Contraction and blood flow patterns in the left ventricle during abnormal electrical activation

We investigated regional blood flow and contraction patterns during abnormal, asynchronous electrical activation of the left ventricle (LV), as induced by ventricular pacing in anesthetized open-chest dogs. 2D deformation of the anterior left ventricular (LV) epicardium was determined with optical markers and, in other experiments, 3D deformation of the entire LV wall using tagged Magnetic Resonance Imaging (MRI). Regional blood flow was determined with radioactive microspheres. Ventricular pacing caused characteristic patterns of systolic fiber shortening, being essentially zero in early and more than doubled in late activated regions. Myocardial blood flow was also (approximately 20%) lower in early and (approximately 35%) higher in late activated regions, as compared to normal activation. It is concluded that during asynchronous activation regional differences in contraction pattern cause differences in oxygen demand which, through autoregulation, lead to differences in blood flow.