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Eur J Cardiothorac Surg 2001;20:913-917
© 2001 Elsevier Science NL

Changes in systolic and diastolic function during multivessel off-pump coronary bypass grafting

S. Biswasa,b, F. Clementsa,b, L. Diodatoa,b, G. Chad Hughesa,b, K. Landolfoa,b

a Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA
b Department of Anesthesia, Duke University Medical Center, Durham, NC 27710, USA

Received 7 October 2000; received in revised form 11 July 2001; accepted 18 July 2001.

Corresponding author. Box 3094, Duke University Medical Center, Durham, NC 27710, USA. Tel.: +1-919-681-2085; fax: +1-919-681-8994
e-mail: cleme004{at}mc.duke.edu


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
 References
 
Objective: To measure the changes in systolic and diastolic left ventricular function that occur during off-pump coronary artery bypass grafting (OPCAB) as a consequence of positioning the heart and interrupting coronary flow. Methods: 2-D Transoesophageal echocardiography was used to derive systolic wall motion indices and pulsed Doppler parameters of diastolic function including the E/A ratio, PVS/PVD ratio, and deceleration time. A continuous cardiac output thermodilution pulmonary artery catheter was used to provide hemodynamic measures of left ventricular function. Data was obtained prior to, during and following coronary grafting. Results: Thirty-four consecutive anastomoses were evaluated, including eight circumflex (LCX), 17 left anterior descending artery (LAD) and nine right coronary artery (RCA) anastamoses. Significant changes in diastolic and systolic cardiac function were identified in those patients who underwent LCX grafting. Specifically during LCX grafting, both wall motion score index (2.4±1.4 vs 1.5±0.63 and 1.9±0.91) and the E/A ratio were significantly increased (3.5±1.4 vs 1.1±0.33 and 1.2±0.44) when compared to RCA and LAD grafting, respectively. The PVS/PVD ratio was significantly decreased during left circumflex grafting (0.7±0.45 vs 1.1±0.19 and 1.0±0.58) when compared to RCA and LAD grafting, respectively. All functional parameters returned to baseline by the end of surgery. Conclusions: Multivessel OPCAB can be achieved with mild impairment of left ventricular function that returns to baseline by the end of the procedure. Impairment of diastolic function is most marked during circumflex grafting as demonstrated by a restrictive filling pattern. Measures of diastolic function may be helpful in developing better strategies for exposure of the circumflex graft site.

Key Words: Off-pump coronary bypass grafting • Left ventricular function


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
 References
 
The performance of off-pump coronary artery bypass grafting (OPCAB) has been limited by the ability of the heart to maintain adequate function throughout the positioning, stabilization and interruption of coronary flow that may be required to perform high-quality coronary anastamoses. In particular, exposure of the circumflex coronary and its marginal branches is more challenging during OPCAB, requiring elevation of the cardiac apex and medial rotation of the heart. Mechanical stabilization of the anastomotic site with an OctopusTM or similar device may also compromise left ventricular filling and ejection. Early experience with OPCAB was confined to easily accessible, anterior vessels, and not recommended for circumflex or lateral marginal grafting [1,2]. The hemodynamic management of patients undergoing OPCAB has been described as challenging, to maintain an adequate cardiac output in the face of impaired left ventricular filling, intermittent myocardial ischemia and occasional heart block. Intravenous fluids, steep Trendelenberg positioning and the use of inotropes and pressors have been advocated to support the blood pressure and cardiac output [3]. Mechanical stabilization of the left anterior descending coronary (LAD) anastomotic site is typically associated with little perturbation of cardiac function but the effects of cardiac positioning and stabilization for the right (RCA) and circumflex (LCX) coronary grafts have not been fully evaluated [4,5].

In addition to abnormalities of systolic regional wall motion, transoesophageal echocardiography (TOE) can provide quantitative measures of diastolic function reflecting the impairment of left ventricular filling. We hypothesized that measurement of systolic and diastolic function would help us to quantitatively evaluate the effect of the different surgical positionings and stabilizations required for multivessel OPCAB. Subsequently, this may be helpful in developing better surgical techniques.


