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Eur J Cardiothorac Surg 1999;15:685-690
© 1999 Elsevier Science NL
Bristol Heart Institute, Bristol Royal Infirmary, Bristol BS2 8HW, UK
Received 21 September 1998; received in revised form 30 January 1999; accepted 2 February 1999.
Corresponding author. Tel.: +44-117-928-3145; fax: +44-117-929-9737; e-mail: g.d.angelini@bristol.ac.uk
| Abstract |
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Key Words: Beating heart surgery Myocardial protection Cardiopulmonary bypass
| Introduction |
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Recently, there has been a revival of interest in performing CABG on the beating heart [8] [9] [10] [11]. Early results suggest better preservation of left ventricular contraction and mitochondrial function than when cardioplegic arrest is used [11] [12] [13]. There is however no data available on the effects of off pump coronary revascularization on myocardial function, myocardial tissue injury and clinical outcome as part of a prospective randomized study in elective patients.
| Material and methods |
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Anaesthetic technique
Anaesthetic technique was standardized for all patients. This consisted of total intravenous anaesthesia with a propofol infusion at 3 mg/kg per h combined with a remifentanil infusion at 0.51 mg/kg per min. Neuromuscular blockade was achieved by 0.10.15 mg/kg pancuronium bromide or vecuronium and the lungs ventilated to normocapnia with air and oxygen (4550%) without positive end expiratory pressure (PEEP). In the on pump group, metaraminol or phentolamine were used as required to maintain the systemic pressure between 5060 mmHg. In the off pump group, mean arterial pressure of 60 mmHg or above was maintained with increments of metaraminol 0.51.0 mg or volume as requested by the haemodynamic condition, in combination with Esmolol to maintain heart rate at <65 beats per min.
Heparin and protamine management
In the on pump group, the heparin was given at a dose of 300 IU/kg to achieve a target activated clotting time (ACT) of 480 s or above before commencement of CPB. The ACT was monitored during the bypass period (every 15 min) and an additional 3000 IU of heparin was administered if required. In the off pump group, heparin 100 IU/kg was administered prior to the start of the first anastomosis. The target ACT in this group was of 250350 s. Protamine was used at the end to reverse the effect of heparin.
Surgical technique
Group A on pump
Cardiopulmonary bypass was instituted using ascending aortic cannulation and a two stage venous cannulation in the right atrium. A standard CPB circuit was used: a Bard tubing set, which included a 40 micron filter, a Stockert roller pump (Sorin Biomedica, Midhurst, UK) and a hollow fibre membrane oxygenator (Monolyth, Sorin Biomedica, Midhurst, UK). The extracorporeal circuit was primed with 1000 ml of Hartmann's solution, 500 ml of Gelofusine, 0.5 g/kg Mannitol, 7 ml of 10% Calcium Gluconate, and 60 mg of heparin. Non-pulsatile flow was used. The flow rate throughout bypass were 2.4 l/m2 per min. Systemic temperature was kept between 34 and 36°C. Myocardial protection was achieved by using intermittent anterograde warm blood cardioplegia as per protocol by Calafiore
[14].
On completion of all distal anastomoses, the aortic cross-clamp was removed and the proximal anastomosis performed with partial clamping.
Group B off pump
The method of exposure and stabilization to perform the anastomosis was a combination of the technique previously described by our group
[15], and the use of the CTS retractor (Cupertino, USA). The target vessel was exposed and snared above the chosen point for anastomosis by using a 40 Prolene suture with a soft plastic snugger to prevent coronary injury. The coronary artery was then opened and the anastomosis performed. Visualization was enhanced by using a surgical blower-humidifier device (model SSVW- 002; Surgical Site Visualization Wand; Research Medical, Midvale, UT, USA) with one-quarter inch PVC gas line and fluid administration set connected to a regulated gas source of medical air. An intra-coronary shunt (Anastoflo Intravascular Shunt; Research Medical, Midvale, UT, USA) was used only in case of relative electrocardiographic or haemodynamic instability and excessive bleeding during the anastomosis construction.
Biochemical analysis
Recent years have shown increased use of myocardial Troponin I (Tn I) as a marker of myocardial injury
[16]
[17]. Determination of blood concentration of cardiac Tn I was conducted preoperatively in the anaesthetic room, on arrival to ITU, and at 4, 12, 24 and 48 h postoperatively. The samples were taken from the radial arterial line in all patients. The analysis was carried out using diagnostic kits provided by Boehringer Mannheim (Lewes, UK) and Sanofi Diagnostics Pasteur (Guilford, UK). Biochemical diagnostic criteria for perioperative myocardial infarction (MI) were peak Tn I concentrations higher than 3.7 µg/l and a Tn I concentration greater than 3.1 µg/l at h 12 or greater than 2.5 µg/l at h 24 as determined by Mair et al.
[18].
Cardiac function evaluation
Haemodynamic parameters (heart rate, mean arterial pressure and central venous pressure) were assessed before the operation and at 1, 4, 12, 24, 36 and 48 h after completion of the last proximal anastomosis.
