Three day Magnesium Administration Prevents Atrial Fibrillation after Coronary Artery Bypass

Transcription

1 REVIEW OF LITERATURE Annals of Cardiac Anaesthesia 2005; 8: Review of Literature 161 Three day Magnesium Administration Prevents Atrial Fibrillation after Coronary Artery Bypass Kohno H, Koyanagi T, Kasegawa H, Miyazaki M Ann Thorac Surg 2005; 79: Despite substantial improvements in surgical techniques and perioperative managements, atrial fibrillation (AF) remains a common complication after coronary artery bypass grafting surgery (CABG). Its onset is usually between 24 and 96 hours after surgery, with a peak incidence on the second to third postoperative days. AF potentially leads to prolonged hospitalization and significant morbidity, particularly haemodynamic deterioration and thromboembolism. Almost 80% of patients undergoing CABG have reduced total and ionised serum magnesium levels postoperatively. The correlation between magnesium deficiency and postoperative AF is still unknown. However, most postulated mechanisms to explain their relationship have consistently referred to the role of magnesium in stabilizing the cellular transmembrane potential, suppressing excessive cellular calcium influx and energy demands, preserving myocardial metabolites and reducing the severity of reperfusion injuries. The efficacy of magnesium administration in preventing the occurrence of AF after CABG remains controversial. Optimal dose and timing also await scientific authentication. In a retrospective study the authors evaluated the effectiveness of postoperative 3-day magnesium sulphate administration and discuss the possible dosing strategies for which the magnesium treatment can be beneficial. Two hundred consecutive patients underwent isolated, initial CABG. The first 100 patients did not receive the prophylactic treatment whereas the next 100 were treated with magnesium postoperatively. Patients in the magnesium-treated group received 10 mmol (2.47 g) of magnesium sulphate infused daily for three days after surgery. All patients had sinus rhythm preoperatively. Perioperative clinical details of the patients were compared between groups with and without magnesium treatment and between patients who did and did not experience AF postoperatively. The electrocardiogram and haemodynamic variables were measured continuously throughout the operation and during the period in the intensive care unit. After discharge from the intensive care unit, all patients were monitored with an alarmtriggered telemetry system and double checked for unnoticed events every morning for at least 6 postoperative days. Serum magnesium concentration was measured before surgery, immediately after surgery and every morning for 4 days postoperatively. Serum potassium and calcium concentrations were also measured and maintained perioperatively within normal limits. AF was considered significant if it persisted for greater than 15 minutes or required treatment because of intolerable symptoms and haemodynamic deterioration. The incidence of AF was 35% in the untreated group compared with 16% in the magnesium-treated group (p = 0.002). Multivariate logistic regression analysis revealed that advanced age, decreased left ventricular ejection fraction, and absence of magnesium therapy were independent predictors of postoperative AF. For patients receiving the magnesium therapy, advanced age and decreased ejection fraction were the independent factors that predicted the arrhythmia. The authors concluded that three day magnesium infusion is effective in reducing the incidence of AF occurring after CABG. However, in older patients or in patients with reduced left ventricular function, magnesium treatment alone is insufficient for prophylaxis of postoperative AF. Annals of Cardiac Anaesthesia 2005; 8:

