Phase analysis of gated blood pool SPECT for multiple stress testing assessments of ventricular mechanical dyssynchrony in a tachycardia-induced dilated cardiomyopathy canine model.

Background: Stress-induced dyssynchrony has been shown to be independently correlated with clinical outcomes in patients with dilated cardiomyopathy (DCM) and narrow QRS complexes. However, the extent to which stress levels affect inter- and intraventricular dyssynchrony parameters remains unknown.

Methods: Ten large dogs were submitted to tachycardia-induced DCM by pacing the right ventricular apex for 3-4 weeks to reach a target ejection fraction (EF) of 35% or less. Stress was then induced in DCM dogs by administering intravenous dobutamine up to a maximum of 20 μg·kg·min. Hemodynamic and ventricular dyssynchrony data were analyzed by left ventricular (LV) pressure measurements and gated blood pool SPECT (GBPS) imaging. In order to assess mechanical dyssynchrony in DCM subjects and compare it with that of 8 normal counterparts, we extracted the following data: count-based indices of LV contraction homogeneity index (CHI), entropy and phase standard deviation, and interventricular dyssynchrony index.

Results: A significant LV intraventricular dyssynchrony (CHI: 96.4 ± 1.3% in control vs 78.6% ± 10.9% in DCM subjects) resulted in an intense LV dysfunction in DCM subjects (EF: 49.5% ± 8.4% in control vs 22.6% ± 6.0% in DCM), compared to control subjects. However, interventricular dyssynchrony did not vary significantly between the two groups. Under stress, DCM subjects showed a significant improvement in ventricular functional parameters at each level (EF: 22.6% ± 6.0% at rest vs 48.1% ± 5.8% at maximum stress). All intraventricular dyssynchrony indices showed a significant increase in magnitude of synchrony from baseline to stress levels of greater than or equal to 5 μg·kg·min dobutamine. There were individual differences in the magnitude and pattern of change in interventricular dyssynchrony during the various levels of stress.

Conclusions: Based on GBPS analyses, different levels of functional stress, even in close intervals, can have a significant impact on hemodynamic and intraventricular dyssynchrony parameters in a DCM model with narrow QRS complex.