| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
J Thorac Cardiovasc Surg 1996;112:1046-1053
© 1996 Mosby, Inc.
CARDIOPULMONARY BYPASS, |
Received for publication Sept. 21, 1995 Revisions requested Nov. 14, 1995; revisions received April 3, 1996 Accepted for publication April 4, 1996. Address for reprints: Arnaud Farge, MD, Chirugie Cardio-vasculaire, Clinique René Leriche, Hôpital Broussais, 96 rue Didot, 75014 Paris, France.
Abstract
Retroperfusion of the coronary sinus does not provide homogeneous distribution of cardioplegic solution. The goal of this study was to analyze the distribution of flow during retrograde cardioplegic infusion in cadaveric human hearts with two different techniques of coronary sinus cannulation: (1) internal occlusion of the coronary sinus by balloon inflation and (2) external occlusion by tightening the orifice of the coronary sinus around a simple catheter. To evaluate differences between the two techniques, angiographic and electron-beam computed tomographic studies were performed. Computed digital angiography was performed on 14 hearts. Angiographic patterns varied according to type of coronary sinus cannulation. With the balloon inflation technique, the marginal vein and the anterior descending vein were perfused first; the posterior descending vein was not perfused. This vein was opacified secondarily through a venovenous anastomosis located at the apex of the heart. Backward flow into the right atrium (steal phenomenon) was demonstrated. At completion of retroperfusion, the inferior part of the septum remained poorly opacified. Conversely, angiographic findings after external occlusion of the coronary sinus revealed simultaneous injection of all venous channels. The entire septum was well opacified at completion of retroperfusion. Electron-beam computed tomographic study was performed on eight hearts with the external occlusion technique and nine with the internal occlusion technique. The computed tomographic findings confirmed the results of digital angiography. The peak myocardial enhancement and the peak rising rate of myocardial enhancement within the interventricular septum were significantly more important (p < 0.0001) when the external coronary sinus occlusion mode was used than when the internal coronary sinus occlusion mode was used. In all hearts except one, the right ventricular wall was not opacified, regardless of the type of cannulation and the type of radiologic analysis. This study demonstrates the importance of coronary sinus cannulation technique in optimizing the protection of the interventricular septum with retrograde cardioplegic infusion. (J THORACCARDIOVASCSURG1996;112:1046-53)
Retrograde cardioplegic infusion through the coronary sinus (CS) is an increasingly popular technique for myocardial protection.
1-3 Recent studies have shown, however, that this technique does notprovide adequate protection for the interventricular septum and the right ventricular wall. 4-6 The goal of this study was to analyze the distribution of flow during retrograde cardioplegic infusion in cadaveric human hearts with two differents techniques of CS cannulation. To evaluate differences between the two techniques, angiographic and electron-beam computed tomographic (EBCT) studies were performed.
Materials and methods
Normal hearts were obtained from adult cadavers aged from 35 to 55 years (mean age 47 years). Cardioplegic solution delivery was achieved through a 12F Foley catheter, that we use clinically. The balloon catheter was placed just inside the CS and not beyond the left anterior descending vein (LADV).
Two different techniques of CS cannulation were used. (1) Internal occlusion was performed as follows: After introduction of the perfusion catheter extremity, the balloon was inflated inside the CS with 4 ml saline solution. The complete occlusion obtained was independent of CS perfusion pressure. (2) External occlusion was performed as follows: the tip of the perfusion catheter was placed inside the CS and kept secured by a purse-string suture around the ostium. In this case, of course, the balloon is not inflated.
Angiographic studies were performed on 14 hearts. Both CS cannulation techniques were tested in all 14 hearts. Between each injection, the hearts were rinsed with 1 L saline solution. After selective cannulation of the CS, retroperfusion of contrast medium (50% saline solution and 50% iopamidol) at room temperature was performed at a constant flow rate of 100 ml/min for 2 minutes. This low flow of contrast medium was used to achieve high-quality sequential venous opacification without myocardial opacification obscuring vessel detail. The mean CS pressure observed was 40 mm Hg.
The progression of the contrast medium was continuously visualized by means of computerized digital angiography. Images were acquired by a Siemens digital radiographic system (Polytron; Siemens Co., Erlangen, Germany) onto a 512 x 512 x 8 bit pixel at 6 frames/sec during a 30-second acquisition period. All angiograms were performed in the left transverse position (orthogonal to the septum) to visualize the venous tributaries to the CS. Digital substraction was performed with a mask of 10 frames before injection of contrast medium. At the end of injection, the quality of the septal perfusion was assessed according to the degree of opacification of the septal veins.
