Serious heart attacks are more likely to happen at the start of the working week than at any other time, according to a new study, by leading cardiovascular researchers including clinician scientists at RCSI, presented at the 2023 British Cardiovascular Society (BCS) conference.

Clinician scientists at the Belfast Health and Social Care Trust and RCSI University of Medicine and Health Sciences analysed data of 10,528 patients across the island of Ireland, including 7,112 in Ireland and 3,416 in Northern Ireland, admitted to hospital between 2013 and 2018 with the most serious type of heart attack.

This is known as an ST-segment elevation myocardial infarction (STEMI) and occurs when a major coronary artery is completely blocked.  

The researchers found a spike in rates of STEMI heart attacks at the start of the working week, with rates highest on a Monday. There were also higher rates of STEMI than expected on a Sunday. 

Scientists have so far been unable to fully explain why this 'Blue Monday' phenomenon occurs. Previous studies suggesting that heart attacks are more likely on a Monday have highlighted an association with circadian rhythm – the body’s sleep or wake cycle. 

STEMI requires emergency assessment and treatment to minimise damage to the heart, and this is normally performed with emergency angioplasty – a procedure to reopen the blocked coronary artery.  

Understanding the triggers

The study was carried out under the supervision of Professor Robert Byrne, Chair of Cardiovascular Research at RCSI School of Pharmacy and Biomolecular Sciences and Director of Cardiology at the Mater Private Hospital and the Cardiovascular Research Institute, Dublin.

“What we found was that the odds of suffering a heart attack were about 13% higher on a Monday as compared with the other days of the week. Similar findings have been previously reported in international studies but it is the first time we have observed the phenomenon in an Irish setting,” he said.

“This study adds to evidence around the timing of serious heart attacks, but we now need to understand what are the triggers that makes them more likely on certain days so we can save more lives in future.”

Circadian rhythm

Cardiologist Dr Jack Laffan, who carried out the research as part of his MD at RCSI and who led the research at the Belfast Health and Social Care Trust, said: “We’ve found a strong statistical correlation between the start of the working week and the incidence of STEMI. This has been described before but remains a curiosity.

“The cause is likely multifactorial, however, based on what we know from previous studies, it is reasonable to presume a circadian element.” 

He said the most likely time of the day to have a cardiovascular event is in the early hours of the morning between 6am and 10am.

“This is when cortisol and other hormones in our blood rise as we wake up and these hormones also rise when we are under stress and the general hypothesis is that the finding is related to alterations in hormone levels to do with the circadian rhythm.”