Interactive Cardiovascular and Thoracic Surgery 2:584-588(2003)
© 2003 European Association of Cardio-Thoracic Surgery
Institutional review - Cardiac general |
Comparison of the immediate post-operative outcome of two different myocardial protection strategies: antegrade–retrograde cold St Thomas blood cardioplegia versus intermittent cross-clamp fibrillation
Joseph Alex*,
Junaid Ansari,
Raphael Guerrero,
Jeysen Yogarathnam,
Alex R.J. Cale,
Steven C. Griffin,
Michael E. Cowen and
Levent Guvendik
Castle Hill Hospital, Hull, UK
* Corresponding author. The Cottage, Main Road, Covenham St Bartholomew, Louth LN11 0PF, UK. Tel./fax: +44-1507-363541
mrjosephalex{at}yahoo.co.uk
Received May 28, 2003;
received in revised form July 21, 2003;
accepted July 28, 2003
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Abstract
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The objective of this study was to compare the immediate post-operative outcome of two myocardial protection strategies. Data of consecutive elective first time coronary artery bypass grafting (CABG) were analysed: Group A ( , antegrade–retrograde cold St Thomas blood cardioplegia) and Group B ( , intermittent cross-clamp fibrillation). Age, angina class, myocardial infarction (MI), pre-operative rhythm, respiratory disease, smoking, diabetes mellitus (DM), hypertension (HT), renal function, cerebrovascular disease, body mass index (BMI) and Parsonnet score were comparable. Significant differences existed in gender ( ), peripheral vascular disease (PVD) ( ), heart failure class ( ), left ventricular (LV) function ( ), disease severity (), left main stem (LMS) () and preinduction intra-aortic balloon pump(IABP) ( ). Group A had more grafts ( ), longer bypass () and cross-clamp time (). Post-operative inotrope, MI, arrhythmias, neurological, renal complications, multi-organ failure, sternal re-wiring, ventilation, length of stay and mortality were comparable. There was higher IABP usage and longer intensive therapy unit (ITU) stay () in Group B. Chronic obstructive airway disease (COAD), renal dysfunction, cross-clamp time, bypass time, post-operative inotrope or IABP and re-exploration predicted longer ITU stay. Intermittent cross-clamp fibrillation is a versatile and cost-effective method of myocardial protection, with the immediate post-operative outcome comparable to antegrade–retrograde cold St Thomas blood cardioplegia in elective first-time CABG.
Key Words: Coronary artery bypass grafting; Myocardial protection; Outcome
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1. Introduction
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The quality of myocardial protection during coronary revascularisation has a profound and direct effect on post-operative cardiac function, recovery and complications. Despite the increasing application of off-pump surgery, by far the vast majority of coronary revascularization the world over continues to be performed on-pump. Two of the commonly used myocardial protection strategies for on-pump coronary revascularisation are antegrade–retrograde cold-blood cardioplegia and intermittent cross-clamp fibrillation. Many studies have compared the results of off-pump to on-pump coronary revascularisation, but to date, very few studies have compared the immediate post-operative outcome of using antegrade–retrograde cold blood cardioplegia to intermittent fibrillatory arrest. In our unit surgeons have been using both methods with good results. The objective of this study was to analyse and compare the immediate post-operative clinical outcome of using the two different myocardial protection strategies.
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2. Materials and methods
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We compared the immediate post-operative results of 1454 consecutive elective first time coronary artery bypass grafting (CABG) done by two surgeons over a 5-year period from December 1997 to December 2002. Emergency, urgent, expedite and redo cases were not included. One surgeon used only antegrade–retrograde cold St Thomas blood cardioplegia for all CABG cases while the other used only intermittent cross-clamp fibrillation. All data were prospectively entered into the patient analysis and tracking system (PATS) database. Subsequent to data entry, it was independently checked, compared to patient notes and validated for completeness and accuracy. Group A (, antegrade–retrograde cold blood cardioplegia) and Group B (, intermittent cross-clamp fibrillation). Chi-square test and Fisher's test was used for categorical data while the Student's t-test was used for numerical data. Statistical significance was set at  . Variables entered for multivariate logistic regression analysis to identify predictors of prolonged intensive therapy unit (ITU) stay were, age, gender, respiratory disease, pre-operative renal function, left ventricular (LV) function, left main stem (LMS) disease, Parsonnet score, bypass time, cross-clamp time, inotropes, intra-aortic balloon pump (IABP) usage, re-exploration, post-operative MI, post-operative renal complications, and neurological complications. The SPSS version 11.0 for Windows program (SPSS Inc, Chicago, IL, USA) was used for statistical analysis.
