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Ann Thorac Surg 2004;77:2061-2065
© 2004 The Society of Thoracic Surgeons

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Original article: cardiovascular

Internal thoracic artery malperfusion: fast decision for an additional vein graft has impact on patient outcome

^a Clinic for Thorax and Cardiovascular Surgery, University Clinic of Essen, Essen, Germany

Accepted for publication October 30, 2003.

^* Address reprint requests to Dr Massoudy, Klinik für Thorax- und kardiovaskuläre Chirurgie, Universitätsklinikum Essen, Hufelandstr. 55, 45147 Essen, Germany.
e-mail: parwis.massoudy{at}uni-essen.de

	Abstract

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
BACKGROUND: Internal thoracic artery (ITA) malperfusion has been described as a potentially devastating and lethal complication of coronary artery bypass grafting (CABG). It is our practice to perform an additional vein graft to the distal left anterior descending (LAD) artery in such cases.

METHODS: From August 1999 to July 2002, 2,877 CABG procedures were performed at our institution. In 65 patients (2.3%) ITA malperfusion was observed. All of them were treated with an additional vein graft to the distal LAD. All patient data were screened for the time interval between the occurrence of ITA malperfusion and the decision to perform an additional vein graft.

RESULTS: Of 65 patients with ITA malperfusion, 54 patients (83%) survived (group 1), 11 patients (17%) died (group 2). There was no difference in preoperative risk status between the groups. Cross clamp time was 88 ± 4 minutes in group 1 and 104 ± 11 minutes in group 2 (p = 0.04). Intraoperative ITA flow to LAD was 6 ± 1 mL/min in group 1 and 10 ± 5 mL/min in group 2 (p = 0.2). Time between release of cross clamp and second period of cross clamping was 50 ± 5 minutes in group 1 and 75 ± 11 minute group 2 (p = 0.02). Time between termination of cardiopulmonary bypass (CPB) and second period of cross clamping was 23 ± 3 minutes in group 1 and 46 ± 7 minutes in group 2 (p = 0.003). Vein graft flow to distal LAD was 54 ± 4 mL/min in group 1 and 52 ± 12 mL/min in group 2 (p = 0.5). Maximum postoperative troponin I was 35 ± 11 ng/mL in group 1 and 136 ± 32 in group 2 (p = 0.003).

CONCLUSIONS: Survivors of ITA malperfusion had shorter cross clamp times and less myocardial damage as evidenced by lower postoperative troponin I levels. Time intervals between first and second cross clamp and between termination of CPB and second cross clamp were lower in survivors, thus indicating that a fast decision for an additional vein graft may influence postoperative patient outcome.

	Introduction

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In coronary artery bypass grafting (CABG), the internal thoracic artery (ITA) is the first choice graft for revascularization of the left anterior descending (LAD) artery. The ITA malperfusion has been described as an imbalance between myocardial demand and nutritional support through the ITA [1]. The clinical symptoms of ITA malperfusion may be hemodynamic instability, various forms of rhythm disturbance, electrocardiographic (ECG) changes indicating myocardial ischemia, or no satisfactory flow obtained during intraoperative graft flow determination. The underlying reasons may be technical problems at the site of the anstomosis, unrecognized surgical ITA lesions compromising flow, or even transient spasm of the artery caused by mechanical or thermic irritation. In cases of perioperative internal thoracic artery malperfusion, the use of an additional saphenous vein graft has been suggested as the treatment of choice [2, 3]. The left (L)ITA anastomosis is left in place and the additional graft is connected with the distal LAD. In the initial report of Jones and colleagues [4], mortality was 66%. In the subsequent reports, mortality ranged between 0% and 10% [1, 2, 5]. Control angiography has shown that the double supply of the LAD does not seem to be a problem for the clinical outcome of the patients. The LITA and additional vein graft were shown to be open and in good function in almost 60% of patients undergoing control angiography after 12 to 24 months [1]. However, thus far the question of whether the time interval between diagnosis and the decision to perform an additional saphenous vein graft to the distal LAD plays a role for patient outcome, has not been addressed. We were interested to see whether, in our cohort of 65 patients with IMA malperfusion, additionally supplied with a saphenous vein graft, the time interval between manifestation of ITA malperfusion and subsequent decision to perform a supplemental vein graft influenced mortality.

	Material and methods

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Patients
From August 1999 to July 2002, 2,877 CABG and combined CABG and valve procedures were performed at our institution. All patients receiving a supplemental vein graft to the distal LAD in addition to a regular LITA graft to the LAD were included in the study.

