Histopathological Correlates of Sinoatrial Disease'
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British Heart Journal, 1978, 40, 1384-1389 Histopathological correlates of sinoatrial disease' JEAN-CLAUDE DEMOULIN AND HENRI E. KULBERTUS From the Department of Morbid Anatomy and the Division of Cardiology, Institute of Medicine, University of Liege, Liege, Belgium SUMMARY Six hearts from patients suffering from rhythm disorders consistent with the diagnosis of sinoatrial disease were histologically examined. Four ofthe patients had shown a tachycardia-bradycardia syndrome, and the remaining two patients episodes of sinus arrest or sinoatrial block with a slow junctional escape rhythm. The rhythm disorders had occurred in the setting of chronic sinoatrial disease (3 cases), acute myocardial infarction (2 cases), and diphtheritic myocarditis (1 case). The abnormalities which were more consistently observed consisted of (1) total or subtotal destruction ofthe sinus node (6 cases); (2) total or subtotal destruction ofthe areas ofnodal atrial continuity (5 cases); (3) inflammatory or degenerative changes of the nerves and ganglia surrounding the node (6 cases); (4) pathological changes in the atrial wall (5 cases). Chronic or acute lesions involving the AV node, the bundle ofHis, and its branches or their distal subdivisions were also found in all 6 hearts. The relationship between the observed pathological changes and the physiological disorders are discussed. The clinical profile (Short, 1954; Birchfield et al., nervous structures were studied. In addition, the 1957; Ferrer, 1968; Rosen et al., 1971; Rubenstein specific tissue of the atrioventricular junction was et al., 1972; Kaplan et al., 1973; Kulbertus et al., also carefully examined. 1973; Guntner et al., 1976) and electrophysiological behaviour (Mandel et al., 1972; Narula et al., 1972; SINOATRIAL REGION Strauss et al., 1973) of patients with sinoatrial The region of the sinoatrial node was obtained in the disease have received much attention in recent years. following manner. A cut was first made from the It is well established that the various components orifice of the inferior vena cava to the upper part of the syndrome may occur not only chronically of the right atrial appendage. The second cut passed but also more acutely, as in myocardial infarction behind the right atrial appendage and was directed or toxic myocarditis. We have examined histologic- towards the orifice of the superior vena cava; ally the sinoatrial region and conducting system finally, a third cut went from the superior to the in 6 hearts from patients with sinoatrial rhythm which disorders; 3 were chronic cases, 2 had a myocardial inferior vena cava, thus separating a block The was fixed in formalin and embedded in paraffin. infarction, and 1 a diphtheritic myocarditis. 1O,u sections were prepared parallel to the long axis histological findings are reported and an attempt of the sinus node. Each fortieth section was stained has been made to correlate the observed alterations with haematoxylin and eosin, Azan-Heidenhain's with the physiological disorders. solution, or Masson's trichrome. Furthermore, in each case, 20 to 40 sections were stained by orcein Techniques or Congo Red in order to study the pathological changes in elastic fibres and to identify amyloid In each case, the sinoatrial node, nodal atrial deposits. Bodian's staining was used to study the junction, atrial myocardium, sinus node artery, and nervous structures. 1The data reported in this paper were included and briefly The following morphological criteria were used. described in the proceedings of a Symposium on Reentrant Arrhythmias held in Liege in 1976 (Demoulin, J. Cl. and Kulbertus, H. E. Pathological correlates of atrial arrhythmias Sinoatrial node in reentrant arrhythmias, mechanisms and treatment. Severe fibrosis was diagnosed when only a few H. E. Kulbertus, Ed. MTP Lancaster, p. 99, 1977). scattered nodal cells remained, embedded in a mass Received for publication 17 August 1977 of collagen tissue. 1384 Histopathological correlates of sinoatrial disease 1385 were graded acoording to Bailey's classification (Bailey et al., 1968): grade I, atrial myocardium grossly normal, or minimal changes only; grade II, moderate to severe fibrosis with preservation of muscle mass and architecture; grade III, extensive fibrosis with loss of muscle and architecture. Ganglia and nerves Chronic alterations of the nervous structures were identified from the description by Rossi (1969). The ganglia were thought to be abnormal when their cells showed vacuolar degeneration or atrophy and when there were changes in the pericellular processes or capsular cells. Haemorrhagic and inflammatory infiltrations of the nerves were also carefully looked for. AVjunctions The AV node, the