Mapping Reentry

• Small-circuit reentry (microreentry) in which extremely slow conduction in a focal area sustains the reentry also presents with centrifugal activation. Unlike automaticity, however, the local bipolar electrograms at the site of the apparent focal source are fragmented and abnormal with microreentry. • When mapping 1 chamber, say the right atrium, but a macroreentry circuit is located within the left atrium, there may be a discrete breakout from the left atrium to the right atrium, such as through Bachmann bundle, and from this breakout, centrifugal spread mimicking an automatic focus may be found. • With macroreentry in highly diseased hearts, although the circuit may be large, there may be a slow area of conduction within the circuit. As a result when exiting from the slow zone of the circuit, centrifugal activation of the rest of the chamber in addition to continued conduction through the circuit will be present and visually difficult to distinguish from the anticipated pattern with focal tachycardia. • Reentrant arrhythmias contained within the cul-desacs of the heart, such as the pulmonary veins, supravalvar myocardium of the great arteries, and the papillary muscles, may have discrete exits from the cul-de-sac to the rest of the myocardium, again producing a pattern of centrifugal activation. Conversely, with focal tachycardia occurring in cardiac chambers with multiple scars, previous surgery or ablation, etc, the point source origin is not allowed to spread centrifugally and may follow a pattern that visually may suggest reentry.