2 162 Review of Literature Annals of Cardiac Anaesthesia 2005; 8: Sildenafil Prevents Endothelial Dysfunction Induced by Ischemia and Reperfusion via Opening of Adenosine Triphosphate Sensitive Potassium Channels; A Human in vitro Study. Gori T, Sicuro S, Dragoni S, Donati G, Forconi S, Parker JD Circulation 2005; 111: Vascular endothelium is important in regulating the vasomotor, thrombotic and inflammatory mechanisms that are critical in the pathophysiology of tissue injury induced by ischaemia and reperfusion (IR). Endothelial cells appear to be more sensitive to IR than myocytes, and during ischaemia, a state of reduced endothelial responsiveness to specific stimuli (endothelial dysfunction) temporarily precedes (and contributes to) the appearance of IR-induced tissue necrosis. Sildenafil citrate is a highly specific inhibitor of type V phosphodiesterase, an enzyme responsible for the catabolism of cgmp in multiple vascular districts. Although currently marketed for the treatment of erectile dysfunction, sildenafil citrate has beneficial effects in other cardiovascular conditions, including congestive cardiac failure and pulmonary hypertension as well as in the setting of endothelial dysfunction. Recent studies have shown that sildenafil administration induces potent cardiac protection against IR. The cardiac protection is consistent with the research reporting that both nitric oxide and nitric oxidederived cgmp can induce the same state of protection via opening of adenosine triphosphatesensitive potassium channels (K ATP ). Although majority of research in this area has involved (cardio)myocytes, multiple lines of evidence suggest that stimuli leading to K ATP channel opening can induce a potent protective effect against IR in different cell types, and recent studies have confirmed that similar mechanisms can also modulate the endothelial response to IR. In a double blind placebo controlled cross over design, the authors investigated whether sildenafil can prevent the impairment in endothelium dependent vasodilatation induced by IR in humans. Ten healthy male volunteers in the age group of years were randomized to oral sildenafil (50 mg) or placebo. Two hours later, endothelium dependent, flow mediated dilatation (FMD) of the radial artery was measured before and after IR (15 min of ischaemia at the level of brachial artery followed by 15 min of reperfusion). Seven days later, patients received the other treatment (i.e. placebo or sildenafil) and underwent the same protocol. Pre-IR radial diameter and FMD as well as baseline radial artery diameter after IR were similar between the visits. After placebo administration, IR significantly blunted FMD (before IR: 7.9±1.1%, after IR 1.2±0.7%, p <0.001). Importantly, sildenafil limited this impairment in endothelium dependent vasodilatation (before IR 7.0±0.9%, after IR 6.2±1.1. p=ns; p<0.01 compared with placebo). The protective effect was completely prevented by previous administration of sulfonylurea glibenclamide (glyburide 5mg), a blocker of K ATP channels (n=7; FMD before IR 10.3±1.5%, after IR 1.3±1.4%, p <0.05) in a separate protocol. The authors concluded that oral sildenafil induces potent protection against IR-induced endothelium dysfunction through opening of K ATP channels. Further studies are proposed to investigate in greater detail the mechanisms of this effect, and most importantly the potential clinical implications of the pharmacological preconditioning of endothelium. 162

3 Annals of Cardiac Anaesthesia 2005; 8: Review of Literature 163 Comparison of Three Anesthetic Techniques for Off-Pump Coronary Artery Bypass Grafting: General Anesthesia, Combined General and High Thoracic Epidural Anesthesia, or High Thoracic Epidural Anesthesia Alone Kessler P, Aybek T, Neidert G, et al. J Cardiothorac Vasc Anesth 2005; 19: General anaesthesia is the most commonly used anaesthetic technique and considered the gold standard for coronary artery bypass grafting (CABG) performed either on-pump or off-pump. Within the last few years, however, high thoracic epidural anaesthesia (TEA) as an adjunct to GA has become more prevalent and has been shown to be potentially beneficial in patients with coronary artery disease. Potential advantages of TEA include thoracic sympathicolysis, decreased heart rate and endogenous stress response, reduced risk of myocardial ischaemia perioperatively, improved haemodynamic stability and postoperative pulmonary functions. The authors conducted this prospective study to compare GA, combined GA and TEA and TEA alone in terms of intra- and early postoperative haemodynamics, blood loss, postoperative pain scores, length of intensive care unit and hospital stay and patient s satisfaction during and after off-pump CABG. Ninety adult patients with symptomatic coronary artery disease were prospectively enrolled in this study. All patients underwent elective CABG on beating