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Ann Thorac Surg 2002;73:1436-1439
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Isolated myocardial revascularization with intermittent aortic cross-clamping: experience with 800 cases

^a Department of Cardiothoracic Surgery, Blackpool Victoria Hospital, Blackpool, United Kingdom

Accepted for publication January 21, 2002.

* Address reprint requests to Dr Raco, Department of Cardiothoracic Surgery, Blackpool Victoria Hospital, Whinney Heys Rd, Blackpool, FY3 8NR, United Kingdom
e-mail: luciaduke{at}netscapeonline.co.uk

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

 
Background. We investigated the clinical outcome of elective and nonelective myocardial revascularization performed with intermittent aortic cross-clamping.

Methods. Prospective data on 800 consecutive patients (from May 1996 to July 2000), who underwent isolated myocardial revascularization with intermittent aortic cross-clamping, were analyzed. A subgroup analysis was performed on the elective (n = 520), urgent (n = 226), and emergency (n = 54) procedures.

Results. The elective group of patients had a mean age of 61.5 ± 9.46 years, mean Parsonnet score of 5.23 ± 5.1, and mean number of distal anastomoses of 3.22 ± 1.04. The hospital mortality was 0.57%. The urgent group of patients had a mean age of 63.06 ± 10.43 years, mean Parsonnet score of 6.73 ± 6.22, and mean number of distal anastomoses of 3.21 ± 1.04. The hospital mortality was 3.09%. The emergency group of patients had a mean age of 63.75 ± 9.63 years, mean Parsonnet score of 11.24 ± 11, and mean number of distal anastomoses of 2.87 ± 0.86. Hospital mortality was 5.55%. Postoperative hospital stay was 7.11 ± 5.47 days for the elective group, 7.59 ± 5.07 days for the urgent group, and 7.40 ± 4.01 days for the emergency group.

Conclusions. Intermittent aortic cross-clamping is a safe technique both in elective and nonelective patients. The mortality and morbidity in the three subgroups analyzed reflects patients’ distribution against Parsonnet score.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

 
D uring the early years of myocardial revascularization, various techniques have been used in an attempt to preserve the myocardium. Methods that involved ventricular fibrillation with varying degrees of hypothermia and either aortic or local vessel occlusion (or both) have been routinely used. In the last decade, a widespread conversion of most surgeons to hypothermic potassium cardioplegia has occurred. This followed numerous modifications of cardioplegic solutions, after the first introduction of the cardioplegic principle by Melrose and associates [1] in 1955. The abandonment of myocardial preservation techniques that use ventricular fibrillation has made many surgeons unaware of modifications made in the older techniques that have resulted in continuously improved operative results.

A respectable minority of surgeons are still using intermittent aortic cross-clamping for myocardial protection. This concept includes ventricular fibrillation and moderate hypothermic perfusion. In particular the new insights into the phenomenon of ischemic preconditioning has also revived the protective concept of intermittent ischemic arrest [2], although results in human myocardium are still controversial [3].

This report reviews the results of 800 consecutive coronary artery bypass grafting (CABG) operations performed by a single surgeon, who uses the technique of intermittent aortic cross-clamping in both elective and nonelective procedures.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

 
Patients
From April 1996 to July 2000, 800 patients had first-time CABG with intermittent cross-clamping technique. Three subgroups were identified:

1. Elective patients (n =520): admitted from home and on a waiting list for CABG.
   
2. Urgent patients (n =226): referred by the cardiologist while in hospital for CABG during the same admission.
   
3. Emergency patients (n =54): referred by the cardiologist for CABG to be performed within 24 hours.
   

Operative procedure
After internal thoracic artery and long saphenous veins were harvested, heparin was administered and total cardiopulmonary bypass was established. A Ross basket was used to ensure venous drainage through the right atrium. Arterial return to the patient was provided through a Sorin cannula placed in the ascending aorta. A centrifugal pump and a membrane oxygenator were used. Heparin was administrated intravenously to achieve an activated clotting time greater than 600 seconds. The patient’s blood temperature was cooled down to 32°C before the aorta was clamped.

