Patient Characteristics and Conditions
The volume of cardiac surgical procedures in elderly people continues to increase as life expectancy improves and benefits outweigh risks. Although perioperative mortality does not vary significantly by age, 1-year mortality is greater in patients greater than 75 years of age.3 Octogenarians have nearly double the mortality rate compared with younger patients (4.1 versus 2.3%) and more than 60% have at least one nonfatal postoperative complication.4,5 The most prevalent complications include prolonged ventilation in intensive care units, reoperation for bleeding, and pneumonia—all of which result in longer hospital stays.5 A higher proportion of complications occur in elderly patients with low body weight (BMI <23).6 There is evidence that off-pump (OP) surgery using only arterial conduits may confer a survival benefit and improve long-term quality of life.7,8 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.9
Some but not all epidemiologic studies suggest that female gender is an independent predictor of postoperative morbidity and mortality.10–12 Gender differences are present in both traditional CABG and off-pump surgery.13 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 BSA.10,11 Possible explanations for worse outcomes in women include smaller coronary arteries (which might enhance the 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.14 Data suggest that benefit in terms of quality of life after cardiac surgery is similar for men and women.15
Although crude post-CABG mortality rates differ significantly by race, data suggest that after controlling for patient and hospital variables, these differences are small.16,17 However, in the United States, self-described 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.18
Patients with diabetes have significantly worse outcomes following cardiac surgery.19–21 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.22,23 Postoperative mortality does not differ significantly between nondiabetic and diabetic patients without diabetic sequelae, although diabetic patients with vascular disease and/or renal failure have an increased risk of mortality.23 Insulin-dependent type II diabetics in particular are at increased risk of major postoperative complications including renal failure, deep sternal wound infection, and prolonged hospital stay.24,25 Strict perioperative glucose control has been shown to lower operative mortality and the incidence of mediastinits.26,27 Off-pump surgery also appears to decrease postoperative morbidity in diabetic patients.28
Renal dysfunction is common in patients undergoing cardiac surgery. Approximately half of patients undergoing CABG have at least mild renal dysfunction and one-fourth have at least moderate renal dysfunction.29 There is a graded increase in operative mortality and morbidity with worsening preoperative renal function.29–31 Renal insufficiency is associated with greater risk of both 30-day (OR = 3.7) and 1-year mortality (OR = 4.6).32 Even mild renal dysfunction (serum creatinine 1.47 to 2.25 mg/dL) is associated with increased rates of operative and long-term mortality, need for postoperative dialysis, and postoperative stroke.33
Renoprotective drugs, such as fenoldopam and N-acetylcysteine, have no effect on the deterioration of renal function in high-risk patients.34,35 Off-pump 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.36
It is well established that patients with compromised pulmonary function, predominantly owing to chronic obstructive pulmonary disease (COPD), have a higher mortality and increased incidence of postoperative complications including arrhythmias, reintubation, pneumonia, prolonged ICU duration, and increased hospital length of stay.37,38 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.39 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.40 There is evidence that intensive inspiratory muscle training prevents postoperative pulmonary complications in high-risk patients.41
The most important hematologic consideration in patients undergoing cardiac surgery is heparin-induced thrombocytopenia type II (HIT). HIT is an immune-mediated, potentially life-threatening thrombotic condition characterized by the formation of antibodies against the heparin-platelet factor 4 (PF4) complex.42 A diagnosis of HIT should be suspected in patients begun on heparin therapy within the preceding 5 to 10 days who have unexplained thrombocytopenia, venous or arterial thrombosis, or a platelet count that has fallen 50% or more from baseline even if absolute thrombocytopenia is not present.42 HIT can occur earlier in patients recently exposed to heparin. HIT can also be caused by exposure to low molecular weight heparin (LMWH), but the incidence is much lower.43 Although the prevalence of HIT antibodies is relatively common preoperatively (4.3%) and postoperatively (22.4%), the occurrence of thrombotic events occurs only in a minority of patients (6.3%) who have a positive antibody.42 CABG patients with HIT have a dramatically increased risk of vein graft occlusion (68% versus 20%); however, they do not appear to have an increased rate of internal mammary graft occlusion.44
There is emerging consensus regarding anticoagulant management of patients with HIT.42 Repeat heparin exposure during CBP is an option for patients with a previous history of HIT if repeat antibody testing is negative on two consecutive daily samples, although it is prudent to use alternative antithrombotic agents for preoperative and postoperative anticoagulation. Patients with prior HIT and detectable antibodies are at higher risk with reexposure and should only be administered heparin if platelet activation assays (ie, serotonin release assay) are negative. For patients with acute HIT, it is recommended to delay surgery if possible. If surgery must proceed, bivalirudin is an alternative, although attention must be given to its several unique pharmacologic properties.42
It is difficult to manage the competing risks of thrombosis and bleeding in patients with hypercoagulable disorders. Aggressive prophylaxis with unfractionated heparin or LMWH is indicated for patients not on chronic anticoagulation.45,46 Special considerations should be given to patients with antiphospholipid syndrome owing to their high risk of thrombotic events and the difficulty in interpreting coagulation parameters.47,48
Preexisting AF in patients undergoing CABG is not associated with increased in-hospital mortality or major morbidity but is a risk factor for reduced 5-year survival.49 However, postoperative AF (POAF) is associated with increased in-hospital and long-term mortality, stroke, hemodynamic compromise, renal failure, longer length of stay, and greater hospitalization costs.50,51 AF is common after cardiac surgery, occurring in up to 40% of CABG patients, 50% of patients undergoing valve surgery and as many of 60% of patients after combined CABG and valve operation.50,52–54 The pathophysiology of postoperative AF is likely related to the age-related degenerative changes in the atrial myocardium coupled with inflammation, bleeding into the pericardial space, and perioperative electrophysiologic abnormalities in atrial refractoriness, conduction velocity, and transmembrane potentials.55 Evaluation of the risk for POAF is an important part of preoperative evaluation because prophylactic therapy can substantially reduce the incidence of AF.
