Excerpt

Multiple imaging modalities including baseline electrocardiography and echocardiography have been investigated for independent prediction of left ventricular mechanical dyssynchrony (LVMD). This cardiac finding is extremely important given the impact that it has both on worsening of cardiac status as well as treatment focus. Cardiac resynchronization therapy (CRT) is a Class I indication for patients with advanced heart failure and the following criteria: severely depressed left ventricular ejection fraction (≤ 35%), left bundle branch block (LBBB) with wide QRS duration on electrocardiogram (≥ 150 ms), and New York Heart Association (NYHA) class II, III, or IV symptoms.1 Although improvement in functional status and quality of life is seen in many patients, it has been reported that up to 30% of patients who meet AHA/ACC guidelines for implantation of CRT fail to respond.2-5 However, what is missing from the patient profile above is confirmation of LVMD. It has been observed that patients demonstrating LVMD are more likely to respond favorably to CRT suggesting that perhaps more refined criteria may be needed to predict which subset of patients will benefit from CRT.6,7 It has also been demonstrated that LVMD may exist in patients with right bundle branch block (RBBB) who may not fulfill the typical criteria for CRT implantation, but who may nevertheless, benefit from resynchronization.8,9 Prior studies have shown that LVMD can be accurately evaluated by gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI).10,11 However, the exact pathogenesis of LVMD remains poorly understood. …