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By the time we reach our 80s, our hearts have beat over 3.3 billion times and and have pumped
250 million litres of blood around the body, enough blood to fill 100 olympic sized pools.
Just 3 weeks after conception the first muscle cells of the heart begin to contract and don’t
stop until the moment we die.
It is quite frankly a marvel that our hearts can last so long.
Pick up a stress ball and see how many times you can squeeze it before arm starts to cramp
and tire.
Unlike skeletal muscle, cardiac muscle has much higher numbers of mitochondria, which
provide the vital energy needed for contractions, and a rich supply of oxygenated blood, it
never has to worry about the build of lactic acid from working when deprived of oxygen.
But just because they do not fatigue does not mean they are invincible.
Heart disease is one of the leading causes of death in the world, as we grow older some
parts of the heart can deteriorate and cause some problems, but we have developed some
incredible technology that has extended our lives.
One of the most common implants in the world being pacemakers, small implantable devices
that help keep our hearts beating when our natural systems need some help.
Before seeing how they are implanted and how they work, let’s first see how our own bodies
have been engineered by nature to keep our blood flowing.
The heart has two sides separated by an inner wall called the septum.
The right side of the heart, which on this diagram is on the left, pumps blood to the
lungs where it is oxygenated and then travels back to the heart where it is pumped by the
left side to the rest of the body.
The walls of the left side are much thicker and stronger because of it has to pump blood
around the entire body, whereas the right side just has to pump it to the lungs and
back.
The heart consists of 4 chambers the left and right ventricles and the left and right
atria, the atria and ventricles are separated by valves.
At the start of the heart beat all 4 chambers are relaxed and the valves are open.
Blood flows into the heart from large veins and the heart reaches max capacity.
Just here there are a bundle of cells called the Sinoatrial node that are capable of producing
a electric impulse that will travel through the heart and cause it to contract in a specific
order.
First the impulse travel to the AV node located here, where it triggers both atria to contract,
squeezing blood out of the atria into the left and right ventricles.
The electric impulse has now travelled down through the heart to fibres located in the
ventricle walls that now cause them to contract, as the pressure rises it forces these valves
to shut and prevents blood from flowing backwards.
You can see each of these stages on the classic electrocardiogram.
The first little bump is the atria contracting, followed by the spike of the stronger ventricles
contracting and finally there is another little bump as ventricles recover.
For most, this sequence of events goes unnoticed thousands of times a day.
But some may need a little help controlling their heart beat. sometimes the Sinoatrial
node’s ability to set the correct pace breaks down, leading to slower heartbeats or long
pauses between heartbeats.
There are a range of reasons why you may need help and this is why the incredible pacemaker
was invented.
And as with most medical inventions it started as an incredibly dangerous and scary device.
The first being invented by Albert S Hyman in the 1930s.
It consisted of a hand cranked spring motor, which would store the hand crank rotation
as potential energy in a spring.
This spring motor then drove a generator, with these large U-Shaped magnets providing
the magnetic flux needed to generate a direct current voltage.
The current was then pulsed by a rotating interrupter disk with four conducting pads
which intermittently made contact with a brush which supplied this huge needle electrode.
Amazingly this little machine was portable, but it proved ineffective due to the low voltage
output.
His work was ultimately abandoned, but other researchers recognised its potential after
the second world war.
A method of inducing hypothermia by cooling the heart until it stopped beating to allow
it to be worked on during surgery was being investigated, but upon rewarming it was found
that the heart needed help with controlling heart rate as metabolic function recovered.
And John A. Hopps developed this device for the job, delivering impulses at the desired
rate through paddles that were placed inside the chest cavity during surgery near the Sinoatrial
Node.
The potential of using such a device on patients suffering from heart defects at normal temperatures
was soon realised, but repeated applications of high voltages cause muscle pain and twitches,
along with burns.
Making it unsuitable for extended use.
What we needed was an implantable device.
Hopps developed a catheter electrode, which removed the need for open chest surgeries
by passing the electrodes through the subclavian vein and into the heart.
On halloween night 1957 a power outage struck a minneapolis hospital, leaving several young
patients without pacing from the mains powered pacemakers, killing one of the children and
pushing famed heart surgeon Dr. C Walton Lillehei to request the hospitals technician Earl Bakken
to develop a battery powered pacemaker.
He returned with this device, a wearable pacemaker powered by mercury batteries that would launch
Earl Bakken’s company Medtronic into the fortune 500.
This was a revolutionary device, but the need to pass the wires through the skin was a constant
infection risk.
What was needed was a fully implantable device and with continual improvements to transistors
allowing for the miniaturization of circuitry, and improvements to batteries this was soon
realised.
This was the first ever fully implantable pacemaker, created and implanted in Sweden
to save Arne Larsson’s life.
With a rechargeable nickel-cadmium battery, which was charged through this induction coil
overnight about once a month.
It utilized some of the first silicon transistors imported into Sweden, allowing it to use less
energy over older Germanium transistors.
All this was encapsulated in a biocompatible epoxy resin.
Arne Larsson survived to 86, with his pacemaker being replaced a total of 25 times over the
course of his life, as the technology improved incrementally. [5]
Current generation pacemakers are now smaller and more reliable than ever.
Medtronic have even developed the world’s smallest pacemaker which is implanted directly
into the right ventricle without any cables, and eliminating the need for the pacemaker
to be implanted under the skin, which can lead to discomfort.
Over 700,000 pacemakers are implanted worldwide every year.
[2] These devices help people live healthier, happier lives and have advanced so far that
many can practically forget that they suffer from heart disease.
This subject is something I spent 4 years studying to work with, and have worked in
the medical device industry in the past with Medtronic.
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