We're not actuaries, but we know that the best practices in anesthesia often require calculating risk. No matter how much number-crunching we do for the pre-operative cardiac evaluation, though, our final assessment will likely rest more with the art than with the science of our clinical trade. It comes down to recognizing the signs and symptoms that can compromise our patient's health and determining if the procedure's benefits are worth the risks.

Figuring out the factors
To define the potential for harm from a cardiac perspective when a patient undergoes anesthesia and surgery, we must examine many factors, including the risk of a dangerous arrhythmia, the likelihood of a perioperative myocardial infarction and the possibility of blood loss or other operative stressors such as hypotension or hypertension.

Begin by considering the type of procedure and the context of the surgery itself. Any patient over 40 is at least potentially at risk for undiagnosed coronary artery disease, but without further information it doesn't seem reasonable or cost-effective to order a stress thallium exam. But if a patient presents with a vague history of angina and is in poor compliance with prescribed nitrates and beta-blockers, you should seriously consider delaying the surgery until after he receives a formal cardiology evaluation.

For the data, consult the American College of Cardiology/American Heart Association Guidelines, which were updated in 2002. These put the combined incidence of non-fatal MI or cardiac death at greater than five percent in cases which are prolonged, involve high blood loss, peripheral vascular surgery, major vascular surgery or emergency surgery - not the sort of work we typically do on an outpatient basis. Likewise, the intermediate category of cardiac risk (roughly one to five percent of non-fatal MI or cardiac death) includes carotid endarterectomy, prostate surgery and intra-thoracic surgery, as well as such more traditional same-day cases as intra-peritoneal, head and neck, and orthopedic surgery.

Other outpatient procedures, such as cataract or endoscopic operations, are considered low risk (a less than one percent association with non-fatal MI or cardiac death). This group doesn't need cardiac evaluation beyond the routine H & P and labs.

Points in the patient history
If after reviewing the patient's medical record and taking an H & P you decide a cardiac evaluation is called for, here's how to quantify the patient's risk:

• a 12-lead EKG that's less than 30 days old, assuming no change in cardiac symptoms or unexplained change in exercise tolerance;
• any chart, history or EKG evidence of a prior myocardial infarction;
• co-morbid conditions such as peripheral vascular disease, renal disease, COPD, severe restrictive pulmonary disease or diabetes mellitus;
• poor exercise/activity tolerance, such as getting tired after climbing a flight of stairs or running a short distance;
• obesity or other mitigating history that may preclude an accurate assessment of exercise function/capacity;
• lab values indicating electrolyte abnormalities, anemia or creatinine > 2mg/dl;
• any chart- or patient-reported history ofangina pectoris or cardiac-suggestive chest pain;
• a history of heart failure or clinical evidence of current heart disease (distended neck veins)
• a history of orthostatic hypotension;
• evidence of new EKG-documented cardiac arrhythmias;
• evidence of a clinically symptomatic irregular heart rhythm; and
• the presence and history of any implanted pacemaker, cardioverter or defibrillator device.

Keep the type of surgery in mind when you weigh this information. Classify as high risk any procedure that involves the vascular system or has a propensity for excessive blood loss (including thoracic, abdominal and ENT procedures), especially if there is any suspicion of a compromised airway.

Picturing the layers of risk
Now that you have the data, it's time to put it all together. This algorithm from the American College of Cardiology can guide us through the "art" stage of assessing patients at risk:

• Assess how urgent the surgery is.
• Has the patient had coronary revascularization surgery or intervention in the past five years? If so, and if there are no changes in underlying function or clinical status, then there is no need for further work-up.
• Has the patient undergone a full cardiac assessment in the past two years? If so, and if there are no changes in underlying function or clinical status, then a repeat exam isn't necessary.
• Does the patient have any cardiac signs or symptoms that indicate a major risk, such as uncompensated heart failure, symptomatic arrhythmias, severe valvular disease, angina pectoris or a recent MI? If so, he warrants further work-up and possibly more treatment and management before undergoing elective surgery. This course of action is still prudent for cataract cases and other minor surgeries.
• Does the patient have signs or symptoms of intermediate risk cardiac disease? If so, minor surgeries with a low risk profile may still be acceptable. Some would argue for further non-invasive testing; others would make the case that further testing for a sedentary patient, who just wants to get his cataract fixed so he can watch television for the last two years of his expected lifespan, is unnecessary.
• Does the patient have a moderate cardiac functional capacity but intermediate risk factors and wants an intermediate-level surgical intervention? If so, most would argue in favor of proceeding with the case depending on the type of surgery, the surgical site and the types of anesthesia appropriate for this case. Patients with two or more intermediate risk predictors but less than moderate cardiac functional ability should be candidates for further, non-invasive, pre-operative cardiac testing.
• Low-risk procedures in patients with low cardiac risk factors and moderate or greater cardiac function should be acceptable in most cases. Again, poor cardiac function in the absence of physiologic or laboratory markers should spark interest in further testing before proceeding with surgery.

Risk-reward
There will always be the question of whether pre-procedure coronary intervention, and pre-procedure non-invasive testing, in patients with known CAD will exceed the risk of elective surgery. Weigh the answer against the potential for an improved duration and quality of life if successful revascularization is achieved.