ABSTRACT
Step 1: Timing of the operation: Emergency versus urgent or elective surgery. Since this is an elective operation there is time for preoperative cardiac evaluation and assessment of postoperative risk. Step 2: Does the patient have one or more of the active conditions listed in Table 30.1. He has a history of hypertension that has been well controlled with a calcium channel blocker. He denies a history of an MI, angina, nitroglycerine use, diabetes
mellitus, or renal dysfunction. Further questions reveal no symptoms of decompensated heart failure such as orthostatic or paroxysmal nocturnal dyspnea. His physical examination reveals no cardiac murmur and no S3 or rales. He has a palpable 6 cm AAA and palpable distal pulses without evidence of edema. His chest X-ray shows no evidence of pulmonary edema and his ECG shows no evidence of a block, bradycardia, supraventricular, or ventricular arrhythmia. Given his lack of an active condition the evaluation should proceed to Step 3. Step 3: Is the patient undergoing low-risk surgery? An open abdominal aneurysm repair is a vascular procedure with a reported cardiac risk of often more than 5% and would not be considered a low-risk surgery. Step 4: Does the patient have a good functional capacity? Functional capacity is measured with metabolic equivalence (MET), which is the oxygen consumption of a 70-kg person in a resting state. Excellent functional capacity is a patient who can perform exercises requiring more than 7 MET or perform activities such as swimming, tennis, or jogging. A good functional capacity (4 MET or greater) without symptoms would involve climbing a flight of stairs or walking on level ground at 4 mph. This patient can walk a block or two, do activities of daily living but he does not walk up stairs, play sports, or do heavy lifting. Thus his functional capacity is unknown or poor.(4, 5) Step 5: If the patient has poor functional capacity, is symptomatic, or has unknown functional capacity, then the presence of active clinical risk factors will determine the need for further evaluation. Given that this patient has poor or unknown functional capacity, further evaluation of risk factors including ischemic heart disease, compensated or prior heart failure, diabetes mellitus, renal insufficiency, and cerebrovascular disease needs to be performed. Laboratory studies reveal he has an elevated creatinine to 2.1 mg/dL and an elevated fasting glucose and HbA1c, consistent with chronic renal insufficiency and diabetes mellitus. Thus this patient now has two clinical risk factors. Given the combination of two risk factors and proposed vascular surgery, the guidelines recommend that he may undergo the planned surgery with heart rate control with a beta blocker or consider noninvasive testing if the latter will change management. In his case it may change management, causing one to consider different approach to his repair; thus, noninvasive testing should be considered. A final important note, if patients have three or more risk factors, the surgery-specific cardiac risk is important. Major vascular surgery represents the highest risk procedures and thus in this latter scenario, noninvasive testing should be considered.(6, 7)
what noninvasive cardiac evaluation should be performed? The patient should first have an ECG. If he does not have a left bundle branch block, left ventricular hypertrophy, pre-excitation syndrome, electronically paced ventricular rhythm, resting ST depression greater than 1 mm or digitalis effect on ECG and he can ambulate on a flat surface, an exercise ECG is chosen for
noninvasive testing. Therre (8), in a study of preoperative testing prior to AAA repair, reported 38 of 70 patients (54%) in whom ET was feasible and who were able to achieve the minimum HR; the specificity of ET was excellent (95.8%), and the sensitivity was 71.4% when compared to coronary angiography. However, these 38 patients accounted for only 42% of the patients in the series. The majority of patients were unable to complete an exercise ECG. Those who were unable to complete ET underwent dobutamine stress echocardiography with a sensitivity of 78%, specificity of 75.5%, and diagnostic accuracy of 100% when compared to coronary angiography. Pharmacological stress with vasodilators or adrenergic stimulation in conjunction with radionuclide or echocardiographic imaging has been shown in a meta-analysis of 68 studies to predict perioperative cardiac events in patients scheduled for noncardiac surgery who are unable to exercise. The cardiac risk by this evaluation is related to the extent of jeopardized viable myocardium identified by stress cardiac imaging.(9)
Resting LV function by echocardiography, radionuclide angiography, or contrast ventriculography has not been found to be a consistent predictor of perioperative ischemic events.(2)
Finally, if noninvasive test results are positive or non-diagnostic in a patient who is intermediate clinical risk and undergoing a high-risk noncardiac surgery is positive, the patient should undergo coronary angiography.(10)
should be considered for all patients at high risk for coronary events who are scheduled to undergo noncardiac surgery.(2, 10-13) Whenever possible, this treatment should be initiated prior to surgery to achieve effective beta blockade with a resting heart rate goal of 50-60 beats per minute and maintaining an intraoperative and postoperative heart rate of less than 80 beats per minute. The beta blocker should be continued several weeks postoperatively. However, the two randomized controlled trials leading to these recommendations have limitations that have led to controversy and reconsideration. The Poldermans (14) trial of 112 patients with positive results on dobutamine echocardiogram were started on oral bisoprolol at least 1 week before surgery and continued on oral bisoprolol or intravenous metoprolol for 30 days postoperatively. The trial was stopped after an interim analysis based on 20 outcome measures which demonstrated a relative risk reduction of 90% in the composite outcome of cardiac death and nonfatal MI. The relative risk reduction for nonfatal MI alone was 100%. Critics of the results of this study for global treatment recommendations point out that the study was not blinded, had unclear randomization strategies, selected a very high-risk population, and the study was stopped early.(15) The second trial, by Mangano (16), included 200 patients with known CAD or two minor risk factors for CAD. Patients were started an atenolol orally or intravenously 30 minutes before surgery and continued postoperative for 7 days. The overall mortality after discharge from the hospital was significantly lower among the atenolol-treated patients. However, the improvement in all cause mortality in this study was no longer statistically significant when patients who died while receiving the study drug were included in the intention to treat analysis. Two recent trials have not shown benefit from beta-blocker therapy (17, 18) but, due to a low number of patients and thus underpowered; these studies have been unable to determine the impact of beta blocker therapy on major cardiovascular outcomes. A recent meta-analysis of eight randomized studies reporting acute perioperative beta blockade, major perioperative cardiovascular outcomes and noncardiac surgery failed to confirm that heart rate control is cardioprotective.(15)
To add to the controversy, at the November 2007, American Heart Association Scientific Sessions, Devereaux et al.(19) presented the results of the PeriOperative Ischemic Evaluation (POISE) trial. The trial had enrolled 8,351 patients to determine the impact of the beta blocker metoprolol on the 30-day risk of major cardiovascular events in noncardiac surgery patients. Patients received an oral dose of 100 mg controlled-release metoprolol or placebo 2-4 h before surgery and between 0 and 6 h after surgery. Twelve hours following the first postoperative dose, patients started taking either daily doses of metoprolol or placebo at 200 mg and continued for 30 days after surgery or 15 mg of the drug or normal saline as a placebo intravenously every 6 h until patients were ready to switch back to oral doses. Like prior studies (17, 18), the POISE data showed that metoprolol was associated with an increased incidence of significant hypotension (15.0% vs. 9.7%; p < 0.0001) and significant bradycardia (6.6% vs. 2.4%; p < 0.0001). The primary end point was a composite of cardiovascular death, nonfatal MI, and nonfatal cardiac arrests at 30 days. A composite end point reduction was primarily due to a reduction in nonfatal MIs, with a hazard ratio of 0.7, equal to a 30% reduction in the risk of nonfatal MIs among those patients given beta-blockers
Table 30.1 Active Condition Which Should Prompt.