heart, either using GA, GA+TEA or TEA alone (n=30 each group). In the GA+TEA and TEA group, an epidural catheter was inserted at the T1/2 or T2/3 interspace on the day before surgery. In the operating room, a continuous epidural infusion with ropivacaine 0.5% and sufentanil 1.66 µg/ml was started at a rate of ml/hr until the desired anaesthetic level was achieved. In case of GA or GA+TEA, anaesthesia was induced with propofol (1.5 mg/kg) and remifentanil (1 µg/kg) and 0.1 mg/kg of cisatracurium was administered to facilitate tracheal intubation. Anaesthesia was maintained with continuous infusion of propofol ( µg/kg/min) and remifentanil ( µg/ kg/min). Patients undergoing GA without TEA received intravenous metamizole (Novalgin) 15 mg/kg before skin incision. Intravenous piritramide, a µ-receptor agonist with a potency of 0.7 compared with morphine 0.1 mg/kg was administered after completion of coronary anastomosis and repeated during wound closure. If patients with an epidural catheter complained of pain exceeding a visual analogue score of 50, the hourly epidural infusion rate was increased by 1 ml and IV piritramide 7.5 mg administered simultaneously for instant pain relief. All the three groups were comparable regarding the surgical approaches and the number of anastomoses. Four patients (GA, n = 2; GA+TEA n = 2) who required unplanned cardiopulmonary bypass, and 4 patients in the TEA group who underwent unexpected intubation because of pneumothorax (n = 2), phrenic nerve palsy, or incomplete analgesia were excluded from further analysis. Intraoperative heart rate decreased significantly with both GA+TEA and TEA. None of the patients with TEA alone was admitted to the intensive care unit, they all were monitored on average for 6 hours postoperatively in the intermediate care unit and allowed to eat and drink as desired on admission. Postoperative pain scores were lower in both groups with TEA. There were no differences among groups in patient s overall satisfaction. The authors concluded that all anaesthetic procedures were equally safe from the clinician s standpoint. However, GA+TEA appeared to be the most comprehensive, allowing for revascularization of any coronary artery, providing good haemodynamic stability and reliable postoperative pain relief. Nonetheless, the actual and potential risks of TEA during cardiac surgery should not be underestimated. 163

4 164 Review of Literature Annals of Cardiac Anaesthesia 2005; 8: Does Preoperative Coronary Angioplasty Improve Perioperative Cardiac Outcome? Godet G, Riou B, Bertrand M, et al. Anesthesiology 2005; 102: Patients with coronary artery disease have a high risk of perioperative myocardial infarction, arrhythmias, cardiac failure and death. Preoperative cardiac evaluation has been recognized as an important objective before major surgery in patients with a high cardiac risk. Based on clinical markers, functional capacity, and/or evidence for high risk of an adverse outcome based on noninvasive test results, coronary angiography may be planned in some patients undergoing aortic surgery, to indicate the need for coronary revascularization before surgery. Coronary artery bypass graft (CABG) has been shown to be effective in reducing perioperative events in patients with significant coronary artery disease and undergoing major noncardiac procedures. Percutaneous coronary intervention (PCI) revascularization is now increasingly used in these patients to reduce perioperative cardiac morbidity and mortality although, few data are available on the impact of this invasive prophylactic procedure on the postoperative outcome. PCI is considered less invasive than CABG but some authors have reported catastrophic cardiac outcome when surgery was performed within 6 weeks after PCI. A controlled trial studying the effect of preoperative coronary revascularization on the outcome of vascular surgery in high-cardiac-risk patients did not report any significant improvement in long term outcome but only 41% of these patients underwent major abdominal vascular surgery. The authors prospectively analyzed a cohort of 1152 patients after abdominal aortic surgery in which 78 patients underwent PCI. They used propensity score analysis, which tends to balance of all the observed co-variates associated with the exposure to PCI. Using a logistic regression model, the authors