Defibrillator Leads at a Large-Volume Implanting Hospital
This was a non-randomized retrospective investigator-initiated study, and was approved by the Winthrop University Hospital Institutional Review Board. Patient and implant data were de-identified according to the Health Insurance Portability and Accountability Act. The patient database was designed and populated to include patient and lead characteristics. Appendix A shows the complete list of variables (Lead Database Glossary).
Lead failure was defined according to the Medtronic System Longevity Study, which included failure to capture and sense, abnormal pacing impedance (less than 400 ohms or greater than 2000 ohms), abnormal defibrillation impedance (less than 20 ohms or greater than 200 ohms), insulation defect, lead fracture, extracardiac stimulation, cardiac perforation, tricuspid valve entrapment, lead tip fracture, and/or lead dislodgment. The review of all lead failures was blinded to the implant doctor's name and patient identifiers.
All Winthrop University Hospital defibrillator leads that were implanted between February 1, 1996 and December 31, 2011 were included in this study. Exclusion criteria included non-Winthrop implants and records missing critical data such as unidentifiable leads. Data were obtained from the Electrophysiology Database Management System, Paceart System, remote web-based device monitoring systems, manufacturer-provided lead analysis data, and mortality status as derived from the Social Security Death Index.
Patient characteristics were compared among the different manufacturers. In addition, the patient characteristics including implant approach were examined as it relates to lead failure. The specific lead manufacturers as well as their families were compared. Leads were also categorized according to recalled and non-recalled status, and their performances were compared as well as their association to patient mortality (obtained from the Social Security DeathIndex). In addition, the study compared lead construction characteristics, which included fixation, polarity, lead diameter, distal coil diameter, lead body design (isodiametric or not isodiametric, insulation coating silicone/polyureth ane combination), construction symmetry (asymmetrical vs symmetrical), steroid elution, number of coils, tip to ring spacing, cathode and anode surface areas, helix extension, coil treatment/overlay (none vs silicone backfield), number of compression lumens, number of filled lumens, total number of lumens, and cable construction (1 x 19 vs 7 x 7).
Continuous data were represented as mean ± standard deviation (unless otherwise specified) and the categorical data as proportions. The main endpoint of the study was time to lead failure. Survival estimates and accumulative event rates were compared by the Kaplan-Meier method using the time to first event from the endpoint. The log-rank test was used to compare the Kaplan-Meier survivor curves between manufacturers and lead families. Hazard ratios with 95% confidence intervals (CIs) were calculated using Cox proportional model. Unadjusted Cox with regression analysis was performed on all appropriate clinical variables using time-dependent failure variables (implant age failures) as the endpoint. All variables with unadjusted P-values of <.25 were considered for a multivariable model except for the co-linear variables, which were not included in the multivariable model. A stepwise multivariable Cox proportional hazard model was built to find risk factors of lead failures. Ties in the failure times were handled by the Exact method. The proportionality assumption was tested using all time-dependent variables in the model to make sure that the assumption was met. All calculations were performed using SAS 9.3 (SAS Institute) for Windows. P<.05 was considered statistically significant.
Methods
This was a non-randomized retrospective investigator-initiated study, and was approved by the Winthrop University Hospital Institutional Review Board. Patient and implant data were de-identified according to the Health Insurance Portability and Accountability Act. The patient database was designed and populated to include patient and lead characteristics. Appendix A shows the complete list of variables (Lead Database Glossary).
Lead failure was defined according to the Medtronic System Longevity Study, which included failure to capture and sense, abnormal pacing impedance (less than 400 ohms or greater than 2000 ohms), abnormal defibrillation impedance (less than 20 ohms or greater than 200 ohms), insulation defect, lead fracture, extracardiac stimulation, cardiac perforation, tricuspid valve entrapment, lead tip fracture, and/or lead dislodgment. The review of all lead failures was blinded to the implant doctor's name and patient identifiers.
All Winthrop University Hospital defibrillator leads that were implanted between February 1, 1996 and December 31, 2011 were included in this study. Exclusion criteria included non-Winthrop implants and records missing critical data such as unidentifiable leads. Data were obtained from the Electrophysiology Database Management System, Paceart System, remote web-based device monitoring systems, manufacturer-provided lead analysis data, and mortality status as derived from the Social Security Death Index.
Statistical Analysis
Patient characteristics were compared among the different manufacturers. In addition, the patient characteristics including implant approach were examined as it relates to lead failure. The specific lead manufacturers as well as their families were compared. Leads were also categorized according to recalled and non-recalled status, and their performances were compared as well as their association to patient mortality (obtained from the Social Security DeathIndex). In addition, the study compared lead construction characteristics, which included fixation, polarity, lead diameter, distal coil diameter, lead body design (isodiametric or not isodiametric, insulation coating silicone/polyureth ane combination), construction symmetry (asymmetrical vs symmetrical), steroid elution, number of coils, tip to ring spacing, cathode and anode surface areas, helix extension, coil treatment/overlay (none vs silicone backfield), number of compression lumens, number of filled lumens, total number of lumens, and cable construction (1 x 19 vs 7 x 7).
Continuous data were represented as mean ± standard deviation (unless otherwise specified) and the categorical data as proportions. The main endpoint of the study was time to lead failure. Survival estimates and accumulative event rates were compared by the Kaplan-Meier method using the time to first event from the endpoint. The log-rank test was used to compare the Kaplan-Meier survivor curves between manufacturers and lead families. Hazard ratios with 95% confidence intervals (CIs) were calculated using Cox proportional model. Unadjusted Cox with regression analysis was performed on all appropriate clinical variables using time-dependent failure variables (implant age failures) as the endpoint. All variables with unadjusted P-values of <.25 were considered for a multivariable model except for the co-linear variables, which were not included in the multivariable model. A stepwise multivariable Cox proportional hazard model was built to find risk factors of lead failures. Ties in the failure times were handled by the Exact method. The proportionality assumption was tested using all time-dependent variables in the model to make sure that the assumption was met. All calculations were performed using SAS 9.3 (SAS Institute) for Windows. P<.05 was considered statistically significant.
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