The anaesthetic technique including premedication, induction, maintenance and reversal of anaesthesia were essentially similar in both groups. Cardiopulmonary bypass was established between the right atrium and ascending aorta using a 34/48-F two-stage venous cannula (Medtronic VC2, 93448C, Minneapolis, MN, USA) and a 24-F straight-tip flexible arch arterial cannula (Medtronic DLP, 71424), respectively connected to the perfusion tubing system (COBE Cardiovascular, 025006021, Sorin Biomedica UK Ltd, Gloucester, UK). The Stockert SIII roller pump bypass machine (Stockert Instrumente GmbH, Munich, Germany) using adult hollow fiber oxygenator with integral hardshell venous cardiotomy reservoir (D903 Avant PHISIO/M, 05334, DIDECO, Mirandola, Italy) and a 38 µm arterial line filter (Medtronic Affinity352, 61399401153, Minneapolis, MN, USA) was used in all cases. Moderate systemic hypothermia (32–33 °C) was maintained during bypass in all cases.
The cardioplegia solution used in Group A consisted of 50 ml of St Thomas formula (Manor Park Pharmaceutical, Bristol, UK) mixed with 450 ml of Ringer's solution and 500 ml of oxygenated blood from the pump maintained at 4 °C. Following cross-clamp application antegrade instillation was done through a 11-F aortic root cannula (Medtronic DLP, 24009) at a pressure of 100 mmHg, followed by retrograde instillation through a 15-F retrograde coronary sinus perfusion cannula with a manual-inflate cuff (Medtronic DLP, 94665) at a pressure of 20–40 mmHg. The first dose of 400 ml antegrade and 600 ml retrograde was followed by 200 ml retrograde every 15 min. This St Thomas blood cardioplegia solution has been used in our unit for the past 12 years and has been found to be safe and efficient. All bottom ends were anastomosed with the aorta cross-clamp and the cardioplegic arrest of the myocardium, followed by declamping and top-end anastomosis during partial aortic occlusion while the heart started beating again.
In Group B ventricular fibrillation was induced using 10 mA alternate current through a fibrillator prior to cross-clamping of the aorta for bottom-end anastomosis. On completion of each bottom end the aorta was declamped, and the heart perfused and defibrillated with 10–15 J direct current shock before the corresponding top end was anastomosed. This sequence was repeated with each graft. Systemic rewarming was commenced during the final distal anastomosis in both groups. In both groups weaning from the bypass machine was attempted when the nasopharyngeal temperature reached 36 °C.
The baseline characteristics of both groups are shown in Table 1. Both groups were comparable in terms of age, Canadian Cardiac Society (CCS) angina class, previous Q wave MI, pre-operative rhythm, pulmonary disease, smoking, diabetes mellitus (DM), hypertension (HT), renal function, cerebrovascular status, peripheral vascular disease (PVD), body mass index (BMI) and Parsonnet score. Group B had greater number of females (), more severe NYHA heart failure class (), more severe coronary disease (), greater number of patients with left main stem disease () and poorer LV function (). There were more patients with peripheral vascular disease in Group A ().
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3. Results
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Table 2 shows intra-operative and post-operative variables. Group A had a greater number of grafts (), longer bypass times () and cross-clamp times (). Post-operative outcome in both groups were comparable in terms of inotrope usage, post-operative myocardial infarction (MI), post-operative arrhythmias, cerebrovascular complications, renal complications, multi-organ failure, sternal re-wiring, duration of ventilation, total length of stay and mortality. Although not statistically significant, IABP usage was higher in Group B (). The duration of intensive care unit (ITU) stay () was also longer in Group B.
