Coronary Artery Bypass Grafting: A Review of Short- and Long-Term Outcomes

Comorbidities and Risk Factors

Patient comorbidities have been found to significantly impact morbidity and mortality rates following CABG. Studies have demonstrated that patients with heart failure had the highest 30-day mortality rates. More specifically, patients with heart failure with reduced ejection fraction had a 5.1% mortality rate compared with the 3.3% mortality rate in patients with heart failure with preserved ejection fraction. ¹² In contrast, those without a diagnosis of heart failure had a 1.3% mortality rate. ¹² Long-term survival after CABG appears to be significantly impacted by the presence of DM and metabolic syndrome. Patients with DM were found to have a lower survival rate compared with nondiabetic patients. ¹³ Amongst the patients with DM, the use of insulin therapy was associated with a poorer survival outcome. ¹³ Nondiabetic patients with metabolic syndrome had a worse long-term survival compared with patients without metabolic syndrome. Interestingly, for diabetic patients, the presence or absence of metabolic syndrome did not appear to influence postoperative survival rates. ¹³

Biomarkers are valuable tools for risk stratification in patients undergoing CABG. Elevated levels of specific biomarkers have been shown to correlate with both perioperative and long-term mortality. Among these, cardiac troponins, N-terminal pro–brain natriuretic peptide (NT-proBNP), and C-reactive protein (CRP) are particularly notable. ^{14 15} NT-proBNP, a marker of ventricular dysfunction has demonstrated significant prognostic value. In a study involving 819 patients undergoing isolated CABG, NT-proBNP levels >430 ng/mL were predictive of elevated in-hospital mortality, while levels >502 ng/mL were associated with increased overall mortality. ¹⁶ Elevated NT-proBNP levels were also significantly correlated with prolonged mechanical ventilation time, extended intensive care unit (ICU) stay, and a higher incidence of postoperative atrial fibrillation. ¹⁶ Similarly, CRP, a marker of systemic inflammation, has been identified as an independent predictor of mortality. A CRP level greater than 10 mg/L was found to be a risk factor for early mortality, while levels exceeding 5 mg/L were associated with late mortality following CABG. ¹⁷ Other patient-specific factors such as advanced age and female sex have consistently been associated with increased risk of adverse outcomes. ¹⁵ Women undergoing CABG are at a higher risk of short-term mortality compared with men. ¹⁸ Women have also been found to have an increased risk of stroke following surgery. ¹⁸ In contrast, men were found to have a higher risk of postoperative atrial fibrillation after CABG. ¹⁸ Furthermore, some studies have shown no significant association between BMI classes and 30-day mortality. ¹⁹

Surgical Technique

One important factor affecting perioperative mortality is CABG technique, which has evolved over the years. These can be primarily categorized into on-pump and off-pump procedures, each with distinct operative methodologies and implications for patient outcomes. Conventional CABG (on-pump) incorporates the use of a cardiopulmonary bypass (CPB) machine to create a blood-free surgical field. This procedure is generally considered safe, with an average risk of complications of ∼1–2% in low-risk patients. ²⁰ It can, however, be associated with several complications, including myocardial infarction (MI), stroke, and renal failure requiring dialysis, which affects 5–9% of patients. ²¹ These complications are often attributed to the use of CPB. To address these risks, off-pump CABG was developed, allowing surgeons to perform the procedure on a beating heart without the use of the CPB machine.

