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The Heart in Sudden Infant Death
J. Forens. Sci. Soc. (1972) 12, 591
The Heart in Sudden Infant Death J. A. J. FERRIS Department of Pathology, University of Newcastle upon Tyne, England I n any sudden death a lethal cardiac arrythmia or conduction disturbance is a vital consideration and pathological changes in the sino-atrial and atrio ventricular nodes have been found in a wide range of cardiac generalized diseases in association with sudden death. If an infant dies suddenly and unexpectedly then one must pay due attention to the heart and in particular search for pathological changes in the conducting tissue. I n 1968 Professor Tom James from Birmingham, Alabama, described histological changes of a n unusual nature in the conducting tissue of infants. These changes were not seen a t or before birth, they were confined to the periphery of the atrioventricular node and His bundle and consisted of a resorptive degeneration of conducting tissue cells. Since the changes were not normally present before birth, and since they were not apparent in adult life, James suggested that this resorptive degeneration was probably part of a post natal remodelling process. He further proposed that episodes of focal degeneration in the conducting tissue might cause temporary disfunction of heart action, during such periods infants would be abnormally vulnerable and exacerbation of this function by an otherwise innocuous upset of infancy could produce a lethal arrythmia. Most of the cases examined by James were cot death hearts and his suggestions underlined the importance of the heart in the cot death syndrome. Two years ago in Newcastle it was decided to investigate these degenerative changes described by James and up to the present time we have examined the hearts of 47 infants up to the age of 2 years who have died of a variety of sudden natural and unnatural causes. I am most grateful to Dr. Tom Marshall who has allowed me to examine the hearts of 12 cases from Northern Ireland and also to several of the pathologists in the Newcastle area who have supplied hearts for this study.
Methods Each heart was processed whole and serially sectioned. Particular attention was paid to the sino-atrial node, the communicating tracts between the sinoatrial node and the AV node, the atrio-ventricular node itself, the His bundle and the bundle branches. Any fibrous replacement was noted and the quality of fibrocartilage within the central fibrous body at the point of penetration of the bundle was graded on its similarity to adult cartilage.
Results The sino-atrial node and the atrio-ventricular node were essentially normal although there was some variation in the size and number of branches of the nodal arteries. I n the His bundle we found evidence of the structural remoulding described by James (1968). I n the penetrating portion of the bundle, which is the first segment of His bundle there were varying degrees of fibrosis and resorptive degeneration of conducting tissue cells. This change was absent in stillborn infants but some degree of fibrosis was noted in every case including controls by the age of 2 months and this fibrosis appeared to be maximal at the age of 9 months (Fig. 1). There was no associated inflammatory reaction, however the fibrous tissue showed a gradual maturation with loss of cellularity after the age of 4 months (Fig. 2).
Birth
9
months
Fig. 1.
5 months
Adult
Progressive remoulding of the His bundle from birth.
I t would appear that as a result of this fibrosis there is a reshaping of the first part of the His bundle and that the conducting tissue at its point of penetration through the central fibrous body becomes incorporated into the central fibrous body. As a result of this a relatively narrow isthmus is formed between the AV node and the main part of the His bundle. Below this level the rest of the His bundle and the right and left bundle branches were essentially normal and in no case was there any evidence of necrosis or fibrosis. I n some cases the fibrous tissue which formed this isthmus was metachromatic and showed fibrocartilaginous changes similar to those seen in the central fibrous body. The presence of metachromatic tissue within the conducting tissue tends to support the view that the fibrous remoulding of the His bundle is degenerative in nature (Ferris and Aherne, 1971). Analysis of the extent of this fibrosis is not complete, but it would appear while there is fibrosis in every case, in a significant proportion of cot deaths the fibrous tissue appears to interfere anatomically and interdigitate with the conducting tissue more than in the control group.
Fig. 2.
Fibrosis of the bundle at 4 months, (H and E x 200)
Discussion There is no doubt that the conducting tissue is normal at birth and that subsequently it becomes reshaped as a result of reduction in the size of the penetrating portion of the His bundle, this part of the His bundle could probably be more appropriately referred to as the isthmus. This degeneration has not been associated with any acute or chronic inflammatory reaction and therefore seems more closely akin to the form of the ischaemic fibrosis that one finds in the myocardium in adults with disease of the coronary arterial tree. These findings therefore tend to suggest that a change of blood supply after birth may be responsible for fibrosis. The atrio-ventricular node receives its blood supply frequently from the right coronary artery, although in a small proportion of cases the circumflex branch of the left coronary artery is responsible. The His bundle and the bundle branches after penetration through the central fibrous body is supplied by the
anterior descending branch of the left coronary artery. I t is the area between these two blood supplies, the isthmus, that maximal fibrosis is found. After birth the muscle fibres of the heart and the size and bulk of the two ventricles undergo rapid change. There must therefore be a redistribution of coronary blood supply which could produce a relative vascular insufficiency in the area of the conducting tissue isthmus leading to fibrosis. Any diminution in conducting tissue through the AV node and His bundle must result in a reduction of conducting reserve, if for some reason the number of impulses passing through this central area is increased then the conducting tissue may be unable to cope with this altered electrical state and may be thrown into a state of disarray and an arrythmia result. If we consider infants in the first 6 months of life are in a critical stage of conducting tissue development, then a fatal arrythmia may follow stimulation of the conducting tissue by an abnormal reaction to a virus infection or some allergic phenomenon. Such a sequence of events would certainly explain the rapidity of death and the relative absence of pathological changes.
References FERRIS, J. A. J., and AHERNE, W. A., 197 1, Lancet, 1,64. JAMES, T. N., 1968, Amer. J.Card., 22,456.
