Clinical and Economic Outcomes of Embolic Complications and Strategies for Distal Embolic Protection during Percutaneous Corona
- Volume 18 - Issue 2 - February, 2006
- Posted on: 8/1/08
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Over 500,000 coronary artery bypass grafts in 314,000 cases were performed in the United States in 2000, however, over half of all vein grafts develop significant stenosis within 10 years.1,2 Percutaneous coronary intervention in saphenous vein grafts is consequently an increasingly common therapeutic modality utilized in the treatment of vein graft stenosis. In contemporary practice, vein grafts develop bulky lesions composed of loose atheroma and thrombotic material, and are often degenerated.3 This poses a significant risk for distal embolization and no-reflow, resulting in a major adverse event in up to 20% of procedures.4
Since management of the no-reflow phenomenon is frequently unsuccessful and its outcome unpredictable,5 prevention is a more effective strategy. Distal embolic protection devices have been shown to reduce the frequency of distal embolization and sequelae. The SAFER trial was first to demonstrate that distal embolic protection provided a 42% relative risk reduction (16.5% versus 9.6%; p < 0.004) in major adverse events.6 The Food and Drug Administration (FDA) approved the PercuSurge Guardwire™ system (Medtronic, Inc., Minneapolis, Minnesota) utilized in SAFER, as well as the FilterWireEX™ (Boston Scientific Corp., Natick, Massachusetts), a second device with similar effectiveness. Cost analysis from SAFER shows increased initial procedure costs (median $1,547; p < 0.001) and slightly increased total hospital costs (median $582; p < 0.001).7
Despite the medical utility of distal embolic protection for vein graft interventions, the incremental cost is not reimbursed by the Centers for Medicare and Medicaid Services. In a cost-conscious era of medicine, strategies for the most cost-effective use of resources are imperative. Distal embolic protection could be routinely used in all patients, but the substantial costs may be prohibitive. However, not utilizing distal embolic protection would result in a significant number of otherwise preventable embolic complications and sequelae, including death. A better strategy may be to balance these competing alternatives to maximize clinical benefit and minimize the economic impact by selectively using distal embolic protection in patients at high risk for embolic complications.
Numerous investigators have consistently identified similar clinical and angiographic variables predictive of embolic complication.8–17 These factors could potentially identify patients at higher risk for embolic complications to receive distal embolic protection. To assess the optimal strategy, we analyzed data from patients undergoing percutaneous coronary intervention in saphenous vein grafts without distal embolic protection to determine the incidence and cost of embolic complications. We then analyzed the effect routine and selective distal embolic protection strategies might have on clinical outcome and resource utilization in comparison to the referent strategy of no distal embolic protection.
Study design. Between 1997 and 2001, a total of 142 consecutive patients at a single academic medical center underwent percutaneous coronary intervention in a saphenous vein graft without distal embolic protection. Sixteen patients were excluded from this study due to incomplete clinical and/or financial data, resulting in a cohort of 126 consecutive patients.
Patient and procedural characteristics were prospectively collected in our catheterization laboratory database and defined as prespecified by the National Cardiovascular Data Registry (NCDR) and the Society of Cardiac Angiography and Interventions (SCAI).18 Embolic complications were defined as angiographic evidence of no-reflow/slow flow with or without postprocedure myocardial infarction. No-reflow/slow flow was quantified as Thrombolysis In Myocardial Infarction (TIMI) grade 2 or less.6 Myocardial infarction was defined as elevation of creatine kinase > 200 mg/dl and a CK-MB index > 10%, or troponin I > 2 mg/dl. Major adverse coronary events, or MACE, includes myocardial infarction, emergency coronary artery bypass graft, and death as defined by the NCDR and SCAI.
Patients were classified into two comparison groups according to the occurrence (EC; n = 22) or absence (non-EC; n = 104) of an embolic complication. Clinical and angiographic predictors of embolic complications previously reported by various investigators2,8–14 have been confirmed by the NCDR14,15 and in our own laboratory.16,17 Furthermore, multivariate analyses demonstrates that graft age greater than or equal to 8 years and preprocedural thrombus are the strongest independent predictors of embolic complication. Patients with one or both characteristics were identified as high-risk, with all others considered low-risk. Based on risk status, three different distal embolic protection strategies were compared: (1) no distal embolic protection (referent); (2) routine distal embolic protection in all patients; and (3) selective distal embolic protection only in high-risk patients.
By intent, no patients in this analysis actually received a distal embolic protection device. The incidence of embolic complication and cost attributed to routine and selective strategies represent theoretical calculations based on a 42% relative risk reduction,3 while the referent analysis represents actual incidence and costs.
Cost analysis. The finance department prospectively collected financial data as patient charges using a consistent accounting method. Charges were converted to costs using a cost center specific ratio of cost-to-charges (RCC) to calculate both direct and indirect costs.19 All cost data are adjusted to 2003 dollars using the United States Consumer Price Index.20
The cost of the distal embolic protection device was based on the average cost of the two FDA-approved distal embolic protection systems: PercuSurge Guardwire™ (Medtronic), a balloon occlusion device, and FilterWireEX™ (Boston Scientific), a filter device. These two different types of distal embolic protection systems provide similar reductions in the incidence of embolic complications.21
Total procedure cost equals cost per individual in the catheterization lab, where the cost of an embolic complication is the difference in mean total procedure cost between patients with and without an embolic complication, adjusted for the relative risk reduction of the distal protection device. Total procedure cost is less confounded than total hospital cost, making it a more direct and accurate measure of embolic complication cost. The cost to theoretically prevent an embolic complication per individual equals total procedure cost plus distal embolic protection device cost, less the cost of an embolic complication. The analysis also accounts for correct and incorrect classification of patients by the model.
Statistical analysis. Categorical variables are expressed as percentages and were compared using the Chi-square or Fisher’s Exact test for differences in proportions when appropriate. Continuous variables are expressed as mean ± standard deviation and median, then compared using the Student’s t-test if normally distributed, or the Mann-Whitney test if not normally distributed. All p-values are two-tailed with statistical significance considered at p < 0.05. All analyses were performed using SPSS software (SPSS Inc., Chicago, Illinois).