Revista chilena de anatomía
versión impresa ISSN 0716-9868
Rev. chil. anat. v.16 n.2 Temuco 1998
STUDY OF THE PARIETAL CORONARY SINUS VALVE UNDER SCANNING ELECTRON MICROSCOPY
ESTUDIO DE LA VALVA PARIETAL DEL SENO CORONADO EN MICROSCOPIA ELECTRONICA DE BARRIDO
** Nadir Eunice Valverde Barbato de Prates
MATZUDA, M. & BARBATO DE PRATES, N. E. V. Study of the parietal coronary sinus valve under scanning electron microscopy. Rev. Chil. Anat., 16(2):199-203, 1998.
SUMMARY: The retrograde cardioplegia is a procedure regularly used to protect the miocardium during cardiac surgeries. The cardioplegic solution is retrogradly perfused through the coronary sinus, the main vein of the heart, and it is useful since the coronary venous system has shown to be free of any obstructing atherosclerotic disease. The opening of the coronary sinus occurs directly in the right atrium and an ostial valve at this level has long been related. However, a parietal valve in the coronary sinus has renewed the interest in this study. These valves could make difficult a perfect perfusion of the cardioplegic solution, particularly when low coronary sinus pressures are used. In order to understand the morphology of the parietal valve of the coronary sinus we decided to perform a study of the valve under SEM. Six fragments of the coronary sinus containing the parietal valve were taken from adult individuals, post mortem, with no gross cardiac pathologies. The samples were submitted to the usual techniques of Scanning Electron Microscopy. The parietal valve of the coronary sinus showed a half-moon shape, with a well defined structure. Its endothelium was arranged in parallel lines, similar to a stem of a tree, where we could evidence the nuclei of the endothelial cells. Under the endothelial layer we found abundant collagen and elastic fibers. Owing to its developed form seen under SEM, the parietal valve of the coronary sinus must play an important role in guiding the blood flow through the coronary sinus to the right atrium in physiological conditions and could raise difficulties to the flow of the cardioplegic solution during the retrograde cardioplegia.
KEY WORDS: 1. Heart; 2. Coronary Sinus; 3. SEM.
In the late 1800, the rediscovery of the anatomy of the coronary venous system by LANGER (1881) stimulated further research endeavors. Subsequent studies on retroperfusion through coronary sinus have continued to fascinate generations of researchers, and have introduced a new era which today again appears to be on the threshold of allowing aplication in clinical trials.Three decades have elapsed since the first serious clinical application of coronary sinus interventions were attempted. Over the last few years a renewed interest and a new demand for protecting myocardial schemia via the coronary sinus have been developed. Today coronary
sinus intervention is generally understood as a method of temporary protection of ischemic myocardium via the coronary venous system and include retroinfusion of a cardioplegic solution during cardiac arrest in surgery, retroperfusion of pharmaceutical agents, and manipulation of the venous blood drainage by pressure- controlled intermitent coronary sinus occlusion (MOHL,1988).
Coronary sinus cardioplegia is now the most widely used technique of myocardial preservation. The delivering of the cardioplegic solution through the coronary sinus is useful since the coronary venous system has shown to be free of any obstructing atherosclerotic disease. This delivering markedly reduces the metabolic requeriments of the heart (MENASCHÉ et al.,1982).
To SALERNO et al. (1991) placement of a cannula in the coronary sinus ostium has been successful in 96 % of their studied cases. They advance the cannula as far as it goes into the coronary sinus.
The coronary sinus approach is based largely on an understanding of the coronary venous and arterial anatomy (ENGELMAN,1991).
The opening of the coronary sinus occurs directly in the right atrium and an ostial valve at this level has long been related ( MOORE, 1992).
SHORMANOV (1985) in an experimental study in dogs just refers that in the coronary sinus there are valves of various complexity. In another study of anatomical human hearts he emphasizes that the regulation of the blood stream in the coronary sinus is performed by a system of simple valves (SHORMANOV,1990). PIFFER et al. (1990) refers a parietal valve in the coronary sinus. PAN-CHIH et al. (1994) observed that the distribution of retrograde cardioplegia may be impaired in the presence of competent valves, particularly when low coronary sinus pressures are used.
Although the existence of one-way valves at the orifices of the major tributary veins of the coronary sinus has long been noted in anatomy textbooks, there is little details of their morphofuntional characteristics.
In order to investigate the presence of such structures we studied under scanning electron microscopy the morphology of the vein valves of the coronary sinus and tried to establish some functional correlation.
MATERIAL AND METHOD
Six fragments of the coronary sinus containing the parietal valve were taken from adult individuals, post mortem, without any evident cardiac pathology.
The samples were washed in a 0.9% sodium chloride and fixed in modified Karnovsky solution containing 2% paraformaldehyde, 2.5% glutaraldehyde in a 0.1M sodium phosphate buffer (pH 7.4), during 24 h, at 4°C.
The material was rinsed in 0.1M sodium phosphate buffer (pH 7.4) and post-fixed in 1% osmium tetraoxide in 0.1M sodium phosphate buffer (pH 7.4) for one hour. Rinsed again in 0.1M sodium phosphate buffer solution and they were dehidrated in an increasing series of alcohol, from 40% to absolute, dried in a critical point Balzers CPD 030 and monted on metal stubs then, the samples were coated with ions 'spputering' and examined under a scanning electron microscope, Jeol JSM-6100.
The parietal valve of the coronary sinus showed a half- moon shape (Fig.1) with a well defined structure. Its endothelium was arranged in parallel lines (Fig.2), similar to a stem of a tree, where we could evidence the nuclei of the endothelial cells.
