Outcomes and the Volume of Cardioverter-Defibrillator Implants Performed
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Synopsis: ICDs implanted by higher volume physicians are associated with lower rates of mechanical complications and infection.
Source: Al-Khatib SM, et al. The Relation Between Patients' Outcomes and the Volume of Cardioverter-Defibrillator Implantation Procedures Performed By Physicians Treating Medicare Beneficiaries. J Am Coll Cardiol. 2005;46:1536-1540.
It has been previously well documented that greater operation volume is associated with improved outcomes for several cardiac procedures. In this paper Al-Khatib and colleagues analyzed the Medicare Provider Analysis and Review (MEDPAR) files and correlated patient short-term outcomes with the volume of implantable cardioverter defibrillator (ICD) insertions performed by the individual implanting physicians. Al-Khatib et al sampled 20% of Medicare part B claims and correlated them with valid physician identifiers for the period between January 1, 1999 and December 30, 2001. Hospital admission and discharge dates that covered the period of implantation were identified, and the hospitalization was classified as elective, urgent or emergent. Patient co-morbidities were assessed using the Charlson Co-Morbidity Score. Outcomes were identified on the claim forms for the initial procedure or for subsequent claims available within 90 days of the index procedure. Al-Khatib et al specifically looked for the presence of codes for device related infections and mechanical complications within this period. Individual physician volumes were estimated using a 5-fold multiplier to calculate an average annual volume of ICD placement. A frequency distribution of physician procedure volumes was created and used to test the relationship between implanter volume and outcomes.
In the 20% sample selected for study, 1672 physicians submitted Medicare claims for ICD implantation in 9854 patients. Adjusted for the sample size, the average annual volume ranged from 1 to 87, with a median of 7 procedures per year. Over 60% of the physicians performed between 1 and 10 ICD implants per year, about 20% performed between 11 and 18, 15% between 19 and 28, only 7% more than 29 implants per year. Of the patients included in the sample, 19.3% were over age 80, 21.6% were women, and 92.4% were white. The Charlson Co-Morbidity Score was 0 or 1 in 79.9%. There were only small differences in patient characteristics across quartiles of physician volume. The overall mortality rate in the entire population was 2.4% within 30 days and 5.8% within 90 days. Mortality rates were not affected by physician volume. There was, however, a significant increase in mechanical complications between the highest volume and the lowest volume implanters, and a significant decrease in infections among the highest volume implanters. The 90-day mechanical complication rate was 7% among physicians who had implanted 1 to 10 ICDs vs 4.4-4.9% in the other 3 quartiles. For 90-day infection, the rate was 1.2% to 1.4% in the 3 lower volume quartiles, and only 0.6% in the highest volume quartile. These observations held true after adjustment for the urgency of the implantation.
Al-Khatib et al conclude that ICDs implanted by higher volume physicians are associated with lower rates of mechanical complications and infection. They suggest that ICD implantation should be directed towards high volume physicians.
Commentary
The data in this paper confirm previous observations that, as a general rule, higher volume operators have better outcomes than low volume operators. This has been shown for percutaneous interventions, CABG surgery, and other cardiac procedures. ICD implantation and follow-up, however, requires 2 separate skills. The surgical skills for placing a lead and making the pocket are now not much different than the skills required for a routine single or dual chamber pacemaker insertion. Programming the devices optimally and trouble shooting during acute defibrillation testing and chronic follow-up, however, require more than just surgical skills. These latter skills are best learned during formal training in clinical cardiac electrophysiology, or by frequent clinical practice in that discipline. This paper really deals with only the surgical part of the issue.
Recently, the Heart Rhythm Society has proposed that experienced pacemaker implanters, either cardiologists or cardiac surgeons, could gain competency in ICD implantation under certain circumstances. The guidelines suggest that physicians who implant more than 35 pacemakers per year, with over 100 within 3 years, could gain competency in ICD implantation after a minimum of 10 mentored initial implants and 5 follow-up procedures. In contrast, clinical cardiac electrophysiology fellowship training programs require at least 25 ICD initial implants, and training in most programs would provide several times this number. The data presented here suggest that both groups need to maintain a reasonable volume to minimize surgical complications. Optimal trouble-shooting and follow-up should also be related to the number of patients followed, and this will usually favor follow-up by electrophysiologists whenever problems arise.
There are several possible limitations of the data presented here that should also be recognized. During the period under study, cardiac resynchronization therapy was just being introduced. These procedures are considerably more involved and risky, and I would expect that they were performed only by the highest volume operators during this time period. MEDPAR coding during this period probably did not allow these procedures to be separately analyzed. This may well have artificially increased the rate of mechanical complications and infections for the highest volume implanter group. We are also not told the specialty training of the operators in this survey. Over the last 15 years, ICD implantation has gradually passed from cardiac surgeons to electrophysiologists in most centers. However, certain complicated cases may still be done by surgeons, and the reasons for the complicated procedure may not be reflected in a co-morbidity index. Few surgeons do many ICD implants per year, yet the cases they do may be the most hazardous. This may account for some of the excess complications noted in the low implanter volume group.
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