Preoperative assessment of operative risk is defined as the probability of morbidity or mortality following an operation because of the patient’s presurgical condition, anesthesia, the surgical procedure itself, or the circumstances of the required postoperative convalescence. The decision to proceed with any operation must be made by weighing the potential risks against the anticipated benefits of the intervention compared with the ultimate outcome of the natural history of the underlying disease. Cardiac risk is particularly important on the risk side of the equation because myocardial ischemia, infarction, heart failure, and arrhythmias are important and common complications that may occur in thoracic surgery patients that can negate any benefit afforded by the operative procedure.

The greatest cardiac risk factor for a patient undergoing a thoracotomy is the presence of known CAD. The likelihood of a perioperative myocardial infarction is <0.5% in the patients without prior evidence of clinical heart disease. In patients with
a documented prior infarction, however, the incidence of reinfarction during a major noncardiac procedure is significantly higher, ranging from 3% to 20%, with a mean of approximately 6%. The mortality for clinically significant perioperative myocardial infarction is high and approaches 50% despite aggressive treatment.^1,3,5

The risk of perioperative infarction is inversely related to the time interval between the original myocardial infarction and the surgical procedure. This risk follows a curvilinear rather than a linear relationship. Major noncardiac surgical procedures performed within 3 months of an acute myocardial infarction have been associated with a high reinfarction rate of approximately 30%, whereas at 3 to 6 months after an infarction, the corresponding rate of reinfarction is approximately 14% and falls to 4% after 6 months.⁵ The institution of aggressive and comprehensive perioperative management guided by invasive hemodynamic monitoring has produced a decrease in reinfarction rates; however, when the postoperative period is complicated by an infarction, it is still associated with high mortality.⁹

A thorough cardiovascular history is vital in the preoperative evaluation of thoracic surgical patients, and the findings must then be correlated with physical findings and relatively simple testing. The factors associated with the cardiac risk in thoracic surgical patients are summarized in Table 40-1. The presence of any of the risk factors noted in Table 40-1 should arouse suspicion of significant cardiac disease, and should lead to a more comprehensive cardiac evaluation and raise the possibility of presurgical cardiac intervention.

Positive clinical cardiac findings must be correlated with electrocardiography (ECG) and echocardiography. The chronology and clinical course of prior myocardial infarction should be elucidated, and any evidence of left ventricular dysfunction as manifested by symptoms of congestive heart failure should be carefully sought. Attention also should be paid to the presence, severity, and pattern of angina pectoris and to the efficacy and appropriateness of the current medical regimen.

Interventional cardiology has added a dimension to the diagnosis and treatment of cardiac conditions that is important in the perioperative period. Patients who are at high risk for cardiac complications should be considered for stress testing before surgery. A patient with an early positive stress test should undergo further diagnostic testing and possibly intervention to correct cardiac problems (usually CAD) before elective thoracic surgery. The occasional patient may need angioplasty and stenting or even a coronary artery bypass before or in conjunction with thoracic surgery to reduce the probability of a postoperative cardiac event.³ Patients who have undergone noncardiac surgery after either coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA) and or stenting have a lower rate of cardiac events than patients with similar medical histories in whom coronary revascularization has not been performed.^22,23 Patients who have been stented in the past several months or with drug eluting stents (DESs) present unique problems. These patients are routinely managed with antiplatelet agents to prevent stent thrombosis.^10,21 These agents make the management of coagulation particularly difficult during surgery of any type. Cessation of antiplatelet drugs increases the risk of acute stent thrombosis. It is presumed that aggressive cardiologic evaluation and treatment before surgery will lower the operative risk in this group of high-risk patients.

Postoperative infarctions are significantly more lethal than infarctions in general, in part because the postoperative time frame is associated with an obligatory increased cardiac workload caused by the physiologic stress of the procedure.⁷ Patients with postoperative infarctions must “keep up” with the increased myocardial workload during the postoperative period, which may result in progressive infarction, heart failure, and death.

In addition, acute changes in coagulation associated with the systemic inflammatory response to surgery make patients hypercoagulable in the early postoperative period. Deep venous thrombosis, pulmonary embolus, and coronary thrombosis are potentiated by the hypercoagulable state, which partially explains the increased incidence of these problems in the postoperative period.

Perioperative myocardial infarction is notoriously hard to recognize. Classic symptoms of chest pain are difficult if not impossible to recognize in the setting of a chest incision. A high index of suspicion, frequent electrocardiograms, and serial cardiac enzymes in high risk patients are the best ways to identify perioperative myocardial infarction (Table 40-2).^{3,11,15,16,24} In patients who develop acute postoperative infarctions, aggressive interventional cardiology using PTCA and stents may be lifesaving. Lytic therapy is relatively contraindicated in most acute coronary artery emergencies that occur early after major surgery. Angiography and catheter-based interventions are the procedures of choice for postoperative myocardial infarction and unstable angina in these patients and should be used as soon as persistent ischemia is recognized. It is very difficult to “cool off” ischemia in postoperative patients with drugs alone.

Patients who are completely asymptomatic, have an active lifestyle, and have no significant risk factors for CAD, with a
normal electrocardiogram (ECG) regardless of age, do not need to undergo further cardiac testing. Patients with symptomatic heart disease or baseline ECG or echocardiographic abnormalities suggestive of cardiac disease need further assessment. If symptoms of ischemic heart disease are present, stress testing should be considered before a major intrathoracic surgical procedure is recommended, particularly if the patient has a history of myocardial infarction, demonstrates symptomatic left ventricular dysfunction, or has hypertension or diabetes mellitus.

A variety of stress test methods have been used to evaluate cardiac reserve. Each has its own characteristics and is particularly useful for certain types of patients. The underlying principle, however, is the same independent of methodology. Stress testing can determine the cardiac reserve in a controlled manner before the patient is subjected to the uncontrolled stress associated with surgery and the postoperative period. Stress testing is the most useful screening procedure for patients during the planning phase of thoracic surgery if they have historical signs and symptoms suggestive of ischemic cardiac disease.

Transthoracic echocardiography and transesophageal echocardiography, when indicated, are useful noninvasive modalities to assess overall ventricular function and detect any evidence of valvular pathology. Echocardiography is an excellent first-line screening examination in patients with any suggestive history or physical finding associated with CAD, heart failure, or valvular heart disease.

Nonexercise stress testing (such as a dobutamine echo stress test) can be used if a physical limitation to exercise exists. Cardiac catheterization and coronary arteriography should be considered when a patient is unable to exercise to an adequate workload required for stress testing. The demonstration of significant anatomic CAD (left main or three-vessel involvement), significant physiologic ischemia, or valvular disease during noninvasive and invasive testing requires consideration of revascularization or valve surgery in certain instances when severe dysfunction is present. Intervention is, however, relatively rare.

The preoperative cardiac evaluation of thoracic surgery patients requires making important and reasonable decisions in a responsible and cost-effective manner. Some authors suggest that all patients above a certain age undergo an extensive noninvasive or possibly even invasive evaluation to determine the presence of coexistent CAD. The intent is to electively revascularize those patients in whom significant disease is identified. This approach is gaining support because evidence is accumulating that prophylactic revascularization by any technique provides greater protection from ischemic events after surgery and is more successful than intensive medical therapy during the postsurgical period. However, the predictive accuracy of some of these strategies remains unclear.⁷