Abstract Body (Do not enter title and authors here): Background: Recent observations suggest that residual left atrial (LA) dyssynchrony after cardiac resynchronization therapy (CRT) may have prognostic significance. Since LA dyssynchrony implies prolongation of the LA reservoir phase, measuring the duration of the LA reservoir phase should offer similar prognostic information.

Purpose: To investigate the impact of LA reservoir phase duration on long-term survival after CRT.

Methods: In a recent prospective multicenter study of 168 patients, LA strain was measured by speckle-tracking echocardiography before and 7±1 months after CRT. LA reservoir strain was measured as the difference between peak and minimum global strain during the atrial cycle and LA reservoir phase duration as the time from onset shortening in the left ventricle to peak LA reservoir strain. Since LA reservoir strain <18% is associated with elevated LV filling pressure, we used 18% as cutoff and for LA reservoir phase duration 516 ms in accordance with a Receiver Operating Curve. All-cause mortality was used as clinical endpoint during follow-up.

Results: After 6.0±1.8 years follow-up, 35 (21%) patients had died. LA reservoir strain ≥18% after CRT was associated with favorable long-term survival (HR: 0.51, 95% CI: 0.26–0.98) (upper panel in the Figure). LA reservoir phase duration was not independently associated with survival. However, when used in patients with LA reservoir strain ≥18% after CRT, LA reservoir phase duration ≤516 ms identified patients with particularly excellent long-term survival (HR: 0.18, 95% CI: 0.05–0.63 vs patients with reservoir strain ≥18% and LA reservoir phase duration >516 ms) (lower panel in the Figure). Patients with preserved LA reservoir strain but prolonged LA reservoir phase duration had similar outcome as patients with reduced LA reservoir strain (HR 1.10, 95% CI: 0.49–2.51).

Conclusions: LA reservoir strain ≥18% combined with reservoir phase duration ≤516 ms is associated with excellent long-term survival after CRT. Prolonged reservoir phase duration is linked to adverse long-term outcomes in patients with preserved LA reservoir strain. Therefore, reservoir phase duration provides added value for risk prediction after CRT that may be clinically important.