On Pump versus Off Pump

Several trials have compared the efficacy of off-pump and on-pump CABG, including the CORONARY trial. The trial found no significant difference in the primary composite outcomes, which included death, nonfatal stroke, nonfatal MI, or new renal failure requiring dialysis at 30 days, between the two techniques. ²² Notably, off-pump CABG resulted in lower rates of re-operation due to perioperative bleeding, blood transfusions, acute kidney injury, and respiratory complications. ²² Off-pump CABG was, however, associated with higher rates of repeat revascularization. ²² Similar results were observed at five-year follow-up with no significant differences in composite outcomes. ²¹ Other studies, such as the ROOBY ²³ and GOPCABE ²⁴ trials, did not find significant differences in 30-day composite outcomes between off-pump and on-pump CABG. In the ROOBY trial, off-pump CABG showed a higher rate of the composite outcome, which included death from any cause, repeat revascularization, or nonfatal MI, compared with on-pump at 1 year. ²³ The GOPCABE trial, similar to the CORONARY trial, found that repeat revascularization occurred more frequently following off-pump CABG compared with on-pump at 30 days. ²⁴

Full Sternotomy versus Minimally Invasive Direct Coronary Artery Bypass

Full sternotomy has been the traditional approach for CABG, however the development of minimally invasive direct coronary artery bypass (MIDCAB) has gained popularity due to its proposed advantages, which include shorter recovery times, reduced surgical trauma, and fewer postoperative complications. ²⁵ MIDCAB is a sternal-sparing procedure for proximal LAD disease. Instead of a sternotomy, a small anterior thoracotomy allows for harvesting and grafting of the left internal mammary artery (LIMA) to bypass the left anterior descending (LAD) artery, providing revascularization to the anterior wall of the left ventricle. ²⁵ A multi-institutional analysis found no significant difference between both methods in terms of operative mortality, wound infection, atrial fibrillation, postoperative stroke or need for revascularization, however, full sternotomy was associated with higher rates of blood transfusion, longer ICU stays, and longer hospital stays. ²⁶ Furthermore, a large observational study comparing MIDCAB and full sternotomy revascularization for isolated LAD disease demonstrated no statistically significant differences in 30-day mortality (2.0 vs. 2.5%), neurological complications (1.4 vs. 1.3%), renal complications (1.4 vs. 1.3%), or surgical site infections (2.4 vs. 1.9%). Long-term survival was also comparable, with similar outcomes observed at a mean follow-up of 12.95 ± 0.45 years. ²⁵ Other studies comparing MIDCAB with full sternotomy off-pump CABG observed similar findings. ^{27 28} Some studies suggest MIDCAB patients require fewer blood transfusions, have shorter mechanical ventilation times, have a decreased incidence of stroke, and experience lower hospital costs, without an increased risk of early or late mortality, repeat revascularization or MI. ^{26 29}

Arterial versus Venous Grafts

CABG involves the use of arterial and venous grafts between the aorta and coronary artery circulation. The long-term outcomes of graft patency are important considerations when evaluating the efficacy of the procedure. Graft patency shows notable variation based on the type of vessel used and the coronary territory it serves. Arterial grafts generally maintain greater patency rates compared with venous grafts. ³⁰ Among these, the left internal mammary artery (LIMA) exhibits the highest patency rates. Indeed, some studies report 90–95% graft patency in over 90% of patients at 10 years post-surgery. ³⁰ The right internal thoracic artery (RITA) and the radial artery (RA) also show favorable long-term outcomes. These grafts maintain patency rates comparable to the IMA, often reaching up to 85–90%. ³¹ Patients receiving radial artery grafts were also found to have a reduced risk of graft occlusion, as well as a lower incidence of myocardial infarction and need for repeat revascularization. ³² Compared with arterial grafts, saphenous vein grafts (SVGs) display lower long-term patency, typically ∼50–60% at 10 years post-surgery. ³⁰ It is worth noting that SVGs have been found to perform better when attached to the left anterior descending artery (69%) compared with the right coronary artery (56%) or the circumflex artery (58%). ³³ The diameter of the recipient vessel also plays a critical role in graft survival. In recipient vessels larger than 2.0 mm, SVGs exhibit an 88% patency, however this drops significantly to 55% in vessels 2.0 mm or smaller. ³³ The advantages of the arterial graft not only lie in their longevity, but also in their greater resistance to atherosclerosis, which contributes to sustained blood flow over time.

