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Ann Thorac Surg 2006;82:620-623
© 2006 The Society of Thoracic Surgeons

Original article: Cardiovascular

Sequential Bypass Grafting on the Beating Heart: Blood Flow Characteristics

Marek Gwozdziewicz, MD, PhD*, Petr Nemec, MD, PhD, Martin Simek, MD, Roman Hajek, MD, Martin Troubil, MD

Department of Cardiac Surgery, University Hospital, Olomouc, Czech Republic

Accepted for publication December 20, 2005.

* Address correspondence to Dr Gwozdziewicz, University Hospital Olomouc, I. P. Pavlova 6, Olomouc 775 15, Czech Republic (Email: gwozdziewicz{at}email.cz).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
BACKGROUND: The sequential bypass technique is a routine method of myocardial revascularization. The aim of this study was to determine flow characteristics of individual and sequential bypass grafts created on the beating heart.

METHODS: Between January 2003 and February 2004, a consecutive series of 50 patients underwent off-pump coronary bypass surgery with at least one venous sequential coronary graft. During the procedure, flow values and pulsatility indexes were measured in both segments of the sequential graft using a CardioMed transit time flow meter (CM 4008; Medi-Stim, Oslo, Norway). The flow values were simultaneously compared with those of individual venous grafts sutured to the same coronary arteries.

RESULTS: The mean flow through the distal anastomosis (individual bypass; D1) was 37.4 mL/min, and this was not significantly influenced by the creation of a proximal sequential anastomosis (D2, 39.0 mL/min). In 32% of the patients, the sequential bypass was unwittingly connected proximally to a larger coronary bed; despite this, the flow in its distal segment was not less than that in the individual bypass.

CONCLUSIONS: The blood flow through an individual bypass is comparable with that through the distal segment (end-to-side anastomosis) of a sequential bypass. The grafting of a sequential bypass proximally to the larger artery (coronary bed) in sequence does not appear to have a significant effect on the blood flow in the distal segment of a sequential bypass.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
The sequential bypass technique is a well-known method for myocardial revascularization [1–3]. However, the patency of the distal end-to-side anastomosis has been questioned by some authors and shown to be inferior to that of an individual graft [4]. It has also been shown that the off pump coronary technique can reduce graft patency [5].

While arterial revascularization is becoming more popular in coronary surgery [6, 7], the application of the sequential technique, which is often obligatory in complete arterial revascularization, should be considered safe.

In most of the studies comparing sequential to individual grafts, the major limiting factor was that grafts were sutured to two different coronary territories [2]. This study was designed to compare—using intraoperative measurement of blood flow and pulsatility index (PI)—blood flow through an individual venous bypass with that in a distal segment of the sequential venous bypass performed on the beating heart. The operative protocol allowing for transformation of an individual graft to a sequential one enabled us to quantitatively compare these two types of bypass.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 Acknowledgments
 References
 
From January 2003 to February 2004, 841 patients with ischemic heart disease underwent coronary surgery in our department. An off-pump coronary bypass was performed on 287 patients (34.1%), of whom 50 consecutive patients (17.4%) had at least one venous sequential aortocoronary bypass graft. This group constituted the study cohort, and comprised 36 men (72%) and 14 women (28%) with a mean age of 69.7 years (range, 48 to 84). The clinical data of the patients are listed in Table 1. All operations were performed by the same surgeon. This study received approval from the Institutional Review Board of University Hospital Olomouc, and informed consent was obtained from all patients.


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  		Table 1. Clinical Profile of Patients
 
A median sternotomy was used for surgical access in all cases. Systemic heparinization with 10,000 U heparin was performed before cardiac manipulation. Hemodynamic stability was achieved by preload management (intravenous fluid administration or the Trendelenburg position, or both) and with vasoactive agents when indicated. The heart was stabilized using two mechanical suction-based tissue stabilizers (Axius Vacuum 2 and Axius Expose 3; Guidant, Santa Clara, California) and one modified "Lima" pericardial traction stitch [8]. After arteriotomy, an intraluminal shunt (Axius coronary shunt; Guidant, or Medtronic, Minneapolis, Minnesota) was inserted to maintain distal myocardial perfusion; it was removed before the completion of anastomosis. After the completion of an individual mammary-to-left anterior descending artery (LAD) bypass, the construction of a venous sequential graft was commenced.

