Emerging role of myocardial perfusion imaging to evaluate patients for cardiac resynchronization therapy.

Left ventricular (LV) dyssynchrony is an increasingly important consideration in the evaluation and management of patients with LV systolic dysfunction. Improvements in clinical status, LV remodeling, and survival have been demonstrated with the use of cardiac resynchronization therapy (CRT). The current selection criteria for patients who undergo CRT include the presence of severe LV dysfunction, significant heart failure symptoms, and electrical dyssynchrony on surface electrocardiography (wide QRS interval). However, up to 40% of patients who undergo CRT do not experience reductions in symptoms or LV functional improvement. Because electrical dyssynchrony is not synonymous with contractile or mechanical dyssynchrony, efforts have been made to more accurately quantify mechanical dyssynchrony in the hope of improving the selection of patients for CRT. These efforts have focused largely on echocardiographic measures of mechanical dyssynchrony. A novel method to quantify LV mechanical dyssynchrony has been developed using phase analysis of gated single photon-emission computed tomographic myocardial perfusion imaging. In conclusion, this report describes potential advantages, compared with other methods, of using myocardial perfusion imaging to evaluate patients for CRT; reviews the method of the phase analysis technique to quantify dyssynchrony; reviews the available evidence of its utility; and describes future directions in research.