Quantitative study of ageing changes in the human 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.