common His bundle, the left and right bundle-branches and their arborisations, were studied using the technique described by Lenegre (1955). Results Six hearts from patients with documented sinoatrial disease were studied. In 4 of the cases, the disease manifested itself by a tachycardia-bradycardia syndrome, and in the remaining 2 instances, there were episodes of sinus arrest or sinoatrial block, :M M .z '... - A..XE.h::--L:: -,W with slow junctional escape rhythm. Fig. 1 Case 5. An example of a sinus node which is The significant clinical features and the gross severely involved by a fibrotic process. Only very few necropsy findings are summarised in Table 1. nodal cells remain (arrow); areas of lipomatosis can Table 2 describes the histopathological changes also be found close to the sinus node artery (san). observed in the sinoatrial region. The lesions seen (Azan x 60.) within the AV node, common His bundle, and bundle-branches are listed in Table 3. Nodal atrial junctions The abnormalities which were more consistently We have never been able to demonstrate morpho- encountered were total or subtotal destruction of logically specialised atrial internodal pathways in the sinus node (6 cases), total or subtotal destruc- the human heart (Janse and Anderson, 1974). tion of the areas of nodal atrial continuity (5 cases), However, areas of nodal atrial continuity are inflammatory or degenerative changes in the nerves consistently seen along the margins of the compact and ganglia surrounding the node (6 cases), and sinus node (Truex, 1976). Such areas of blending grade III pathological changes in the atrial myo- of nodal and atrial muscle cells are notably found cardium (5 cases). Chronic or acute lesions involving along the tail of the node, along its anterior aspect, the AV node (Tawara), the bundle of His, its and along its endocardial margins, the regions branches, or their distal subdivisions were also found presumed to be the site of origin of the bundles in all 6 hearts. described by Thorel (1909), Bachmann (1916), and Wenckebach (1906-1907) respectively. These Discussion areas most probably represent important structural bridges between the node and the atrial myocardium Very few reports relating the histopathological and were, therefore, carefully studied. anomalies associated with the syndrome of sinoatrial rhythm disturbances have been published (Hudson, Atrial myocardium 1960; James and Birk, 1966; Rossi, 1969; Acar The pathological changes in the atrial myocardium et al., 1970; Rasmussen, 1971;Rosenetal., 1971b; 138616.-C. Demoulin and H. E. Kulbertus ' Ofi"N;i ,. ,f Fig. 2 Case 4. A nerve close to the sinus node. Severe haemorrhagic infiltration of the nerve is easily recognised. (Azan x 60.) Kaplan et al., 1973; Kulbertus et al., 1973; Warem- sinus node automaticity or impaired conduction bourg et al., 1974). Two recent reports have appeared from the centre of the node to its periphery or during the preparation of this paper. Thery et al. from the node to the atrial myocardium. These (1977) described their findings in a group of patients disorders can surely be accounted for by the severe of whom 6 had a bradycardia-tachycardia syndrome, changes observed within the node itself, by the 12 had evidence of sinoatrial block, and 1 had disruptive lesions located along the areas of nodal permanent atrial standstill. Evans and Shaw (1977) atrial continuity and, finally, by the pathological also described the pathological data from 8 patients involvement of the perinodal nervous structures. diagnosed during life as having chronic sinoatrial Similar pathological features are sometimes seen disorder. The results of these different studies were though rarely, in individuals maintaining a normal consistent: lesions of the sinus node and of the sinus rhythm (Demoulin and Kulbertus, 1977). atrial wall were commonly found in sinoatrial At present, the minimum number of functioning disease. nodal cells needed to ensure the formation of a The present investigation corroborates those proper sinus impulse remains unknown. Further- findings and stresses two additional features. more, it seems well established that the distribution First, the structural bridges which connect the of pacemaker cells is not limited to the area of the node to the common atrial myocardium seem to be node itself and that pacemaker cells can also be frequently damaged in this clinical syndrome. found around the node, more particularly towards Secondly, the nervous structures surrounding the the region of the crista terminalis. This might node are also often the site of pathological changes. explain the persistence of a satisfactory sinus rhythm It seems generally agreed that the syndrome in some patients in spite of very severe intranodal under discussion comprises: (1) bradyarrhythmias fibrosis