Preoperative Assessment

The purpose of preoperative evaluation for cardiac risk is to answer the question "Can this patient safely undergo major non-cardiac surgery?" 1 Operative risk is a function of the balance between the ability of the patient’s heart to pump blood (cardiopulmonary fitness or functional capacity) during time of need (patient-specific risk) and the amount of cardiac output demanded by the procedure (surgery-specific risk).  These components must be addressed independently.  The inability to pump adequate blood volume to meet the body's needs during a surgical procedure will result in hemodynamic compromise with subsequent cardiovascular and non-cardiovascular complications.

Cardiac output is a function of stroke volume and heart rate.  Cardiac disease states that compromise stroke volume and HR response will impair the heart's ability to deliver adequate blood supply to the peripheral tissues during the times of highest demand.  Cardiac output can be impaired by ischemic as well as non-ischemic etiologies and multiple etiologies can work synergistically to impair cardiac output response under duress (e.g., diastolic dysfunction + valve disease + microvascular ischemia).  All too often, the preoperative cardiac evaluation process attempts to answer “does the patient have coronary artery disease”.  A series of tests designed to assess the state of the coronary arteries will miss an underlying impaired cardiac output response with exertion, if it exists.  Assessment of global cardiac output provides the most precise method to assess cardiac risk.  There is good evidence that patients with coronary artery disease without heart failure are at no higher risk for postoperative cardiac events than the general population2.  If one does find abnormalities in the state of the coronaries, there is little to no evidence to suggest that procedures on the coronary vasculature improve the outcome of major non-cardiac surgery 3, 4.  Therefore, current ACC-AHA guidelines do not recommend prophylactic revascularization in patients with stable CAD that are undergoing high risk surgery.

According to the executive summary issued by the ACC-AHA task force on preoperative cardiac risk assessment 5, the purpose of exercise stress testing is two-fold:

    Quantify functional capacity
    Indentify inducible ischemia

Measurement of oxygen uptake at peak exercise (peak VO2) is recognized gold standard for quantifying exercise/functional capacity. Estimates of functional capacity have been demonstrated not to be objective or accurate in patients with heart disease. Monitoring of stroke volume, HR response and cardiac output as a function of work rate on a breath-by-breath basis has been demonstrated to be effective in identifying onset of LV dysfunction from ischemia in late exercise 6, 7. Myocardial ischemia is only important if the ischemia limits LV function and cardiac output. Thus, a good quality CPET study will quantify peak cardiac output (functional capacity) as well as identify physiologically significant ischemia in late exercise. Identifying the rate-pressure product at the ischemic threshold (RPP@IT) provides important clinical insight to the anesthesiologist to proactively avoid myocardial ischemia during surgery (intervene with intravenous anti-ischemic agents). This will avoid myocardial stunning and infarction during the procedure which in turn will reduce post-operative complications.

There is a false belief that ejection fraction calculated by transthoracic echocardiography (echo) or radionuclide ventriculography (MUGA) studies assess functional capacity. There is a poor correlation (non-linear relationship) between ejection fraction and functional capacity. Routine use of echocardiogram is not supported for preoperative assessment 8. Froelicher showed a poor correlation between ejection fraction on MUGA scans and maximal oxygen uptake in patients with coronary artery disease not limited by angina 9, 10.

Dobutamine stress echocardiography (DSE) is not suitable for preoperative assessment because it does not quantify functional capacity and the functional significance of wall motion abnormalities to impair stroke volume and cardiac output response cannot be assessed. Myocardial perfusion imaging (MPI - nuclear stress testing) has also been shown not to be effective in assessing cardiac risk prior to major surgery 11, 12. DSE and MPI studies can be helpful to predict perioperative cardiovascular events in patients not capable of exercising. This information may not necessarily change management.

Estimating functional capacity on treadmill testing (TMST) is unreliable as the accuracy of the methodology is very poor in cardiac patients 13, 14.

Peak VO2 quantifies peak cardiac output. The anaerobic threshold (AT) is an effort independent measure of peak cardiac output and has been demonstrated to be effective in risk stratifying patients prior to major surgery. This data is in turn used to improve peri-operative management to reduce unnecessary costs in the healthier patients and decrease morbidity and mortality in the sicker patients.

Outcomes Data (15-18)

For high risk surgeries, the anaerobic threshold (AT) provides an objective, effort independent measure of cardiopulmonary fitness:

    1. AT > 11 ml/kg/min good cardiopulmonary functional reserve and high postoperative survival [LOW].

    2. AT 8.1 - 10.9 ml/kg/min without inducible ischemia [INTERMEDIATE].

    3. AT < 11 ml/kg/min with inducible ischemia very high postoperative mortality [HIGH].

    4. AT < 8 ml/kg/min poor peak cardiac output/CV reserve and high postoperative mortality [HIGH]

Not all ischemia has the same significance and a low AT combined with ischemia has a high mortality risk.

For low and intermediate risk surgeries, the cardiac risk is proportionally less depending on the degree of cardiac reserve demanded by the procedure.

