Coronary Artery Bypass Surgery

Surgical treatment of coronary artery disease should increase regional coronary flow reserve and not increase any early or late morbidity and mortality more than the other treatment modalities. In the past 50 years, surgical treatment of coronary artery disease has been adapted rapidly worldwide and several techniques have been developed to decrease total surgical risks and to improve early and late results with the highest level of quality of life. In spite of the last guidelines that offer stents for single or multiple vessels disease, the fact is that surgical revascularization has better outcomes in all groups of coronary artery patients. In the past two decades, the main target has been to limit or eliminate side effects of extracorporeal circulation and cardioplegia (off-pump), and general anesthesia (awake coronary bypass). The prime goal of surgical revascularization is to obtain complete revascularization by bypassing all severe stenotic coronary arteries having a diameter larger than 1 mm. Surgical revascularization with cardiopulmonary bypass through a full sternotomy remains the most widely used surgical technique. With the development of stabilization devices, off-pump procedures can be safely performed in most patients with single or multivessel disease. Minimal invasive and/or robotic surgery is an attractive procedure to catch invasive cardiology. The gold standard strategy involves single graft to single target vessel bypass, especially the left internal mammary artery to the left anterior descending artery. The early cumulative mortality rate is below 3%, but lower than 1% in lower-risk patients. There are some variables most predictive of early mortality: older age, female, reoperation, non-elective surgery, left ventricular dysfunction, accelerated atherosclerosis. The survival rate is higher than 65% for 15 years. Late mortality is dependent not only on non-use of internal mammarian artery, closure of grafts, progression of native arterial disease but also on comorbidities. Satisfactory quality of life after surgery depends on the long-term duration of the freedom from angina, heart failure, rehospitalization and reintervention, and improvement of the exercise capacity. Return of angina during the first 6 months depends on incomplete revascularization or graft failure, whereas progression of native-vessel disease and grafts are serious risk factors for the late recurrence of angina. Venous graft occlusion is the most common reason for reintervention, and native vessel disease is the second

Sequential left internal mammary artery grafting in combination with the aortic no-touch technique

Aim: This study aimed to investigate the short-term outcomes achieved with off-pump bypass combined with the aortic no-touch technique where sequential anastomoses between the left internal mammary artery (LIMA), left anterior descending (LAD) and diagonal artery were employed. Material and methods: A total of 583 patients (mean age 63, 80% male) who underwent off-pump bypass (LIMA-diagonal-LAD sequential) were enrolled in this retrospective analysis. Data regarding the frequency of in-hospital postoperative complications, intra-aortic balloon pump (IABP) and inotropic agent requirement, re-exploration for bleeding, and length of hospital stay were collected. Anastomosis patency was evaluated in 49 patients who underwent angiography. Results: 2.6% of the participants received inotropic agents and 0.5% required IABP. Frequency of acute renal failure, sternal wound infection, cerebrovascular event, respiratory failure, and hemodialysis was less than 1% in total. Among the 49 patients undergoing angiography at an average 41 ±17 months after bypass, the LIMA-LAD was patent in 98% and the LIMA-diagonal was patent in 84% of the subjects. Preoperative left ventricle ejection fraction (LVEF) and recent myocardial infarction (MI) prior to bypass were significantly correlated with postoperative IABP and inotropic agent requirement (r = 0.165, p < 0.01 for LVEF, p = 0.021 for recent MI). Conclusions: Off-pump bypass in combination with the aortic no-touch technique is associated with favorable postoperative outcomes including reduced postoperative stroke, renal dysfunction, IABP, and inotropic agent requirement compared to the results of previous randomized prospective studies published in the literature. © 2022 Termedia Publishing House Ltd.. All rights reserved

Quantitative Cardiac Magnetic Resonance Imaging Biomarkers for the Characterisation of Ischaemic Cardiomyopathy