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Results
 4. Discussion
 Appendix A. Conference...
 References
 
Twenty-two consecutive patients underwent multivessel OPCAB with intraoperative transoesophageal echocardiography monitoring (TOE). Two patients converted to conventional CABG utilizing cardiopulmonary bypass because of intramyocardial LAD. Three patients had incomplete TOE data. The remaining 17 patients comprise the study population.

All patients underwent median sternotomy following placement of a radial arterial line, insertion of a continuous cardiac output pulmonary artery catheter and induction of anesthesia. A five lead electrocardiogram with continuous ST segment analysis (Hewlett-Packard) was used. Anaesthetic management included the use of intravenous fluids, pressors and inotropes as necessary to maintain a mean arterial blood pressure of >=60 mmHg and a cardiac index of >=2 l/min/m2.

2.1. Transoesophageal echocardiography
An omniplane transoesophageal transducer (Hewlett-Packard) was placed following induction of anesthesia. Baseline views were obtained prior to surgical manipulation of the heart. Imaging was repeated at 10 min of occlusion for each coronary anastamosis, and at the end of surgery. Systolic wall motion was evaluated by short axis imaging at the mid-papillary muscle level when obtainable and also by long axis imaging. (mid-esophageal four-chamber, mid-esophageal two-chamber and mid-esophageal long axis [6]) Short axis imaging was frequently unobtainable when the apex of the heart was elevated for completion of coronary anastamoses. Systolic wall motion was evaluated offline for wall thickening of the six mid-ventricular and four apical segments, using the numerical grading system: 1=normal, 2=mild hypokinesia, 3=severe hypokinesia, 4=akinesia, 5=dyskinesia. A regional wall motion score index (WMSI) was calculated for each time point by dividing the sum of the ten segmental wall motion scores by ten. A WMSI of 1 therefore corresponds to completely normal wall motion whereas a WMSI of greater than 1 indicates abnormal wall motion in one or more segments. WMSI has been correlated with the extent of myocardial ischemia and infarction determined by perfusion imaging and autopsy studies. For evaluation of diastolic function, pulsed Doppler flow profiles were recorded at each time point for mitral inflow and pulmonary venous flow. The pulsed Doppler sample volume was positioned at the tips of the mitral leaflets for mitral inflow and 1–2 cm inside the pulmonary vein for pulmonary venous flow [7]. Offline measurements of E and A velocities, deceleration time, and S and D waves were recorded for each time point. The mean of three values was entered for each time point.

2.2. Haemodynamic data
At each time point the cardiac output as recorded by the continuous cardiac output catheter (Baxter Vigilance Monitor Model VGS, Baxter Healthcare Corp., Irvine, CA) was noted, together with the mixed venous oxygen saturation (Sv02) and the pulmonary artery diastolic pressure (PAD).

2.3. Surgical technique
Following median sternotomy, dissection of the left internal mammary artery and vein harvesting, heparin was given and the distal anastamotic sites identified. Two posterior pericardial sutures were placed to assist in elevating the heart and an OctopusTM stabilizer (Medtronic) was used for each anastamosis. A 5-min test occlusion of each coronary artery was performed to assess tolerance to myocardial ischemia prior to beginning the anastamosis. Epicardial pacing wires were placed as necessary. The order of grafting was dictated by tolerance to ischemia. Proximal anastamoses were performed with a partial occlusion clamp following completion of the distal anastamoses.

2.4. Statistical analysis
Data were analyzed using SigmaStat for Windows version 2.0 (SPSS Inc., Chicago, IL). All data are presented as the mean±standard deviation. Baseline, 10-min anastomotic time, and end operation data points were compared within groups using one-way repeated measures ANOVA (RM ANOVA) with post hoc Tukey's tests for multiple comparisons. Statistical significance was considered a P value less than 0.05.


