Three-dimensional echocardiographic evaluation of mechanical dyssynchrony in systolic heart failure with narrow QRS complex

OBJECTIVES: To investigate the role of three-dimensional echocardiography (3DE) in evaluation of left ventricular mechanical dyssynchrony (LVMD) in heart failure (HF) patients with narrow QRS. METHODS: 143 subjects (70 with HF and narrow QRS, 23 with HF and LBBB and 50 controls) were subjected to 3DE, evaluating global and regional dyssynchrony using systolic dyssynchrony index, maximum segmental dyssynchrony and opposite segment dyssynchrony. Spatial distribution of LVMD was studied in each patient using 3DE derived regional time volume curves. Extent of LVMD in HF patients with narrow QRS was compared to those with left bundle branch block (LBBB). RESULTS: Frequency of LVMD was similar in HF patients with narrow QRS or LBBB (55.7% vs. 47.8%, p = NS). There was no difference in the severity of LVMD between these two groups (10.7 ± 6.7% vs. 12.1 ± 7.4%, p = NS). Both HF groups had significantly more dyssynchrony than controls. A scattered pattern of distribution of asynchronous segments was seen in narrow QRS patients; 33.96% of them had their earliest contracting segment, instead of delayed segment, located in areas conventionally targeted for LV pacing i.e. anterolateral, inferolateral or inferior segments. CONCLUSIONS: 3DE confirmed significant dyssynchrony in > 50% HF patients with narrow QRS as demonstrated by other imaging methods. 3D distribution patterns of asynchronous segments indicate possibility of left ventricular mechanics related reasons responsible for lack of CRT responsiveness, an observation that generates hypothesis on possible reasons of CRT non-responsiveness.