Heart block: cause of condition which affects endurance athletes identified in study using racehorses
MANUSHER BHASHA EXCLUSIVE-
By Debopam Rai Chaudhuri -
Endurance athletes (such as tri-athletes,
footballers, or marathon runners) can be some of the healthiest people in
society. Yet paradoxically, some can also be prone to developing a range of
heart rhythm disturbances (known as arrhythmias) as a result of exercise.
Image -Euro 2020: Christian Eriksen
has never had heart issues but will likely have tests after collapsing- Google Image
WATCH NOW -
There are many different
types of arrhythmias, but heart block (also known as AV block), is one of the
most common arrhythmias endurance athletes develop. While the condition is well
documented in athletes – and the potential dangers of it are understood –
little is actually known about the triggers of heart block and how it can be
prevented.
But our recent study has been
able to pinpoint the cause of heart block – and has shown that it can even be
prevented.
Heart block happens when the
AV node – a part of the heart responsible for sending electrical signals which
help the heart pump – becomes impaired. When these heart rate signals are blocked,
it can result in the heart beating more slowly or skipping beats. Athletes
aren’t the only people affected, and other factors – such as ischemic heart
disease, genetic heart disorders, and certain drugs – may increase a person’s
risk of developing heart block.
Normally, this doesn’t cause
any problems for young athletes, and many do not experience any symptoms. But
heart block in later life can progress to a more serious form, called
second-degree heart block, which can cause dizziness, fainting, and increase
likelihood of needing an electronic pacemaker later on.
Google Image -Five football players who died after collapsing on the field
Heart block has also been
associated with the development of atrial fibrillation, a more serious
arrhythmia that can cause an irregular or abnormally fast heart rate, and has
been linked to an increased risk of heart failure and stroke.
Because of the potential
dangers that can arise from heart block, our team wanted to uncover its causes
and see if it can be prevented. We found that long-term exercise (equivalent to
ten years of regular high-intensity exercise in humans) triggers a reduction in
key proteins – called ion channels – which control AV node function. This
reduction in ion channels leads to heart block.
The AV node is made up of specialized
heart cells which contain a set of unique ion channels that allow it to
spontaneously generate and send electrical signals from the top of the heart to
the bottom of the heart. Normally, the AV node receives input from the
automatic nervous system, which regulates involuntary functions – such as
digestion, blood flow and breathing.
It used to be thought that
changes to the nerves that slow down AV node function led to heart block. But a
previous study in human athletes showed that blocking nerve input had no effect
on impaired AV node function. This suggested something was happening to AV node
cells instead.
To explore whether something
was happening to the AV node cells themselves, we used the best available model
of an athlete’s heart: the racehorse. Racehorses easily adjust to training
routines and they also develop exercise-induced changes in their heart similar
to those seen in endurance athletes.
By taking electrocardiograms
or ECGs (a simple test that checks the heart’s rhythm and electrical activity)
of the racehorses, we were able to find that the incidence of heart block was
greater in racehorses that were exercising regularly. We also found that heart
block was associated with lower levels of two key ion channels responsible for
sending electrical signals in the AV node.
To study these ion channel
changes in greater detail, we then used mice in an experiment designed to
replicate the effect of long-term endurance exercise in humans. We found that
the reduction of ion channels in the AV node as a result of exercise could be
traced to an increase in small molecules known as micro RNAs. These molecules
directly bind to genes and inhibit their activity – so in this case, they
prevented the ion channels from being able to work properly.
But when we gave the mice a
drug that suppresses certain micro RNAs, the reduction in ion channels was
prevented – essentially preventing heart block from happening. These findings
may hold promise in developing new therapies for AV block.
But there’s still much we
don’t know – including how much impact micro RNAs really have, and whether
targeting them is a long-lasting solution. It’s also still unknown what aspects
of endurance exercise cause the increase in micro RNAs.
Currently, we’re looking into
these questions, and are also developing methods to deliver micro RNAs only to
AV node cells. This would be the first step in developing new ways of treating
heart rhythm disturbances in both endurance athletes and others.
At a time when more people
are participating in endurance and ultra-endurance events, our findings
highlight the ways in which our heart can adapt as a result. Of course, our
work doesn’t imply exercise is bad for heart health – rather, our research
helps improve our understanding of this condition and its causes, and why some
athletes may need an electronic pacemaker later in life. Exercise remains a
great way to improve heart health, and can lower risk of artery disease and
heart attack.
No comments:
Post a Comment
Thank You .Please do not enter any spam link in the comment box.