   3. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
4. Discussion
 Appendix A. Conference...
 References
 
Thirty-four consecutive OPCAB anastamoses were evaluated in 17 patients (Table 1). All patients underwent LIMA to LAD anastomoses. There were 17 LAD, nine RCA, and eight LCX grafts evaluated in this study. There were no postoperative deaths or major morbidity following each of the procedures. Heart rate was not significantly different during each anastamosis. Similarly, pulmonary arterial diastolic pressure (PAD) was not significantly changed before, during, or after each anastamosis (Fig. 1, Table 1), demonstrating similar loading conditions in each patient.


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  		Table 1. Measurements made at baseline, 10 min during the anastomoses, and at the end of the operationa

 


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  		Fig. 1. Pulmonary arterial diastolic pressure (PAD) at baseline, 10 min into grafting of the right, left anterior descending and left circumflex coronary arteries, and at the end of each operation.

 
Wall motion score index (WMSI) significantly declined during grafting of the LCX as demonstrated by a higher WMSI (2.4±1.4 vs 1.5±0.63 and 1.9±0.91) when compared to the RCA and LAD grafts with one-way repeated measures ANOVA (Fig. 2). This significant decline in systolic wall thickening during LCX grafting, however, returned to baseline at the end of the operation (1.5±0.66). This represented a reversible regional systolic dysfunction during LCX grafting that was not seen during RCA and LAD grafting.



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  		Fig. 2. Wall motion score index (WMSI)) at baseline, 10 min into grafting of the right, left anterior descending and left circumflex coronary arteries, and at the end of each operation.

 
The E/A ratio was significantly higher (3.5±1.4 vs 1.1±0.33 and 1.2±0.44) during LCX grafting when compared to the RCA and LAD grafting, and returned to baseline at the end of the operation (1.1±0.42) (Fig. 3). This represented a reversible restrictive diastolic filling pattern during LCX grafting, which was not seen during RCA and LAD grafting.



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  		Fig. 3. E/A ratio at baseline, 10 min into grafting of the right, left anterior descending and left circumflex coronary arteries, and at the end of each operation.

 
The PVS/PVD ratio was significantly lower during LCX grafting (0.7±0.45) as compared to the RCA and LAD grafts(1.1±0.19 and 1.0±0.58), and also returned to baseline at the end of the operation. This was also indicative of reversible diastolic filling during LCX grafting (Fig. 4).



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  		Fig. 4. PVS/PVD ratio at baseline, 10 min into grafting of the right, left anterior descending and left circumflex coronary arteries, and at the end of each operation.

 
Deceleration time was shorter during LCX grafting (147±59.0 ms) when compared to RCA (184±98.7 ms) and LAD (171±55.7 ms) grafting, though a statistically significant difference was not detected. As with the other hemodynamic variables, deceleration time returned to baseline at the end of the operation (191±58.6 ms).

Continuous cardiac output was unchanged during RCA, LCX, and LAD grafting at baseline, during grafting, and at the end of the operation (Table 1). Similarly, mixed venous oxygen saturation was unchanged at baseline, during grafting, and at the end of the operation during RCA, LCX and LAD grafting (Table 1). Fig. 5 plots continuous cardiac output versus mixed venous oxygen saturation at the 10 min timepoint during grafting of the RCA, LAD, and LCX arteries.



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  		Fig. 5. Continuous cardiac output (CCO) versus mixed venous oxygen content (SVO2) 10 min into grafting of the right, left anterior descending, and left circumflex coronary arteries.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
Appendix A. Conference...
 References
 
In this study, we have demonstrated that significant changes in cardiac function occur with surgical exposure of the left circumflex coronary artery during beating heart surgery. Specifically, a significant reduction in left ventricular compliance with restrictive diastolic filling was demonstrated during LCX positioning and grafting, as indicated by an increased E/A ratio and a decreased PVS/PVD ratio, which returned to baseline at the end of surgery. Concomitant reversible systolic dysfunction was demonstrated by an increased wall motion score index during LCX grafting. Despite these significant changes in cardiac function during grafting of the left circumflex artery, these changes resolved spontaneously upon completion of the LCX graft and did not persist postoperatively. One explanation may be that exposure of the LCX remains difficult in some patients and hypertrophied hearts are more difficult to rotate and expose safely. Maneuvers such as selective lung ventilation and deliberate herniation of the heart into the right thorax can sometimes be helpful in gaining adequate exposure of the heart.

