HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Search for Related Content Related Collections Related Article

Ann Thorac Surg 2000;70:1360-1361
© 2000 The Society of Thoracic Surgeons

---

Original articles: cardiovascular

Discussion

	Dr Paul F. Grü;-14undeman

Top Dr Paul F. Gru;-14undeman Dr Kit V Arom Dr Edgerton

 
(Utrecht, The Netherlands): Doctor Ergin, Dr Glower, members and guests, Dr Edgerton.

To my knowledge, this is the first clinical report on detailed hemodynamic changes with vertical displacement of the human beating heart. We have to congratulate Dr Edgerton and his group for successfully taking complex measurements during off-pump coronary artery bypass grafting, which by itself is not a simple routine procedure. Although not taken with position-independent Millar catheters, their data make sense. Their results mimic largely our displacement experiments in the porcine model.

The important observation in this study is that stroke volume is not restored despite enhanced ventricular preloads. This contrasts with our animal studies, in which stroke volume was almost normalized in the presence of highly enhanced preload pressures (> 200% change from baseline). Although arterial pressure almost reached normal values, one may have concerns about kidney and bowel perfusion.

I agree with the speaker that a biventricular heart failure is created because of strangulation and deformation of both ventricles. In a 90-kg pig, we demonstrated previously that by displacing the heart, geometric changes of the ventricles occur, which predominantly interfere with pumping action of the right ventricle. A video illustrates changes in ventricular cross-sectional areas. (Video shown.)

We used an experimental Octopus stabilizing platform, mounted on a single-handle system, including echocardiography. The echocardiography probe is advanced close to the epicardium, making contact with the posterior aspect of the heart. Millar pressure-tip catheters are inserted into the heart, and they obtain measurements independent of body position. We attach the suction device to the posterior territory. Note the difference in anatomy: the pig’s apex is more or less in the midline.

Now we expose the posterior territory by lifting the heart in the midline. Subsequently, we put the table head-down, while the heart remains displaced 90 degrees anteriorly. In this way, we keep the same echocardiography plane through both ventricles during maneuvers.

Echocardiography shows the following: the right ventricle becomes folded and crumpled. The free wall is pressed between the septum and its surrounding tissues. The right ventricular outflow tract is somewhat narrowed. Note the oval shaped left ventricle with a diminished cross-sectional area. No valve showed insufficiency here. As we discovered, Trendelenburg position normalizes stroke volume and blood pressure when the heart is lifted. The right ventricle is pushed open. Note that the cross-sectional area of the left ventricle increases dramatically. After replacing the heart in anatomic position, in horizontal table position, you see that the right ventricle is temporarily overdistended by increased filling, but heart function recovered shortly after repositioning.

In my opinion, the key issue here is to keep the heart filled and to preserve diastolic function of both the right and left ventricles as much as possible at all times.

Doctor Edgerton, my questions are, did you observe aortic valve regurgitation that may explain the depressed stroke volume after all the corrective maneuvers were done? Second, were creatine kinase-MB levels elevated, indicating ischemia or coronary underperfusion? Third, what strategy do you advocate to expose circumflex territories in the hypertrophied, impaired left ventricle? And fourth, to what extent did mechanical stabilization affect cardiac function in addition to cardiac displacement?

Thank you for the privilege of discussing this interesting paper.

	Dr Kit V Arom

Top Dr Paul F. Gru;-14undeman Dr Kit V Arom Dr Edgerton

 
(Minneapolis, MN): Mister Chairman, I rise to congratulate Dr Edgerton and his associates for bringing this matter to our attention in a timely fashion.

We have observed hemodynamic changes during the 90-degree displacement of the heart in the clinical setting. Our findings, however, are somewhat different from Dr Edgerton’s. During our off-pump coronary artery bypass grafting procedure, particularly when we were working on the circumflex system, we always put the patient in the Trendelenburg position and allow the filling pressure to rise to 20 mm Hg or higher. We wait for a while until the hemodynamic variables return to near normal before we start the anastomosis. It is important not to perform the anastomosis right after the heart is elevated. We always wait 3 or 4 minutes and a few times as long as 10 minutes before we start to put the stitches in. Using this maneuver allows us to complete the anastomosis most of the time.

I think there are three areas that would lead to success: (1) it is very important to put the patient in the Trendelenburg position and allow the filling pressure to reach at least 20 mm Hg; (2) be patient and wait until hemodynamic variables return to near normal; and (3) having a proactive, friendly anesthesiologist on the opposite side of the ether screen to manage the ups and downs of the blood pressure is also important.

