Abstract
The synchronized pacemaker has proved to be effective in the treatment of symptomatic A-V block. However, several complex arrhythmias have appeared after its implantation, during its normal behavior as well as during its malfunction. In some cases, the ectopic rhythms were iatrogenically created with the purpose of studying the response of the pacemaker. Four possible mechanisms by which synchronized stimulus artefact could appear during an antecedent T wave were presented. Differences between true and false escapes were stressed. One tracing showed a rare form of pacemaker capture by a high A-V nodal rhythm. In another patient, the synchronized pacer was captured by a continuous unit. An increase in rate of the latter led to a previously undescribed arrhythmia, hereby labelled pacemaker-topacemaker block. In this case, there were two different centers competing to capture the synchronized pacemaker. The analysis of these arrhythmias has increased our knowledge of clinical and pacemaker electrophysiology.
