Aj Bryan

Beating versus arrested heart revascularization: evaluation of myocardial function in a prospective randomized study

OBJECTIVE Conventional coronary artery bypass grafting (CABG) is both safe and effective. Nevertheless, the use of cardiopulmonary bypass (CPB) and cardioplegic arrest are associated with several adverse effects. Over the last 2 years there has been a revival of interest in performing CABG on the beating heart. In this prospective randomized study we evaluated the efficacy and safety of on and off pump coronary revascularization on myocardial function. METHODS Eighty patients (65 males, mean age 61+/-9.7 years) undergoing first time CABG were prospectively randomized to: (i) conventional revascularization with CPB at normothermia and cardioplegic arrest with intermittent warm blood cardioplegia (on pump) or (ii) beating heart revascularization (off pump). Troponin I (Tn I) release was serially measured as a specific marker of myocardial damage. Haemodynamic measurements as well as inotropic requirement, incidence of arrhythmia and postoperative myocardial infarction were also recorded. RESULTS There were no significant differences between the two groups in terms of age, sex, extent of disease, left ventricular function and number of grafts. There were no deaths or intraoperative myocardial infarctions in either group. Tn I release was constantly lower in the off pump group and this was significant at 1, 4, 12 and 24 h postoperatively. Furthermore, in this group there was a significantly reduced incidence of arrhythmias. Inotropic requirements were less in the off pump group but this did not reach statistical significance. CONCLUSION These results suggest that off pump coronary revascularization is a safe and effective strategy for myocardial revascularization. Myocardial injury as assessed by Tn I release is also reduced when compared with conventional coronary revascularization with CPB and cardioplegic arrest.

Prevention of spinal cord ischaemia during descending thoracic and thoracoabdominal aortic surgery

Surgery of the descending and thoracoabdominal aorta has been associated with post-operative paraparesis or paraplegia. Different strategies, which can be operative or non-operative, have been developed to minimise the incidence of neurological complications after aortic surgery. This review serves to summarise the current practice of spinal cord protection during surgery of the descending thoracoabdominal aortic surgery. The pathophysiology of spinal cord ischaemia will also be explained. The incidence of spinal cord ischaemia and subsequent neurological complications was associated with (1) the duration and severity of ischaemia, (2) failure to establish spinal cord supply and (3) reperfusion injury. The blood supply of the spinal cord has been extensively studied and the significance of the artery of Adamkiewicz (ASA) being recognised. This helps us to understand the pathophysiology of spinal cord ischaemia during descending and thoracoabdominal aortic operation. Techniques of monitoring of spinal cord function using evoked potential have been developed. Preoperative identification of ASA facilitates the identification of critical intercostal vessels for reimplantation, resulting in re-establishment of spinal cord blood flow. Different surgical techniques have been developed to reduce the duration of ischaemia and this includes the latest transluminal techniques. Severity of ischaemia can be minimised by the use of CSF drainage, hypothermia, partial bypass and the use of adjunctive pharmacological therapy. Reperfusion injury can be reduced with the use of anti-oxidant therapy. The aetiology of neurological complications after descending and thoracoabdominal aortic surgery has been well described and attempts have been made to minimise this incidence based on our knowledge of the pathophysiology of spinal cord ischaemia. However, our understanding of the development and prevention of these complications require further investigation in the clinical setting before surgery on descending and thoracoabdominal aorta to be performed with negligible occurrence of these disabling neurological problems.

How does EuroSCORE II perform in UK cardiac surgery; an analysis of 23 740 patients from the Society for Cardiothoracic Surgery in Great Britain and Ireland National Database

Objective The original EuroSCORE models are poorly calibrated for predicting mortality in contemporary cardiac surgery. EuroSCORE II has been proposed as a new risk model. The objective of this study was to assess the performance of EuroSCORE II in UK cardiac surgery. Design A cross-sectional analysis of prospectively collected multi-centre clinical audit data, from the Society for Cardiothoracic Surgery in Great Britain and Ireland Database. Setting All NHS hospitals, and some UK private hospitals performing adult cardiac surgery. Patients 23 740 procedures at 41 hospitals between July 2010 and March 2011. Main outcome measures The main outcome measure was in-hospital mortality. Model calibration (Hosmer–Lemeshow test, calibration plot) and discrimination (area under receiver operating characteristic curve) were assessed in the overall cohort and clinically defined sub-groups. Results The mean age at procedure was 67.1 years (SD 11.8) and 27.7% were women. The overall mortality was 3.1% with a EuroSCORE II predicted mortality of 3.4%. Calibration was good overall but the model failed the Hosmer–Lemeshow test (p=0.003) mainly due to over-prediction in the highest and lowest-risk patients. Calibration was poor for isolated coronary artery bypass graft surgery (Hosmer–Lemeshow, p<0.001). The model had good discrimination overall (area under receiver operating characteristic curve 0.808, 95% CI 0.793 to 0.824) and in all clinical sub-groups analysed. Conclusions EuroSCORE II performs well overall in the UK and is an acceptable contemporary generic cardiac surgery risk model. However, the model is poorly calibrated for isolated coronary artery bypass graft surgery and in both the highest and lowest risk patients. Regular revalidation of EuroSCORE II will be needed to identify calibration drift or clinical inconsistencies, which commonly emerge in clinical prediction models.