Ventricular fibrillation was induced electrically using a fibrillator delivering 10 mA. The flow delivered through the pump was reduced, and the heart emptied before the aorta was cross-clamped for the first distal anastomosis to be performed. Local vessel occlusion was obtained using 2-0 Vicryl (Ethicon, Somerville, NJ) stay sutures passed around the targeted vessel. Once the distal anastomosis was completed, the stay sutures were divided, the aortic clamp was released, and the heart was defibrillated. The heart was allowed to beat during partial aortic occlusion for completion of the proximal anastomosis. The flow delivered through the centrifugal pump was reduced every time a manipulation of the aorta was required during the procedure.

The left internal thoracic artery to the left anterior descending artery was generally the last distal anastomosis to be performed, and the last proximal anastomosis was performed during rewarming of the patient.

Patients were weaned from cardiopulmonary bypass when the esophageal temperature reached 36°C.

Data analysis
Data were prospectively collected into a commercial database (PATS Dendrite Clinical Systems Inc, Portland, OR). Statistical analysis of the data were performed using ² tests and analysis of variance (Kruskal-Wallis) when appropriate. The mortality rate was compared with the expected mortality for average Parsonnet score calculated at 0.75 of Parsonnet score. This criterion is widely applied in most cardiac centers across the United Kingdom. The surgeons working in the North West of England are asked to achieve mortality at 0.53 of Parsonnet score, and therefore the actual mortality was also compared with the predicted mortality for the North West of England.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

 
Population analysis
Tables 1 and 2 show the differences in the population characteristics in the three groups with the respective probability values for level of significance.

The average Parsonnet score was higher in both the urgent (6.73 ± 6.22) and the emergency groups (11.24 ± 11) when compared with the elective group (5.23 ± 5.1). The number of grafts was slightly lower in the emergency group (2.87 ± 0.86) when compared with the urgent (3.21 ± 1.04) and the elective (3.22 ± 1.04) patients. The cross-clamp time was also shorter in the emergency group (21.50 ± 8.72 minutes) when compared with the elective (27.07 ± 9.94 minutes) and the urgent group (27.84 ± 17.35 minutes). There were no significant differences in the length of bypass in the three groups.

Morbidity
Morbidity figures, expressed in percentages, for the three subgroups of patients are shown in Table 3. As expected, the use of inotropic agents and intraaortic balloon pump was higher in the emergency group when compared with both the urgent (p = 0.016) and the elective patients (p = 0.0003). When compared with the elective patients, the urgent patients had significantly higher occurrence of cerebrovascular accident (p = 0.03) and so did the emergency patients (p = 0.049). The emergency patients were more likely to need reintubation when compared with both the urgent (p = 0.008) and the elective patients (p = 0.018). The need for hemofiltration was also significantly higher in the emergency group (p = 0.006) when compared with the elective group. A rise in serum creatinine, the incidence of chest infection, the use of continuous positive airways pressure, and the average postoperative stay were not significantly different in the three subgroups of patients.

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

The method of intermittent aortic cross-clamping is based on moderate hypothermia (32°C) with a decrease of oxygen demand. This allows the effects of a short period of ischemia (less than 20 minutes) to be rapidly reversed by reperfusion with normal blood. Studies of Anderson and colleagues [4], Bonchek and associates [5], and Antunes and coworkers [6] showed that intermittent aortic cross-clamping provides a simple and safe protective method for coronary artery bypass grafting.

There are only a few prospective randomized trials in the literature dealing with the comparison of both different methods. In the early 1980s the study of Pepper and associates [7] revealed no significant differences in myocardial preservation between these methods in patients with at least a good left ventricular function. These results were confirmed by the study of Bonchek and colleagues [5] and by echocardiographic analysis of systolic and diastolic function by Casthely and coworkers [8]. Also, Taggart and colleagues [9] and Cohen and associates [10] showed by determining troponin T release and assessing free radical activity that both techniques provide a similar degree of myocardial protection.

In our study we reviewed a single surgeon’s series of CABG performed with intermittent aortic cross-clamping purely in terms of clinical outcome. The mortality was consistently lower than the predicted mortality for average Parsonnet score in all three groups of patients, with a global mortality for all comers of 1.62%.

