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Background Phase imaging derived from equilibrium radionuclide angiography presents the ventricular contraction sequence. It has been widely but only indirectly correlated with the sequence of electrical myocardial activation. Objectives We sought to determine the specific relationship between the sequence of phase progression and the sequence of myocardial activation, contraction and conduction, in order to document a noninvasive method that could monitor both. Methods In 7 normal and 9 infarcted dogs, the sequence of phase angle was correlated with the epicardial activation map in 126 episodes of sinus rhythm and pacing from three ventricular sites. Results In each episode, the site of earliest phase angle was identical to the focus of initial epicardial activation. Similarly, the serial contraction pattern by phase image analysis matched the electrical epicardial activation sequence completely or demonstrated good agreement in approximately 85% of pacing episodes, without differences between normal or infarct groups. Conclusions A noninvasive method to accurately determine the sequence of contraction may serve as a surrogate for the associated electrical activation sequence or be applied to identify their differences.

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Background. The pacing site has been shown to influence functional improvement with cardiac resynchronization therapy. We evaluated the effects of the pacing site on left ventricular (LV) function in an animal model.Methods and Results. Equilibrium radionuclide angiography was acquired in sinus rhythm (NSR) and with ventricular pacing, from three pacing sites in seven normal and eight infarcted dogs. QRS duration, electrical activation pattern, wall motion, LV ejection fraction (EF), synchrony of ventricular contraction, and mean arterial pressure (MAP), were related to the pacing site and infarct size, during each of 120 episodes. Little changed during pacing in normals. In infarcted dogs, LV wall motion, and synchrony worsened, LVEF and MAP often fell. These changes related to altered activation patterns which were influenced by the pacing site but were not related to infarct size.Conclusions. Hemodynamic and functional LV changes after infarction were found to vary with the pacing site and associated conduction and synchrony. (J Nucl Cardiol 2009;16:904-13.)