Left-ventricular-volume reduction for end-stage heart failure

See Commentary page 456 L/m per min (p=0·001). There were three deaths in hospital. Two patients died of technical complications: one from dehiscence of the left-ventricle suture line (day 1) and the second from rupture of the pulmonary artery, a recognised complication of Swan-Ganz catheterisation (day 6). A third patient had chronic renal failure preoperatively, and died on day 6 from multiorgan failure. Inhospital survival was 78·5% and mean hospital stay was 19 (range 8–31) days. At mean follow up of 6 (1–20) months, nine patients were in NYHA functional class I or II and one was in class III. There was one late death: a patient died suddenly 3 months after operation, probably from an arrhythmia. This death prompted us to use amiodarone prophylactically and no episodes of arrhythmia have since been reported. Repeated transthoracic echocardiography did not show any significant change in left-ventricular dimension or function from early postoperative assessment (table). Contrary to the early experience reported by the Cleveland Clinic in the USA, 13 of the candidates for ventricular reduction in our series were patients unsuitable for heart transplantation. The aetiology was not exclusively idiopathic, age was not a contraindication (mean age 65 years compared with 50 years in the Cleveland Clinic series). Two of the inhospital deaths were in the first four patients and only one patient died in the last ten. Our preliminary findings encourage the belief that surgical remodelling of the patient’s own heart can cause sustained improvement in ventricular function. We do not believe that, at this stage, ventricular reduction has been sufficiently evaluated to be offered to patients suitable for heart transplantation. We appreciate, however, that the demand for donor hearts is much greater than supply, and this means that more thorough clinical evaluation of left-ventricular reduction is required.

The effects of cardiopulmonary bypass temperature on inflammatory response following cardiopulmonary bypass

OBJECTIVES The inflammatory response to cardiopulmonary bypass is believed to play an important role in end organ dysfunction after open heart surgery and may be more profound after normothermic systemic perfusion. The aim of the present study was to investigate the effects of cardiopulmonary bypass temperature on the production of markers of inflammatory activity after coronary artery surgery. METHODS Forty-five low risk patients undergoing elective coronary artery surgery were prospectively randomized into three groups: hypothermia (28 degrees C, n = 15), moderate hypothermia (32 degrees C, n = 15), and normothermia (37 degrees C, n = 15). All patients received cold antegrade crystalloid cardioplegia and topical myocardial cooling with saline at 4 degrees C. Serum samples were collected for the estimation of neutrophil elastase, interleukin 8, C3d, and IgG under ice preoperatively, 5 min after heparinisation, 30 min following start of CPB, at the end of CPB, 5 min after protamine administration, and 4, 12 and 24 h postoperatively. RESULTS Patients were similar with regard to preoperative and intraoperative characteristics (age, sex, severity of symptoms, number of grafts performed, aortic cross clamp time, cardiopulmonary bypass time). Neutrophil elastase concentration increased markedly as early as 30 min after the onset of cardiopulmonary bypass and peaked 5 min after protamine administration. Levels were not significantly different between the three groups. A similar finding was apparent for C3d release. Interleukin 8 concentrations also demonstrated a considerable increase related to cardiopulmonary bypass in all groups, but there was a significantly more rapid decline in interleukin 8 concentrations in the normothermic group in the postoperative period. Eluted IgG fraction showed a much earlier peak concentration than the other markers, occurring within 30 min of the start of cardiopulmonary bypass. Levels reached a plateau, before declining soon after the end of bypass and remained higher than preoperative values at 24 h. There was no difference between the three groups. The cumulative release of all markers was calculated from the concentration-time curves, and was not statistically different between groups. CONCLUSION Normothermic systemic perfusion was not shown to produce a more profound inflammatory response compared to hypothermic and moderately hypothermic cardiopulmonary bypass.

