Assessing the Prevalence of Mechanical Dyssynchrony with Activity in Patients with Low Ejection Fraction and Narrow QRS at Rest

Abstract

Introduction: Cardiac Resynchronization Therapy (CRT) improves hemodynamics, symptoms, and overall mortality in patients with advanced heart failure (HF) and ventricular electrical dyssynchrony (QRS duration >120 msec). Previous studies have shown that mechanical dyssynchrony (MD) may be present in up to 45% of patients with advanced HF and QRS duration <120 ms at rest. We determined whether activity induces MD in patients with QRS duration <120 msec.Methods: A total of 47 consecutive patients with left ventricular ejection fraction (LVEF) ≤ 30%, New York Heart Association (NYHA) class II-IV HF, and a QRS complex <120 ms were evaluated for MD at rest and exercise utilizing a modified Bruce protocol and three dimensional echocardiography. Time to peak systolic velocity was measured via Tissue Doppler and MD was defined as a time delay of >65 msec from peak systolic activation of the septal wall to the lateral wall of the left ventricle. Minnesota living with heart failure questionnaire (MLWHFq), EF and NYHA class were assessed to determine risk factors for exercise induced MD. Results:Of the 47 patients, MD occurred in 11 patients (23%) at rest and 5 patients (13%) at exercise. The mean time to peak systolic velocity in the rest and exercise dyssynchrony groups was 105 ± 32 msec and 124 ± 29 msec respectively, compared with 45 +/-15 msec in patients not experiencing dyssynchrony. No patients experienced electrical dyssynchrony with activity. EF, NYHA class or MLWHF questionnaire were not predictive. Conclusion:MD with activity is not uncommon in patients with HF and a narrow QRS. MD should consider including patients with exercise induced MD as this population otherwise may go ignored. Additionally, patients with pre-existing electrical dyssynchrony who develop MD with exercise may benefit from optimization of their device settings to meet the potential hemodynamic challenge rendered by increased physical activity and heart rate.