Multivariate logistic regression analysis identified chronic obstructive airway disease (COAD) ( ), pre-operative renal dysfunction ( ), prolonged cross-clamp time ( ), bypass time ( ), inotrope usage () or IABP support () and re-exploration (), to be predictors of longer ITU stay (Table 3).
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4. Discussion
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The principle of cardioplegic arrest is to minimize cellular metabolism and maximize cellular energy preservation without causing myocardial injury. In addition to variations in temperature and composition of cardioplegia, different perfusion strategies to maximize coronary distribution can be adopted [1–10]. Simply arresting the heart reduces the myocardial oxygen demand by nearly 90%; by cooling the myocardium cold cardioplegia significantly reduces the remaining 10% myocardial oxygen demand. Warm and tepid blood cardioplegia, on the other hand, is believed to better preserve cellular enzymes systems, and to limit cellular swelling and myocardial oedema. The major concern with the antegrade method is poor preservation of the myocardium distal to coronary occlusion or stenosis. In 1994 Weisel and his colleagues used the antegrade–retrograde technique which allowed a better distribution of cardioplegia into the myocardium.
The technique of intermittent cross-clamp fibrillation depends on reducing myocardial oxygen demand by moderate hypothermia (32–33 °C), simultaneous work-load reduction by emptying the heart and ischaemic preconditioning of the myocardium [11–15]. The effect of short periods, 15–20 min, of ischaemia can be rapidly reversed by coronary reperfusion on releasing the aortic cross-clamp. This method offers greater versatility and intra-operative flexibility, at a reduced cost. Blood cardioplegia, owing to its ability to reduce metabolic oxygen demand and conserve myocardial energy stores. is generally considered to be superior to intermittent cross-clamp fibrillation in cases presenting with cardiogenic shock, extending myocardial infarction and when a prolonged cross-clamp time is expected. However, in elective cases the advantages of blood cardioplegia over intermittent cross-clamp fibrillation are not so clear cut. The few studies to date measuring biochemical markers of myocardial injury and intracardiac hemodynamics have revealed both techniques to be comparable. Although elevation of biochemical markers and acute intracardiac hemodynamic changes may indicate myocardial injury, it fails to predict the clinical outcome in most cases. Thus the relevance of using clinical end points, especially the immediate post-operative clinical outcome, morbidity and mortality, lies in the fact that poor outcome is usually a manifestation of injury to a critical mass of myocardial tissue beyond the compensatory capacity of the uninjured myocardium.
In our study the post-operative outcome of both groups were essentially comparable. The additional cost of the antegrade–retrograde cannulae and perfusion kits was £77 adding up to a total of £60 291 for the 671 patients in Group A. Although the cross-clamp time was significantly higher in Group A this was not reflected by an increase in post-operative inotropic or IABP support. As mentioned earlier, due to the higher level of persistent cellular metabolism, the risk of myocardial injury during prolonged cross-clamp time is higher with the technique of intermittent cross-clamp fibrillation than with antegrade–retrograde cold blood cardioplegia. The subgroup requiring IABP support in both groups had a longer cross-clamp time compared to the corresponding group mean (Group A 40.8±15 vs. 39.1±12.4; Group B 30.7±9.5 vs. 25.9±8.6). The significantly higher critical LMS disease and poor LV function in Group B necessitated more pre-operative IABP insertion prior to induction of anaesthesia, which was continued post-operatively. The slightly longer ITU stay in Group B was a direct result of the higher post-operative IABP usage and significantly poorer LV function in this group. The diagnosis of neurological complications – confusion/transient ischaemic attack (TIA)/cerebrovascular accident (CVA) – was based on clinical and/or radiological findings by the surgeons and later confirmed by the neurologist in cases of CVA. Interestingly, there was no significant difference in the incidence of TIA or CVA between the groups. From the results of our analysis we conclude that intermittent cross-clamp fibrillation is a versatile and cost-effective technique of myocardial protection, in elective cases, with immediate post-operative results comparable to antegrade–retrograde cold blood cardioplegia.
doi:10.1016/S1569-9293(03)00170-1
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Abstract
1. Introduction