It’s the season for parties and celebrating the end of another year, but having a few too many drinks can leave you feeling less than merry.
Perhaps it’s a thumping headache, a feeling of “jitteriness”, or an unquenchable thirst that has you reaching for some electrolytes the day after drinking.
But for some, hangover symptoms might be a sign of something more sinister, especially if you experience heart palpitations, breathlessness or light-headedness.
Those are all characteristic of “holiday heart syndrome”, a term coined in 1978 after doctors in the US noticed a suspicious pattern.
On Mondays, they saw a spike in patients presenting to emergency departments after a weekend of binge drinking with a heart condition called atrial fibrillation, which is characterised by an irregular and sometimes rapid heartbeat.
They also found rises in atrial fibrillation rates during holidays.
This led to the finding that two-thirds of people under 65 who showed up at emergency with atrial fibrillation had their heart arrhythmia caused by binge drinking.
Now, a study by a group of German researchers has looked into the mechanisms behind alcohol-induced atrial fibrillation, speculating that the part of the nervous system which helps us “rest and digest” plays a critical role.
But first, how common is alcohol-induced atrial fibrillation, and how concerning is it?
What is atrial fibrillation?
“Atrial fibrillation is a common cause of what we call palpitations, or the awareness of an irregular heartbeat,” Peter Kistler, head of cardiac electrophysiology at the Baker Heart and Diabetes Institute in Melbourne, says.
“It can make people feel breathless, fatigued, washed out and light-headed.”
Atrial fibrillation is diagnosed by ECG (a test which measures the heart’s electrical activity) and is usually treated with medication or a “shock” from a defibrillator.
It can be triggered by factors such as high blood pressure and heart disease. Sometimes it has no obvious cause.
It’s difficult to put an exact figure on how many people experience atrial fibrillation after consuming alcohol, but the German study, which was published in March in the European Heart Journal, suggests it affects around five to 10 per cent of “otherwise healthy” binge drinkers.
And while binge-drinking-induced atrial fibrillation affects all ages, Professor Kistler says it can be particularly problematic for older people.
“In the younger population, [we are more worried] more about the symptoms of atrial fibrillation, but for older people, it is a very common cause of stroke and heart failure.”Even a few weeks off the booze has noticeable health effects
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Perhaps most concerning is evidence to suggest that episodes of atrial fibrillation can have long-term health consequences, even in younger people.
“We have this phrase: atrial fibrillation begets atrial fibrillation,'” Professor Kistler says.
“So the more episodes of atrial fibrillation that you have, the more changes we see in the heart that leave you vulnerable to more episodes that then last longer.”
But people who’ve had atrial fibrillation can lower their future risk.
A 2019 randomised control trial led by Professor Kistler showed that abstaining from alcohol significantly reduced the condition’s recurrence.
How does alcohol cause atrial fibrillation?
Until recently, the time frame in which atrial fibrillation occurs after binge drinking was poorly understood.
The German study sought to rectify this. It followed more than 200 volunteers who planned to binge drink, and fitted them with Holter monitors, collecting a range of heart rate and rhythm readings over 72 hours.
When study participants drank, their heart beat faster. But it wasn’t until during what the researchers called the “hangover” period, six to 19 hours after drinking, that participants generally experienced atrial fibrillation.
Professor Kistler says this finding — that atrial fibrillation is more common during a hangover than while drinking — suggests the condition is likely triggered when a part of the body’s nervous system called the parasympathetic nervous system is suppressed.
The parasympathetic nervous system is responsible for resting and relaxing the body. When activated, it slows the heart, among other effects.
When it’s suppressed, though, it’s like taking a foot off the heartbeat brake. The heart is then more likely to beat irregularly and lead to atrial fibrillation, Professor Kistler says.
“We found that the suppression of the parasympathetic nervous system becomes more prominent during that hangover period [than while drinking].
“So we believe the parasympathetics are very important in triggering atrial fibrillation.”
Heart ‘not performing as effectively’
Professor Kistler and his team have also studied what happens after the initial “hangover” period (between 24 and 48 hours after binge drinking), finding that the cardiovascular system does its best to “rebalance”.
“There’s this rebound that happens afterwards … where the parasympathetic nervous system may ‘overcorrect,'” he explains.
This was characterised by a slowed heart rate (even slower than the period pre-drinking), while they also noted changes to the heart on MRI scans.
While the research team initially looked for signs of alcohol causing inflammation in the heart, they instead found what Professor Kistler describes as a “reduction in the squeezing function of the upper chamber”, otherwise known as atrial mechanical dysfunction.
“That’s why people don’t feel as good in that 24 to 48 hours after drinking, because their heart is not performing as effectively,” he says.
“That’s why athletes and sportspeople are told they can’t drink in season: because it diminishes their cardiac performance.”
All in all, Professor Kistler says the evidence adds up to a clear message.
“There’s this whole concept that alcohol is good for the heart, but that’s definitely not true if you have an electrical heart problem, and [as general advice] it’s highly questionable anyway.”
National Australian guidelines recommend healthy adults drink no more than 10 standard drinks a week, while Professor Kistler advises consuming even less if you have any kind of heart arrhythmia.
“Ideally you’d [cease drinking entirely], but we say [stick to] up to three standard drinks a week.”
Could it be ‘hangover anxiety’?
Alcohol’s effect on the parasympathetic nervous system could also be responsible for another notorious hangover feature: the phenomenon known as “hangxiety” (or hangover anxiety).
Up to 22 per cent of people report experiencing anxiety after drinking alcohol.
And, given the symptoms of anxiety include palpitations, Professor Kistler acknowledges that it can be hard to distinguish from atrial fibrillation.
“They are really commonly mixed up,” he says.
“Sometimes people are treated for anxiety or panic attacks for years, and then it’s discovered that they have an arrhythmia.”
One way to distinguish the two, he says, is that your heart may feel like it’s “racing” when you are anxious, but you shouldn’t have the sense that your heart is beating “irregularly”.
If in doubt, he advises seeing a doctor, or presenting to the emergency department.
“[Go to hospital] if you feel very unwell, but more specifically if you’re breathless, light-headed, or feel that your heart is beating uncontrollably.”
Also read: Six invisible things that might be putting your heart health at risk
