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Ann Thorac Surg 2008;86:823-827. doi:10.1016/j.athoracsur.2008.05.018
© 2008 The Society of Thoracic Surgeons
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Original Articles: Adult Cardiac

Effects of Intra-Aortic Balloon Pumping on Graft Flow in Coronary Surgery: An Intraoperative Transit-Time Flowmetric Study

Yoshiyuki Takami, MDa,*, Hiroshi Masumoto, MDb

a Department of Cardiovascular Surgery, Nagoya Daini Red Cross Hospital, Nagoya
b Division of Cardiovascular Surgery, Kasugai Municipal Hospital, Kasugai, Japan

Accepted for publication May 5, 2008.

Abbreviations and Acronyms A-C = aorta-coronary; CABG = coronary artery bypass graft surgery; DFI = diastolic filling index; IABP = intra-aortic balloon pumping; LAD = left anterior descending artery; LCX = left circumflex artery; LITA = left internal thoracic artery; PI = pulsatility index; Qd = diastolic flow; Qm = mean flow; Qs = systolic flow; RA = radial artery; RCA = right coronary artery; SVG = saphenous vein graft

* Address correspondence to Dr Takami, Department of Cardiovascular Surgery, Nagoya Daini Red Cross Hospital, 2-9 Myouken-cho, Showa-ku, Nagoya, 466-8650, Japan (Email: takami{at}nagoya2.jrc.or.jp).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 References
 
Background: We investigated hemodynamic effects of intra-aortic balloon pumping (IABP) in in-situ and aorta-coronary (A-C) grafts during coronary artery bypass grafting (CABG).

Methods: One hundred seventy-two grafts, including 84 in-situ left internal thoracic arteries (LITAs), were examined intraoperatively with a transit-time flowmeter in 84 patients who had prophylactic IABP. The following measurements were obtained for each graft during off-IABP and on-IABP: mean flow, maximal flow, pulsatility index, and diastolic filling index. Coronary angiograms were performed 14 ± 5 days after coronary artery bypass graft surgery to verify the patency of the grafts.

Results: All measurements of 163 patent and measurable grafts were significantly increased with IABP: mean flow 46 ± 27 to 51 ± 29 mL/min; maximal flow 87 ± 52 to 121 ± 69 mL/min; pulsatility index 2.2 ± 1.4 to 3.1 ± 1.4; and diastolic filling index 64% ± 8% to 71% ± 9% (p < 0.001). Among them, the degrees of increase of mean flow and diastolic filling index were significantly different between the in-situ LITAs and A-C grafts (mean flow 18% ± 20% versus 10% ± 15%, p = 0.04; diastolic filling index 10% ± 8% versus 14% ± 9%, p = 0.04).

Conclusions: IABP assist significantly increases graft flow and also diastolic components of flow. The degree of increase is greater in the in-situ LITA supplying the left anterior descending artery than in A-C grafts anastomosed to other coronary arteries. IABP increases the diastolic component more in A-C grafts than in in-situ LITAs, probably because of different flow characteristics of the two grafts.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 References
 
Among patients with coronary artery disease, intra-aortic balloon pumping (IABP) has been widely used in patients with cardiogenic shock and low cardiac output syndrome [1–3]. The synchronized counterpulsation produced augmentation of diastolic pressure and also reduction of cardiac afterload resistance with decreased systolic pressure [4]. It has been used in cardiac surgery, as well as in diagnostic and therapeutic coronary catheterization. The IABP provides circulatory support for patients experiencing postoperative hemodynamic instability, especially as an aid in weaning from cardiopulmonary bypass [5, 6]. Furthermore, IABP has been more frequently used prophylactically in high-risk patients undergoing cardiac surgery [7–9]. Although the efficacy of IABP has consistently been demonstrated, the effects of IABP on coronary bypass graft flow remain uncertain. In the present study, we investigated the hemodynamic effects of IABP support upon graft flow in coronary artery bypass graft surgery (CABG), especially comparing the effects on in-situ versus aorta-coronary (A-C) graft flows.


   Material and Methods
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 Abstract
 Introduction
 Material and Methods
Results
 Comment
 References
 
Study Patients
The study group comprised 84 patients (59 men and 25 women, aged 65 ± 9 years), who underwent CABG with the assist of prophylactic IABP. They were 74% of all patients who underwent CABG during the same period. The preincision prophylactic IABP was indicated for one of the following reasons: left main trunk disease, left ventricular dysfunction (left ventricular ejection fraction < 0.40), emergency, and severe cerebrovascular or carotid disease. The study protocol was approved by the Institutional Review Board of our hospital. Written informed consent for the study was obtained from each patient before the surgery.

