Abstract Body (Do not enter title and authors here): Background: During left bundle branch block (LBBB), tachycardia causes marked elevation of left ventricular (LV) filling pressures due to insufficient time for LV relaxation. Cardiac resynchronization therapy (CRT) may reduce pulmonary congestion during exercise by facilitating more time for LV filling, thereby reducing the need for increased left atrial (LA) pressures to accelerate blood into the LV.

Purpose: Investigate if successful CRT increases LV filling time and if this is reflected in shorter LA reservoir phase duration.

Methods: In a multicenter study of 168 patients, LA and LV global strain was measured by speckle-tracking echocardiography before and 7 ± 1 months after CRT. LA reservoir phase duration was measured from onset shortening in the LV to peak global LA strain, and LV filling time from mitral valve opening to closure. A volumetric response was defined as ≥ 15% decrease in LV end-systolic volume at follow-up.

Results: The patient in Figure 1 exemplifies LV/LA mechanical interactions in a volumetric responder. In the LV, resynchronization increases filling time (four areas shaded in gray in Figure 1). This is mirrored in the LA, where resynchronization reduces LA reservoir phase duration (white arrows, upper panels).

In all responders, resynchronization was associated with increased LV filling time (p<0.0001) and decreased LA reservoir phase duration (p<0.0001), regardless of heart rate (Figure 2). Reduction in LA reservoir phase duration correlated with a reduction in LV filling time (β=–0.302, p<0.0001 corrected for change in heart rate). These improvements in filling dynamics were not observed in non-responders.

Conclusions: LA reservoir phase duration mirrors LV filling time and may be an important diastolic marker of successful CRT.