Table 3 Synthesized mechanisms proposed for case-mix characteristics, structures, processes, and intermediary outcomes in reviewed articles

Structures

Treatment era

Earlier year of operation

Improved perioperative care, including surgical techniques, and the increased rate of complete revascularization, have reduced in-hospital mortality over time [35, 42, 68, 102]

Care setting

Hospital type

Lower volume CABG programs are present at Veterans Affairs hospitals compared to private hospitals with higher volume [82]

Hospital volume

Increased procedure volume drive better care processes [23]

Operator qualification

Operator volume

An inverse volume-outcome relationship, selective referral, and differences in case-mix characteristics drive differences in mortality between low-volume and high-volume operators [99]

Processes

Preoperative care

ASA administration

ASA has an irreversible effect on platelets, decreasing production of Thromboxane A2, reducing graft occlusion [29, 33]

Beta blocker administration

Beta blockade may reduce the incidence of myocardial ischemia, through attenuation of heart rate [59]

Insulin infusion

Pre-operative insulin reverses metabolic deficiencies in diabetics through a direct reduction of hyperglycemia [38]

Intra-aortic balloon pump

Pre-operative intra-aortic balloon pump reduces left ventricular afterload and increases coronary perfusion [43]

Statin administration

Statins confer protection from the inflammatory response by reducing cytokine release and neutrophil adhesion, improving post-operative myocardial perfusion [39, 48, 57, 64]

Intraoperative management

Allogenic blood transfusion

Leukocytes in allogenic blood cause widespread leukoreduction of blood components [81]

Intra-aortic balloon pump

Intraoperative intra-aortic balloon pumps support circulation by reducing cardiac load and decreasing dependence on vasoactive medications [47]

Off-pump cardiopulmonary bypass

Selection of off-pump cardiopulmonary (OPCAB) bypass is a function of the patient’s perioperative risk profile, including sex, comorbidities, extent of disease, and physician practice. OPCAB removes the systematic inflammatory response and complications associated with the use of cardiopulmonary bypass, possibly due to less aortic manipulation [28, 52, 55, 62, 71, 78, 84, 85]

Pulmonary artery catheterization

Increased experience with pulmonary artery catheter insertion may affect in-hospital mortality [79]

Red blood cell transfusion

Immunosuppressive and inflammatory effects, poor oxygen delivery, and red blood cell deformity may contribute to poorer outcomes [76]

Postoperative care

Red blood cell transfusion

Transfusion may cause an increase in blood viscosity and shear forces with subsequent increases in platelet activation [72]

Intermediary Outcomes

Complications

Pulmonary artery temperature

Patients with warmer pulmonary artery temperatures are at higher risk of adverse events [53]

Case-mix characteristics

Sociodemographic factors

Medicaid insurance and uninsured status

The type of insurance affects access to preoperative care in the United States [32]

Native American status

Diet and lifestyle behaviors increase the prevalence of diabetes [75]

Sex

Females have lower body surface area, thought to correspond to smaller coronary artery size resulting in technical difficulties grafting to smaller targets and longer lifespan resulting in later CAD presentation [22, 27, 88, 100]

Health risks

Body mass index

Obese patients have lower systemic vascular resistance and higher plasma renin activity, while patients who are underweight may have increased levels of inflammation which could lead to myocardial dysfunction [24]

Disease history

Prior percutaneous coronary intervention [PCI]

PCI procedures cause inflammatory reactions leading to post-stenting endothelial injury and dysfunction. Intimal hyperplasia, along with platelet and neutrophil adhesion increase the risk of thrombosis [67, 89, 90]

Comorbidity burden

Atrial fibrillation

Patients with AF have higher incidence of thromboembolic events and post-operative low cardiac output syndrome [65]

Dialysis-dependent renal failure

Dialysis-dependent patients in renal failure may have a higher burden of atherosclerotic disease involving multiple organs, be immunocompromised, and have poorer myocardial function [31, 60]

Metabolic syndrome

Multiple complex metabolic reactions may directly or indirectly impact myocardial function and increase mortality [30]

QT Prolongation

Demographic, congenital, structural, electrophysiological, and endocrine factors, along with medication use, may contribute to QT prolongation [37]

Peripheral vascular disease

Patients with PVD may be ineligible for intra-aortic balloon pump support due to calcified ascending aortas [70]

Peritoneal dialysis

Peritoneal dialysis patients had more postoperative complications, including sternal wound infection, stroke, higher usage of intra-aortic balloon pumps and extra-corporeal life support, and may have increased complications for early reintroduction of PD post-operatively [56, 104]

Right ventricular systolic dysfunction

Increased pulmonary pressure and myocardial ischemia may contribute to right ventricular systolic dysfunction [77]

Operative risks

Cockcroft-Gault formula

Cockcroft-Gault formula for calculating glomerular filtration rate (GFR) includes more variables than the MDRD equation and therefore may be more predictive kidney disease leading to increased risk of mortality [58]

Forced expiratory volume 1 (FEV1)

Tobacco use may lead to COPD resulting in impaired lung function, compromising outcomes [40]

Left atrial expansion index

Hypoxic, ischemic, and hyperkalemic changes after CABG increase left atrial expansion and atrial fibrillation, increasing risk of death [94]

Red cell distribution width

Nutritional deficiency and recent blood transfusion could lead to increased mortality [96]

White blood cell count

Increased white blood cell count may be a sign of preoperative infection [34]