Our understanding of the processes that determine outcomes in patients with ischaemic cardiomyopathy is based on conventional physiological concepts such as ischaemia and viability. Qualitative methods for characterising these processes tend to be binary and often fail to capture the complexity of the underlying biology. Importantly, these are perhaps inadequate to evaluate treatment effects, including the impact of coronary revascularisation. The aim of this thesis was to deploy novel quantitative cardiac magnetic resonance (CMR) techniques to evaluate and distinguish between the pathophysiological processes that determine outcomes in patients with ischaemic cardiomyopathy, through integration of anatomical, functional, perfusion and tissue characterisation information. The work is centred around the use of coronary artery bypass graft (CABG) surgery as the method for revascularisation, and focuses on the impact of myocardial blood flow alterations on cardiac physiology and clinical outcomes. In this work, I first evaluate the impact of surgical revascularisation on myocardial structure and function in patients with impaired left ventricular (LV) systolic function, using paired assessments before and after CABG. I found that at 6 months following revascularisation, despite improvement in functional capacity, more than a third of total myocardial segments examined are no longer considered revascularised. As a result, the overall augmentation in global myocardial blood flow (MBF) following CABG surgery is significantly blunted. There are however technical concerns regarding the quantitative estimation of myocardial blood flow in patients with coronary artery grafts, particularly in relation to the impact of long coronary grafts on contrast kinetics. I therefore evaluated the impact of arterial contrast delay on myocardial blood flow estimation in patients with left internal mammary artery (LIMA) grafts. I showed that absolute MBF estimation is minimally affected by delayed contrast arrival in patients with LIMA grafts, and that irrespective of graft patency, residual native disease severity is a key determinant of myocardial blood flow. Following these findings, I then assessed the prognostic impact of myocardial blood flow in a large cohort of patients with prior CABG. The only imaging study to date examining the prognostic role of quantitative perfusion indices in this population, it demonstrated that both stress MBF and myocardial perfusion reserve (MPR) independently predict adverse cardiovascular outcomes and all cause-mortality. Finally, using the existing quantitative perfusion technique and its associated framework, I co-developed and implemented a non-invasive, in-line method of measuring pulmonary transit time (PTT) and pulmonary blood volume (PBV) during routine CMR scanning. I then found that both imaging parameters can be used as independent quantitative prognostic biomarkers in patients with known or suspected coronary artery disease

Assessing the Near-Wall Hemodynamics in the Left Coronary Artery Using CFD

The objective of this thesis is to computationally investigate the flow mechanics and the near-wall hemodynamics associated with the different take-off angles in the left coronary artery of the human heart. From this study, we will be able to evaluate if the increase in the take-off angles of the left coronary artery will significantly increases or decrease the likelihood of plaque (atherosclerosis) buildup in the left coronary artery bifurcations. This study quantifies the effects of the varying take-off angles on the branches along the left anterior descending (LAD) of the left coronary artery using computational fluid dynamics (CFD) simulations. The study aims to compare five test cases of the different take off-angles of the left coronary artery (LCA) and four different branch angles between the LAD and the left circumflex (LCx). It also considered the branch angles of the coronary artery downstream the LAD. The idealized geometries used for this study were constructed in SolidWorks 2015 and imported as surface meshes into Star-CCM+, a commercially available CFD solver. In this study, the LCA inlet boundary conditions was set as a pulsatile mass flow inlet and flow split ratios were set for the outlets boundary conditions that are representations of a middle age man at rest. The nature of blood pulsatile flow characteristic was accounted for and the properties of blood which include the density (1,050Kg/m3) and dynamic viscosity (0.0046Pa) were obtained from previous research. The results from the simulations are compared using established scales for the parameters evaluated. The parameters evaluated were: (i) Oscillatory Shear Index (OSI); which quantifies the extent in which the blood flow changes direction as it flows (ii) Time Average Wall Shear Stress (TAWSS); which quantifies the average shear stress experienced by the wall of the artery and (ii) Relative Residence Time (RRT); which defined how long blood spends in a location during blood flow. These parameters are used to predict the likelihood of blood clots, atherosclerosis, endothelial damage, plaque formation, and aneurysm in the blood vessels. The data from the simulations were analyzed using functional macros to quantify and generate threshold values for the parameters. Computational Fluid Dynamics has gain more recognition in field of medicine because it has been used to obtain the various mechanic behaviors of most artificial implanted devices used for endovascular and cardiovascular treatments before these devices are used in patients’ treatment. This can be a useful insight in coronary stenting, solid and stress analysis of biodegradable stent and can also provide insight into stenting for more complex arterial networks like brain stent grafts. In addition, it is important to understand the hemodynamics of the LCA before carrying out stent graft or angioplasty procedures. This will help determine the effectiveness of the stent graft in the coronary artery

