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Ann Thorac Surg 1996;61:33-35
© 1996 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Uniformity of Perfusion in All Regions of the Human Heart by Warm Continuous Retrograde Cardioplegia

Division of Cardiothoracic Surgery, Department of Surgery, Loma Linda University Medical Center, Loma Linda, California

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Animal models have suggested that retrograde cardioplegia may be poorly distributed to septal and right ventricular regions of the heart; if true, this may have dangerous implications for warm continuous retrograde cardioplegia in humans. We have previously shown that blood gases from coronary arteries during warm continuous retrograde cardioplegia represent postcapillary ``venous'' gases and are reflective of myocardial perfusion.

Methods. To determine regional differences in perfusion during warm continuous retrograde cardioplegia we obtained blood gases from three regions of the heart in 141 consecutive patients undergoing coronary artery bypass grafting, aortic valve replacement, or both. Right heart perfusion was determined by blood gases from the right coronary artery orifice, acute marginal, or posterior descending coronary arteries; circumflex or lateral wall perfusion was determined by samples from obtuse marginal or intermediate coronary arteries; and anterior wall/septal perfusion was determined by left anterior descending and diagonal coronary artery blood gases. Warm continuous retrograde cardioplegia flow ranged from 150 to 300 mL/min depending on heart size. A mean of 4 ± 1 samples/patient were obtained.

Results. There were no regional differences in postcapillary pH, carbon dioxide tension, or CO₂ production during warm continuous retrograde cardioplegia. Oxygen tensions were lower in the right and anterior/septal regions of the heart, implying more O₂ uptake. No regional acidosis, consistent with poor perfusion, could be detected.

Conclusions. We conclude that, unlike experimental models, regional myocardial perfusion, including the right heart, is uniform during ``high-flow'' warm continuous retrograde cardioplegia in humans.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Clinical success with warm continuous retrograde cardioplegia (WCRC) seems to be at variance with experimental models of retrograde cardioplegic distribution, which suggest that flow is deficient to the right ventricle and septum [1, 2]. We have previously shown good preservation of right ventricular function, both experimentally and clinically, using intermittent cold blood retrograde cardioplegia [3, 4]. Recently, we demonstrated that global myocardial homeostasis was preserved in humans by WCRC, using blood gas analysis of blood egressing from coronary arteriotomies [5]. During retrograde cardioplegia, blood can only reach a coronary artery by traversing a capillary bed; thus, measurement of blood gases from coronary arteries represents true myocardial ``venous'' gases [5]. To determine regional myocardial metabolism and, hence, the adequacy of retrograde perfusion, we compared the blood gases obtained from regional coronary arteries during aortic cross-clamping with WCRC in 141 patients undergoing coronary artery bypass grafting, aortic valve replacement, or both.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Patients who presented for myocardial revascularization, aortic valve replacement, or both on the service of the primary author (S.R.G.) from April 1992 to September 1993 were available for study. Myocardial protection was provided by continuous retrograde infusion of warm (37°C) blood cardioplegia (9:1 dilution) administered through a flexible catheter with a manually inflated distal balloon and with constant monitoring of coronary sinus pressure (Gundry RSCP catheter; DLP, Inc, Grand Rapids, MI). The catheter was placed into the coronary sinus via a pursestring suture in the high right atrium using a flexible stylet within the catheter. In the case of aortic valve replacements, care was taken to avoid distal placement of the balloon; instead, the catheter tip was aligned with the myocardial septum.

Induction of myocardial arrest was accomplished by the infusion of warm retrograde blood cardioplegia at 300 mL/min using a final KCl concentration of 27 mEq/L into the coronary sinus RSCP catheter until arrest was achieved and then switching to continuous infusion of a 9:1 blood cardioplegia mixture with a KCl concentration of 9 mEq/L at 150 to 300 mL/min flow depending on heart size. All aortic valve replacements and operations on hypertrophied hearts began with 250 mL/min flow rates. Flow rates were adjusted based on blood gases from the coronary arteries to maintain ``venous'' pH greater than 7.30. Assessment of perfusion was based on these gases, the presence of flow of desaturated blood from coronary arteriotomies, and a low pressure alarm on the coronary sinus pressure line (DLP, Inc), which was set to alarm whenever the coronary sinus pressure was less than 15 mm Hg.