We have wondered what this hemodynamic derangement during cardiac displacement could do to patients who have a poor left ventricular function and undergo off-pump coronary artery bypass grafting. We ask the questions: "Is low ejection fraction safe for off-pump coronary artery bypass grafting? And does it lead to more complications or death?" Looking at the subset of our patients who underwent operations during the same time span, there were 44 patients in the off-pump group and 132 patients in the on-pump group. They both had an ejection fraction equal to or less than 30%. Univariate analysis of the variables and complications or death shows that there were no significant differences between the two groups, except there is more significant blood loss in the on-pump group and significantly less enzyme leak in the off-pump group. Multivariate analysis showed that the pump alone is a predictor of more complications. Otherwise, there was no statistical difference among the variables.

So I believe that if we put the patient in the Trendelenburg position during cardiac displacement and allow the hemodynamic variables to return to near normal by raising the filling pressures to at least 20 mm Hg, this will allow the surgeon to perform off-pump operations successfully in the circumflex territory in the majority of patients.

Thank you very much.

	Dr Edgerton

Top Dr Paul F. Gru;-14undeman Dr Kit V Arom Dr Edgerton

 
I wish to thank both Dr Gründeman and Dr Arom for rising to discuss this paper. Doctor Arom, you have stated that by simply putting the head down, the hemodynamics return to normal. Yet many clinicians continue to have difficulty maintaining stability during off-pump techniques with decompensated ventricles. It is, however, this group of the sickest patients that we believe will benefit most from beating heart techniques. We agree that, on first look, the hemodynamics appear to be returning to normal simply by putting the patient in Trendelenburg. With the variables that are normally measured, this indeed seems to be the case. In our study, the mean arterial pressure decreased from 77 to 63 mm Hg in the circumflex positioning. This represents only an 18% decrement, and this subtle change may escape the attention of some clinicians who are busy with the technical aspects of the procedure. We have, however, shown that it is associated with a very significant decrement in both stroke volume and cardiac output. I caution that the cardiac output determinations you are receiving in the operating room may provide a false sense of security. Specifically, the catheters that provide "continuous cardiac output" reading actually lag by 5 minutes. Accordingly, the seemingly normal cardiac outputs that you are reading off the monitor during displacement of the heart are actually those from 5 minutes earlier, when the heart was in its normal anatomic position. If cardiac output is measured by thermal dilution techniques, you must be aware that small amounts of tricuspid insufficiency induced by displacement of the heart will render these measurements falsely high. Thus, we think that there are indeed significant hemodynamic changes occurring during displacement of the heart and only by understanding these will we be able to develop techniques to extend the benefits of off-pump surgical procedures to our sickest patients.

We are fascinated to learn of your results in analyzing your on-pump and off-pump patients for mortality. Your findings parallel those of our group. We examined the results of multivessel coronary artery bypass grafting from January 1995 through June 1999 in a total of 8,754 patients, 513 of which were performed off-pump. Similar to your findings, univariate analysis did not reveal use of the pump to be a risk factor for mortality. However, in stepwise logistic regression analysis, the use of cardiopulmonary bypass emerged as a strong independent risk factor for mortality with an odds ratio of 2.32.

Doctor Gründeman, we acknowledge the contributions of you and your group and thank you for rising to comment. You have asked about aortic insufficiency. We did not note any new aortic insufficiency produced by displacement of the heart. You also asked whether we measured creatine kinase levels as a determination of myocardial ischemia. We did not measure them; however, other studies have looked at troponin levels after off-pump techniques and shown no increase. We presume this is because the intervals of transient vessel occlusion, which ranged from 7 to 10 minutes, are too short to induce an enzyme leak. Perhaps a more sensitive indicator would be to measure coronary sinus lactates, which we have not yet done.

All of our studies were conducted with the single suction stabilization device, and thus we did not compare the results of compression versus suction for stabilization.

I thank you for the privilege of presenting these data.

Related Article

Analysis of hemodynamic changes during beating heart surgical procedures

Megumi Mathison, James R. Edgerton, Jeffrey L. Horswell, Jodi J. Akin, and Michael J. Mack
Ann. Thorac. Surg. 2000 70: 1355-1360. [Abstract] [Full Text] [PDF]

This article has been cited by other articles:

				P.-G. Chassot, P. van der Linden, M. Zaugg, X. M. Mueller, and D. R. Spahn Off-pump coronary artery bypass surgery: physiology and anaesthetic management{dagger} Br. J. Anaesth., March 1, 2004; 92(3): 400 - 413. [Abstract] [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Search for Related Content Related Collections Related Article