Predictors of Systolic Augmentation From Left Ventricular Preexcitation in Patients With Dilated Cardiomyopathy and Intraventricular Conduction Delay

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Abstract
Background —VDD pacing can enhance systolic function in patients with dilated cardiomyopathy and discoordinate contraction; however, identification of patients likely to benefit is unclear. We tested predictors of systolic responsiveness on the basis of global parameters as well as directly assessed mechanical dyssynchrony. Methods and Results —Twenty-two DCM patients with conduction delay were studied by cardiac catheterization with a dual-sensor micromanometer to measure LV and aortic pressures during sinus rhythm and LV free-wall pacing. Pacing enhanced isovolumetric (dP/dt max ) and ejection-phase (pulse pressure, PP) systolic function by 35±21% and 16.4±11%, respectively, and these changes correlated directly ( r =0.7, P =0.001). %ΔdP/dt max was weakly predicted by baseline QRS ( r =0.6, P max ( r =0.7, P =0.001), and best by bidiscriminate analysis combining baseline dP/dt max ≤700 mm Hg/s and QRS ≥155 ms to predict %ΔdP/dt max ≥25% and %ΔPP ≥10% ( P 2 ), with no false-positives. Benefit could not be predicted by %ΔQRS. To test whether basal mechanical dyssynchrony predicted responsiveness to LV pacing, circumferential strains were determined at ≈80 sites throughout the LV by tagged MRI in 8 DCM patients and 7 additional control subjects. Strain variance at time of maximal shortening indexed dyssynchrony, averaging 28.0±7.1% in normal subjects versus 201.4±84.3% in DCM patients ( P =0.001). Mechanical dyssynchrony also correlated directly with %ΔdP/dt max ( r =0.85, P =0.008). Conclusions —These results show that although mechanical dyssynchrony is a key predictor for pacing efficacy in DCM patients with conduction delay, combining information about QRS and basal dP/dt max provides an excellent tool to identify maximal responders.