Peri- and Postoperative Complications

Complications following CABG can significantly impact short- and long-term outcomes. According to the Society of Thoracic Surgeons Adult Cardiac Surgery Database (STS ACSD), the operative mortality rate which includes both in-hospital and 30-day mortality following isolated CABG has remained around 2% in recent years, reflecting ongoing improvements in surgical techniques and postoperative care. ³⁴ Common in-hospital perioperative complications include atrial fibrillation, stroke, renal failure, wound infection, need for reoperation, and myocardial infarction, which is typically due to acute graft occlusion or intraoperative ischemia. ³⁵ In one query of clinical records from the STS ACSD Database, patients undergoing isolated CABG, aged 65 years or older, between 2007 and 2012, were examined for select postoperative complications. The incidence of postoperative complications was found to be: atrial fibrillation 30%, renal failure 4.5%, need for reoperation 3.5%, stroke 1.9%, mediastinitis or deep sternal wound infection 0.4%. ³⁶ Patients who experienced complications were more likely to have a history of prior MI, have a left ventricular ejection fraction <55%, be New York Heart Association class IV, have end-stage renal disease requiring dialysis, have severe chronic lung disease or have a history of cerebrovascular disease. ³⁶

It is important to consider complications and adverse effects between CABG and PCI. One study found that acute kidney injury occurred more frequently in patients undergoing CABG (15.6%) when compared with those undergoing PCI (9.1%). ³⁷ Furthermore, the incidence of stage 2 or 3 AKI was also found to be higher in patients undergoing CABG (3.4%) when compared with PCI (1.7%). ³⁷ The more recent FAME 3 trial found that CABG was associated with higher rates of atrial fibrillation (14.1 vs. 2.1%), acute kidney injury (0.9 vs. 0.1%), and 30-day rehospitalization (10.2 vs. 5.5%) compared with PCI. ¹⁰ The SYNTAX trial, which enrolled patients with de novo three-vessel and/or left main CAD, demonstrated no significant differences in in-hospital major adverse cardiac and cerebrovascular events or 30-day outcomes between those treated with PCI and CABG. ³⁸ However, the CABG group exhibited a significantly lower incidence of graft occlusion or stent thrombosis between 2 and 30 days' postprocedure. ³⁸ In the FREEDOM trial, which focused on diabetic patients with multivessel CAD, 30-day outcomes revealed no significant differences in rates of death, myocardial infarction, stroke, or repeat revascularization between the two treatment arms. ⁴ Similarly, the EXCEL trial reported no significant differences in death, MI, or stroke at 30 days; however, patients undergoing CABG had a higher incidence of therapy failure (graft stenosis or occlusion) compared with stent thrombosis in those receiving PCI. ³⁹

Amongst pooled studies, 30-day readmission rates ranged from 0.50 to 23.3%. ⁴⁰ The most common cause for readmission was congestive heart failure and arrhythmias. Other common causes of readmission, in order of frequency, included infection and sepsis, pleural effusions, respiratory complications, thromboembolic disorders, and gastrointestinal complications. Risk of readmission was found to be higher for female sex, non-White race, and having nonprivate insurance. ⁴⁰ Comorbidities that increased risk of readmission included DM, heart failure, prior MI, atrial fibrillation, stroke, peripheral vascular disease, pulmonary disease, liver disease, and immunosuppression. ⁴⁰ Perioperative and postoperative complications are associated with increased long-term mortality, extended hospitalizations, and readmissions. While difficult to predict these complications, it is important to allow for appropriate risk stratification and preparation to reduce individual patient risk.