Just before anesthesia induction, an 8F sheathless IABP with a 34 mL balloon catheter (TRUE8-Super Track; Edwards Lifescience, Irvine, California) or 7.5F IABP with a 25 mL balloon (TOKAI 7Fr-Clear; Tokai Medical Products, Kasugai, Japan) was inserted percutaneously under fluoroscopic guidance into the descending thoracic aorta, with its tip just distal to the aortic arch. The IABP catheter was connected to a System 98XT (Datascope, Montvale, New Jersey), triggered by the electrocardiogram signal, and regulated manually to make the balloon inflation occur immediately after the aortic dicrotic notch and to adjust its deflation on the R wave of the electrocardiogram. The patients received 172 grafts including 84 in-situ left internal thoracic arteries (LITAs), 31 radial arteries (RAs), 50 saphenous vein grafts (SVG), and 7 in-situ right gastroepiploic arteries, with (n = 38) or without (n = 46) cardiopulmonary bypass. All LITAs were anastomosed with the left anterior descending artery (LAD), while the target vessels of the A-C grafts were 49 left circumflex arteries (LCX), 31 right coronary arteries (RCA), and 8 diagonal branches. Combined procedures included mitral valve plasty (n = 4), mitral valve replacement (n = 2), aortic valve replacement (n = 2), and abdominal aneurysmectomy (n = 2).

Intraoperative Graft Flow Measurement
Graft flow tracing was obtained intraoperatively using a transit-time flowmeter (BF 2000; Medi-Stim AS, Oslo, Norway). A flow probe of 2 or 3 mm was placed around the graft during the hemodynamic stabilization period with and without use of IABP just before the chest closure. Based upon the obtained flow profile, the following variables were calculated: mean graft flow (Qm, mL/min); maximal flow; pulsatility index (PI = [maximal – minimal flow]/Qm); and diastolic filling index (DFI = 100{int}Qd/[{int}Qs + {int}Qd]), where Qd is diastolic flow and Qs is systolic flow based upon the definition that the systole is the duration from the peak of R wave to the peak of T wave in electrocardiogram-gated flow analysis. The flow profiles were obtained continuously during the IABP support of 1:1 (IABP on) and were also obtained after IABP was stopped for the 20 cardiac beats (IABP off). The change of each variable during IABP-on was also calculated as percentage of baseline value during IABP-off.

Every patient underwent a postoperative cardiac catheterization 14 ± 5 days after CABG with a standard technique through the femoral or brachial route. All grafts were examined from at least three different views. Strictly considering, a graft with stenosis less than 50% at anastomosis site was considered to be "patent."

Statistical Analysis
All data were expressed as means ± SD. Paired t tests were used to comparison the data during IABP-on and IABP-off. The Mann-Whitney U test was also used to compare the effects of IABP between the in-situ LITAs and A-C bypass grafts. A p value of less than 0.05 was considered to be statistically significant.


   Results
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 Abstract
 Introduction
 Material and Methods
 Results
Comment
 References
 
The prophylactic IABP was removed on the first postoperative day in all patients. They experienced no complication associated with IABP use. No patients died during the hospital stay. Postoperative complications included deep wound infection (n = 2), prolonged ventilatory support (n = 2), acute renal failure (n = 2), and perioperative myocardial infarction (n = 1).

Of 172 grafts, we found that all in-situ LITA grafts were patent and five grafts were nonpatent. The occluded grafts were one SVG and one RA, and stenotic grafts were one gastroepiploic artery, and two SVGs. We excluded these nonpatent grafts from the analysis of this study because we focused on the effects of IABP upon graft flow through the intraoperative flow analysis of definitively patent grafts that were angiographically proved. Figure 1 shows the transit-time recordings of an in-situ LITA and an A-C RA graft in a 76-year-old woman, which were both revealed to be patent well in the postoperative angiograms. The patent graft flow waveform, whether in-situ or A-C, showed two phases of antegrade systolic and diastolic flow with diastolic dominance.