Fig.1 - Low magnification scanning electron microscopic image of the the coronary sinus parietal valve (arrow) of the endothelial cells. 130X.
Fig.2 - Scanning electron microscopic image of the region of the parietal valve showing the endothelium and the nuclei (arrow) of the endothelial cells. 1200 X.
Under the endothelial layer we found abundant elastic fibers (Fig. 3), which formed a tridimensional net and bundles of collagen fibers organized in a wavy disposition. In the sub-endothelial layer we could still find a monocyte resting on elastic fibers.
Fig. 3 - Scanning electron microscopic image of the region of the parietal valve of the coronary sinus. Shows the elastic fibers (ef) of the sub-endothelial layer. 4800 X.
In recent years there has been an increasing interest in the retrograde administration of cardioplegia. This technique offers a number of potential advantages: it avoids trauma to the coronary ostia, minimally interferes with surgical procedures, and affords access of cardioplegia to the myocardium distal to acutely occluded coronary arteries. A possible reason for a prolonged time to diastolic arrest with retrograde cardioplegia may have to do with the existence of one-way venous valves at the entrances of the major tributary veins of the coronary sinus. Anatomic variations, which are much more common in coronary veins than arteries further complicate the prediction on an optimal range of coronary venous perfusion (PAN- CHIH et al.).
We did not find any report in the literature about a SEM study of the parietal valve of the coronary sinus. SHORMANOV (1985) in an experimental study in dogs just refers that in the coronary sinus there are valves of various complexity. In another study of anatomical human hearts he enphasizes that the regulation of the blood stream in the coronary sinus is performed by a system of simple valves. (SHORMANOV,1990).
In the ligth of the growing interest in experimental and clinical use of retrograde cardioplegia for myocardium protection both animal and human cadaver hearts were examined to assess the incidence and morphology of one-way coronary vein valves by PAN-CHIH et al.
Our findings confirm statements made in histological and gross anatomical studies by SHORMANOV (1990) and by PIFFER et al. (1990) respectively and moreover, our results show in details the morphology of this valve.
We also believe based in the SEM study that the regulation of the blood stream through the coronary sinus is facilitated by the parietal valve.
SALERNO et al. reported 4% of failure in placing the cannula in the coronary sinus. PAN-CHIH et al. observed that the distribution of retrograde cardioplegia may be impaired in the presence of competent valves, particulaly when low coronary sinus pressures are used. The observations made by these authors could be explained by the existence of the parietal valve, for us described, in the coronary sinus.
Owing to its developed form seen under SEM, the parietal valve of the coronary sinus must play an important role in guiding the blood flow through the coronary sinus to the right atrium in physiological conditions and could raise difficulties to the flow of the cardioplegic solution during the retrograde cardioplegia. Further hemodynamic studies must be done in order to determine more accurately the influence of these valves in patients submitted to retrograde cardioplegia.
MATZUDA, M. & BARBATO DE PRATES, N. E. V. Estudio de la valva parietal del seno coronario en microscopía electrónica de barrido. Rev. Chil. Anat., 16(2):199-203, 1998.
RESUMEN: La cardioplegia retrógrada es un procedimiento usado regularmente para proteger el miocardio durante las cirugías del corazón. Consiste en hacer una perfusión retrógrada, a través del seno coronario, la principal vena cardíaca. Este método ha mostrado ser muy útil, pues el sistema venoso del corazón no presenta procesos obstructivos ateroscleróticos. La desembocadura del seno coronario ocurre directamente en el atrio derecho, donde una valva ostial es referida a este nivel. Pero la presencia de una valva parietal en el seno coronario ha renovado el interés de estudio. Esta valva podría dificultar la perfecta perfusión de la solución cardioplégica, particularmente cuando se usan presiones bajas. Para entender mejor la morfología y por tanto la función de la valva parietal del seno coronario, realizamos un estudio de esta valva en microscopio electrónico de barrido (MEB). Utilizamos 6 muestras de 1cm2, conteniendo el seno coronario a nivel de la valva parietal, las que fueron retiradas de individuos adultos post mortem, sin patologías macroscópicas. Las muestras fueron sometidas a las técnicas habituales de MEB. La valva parietal mostró un aspecto en media luna bien definido. Su endotelio presentó estructuras paralelas, semejantes a troncos de árboles, en los cuales se pudieron evidenciar los núcleos de las células endoteliales. Por debajo de la capa endotelial encontramos abundantes fibras colágenas y elásticas. Debido al gran desarrollo de la valva del seno coronario observada al MEB, ésta debe tener un papel importante en la orientación del contenido sanguíneo por el seno coronario, en dirección al atrio derecho, en condiciones fisiológicas y podrá crear dificultades al flujo de la solución durante el procedimiento de la cardioplegia retrógrada.
PALABRAS CLAVE: 1. Corazón; 2. Seno coronario; 3. MEB.
* São Paulo Medical School - University of São Paulo.
** Department of Anatomy- Institute of Biomedical Sciences University of São Paulo.
Financial Support: PIBIC/CNPq/USP Process number: 107253/96-8
Dirección para correspondencia:
Prof. Dra. Nadir Eunice Valverde Barbato de Prates
Department of Anatomy
Institute of Biomedical Sciences
University of São Paulo.
Av. Prof. Lineu Prestes, 2415
Cidade Universitária- Prédio da Biomédicas III
05508-900 - São Paulo, Brazil.
Fone-Fax: 55 -1- 818 7391 and 818 7258
E-mail: firstname.lastname@example.org and email@example.com
Recibido : 23-02-1998
Aceptado : 10-09-1998
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