Regional variation in myocardial blood flow in patients with left bundle branch block evaluated with quantitative perfusion CMR

Background This study is the first to use quantitative perfusion CMR to evaluate regional differences in myocardial blood flow (MBF) in patients with left bundle branch block (LBBB). LBBB is often associated with underlying CAD but its presence can limit the diagnostic accuracy of non-invasive imaging tests. In particular, there is a high incidence of false-positive results with exercise SPECT due to apparent septal perfusion defects. The use of vasodilator stress has reduced but not eliminated this problem. Several hypotheses have been postulated to explain the cause of such perfusion defects, and these include early activation of the septum, leading to shortened diastole and reduced blood flow; partial volume effects caused by impaired septal thickening; and increased septal intra-myocardial pressure during diastole, resulting in reduced flow reserve. A number of small studies using PET or early quantitative SPECT techniques have evaluated regional differences in MBF in patients with LBBB, but the results have been conflicting and have shown either no regional differences or a relative but not absolute reduction in septal perfusion. This study re-evaluates the unresolved question of septal perfusion in LBBB using quantitative perfusion CMR.