Electrocardiogram
Twelve-lead electrocardiographic recordings were performed preoperatively, at 2 h, postoperatively, and then daily thereafter until day 6. All patients had continuous electrocardiogram monitoring for the first 48 h postoperatively. The incidence of dysrhythmias as well as atrial fibrillation, atrial flutter and atrio-ventricular block were recorded together with transient ischaemic events (ST segment elevation>1 mm). Clinical diagnostic criteria for perioperative MI were new Q waves of greater than 0.04 ms, and/or a reduction in R waves greater than 25% in at least two leads.
Statistical analysis
Data are presented as mean±standard deviation (SD) unless otherwise specified. Repeated measures analysis of variance (ANOVA) was used to assess haemodynamic and biochemical changes with time. Comparisons between the groups were performed using the non-parametric MannWhitney test and Fisher's Exact test where appropriate and comparisons were considered significant if P<0.05.
| Results |
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| Discussion |
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To investigate perioperative myocardial function and clinical outcome, early mortality and MI are clearly of most value. The relatively low incidence of these adverse events means that large cohorts of patients are required in order to be able to show statistically significant differences. The need for markers with improved sensitivity and specificity is required for accurate and reliable information concerning myocardial biochemistry. Electrocardiographic changes and perioperative Tn I release are non-invasive tests and are useful in the diagnosis of acute myocardial infarction [16] [18]. During myocardial injury there is a release into the serum of Tn T and I. Recent years have shown increased use of Tn I as a highly specific marker for the detection of myocardial injury [16] [18]. In the present study there were no MI's in either group as per pre-defined electrocardiographic or Tn I release criteria. Perioperative changes demonstrated a significantly lower release of Tn I during CABG performed off pump, in the first 24 h, which is a critical time for postoperative cardiac events. The off pump group also required less inotropic support in the perioperative period but this did not reach statistical difference. This data suggests that despite the many advances in terms of myocardial protection and CPB conduction, there is still an important, transient myocardial injury during cardioplegic arrest and myocardial reperfusion. Although this may not effect mortality or the incidence of MI, it may account for an increase in morbidity.
Atrial fibrillation and flutter are the most common arrhythmias occurring after cardiac surgery with an incidence in the perioperative period of 3650% [25] [26]. Atrial fibrillation is frequently not well tolerated by the patients, inducing various symptoms such as temporary haemodynamic instability, shortness of breath or chest discomfort and has also been shown to substantially lengthen hospital stay [27] [28]. In our study this was significantly reduced in the off pump group.
The present study also showed a higher incidence of blood loss and transfusion requirement in the on pump group. This may be related to the relatively high proportion of unstable (in hospital) patient procedures performed (on pump 30%, off pump 25%). Most of these patients were on aspirin and low molecular weight heparin therapy at the time of their surgery. In addition, aprotonin and tranexamic acid are not routinely used for prophylaxis against bleeding in our unit.
The overall ITU and hospital length of stay in the on pump group was higher when compared with the off pump group which reflects the earlier mobilization and fewer complications in the off pump group.
In conclusion, this prospective randomized study shows that beating heart coronary grafting is a safe and effective surgical strategy, which offers better myocardial protection and less perioperative morbidity when compared with conventional revascularization with CPB and cardioplegic arrest.
| Acknowledgments |
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| Footnotes |
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| Appendix A. Conference discussion |
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Mr Ascione: Seventeen patients required inotropic support. However, mostly, this was minimum or moderate requirement which means only 3 or 5 µg/kg per min of dopamine.
Dr T. Mesana (Marseille, France): What is your technique of myocardial protection on your on-pump series?
Mr Ascione: We used the intermittent antegrade warm blood cardioplegia supplemented with magnesium.
Dr Mesana: And did you observe echographically the paradoxical septum after your on-pump cases, observed the myocardial function?
Mr Ascione: We did not perform intraoperative echocardiographic evaluation in terms of segmental wall motion.
Dr L von Segesser (Lausanne, Switzerland): Can you tell us something about the patency rate of your beating heart circumflex anastomoses?
Mr Ascione: We did not perform postoperative angiography. Currently, we have got the clinical follow-up at a mean of 1012 months. This shows that all patients are asymptomatic in NYHA class I and with no cardiac events occurring.
Dr E. Buffolo (Sao Paulo, Brazil): We would like to confirm that our results are exactly the same.
We have experience with the beating heart surgery, and if you compare the beating and non-beating heart, operating on the beating heart, low ejection fraction is not a risk factor anymore for death. So this conclusion makes us think that perhaps what we call myocardial protection, is not really myocardial protection; it is some kind of myocardial aggression. When I have to operate the patient on pump, I use the empty beating heart technique with selective occlusion of the target coronary artery, usually marginal branches of the circumflex.
Mr Ascione: I would like to thank Professor Buffolo for his comment. I do agree that coronary beating heart surgery could further protect the myocardium in high-risk patients with low ejection fraction, by avoiding cardiopulmonary bypass and cardioplegic arrest.
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