Figure 1
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  		Fig 1. Intraoperative recordings of transit-time flow measurement in a 76-year-old woman. The electrocardiogram-gated analysis identifies systolic (dark shadow) and diastolic (bright shadow) components of the graft flow, calculating diastolic filling index (DFI). (Upper Panel) In-situ left internal thoracic artery (LITA) anastomosed with the left anterior descending artery (LAD): mean graft flow (Qm) = 66 mL/min, pulsatility index (PI) = 1.3, DFI = 65% during intra-aortic balloon pump off (IABP-off); and Qm = 72 mL/min, PI = 2.1, DFI = 72% during IABP-on. (Lower panel) Aorta-coronary graft of radial artery (RA) anastomosed with the diagonal branch (DIAG): Qm = 36 mL/min, PI = 1.4, DFI = 64% during IABP-off; and Qm = 41 mL/min, PI = 2.3, DFI = 74% during IABP-on.

 
The IABP significantly increased all determinants of the transit-time flow measurement: Qm: IABP-off, 44 ± 27 mL/min; IABP-on, 54 ± 29 mL/min (p < 0.001); maximal flow: IABP-off, 87 ± 52 mL/min; IABP-on, 121 ± 69 mL/min (p < 0.001); PI: IABP-off, 2.2 ± 1.4; IABP-on, 3.1 ± 1.4 p < 0.001); and DFI: IABP-off, 64% ± 8%; IABP-on, 71% ± 9% (p < 0.001). Among these variables, as shown in Table 1, there were no significant differences in the degrees of increase of maximal flow and PI with IABP support between the in-situ LITAs (n = 84) and the A-C bypass grafts (RAs and SVGs, n = 77). However, the degree of increase of Qm with IABP was greater in the in-situ LITAs than in the A-C grafts (Qm: 18% ± 20% versus 10% ± 15%, p = 0.04). In contrast, the increase ratio of DFI with IABP was greater in A-C bypass than in the in-situ LITAs (DFI: 14% ± 9% versus 10% ± 8%, p = 0.04).


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  		Table 1 Changes of Determinants of Intraoperative Transit-Time Flow Measurement by Use of Intra-Aortic Balloon Pumping (IABP) and Comparison of Them Between In-Situ Left Internal Thoracic Artery (LITA) Grafts and Aorta-Coronary (A-C) Bypass Grafts
 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
References
 
There have been few studies regarding hemodynamic effects of IABP upon CABG graft flows. In the experimental study, it was revealed that the diastolic flow in the LITA increased less than in the A-C bypass graft during IABP or ventricular assist device support [10]. The main findings of our clinical study were threefold: (1) The IABP assist significantly increases graft flow and its diastolic components of all grafts. (2) The degree of increase of flow is greater in the in-situ LITA onto the LAD than in the A-C grafts anastomosed with other coronary arteries. (3) The effect of IABP to increase the diastolic component is greater with the A-C grafts than with the in-situ LITAs. We should interpret the different effects of IABP upon the in-situ and A-C grafts, although the potential consequences of such differences are not analyzed, by taking the following affecting factors into consideration.

First, the effects of IABP upon CABG grafts are affected by flow characteristics of the graft conduits. The flow of the in-situ LITA graft onto LAD is originally more diastolic-dominant than that of the A-C grafts onto LCX or RCA. This is revealed by the comparison of the DFI during IABP-off in our study (A-C bypass 60% ± 8%, in-situ LITA 67% ± 8%, p < 0.0001). Such difference might be related to the anatomical graft length, flow measurement site, and also the physiology of the target vessels. The LITA flow measurement made close to the anastomosis may reflect coronary phasic pattern. The RCA has relatively systolic dominance in coronary blood flow compared with the LAD and LCX [11, 12]. These characteristics support our finding that diastolic augmentation of IABP is more pronounced to increase the diastolic component, DFI, of flow in the A-C bypass, which is relatively systolic-dominant. However, further examination is required based upon the relationship between perfusion territory and coronary flow being different between RCA and LCX.

Second, the effects of IABP upon CABG grafts are affected by flow reserve, perfused bed, and its viability of grafted native coronary arteries. The flow reserve during hyperemia of the LITA graft onto LAD was significantly greater than that of the SVG to RCA or LCX [13, 14], although it has been reported that there was no significant difference in coronary flow reserve among three vessels, LAD, LCX, and RCA, in an normal adult population [11, 12]. There is also a close association between decreased regional ventricular function and reduced regional myocardial perfusion reserve in patients with coronary artery disease. This relation was most pronounced in the inferior and posterior walls of the left ventricle corresponding to the RCA and LCX perfusion territories, whereas no significant association was seen in the anterior wall [15]. These characteristics support our finding that the degree of increase of flow by IABP counterpulsation is greater in the in-situ LITA onto the LAD than in the A-C grafts anastomosed with other coronary arteries. However, further comparison is required between the grafts to nonviable myocardium and those to viable myocardium.

