Normal and abnormal rhythms associated with dual-chamber pacemakers.

Except for the unique eccentricities of individual devices, most dual-chamber paced rhythms, both normal and abnormal, are readily understood and lend themselves to analysis if the programmed parameters are known. Although they may appear intimidating, this need not be the case if the physician is initially willing to devote both time and effort to understanding them. Learning is not a passive exercise. It is therefore suggested that when the patient is clearly stable and doing well and there is no active concern about a possible pacing system malfunction, the physician should obtain and carefully analyze selected tracings. This analysis should include the diagramming of all pertinent intervals (atrial escape interval, AV delay interval, maximum tracking rate interval, postventricular atrial refractory period, blanking period, and ventricular refractory period) by placing these cycles under the respective P and R waves and atrial and ventricular pacing pulses on the selected rhythm strips. Then, if something does not appear to fit or make sense, a colleague or the manufacturer can be contacted for clarification. These exercises will help develop one's ability to handle these rhythms. This exercise is preferable to first attempting such an analysis when presented with a patient in whom a problem is already suspected. Despite this effort, confusing rhythms will occasionally be encountered. In these cases, the added features of telemetry, enabling interrogation of programmed and measured data (see Fig. 30), endocardial electrograms (see Fig. 2), and generation of marker pulses are proving to be extremely valuable in the rapid and accurate assessment of the more complex pacemaker rhythms.