Does the time of day when heart surgery is performed influence patient outcomes?

Key messages

• The time of day when on-pump heart surgery (which uses a heart-lung machine) is performed may affect patient outcomes.

• We found one small study suggesting that late surgery (afternoon start) could reduce heart muscle injury compared to early surgery (morning start), but it did not provide clear evidence on survival during hospitalisation, heart attacks, complications such as irregular heartbeats, or how long someone needed to stay in hospital. We did not find any studies looking at short-term or long-term survival after hospital discharge, heart function, how long someone needed intensive care, and quality of life after surgery.

• More research is needed to determine whether scheduling heart surgery later in the day improves patient outcomes.

What is heart surgery, and why does timing matter?

Heart surgery is commonly used to treat problems involving the valves that control blood flow through a person's heart and the vessels that control blood supply to the heart. Many operations require a heart-lung machine (on-pump surgery) to temporarily take over the function of the heart and lungs during surgery.

The body follows a natural 24-hour cycle, known as the circadian rhythm, which we know affects heart function. Some studies suggest the heart may tolerate the stress of surgery better in the afternoon, reducing the risk of complications. However, the evidence is unclear, and it is important to determine if changing surgery schedules could improve patient outcomes.

What did we want to find out?

We wanted to find out whether having heart surgery in the afternoon improves survival, reduces heart damage, and prevents complications compared to having surgery in the morning.

What did we do?

We searched for high-quality studies (randomised controlled trials) that compared outcomes between people who had heart surgery in the morning versus those who had it in the afternoon. We summarised the results of the studies and rated our confidence in the evidence, based on factors such as study methods and sizes.

What did we find?

We found one study with 88 participants that compared early and late surgery.

• Survival: no study reported whether the time of surgery affected survival in the short term or long term. In the included study, no patients died in either group while in the hospital.

• Heart attacks: the included study found no clear difference in the number of heart attacks that occurred during or after surgery between morning and afternoon groups.

• Heart muscle injury: the included study suggested that heart muscle injury (measured by a blood test called troponin) was lower in patients who had surgery in the afternoon.

• Complications: there was no difference in complications such as irregular heartbeats (atrial fibrillation), heart function (left ventricular ejection fraction), or hospital length of stay.

What are the limitations of the evidence?

The evidence is limited because we found only one small study. We cannot be certain whether surgical timing truly affects outcomes or whether the results were due to chance. More high-quality studies that include more patients are needed.

How up to date is this evidence?

The evidence in this review is up to date as of 26 January 2025.