To create an individual venous aortocoronary bypass, a distal (end-to-side) coronary anastomosis was performed, followed by a proximal vein-to-ascending aorta anastomosis. At the same time, the first measurement (D1) of coronary flow through the distal anastomosis (individual bypass) was made using the CardioMed transit time flow meter (CM 4008; Medi-Stim, Oslo, Norway [Fig 1]).


Figure 1
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  		Fig 1. Diagrams of the flow measurements. (A) Individual graft with the measurement of the flow through the distal anastomosis (D1, D1p). (B) Sequential bypass graft with flow measurements in the distal (D2, D2p) and proximal (P, Pp) anastomoses, and total bypass flow assessment (T, Tp). The flow was recorded before and after the administration of papaverine (p). The proximal flows (P, Pp) were measured after clamping the vein with a bulldog clamp behind the side-to-side anastomosis (not shown).

 
The operation continued with suturing of the proximal, sequential, side-to-side anastomosis to another coronary artery. This transformed the previous individual bypass into a sequential one. At that point, blood flow through the distal (D2) and proximal (P) anastomoses and the whole sequential graft (T) was measured. All the measurements were repeated after the administration of 6 mg saline-diluted papaverine (p) into the graft when the maximal flow (D1p, D2p, Pp, Tp) was estimated. This provided assessment of the flow reserve. To test the quality of the sutured anastomoses, in addition to flow measurement, PIs were recorded [9, 10]. The PI equals the difference between the maximum (systolic) and minimum (diastolic) blood flows divided by the mean flow, and its value should not exceed 5.0, in the case of a well-constructed bypass [10].

For each recording, attempts were made to maintain the mean arterial pressure at 70 mm Hg.

The recorded data were statistically analyzed using Statistica 6.0 software (StatSoft, Tulsa, Oklahoma). The recorded variables were compared using analysis of variance (ANOVA) for dependent measurements, and pairs of flow values and PIs were subsequently tested using Scheffe's test. Differences among the pairs were assessed by the Sign test. Correlations between variables were evaluated by Pearson's correlation coefficient.


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 Acknowledgments
 References
 
A mean of 3.6 grafts per patient were completed in our 50 patients. All grafted vessels had significant (>70%) proximal stenosis. Because both an individual bypass and the distal segment of a sequential graft were anastomosed to the same coronary arteries, no attempt was made to statistically evaluate the effect of the degree of stenosis or the diameter of native coronary arteries on differences in flow.

Each patient received an individual mammary artery-to-LAD bypass as one of the grafts. Table 2 lists the types of sequential bypass used. None of the sequential grafts required revision owing to technical errors.


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  		Table 2. Types of Sequential Graft Used in 50 Patients
 
Table 3 lists the blood flow values in relation to hemodynamic parameters in a group of 50 consecutive patients. The mean flow through the distal anastomoses (individual bypass) before papaverine administration (D1) was 37.4 mL/min. After the creation of a proximal side-to-side anastomosis, the blood flow through the distal anastomosis (D2) was 39.0 mL/min (p > 0.9). A similar relationship between the groups of flow values was found after papaverine administration (D1p and D2p). The mean flow through the proximal anastomoses (P) of the sequential bypass was 36.9 mL/min. The mean total flow through the sequential graft (T) was 69.4 mL/min.


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  		Table 3. Blood Flow Through Anastomoses of Individual and Sequential Bypass, and Related Hemodynamic Variables in 50 Consecutive Patients
 
The increase in blood flow through the proximal anastomosis of the sequential bypass after papaverin administration was larger than the increase in flow through its distal anastomosis in 32% of the patients. We believe that the measurement /degreeof the flow increase may be related to the capacity of the coronary bed (which is responding to papaverine) supplied by the grafted coronary artery.

All PI values remained within the normal range, thus confirming the good patency of the sutured anastomoses.

No deaths occurred in our cohort. One patient had to be converted to the on-pump procedure owing to perforation of the right ventricle during the intramyocardial preparation of the LAD. One patient required repeat surgery owing to bleeding. There were five wound complications, two with complete sternum dehiscence. One patient suffered a mild pulmonary embolism. The postoperative course in the remaining 45 patients was uneventful.


   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
Acknowledgments
 References
 
The advantages of the sequential bypass technique over individual bypass conduit surgery have been reported previously [1–3].

To assess the quality of sequential bypasses performed on the beating heart, and to determine whether a construction of a proximal side-to-side anastomosis alters flow across the distal end-to-side anastomosis, we measured the blood flow and PI in an individual bypass, and then in both segments of a sequential graft. An individual bypass was first constructed using the off-pump technique, which was subsequently transformed into a sequential type by creating side-to-side anastomosis. That allowed us to maintain the same pathophysiologic conditions in relation to vascular resistance, which was crucial for measuring the blood flow.

