Morphology of endocardial T-waves of fusion beats.

Recently developed stimulation techniques are capable of eliminating polarization afterpotentials caused by the emitted stimulus. A well-controlled study method was developed to initiate various degrees of fusion and to monitor changes in the morphology of the endocardial signal. The study was performed on two dogs. The zone during which fusion could be provoked was less than 30 ms in both dogs. In addition, the results show a significant decrease in the endocardial T-wave amplitude as soon as fusion was noticed, while the QT interval then slightly lengthened. Furthermore, the evoked R-wave duration shortened during fusion, while the stimulus to R-wave interval lengthened. These results have consequences for pacemakers that use evoked endocardial signal characteristics for driving a pacemaker function.