Survival Rates

Secondary prevention and risk factor modifications are predictors of outstanding long-term outcomes in patients that underwent CABG. However, suboptimal modifications may lead to detrimental clinical outcomes, decreased survival rates, and overall worse prognosis of cardiovascular disease. ⁴¹ Multiple studies have evaluated the long-term survival rates associated with CABG compared with PCI. The BEST trial, which examined patients with multivessel CAD, demonstrated a similar mortality rates in both CABG and PCI groups over a median follow-up of 4.6 years (3.6 vs. 4.1%; hazard ratio [HR]: 1.15, 95% confidence interval [CI]: 0.58–2.25). ⁷ At extended follow-up (median: 11.8 years), mortality differences remained statistically insignificant. ⁸ Conversely, the large observational ASCERT trial found a significant survival benefit for CABG patients aged ≥ 65 with two- or three-vessel disease (Relative risk [RR]: 0.79, 95% CI: 0.76–0.82). ⁶ In diabetic patients with multivessel CAD, the FREEDOM trial showed a superiority of CABG over PCI. At 5 years, all-cause mortality was significantly lower with CABG (10.9 vs. 16.3%, p  = 0.049), ⁴ and this benefit persisted at a median follow-up of 7.5 years (18.3 vs. 24.3%; HR: 1.36, 95% CI: 1.07–1.74). ⁵ Most recently, the FAME 3 trial—a multicenter randomized controlled trial (RCT) reported no significant difference in mortality between CABG and PCI over 5 years. ¹⁰

Trials focusing on left main CAD produced mixed results. The EXCEL trial reported higher 5-year all-cause mortality with PCI compared with CABG (13.0 vs. 9.9%; odds ratio [OR]: 1.38, 95% CI: 1.03–1.85). ³⁹ In contrast, the NOBLE trial found no significant difference in mortality between the both groups over a median of 4.9 years (9.0% in both arms; HR: 1.08, 95% CI: 0.74–1.59). ⁹ Similarly, the PRECOMBAT trial, with 10-year follow-up, showed slightly higher mortality with PCI (14.5 vs. 13.8%; HR: 1.13, 95% CI: 0.75–1.70), although the result was not statistically significant. ⁴² The SYNTAX trial showed lower all-cause mortality with CABG at 5 years (13.9 vs. 11.4% with PCI), although the difference was not statistically significant. An individual patient-data meta-analysis including all four RCTs (SYNTAX, PRECOMBAT, NOBLE, and EXCEL) revealed no significant difference in 5-year all-cause mortality between patients undergoing CABG and those receiving PCI. However, CABG was associated with significantly lower rates of spontaneous MI (2.6 vs. 6.2%; HR: 2.35, 95% CI: 1.71–3.23) and repeat revascularization (10.7 vs. 18.3%; HR: 1.78, 95% CI: 1.51–2.10). ⁴³

Several trials have assessed the impact of coronary revascularization plus optimal medical therapy (OMT) compared with OMT alone. In the extended follow-up of the ISCHEMIA trial, there was no significant difference in all-cause mortality between the invasive group (coronary revascularization with CABG or PCI and OMT) and the group receiving OMT alone. However, cardiovascular mortality was lower in the invasive group (6.4%) compared with the OMT group (8.6%), with HR of 0.78 (95% CI: 0.63–0.96). ⁴⁴ A large systematic review and meta-analysis involving patients with stable CAD showed that coronary revascularization combined with OMT was associated with a 21% reduction in cardiac mortality (RR: 0.79; 95% CI: 0.67–0.93) and a 26% reduction in spontaneous myocardial infarction (RR: 0.74; 95% CI: 0.64–0.86). ⁴⁵ A separate trial evaluating patients with ischemic cardiomyopathy (EF ≤ 35%) and CAD showed no significant difference in cardiovascular or all-cause mortality during short-term follow-up between the groups. ⁴⁶ However, over a longer follow-up period of approximately 10 years, CABG + OMT was associated with significantly lower cardiovascular mortality(40.5 vs. 49.3%; HR: 0.79; p  = 0.006) and all-cause mortality (58.9 vs. 66.1%; HR: 0.84; 95% CI: 0.73–0.97). ⁴⁷ Notably, the mortality benefit diminished with increasing age, although the reduction in cardiovascular mortality remained consistent across all age groups. ⁴⁷

