The ventricular endocardial paced evoked response.

The endocardial ventricular evoked response which follows delivery of a unipolar stimulus down the sensing electrode is remarkably uniform, and is of slightly longer duration at the base than at the apex of the heart. As the same lead is used for both pacing and sensing, it is possible to record the evoked T wave representing dominantly local repolarization which follows a pacing-induced depolarization from the same site. Studies of the pacing evoked response following administration of drugs with class 3 mode of action are similar to those obtained by monophasic action potential recordings, and suggest that myocardial repolarization can be accurately assessed by this technique. The stimulus to evoked T wave timing has been used to design a pacing system which offers the advantage of physiological control of pacing rate, independent of atrial activity, using a conventional endocardial electrode lead system. The potential advantages of this system are reviewed.