Previous studies [6, 11, 12] reported a low mortality of 1% to 3%. They all reported that operative deaths occurred mainly in high-risk patients. In our series, in the elective group of patients, the first death occurred at a Parsonnet score of 9, with no deaths occurring in 410 patients up to this score and no deaths occurring in patients younger than 70 years.

Aortic clamping, and, particularly, repeated aortic clamping, is considered one of the major risks for perioperative stroke in patients with atherosclerotic disease of the ascending aorta. Bonchek and associates [12] reported 1.1% transient and 1.8% permanent neurologic events in a series of 3,000 patients operated on with repeated aortic cross-clamping. Musumeci and coworkers [13] showed that in patients with no preoperative evidence of aortic or cerebrovascular disease, repetitive clamping of the aorta in intermittent ischemic arrest is not associated with a higher rate of cerebrovascular events compared with the single-clamp technique.

In this series, neurologic disorders were seen mainly in the nonelective patients with a total incidence of stroke of 1.1% and transient ischemic attacks of 0.4% for all comers.

Some studies [11, 12] suggest that when diffuse arteriosclerotic plaques are found, the risk of thromboembolic complications is markedly higher and the operative technique should be changed toward application of cardioplegia. However, even the single cross-clamp used in cardioplegic arrest may be unsafe in patients with severe diffuse aortic arteriosclerosis; thus other methods without clamping of the aorta and local control of the coronary arteries (including off-pump CABG) are our methods of choice in such patients. In the time scale of this series, only 3 patients were revascularized by either off-pump or single-clamp cardioplegic techniques, and these patients are excluded from this series

Incidence of low cardiac output was, in this series, quantified by the postoperative need for inotropic agent infusion together with intraaortic balloon pump support. As expected this was higher in the emergency group of patients, and it is more likely to be a reflection of the poorer preoperative clinical status of the patient than a true expression of the incidence of postoperative low cardiac output related to the technique.

Interestingly, studies from Musumeci and associates [13] and Anderson and colleagues [4] found lower levels of cardiac creatine kinase and troponin T in patients with intermittent aortic cross-clamping compared with cold-blood cardioplegic arrest. These results may be related to the significantly shorter ischemic time in patients with aortic cross-clamping than in patients with cardioplegic arrest.

In conclusion, the present study shows on the simple basis of clinical outcome that intermittent aortic cross-clamping is a safe and effective technique that allows complete revascularization during both elective and nonelective CABG procedures.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

 
This article has been selected for the open discussion forum on the CTSNet Web site: http://www.ctsnet.org/doc/5499

	Invited commentary

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

 
There is probably no field that has stimulated so many studies aimed at identifying the best operative strategy or the optimal composition of cardioplegia than intraoperative myocardial protection. Although cardioplegic techniques for coronary artery bypass grafting are widely used around the world, a minority of surgeons still prefer the simplicity of noncardioplegic techniques such as intermittent aortic cross-clamping. Strengthened by new knowledge and insights into the mechanisms of ischemic preconditioning, authors of many recent studies compared the intermittent cross-clamping technique with the use of various cardioplegic solutions. In most studies, there were no substantial differences in mortality and morbidity between the two methods. However, given the low operative mortality for routine coronary artery bypass grafting, a truly randomized trial comparing differ-ent techniques would require such a large number of patients that it would be impractical.

In their excellent, provocative study, Raco and colleagues showed that in the hands of a single experienced surgeon, the intermittent cross-clamp technique is a safe and effective method. The low average duration of ischemia appears to be the most important factor for their outstanding clinical results. Many reports on intermittent aortic cross-clamping present the results of a single surgeon or a few experienced surgeons, which underlines the importance of brief ischemia times.

Although excellent results can be achieved with the intermittent cross clamp technique, recommending this technique for large-scale application or transferring these results to other cardiac centres is another matter. Intermittent cross-clamping is not preferred by trainees because longer periods of ischemia could contribute to unfavorable outcomes. Furthermore, there is no sound evidence that this technique can be applied safely to all coronary artery bypass grafting procedures. In this respect, there is no doubt that the severely atherosclerotic aorta should be approached with a no-touch technique that avoids aortic cannulation. In addition, in patients with unrecognized atherosclerotic disease of the ascending aorta, a single cross-clamp can be devastating, and multiple cross-clamping cannot be any better.