Intermittent antegrade hyperkalaemic warm blood cardioplegia supplemented with magnesium prevents myocardial substrate derangement in patients undergoing coronary artery bypass surgery

OBJECTIVE The influence of the addition of magnesium on myocardial protection with intermittent antegrade warm blood hyperkalaemic cardioplegia in patients undergoing coronary artery surgery was investigated and compared with intermittent antegrade warm blood hyperkalaemic cardioplegia only. METHODS Twenty-three patients undergoing primary elective coronary revascularization were randomized to one of two different techniques of myocardial protection. In the first group, myocardial protection was induced using intermittent antegrade warm blood hyperkalaemic cardioplegia. In the second group, the same technique was used except that magnesium was added to the cardioplegia. Intracellular substrates (ATP, lactate and amino acids) were measured in left ventricular biopsies collected 5 min after institution of cardiopulmonary bypass, after 30 min of ischaemic arrest and 20 min after reperfusion. RESULTS There were no significant changes in the intracellular concentration of ATP or free amino acid pool in biopsies taken at the end of the period of myocardial ischaemia. However, the addition of magnesium prevented the significant increase in the intracellular concentration of lactate seen with intermittent antegrade warm blood hyperkalaemic cardioplegia. Upon reperfusion there was a significant fall in ATP and amino acid concentration when the technique of intermittent antegrade warm blood hyperkalaemic cardioplegia was used but not when magnesium was added to the cardioplegia. CONCLUSIONS This work shows that intermittent antegrade warm blood hyperkalaemic cardioplegia supplemented with magnesium prevents substrate derangement early after reperfusion.

Coronary artery bypass surgery: current practice in the United Kingdom.

OBJECTIVE--To assess current clinical practice in coronary artery bypass surgery and compare it with a previous survey conducted five years ago. SETTING--United Kingdom. DESIGN--Postal questionnaires were sent in March 1993 to 120 consultant cardiac surgeons currently performing coronary artery bypass surgery. 104 (87%) were returned by May 1993. RESULTS--The 104 surgeons who returned the questionnaire performed an estimated total of 25,234 coronary artery bypass operations in 1992 with an average case load per surgeon similar to that in 1987 (243 v 214, NS). The internal mammary artery was regarded as the conduit of choice by 101 surgeons (97%) and was used in 93% of bypass grafts to the left anterior descending coronary artery compared with 73% in 1987 (p < 0.001) but only in 7% of grafts to the circumflex and right coronary systems. There was also a significant increase in the number of surgeons using both internal mammary arteries (88% v 59%, p < 0.01) but only a small increase in those using the internal mammary artery as a sequential graft (55% v 44%, NS). The age of the patient remains one of the main contraindications to the use of the internal mammary artery (40%), together with insufficient mammary flow (42%), endarterectomy (22%), and unstable angina (17%). The right gastroepiploic and inferior epigastric arteries were used only occasionally (3%) when the internal mammary artery or the saphenous vein were not available. Most surgeons (96%) still advocate the use of aspirin to enhance graft patency, with 87% of surgeons continuing treatment indefinitely, compared with 50% in the previous survey (p < 0.001). As for methods of myocardial protection, 72% of surgeons used cardioplegic arrest whereas 28% preferred intermittent aortic cross clamping and fibrillation. CONCLUSIONS--It is the consensus among British cardiac surgeons that the internal mammary artery is the graft conduit of choice. Its use has been significantly extended over the past five years (1987 to 1992) suggesting a quick response to advancing scientific knowledge. The use of alternative arterial conduits is still limited, perhaps as a reflection of the relative lack of information on their long-term performance. The recently advocated technique of retrograde cardioplegia and continuous warm cardioplegia is not yet popular.

Distribution of endothelin-1 (ET) receptors (ETA and ETB) and immunoreactive ET-1 in porcine saphenous vein–carotid artery interposition grafts

Proliferation of vascular smooth muscle cells (VSMC) is a principal event in neointima formation in saphenous vein-coronary artery bypass grafts. Since endothelin-1 (ET-1) promotes VSMC replication and ET-1 receptor antagonists inhibit neointima formation in arterial injury models, it is reasonable to propose that ET-1 may be involved in neointima formation in vein grafts. However, it is not known what alterations of ET-1 and its receptors (if any) occur in vein grafts. The objective of this study, therefore, was to investigate the distribution of ET-1 and ET-1 receptor subtypes (ET(A) and ET(B)) in porcine vein grafts. Unilateral interposition saphenous vein grafting was performed by end to end anastomosis after excision of a segment of carotid artery in Landrace pigs. One month after surgery, vein grafts, ungrafted saphenous veins and carotid arteries were excised, ET-1 immunoreactivity identified by immunocytochemistry and ET(A) and ET(B) receptor subtypes studied using autoradiography. In vein grafts, there was a greater density of ET(A) compared to ET(B) receptors in both the tunica media and neointima. ET(A) binding in the tunica media of ungrafted saphenous vein was greater than that in the carotid artery or vein grafts, but greater in the vein graft compared to the carotid artery. Immunoreactive ET-1 was located in endothelial cells and throughout the neointima of the vein graft. Dense ET-1 binding (to both ET(A) and ET(B) receptors) was also associated with microvessels in the adventitia within the graft. In vein grafts, there was strong ET(B) binding to neutrophils which were present in high numbers at the subendothelium and within the adventitia. It is concluded ET(A) receptors may play a role in vein graft thickening at the medial and neointimal VSMC level, whereas ET(B) receptors may play a role in microangiogenesis. The higher levels of ET(A) receptors in the tunica media of ungrafted saphenous vein relative to the carotid artery and vein graft may also render this conduit susceptible to neointima formation. These data indicate that studies on the effect of ET receptor antagonists on the pathobiology of vein graft disease is warranted.

