Provocation of Masked Left Ventricular Mechanical Dyssynchrony by Treadmill Exercise in Patients With Systolic Heart Failure and Narrow QRS Complex

Tissue Doppler imaging-derived intra-left ventricular (LV) contractile dyssynchrony is an evolving prognostic parameter for patients with systolic heart failure (HF). However, whether and how exercise could abolish the synchronicity in HF patients with narrow QRS remains less studied. We evaluated a total of 33 HF patients with impaired LV ejection fraction (<50%), QRS duration ≤120 ms, and baseline dyssynchrony index (DI; standard deviation of electromechanical delay of 12 LV segments by tissue Doppler imaging) <33 ms. After a 6-minute treadmill exercise by modified Bruce protocol, the absolute time difference from QRS onset to peak systolic myocardial velocity of each segment was recorded immediately. With similar DI at rest and peak heart rates during exercise, 11 patients (33%) developed dyssynchrony (DI ≥33 ms) after exercise, and the others did not (44.7 ± 8.0 vs 16.2 ± 8.3 ms, p <0.001). Patients with dyssynchrony after exercise had greater baseline mitral early diastolic velocity/annular early diastolic velocity (E/Ea) (19 ± 17 vs 10 ± 5, p <0.026). Multivariate analysis revealed mitral E/Ea >10 at rest, indicating higher LV filling pressure, independently predicted the exercise-evoked dyssynchrony (odds ratio 18, 95% confidence interval 2 to 163, p <0.012). In conclusion, exercise uncovered masked LV dyssynchrony in 1/3 of systolic HF patients with narrow QRS, and exercise-provoked dyssynchrony could be predicted by mitral E/Ea >10 at rest.