Advances in surgical techniques and improved patient outcomes have enabled the application of cardiac surgery in patient populations previously considered ineligible for an intervention of this magnitude. The decision to intervene surgically, as well as the type of intervention best suited to the patient, should be based on an individual risk-benefit analysis. The risks of the procedure, including major morbidities and short- and intermediate-term mortality, must be weighed against the expected benefits with respect to longevity, symptom relief, and improved functional capacity. This chapter reviews the essential information that the cardiologist and surgeon must collect and review to evaluate a patient for cardiac surgery (Table 10-1). This information includes patient and disease characteristics as well as surgical considerations that can be integrated into scoring systems that provide a semi-quantitative risk assessment. With the ever-evolving complexity of patients requiring specialized cardiovascular care, the refinement of surgical techniques, and the emergence of less invasive alternatives for high-risk patients, it has become apparent that there are important limitations to these scores in that they do not adequately account for procedure-specific impediments, major organ system compromise, and patient frailty. In addition, there has been recognition that risk assessment must occur in a framework of shared decision making that ensures that patients and their families have a thorough understanding of the relative risks and benefits of the various treatment options and, most importantly, that their wishes and preferences are respected in the therapeutic plan. There has been increasing recognition that a Heart Team approach that draws on the strength of multidisciplinary participation in decision making may be ideally suited to meet this challenge.

Patient Characteristics and Conditions

AGE

The volume of cardiac surgical procedures in the elderly continues to increase as life expectancy improves and the benefits of surgery outweigh the risks in appropriately selected individuals. While perioperative mortality rates do not vary significantly by age, mortality 1 year after surgery is generally higher in patients over 75 years of age, compared with those who are younger.¹ Octagenarians have nearly double the mortality rate compared with younger patients (4.1 vs 2.3%) and more than 60% of octogenarians have at least one nonfatal postoperative complication.^2,3 The most frequent complications include the need for prolonged ventilatory support in intensive care units, reoperation for bleeding and pneumonia—all resulting in longer hospital stays.³ A higher proportion of complications occur in elderly patients with low body weight ((body mass index) BMI < 23).⁴ With improved surgical techniques and careful patient selection, nonagenarians can safely undergo cardiac surgery with a 95% 30-day survival and 93% survival to hospital discharge.^5-7

GENDER

Some but not all epidemiologic studies suggest that female gender is an independent predictor of postoperative morbidity and mortality.^8–10 Gender differences are present in both traditional coronary artery bypass graft (CABG) and off-pump surgery.¹¹ Several large retrospective cohort studies of patients undergoing CABG found that women had higher mortality rates than men even after adjusting for comorbidities and confounding factors, including body surface area.^8,9 Possible explanations for worse outcomes in women include smaller coronary arteries (which might enhance the technical difficulty of performing anastomoses and limit graft flow), differences in referral for surgery (ie, women being referred at later disease stages), and gender differences in self-reported outcomes.¹² Data suggest that benefit in terms of QOL after cardiac surgery is similar for men and women.¹³

RACE

Although crude post-CABG mortality rates differ significantly by race, data suggest that after controlling for patient and hospital variables, these differences are small.^14,15 However, in the United States, self-reported black race is associated with an increased risk of postoperative complications, including prolonged ventilatory support, length of stay, reoperation for bleeding, and postoperative renal failure.¹⁶

DIABETES

Patients with diabetes have significantly worse outcomes following cardiac surgery.^17–19 Studies have shown diabetes to be an independent predictor of in-hospital mortality after CABG although emerging evidence indicates that the severity of diabetes, specifically target organ damage, may be important in risk stratification.^20,21 Postoperative mortality does not differ significantly between nondiabetic and diabetic patients without diabetic sequelae, though diabetic patients with vascular disease and/or renal failure have an increased risk of mortality.²¹ Patients with insulin-dependent type II diabetes in particular are at increased risk of major postoperative complications including renal failure, deep sternal wound infection, and prolonged hospital stay.^22,23 Strict perioperative glucose control has been shown to lower operative mortality and the incidence of mediastinits.^24,25 Off-pump surgery also appears to decrease postoperative morbidity in diabetic patients.²⁶