Third, the effect of IABP upon graft flows is affected by the degree of sclerosis and vascular resistance of the coronary arteries distal to the graft anastomosis. Although augmentation of diastolic average coronary pressure by the IABP is theoretically expected, the effects of IABP on diastolic coronary pressure distal to the critical stenosis is minimal [16, 17]. There is also a significant correlation between the degree of coronary stenosis and the change in coronary artery pressure distal to the stenosis after initiation of IABP support. Therefore, it might be possible that vascular resistance distal to the graft anastomosis affects the different effects of IABP in our clinical study. Further studies are required to investigate stratified effects of IABP upon graft flow by stenosis of the target coronary arteries.

For intraoperative assessment of the anastomotic quality in CABG, we have been using the transit-time flow measurement, which is more convenient, less invasive, and less time consuming [18–20]. It is neither necessary to know the vessel diameter or perform any complex calibrating procedures. The main drawback of this method is the absence of well-recognized cutoff point for revision of the anastomosis. Also, we did not strictly even the variables that affect the graft flow, including blood pressure, heart rate, coronary resistance, and graft diameter, because it is not practical.

In conclusion, IABP significantly increases CABG graft global flow and also its diastolic components. The degree of increase of flow is greater in the in-situ LITA onto the LAD than in the A-C grafts anastomosed with other coronary arteries. The effect of IABP to increase the diastolic component is greater in the A-C grafts than in the in-situ LITAs, probably owing to different flow characteristics of the in-situ LITA and A-C grafts.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 References
 

  1. Moulopoulos S, Stamatelopoulos S, Petrou P. Intraaortic balloon assistance in intractable cardiogenic shock Eur Heart J 1986;7:393-403.
  2. Ishihara M, Sato H, Tateishi H, et al. Intraaortic balloon pumping as adjunctive therapy to rescue coronary angioplasty after failed thrombolysis in anterior wall acute myocardial infarction Am J Cardiol 1995;76:73-75.[Medline]
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  7. Gutfinger DE, Ott RA, Miller M, et al. Aggressive preoperative use of intraaortic balloon pump in elderly patients undergoing coronary artery bypass grafting Ann Thorac Surg 1999;67:610-613.[Abstract/Free Full Text]
  8. Christenson JT, Simonet F, Schmuziger M. Economic impact of preoperative intraaortic balloon pump therapy in high-risk coronary patients Ann Thorac Surg 2000;70:510-515.[Abstract/Free Full Text]
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  10. Tedoriya T, Kawasuji M, Sakakibara N, Takemura H, Watanabe Y, Hetzer R. Coronary bypass flow during use of intraaortic balloon pumping and left ventricular assist device Ann Thorac Surg 1998;66:477-481.[Abstract/Free Full Text]
  11. Ofili EO, Labovitz AJ, Kern MJ. Coronary flow velocity dynamics in normal and diseased arteries Am J Cardiol 1993;71:3D-9D.[Medline]
  12. Hamaoka K, Onouchi Z, Ohmochi Y, Sakata K. Coronary artery flow-velocity dynamics in children with angiographically normal coronary arteries Circulation 1995;92:2457-2462.[Abstract/Free Full Text]
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  14. Chirillo F, Bruni A, Balestra G, et al. Assessment of internal mammary artery and saphenous vein graft patency and flow reserve using transthoracic Doppler echocardiography Heart 2001;86:424-431.[Abstract/Free Full Text]
  15. Rosen BD, Lima JAC, Nasir K, et al. Lower myocardial perfusion reserve is associated with decreased regional left ventricular function in asymptomatic participants of the Multi-Ethnic Study of Atherosclerosis Circulation 2006;114:289-297.[Abstract/Free Full Text]
  16. Kimura A, Toyota E, Songang L, et al. Effects of intraaortic balloon pumping on septal arterial blood flow velocity waveform during severe left main coronary stenosis J Am Coll Cardiol 1996;27:810-816.[Abstract]
  17. Yoshitani H, Akasaka T, Kaji S, et al. Effects of intra-aortic balloon counterpulsation on coronary pressure in patients with stenotic coronary arteries Am Heart J 2007;154:725-731.[Medline]
  18. Takami Y, Ina H. Relation of intra-operative flow measurement with post-operative quantitative angiographic assessment of coronary artery bypass grafting Ann Thorac Surg 2001;72:1270-1274.[Abstract/Free Full Text]
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Related Article

Invited Commentary
Jan T. Christenson
Ann. Thorac. Surg. 2008 86: 827. [Extract] [Full Text] [PDF]




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