Survival rates after CABG have been shown to be multifactorial and dependent on the immediate postoperative clinical course. This includes, but is not limited to, factors such as early liberation of mechanical ventilation and hemodynamic support, kidney failure, postoperative infection, and readmission. ⁴⁸ Readmissions after CABG are strongly associated with poorer long-term outcomes and an increase in mortality rate. The amount of vessel involvement with multiple arterial grafts has been associated with lower all-cause death when compared with single arterial graft in a long-term follow-up. In contrast, involvement of left main disease has not shown a difference in survival rates following CABG. ⁴⁹

Quality of Life

Patient quality of life (QoL) following CABG serves as one measure of the overall success of the procedure. Long-term QoL after CABG is frequently improved compared with presurgical levels. QoL after CABG can be assessed using a variety of tools, such as the Seattle Angina Questionnaire (SAQ), which is a validated 19-item questionnaire that specifically focuses on disease-related symptoms. The SAQ measures five domains related to CAD, including angina frequency, physical limitations, QoL, angina stability, and treatment satisfaction, with scores ranging from 0 to 100, with higher scores indicating reduced symptom burden. Other methods to quantify and track QoL can be done with the Short Form Health Survey (SF-12/36), which measures both physical and mental components, and the EuroQoL-5D (EQ-5D).

Outcomes post-CABG are influenced by multiple factors, including surgical technique, psychosocial factors, and rehabilitation efforts. Many patients often experience significant improvement and relief from symptoms, including reduction in angina, increased exercise capacity, and enhanced psychological health. ⁵⁰ A key trial, the EXCEL trial, revealed significant improvements across all SAQ subscales at 12- and 36-month postsurgery compared with baseline. ⁵¹ When comparing CABG to PCI, there were no significant differences observed on any of the SAQ subscales. Interestingly, the rate of daily or weekly angina was nearly double in the CABG group compared with PCI (10.4 vs. 5.5%), although this difference diminished at later time points. Regarding general QoL, no significant differences were found between CABG and PCI groups at the 36-month mark. ⁵¹ In contrast, the FREEDOM trial found that the CABG group exhibited slightly higher scores on the angina frequency subscale at both 1- and 2-year follow-ups. Of note, by 3 years, there was no significant difference between the two groups. ⁵⁰

In trials comparing revascularization plus OMT compared with OMT alone, improvements in QoL have been observed with an invasive approach. A meta-analysis of patients with stable CAD measuring QoL defined as “freedom from angina” found that patients undergoing routine Revascularization were significantly more likely to be angina-free with a 10% greater likelihood compared with those managed with OMT alone (RR: 1.10; 95% CI: 1.05–1.15). ⁵² Similarly, the ISCHEMIA trial showed a mean difference in SAQ scores between the invasive and OMT group was +4.2 points at 12 months (95% CI: 3.3–5.1) and +2.9 points at 36 months (95% CI: 2.2–3.7). ⁵³ In this trial, the most benefits were observed in patients with daily or weekly angina at baseline.

Moreover, the findings of a systematic review examining QoL post-CABG demonstrated a significant trend toward improved QoL scores from presurgery to 1-year postsurgery, particularly for the SAQ subscales of angina frequency and general QoL, SF-36 physical component, and the EQ-5D. Notably, the SF-36 MCS did not show significant improvement during this period. Similarly, a recent systematic review and meta-analysis observed considerable improvements in QoL between 6 weeks and 3 months following surgery, with notable improvement in physical health. ⁵⁴ This study also identified several factors that could hinder recovery or delay improvements in QoL postsurgery, which include advanced age, female sex, hypertension, obesity, renal failure, cerebrovascular disease, unstable angina, smoking, and the presence of psychiatric conditions. ⁵⁴ While not all of these risk factors are able to be controlled or prevented, their recognition can allow for timely intervention of psychosocial factors and further tailoring of rehabilitation efforts. This personalization of care can allow for optimization of postsurgical patient outcomes, in both the physical and mental spheres.