Temporary biventricular pacing after cardiac surgery in patients with severe left ventricular dysfunction. Short title: Pacing after cardiac surgery.

Left ventricular (LV) function is an important predictor of outcome after cardiac surgery. Severely impaired LV function (EF40%. Optimising LV function in the peri-operative setting may improve outcomes. Haemodynamic studies of permanent BiV pacing have reported a relative 25% increase in EF compared to dual-chamber right ventricular pacing. Methods: 38 patients in sinus rhythm, ejection fraction ≤35%, undergoing on-pump cardiac surgery were enrolled into the main study. All patients received temporary pacing wires attached to the right atrium, right ventricular outflow tract and left ventricle. Patients were randomly assigned to post-operative biventricular pacing or atrial-inhibited/dual-chamber right ventricular pacing. The primary endpoint was the transition from level 3 to level 2 care. The cardiac output measurements obtained using the PA catheters were compared to simultaneous measurements obtained from a FloTrac device (Edwards Lifesciences, arterial pulse-wave analysis). The measurements were compared using a Bland-Altman analysis. Results: The median duration of level 3 care was 22.0 (IQR: 16.0-66.5) hours and 37.5 (IQR: 16.3-55.0) hours in the BiV and standard pacing groups respectively (log-rank p=0.58, 95% CI: 0.43-1.61). At 18 hours, cardiac output with biventricular pacing (5.8 L/min) was 9% higher than dual chamber right ventricular pacing (5.3 L/min), ( p=0.001). Optimisation of the VV interval produced a further 4% increase in cardiac output (p=0.005). Analysis of the cardiac output measurements taken simultaneously from the PA catheter and FloTrac system yielded a bias -0.33L/min±2.2 L/min and a percentage error of 42%. Conclusions: Patients who require post-operative pacing or a prolonged haemodynamic support after surgery may benefit from optimised BiV pacing. However, for the majority of patients BiV pacing does not alter the clinical outcome compared to atrial-inhibited or dual chamber RV pacing. Although the FloTrac system is easy to use and rapidly reports changes in cardiac output, its precision requires refinement before it can be used instead of a PA catheter