Image acquisition
EBCT studies were carried out in 17 hearts. The EBCT technique used for this study has been described in detail elsewhere. 7-9 With the multislice flow mode used for this study, image acquisition required 50 msec and yielded an in-plane resolution of 1.5 mm and a slice thickness of 8 mm. Each heart was positioned to obtain tomographic acquisition in left ventricular short-axis planes. A series of eight tomograms were acquired without dye injection to ensure proper positioning. For retrograde perfusion assessment, a series of four midventricular tomograms was acquired at room temperature during a 30-second manual bolus injection through the catheter of 50 ml contrast medium (iopamodol, 100 mg iodine/ml). The mean CS pressure observed was 40 mm Hg. At each level, 20 time points were obtained every second during a first set of 10 seconds and every 2 seconds during a second set of 20 seconds. The scanning time covered the entire injection period. Hearts used for EBCT studies were different than hearts used for angiographic studies. Myocardial retrograde perfusion results of nine hearts injected with the CS internal occlusion technique and eight other hearts injected with the CS external occlusion technique were compared.
Image analysis
Regions of interest (ROIs) were focused on four left ventricular myocardial regions in a midventricular tomogram: anterior interventricular septum and anterior, lateral, and inferior walls. The C-100 scanner software (Imatron Inc., South San Francisco, Calif.) calculated the average and standard deviation of the pixel density values for the same spatially fixed ROI throughout the time-repeated scans at the same level. A time versus radiodensity plot was generated for each ROI.
Relative retrograde perfusion index calculation
In each heart, the relative quality of the retrograde flow measurement was determined by comparing the myocardial enhancements obtained within the four ROIs. The maximal myocardial enhancement in a specific heart was defined as the maximal value of the four ROIs in that heart and expressed as a percentage. Peak myocardial enhancements within the three other ROIs were expressed as percentages of that maximal myocardial enhancement. Furthermore, the peak rising rate of myocardial enhancement was defined within each ROI by calculating the maximal slope of the curve time versus myocardial enhancement and was expressed as a percentage of maximal myocardial enhancement.
Statistical analysis
Differences in myocardial enhancement obtained in hearts injected with the CS internal occlusion technique and in hearts injected with the CS external occlusion were compared with 0 (baseline) with the unpaired t test. A p value less than 0.05 was considered as a significant difference.
Anatomic study
The CS was anatomically defined as the portion of the cardiac venous system that begins where the oblique vein of Marshall stems and ends at its ostium in the right atrium. 10-14 The ostium of the CS can be identified by using the thebesian valves as a landmark. The valve of Vieussens is made of one or two cusps located at the origin of the great cardiac vein.
At the end of the experiment, the main branches of the CS were dissected. The length of the CS was measured between the thebesian valve (CS orifice) and the valve of Vieussens by means of a ruler graduated in millimeters. The distance between the CS orifice and the origin of its main branches was also calculated. The orificial diameter of each vessel was measured by means of internal probes. Each heart was then completely dissected to inspect the coronary arteries.
Results
Angiographic results
Angiographic results varied according to the type of cannulation used. In all hearts cannulated with the internal occlusion technique, the sequence of perfusion was identical. The posterior descending vein (PDV) was consistently not perfused at the initial phase of the injection, and the contrast medium was directed toward the other branches of the CS (LADV and obtuse marginal vein [OMV]). After 30 seconds, however, filling of the PDV was most often observed through a direct venovenous anastomosis located at the apex of the heart between the LADV and the PDV (Fig. 1).
|
|
|
Table I). No significant differences were observed in other myocardial ROIs. Subjectively more delayed septal myocardial enhancement was observed with CS occlusion mode. In all hearts with the CS external occlusion mode except for one, the right ventricular free wall remained unopacified regardless of the type of cannulation.
|
|
|
Table II).
|
Retrograde cardioplegic infusion through the CS is currently a technique widely used for myocardial protection in heart operations. 1,2,15-17 Compared with the anterograde technique, retrograde infusion through the CS has the following advantages: (1) absence of selective cannulation of the coronary ostia during aortic valve operations, (2) the possibility of repeated injections of cardioplegic solution without interruption of the surgical procedure, and (3) better cardioplegic delivery in case of coronary lesions.
The major limitation of this technique is a poor protection of the right ventricular wall and of the interventricular septum. 4,6,17 Several authors have used sophisticated techniques to evaluate the myocardial distribution through CS perfusion, such as a corrosion-casting technique with a low-viscosity resin 6 and distribution of radioactive microspheres. 4,17 In all of these studies, CS perfusion was achieved with a balloon catheter inflated inside the lumen. As reported by Menasché and coworkers, 1 this technique can result in nonhomogeneous myocardial distribution.
