The goal of this clinical trial is to learn whether temporary atrial pacing improves heart function after cardiac surgery under cardiopulmonary bypass (CPB). It will also help determine the best pacing rate during the first 24 hours after surgery. The main questions it aims to answer are:

• Does atrial pacing improve cardiac output after surgery?
• Is 70, 80, or 90 bpm the most effective pacing rate?
• Does pacing reduce the risk of atrial fibrillation after surgery?

Cardiac surgery under cardiopulmonary bypass (CPB) frequently leads to immediate postoperative rhythm or conduction disturbances, especially atrial fibrillation or atrioventricular block (AV Block), along with hemodynamic instability and transient reduction in cardiac output due to myocardial contractility impairment.

Temporary pacing wires are placed in the operating room and have been used since the 1960s to manage cardiac conduction disorders in these patients, allowing for atrial (AAI) or dual-chamber (DDD) pacing if necessary. Atrial pacing, by restoring synchronized atrial contraction with ventricular filling, helps maintain optimal cardiac output.

Cardiac output is defined as the product of heart rate (HR) and stroke volume (SV). To optimize cardiac output, increasing heart rate is possible, hence the need for atrial pacing.

A pacing rate slightly higher than spontaneous sinus rhythm appears to prevent pauses, limit rhythm instability, and reduce the risk of atrial fibrillation. However, the optimal pacing rate postoperatively has not been clearly defined, and data comparing different rates (70, 80, or 90 bpm) are scarce.

In our center, postoperative atrial pacing is nearly routine and commonly set at 90 bpm, a rate we consider optimal due to its alignment with the Frank-Starling curve. This rate maximizes venous return and stroke volume, thereby optimizing postoperative cardiac output.

Nevertheless, several studies have suggested that routine postoperative temporary pacing wire insertion may not always be necessary and should be reserved for patients identified as high-risk for postoperative rhythm disturbances.

Nowadays, in many international centers, the absence of routine temporary pacing has become the norm. Although 90 bpm is theoretically the optimal rate for atrial pacing, important questions remain: Is postoperative pacing absolutely necessary? If so, could a rate lower than 90 bpm suffice to maintain adequate hemodynamic profile (HDP)?

This study aims at determining whether routine temporary pacing is necessary during the first 24 hours after cardiac surgery under CPB, and what the optimal pacing rate is (AAI or DDD: 70 bpm vs. 80 bpm vs. 90 bpm) in terms of its impact on the HDP.

Inclusion Criteria:

• Patients aged 18 years or older
• Cardiac surgery under CPB (coronary artery bypass grafting, valve replacement or repair, or combined procedures)
• Placement of epicardial atrioventricular pacing wires during surgery
• Placement of a Swan-Ganz catheter intraoperatively
• Signed informed consent

Exclusion Criteria:

• Emergency surgery
• Patients with an internal pacemaker
• History of permanent atrial fibrillation
• Complete atrioventricular block upon weaning from CPB
• Junctional rhythm upon weaning from CPB
• Sinus rhythm < 50 bpm upon weaning from CPB
• Failure of atrial or dual-chamber pacing (patients paced in ventricular mode VVI)
• Contraindication to Swan-Ganz catheter placement
• Hemodynamic instability defined by significant bleeding or tamponade requiring surgical re-intervention, or the need for escalating doses of vasopressors (Norepinephrine > 1 μg/kg/min, Dobutamine > 10 μg/kg/min)