The clinical relevance of this study is that in the setting of left circumflex disease, this area of the heart can be revascularized safely despite intraoperative changes in cardiac function. In the patient with multivessel coronary disease, these findings become increasingly important as we expand off-pump coronary revasularization to patients with multi-vessel disease and decreased left ventricular function. Surgical exposure of the left circumflex artery has always remained difficult in beating heart surgery given the hemodynamic consequences involved in with exposure, though our study might suggest that the temporary restrictive filling pattern seen during grafting reverses at the end of the procedure, thus allowing surgeons tom consider patients with difficult left circumflex disease.

Diastolic function is characterized by a rapid filling wave (E) followed by a period of diastasis with no flow, and then a late filling wave (A) produced by atrial systole. In normal subjects, the E wave velocity is greater than the A wave velocity and the E/A ratio is between 1 and 2. With severe diastolic dysfunction and higher filling pressures as seen with restrictive filling, the E wave velocity becomes greater and the A wave velocity smaller, resulting in E/A ratios of 2–5. This is because the high left atrial pressure produces a greater transmitral gradient in early diastole. In our study, the increase in the E/A ratio of 3.5 during LCX grafting was significantly higher than that occurring with RCA and LAD grafting, indicating a restrictive filling pattern during positioning and grafting of the left circumflex artery [7].

There are three distinct velocity components in pulmonary vein Doppler recordings: atrial inflow during ventricular systole (PVS), atrial inflow during ventricular diastole (PVD), and flow reversal during atrial systole (PVA). In the presence of restrictive ventricular filling, PVS is smaller than PVD and resultant PVS/PVD ratio becomes less than 1. In our study, the PVS/PVD ratio was significantly lower during LCX grafting when compared to RCA and LAD grafting, which returned to baseline at the end of surgery, indicating a restrictive pattern of diastolic filling [7].

Our evaluation of systolic function was confined to the mid and apical left ventricular segments because wall thickening is usually less uniform in the basal segments and more difficult to evaluate. Likewise our evaluation of diastolic function was confined to those parameters that are reliably obtainable in a short period of time. Long axis images were reliably obtainable, even with elevation of the cardiac apex, since the left atrium is still in contact with the esophageal wall, providing an imaging window. Haemodynamic measurements were altered intra-operatively not only by surgical maneuvers but also by Trendelenburg positioning. Mixed venous oxygen measurements were also affected not only by cardiac output but also by alterations in lung ventilation during parts of the procedure, as required by the surgeon.

The majority of early OPCABs were confined to single coronary anastamoses of the LAD. Refinements in surgical technique, notably with the development of epicardial stabilizers, are now making multivessel CABG much more feasible.


   Footnotes
 
Presented at the 14th Annual Meeting of the European Association for Cardio-thoracic Surgery, Frankfurt, Germany, October 7–11, 2000.


   Appendix A. Conference discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
References
 
Dr V. Subramanian (New York, NY, USA): Can you tell us in relation to your measurements, were they before the stabilization was deployed or before the coronary occlusion? I am not sure when the diastolic filling changes you saw, because that may be very important to look at it. And also if the patient population had any preoperative mitral regurgitation, it may offset all of your findings.

Dr Clements: We had one or two patients who had mild mitral insufficiency. One or two of those did get worse during the period of cardiac displacement. We did measure the changes in function both before and after the displacement, before and after the coronary occlusion, and I think that in the end, most of the changes occurred with the displacement rather than with the coronary occlusion themselves.

Dr Subramanian: You didn't answer the question. Are the changes in diastolic function before or after stabilization? You displace the heart and then you stabilize, and then you have another compressive effect after stabilizer.