Perioperative Management

    1. [LOW RISK] patients can go straight to the floor after surgery to optimize resource utilization and save money.

     

    2. [INTERMEDIATE RISK] patients should get optimization of risk factors and medical therapy (peri-operative beta blockers, statins and aspirin) 19 based upon the nature of the procedure.

    3. [HIGH RISK] patients require more aggressive monitoring and treatment to minimize morbidity and mortality.  They typically get admitted to the ICU for placement of a pulmonary catheter to optimize fluid status throughout surgery.  A low threshold should be maintained for ionotropic support and pacing.  Medical therapy should be optimized (peri-operative beta blockers, statins and aspirin) 19.  Intravenous anti-ischemic agents (afterload reducers, beta-blockers, nitroglycerin, calcium channel blockers) should be administered if the rate-pressure product at the ischemic threshold is encroached during the procedure.

The London Clinic has been utilizing CPET technology for peri-operative management with excellent success (view flyer). In comparing the first 50 patients screened and managed with this approach vs. 223 patients that were not during the same period, the 50 screened patients had no readmissions and no cardiovascular complications. In the non-screened group, 12% were readmitted to the ICU, almost all with cardiovascular complications and organ failure requiring 87 days of prolonged ICU care with 5% mortality.

In Conclusion

CPET evaluates cardiac and respiratory function and detects physiologically significant myocardial ischemia in a single, non-invasive, cost-effective test and accurately identifies patients at high risk for complications, morbidity and mortality after major surgery.

Case Study

Anaesthesia - Journal of the Association of Anaesthetists of Great Britain and Ireland. 2009. (view Case Study)

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3. Poldermans D, Schouten O, Vidakovic R, Bax JJ, Thomson IR, Hoeks SE, Feringa HH, Dunkelgrun M, de Jaegere P, Maat A, et al. A clinical randomized trial to evaluate the safety of a noninvasive approach in high-risk patients undergoing major vascular surgery: the DECREASE-V Pilot Study. J Am Coll Cardiol 2007;49:1763-1769.

4. McFalls EO, Ward HB, Moritz TE, Goldman S, Krupski WC, Littooy F, Pierpont G, Santilli S, Rapp J, Hattler B, et al. Coronary-artery revascularization before elective major vascular surgery. N Engl J Med 2004;351:2795-2804.

5. Eagle KA, et al. ACC/AHA Guideline Update for Perioperative Cardiovascular Evaluation for Noncardiac Surgery-Executive Summary. J Am Coll Cardiol 2002; 39:542-53.

6. Chaudhry S, Ross A, Wasserman K, Hansen JE, Lewis GD, Myers J, Chronos N, Boden WE. Exercise-induced myocardial ischemia detected by cardiopulmonary exercise testing. Am J Cardiol 2009; 103:615-619.

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9. Froelicher V: Interpretation of specific exercise test responses. In Exercise and the Heart, 2nd edition. Edited by Froelicher V. Chicago, IL: Year Book Medical Publishers; 1987:83-145.

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11. Mangano DT, London MJ, Tubau JF, Browner WS, Hollenberg M, Krupski W, Layug EL, Massie B: Dipyridamole thallium-201 scintigraphy as a preoperative screening test. A reexamination of its predictive potential. Study of Perioperative Ischemia Research Group. Circulation 1991, 84:493-502.

12. Baron JF, Mundler O, Bertrand M, Vicaut E, Barre E, Godet G, Samama CM, Coriat P, Kieffer E, Viars P: Dipyridamole-thallium scintigraphy and gated radionuclide angiography to assess cardiac risk before abdominal aortic surgery. N Engl J Med 1994, 330:663-669.

13. Milani R, Lavie C, Spiva H. Limitations of estimating metabolic equivalents in exercise assessment in patients with coronary artery disease. Am J Cardiol 1995;75(14); 940-942.

14. Arena R, Myers J et al. Assessement of functional capacity in clinical and research settings. A scientific statement from the AHA committee on exercise, rehabilitation and prevention of the Council on Clinical Cardiology and the Council on Cardiovascular Nursing. Circulation. 2007; 116.

15. Wilson R, Davies S, Yates D, Redman J, Stone M. Impaired functional capacity is associated with all-cause mortality after major elective intra-abdominal surgery. Br J Anaesth 2010; 105 (3):297-303.

16. Snowden CP et al. Submaximal Cardiopulmonary Exercise Testing Predicts Complications and Hospital Length of Stay in Patients Undergoing Major Elective Surgery. Ann Surg 2010;251: 535–541.

17. Older P, Smith R, Courtney P, Hone R: Preoperative evaluation of cardiac failure and ischemia in elderly patients by cardiopulmonary exercise testing. Chest 1993, 104:701-704.

18. Older P, Hall A, Hader R: Cardiopulmonary exercise testing as a screening test for perioperative management of major surgery in the elderly. Chest 1999, 116:355-362.

19. Poldermans D, Hoeks SE, Feringa HH. Pre-operative risk assessment and risk reduction before surgery. J Am Coll Cardiol 2008 May 20;51(20):1913-24.

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