Timing Cycles

Understanding the basic timing cycles of each pacing mode and the function and interaction of all components of a timing cycle is critical to interpreting the electrocardiogram of a patient with a pacemaker, implantable cardioverter-defibrillator (ICD) or cardiac resynchronization therapy (CRT) device. Although these devices continue to become more sophisticated even the most complex device and associated electrocardiographic tracing can be interpreted if the basic timing cycles and parameters are understood. This chapter initially goes through individual pacing modes, followed by an explanation of the different portions of the timing cycle including response to magnet application. The final portion of the chapter provides an approach to the biventricular paced electrocardiogram.