Phase analysis of myocardial SPECT to understand mechanisms of disease and therapy

Excerpt

Right ventricular (RV) pacing is lifesaving in patients with advanced sinus node and atrioventricular node dysfunction. The resultant conduction pattern, however, has been associated with progressive deterioration in left ventricular (LV) function.1 The pathophysiological basis of this association is attributed to the fact that LV activation originating from the RV apical pacing site proceeds through myocardial rather than specialized conduction tissues, thus causing dyssynchrony.2 Evidence of this lies in the surface electrocardiogram, which shows a wide left bundle-branch block when the RV is paced. Interestingly, in patients with symptomatic LV systolic dysfunction and wide QRS in whom cardiac resynchronization therapy with biventricular pacing has established prognostic benefit, it is those with widest QRS (>150 ms) LBBB that derive the most consistent benefit, indicating that these patients perhaps have the most severe degrees of LV dyssynchrony.3 In order to place the origin of LV activation closer to specialized conduction tissue, alternative approaches to RV apical pacing including RV septal and RV outflow tract pacing have been explored. …