Comparison of scintigraphic phase maps to epicardial activation maps in dogs

To validate the accuracy of scintigraphic phase analysis in characterizing ventricular (V) activation patterns, and to gain insight into electromechanical coupling, the authors studied 12 activation sequences during atrial and right and left (V) pacing in 4 normal dogs. For each sequence, phase maps generated from equilibrium blood pool scintigrams in multiple projections were compared to epicardial (E) maps obtained from a roving bipolar electrode after thoracotomy. Thirty to forty sites were recorded and referenced to 2 intracardiac and 2 surface electrograms for each sequence. Pacing catheters were kept stationary during phase and (E) mapping. In 11/12 sequences (E) breakthrough and site of earliest contraction (phase angle) occurred in the same region. Areas with secondary breakthrough showed islands of early contraction. Sequences were comparable in direction of spread, and location of terminal activity. Regions of synchronous excitation were comparable in distribution to regions with homogeneous contraction. In 1/12 the phase map showed fusion due to competing sinus and (V) pacing rates, while the later (E) map reflected only (V) pacing. Phase sequences closely follow (E) activation patterns in normal hearts, and provide a unique method of characterizing the interaction of electrical and mechanical events.