Our main goal in coronary surgery is to provide a long-lasting reconstruction of the coronary artery system with good graft patency. One of the recommended principles that should guarantee good patency of sequential grafts is suturing the last anastomosis in the sequence onto the largest vessel (coronary bed). That was not the case in 32% of our patients. The flow capacity of a coronary bed observed during papaverine-induced flow measurement was not consistent with prior angiographic estimation in these patients. Despite this, the blood flow in the distal segment of the sequential bypass was not less than that in the individual bypass.

In our 50 consecutive patients, we have proved that the flow through an individual bypass was comparable with that through the distal segment (end-to-side anastomosis) of a sequential bypass (p > 0.9), and this remained unchanged after papaverine administration. The experimental studies of Rittgers and coworkers [11] and Meyerson and colleagues [12] have shown that it is bypass flow (namely, the wall shear stress) that determines the degree of intimal proliferation, which may lead to bypass closure. Comparable blood flows through an individual bypass with those across end-to-side anastomosis of the sequential graft performed on a beating heart might predict similar patency of both types of bypass.

The long-term patency of sequential off-pump bypasses has not been reported yet. A meticulous operative technique and intraoperative blood flow measurement in sutured grafts may disclose the presence of insufficient flow due to technical errors, and prevent early bypass closure. The grafting of a sequential bypass proximally to the larger artery in sequence does not appear to have a significant effect on the blood flow in the distal segment of a sequential bypass.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
References
 
We gratefully acknowledge the contribution of Zdenka Michaliková, who prepared the diagrams for this article.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Christenson JT, Schmuziger M. Sequential venous bypass graftsresults 10 years later. Ann Thorac Surg 1997;63:371-376.[Abstract/Free Full Text]
  2. Vural KM, Sener E, Tasdemir O. Long-term patency of sequential and individual saphenous vein coronary bypass grafts Eur J Cardiothorac Surg 2001;19:140-144.[Abstract/Free Full Text]
  3. Yamaguchi A, Kitamura N, Miki T, Kawashima M, Tamura H. Comparative study in graft patency of individual and sequential grafting as coronary bypass Kokyu To Junkan 1993;41:577-580.[Medline]
  4. Kieser TM, FitzGibbon GM, Keon WJ. Sequential coronary bypass grafts. Long-term follow-up J Thorac Cardiovasc Surg 1986;91:767-772.[Abstract]
  5. Kim KB, Lim C, Lee C, et al. Off-pump coronary artery bypass may decrease the patency of saphenous vein grafts Ann Thorac Surg 2001;72(Suppl):1033-1037.
  6. Kobayashi J, Tagusari O, Bando K, et al. Total arterial off-pump coronary revascularization with only internal thoracic artery and composite radial artery grafts Heart Surg Forum 2002;6:30-37.[Medline]
  7. Kobayashi J, Sasako Y, Bando K, et al. Multiple off-pump coronary revascularization with "aorta no-touch" technique using composite and sequential methods Heart Surg Forum 2002;5:114-118.[Medline]
  8. Bergsland J, Karamanoukian HL, Soltoski PR, Salerno TA. "Single suture" for circumflex exposure in off-pump coronary artery bypass grafting Ann Thorac Surg 1999;68:1428-1430.[Abstract/Free Full Text]
  9. Walpoth BH, Bosshard A, Kipfer B, Berdat PA, Althaus U, Carrel T. Failed coronary artery bypass anastomosis detected by intraoperative coronary flow measurement Eur J Cardiothorac Surg 1998;14:S76-S81.[Abstract/Free Full Text]
  10. D'Ancona G, Karamanoukian HL, Bergsland J. Is intraoperative measurement of coronary blood flow a good predictor of graft patency? Eur J Cardiothorac Surg 2001;20:1075-1077.[Free Full Text]
  11. Rittgers SE, Karayannacos PE, Guy JF, et al. Velocity distribution and intimal proliferation in autologous vein grafts in dogs Circ Res 1978;42:792-801.[Free Full Text]
  12. Meyerson SL, Skelly CL, Curi MA, et al. The effects of extremely low shear stress on cellular proliferation and neointimal thickening in the failing bypass graft J Vasc Surg 2001;34:90-97[Erratum appears in J Vasc Surg 2001;34:580].[Medline]



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