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CON: Preoperative Stress Testing According to ACC/AHA Guidelines is a Valuable Triage Adjunct For High Risk Cadiac Patients Prior to Noncardiac Surgery
Paul Barash, MD
Anesthesiology is a specialty that thrives on data. It is difficult to argue with that more data available for a given patient will not improve their care. However, this notion is starting to undergo rigorous scientific investigation. In an area parallel to the topic under discussion, Schein et al. examined pre-operative evaluation strategies in patients (n=18,819) undergoing cataract surgery.1 They found no difference in outcome between the group who had a minimal assessment versus those who had a more extensive work-up. In an effort to encourage rational use of pre-operative testing in an era of cost containment, the American Heart Association with other sponsoring organizations promulgated Guideline Update on Perioperative Cardiovascular Evaluation for Non-Cardiac Surgery (AHA Guidelines).2 The primary focus of the guideline is that .intervention is rarely necessary simply to lower the risk of surgery unless such intervention in indicated irrespective of the clinical context. No test should be performed unless it is likely to influence patient treatment. The Con argument covers eight areas:
For purposes of this debate, I will use the patient undergoing vascular surgery as the clinical model since these patients usually have a higher number of risk factors and usually undergoing higher risk operations. 1. AHA Guideline admonition regarding pre-operative testing. The intermediate risk factor group encompasses the largest percent of patents undergoing vascular surgery. Taken with the potential for higher risk surgery, a large number of patients would be exposed to a testing strategy that is not only costly (hundreds of million dollars), but would most likely have beta blockers therapy instituted.3 Direct coronary interventions would add unnecessary delay to the surgical procedure.4-8 2. Previous attempts at a "universal" testing approach have not been sustained. Based on available data older studies have advocated the use of "routine" coronary angiography, LVEF by radionuclear testing, etc.9-10 None of these pre-operative evaluation strategies have stood "the test of time." They have been associated with no difference in outcome, increased cost or adding morbidity and mortality to the preparation of the patient for vascular surgery. 3. Pharmacologic stress testing has a poor positive predictive value. On the basis of claudication, many patients cannot undergo exercise stress testing. Therefore, I will focus on pharmacologic stress tests. Selection bias plays a large role in reported results. However, combining the data from larger series demonstrates an excellent specificity (>90%) but a poor positive predictive value (~< 25%).11-16 Although a negative result nearly excludes the presence of CAD risk of post-operative CV complications, a positive result may lead to more testing, e.g., coronary angiography with the significant possibility of normal coronaries. A recent publication using a randomized trial design showed no difference in outcome between vascular surgical patients who underwent a testing protocol versus those who did not.16 4. The area of ischemia revealed by pharmacologic stress testing may not be the source (location) of a peri-operative MI. Two studies report that the myocardial area at risk, as predicted by various stress tests, is not accurate.16-17 In 50% of patients who sustained an acute perioperative MI, the territory of injured myocardium extended beyond that predicted by the dobutamine stress echo examination.17 This was further buttressed by a report showing that collateral total occlusions and "nonobstructive" coronary lesions were the apparent cause of a perioperative MI.16 5. The societal cost associated pharmacologic stress testing is excessive. As noted previously, the costs of these tests are significant for the individual patient and society.3 In the absence of definitive outcome data, I would question such a large investment in an unproven testing strategy. 6. Direct coronary interventions (angioplasty +/-stent and CABG) add significant delay to timing of vascular operation. No data exists showing the optimal timing between a coronary intervention (PCI or CABG) and the vascular procedure.4-8 Although one report shows a small delay (e.g. 10 days) between PTCA and vascular operation had excellent results, the results of three other reports calls this into question. In patients who have had PTCA + stent (and anti-platelet drugs) waiting six to eight weeks after the PCI seems preferable. How realistic is this strategy of testing plus PCI in a patient who requires urgent vascular surgery? 7. Medical treatment with beta blockers and alpha-2 agonists will further obviate the need for an extensive stress testing strategy. The area that has garnered the most interest is the place of beta blockers in the management of high risk cardiac patients undergoing vascular surgery.18-20 The study of Poldermans et al raises the possibility of using beta blockers in patients undergoing vascular surgery with a reduction in CV complication rate equivalent to that of CABG. If this treatment regime is adopted it would certainly reduce the need for supplemental stress testing. Further, adding to the benefit of pharmacologic protection is the use of alpha-2 agonists.21 This class of drugs has been shown to be of benefit to patients with ischemic heart disease. 8. The use of endovascular techniques will further reduce peri-procedure morbidity. The introduction of endovascular stents, grafts via interventional radiology appears to have revolutionized the approach to the vascular patient. There appears to be both a short and long term benefit in terms of complication rate and cost.22 If data continues to show similar results this would also serve to reduce the number of patients requiring stress testing (e.g. reduce risk of procedure). In summary, these points taken together support the fundamental aim of the AHA Guidelines to avoid unnecessary testing. As such Supplemental Pre-operative Evaluation should be limited to those patients who are not candidates or do not respond to beta blocker therapy. A report by Grayburn and Hillis emphasize such an approach.23 However, until large scale randomized controlled trials are undertaken, we will not have definitive data to guide the clinician in management of this challenging group of patients. References
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