Quantitative study of ageing changes in the human sinoatrial node and internodal tracts.

Abstract

Quantitative analysis of the amount of muscle,fat, and collagen in the human sinoatrial node and internodal tracts has been carried out. Subjects under 50 were compared with those over 75 years of age at death. In old age there is a significant fall in the amount of muscle present in the sinoatrial node and internodal tracts.It has long been accepted that the sinoatrial node is the normal pacemaker of the heart. More recently it has been established that specialized atrial myogenic conduction paths carry the impulse to the atrioventricular node (James, I963; Merideth and Titus, I968); it is now universally accepted that the automaticity of the sinoatrial node is a function of cardiac muscle fibres. Elderly subjects seem particularly prone to develop atrial arrhythmias (Taran and Szilagyi, I958), and ageing changes in the sinoatrial node and internodal tracts may be a factor accounting for this phenomenon. However, the very existence of such ageing changes is debated; Lev did note (i194) and has illustrated (I968) fibrosis in the sinoatrial nodes of elderly subjects but these findings were not confirmed by Rossi (I969). The present study is designed to resolve this point on a quantitative basis. Materials and methodsThe hearts of 50 subjects under 50 years of age were compared with 50 hearts from subjects over 75 years of age at death; the minimum age was 37 years and the maximum 89 years. Hearts were taken only from subjects with no principal causes of death were malignancy including many cerebral tumours, trauma, drug overdose, and bronchopneumonia.The entire sinoatrial ring was excised, opened posteriorly, and pinned flat for fixation. Subsequently the entire ring was divided into blocks, one or more of which contained the sinoatrial node, for examination by subserial section (Hudson, I965; Davies, I971). Serial blocks were taken of the three main internodal tracts, anterior, middle, and posterior, down to immediately above the atrioventricular node. In practice, therefore, the entire sinoatrial ring, interatrial septum, and posterior wall of the right atrium was blocked.Cavity size of the right and left atria was determined by filling them with molten paraffin wax. The weights of the solid casts of the atria were subsequently used to calculate volumes. In order to eliminate variation due to fixation shrinkage every heart was fixed for between 5 and 7 days in 4 per cent formaldehyde in saline.Histological slides were stained routinely by haematoxylin and eosin, elastic van Gieson, and a modification of the picro-Mallory stain.Identification of the sinoatrial node by naked eye is easily made in the slides stained by the picro-Mallory technique because of its collagen content, and its outline was marked on the cover glass in Indian ink. Subsequently the ratio of collagen (blue staining) to muscle (red staining) was calculated within this circle using a Zeiss i integrating eyepiece (Dunnill, I962). In all, 8 to I2 slides evenly distributed through the node were so assessed. The figures were used to calculate th...

Characterization of Reentrant Circuits in Left Atrial Macroreentrant Tachycardia

“…Such acquired anatomic barriers confirmed the previous studies that atrial fibrosis could be found in patients with rheumatic 7,10,11 and nonrheumatic heart disease, such as hypertrophic or dilated cardiomyopathy and coronary artery disease, 7,12 and even in aging without structural heart disease. 7,13 However, the ESAs or LDPs were variably located in those patients, even in patients with the same disease. Our findings suggest that the atrial fibrosis may be related not only to mechanic overload but also to some unknown atrial myopathy.…”

Location of the Human Sinus Node in Black Africans

“…Our method has similarities to that used by some authors such as Reginald Hudson [8] in 1960, Davies [9] in 1972 and Kenneth Anderson [10] in 1979, all in Britain, which after removal of the sinoatrial node, made vertical cuts for the first two, and mixed, vertical and cross-sections for the last.…”

P Wave Duration and Dispersion as a Useful Conventional Electrocardiographic Marker for Atrial Fibrillation Prediction

“…It has been shown that there is clear evidence in the human atrial myocardium of age-related electrical uncoupling of the side-to-side connections between bundles. This is histologically related to the proliferation of extensive collagenous tissue septa in intracellular spaces [4][5][6]. In pathological studies, it was demonstrated that these age-induced changes include a reduction in the number of myocardial cells within the sinus node, a generalized loss of atrial myocardial fibers, as well as an increase in fibrosis which leads to an apparent loss of myocardial fiber continuity [1][2][3][4][5][6].…”