Dr Clements: The measurements were taken with the stabilization and the displacement together.

Dr Subramanian: So it is not a question of displacement alone then?

Dr Clements: Right.

Dr C. Mullangi (Dallas, TX, USA): We did a lot of work with the right heart support using the displacement with and without support. My question is, in the animal models when you use the heart displacement to the circumflex portion, one of the major factors and which is very difficult to demonstrate is the inflow obstruction at the caval junction, cavoatrial junction, inferior vena caval, right atrium, superior vena cava and right atrium. There is an amount of calcium, anywhere from 10 to 45%. It is a very difficult area to investigate. Have you got any experience on that apart from decreased ventricular function? This is a major contributing factor.

Dr Clements: Well, we don't have any information on directly how much of the right ventricular inflow is compromised, however, the pulmonary artery diastolic pressures were elevated during the procedure and the cardiac outputs were maintained. So I think by virtue of compensating for the displacement with a Trendelenburg positioning we were able to get flow through to the left side.

Dr W. Flameng (Leuven, Belgium): Could you give us some more information about the operative technique you used? Did you use complete occlusion of the coronary artery? Did you use shunts or anything?

Dr Clements: Shunts were not used in this group. Almost all of them had Octopus stabilization and sutures through the posterior pericardium to elevate the heart.

Dr Flameng: Do you have evidence of graft patency in these cases, is there a difference between the different grafts in the different areas?

Dr Clements: You mean at the end of surgery?

Dr Flameng: Yes.

Dr Clements: No, we do not have confirmation in all patients, however, the wall motion returned to normal at the end of surgery, and we don't have clinical evidence of graft compromise.


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
 References
 

  1. Reichenspurner H., Boehm D.H., Welz A., Schmitz C., Wildhirt S., Schulze C., Meiser B., Schuetz A., Reichart B. Minimally invasive coronary artery bypass grafting: port access approach versus off-pump techniques. Ann Thorac Surg 1998(66):1036-1040.
  2. Puskas J.D., Wright C.E., Ronson R.S., Brown W.M., Gott J.P., Guyton R.A. Off-pump coronary bypass via sternotomy is safe and effective. Ann Thorac Surg 1998;66:1068-1072.[Abstract/Free Full Text]
  3. Krucylak P.E. Intraoperative considerations during minimal-access cardiac surgery. Sem Thorac Cardiovasc Surg 1999;11(2):116-124.[Medline]
  4. Jurmann M.J., Menon A.K., Haeberle L., Salehi-Gilani S., Zeimer G. Left ventricular geometry and cardiac function during minimally invasive coronary artery bypass grafting. Ann Thorac Surg 1998;66:1082-1086.[Abstract/Free Full Text]
  5. Moises V.A., Mesquita C.G., Campos O., Andrade J.L., Bocanegra J., Andrade J.C., Buffulo E., Carvalho A.C. Importance of intraoperative transesophageal echocardiography during coronary artery surgery without cardiopulmonary bypass. J Am Soc Echocardiogr 1998;11:1139-1144.[Medline]
  6. Shanewise J.S., Cheung A.T., Aronson S., Stewart W.J., Weiss R.L., Mark J.B., Savage R.M., Sears-Rogan P., Mathew J.P., Quinones M.A., Cahalan M.K., Savino J.S. ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal echocardiography examination: recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists task Force for Certification in Perioperative Transesophageal Echocardiography. Anesth Analg 1999;89(4):870-890.[Free Full Text]
  7. Rakowski H., Appleton C., Chan K-L., Dumesnil J.G., Honos G., Jue J., Koilpillai C., Lepage S., Martin R.P., Mercier L-A., O'Kelly B., Prieur T., Sanfilippo A., Sasson Z., Alvarez N., Pruitt R., Thompson C., Tomlinson C. Danadian consensus recommendations for the measurement and reporting of diastolic dysfunction by echocardiography. J Am Soc Echocardiogr 1996;9(5):154-178.



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