Role of nuclear imaging in cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) has become an integrated treatment option for patients with drug-refractory heart failure. Selection of patients for CRT is based on moderate-to-severe heart failure (New York Heart Association functional class III or IV), depressed left ventricular (LV) systolic function of 35% or below and prolonged QRS interval of 120 ms or more. However, 30-40% of selected patients do not exhibit improvement in heart failure symptoms or LV systolic performance. Efforts have been made to improve patient selection criteria and several studies using echocardiography have demonstrated the significance of LV dyssynchrony for prediction of CRT response as an additional selection criteria. In addition, (location and extent of) viability and scar tissue are important for outcome following CRT. Nuclear imaging with ECG-gated myocardial perfusion single-photon emission computed tomography (GMPS) permits assessment of viability, scar tissue and LV dyssynchrony from one dataset; the potential value of GMPS in CRT patients is discussed in this review. In addition, the use of nuclear imaging (and particularly PET) for evaluation of changes in blood flow, metabolism and innervation after CRT is addressed.