RENAL FUNCTION

Renal dysfunction is common in patients undergoing cardiac surgery. Approximately half of patients undergoing CABG have at least mild renal dysfunction and one quarter have at least moderate renal dysfunction.²⁷ There is a graded increase in operative mortality and morbidity with worsening preoperative renal function.^27–29 Renal insufficiency is associated with greater risk of both 30-day (odds ratio, OR = 3.7) and 1-year mortality (OR = 4.6).³⁰ Even mild renal dysfunction (serum creatinine 1.47–2.25 mg/dL) is associated with increased rates of operative and long-term mortality, need for postoperative dialysis, and postoperative stroke.³¹

Renoprotective drugs, such as fenoldopam and N-acetylcysteine, have no effect on the deterioration of renal function in high-risk patients.^32,33 Off-pump CABG (OP CABG) is associated with a lower prevalence of the need for postoperative renal replacement therapy; larger studies are needed to determine if this correlates with improved outcomes.³⁴

PULMONARY FUNCTION

It is well established that patients with compromised pulmonary function, predominantly due to chronic obstructive pulmonary disease (COPD), have a higher mortality and increased incidence of postoperative complications including arrhythmias, reintubation, pneumonia, prolonged intensive care unit (ICU) length of stay (LOS), and increased LOS.^35,36 Postoperative respiratory failure is a common complication (14.8% in a New York State database) with a higher incidence (14.8%) in combined CABG and valve operations.³⁷ Optimizing respiratory status prior to surgery, including smoking cessation, antibiotics for pneumonia, and treatment of COPD flares with bronchodilator therapy and steroids is a critical part of preoperative management.³⁸ There is evidence that intensive inspiratory muscle training prevents postoperative pulmonary complications in high-risk patients.³⁹

Surgical Considerations

REOPERATION

Hospital mortality among patients undergoing reoperative cardiac surgery has traditionally been higher than among patients undergoing primary operation.^40–42 This is likely due to the higher-risk profile of patients undergoing reoperation (older, more extensive vascular and coronary disease, multiple comorbidities) and the demanding surgical aspects including sternal reentry, pericardial adhesions, in situ arterial grafts and diseased saphenous vein grafts.⁴³

Despite these factors, hospital mortality rates associated with coronary reoperation have decreased with greater surgical experience and now approach those observed with primary CABG.^43,44 With careful preoperative risk evaluation and surgical management, reoperation can be performed safely.

PRIOR RADIATION

Patients receiving thoracic radiation for treatment of malignancies before cardiac surgery have poorer short- and long-term outcomes.^45,46 Thoracic radiation exposure is heterogeneous with respect to different malignancies and there is a gradient of risk.

A study dividing patients undergoing cardiac surgery into three levels of radiation exposure: extensive (Hodgkin’s disease, thymoma, and testicular cancer), variable (non-Hodgkin’s lymphoma and lung cancer), and tangential (breast cancer), demonstrated that patients with extensive radiation exposure had longer radiation-to-operation interval, poorer pulmonary function, and more severe aortic regurgitation, diastolic dysfunction and left main coronary stenosis.⁴⁷ Hospital deaths (13% vs 8.6% vs 2.4%) and respiratory complications (24% vs 20% vs 9.6%) were higher after more extensive radiation and 4-year survival was poorer (64% vs 57% vs 80%).

SURGICAL COMPLEXITY AND TECHNIQUE

It is important to consider the type of cardiac surgical procedure (CABG, valve, or combined) as well as the surgical technique (on-pump, off-pump, minimally invasive, robotic, and hybrid) when providing preoperative risk assessment as mortality and morbidity risks may vary.