Effect of ischaemia and reperfusion on the intracellular concentration of taurine and glutamine in the hearts of patients undergoing coronary artery surgery.

Taurine and glutamine are the most abundant intracellular free amino acids in mammalian hearts where changes in their intracellular concentrations are likely to influence a number of cellular activities. In this study we investigated the effects of ischaemia and reperfusion on the intracellular concentrations of taurine and glutamine in the hearts of patients undergoing coronary artery bypass surgery using cold crystalloid or cold blood cardioplegic solutions. Ischaemic arrest (30 min), using cold crystalloid cardioplegic solution (n = 19), decreased the intracellular concentrations (micromol/g wet weight) of taurine (from 9.8 +/- 0.8 to 7.7 +/- 0.7, P < 0.05) and glutamine (8.7 +/- 0.5 to 7.2 +/- 0.6). After 20 min of normothermic reperfusion the fall in taurine and glutamine was maintained (7.5 +/- 0.5 and 7.4 +/- 0.7 for taurine and glutamine respectively). Myocardial ischaemic arrest with cold blood cardioplegic solution (n = 16) did not cause a significant fall in tissue taurine or glutamine. However, on reperfusion there was a marked fall in the intracellular concentrations of taurine (9.4 +/- 0.5 to 6.5 +/- 0.7) and glutamine (8.0 +/- 0.7 to 5.8 +/- 0.4). The fall in amino acids was associated with a fall in ATP and a rise in tissue lactate. This work demonstrates that irrespective of the cardioplegic solution used to arrest the heart, there is a marked fall in tissue taurine and glutamine which may influence the extent of recovery following surgery. The fall in taurine is largely due to efflux whereas changes in glutamine are due to both transport and metabolism. Ischaemia, hypothermia and changes in the transmembrane concentration gradients are the likely factors responsible for the changes in tissue amino acids.

Evaluation of the hemodynamic performance of small carbomedics aortic prosthesis using dobutamine-stress doppler echocardiography

BACKGROUND The well-known correlation between prosthetic valve orifice area and transvalvular gradients has raised concerns about the presence of significant residual gradients when the size of the prosthesis that can be implanted is limited by the presence of a small aortic annulus. METHODS Dobutamine-stress Doppler echocardiography was used to evaluate the hemodynamic performance of small CarboMedics aortic prostheses (19 mm and 21 mm) in 18 patients (16 women; mean age, 64 years) who had undergone aortic valve replacement 23.5 +/- 19 months (standard deviation) previously. Dobutamine infusion was started at a rate of 5 micrograms.kg-1.min-2 and increased to 10 and 20 micrograms.kg-1.min-2 at 15-minute intervals. Pulsed and continuous wave Doppler studies were performed at rest and at the end of each stage. Effective orifice area, performance index, and discharge coefficient of both valves were calculated, and peak and mean velocity and pressure drop across the prostheses were measured. RESULTS Heart rate and cardiac output increased by 74% and 94%, respectively, and mean arterial blood pressure decreased by 9% at maximum stress. Effective orifice area, discharge coefficient, and performance index were comparable in both valve sizes at rest and maximum stress. Also, there was no significant difference in mean transvalvular pressure drop (gradient) for 19-mm and 21-mm prostheses at rest (8.1 +/- 8.4 and 4.8 +/- 3.8 mm Hg) or maximum stress (15.1 +/- 14.2 and 8.8 +/- 5.8 mm Hg, respectively). No significant correlation could be demonstrated between transvalvular pressure drop and patients body surface area. CONCLUSIONS These data show that 19-mm and 21-mm CarboMedics aortic prostheses exhibit equally favorable hemodynamic performance with minimal pressure gradient, both at rest and under stress conditions.