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ORIGINAL ARTICLE

Anatomical relashionship between the posterior mitral valve annulus and the coronary arteries. Implications to operative treatment

Clodualdo J. N. PESSA; Walter J Gomes; Roberto Catani; José Carlos PRATES; Enio Buffolo

DOI: 10.1590/S0102-76382004000400008

ABSTRACT

OBJECTIVE: This work aimed to analyze the anatomical relationship among the mitral annulus, the circumflex artery and the posterior left ventricular artery, correlating the distance among the structures mentioned to the pattern of coronary network dominance. METHOD: Eighty-five human hearts, previously preserved in 10% formaldehyde solution, were studied. The coronary network dominance pattern was initially evaluated. Next, atriotomy and left ventriculotomy in the posterior wall of the heart were performed, starting from the lung veins toward the heart apex through the mitral annulus. The atrial wall was removed at the level of the annulus, all around the posterior annulus. Onto the annulus, five points were demarcated: 1 - anterior commissure, 2 - between the anterior commissure and the half-point of the posterior annulus, 3 -half- point of the posterior annulus, 4 - between the half-point of the posterior annulus and the posterior commissure, 5 - posterior commissure. In these points the distance was measured among the structures with an electronic calliper. RESULTS: Right dominance was observed in 81.17% of the cases, balanced dominance in 16.47% and left dominance in 2.35%. Right dominance hearts showed that the area of lower distance between the annulus and the coronary arteries was the anterior commissure, where the circumflex artery was distant to the annulus 3.996 ± 1.865mm while the area of greater distance was the posterior comissure, measuring 7.783 ± 2.615mm. CONCLUSION: This study provided better understanding of the anatomical relationship between the mitral valve and the adjacent coronary arteries, therefore helping cardiac surgeons to prevent operative complications.

RESUMO

OBJETIVO: Este trabalho objetivou analisar a relação anatômica entre o ânulo da valva atrioventricular esquerda (mitral), a artéria circunflexa e a artéria posterior do ventrículo esquerdo, relacionando a distância entre as estruturas citadas ao padrão de dominância coronariano. MÉTODO: Foram estudados 85 corações humanos, previamente fixados em solução de formaldeido a 10%. Inicialmente, avaliou-se o padrão de dominância coronariana. A seguir, realizou-se atriotomia e ventriculotomia esquerdas na parede posterior do coração, a partir das veias pulmonares em direção ao ápice cardíaco, seccionando-se o ânulo mitral. Removeu-se a parede atrial ao nível do ânulo, em toda a porção da cúspide posterior. Sobre o ânulo foram demarcados cinco pontos: 1 - comissural anterior, 2 - entre o comissural anterior e o ponto médio posterior do ânulo, 3 - ponto médio posterior do ânulo, 4 - entre o ponto médio posterior do ânulo e o comissural posterior, 5 - comissural posterior. Nestes pontos foi medida a distância entre as estruturas com um paquímetro eletrônico. RESULTADOS: Padrão de dominância direita foi observado em 81,17% dos casos, circulação balanceada em 16,47% e dominância esquerda em 2,35%. Nos corações que apresentaram dominância direita observou-se que a região de maior proximidade entre o ânulo e as estruturas vasculares foi a comissural anterior, 3,996 ± 1,865mm, enquanto a região de menor proximidade foi a comissural posterior, medindo 7,78 ± 2,615mm. CONCLUSÃO: Este estudo propiciou melhor compreensão da relação anatômica entre a valva mitral e as artérias coronárias adjacentes, podendo auxiliar o cirurgião na diminuição de complicações cirúrgicas.
INTRODUCTION

Surgical procedures involving the left atrioventricular valve (mitral valve) have always been associated with a potential risk of acute myocardial infarction [1-4], and secondarily with the iatrogenic injury of the circumflex artery and of the posterior artery of the left ventricle. This complication is caused by the variability of the anatomical relationships that exist between the posterior segment of the mitral annulus and the coronary arteries that run through the left portion of the coronary network.

