shocked in the setting of sinus tachycardia, SVT (supraventricular tachycardia), or electrical noise/artifact had the same survival as those who never received a shock,” Dr. Powell said. “There was no evidence that inappropriate shocks caused long-term harm.”
Dr. Powell and colleagues had access to data from implantable cardioverter-defibrillators (ICDs) and cardiac resynchronization therapy-defibrillators (CRT-D) in more than 28,000 patients being followed on a remote monitoring system.
For the study to be published online in the Journal of the American College of Cardiology, they identified a random sample of 3809 patients with at least one spontaneous defibrillator shock.
Most shocks were appropriate for sustained ventricular arrhythmias, but 41.3% were inappropriate shocks for non-ventricular arrhythmias, most commonly atrial fibrillation/flutter (AF/AFL) (18%) and sinus tachycardia or supraventricular tachycardia (17%).
Patients shocked for a ventricular arrhythmia had a higher risk of death during follow-up than those shocked for non-ventricular arrhythmia. The risk of death was similar whether patients were shocked for monomorphic ventricular tachycardia or AF/AFL, but mortality was significantly lower after shocks for sinus tachycardia/SVT or noise/artifact/oversensing.
Among patients matched by rhythm, shocked patients had a higher risk of death, but only when the shock was for a ventricular arrhythmia or for AF/AFL.
There was no significant difference in survival for matched patients who received shocks for sinus tachycardia/SVT, noise/artifact/oversensing, or nonsustained arrhythmias, the authors said.
In contrast, patients who received inappropriate shocks for AF/AFL faced an increased risk of death.
“Physicians can learn from the ALTITUDE study that if their patient receives a shock for atrial fibrillation, they should not only adjust the programmed settings on the ICD to minimize the chance for future shocks, but also make sure the patient is appropriately treated with anticoagulation and medical therapy as indicated,” Dr. Powell said.
“ICDs sometimes detect episodes of atrial fibrillation that are not symptomatic,” he continued. “It is important that we address these episodes with medical therapy to reduce the risk of stroke and other complications that likely account for the decreased survival seen with atrial fibrillation in patients who receive ICD shocks.”
Dr. Powell added, “Patients can take away some reassurance that if they receive an ICD shock due to electrical noise/interference or during normal rhythm, that it does not appear to cause long-term harm. In these situations, programming changes can often be made to the ICD to lower the chance of a future shock.”
“When used and programmed appropriately, the ICD reprises its role as the Good Samaritan, providing the best line of defense against sudden death in patients at risk of lethal ventricular arrhythmias,” write Dr. Eric S. Williams and Dr. Jeanne E. Poole from University of Washington Medical Center, Seattle, in an editorial. “It is important to note that the majority of patients who received a shock for ventricular tachycardia or ventricular fibrillation in the ICD clinical trials were alive at the end of each study.”
“That all patients do not survive should not come as a surprise,” they note. “Ventricular arrhythmias may represent a final common pathway in otherwise terminal conditions such as end-stage heart failure or multi-organ failure.”
“We still should seek to decrease ICD shocks, primarily to reduce unnecessary ICD therapy and to alleviate the adverse psychological effects associated with inappropriate ICD shocks in patients,” the editorial concludes. “However, in the case of the increased risk after ICD shock, it is the associated arrhythmia in a vulnerable patient that explains the increased cardiovascular risk, and not the shock in isolation.”
Dr. Ryan T. Borne from Denver Health in Denver, Colorado, who coauthored a review of ICD shocks published May 27 in JAMA Internal Medicine, told Reuters Health by email, “I do not think that these results are surprising, but it adds more data to what currently exists.”
“Appropriate shocks for ventricular rhythms and AF are associated with increased mortality while inappropriate ICD shocks for non-AF SVTs/noise/artifact are not,” Dr. Borne added. “However, other patient centered outcomes are still worse with any ICD shock. Care must be taken to ensure that patients with ICDs are cared for ‘upstream’ of shocks including personalized programmed settings and optimal medical therapy.”
The journal does not announce its publication dates in advance.
J Am Coll Cardiol 2013.