Introduction: In patient with reduced systolic function, LV dyssynchrony associated with LBBB has been identified as an independent predictor of cardiac morbidity or mortality. However, in patients with LBBB and preserved systolic function (LBBB-PSF), there is a paucity of data related to the effect of LV dyssynchrony on the exercise capacity. We hypothesized that LV dyssynchrony is related to the poor exercise capacity in these patients. Method: Echocardiographic examination including tissue dopper imaging and cardiopulmonary exercise test were performed in 12 patients with LBBB-PSF and 10 healthy volunteers. Severity of LV dyssynchrony was accessed by the standard deviation of time intervals from the QRS complex to the peak systolic velocity measured in 12 segments of LV (SDdys). In exercise test, the peak oxygen consumption rate (peak VO2) was obtained. Result: LBBB-PSF group showed significantly lower exercise capacity (peak VO2; 21.8±5.3 vs. 29.7±8.9 ml/kg/min, P=0.04) and higher SDdys (101.8±44.2 vs. 42.1±8.8, P=0.02). In subgroup analysis focusing on LBBB-PSF group, SDdys correlated with poor exercise capacity(correlation coefficient = -0.660, p=0.038). Conclusion: Patients with LBBB-PSF have a significant LV dyssynchrony compared with healthy volunteers. Moreover, patients with LBBB-PSF showed variable degree of LV dyssynchrony (see a graph), which correlates with poor exercise capacity. It is suggested that LV dyssynchrony measured by tissue doppler imaging is useful to assess the clinical significance of LBBB-PSF patients.
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