An algorithm using only implantable cardioverter-defibrillator (ICD) diagnostics identifies leads with over-sensing or high impedance as fractures or connection problems with a high degree of accuracy, according to a study published in the June 7 issue of the Journal of the American College of Cardiology.
“Early diagnosis of ICD lead fractures is important to reduce morbidity from loss of pacing, inappropriate ICD shocks, and/or ineffective treatment of ventricular tachyarrhythmias; however, overdiagnosis may result in unnecessary lead replacement risking morbidity and rare deaths,” the study authors wrote. “ICD diagnostics facilitate identification of fractures, but individual diagnostics are non-specific.”
ICD diagnostics facilitate identification of fractures, but there are no accepted criteria for discriminating fractures from other causes of high pacing impedance and/or over-sensing of characteristic, non-physiological signals (or ‘noise’).
Therefore, Charles D. Swerdlow, MD, of the Cedars-Sinai Heart Institute in Los Angeles, and colleagues sought to use ICD diagnostics to discriminate ICD lead fractures from normally functioning leads with high impedance and from connection problems between the lead and header.
The researchers analyzed a development set of 91 leads to construct a stepwise algorithm based on ICD diagnostics, including 40 fractures, 30 connection problems and 21 functioning leads that triggered high-impedance alerts. Then, they applied this algorithm to an independent test set of 100 leads: 70 fractures and 30 intact leads with connection problems that were misdiagnosed clinically as fractures.
In the algorithm, either extremely high maximum impedance or noise over-sensing with a normal impedance trend indicated a fracture. A short interval from surgery to impedance rise or prolonged stable impedance after an abrupt rise indicated a connection problem. A gradual impedance increase or stable, high impedance indicated a functioning lead.
In the test set, the algorithm correctly classified 100 percent of fractures and 87 percent of connection problems that were misdiagnosed as fractures, according to the study authors. In the study, most connection problems that were misdiagnosed as fractures presented after the peri-operative period; and 46 percent presented more than six months later. The earliest presented at 256 days.
Swerdlow and colleagues found that all impedance rises were abrupt in confirmed fractures or connection problems; stable high impedance occurred in only one connection problem without clinical consequence. In contrast, 43 percent of functioning leads had only gradual increases or increases to stable high impedance, suggesting a different mechanism of impedance rise. “From a clinical perspective, these leads do not require prompt replacement,” the researchers wrote.
With sufficient follow-up, all functioning leads with abrupt, unstable impedance increases showed impedance trends typical of connection problems. While the researchers did not have radiographs to determine if lead pins were inserted incompletely, all functioning leads had impedances less than the maximum displayed by the programmer or remote monitoring. “This raises the possibility that physicians' decisions to replace functioning leads may be influenced by the range of displayed data,” they wrote.
Outside the peri-operative period, noise over-sensing with normal impedance trend indicates a fracture rather than a connection problem, Swerdlow and colleagues concluded. “If noise over-sensing and abrupt impedance rise occur, our algorithm assists in differentiating fractures from connection problems,” they reported.
“Intraoperatively, the ICD should be inspected for incomplete insertion of the lead pin into the header, loose set screws, and other header problems before disconnecting the lead." the researchers noted. "For leads with an abrupt rise and no other evidence of ICD system malfunction, operative intervention is indicated if the algorithm indicates a fracture; however, we cannot provide an evidence-based recommendation if the algorithm indicates a connection problem.”