Finally, in this context it seems appropriate to mention the technique of intermittent antegrade warm blood cardioplegia that is rapidly being adopted worldwide because of its simplicity, low cost, and efficacy. To some extent, it is a simpler form of ischemia and reperfusion and is in some ways similar to the intermittent cross-clamp technique. After placement of a single cross-clamp, the heart is intermittently perfused with the patient’s whole blood enriched with potassium only. Because the heart has no electrical or mechanical activity, accumulation of oxygen debt is much slower than with the intermittent cross-clamp technique, therefore, the ischemia period can be more safely prolonged. During the period of warm reperfusion, oxygen debt is repaid, cardiac metabolism is restored, and new episodes of ischemia can be tolerated safely.

Ruggero De Paulis, MD

Cattedra di Cardiochirurgia

Università di Roma, Tor Vergata

European Hospital

via Portuense 700

00149 Rome, Italy

e-mail: depauli@tin.it.

	References

Top Footnotes Abstract Introduction Material and methods Results Comment Invited commentary References

 

1. Melrose D.G., Dreyer B., Bentall H.H., Baker J.B. Elective cardiac arrest: preliminary communication. Lancet 1955;2(Suppl 1):21.
2. Abd-Elfattah A.S., Ding M., Wechsler A.S. Intermittent aortic crossclamping prevents cumulative adenosine triphosphate depletion, ventricular fibrillation and dysfunction (stunning): is it preconditioning?. J Thorac Cardiovasc Surg 1995;110:328-339.[Abstract/Free Full Text]
3. Yellon D.M., Alkulaifi A.M., Pugsley W.B. Preconditioning the human myocardium. Lancet 1993;342:276-277.[Medline]
4. Anderson J.R., Hossein-Nia M., Kallis P., et al. Comparison of two strategies of myocardial management during coronary operations. Ann Thorac Surg 1994;58:768-773.[Abstract]
5. Bonchek L.I., Burlingame M.W. Coronary artery bypass without cardioplegia. J Thorac Cardiovasc Surg 1987;93:261-267.[Abstract]
6. Antunes M.J., Bernardo J.E., Oliveira J.M., Fernandes L.E., Andrade C.M. Coronary artery bypass surgery with intermittent aortic cross-clamping. Eur J Cardiothorac Surg 1992;6:189-194.[Abstract]
7. Pepper J.R., Lockey E., Cankovic-Darracott S., Braimbridge M.V. Cardioplegia versus intermittent ischemic arrest in coronary bypass surgery. Thorax 1982;37:887-892.[Abstract/Free Full Text]
8. Casthely P.A., Shah C., Mekhijian H., et al. Left ventricular diastolic function after coronary bypass grafting: a correlative study with three different myocardial protection techniques. J Thorac Cardiovasc Surg 1997;114:254-260.[Abstract/Free Full Text]
9. Taggart D.P., Bhusari S., Hooper J., et al. Intermittent ischemic arrest in coronary artery surgery: coming full circle?. Br Heart J 1994;72:136-139.[Abstract/Free Full Text]
10. Cohen A.S., Hadjinikolaou L., McColl A., Richmond W., Sapsford R.A., Glenville B.E. Lipid peroxidation, antioxidant status and troponin-T following cardiopulmonary bypass. A comparison between intermittent crossclamp with fibrillation and crystalloid cardioplegia. Eur J Cardiothorac Surg 1997;12:248-253.[Abstract]
11. Alhan H.C., Karabulut H., Tosun R., et al. Intermittent aortic cross-clamping and cold crystalloid cardioplegia for low-risk coronary patients. Ann Thorac Surg 1996;61:834-839.[Abstract/Free Full Text]
12. Bonchek L.I., Burlingname M.W., Vazales B.E., Lundy E.F., Gassmann C.J. Applicability of noncardioplegic coronary bypass to high-risk patients. Selection of patients, technique, and clinical experience in 3000 patients. J Thorac Cardiovasc Surg 1992;103:230-237.[Abstract]
13. Musumeci F., Feccia M., MacCarthy P.A., et al. Prospective randomized trial of single clamp technique versus intermittent ischemic arrest: myocardial and neurologic outcome. Eur J Cardiothorac Surg 1998;13:702-709.[Abstract/Free Full Text]

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