Building a better bypass with emphasis on bilateral internal mammary grafting

Abstract The goals for this thesis are 1) to encourage the use of bilateral internal mammary artery (BIMA) grafting more frequently so that many more patients receive the ‘BIMA benefit’ and 2) to ensure that an increase in bilateral IMA grafting is achieved with accuracy and no greater morbidity than that which is achieved with one IMA and the rest of bypasses with a saphenous vein. Revascularization of diseased coronary arteries may be accomplished in one of two ways: by percutaneous coronary intervention (PCI) or by coronary artery bypass graft surgery (CABG). The principal difference between the two procedures involves the length of coronary artery needed to be addressed to improve blood flow to the heart. PCI with placement of stents must open all significantly obstructed areas along a coronary artery whereas in CABG, a surgeon needs only a ‘postage-stamp’ size of disease-free artery in order to perform an anastomosis. However as with everything in life, there are pros and cons to both approaches. PCI is quicker and requires no surgical incision from which a patient must recover. CABG is a major surgical procedure with all the inherent risks associated with a median sternotomy and the use of a heart-lung machine (or not, in the case of off-pump CABG). Patients are naturally drawn to the less invasive PCI but recent publications, most notably the recent 5 year SYNTAX trial (Ref1) results have clearly shown an advantage for CABG for the majority of patients needing revascularization. ‘Pay me now or pay me later’ is a saying that comes to mind… Coronary artery bypass grafting (CABG) has remained the cornerstone treatment for obstructive coronary artery disease for more than 50 years. Chapters 3 and 4 outline the past and the present/future of the CABG procedure, respectively. Chapters 5 and 6 are commentary articles on the benefit of bilateral IMA grafting. Chapter 7 addresses the possibility of an age cut-off as to the survival benefit of BIMA use. BIMA grafting is technically more challenging – all the more reason to use an intra-operative assessment of graft function to ensure bypasses are functioning to the best of a surgeon’s ability before the patient leaves the operating room. (Chapter 8) Operative revascularization is more invasive compared to that with PCI but cementing a sternum solid within 24 hours of operation may possibly reduce the relative invasiveness of CABG, especially when the revascularization rate for CABG is so much lower than PC I (Chapter 9) BIMA grafting is definitely associated with an increase in deep sternal wound infection, one of the most dreaded complications of CABG surgery and commonest reason for not performing BIMA grafting. However if many preventive measures/procedures are used meticulously and consistently on every patient, the risk for this complication can be reduced to almost zero. (Chapter 10) Complete revascularization has been found to improve the survival of patients undergoing CABG surgery; however it is not always possible to completely revascularize a patient. For example if coronary arteries are very small, diffusely diseased or are mostly in scar tissue it may not be possible or even advisable to perform bypasses to such arteries. We have shown that if total arterial grafting (with the majority of arterial grafts of internal mammary artery origin) is used, there is no difference in midterm survival if a patient is incompletely revascularized by inability to bypass one of three artery systems. This is a valuable point as there is only a finite amount of arterial conduit available and there may not be enough to perform all bypasses desired. (Chapter 11 and 12) BIMA grafting does take increased operative time but harmonic ultrasound technology used to skeletonize IMAs helps shorten this time. (Chapter 13 and 14) Chapter15 discusses sequential bypass grafts and the inherent risk of losing the second anastomosis in preference to the first, a serious problem if the second anastomosis is to the more important artery. Chapter 16 presents a rare complication of CABG surgery but from this problem, an operative technique has been developed that is applicable to similar patients with prohibitively calcified coronary arteries. To summarize: It is the author’s wish to 1) refute every reason used as to why BIMA grafting is not performed more frequently and 2) to establish credible studies and guides to encourage their use

Special Topics in Cardiac Surgery

This book considers mainly the current perioperative care, as well as progresses in new cardiac surgery technologies. Perioperative strategies and new technologies in the field of cardiac surgery will continue to contribute to improvements in postoperative outcomes and enable the cardiac surgical society to optimize surgical procedures. This book should prove to be a useful reference for trainees, senior surgeons and nurses in cardiac surgery, as well as anesthesiologists, perfusionists, and all the related health care workers who are involved in taking care of patients with heart disease which require surgical therapy. I hope these internationally cumulative and diligent efforts will provide patients undergoing cardiac surgery with meticulous perioperative care methods