Anesthesia and surgery
Anesthesia was induced with intravenous sufentanil (1 µg/kg), etomidate (50 µg/kg), and pancuronium (100 µg/kg). After endotracheal intubation, patients were mechanically ventilated with an end-expiratory pressure of 5 cm H₂O. Inspired oxygen fraction was 0.5 and endtidal carbon dioxide tension at 30 to 35 mm Hg. Anesthesia was maintained with isoflurane (0.6% to 1.0%), discontinuously given sufentanil (0.3 to 0.5 µg/kg), and pancuronium (30 µg/kg). Lungs were mechanically ventilated with a tidal volume of 8 mL/kg with a respiratory rate adjusted to obtain an end-expiratory carbon dioxide tension of 35 to 40 mm Hg. A PaO₂ of at least 200 mm Hg was the target during bypass. Aprotinin (Trasylol, Bayer, Leverkusen, Germany) was given according to the Hammersmith protocol (total dose 6 million Kallikrein inactivator unit [KIU]). After systemic heparinization, the target activated clotting time (ACT) was 400 seconds. With a systemic flow of 2.4 L · min^–1 · m^–2 mean arterial pressure was adjusted to 60 mm Hg by repetitive intravenous neosynephrine injections, if required. The patient was cooled (32°C) and 1,500 mL of cold Bretschneider cardioplegic solution (Custodiol, Köhler Chemie, Alsbach-Hähnlein, Germany) were infused into the aortic root after cross clamping. The lowest hematocrit accepted was 18%, with packed red cells transfused, if necessary. Heparin (5,000 IU; Ratiopharm, Ulm, Germany) and aprotinin (2 million KIU) were added to the prime. After termination of bypass, blood remaining in the bypass (CPB) circuit was retransfused.

All operations were performed using CPB. Conventional CPB roller pumps (Stöckert, Munich, Germany) and a disposable membrane oxygenator (Jostra, Hirrlingen, Germany) were used following priming with 1,600 mL (1,030 mL of lactated Ringer's solution, 445 mL hydroxy-ethyl-starch, 10%, 90 mL Mannitol, and 35 mL sodium bicarbonate). Implementation of CPB after cannulation of the ascending aorta and right atrium was followed by routine cross clamping of the aorta. During bypass, a positive end expiratory pressure of 5 cm H₂O was applied using an oxygen flow of 200 mL/min without phasic ventilation.

The LITA anastomosis to the LAD was the last anastomosis to be performed. After termination of the LITA anastomosis, the aortic cross clamp was released and a side clamp was applied to allow for performance of the proximal anastomoses. Thereafter, CPB was reduced and terminated. This would be the time point for routine flow determination of all grafts (including ITA) using transit time measurement. When there was no or insufficient flow on the LITA graft, the surgeon would now decide to electively reinstitute CPB and perform an additional vein graft to the distal LAD. In other cases, hemodynamic problems may have occurred later during the operation and were the reason to reinstitute CPB and perform an additional vein graft. In some cases, the surgeon may have determined ITA flow with the aortic cross clamp still on, possibly because he anticipated insufficient graft flow.

In all cases, the decision was taken in the operating room during the initial session. Cardiopulmonary bypass may have been terminated and then reinstituted or may not yet have been terminated. All additional vein grafts were performed during cardiac arrest using 800 mL of Bretschneider' cardioplegic solution.

Measurements
For pressure measurements, a pulmonary artery catheter (7.5 F, Baxter, Irvine, CA) was inserted via the right internal jugular vein through an introducer sheath (8.5 F, Arrow, Reading, MA), in addition to a central venous catheter, and two large-bore peripheral intravenous catheters. Heart rate (ECG) and mean pressures in the radial artery, the superior caval vein, the pulmonary artery, and in the pulmonary capillary wedge position were measured by electromanometry relative to barometric pressure and referenced to the midaxillary line. Cardiac index (CI) and systemic vascular resistance index were calculated using standard formulas. Dopplersonographic flow probes with a diameter of 2 to 4 mm (CardioMed, Oslo, Norway) were used to intraoperatively determine graft flow on LITA and vein grafts.

Statistical analysis
Results are expressed as means ± standard error of the mean (SEM). Differences of means between groups were evaluated using Student's t test using standard software (Excel). An a priori null hypothesis was rejected with an -error p of less than 0.05. According to the statistician, the population of nonsurviving patients is too small to perform a multivariate analysis.

	Results

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
From August 1999 to July 2002, 2,877 CABG procedures were performed. In 64 patients, ITA malperfusion was observed. Forty-one were male, 23 were female. All 64 patients received an additional vein graft to the distal LAD. Of the 65 patients, 54 patients (83%) survived (group 1), 11 patients (17%) died (group 2).

