Score predicts patients at risk of ICD testing glitch

Researchers developed and validated a simple risk model that identifies implantable cardioverter-defibrillator (ICDs) patients at risk of an inadequate defibrillation safety margin during defibrillation testing. By predicting who is at risk, physicians may be able to avoid related complications and better manage patients.

Some physicians test ICDs at the time of implantation to make sure the devices can detect and terminate ventricular fibrillation. A defibrillation safety margin test may substitute for a defibrillation threshold test by allowing the physician to use a lower energy shock and then programming the device at least 10 J above it. An inadequate defibrillation safety margin requires extra steps and possibly repeated tests.

Jonathan C. Hsu, MD, of the University of California, San Diego, and colleagues reasoned that a risk score would help physicians identify patients at risk of an inadequate defibrillation safety margin and plan the procedure accordingly. They speculated that the National Cardiovascular Data Registry ICD registry would have sufficient data to tease out preprocedural variables to characterize at-risk patients and possible adverse outcomes.

Their analysis started with 28 variables that were registry-compatible and suitable for the risk model. Outcomes of interest included in-hospital complications during or after ICD implantation, duration of hospitalization and in-hospital death.  

They assessed registry data submitted between April 1, 2010, and June 30, 2012, on 132,477 patients from 1,457 facilities. Beginning in April 2010, the registry included defibrillation testing data.

An inadequate defibrillation safety margin occurred in 9.4 percent of the patients. Using derivation and validation groups, they identified eight variables to predict risk and created a scoring system: age (older than 70 years, one point); sex (male, one point); race (black four points, Hispanic two points and other one point); New York Heart Association functional class (III one point and IV three points); no ischemic heart disease (two points); renal dialysis (three points); secondary prevention indication (one point); and ICD type (single chamber two points and biventricular one point).

They determined that the risk of an inadequate defibrillation safety margin jumped from 4.9 percent for a score of 0 to 24.5 percent for scores of 12 or more. An inadequate defibrillation safety margin increased the odds of other procedural complications and a hospital stay of more than three days by 20 percent and almost doubled the odds of in-hospital death.

Hsu and colleagues proposed that physicians could use the risk score to prepare for procedures.

“It is particularly important to identify ICD recipients with high risk for an inadequate DSM [defibrillation safety margin], given the greater likelihood that a change in clinical management may be required,” they wrote. “Also, armed with information from the simple risk score, operators may be better able to counsel patients regarding the probability of requiring additional steps to the procedure.”

The results were published in the July 22 issue of the Journal of the American College of Cardiology.