Samples for blood gas analysis were taken from the inflow cardioplegia line and from each arteriotomy at the time of bypass graft placement, or from the coronary ostia in the case of aortic valve replacement, at 10, 30, and if necessary at 45 minutes into the cross-clamp period. All blood gas samples were analyzed for pH, oxygen tension, and carbon dioxide tension; base excess was calculated. Right heart perfusion was determined by blood gases from the right coronary artery orifice, the distal right coronary artery, the acute marginal, or the posterior descending coronary arteries; circumflex or lateral wall perfusion was determined by samples from the obtuse margin or intermediate coronary arteries; and anterior wall/septal perfusion was determined by sampling from the left anterior descending or diagonal coronary arteries. These samples were compared with blood gases obtained from the inflow cardioplegia to examine regional O₂ uptake and CO₂ production. All patients were maintained at 37°C by active warming while on cardiopulmonary bypass.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
The results of the blood gas analysis for the 141 patients studied are shown in Table 1. A total of 560 samples were analyzed (4.0 ± 1.0 samples per patient). The inflow cardioplegia reflected a 9:1 mixture of pump blood with Roe's crystalloid cardioplegia with a resultant delivered pH of 7.4 ± 0.1. Samples representing the right heart, lateral heart, and anterior/septal portions of the heart showed pHs of 7.34 ± 0.1, 7.35 ± 0.1, and 7.33 ± 0.1, respectively. No regional acidosis was detected.

The inflow cardioplegia oxygen tension fell from 179 ± 19 to 36 ± 12, 42 ± 10, and 36 ± 10 mm Hg in the right, lateral, and anterior/septal portions of the heart, respectively. As can be seen, the most avid extractions of oxygen occurred in the right ventricle and anterior/septal portions of the heart. Indeed, 10/141 right ventricular samples (7%) had pHs less than 7.30-all occurred early in our experience with flow rates of 150 mL/min. No patient with flow rates greater than 200 mL/min had a right ventricular pH less than 7.30.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Retrograde continuous warm (or normothermic) cardioplegia for myocardial protection has seen a recent resurgence of interest owing to its theoretic ability to prevent myocardial ischemia during aortic cross-clamping. Indeed, studies by our group have shown that global myocardial homeostasis is preserved in humans with WCRC [5]. However, these apparent good clinical results are at odds with results obtained from experimental animals, where there is evidence of poor distribution of retrograde solutions to the right ventricle or ventricular septum. Stirling and associates [2], in examining microsphere distribution in dog hearts receiving either retrograde or antegrade cardioplegia, showed very poor distribution of microspheres or Evans blue dye to either the septum or the right ventricle by retrograde cardioplegia. Cooke and colleagues [1] observed similar findings in dogs even with changes in the total dose of cardioplegia or with changes in coronary sinus pressure.

Despite these experimental studies of retrograde cardioplegia distribution, our group found no difference in right ventricular cooling with retrograde blood cardioplegia versus antegrade cardioplegia in dogs [6], and equal or better right ventricular function with retrograde cardioplegia in dogs [3]. Moreover, in a clinical study involving 225 patients receiving cold intermittent retrograde blood cardioplegia, right ventricular function as assessed by intraoperative transesophageal echocardiography was either the same or improved postoperatively [4].

Why experimental studies of the distribution of microspheres in experimental animals may not correlate to the results of functional studies in either animals or humans has concerned practicing surgeons since the use of continuous retroperfusion of the heart was introduced by Lillihei and associates in the 1950s [7]. As early as 1957, Gott and co-workers [8] observed that the coronary venous anatomy of the right ventricle in humans was substantially different from that of dogs, and probably accounted for the good results observed in humans with retroperfusion of the heart.

