[Physiopathology of the sinus node and sinoatrial conduction]

New information about the pathophysiology of the sinus node and sino-atrial conduction has been published in the last few years. The sinus node consists of cells separated by a network of collagen fibres. This anatomical disparity explains the different electrophysiological characteristics of the node; the morphology of cellular action potentials depends on the site of recording. The dominant and most automatic pacemaker cells are situated in the cephalic region and the latent pacemaker cells in the caudal region. However, synchronisation of these different cellular activities is possible and results in a coherent signal. This complex synchronisation has been the object of several recent papers. The phenomenon of intrasinusal pacemaker shift and the stimuli which induce it have been studied in depth. In general, positive chronotropic stimuli tend to shift the dominant pacemaker towards the cephalic part and negative chronotropic stimuli towards the caudal part of the node. It is possible to assess pacemaker shift clinically and this phenomenon must be taken into consideration when studying sinus node function. Intercellular conduction and especially electrotonic conduction does not play a role in the genesis of the flux, which represents spontaneous cellular automatism, but in its mode of expression, that is to say the sinus rhythm. The pathophysiology of sinoatrial block is complex because it may be situated within and/or around the sinus node. The extrinsic or intrinsic mechanisms of these blocks may be interrelated. Variations in sinus rhythm must be taken into account in the genesis of sinoatrial block; an acceleration in rhythm may block conduction in the perisinusal region. Finally, our knowledge of the ionic fluxes underlying sinus automatism has also improved with individualization of the pacemaker current (if).(ABSTRACT TRUNCATED AT 250 WORDS)