Electrocardiographic manifestations of a dual-chamber, rate-modulated (DDDR) pacemaker

Dual-chamber, rate-modulated pacing (DDDR) has only recently been made available. During exercise, the pacemaker is capable of tracking not only the patient's intrinsic P wave but also the AV sequential sensor-indicated rate response, which depends on the programmed variables of the specific sensor in the DDDR pulse generator. Programmed options that affect the operation of a rate-modulated DDDR device are slope, threshold, reaction time, and recovery time. In addition, one is required to program a base or minimum pacing rate and a maximum tracking rate, as in any DDD device, as well as a maximum sensor rate. It is essential to know and understand all these programmed options if one is to correctly interpret electrocardiograms from a DDDR pacemaker. Interpreting the electrocardiograms also requires an understanding of the sensor-indicated rate of the pacemaker at any given level of exercise, which is determined by the options previously listed and the interaction between the sensor-indicated rate and the patient's intrinsic atrial and ventricular activity. This paper presents electrocardiograms typical of a new DDDR pacemaker undergoing clinical investigation.