Additional reasons for the observed good clinical results have been learned in the clinical application of WCRC that were also not predicted by experimental models. Specifically, the predicted metabolic demands of the arrested warm human heart, which were based on experimental models by Buckberg and colleagues [9], grossly underestimated the amount of retrograde blood flow needed by the human heart [5]. Furthermore, the degree to which myocardial hypertrophy affects the outcome of WCRC was largely unappreciated until only recently [10]. These new studies have demonstrated that substrate delivery to the myocardium is best met retrogradely when high flows are used routinely, usually in the range of 200 to 300 mL/min [10]. The present study was performed for the most part in such a setting, with the results reflecting uniform myocardial perfusion and metabolism. Only in those few patients in whom the flow rate was 150 mL/min did regional acidosis appear. When additional attention was given to increasing retrograde cardioplegia flow rates when regional acidosis was recognized, as was done in this study, regional inequalities of retroperfusion to the right ventricle and septum appeared to be avoided. Such adjustment of flow rates might have prevented the occasional right ventricular dysfunction observed by Okike and colleagues [11], who used lower flow rates and a nonocclusive self-inflating balloon-tipped retrograde catheter.

We conclude, on the basis of regional blood gas sampling in 141 patients receiving high-flow WCRC, that there is uniform perfusion to all regions of the human heart using this modality. These results contradict experimental animal studies but provide confirmation of the observed good clinical results obtained from WCRC.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Presented at the Poster Session of the Thirtieth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 31-Feb 2, 1994.

Address reprint requests to Dr Gundry, Division of Cardiothoracic Surgery, Loma Linda University Medical Center, 11234 Anderson St, Loma Linda, CA 92354.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

1. Cooke GA, Harris LJ, Grossi EA, Baumann FG, Galloway AC, Colvin SB. Biventricular distribution of cold blood cardioplegia solution determined by different retrograde techniques. J Thorac Cardiovasc Surg 1991;102:631–8.[Abstract]
2. Stirling MC, McClanahan TB, Schott RJ, et al. Distribution of cardioplegic solution infused antegradely and retrogradely in normal canine hearts. J Thorac Cardiovasc Surg 1989;98:1066–76.[Abstract]
3. Gundry SR, March R, Kirsh MM, et al. The coronary sinus is the superior route for cardioplegia in hearts with multivessel coronary artery lesions. Curr Surg 1982;43:200–2.
4. Gundry SR, Sequiera A, Razzouk AJ, et al. Facile retrograde cardioplegia: transatrial cannulation of the coronary sinus. Ann Thorac Surg 1990;50:882–7.[Abstract/Free Full Text]
5. Gundry SR, Wang N, Bannon D, et al. Retrograde continuous warm blood cardioplegia: maintenance of myocardial homeostasis in humans. Ann Thorac Surg 1993;55:358–63.[Abstract/Free Full Text]
6. Gundry SR, Kirsh MM. A comparison of retrograde cardioplegia versus antegrade cardioplegia in the presence of coronary artery obstruction. Ann Thorac Surg 1984;38:124–8.[Abstract/Free Full Text]
7. Lillehei CW, DeWall RA, Gott VL, Varco RL. The direct vision correction of calcific aortic stenosis by means of a pump-oxygenator and retrograde coronary sinus perfusion. Dis Chest 1956;30:123–32.[Medline]
8. Gott VL, Gonzalez JL, Zuhdi MN, et al. Retrograde perfusion of the coronary sinus for direct-vision aortic surgery. Surg Gynecol Obstet 1957;104:319–24.
9. Buckberg GD, Brazier JR, Nelson RL, et al. Studies of the effects of hypothermia in regional blood flow and metabolism during cardiopulmonary bypass. J Thorac Cardiovasc Surg 1977;73:87–94.[Abstract]
10. Gundry SR, Wang N, Sciolaro CM, et al. Warning! In human hypertrophied hearts and/or redos, warm cardioplegia may not be so hot! [Abstract] Circulation 1992;86(Suppl 1):102.
11. Okike ON, Zheng JJ. Continous warm blood retrograde cardioplegia: Metabolic and functional status of the right ventricle in humans [Abstract]. Circulation 1992;86(Suppl 1):102.

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This Article Abstract 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): Steven R. Gundry Nan Wang Charles M. Sciolaro Glen S. Van Arsdell Anees J. Razzouk Leonard L. Bailey Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gundry, S. R. Articles by Bailey, L. L. Search for Related Content PubMed PubMed Citation Articles by Gundry, S. R. Articles by Bailey, L. L.