Valve surgeries generally have a higher complication rate than isolated CABG, and combined surgeries have the highest risk (Fig. 10-1). Participants in the Society of Thoracic Surgeons National Adult Cardiac Surgery Database collected data between 2002 and 2006 on more than 3.6 million procedures.^48–50 They reported 30-day mortality and a composite end point of mortality and major in-hospital morbidity including stroke, renal failure, prolonged ventilation, deep sternal wound infection, and reoperation. CABG mortality was 2.3% with a 14.4% rate for the combined end point of mortality and major morbidity.⁴⁸ Isolated valve procedures had higher mortality rates, including 3.2% for aortic valve replacement (AVR), 5.7% for mitral valve replacement (MVR), and 1.6% for mitral valve repair (MVP).⁴⁹ Combined mortality and major morbidity was also higher for valve surgery at 18.3% (AVR 17.4%, MVR 26.7%, MVP 12.7%). Combined CABG and valve procedures had the highest mortality rate at 6.8% (AVR + CABG 5.6%, MVR + CABG 11.6%, and MVP + CABG 7.4%) with a combined mortality and major morbidity of 30.1% (AVR + CABG 26.3%, MVR + CABG 43.2%, and MVP + CABG 33.5%).⁵⁰

Minimally invasive surgical techniques can be divided by approach and use of cardiopulmonary bypass (CBP). The use of alternatives to standard median sternotomy has been increasingly adopted in surgical centers for performance of both CABG and valve procedures. The potential benefits of minimally invasive surgery are earlier extubation, reduced discomfort, lower rates of wound infection, less blood loss, and shorter recovery times.⁵¹

Off-pump CABG is performed with stabilization devices to reduce motion of target vessels while anastomoses are performed without CBP. Current surgical approaches to valve surgery require CBP and cardioplegic arrest. Meta-analyses of observational and randomized trials of OP CABG versus on-pump CABG have not demonstrated a clear advantage of OP CABG with respect to mortality or morbidity.^52,53 Postoperative complications with OP CABG generally show consistent reductions in postoperative AF, blood loss, wound infections and myocardial injury with nonsignificant trends toward lower death, myocardial infarction (MI) and stroke.^53–55 The benefits of OP CABG are particularly notable in the elderly and in patients with heavily calcified aortas.⁵⁴

There have been continued advances in optics, instrumentation and perfusion technology that have facilitated use of totally endoscopic robotic cardiac surgery.⁵⁶ This technology has been applied to many cardiac surgical procedures, in particular MVP and totally endoscopic coronary artery bypass grafting (TECAB). Short-term results are promising in some series but long-term studies are lacking and a steep learning curve characterizes the early phase of application.

Simultaneous “hybrid” percutaneous coronary intervention with drug-eluting stents and minimally invasive surgical bypass grafting procedures in a specially designed operating suite (hybrid OR) are also gaining more widespread acceptance. Hybrid procedures require close cooperation between surgical and interventional teams. Although there are limited data available, hybrid patients have similar angiographic vessel patency and major adverse cardiac events (MACE) at six months with shorter hospital lengths of stay, intubation times and less blood loss despite aggressive antiplatelet therapy.⁵⁷

Preoperative risk assessment has important implications not only for individual patient well-being but as a qualitative tool to serve as a reference standard to compare outcomes among surgeons, institutions, or assessment of new procedures and techniques. There are numerous risk stratification scores and systems that have been developed from large databases to quantity the mortality and morbidity risks of cardiac surgery. Both patient and surgical factors are considered preoperatively and assessed for their ability to predict postoperative complications. This section will focus on two of the most widely used risk scoring systems: European System for Cardiac Operative Risk Evaluation (EuroSCORE) and Society for Thoracic Surgeons (STS) risk estimate (Table 10-2).

The European System for Cardiac Operative Risk Evaluation (EuroSCORE)

The EuroSCORE, initially published in 1999, is the most rigorously evaluated scoring system in cardiac surgery.⁵⁸ The score is calculated by assessing 17 risk factors (patient, cardiac, and operation) known to affect outcome. There are two available methods: the original additive model and the more recent logistic model.^59,60 Studies have indicated that the additive model overestimates mortality in low-risk patients and underestimates mortality in high-risk patients.^60–62 The logistic model was designed to address these issues but there is still concern that this model overestimates mortality in many risk groups.⁶⁰ The logistic EuroSCORE is more accurate at predicting mortality in combined CABG and valve surgery.⁶³ The EuroSCORE calculator is available online (www.euroscore.org).