Ventricular escape beat reaching the ventricles (normally initiated by the heart's sinoatrial node (SA node), transmitted to the atrioventricular node (AV node), and then further transmitted to the ventricles) falls below the base rate determined by the rate of Phase 4 spontaneous depolarisation of ventricular pacemaker cells. An escape beat usually occurs 2–3 seconds after an electrical impulse has failed to reach the ventricles. This phenomenon can be caused by the sinoatrial node (SA node) failing to initiate a beat, by a failure of the conductivity from the SA node to the atrioventricular node (AV node), or by atrioventricular block (especially third degree
Node influence metric probabilities. The accessibility has been shown to reveal community structure in urban networks, corresponds to the number of nodes which can be visited in a defined time period, and is predictive of the outcome of epidemiological SIR model spreading processes on networks with large diameter and low density. The expected force measures node influence from an epidemiological perspective. It is the expected value of the force of infection generated by the node after two transmissions. The expected force of a node formula_4 is given by where the sum is taken over the set formula_9 of all possible transmission clusters resulting