One billion heartbeats

One of the defining features of mammals is the four chambered heart. A curiosity of biology is that all mammals have more or less the same lifespan, if you measure it in heartbeats: one billion beats, give or take a billion.

If you’re a large mammal, like an elephant, your heart beats slowly, and you live many years. If you’re a mouse, your tiny heart beats far faster, and you’re lucky to live more than a handful of years. If you’re a human, your heart usually beats around 70 times a minute. Mine is a little different. It likes to throw in an extra beat here and there.

Humans have known for a long time that the heart is a critical part of the biological machine, though the exact purpose has sometimes eluded us. The ancient Egyptians would carefully preserve the heart after death, believing that it held not only the soul, but also all the knowledge collected during life, and that this knowledge would be used to determine whether the deceased deserved to experience the afterlife.

Ironically, the Egyptians thought the brain was just grey sponge wasting space in the head; it was the first thing they removed and threw away during mummification. We now know that the brain is in fact where our consciousness and knowledge resides; but we still believe that the heart is really all that stands between us and oblivion.

If your heart stopped right now, you would notice pretty quickly. Blood would stop flowing, and the steady supply of oxygen to your body would cease. You would feel dizzy, nauseous, as your brain began to choke. You might suddenly feel hot before passing out; perhaps this is where the idea of the firey pits of hell originated. If your heart started again, you’d be left sweating, with a ringing sound in your ears.

It’s called cardiac arrest. It’s not a heart attack; that’s when the heart goes into spasm, often triggered by lack of oxygen, often in turn triggered by blocked arteries. This is something different, though the end result is often the same.

One minute after your heart stops, you have about a 90% chance of survival. For each additional minute after that, your chances of survival drop by around 10%. After 10 minutes, you are almost certainly dead.

In Austin, first responder for cardiac arrest victims is provided by the fire department. I estimate that they could get from South Congress to our house in about three minutes if they really floored it. Nevertheless, I’ve spent a few hours lying awake at night, listening to my heartbeat, wondering if I might go to sleep and never wake up, counting my life as it pulsed away.

An irregular heartbeat may not be serious at all. I’ve had mine since birth, and I’m not dead yet. However, on a couple of occasions in the last year I’ve woken up during the night, gotten out of bed for whatever reason, and after a minute or two suddenly become dizzy, nauseous. I’ve not actually blacked out, but I’ve been left with a ringing in my ears and a feeling of uncomfortable heat.

I’m a deep sleeper. I’ve slept through earthquakes and sirens. Sometimes when I wake up, it feels as though my body would rather I stayed in the dream world. Perhaps that’s all there is to it, but my conscious mind has other plans which involve waking up from time to time on a continuing basis.

So it was that I found myself at the Austin Heart Hospital, watching my heart beat on a screen. The control console was covered in lights, buttons and adjustable knobs, like an old analog synth. The technician turned a control, moved the ultrasound probe against my chest, and I heard my blood rushing through the chambers of my heart. A few more adjustments and I could hear the valves doing their vital work; it was a wet rhythmic slapping noise, recognizable yet at the same time somehow disturbing.

Today the cardiologist reported his analysis of the recordings. There appears to be nothing wrong. No abnormality of the valves, no weakness of the muscles, no reduction in capacity of the atria or ventricles. All the other tests are similarly unexciting: blood pressure normal, cholestrol level normal, blood sugars normal. As far as medical science can determine, there’s nothing wrong with my circulatory system. That’s pretty unusual, these days.

So I go to bed tonight knowing that if I should fail to wake up, it’ll at least make for a good epitaph: “He died as he lived: ironically”.