determined variables associated with a severe postoperative coronary event or death in patients without PCI. Five variables (age >75 years, blood transfusion >3units, repeated surgery, preoperative haemodialysis and previous cardiac failure) independently predicted (with 94% correctly classified) a severe postoperative coronary event and five variables (age >75 years, repeated surgery, previously abnormal ST segment/t waves, previous hypertension and previous cardiac failure) independently predicted (with 97% correctly classified) postoperative death. In the PCI group, the observed percentage of patients with a severe postoperative coronary event (9.0% [95% confidence interval, ] or death (5.1% [95% confidence interval, ]) were not significantly different from the expected percentages (8.2 and 6.9 % respectively). When all the patients were pooled together, the Odds ratios of PCI were not significant. The authors conclude that preoperative PCI when necessary, can be performed safely but does not seem to modify significantly the immediate postoperative cardiac risk. 164

5 Annals of Cardiac Anaesthesia 2005; 8: Review of Literature 165 First Clinical Experience with the VSTENT: A Device for Direct Left Ventricle-to-Coronary Artery Bypass Vicol C, Reichart B, Eifert S, et al. Ann Thorac Surg 2005; 79: Traditional myocardial revascularization involves either surgical restoring of coronary blood flow, using a conduit, or percutaneous treatment of the native coronary artery stenosis using balloon angioplasty and stenting. In bypass conduits like saphenous vein graft, in situ and internal thoracic artery, the graft-to-coronary blood flow occurs almost exclusively during diastole similar to native coronary circulation. In contrast, ventricular sourcing is an alternative approach to myocardial revascularization based on the concept of systolic filling of the epicardial coronary arteries serving as a reservoir to deliver arterial blood to the capillaries. Recently, a stent-based approach for surgical implantation of an expanded polytetrafluoroethylene (EpTFE) membrane covered stent (VSTENT) to provide a left ventricleto-coronary artery bypass (VCAB) was developed. The authors present their initial experience using this technique. 12 patients 21 years of age who required non-emergency, multivessel coronary artery bypass grafting (CABG) with or without cardiopulmonary bypass (CPB) were included in the study. Surgery was performed on-pump with arrested heart in 4 patients, on-pump with beating heart in 6 patients, and off-pump in 2 patients. All the patients underwent a VCAB procedure concomitant to CABG. Diagnosis of myocardial infarction was based on ECG changes as new persistent Q wave and ST-segment elevation greater than 1 mm in two or more limb leads and / or greater than 2 mm in two or more precordial leads as well as a serum creatinine kinase MB (CK- MB) activity greater than 40 IU/L, 6 to 48 hours after operation. Selective angiography of the native coronary arteries and the bypass conduits was performed before discharge from the hospital in all patients. Target coronary artery for the VSTENT was a diagonal branch in 5 patients, an intermediate branch in 1 patient, and a marginal branch in 6 patients. The diameter of the target vessel was 2.0 mm in 8 cases and 2.5 mm in 4 cases and the grade of stenosis of the target artery was higher than 75%. In each patient only one VSTENT was implanted. Mean time for the VCAB was 23+5 minutes. Successful VSTENT implantation was achieved in 11 to 12 patients without complications. In one patient VCAB was not successful and an aortocoronary venous bypass was performed to revascularize the target artery distal to the failed VCAB. The further intraoperative course of this patient was uneventful. In addition to the VCAB, all patients received a left internal thoracic artery (LITA)-to-left anterior descending (LAD). In 2 patients, a total arterial myocardial revascularization was performed and in 9 patients aorta to coronary venous conduits were implanted. Mean number of anastomoses per patient was 2.4±0.8. Left ventricular ejection fraction did not change significantly postoperatively; 77±3.3 % before surgery versus 83±4.1 % after surgery. The mean chest tube drainage on the operative day was 1,276±1,058 ml which decreased to 557±326 ml on the second postoperative day in 5 patients. A re-thoracotomy and blood substitution in 5 of the first 6 patients was required. Mean CK-MB activity measured 6 hours postoperative was 19.7±8.4 IU/L (9.2 to 31.7 IU/L) and 24±19.5 IU/L (8.9 to 75.1 IU/l) on the second postoperative day. Mean postoperative ventilation time was 16.4±20.7 hours. The preliminary observations in this study suggest that VCAB is feasible and potentially safe in the shortterm postoperative follow-up, particularly with increasing experience. Though the VSTENT is a promising tool for myocardial revascularization, long-term safety, patency, and performance of the device need to be determined. 165