Previous studies have shown there is a relationship between the mean distance of the mitral annulus from the adjacent coronary arteries and the dominance pattern of the coronary network. However, there have been few works that analysed this anatomical relationship, just as the numbers of patients that have been studied is small [1,2,5-17].

The aim of this study is to analyze the anatomical relationship between the mitral valve annulus and the coronary arteries located in the left portion of the coronary network near to the posterior cusp of the mitral valve.

METHOD

Hearts, which had been previously preserved in 10% formaldehyde solution, from 85 adult men and women with ages ranging from 24 to 74 were studied. The hearts came from the Topographic and Descriptive Anatomy Section of the Morphology Department of the Paulista School of Medicine, Federal University of São Paulo.

Left atriotomy and ventriculotomy in the posterior wall of the heart were performed from the pulmonary veins towards the heart apex, sectioning the mitral annulus. By opening this line, the transition region between the mitral valve system, left atrial wall and the left ventricle was identified.

Posteriorly, the entire portion of the atrial wall near to the mitral annulus corresponding to the posterior cusp was removed. Thus it was possible to see the whole valvar annulus and the coronary arteries that exist in the left portion of the coronary network.

By anatomical dissection, the parts were classified according to the coronary dominance pattern either as: right dominance, left dominance or balanced dominance, according to the description shown in Table 1 [1,6,12,18-22].



The posterior portion of the mitral annulus was delineated using five main points, which were numbered from 1 to 5 in an anticlockwise direction [1]: the two commissures (anterior and posterior), one point in the posterior midpoint of the annulus and the other two, at the midpoint between the commissures and the posterior midpoint of the annulus. The distances were measured, in millimeters, between the mitral annulus through these points to the coronary arteries, as shown in the Figures 1 and 2.





Statistical analysis of the data was achieved using the Student-Newman-Keuls test to compare the mean distances. The data are presented as means and standard-deviations. A p-value < 0.05 was considered significant.

The study was approved by the Ethics Committee on Research of the Federal University of São Paulo.

RESULTS

Pattern of coronary dominance

Sixty-nine patients (81.17%) presented with right coronary dominance, fourteen patients (16.47%) with balanced dominance and two patients (2.35%) with left coronary dominance.

Distance between the mitral annulus and the coronary arteries in hearts with right dominance

The shortest distance between the mitral annulus and the coronary arteries occurred at Point 1 (3.99 ± l.86 mm), while the longest distance occurred at Point 5 (7.78 ± 2.61 mm), as demonstrated in Figure 3.



Statistical analysis revealed that there were statistically significant differences between the mean distances at Point 1 compared to other points (p< 0.01). The same occurred when comparing the mean distance at Point 2 and at Points 3, 4 and 5. However significant differences were not observed when comparing the distances at Points 3, 4 and 5 as shown in Table 2.



Distance between the mitral annulus and the coronary arteries in hearts with balanced dominance

In the hearts with balanced dominance, the shortest distance between the structures was also observed at Point 1 (3.56 ± l.63 mm), whilst the longest distance was found at Point 3 (6.52 ± 2.48 mm), as shown in Table 3.



Distance between the mitral annulus and the coronary arteries in hearts with left dominance

In this study only two hearts were observed with left dominance (incidence of 2.35%). The data which refer to these patients are shown in Table 4.



Passage of the arteries in the left portion of the coronary network in hearts with right dominance

In this study, the circumflex artery was present in the left portion of the coronary network at Points 1 and 2 in 100% of cases. In 55% of the patients, the circumflex artery reached Point 3 and only in 7.24% of cases it was present at Point 4. The circumflex artery was never present at Point 5.

The posterior artery of the left ventricle, a branch of the right coronary artery, was present in the left portion of the coronary network mainly at Points 3, 4 and 5. At Point 5 it was present in 81% of the cases, at Point 4 in 46% and only in 2.89% it reached Point 3. The posterior artery of the left ventricle was never present at Points 1 and 2.

