Figure 2:  .

The mapping data are from a patient with VT late after anterior wall myocardial infarction. Mapping was performed using a system that plots the precise catheter position along with colour coded electrophysiologic information (CARTO Biosense Webster, Diamond Bar, California, USA). The top two panels show the left ventricle in right anterior oblique (RAO) and left lateral views. In this case, colours indicate the electrogram voltage, rather than timing. The lowest voltage regions are shown in red, progressing to greater voltage regions of yellow, green, blue, and purple. A large anteroapical infarction is indicated by the extensive low voltage, red region. The lower right panel shows the map of VT in the same patient. The ventricle is again shown in a right anterior oblique projection with the apex at the right and the base at the left hand side of the image. The colours indicate the activation sequence and arrows have been drawn to clarify the activation sequence of the circuit. The re-entry circuit is located in the septum. The wavefront starts at the red area (exit) near the base of the septum and splits into two loops that circle around the superior and inferior aspect of the septum toward the apex, re-entering an isthmus in the circuit that is proximal to the exit region. RF ablation in the isthmus abolished tachycardia. The mechanism of slow conduction through the infarct region that has been observed in previous histopathologic studies is illustrated schematically in the inset at lower left. Surviving myocyte bundles are separated by fibrous tissue that forces the wavefront to take a circuitous path through the region.