Preoperative characteristics are shown in Table 1. In group 2 patients the incidence of left main stem stenosis and peripheral arterial disease was significantly higher compared with group 1 patients. Group 2 patients were older than group 1 patients. No difference was found for preoperative left ventricular ejection fraction.

View larger version (34K): [in this window] [in a new window]   Fig 1. Time interval between cross clamp release and second cross clamping and between termination of CPB and second cross clamping in group 1 (hatched bars) and group 2 (cross hatched) patients. Means ± standard error of the mean. Numerical values above error bars indicate level of statistical significance between the groups. (CPB = cardiopulmonary bypass; X clamp = aortic cross clamp.)

	Comment

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Thus far, the time point of decision to perform an additional vein graft to the LAD has not been a matter of discussion in patients with ITA malperfusion. In the present study, the time interval between release of first cross clamp and second cross clamping and between termination of CPB and second cross clamping, both were significantly longer in group 2 patients. After release of the first cross clamp, the patients were still on CPB and the hearts were decompressed. This period of compromised LAD supply, which was partially protected by CPB, was 50% longer in nonsurviving patients. After termination of CPB, the unprotected period of compromised LAD supply was twice as long in nonsurviving patients. Of the 11 patients who died, 6 died of noncardiac causes. When we only look at the patients dying from cardiac causes, ITA malperfusion even lasted 98 ± 13 minutes, compared with 75 ± 11 minutes in all nonsurviving patients. In the case of recognized ITA malperfusion, independent of the underlying reason, a fast decision for an additional vein graft improves patient outcome.

None of the patients reported in this study had left the operating room after the initial revascularization, but the time points at which the decision for an additional graft was made varied considerably. In 17% of the surviving group 1 patients, there was only 1 period of aortic cross clamping. Having determined LITA flow to the arrested heart, the surgeon decided to perform an additional graft before even releasing the aortic cross clamp. In these cases, a subsequent development of hemodynamic instability was presumed (6 of 8 patients had no ITA graft flow), and probably prevented, by an additional vein graft.

In the presence of ITA malperfusion, multiple reasons have been given for compromised flow. In addition to technical anastomotic problems, arterial spasm [6], steal phenomena by coronary-subclavian steel [7] or by side branches of the internal thoracic artery [8], irritation by an intraaortic balloon pump [9], imbalance between ITA flow, and myocardial demand [1] have been described. Although no data exist about the prevalence of the individual causes, internal thoracic artery spasm may be responsible for most instances of ITA malperfusion. This is supported by a study performing reangiography in 43 patients with ITA malperfusion who received an additional vein graft [1]. In 56% of patients, LITA was wide open at between 3 and 24 months postoperatively. The majority of these patients probably had ITA spasm. However, 35% of ITA anastomoses showed narrowing and 9% were occluded, indicating that technical anastomotic problems were also present in a large number [1].

In our institution, additional vein grafting to the LAD is only performed when the respective surgeon is sure to rule out a significant anastomotic problem. There is no proof, however, for this subjective judgment and this is certainly a limitation of the present study. Under the suspicion that ITA spasm (which is itself caused by improper harvesting in most instances) is present, we would suspect ITA flow to recover and offer the patient the benefit of the better long-term patency reported for ITA grafts [10]. In the early postoperative period one could expect competitive flow between vein graft and ITA graft, which is supported by an experimental study using a model of dual supply of the LAD with an internal thoracic artery and a vein. Flow values in ITA grafts were decreased when venous grafts were anastomosed adjacent to ITA grafts [11].

In the abovementioned study, reangiography was performed in patients with double supply of the LAD by a LITA graft and a venous graft [1]. In 98% of patients the venous graft to the LAD was patent at late reangiography, which was performed between 12 and 24 months after CABG. This is a little surprising because one could expect the vein graft to occlude because of the growing competition between ITA and vein graft. Indeed, in preliminary reangiography data that we have obtained from 5 of our patients, at 19 ± 1 months after CABG (range 8 to 26 months), all LITA grafts were patent, while 2 vein grafts are occluded, presumably because of competitive flow.

Although maximum troponin I in group 1 patients was significantly lower than in group 2 patients, a mean maximum troponin I level of 35 ng/mL is higher than a mean maximum troponin I level of 5 ng/mL that would be expected in uncomplicated CABG cases (nonpublished observation). This indicates a certain amount of myocardial damage after the short period of time during which nutritional flow to parts of the LAD may have been compromised because of malperfusion. On the other hand, all but 8 patients underwent two periods of aortic cross clamping, which by itself may be responsible for elevated troponin I levels.

