· Despite numerous studies in the 1960s and 1970s, only 2 risk factors for pre-op cardiac morbidity were definitely identified:

1. recent MI

2. current CHF

· In the late 1970s and the 1980s, multivariable analyses identified combinations of factors (risk indexes) that could be used to estimate the risk of cardiac complications

· Most recently, some investigators have argued that routine clinical evaluation before surgery is neither sufficiently sensitive nor specific enough for risk assessment & have recommended the use of specialized testing

· Implications of these recommendations are substantial, for

· the tests are costly and

· ­ likelihood that other costly tests & treatments will be used

· unclear which, if any, subgroups of patients need such testing

Routine Clinical Data & Risk Indexes

· Studies of peri-op. cardiac risk can generally be divided into 2 groups (Table 1)

1. consecutive, unselected patients before major surgery

2. selected high risk patients with known cardiac/ vascular disease

· In group 1, risk of peri-op MI <2%

· In group 2 studies, risk is 2x the risks in group 1 studies

· In patients undergoing peripheral vascular/ aortic surgery, the combined risk of death due to cardiac causes can be as high as 29%

· Peri-op risk estimation using multifactorial indexes (Table 2)

· The original multifactorial index performed well in stratifying unselected, consecutive patients according to risk, but it has not performed as well in selected subgroups

· Probabilistic decision making: probability of a bad outcome depends on the prior probability of that outcome in the group as a whole; it is then modified by the additional information obtained from a risk score or diagnostic test

· Risk can also be estimated on the basis of a patient's functional status (class I to IV)

· Class I or II patients or those who can ­ their HR with exercise have a lower risk of complications

· Therefore,

1. Cardiac functional status

2. History of coronary heart disease

3. Multifactorial risk index score

Results of pre-op diagnostic tests and the score of multifactorial risk index should be interpreted in the context of patient's prior probability of complications

Specialized Testing

ECG

· Pre-op assessment using tests that ­ HR, e.g. exercise stress testing, is potentially appealing because:

· Peri-op ­ in myocardial O2 consumption are common,

· Peri-op myocardial ischaemia is often accompanied by tachycardia

Cutler et al. (1981) significant ­ in peri-op MI in patients who had ischaemic changes on exercise ECG at <75% max. predicted HR

McPhail et al. (1988) ­ in CVS complications in patients who had ischaemic ECG changes and impaired exercise tolerance (unable to achieve 85% of predicted HR)

Carliner et al. (1985) exercise ECG not a helpful predictor of peri-op complications, but exercise tolerance is more important

· Pre-op exercise testing should be reserved for patients who satisfy standard medical criteria for specialized testing:

· New, unexplained chest pain

· Current coronary disaese status is uncertain or poorly characterized on the basis of history alone

· 20-40% of patients with CAD or at high risk for such disease have frequent and often silent episodes of myocardial ischaemia during the 48 hrs before surgery , on pre-op ambulatory ECG

· Presence of silent ECG changes is a significant independent predictor of adverse outcomes in several studies

· Role of ambulatory ECG undefined

Echocardiography

· LV dysfunction, valvular heart disease, and previous MI are all predictors of peri-op cardiac morbidity

· No evidence that resting Echo. adds much to the information provided by clinical and ECG data

· Indications for Echo. same as for non-surgical patients

· Adverse outcomes assoc. with new/ ­ wall-motion abnormalities on Echo. inducible by exercise or pharmacologic agents (dipyridamole, dobutamine, dobutamine + atropine)

· Poldermans et al. (1995): 300 patients undergoing major vascular surgery, all post-op cardiac complications occurred in the patients with +ve stress echo. after dobutamine +/- atropine

· Patients with +ve results at lower HR ---> higher risk

Radionuclide Ventriculography

· In early studies, low EF (<35%) ---> ­ peri-op MI

· However, subsequent studies failed to confirm this relation

· In a study of 457 patients undergoing abdominal aortic surgery, low EF predicted post-op LVF only

· Thus, determination of EF not appear to provide added information for the prediction of peri-op MI

Thallium Scintigraphy

· Early studies showed that dipyridamole-thallium scan was sensitive (90-100%) and specific (50-80%) for peri-op. cardiac complications

· Subsequent studies showed that the specificity of the test could be improved by

· using it in patients at moderate risk

· measuring the amount of myocardium at risk

· However, in most studies:

1. physicians were not blinded

2. patients were referred for testing before surgery, rather than all consecutive patients scheduled for surgery

· Baron et al. (1994): in 457 consecutive, unselected patients -- thallium redistribution was not significantly assoc. with the incidence of peri-op MI or other adverse outcomes

· Thallium scan may be more cost effective if restricted to those:

1. who cannot exercise

2. whose risk status cannot be reasonably estimated on the basis of clinical factors alone

Pathophysiologic Limitations of Testing

· Peri-op MI can be ppt. by a number of different pathophysiologic mechanisms, including:

1. ­ myocardial O2 consumption

2. alterations in coagulation ppt. thrombosis

3. changes in vascular tone & endothelial function

4. intra-op. and post-op. ischaemia/ stress

· No single test can assess all these factors

A Recommended Approach

· Patients can be divided into subgroups according to (Table 4):

1. History of coronary disease

2. Cardiac functional status

3. Multifactorial indexes

· But no randomized trials or comparable outcome data

· Non invasive pre-op. testing should be reserved for cases in which the results will be critical for guiding therapy

· For high risk patients:

? intra-op. 12-lead ECG monitor

· Intra-op. monitoring of PAP or TEE for:

1. advanced HF

2. tight AS

3. unstable angina

4. recent MI

5. thoracic aortic aneurysm surgery

· For post-op. ischaemia:

· Continuous ECG monitoring is useful for detection

· usually asymptomatic

· predicts adverse cardiac outcome

· may precede a detectable clinical event

· at present, no recommendations can be made regarding the use of post-op. ECG monitoring

· Coronary Artery Surgery Study (CASS), 1986

· Cardiac mortality after non-cardiac surgery (in post-MI patients with mild angina or no symptoms)

· 0.4% for CABG

· 1.3% for medical therapy

· Risks & benefits for PTCA are similar to CABG

· In patients whose coronary disease warrant revascularization regardless of their non-cardiac condition, revascularization should precede any non-cardiac procedure if feasible

1. No pre-op. testing necessary 2. Non-invasive tests

Low risk High risk

Intensive Alternative surgical

monitoring procedures or need

coronary revascularization

· The primary challenge is to distinguish group 1. from group 2. patients

· Rational use of noninvasive tests depends on

1. ability of these tests to stratify risk

2. whether treatments guided by risk stratification lead to improved outcomes

· Relative merits of various peri-op. management strategies remain uncertain until randomized trials

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