Tools for rapid preoperative cardiovascular risk assessment

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Commentary

Tools for rapid preoperative cardiovascular risk assessment

J Fam Pract. 2003 April;52(4):313-320

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References

1. Eagle KA, Berger PB, Calkins H, et al. ACC/AHA guideline update for perioperative cardiovascular evaluation for noncardiac surgery—executive summary: a report of the American College of Cardiology/American Heart Association Task Force onPractice Guidelines (Committee to Update the 1996 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery). J Am Coll Cardiol 2002;39:542-53.

2. Guidelines for assessing and managing the perioperative risk from coronary artery disease associated with major noncardiac surgery-American College of Physicians. Ann Intern Med 1997;127:309-12.Also available at: http://www.acponline.org/journals/annals/15aug97/ppcad1.htm.

3. Detsky AS, Abrams HB, Forbath N, Scott JG, Hilliard JR. Cardiac assessment for patients undergoing noncardiac surgery. A multifactorial clinical risk index. Arch Intern Med 1986;146:2131-4.

4. Mangano DT, Goldman L. Preoperative assessment of patients with known or suspected coronary disease. N Engl J Med 1995;333:1750-6.

5. Lee TH, Marcantonio ER, Mangione CM, et al. Derivation and prospective validation of a simple index for prediction of cardiac risk of major noncardiac surgery. Circulation 1999;100:1043-9.

6. Detsky AS, Abrams HB, McLaughlin JR, et al. Predicting cardiac complications in patients undergoing non-cardiac surgery. J Gen Intern Med 1986;1:211-9.

7. Steyerberg EW, Kievit J, de Mol Van Otterloo JC, van Bockel JH, Eijkemans MJ, Habbema JD. Perioperative mortality of elective abdominal aortic aneurysm surgery. A clinical prediction rule based on literature and individual patient data. Arch Intern Med 1995;155:1998-2004.

8. L’Italien GJ, Paul SD, Hendel RC, et al. Development and validation of a Bayesian model for perioperative cardiac risk assessment in a cohort of 1,081 vascular surgical candidates. J Am Coll Cardiol 1996;27:779-86.

9. Goldman L, Caldera DL, Nussbaum SR, et al. Multifactorial index of cardiac risk in noncardiac surgical procedures. N Engl J Med 1977;297:845-50.

10. Wasson JH, Sox HC, Neff RK, Goldman L. Clinical prediction rules. Applications and methodological standards. N Engl J Med 1985;313:793-9.

11. Romero L, de Virgilio C. Preoperative cardiac risk assessment: an updated approach. Arch Surg 2001;136:1370-6.

12. Hollenberg SM. Preoperative cardiac risk assessment. Chest 1999;115(suppl):51S-57S.

13. Paul SD, Eagle KA. A stepwise strategy for coronary risk assessment for noncardiac surgery. Med Clin North Am 1995;79:1241-62.

However, at break points in the classification system, marked changes in risk occur with a 1-point differential in score. For example, for major noncardiac surgery, no difference in risk is reported between 6 and 12 points (4%) and no difference between 13 and 25 points (12%), but risk triples from 4% to 12% by adding 1 point from 12 to 13 points.

MedRules’ third algorithm, Lee’s Simple Cardiac Risk Score,⁵ fits on 2 screens. The maximum Lee score is 6 points. However, 1 point yields a risk of about 1%, whereas “class IV” is 3 or more points, for which the risk according to Lee et al⁵ is 9.1% in the derivation set and 11.0% in the validation set. For 3 or more points, MedRules’ calculator indicates “at high risk, >10% risk of major cardiac complications.” At 2 points, the risk is estimated at 7%, regardless of which factors are selected. With either 0 or 1 point, the Lee calculator returns a “<1% risk of major cardiac complications,” even if that risk is abdominal aortic aneurysm repair or a positive exercise stress test.

Obviously, with a 6-point scale and essentially 3 risk categories (in MedRules’ implementation, <1%, 7%, >10%), the Lee algorithm is extremely insensitive to small changes in risk.

FIGURE 2
MedRules’ Detsky calculator

InfoRetriever

The 3 preoperative risk assessment tools on InfoRetriever (version 4.2 for Palm OS, 2002) comprise a tiny piece of this large (by palmtop standards) 2088K (2.1MB) collection of 90 clinical decision rules and other clinical tools. InfoRetriever’s opening screen offers a choice among “Clinical decision rules,” “Diagnostic tests,” and “History and physical.” After choosing “Clinical decision rules,” the user taps to invoke a drop-down menu, and then selects “CV–pre-op eval.” At this point, choices for 3 decision rules appear: “AAA surgery” (Steyerberg), “Non-vascular surgery” (Detsky), and “Vascular surgery” (L’Italien).

The major difference between InfoRetriever’s and MedRules’ Detsky calculators is that InfoRetriever divides surgery into major or minor procedures. The 2 algorithms also differ in asking whether unstable angina has been present in the past 3 months (MedRules) or past 6 months (InfoRetriever). Interestingly, Detsky’s 2 publications about his 1 study also differ in this regard.^3,6 InfoRetriever defines angina class, eg, “class III: symptoms w/ level walking of 1 to 2 blocks or climbing ≥1 flight stairs,” whereas MedRules does not. Both of Detsky’s publications allow users to choose any desired pretest probability (overall operation-specific surgical risk) and, from a nomogram that includes the Detsky score, find the corresponding posttest probability (patient’s specific calculated risk).

Neither InfoRetriever’s nor MedRules’ Detsky calculators allow user input of pretest probability. InfoRetriever uses 2 stated, predetermined pretest probabilities (eg, 5% and 10%) and generates 2 corresponding, patient-specific posttest probabilities. MedRules uses a single, unstated pretest probability. Therefore, although both programs accurately calculate Detsky point totals, we conclude that neither completely reproduces the originally published material.

Comparing results between InfoRetriever’s and MedRules’ Detsky calculators, entering the same data for a patient whose MedRules’ Detsky result is 25/100 points, or a 20% risk of major cardiac complications, into InfoRetriever’s Detsky calculator results in “Moderate risk (II): Peri-operative risk of MI, CHF, or death is 15.9% given a pretest risk of 5%; 28.5% given a pretest risk of 10%.” Entering a higher-risk patient, MedRules’ Detsky calculates 40/100 points, and a “100% risk of major cardiac complications,” whereas InfoRetriever’s Detsky calculation produces “44% given a pretest risk of 5%, 62.3% given a pretest risk of 10%.” In contrast to MedRules, for this (and its other indices), InfoRetriever’s information screens discuss the patient population, provide a “quality score” (but no explanation of it) for the index’s referenced study, and specify the number of patients in the study. However, we believe this information is inadequate to guide clinicians in using the indices.

InfoRetriever’s vascular surgery risk index includes risk stratification based on whether a dipyridamole-thallium stress test was performed and, if so, whether a fixed defect, reversible defect, ≥1 mm ST segment depression, or any combination of these findings, was identified.⁸ The calculator requires the “complication rate at your institution (%),” without providing additional assistance. From the article by L’Italien et al,⁸ the reader can infer that the “average risk of a major perioperative cardiac event among vascular surgery candidates” would be acceptable as the input for the complication rate. However, the pretest probability for the specific type of vascular surgery (eg, carotid, infrainguinal) would be preferable (Table 2). Study end points were cardiac death, fatal and nonfatal MI, but not pulmonary edema caused by cardiac ischemia.