Limitations of the present study are as follows: The incidence of left main stem stenosis and of peripheral arterial disease was higher in nonsurvivors than in survivors. In addition, group 2 patients were older than group 1 patients. These are risk factors for an increased mortality in CABG patients and may contribute to a worse outcome.

Cross clamp time was about 20% higher in nonsurvivors than in survivors. This may be explained by a higher number of distal anastomoses in group 2 patients. The difference in cross clamp time and the absolute cross clamp time are, however, not long enough to account for a higher mortality of group 2 patients. Bypass time was almost 50% higher in nonsurvivors than in survivors, which is partly explained by problems on weaning the patients off bypass, which was subsequently achieved by using intraaortic balloon pumping in 64% of group 2 patients, whereas only 18% of group 1 patients needed intraaortic balloon pumping.

The fact that the decisions were made upon subjective judgment and by surgeon's preference also represents a limitation of the study. In cases of very early decision to perform an additional vein graft, hemodynamic problems had not yet developed and might not have come at all. On the other hand, it is the aim of the study to demonstrate that if malperfusion is present an early decision, possibly taken before problems occur, improves outcome.

In two other studies reporting 45 and 21 patients with dual supply of the LAD, the distal venous anastomosis was made without a second period of aortic cross clamping during ventricular fibrillation [1, 3]. In our study, all additional vein grafts were performed during cardiac arrest. The higher mortality rate in our patients may suggest that the avoidance of an additional period of cardiac arrest may be a safer alternative. Moreover, application of an off-pump technique even prevents additional bypass time.

In conclusion, performance of an additional saphenous vein graft to the distal LAD remains to be the treatment of choice in cases of ITA malperfusion. The present study suggests that the time interval between occurrence of ITA malperfusion and the decision to supply the LAD with a supplemental vein graft may be crucial for patient outcome.

	Acknowledgments

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The authors acknowledge the excellent work of the perfusionists Horst Schmidt, Wolf Ingo Wiese, Markus Deus, Josef Graban, Jörg von Manstein, and Franz Schön, who take care of transit time flow measurement in our department. The work was performed in the Department of Cardiothoracic Surgery, University of Essen, Germany.

	References

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1. Carrel T., Kujawksi T., Zünd G., et al. The internal mammary artery malperfusion syndrome: incidence, treatment and angiographic verification. Eur J Cardiothorac Surg 1995;9:190-197.[Abstract]
2. Vajtai P., Ravichandran P.S., Fessler C.L., et al. Inadequate internal mammary artery graft as a cause of postoperative ischemia: incidence, diagnosis and management. Eur J Cardiothorac Surg 1992;6:603-608.[Abstract]
3. Zünd G., Hauser M., Vogt P., et al. New approach to patency and flow assessment after left internal thoracic artery hypoperfusion syndrome with additional saphenous vein graft to the left anterior descending artery with phase-contrast magnetic resonance angiography. J Thorac Cardiovasc Surg 1997;114:428-433.[Abstract/Free Full Text]
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6. Stone G.W., Hartzler G.O. Spontaneous reversible spasm in an internal mammary artery graft causing acute myocardial infarction. Am J Cardiol 1989;64:822-823.[Medline]
7. Olsen C.O., Dunton R.F., Maggs P.R., Lahey S.J. Review of coronary-subclavian steel following internal mammary artery-coronary artery bypass surgery. Ann Thorac Surg 1988;46:675-678.[Abstract]
8. Schmid C., Heublein B., Reichelt S., Borst H.G. Steal phenomenon caused by a parallel branch of the internal mammary artery. Ann Thorac Surg 1990;50:199-200.
9. Rodigas P.C., Briges K.G. Occlusion of left internal mammary artery with intra-aortic balloon: clinical implication. J Thorac Cardiovasc Surg 1986;91:142-149.[Abstract]
10. Boylan M.J., Lytle B.W., Loop F.D., et al. Surgical treatment of isolated left anterior descending coronary artery stenosis. Comparison of left internal mammary artery and venous autograph at 20 years of follow-up. J Thorac Cardiovasc Surg 1994;107:657-662.[Abstract/Free Full Text]
11. Pagni S., Salloum E., Storey J., et al. Double grafting of the left anterior descending artery: is the distance between the internal mammary artery and the supplemental vein graft anastomoses relevant in graft survival?. Eur J Cardiothorac Surg 1998;13:36-41.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Parwis Massoudy Ulf Herold Markus Kamler Heinz Jakob Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Massoudy, P. Articles by Jakob, H. Search for Related Content PubMed PubMed Citation Articles by Massoudy, P. Articles by Jakob, H. Related Collections Coronary disease