The Heart in Sudden Infant Death J. A. J. FERRIS Department of Pathology, University of Newcastle upon Tyne, England I n any sudden death a lethal cardiac arrythmia or conduction disturbance is a vital consideration and pathological changes in the sino-atrial and atrio ventricular nodes have been found in a wide range of cardiac generalized diseases in association with sudden death. If an infant dies suddenly and unexpectedly then one must pay due attention to the heart and in particular search for pathological changes in the conducting tissue. I n 1968 Professor Tom James from Birmingham, Alabama, described histological changes of a n unusual nature in the conducting tissue of infants. These changes were not seen a t or before birth, they were confined to the periphery of the atrioventricular node and His bundle and consisted of a resorptive degeneration of conducting tissue cells. Since the changes were not normally present before birth, and since they were not apparent in adult life, James suggested that this resorptive degeneration was probably part of a post natal remodelling process. He further proposed that episodes of focal degeneration in the conducting tissue might cause temporary disfunction of heart action, during such periods infants would be abnormally vulnerable and exacerbation of this function by an otherwise innocuous upset of infancy could produce a lethal arrythmia. Most of the cases examined by James were cot death hearts and his suggestions underlined the importance of the heart in the cot death syndrome. Two years ago in Newcastle it was decided to investigate these degenerative changes described by James and up to the present time we have examined the hearts of 47 infants up to the age of 2 years who have died of a variety of sudden natural and unnatural causes. I am most grateful to Dr. Tom Marshall who has allowed me to examine the hearts of 12 cases from Northern Ireland and also to several of the pathologists in the Newcastle area who have supplied hearts for this study.
Methods Each heart was processed whole and serially sectioned. Particular attention was paid to the sino-atrial node, the communicating tracts between the sinoatrial node and the AV node, the atrio-ventricular node itself, the His bundle and the bundle branches. Any fibrous replacement was noted and the quality of fibrocartilage within the central fibrous body at the point of penetration of the bundle was graded on its similarity to adult cartilage.
Results The sino-atrial node and the atrio-ventricular node were essentially normal although there was some variation in the size and number of branches of the nodal arteries. I n the His bundle we found evidence of the structural remoulding described by James (1968). I n the penetrating portion of the bundle, which is the first segment of His bundle there were varying degrees of fibrosis and resorptive degeneration of conducting tissue cells. This change was absent in stillborn infants but some degree of fibrosis was noted in every case including controls by the age of 2 months and this fibrosis appeared to be maximal at the age of 9 months (Fig. 1). There was no associated inflammatory reaction, however the fibrous tissue showed a gradual maturation with loss of cellularity after the age of 4 months (Fig. 2).
Birth
9
months
Fig. 1.
5 months
Adult
Progressive remoulding of the His bundle from birth.
I t would appear that as a result of this fibrosis there is a reshaping of the first part of the His bundle and that the conducting tissue at its point of penetration through the central fibrous body becomes incorporated into the central fibrous body. As a result of this a relatively narrow isthmus is formed between the AV node and the main part of the His bundle. Below this level the rest of the His bundle and the right and left bundle branches were essentially normal and in no case was there any evidence of necrosis or fibrosis. I n some cases the fibrous tissue which formed this isthmus was metachromatic and showed fibrocartilaginous changes similar to those seen in the central fibrous body. The presence of metachromatic tissue within the conducting tissue tends to support the view that the fibrous remoulding of the His bundle is degenerative in nature (Ferris and Aherne, 1971). Analysis of the extent of this fibrosis is not complete, but it would appear while there is fibrosis in every case, in a significant proportion of cot deaths the fibrous tissue appears to interfere anatomically and interdigitate with the conducting tissue more than in the control group.
Fig. 2.
Fibrosis of the bundle at 4 months, (H and E x 200)
Discussion There is no doubt that the conducting tissue is normal at birth and that subsequently it becomes reshaped as a result of reduction in the size of the penetrating portion of the His bundle, this part of the His bundle could probably be more appropriately referred to as the isthmus. This degeneration has not been associated with any acute or chronic inflammatory reaction and therefore seems more closely akin to the form of the ischaemic fibrosis that one finds in the myocardium in adults with disease of the coronary arterial tree. These findings therefore tend to suggest that a change of blood supply after birth may be responsible for fibrosis. The atrio-ventricular node receives its blood supply frequently from the right coronary artery, although in a small proportion of cases the circumflex branch of the left coronary artery is responsible. The His bundle and the bundle branches after penetration through the central fibrous body is supplied by the
anterior descending branch of the left coronary artery. I t is the area between these two blood supplies, the isthmus, that maximal fibrosis is found. After birth the muscle fibres of the heart and the size and bulk of the two ventricles undergo rapid change. There must therefore be a redistribution of coronary blood supply which could produce a relative vascular insufficiency in the area of the conducting tissue isthmus leading to fibrosis. Any diminution in conducting tissue through the AV node and His bundle must result in a reduction of conducting reserve, if for some reason the number of impulses passing through this central area is increased then the conducting tissue may be unable to cope with this altered electrical state and may be thrown into a state of disarray and an arrythmia result. If we consider infants in the first 6 months of life are in a critical stage of conducting tissue development, then a fatal arrythmia may follow stimulation of the conducting tissue by an abnormal reaction to a virus infection or some allergic phenomenon. Such a sequence of events would certainly explain the rapidity of death and the relative absence of pathological changes.
References FERRIS, J. A. J., and AHERNE, W. A., 197 1, Lancet, 1,64. JAMES, T. N., 1968, Amer. J.Card., 22,456.