Risk reduction in cardiac surgery

Abstract

Introduction: Cardiac surgery, even in the non-urgent setting, presents an enormous physiological burden to the body. With or without extra-corporeal circulation, manipulation of the heart can affect any system of the body, with potentially catastrophic complications.

Mortality risks: The advent of risk stratification tools began with simple scoring systems to determine mortality after cardiac surgery. These were additive tools which matured into the simple but well-validated Logistic EuroSCORE. The second iteration of the EuroSCORE employed an equally parsimonious array of variable, which was no less accurate than the significantly more complex STS score (1). As surgical safety has improved, patients who were once considered inoperable, such as the octogenarian requiring cardiac surgery, can now be riskstratified to derive maximum benefit from a surgical strategy (2).

Risks of serious complications: Alongside the risk of death, a better understanding of major adverse outcomes has also been sought. The external validity of such tools, such as that for predicting the devasting complication of deep sternal wound infection, are often less well established, and therefore these tools are not as widely adopted (3). Equally, prophylactic efforts to reduce the incidence of such devastating complications using novel methods such as the application of platelet gel have not been shown to reduce risk (4). More common but less debilitating risks such as bleeding can be mitigated by intra-operative point of care measurements such as platelet aggregation (5) and thromboelastography (6). Such diagnostic tests, including crosssectional imaging in appropriate cases, help to alert clinicians to the need for strategy change that can reduce the risks of complications (7).

Surgical strategy: There are multiple approaches to performing the same procedure in cardiac surgery, each with opponents and advocates. It is likely that no single technique is applicable in all scenarios. For example, the anastomosis of the left internal mammary artery to the left anterior descending coronary artery is considered the gold standard of bypass grafts, with the expectation that it is used universally in coronary artery surgery. However, surgeons must exercise discretion when utilising the mammary artery as conduit in all patients and should be cognisant of the potential for steal from other branches of the subclavian, such as in dialysis dependent renal failure (8). Similarly, the use of arterial grafts such as the radial artery may be associated with greater benefit in men than women (9).

Minimising invasiveness: Reducing the size of surgical incisions to reduce risk has also been increasingly sought after in the last five decades. In cardiac surgery, the benefit of these procedures has been less compelling than for thoracic, abdominal or pelvic surgery. Concerns about the quality of coronary artery bypass grafts undertaken using minimally invasive methods was raised and, over a period of time, dismissed (10). The impact of the learning curve may also be relevant to delivering minimally invasive options to patients (11). Minimally invasive methods in cardiac surgery are still immature and while they have not shown any benefits over open surgery in aortic valve replacement (12), they appear to be non-inferior (13).

Off-pump coronary artery bypass grafting: Surgery on the beating heart (without the aid of cardiopulmonary bypass, or “off-pump”) has seen a resurgence as a technique to maintain physiological blood flow through the heart and to reduce the exogenous activation of the inflammatory cascade associated with extracorporeal circulation. Early studies indicated that off-pump coronary artery bypass (OPCAB) was most advantageous for certain patient subgroups (14), but large studies have now demonstrated that this is at least as effective for long-term survival (15) and reintervention (16) as bypass grafting on-pump. The technique might even confer an advantage (17). The corollary to this is that OPCAB is exquisitely sensitive to operator experience (18), and the inexperienced may struggle to derive all its benefits (19) (20).

Conclusion: Outcomes in cardiac surgery in the United Kingdom are enviable and arise from the close scrutiny of surgeon-specific mortality. In order to achieve this, a multi-faceted approach to risk-reduction must be adopted, consisting of thorough pre-operative assessment, multimodal investigation and the use of strategy changes in response to those findings.

Date of Award	17 Jun 2022
Original language	English
Awarding Institution	University of St Andrews