Our goal was to compare two occlusions modes to analyze myocardial distribution with retrograde cardioplegic infusion. We used a dynamic approach and an alternative technique not requiring balloon inflation, with low-flow perfusion to refine the dynamic angiographic and EBCT analyses. Direct observation of the progression of the perfusate into the coronary veins was studied with digital angiography. The distribution of contrast medium within the myocardium was directly analyzed by EBCT. This technique has been well described in previous reports as an interesting tool for evaluating myocardial perfusion. 7-9 Regional myocardial perfusion was assessed by recording contrast medium clearance curves within a defined ROI. Our studies were conducted on normal cadaveric hearts without coronary disease or hypertrophy.
The results obtained with both techniques showed significant differences according to type of cannulation (Figs. 1 and 3). When the standard technique of internal occlusion (intraluminal balloon inflation) was employed, poor opacification of the posterior part of the interventricular septum was observed. This area is supplied primarily by the PDV branches. Careful analysis of the computerized digital angiograms and of the anatomic studies enabled us to propose two mechanisms possibly explaining this observation: (1) The PDV is initially unopacified because its origin lies proximal to the balloon. As angiographically demonstrated, perfusion of the LADV and the OMV occurred first and was followed by perfusion of the PDV, which was filled by venovenous anastomosis. The perfusate returned toward the area of lower pressure through the PDV proximal to the inflated balloon. Consequently, the contrast medium drained into the CS may not penetrate into septal branches (steal phenomenon; Fig. 1). In only two cases, however, was opacification of the PDV observed in association with a satisfactory perfusion of the septum. The complete occlusion of the PDV by the inflated balloon was the likely cause of a high PDV pressure and consequently of the good perfusion of the septal branches. (2) With intraluminal inflation, regardless of the balloon position, filling by venovenous anastomosis between LADV and PDV was not consistently sufficient to correctly perfuse the interventricular septum.
By quantifying myocardial enhancement, this EBCT study confirmed angiographic findings. A relative underperfusion of the septum was observed with the internal CS occlusion mode (Fig. 4), thus confirming the potential role of the PDV shunt in the nonhomogeneous distribution during retrograde cardioplegic infusion. In the remaining left ventricle (inferior, lateral, and anterior ROIs) no difference in myocardial enhancement was observed between the two CS occlusion modes. EBCT findings further confirmed the absence of retrograde perfusion of the right ventricular free wall. Such a finding would be expected because the venous drainage of the free wall of the right ventricule is known to occur through the thebesian veins and the right coronary veins, both of which are directly connected to the right cavities. EBCT lacks the sensitivity needed to demonstrate the small-caliber flow through the thebesian system. These results further substantiate concerns of many authors regarding poor right ventricular protection with retrograde cardioplegic infusion.
Finally, this study demonstrated that the interventricular septum was poorly perfused with retrograde cardioplegic administration with the internal occlusion technique, which may be due in part to the fact that the PDV was not perfused at the beginning of perfusion.
In vitro analysis, a retrograde flow rate of 100 ml/min, and retrograde injection of solutions at room temperature were used in our experimental study. Extrapolation of our results during retrograde cardioplegic infusion at higher flow rates (200 to 300 ml/min) should be performed with caution. In fact, in our study the right ventricular myocardium was not perfused (except in one case), whereas clinical studies indicate good right ventricular function despite the absence of antegrade perfusion. 1 The use of high retrograde flow, the existence of venovenous anastomoses, and the low metabolic need of the right ventricle may explain this apparent contradiction. Our observations may, however, be a partial answer to the inadequacy of retrograde cardioplegic infusion to protect the myocardium in some clinical cases. Furthermore, this study suggests that techniques to securely close the ostium of the CS may be advantageous in retrograde cardioplegic infusion. Further studies are required to determine whether the positioning of the inflated balloon catheter in the CS has an effect on the diffusion of retrogradely perfused solution.
Footnotes
From the Departments of Cardiovascular Surgerya and Radiology and INSERM,b Hôpital Broussais, and the Anatomic Institute of Paris, UFR Biomédicales des St-Pères,c Paris, France. 
References
This article has been cited by other articles:
|
|
 |
|
  A. Cerillo, S. Storti, D. Haxhiademi, M. Solinas, P. D. Sarto, P. A. Farneti, A. Clerico, and M. Glauber The double balloon cannula: a means to prevent backward flow of retrograde cardioplegia to the right atrium Interactive CardioVascular and Thoracic Surgery, June 1, 2006; 5(3): 289 - 293. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Ruengsakulrach and B. F. Buxton Anatomic and hemodynamic considerations influencing the efficiency of retrograde cardioplegia Ann. Thorac. Surg., April 1, 2001; 71(4): 1389 - 1395. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. N. Gates, H. Laks, and D. C. Drinkwater Angiographic and electron-beam computed tomography studies of retrograde cardioplegia via the coronary sinus J. Thorac. Cardiovasc. Surg., September 1, 1997; 114(3): 518 - 519. [Full Text]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