Established risk factors for the development of POAF include history of AF, male gender, decreased left ventricular ejection fraction (LVEF), left atrial enlargement, valvular heart surgery, COPD, diabetes, chronic renal failure, rheumatic heart disease, and withdrawal from beta blocker and angiotensin 1 converting enzyme inhibitor (ACE inhibitor) therapy.50,56
A large Cochrane Database meta-analysis reviewed 58 randomized trials of more than 8500 patients and determined that beta blockers (OR 0.35), sotalol (OR 0.36), amiodarone (0.54), and atrial pacing (OR 0.57) were all highly effective in reducing postoperative AF.57 Overall, prophylactic therapy was associated with a nonsignificant 24% reduction in stroke. In a meta-analysis of randomized trials and risk-adjusted observational studies, off-pump (OP) CABG was associated with significant reductions in postoperative AF (41 and 22%, respectively).58
Practical recommendations include the continued use of beta blockers through the perioperative period because they are effective and safe in most patients.56 Amiodarone can be added to high-risk patients but should be a second-line agent because of its short- and long-term safety profile. There are limited but emerging data suggesting that the addition of magnesium, statins, N-3 polyunsaturated fatty acids, nitroprusside, and corticosteroids might be of additional benefit.56 Although prophylaxis is effective, it is still controversial whether preventing POAF translates into a reduction in stroke and postoperative complications.
Hospital mortality among patients undergoing reoperative cardiac surgery has traditionally been higher than among patients undergoing primary operation.59–61 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.62
Despite these factors, hospital mortality associated with coronary reoperation has decreased with greater surgical experience and now approaches that of primary CABG.62,63 With careful preoperative risk evaluation and surgical management, reoperation can be performed safely.
Patients receiving thoracic radiation for treatment of malignancies before cardiac surgery have poorer short- and long-term outcomes.64,65 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.66 Hospital deaths (13 versus 8.6 versus 2.4%) and respiratory complications (24 versus 20 versus 9.6%) were higher after more extensive radiation, and 4-year survival was poorer (64 versus 57 versus 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 risk may vary.
Valve surgeries generally have a higher complication rate than isolated CABG and combined surgeries have the highest risk (Fig. 9-1). Participants in the Society of Thoracic Surgeons National Adult Cardiac Surgery Database (STS NCD) collected data from 2002 and 2006 on more than 3.6 million procedures.67–69 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.67 Isolated valve procedures had a higher mortality rate of 3.4% (aortic valve replacement [AVR] 3.2%, mitral valve replacement [MVR] 5.7%, and mitral valve prolapse [MVP] 1.6%).68 Combined mortality and major morbidity was also higher 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 combined mortality and major morbidity of 30.1% (AVR + CABG 26.3%, MVR + CABG 43.2%, and MVP + CABG 33.5%).69
Thirty-day mortality and a composite end point of mortality and major in-hospital morbidity (stroke, renal failure, prolonged ventilation, deep sternal wound infection, and reoperation) from the Society of Thoracic Surgeons National Adult Cardiac Surgery Database (STS NCD).67–69 CABG = coronary artery bypass graft surgery.
Minimally invasive surgical techniques can be divided by approach and use of cardiopulmonary bypass (CBP). The use of alternatives to standard median sternotomy has become increasingly adopted in surgical centers for both CABG and valve surgeries. The potential benefits of minimally invasive surgery are earlier extubation, reduced incisional and thoracic discomfort, lower rates of wound infection, less blood loss, and shorter recovery times.70
Off-pump CABG (OP CABG) is performed with small skin incisions and stabilization devices to reduce motion of target vessels while anastomoses are performed without CBP. Current surgical approaches to valve surgery require cardiopulmonary bypass and cardioplegic arrest. Meta-analyses of observational and randomized trials of OP CABG versus CBP have not demonstrated a clear advantage of OP CABG over CBP with respect to mortality or morbidity.58,71 Compared with on-pump surgery, OP CABG generally shows consistent reductions in postoperative AF, blood loss, wound infections, and myocardial injury, with nonsignificant trends toward lower death, MI, and stroke.58,72,73 The benefits of OP CABG are particularly notable in elderly patients and those with heavily calcified (porcelain) aortas.72
There have been steady technologic advancements in optics, instrumentation, and perfusion technology that have facilitated use of totally endoscopic robotic cardiac surgery.74 This technology has been applied to many cardiac surgical procedures, in particular mitral valve repair (MVP) and totally endoscopic coronary artery bypass (TECAB) grafting. Short-term results are promising but long-term studies are lacking.
Simultaneous “hybrid” percutaneous coronary intervention and minimally invasive surgical bypass grafting procedures in a single, specially designed operating suite 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 6 months with shorter hospital length of stay, intubation times, and less blood loss despite aggressive antiplatelet therapy.75