Passage of the arteries in the left portion of the coronary network in hearts with balanced dominance

In this subgroup, the circumflex artery was present in the left portion of the coronary network at Points 1 and 2 in 100% of the cases. In 92.8% of them, it arrived at Point 3 and in 64.2%, Point 4. However, only in 14.2% of the cases it reached Point 5.

In two cases (14.2%), an arterial branch from the right coronary artery was observed in the coronary network near to the posterior commissural region - Point 5.

COMMENTS

In our sample, the distribution of the hearts according to the pattern of coronary artery dominance gave right dominance supremacy, observed in 81.17% of the cases. In the literature [18,19], we observed a small number of hearts in the subgroup of hearts with left dominance, which in our sample was equivalent to only 2.35%. Thus, our results are similar to previously published studies.

Considering the passage of the arteries in the left portion of the coronary network, we verified that the circumflex artery was more prevalent at Points 1 and 2, while the posterior artery of the left ventricle was mainly observed at Points 4 and 5.

Analyzing the data from the hearts with balanced dominance, we noted that the results were similar to those found the hearts with right dominance. The number of hearts with left dominance (only two cases) was insufficient to make any statistical analysis realistic.

In respect to the subgroup with right dominance, we observed that the anterior commissural region was on the shortest line between the circumflex artery and the mitral valvar annulus (3.99 ± 1.86 mm); in some cases these structures were separated by only l.01 mm. The posterior commissural region - Point 5, was at a point of greatest separation of the posterior artery of the left ventricle from the mitral annulus (7.78 ± 2.61 mm).

Our data were discordant to the results presented by CORNU et al. [1], as, according to these authors, the distance between the structures in the anterior commissural regions, in the case of right dominance, is 8 mm. Using a different methodology, VIRMANI et al. [13] affirmed that, in this subgroup of patients, the distance between the structures in question, in the proximal portion of the circumflex artery, is 8.4 mm.

Before this paper, published results suggested that if an injury of the circumflex artery in patients with right dominance is not observed, it was due to the great distance between these structures. However, our results decisively contradict and discarded this possibility. Thus, we understand that susceptibility to iatrogenic injury of the circumflex artery is not related to the pattern of coronary network dominance.

Iatrogenic injuries of the coronary arteries associated with mitral valve surgery as mentioned in the literature occurred predominantly in the anterior commissural region. Vascular injury appeared in two situations: in the first case the suture that anchors the prosthesis in the annulus of the valve transfixed the artery [5], changing its shape and causing partial or subtotal obstruction. The other possibility was total occlusion of the artery due to its inclusion by the suture [14,16]. The repercussions of the vascular lesion are associated to the type of injury, partial obstruction or occlusion [5,14,16], the location of the injured artery, the preoperative myocardial reserve and the coronary network dominance. Its clinical manifestation is expressed by unexpected cardiogenic shock in the intraoperative or the immediate postoperative periods, followed by an increase in the ST segment, the appearance of refractory ventricular arrhythmias, an increase in the levels of the cardiac enzymes and difficulty to take the patient off the bypass (CPB) [16].

According to the authors, injury of the circumflex artery may be suspected in the intraoperative period due to the absence of blood flow, which can be demonstrated by coronary Doppler ultrasound or by hypokinesia of the lateral-posterior wall of the left ventricle seen using intraoperative echocardiogram [12]. Treatment may involve venous grafting to the infarcted area [6,11,12,16] or reopening of the left atrium and re-suturing the posterior portion of the mitral annulus [14].

We concluded that the present study adds to previously published data and thus improves the understanding of the surgical anatomy of the mitral valve, and may contribute to reducing the incidence of iatrogenic injuries of arteries that circle the posterior portion of the annulus.

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Article receive on Wednesday, September 1, 2004

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