6 166 Review of Literature Annals of Cardiac Anaesthesia 2005; 8: Resource Utilization in On-and Off-Pump Coronary Artery Surgery: Factors Influencing Postoperative Length of Stay - an Experience of 1,746 Consecutive Patients Undergoing Fast-Track Cardiac Anesthesia Scott BH, Seifert FC, Grimson R, Glass PS J Cardiothorac Vasc Anesth 2005; 19: Coronary artery bypass surgery without cardiopulmonary bypass (off pump coronary bypass [OPCAB]) has gained popularity in the last few years as it avoids the deleterious effects of extracorporeal circulation that persist despite technological advances in perfusion techniques. Recent reports have shown that OPCAB is a safe and effective alternative to conventional CABG especially in women and elderly patients. During the initial development of cardiac surgery, the focus was on reducing mortality that has gradually shifted towards reducing morbidity and costs. Resurgence of interest in OPCAB is associated with the expectation that avoiding deleterious effects of cardiopulmonary bypass pump leads to better resource utilization. The authors hypothesized that there would be a difference in resource utilization between the on- and off-pump groups. The goal of the present study was to examine factors influencing resource utilization in patients undergoing on-pump coronary artery bypass surgery and OPCAB. In an observational study of 1746 consecutive male and female patients undergoing primary coronary artery bypass graft (CABG) surgery over a period of 3 years, the authors examined time to extubation, packed red blood cell (PRBC) transfusion, intensive care length of stay (ICULOS), preoperative and postoperative length of stay (PLOS) and total length of stay (LOS). Eight hundred eighty one patients underwent CABG with pump and 865 patients underwent OPCAB. The mean time to extubation after surgery was 7.4 hour for on-pump patients and 5.8 hour for OPCAB group (p <0.001); 73.7 % of patients in the on-pump group received PRBC transfusion as compared with 48.6% of the OPCAB group (p<0.001). The mean ICULOS for on-pump group was 1.6 days and for OPCAB group 1.45 days (p=0.006). PLOS was 6.5 days for the on-pump group and 5.6 days for the OPCAB group (p<0.001). Mean total LOS was 9.7 days for the on-pump group and 8.8 days for the OPCAB group (p<0.001). PLOS is correlated with several clinical and demographic variables. Linear and Logistic Regression models were used to assess the effects of on/off pump on PLOS. Use of pump is significantly correlated with increased PLOS (p< 0.001, Kendall s correlation) and pump use is strongly associated with transfusion (odds ration = 2.95, p < 0.001), which in turn is a determinant of PLOS. There were no significant differences between the on-and off-pump groups in the incidence of postoperative complications except for bleeding requiring re-exploration and ventilatory support for more than 72 hours. Incidence of bleeding was 3.3 % in the on-pump group and 1.7% in the OPCAB group (p=0.038). In the on-pump group, 3% of the patients required >72 hours to postoperative tracheal extubation as compared with 1.5% in the OPCAB group (p=0.041) and the hospital morbidity and mortality was 2.7% and 1% (p=0.010) respectively. In conclusion, the authors examined differences in resource utilization between on- and off-pump surgery in a large group of patients at a tertiary care heart centre. The data shows that patients undergoing on-pump CABG have significantly longer time to tracheal extubation, increased blood use, longer ICULOS, PLOS and total LOS and higher hospital morbidity and mortality which would translate into significant differences in the expenses associated with these two surgical approaches to coronary surgery. 166