(Beating) Hearts

I guess I can’t stop thinking about hummingbirds. The little engine that powers that tiny bird is a marvelous thing. The hummingbird’s heart averages 250 beats per minute, and it can be as high as 1200 per minute under times of stress. To put this in perspective, the human heart beats an average of 60-100 beats per minute, and never really gets above 200.


It must be loud, don’t you think? All that beating. So much work for such a small thing. The little “lub-dubs” must almost blend together.


The human heart, while it doesn’t beat as fast, is equally marvelous. Its complex electrical system maximizes its efficiency, making it torque in such a way to maintain blood pressure and deliver freshly oxygenated blood to each and every cell in our bodies.


Of course, during open heart surgery we often stop the heart. A machine that is roughly 5 feet long and consists of various tubes, pumps, and canisters, and which is run by a specialty trained individual, takes the place of the heart and lungs. Dark red blood is diverted from the venous system into this machine where it is oxygenated, turned bright red, and is then pumped back to the systemic circulation. And to make sure the heart doesn’t die during this process (it too needs oxygenated blood), we shut it down. It is infused with a cold cardioplegic solution (ice water, blood, potassium…) and submerged in ice. And that’s it – the heart stops, and the machine circulates the blood. A gentle and continuous hum replaces the familiar “lub-dub.” The monitors become irrelevant. The operation can proceed.


And proceed it does. Carefully placed incisions and even more carefully placed sutures are used to replace valves or bypass blocked arteries. The stakes are high – a slipped knot can literally end a life.


And then it is time to finish, and re-warm the heart. The ice is removed; the solution is switched to something warmer. The tubes are removed in sequence. And like a moon or the sun coming out of an eclipse, the heart comes back to life. A bit shaky at first, but in time a regular rhythm, and a good blood pressure. The chest can be closed; the operation is complete.


Except in our last patient. He was only in his 40s, and was the victim of advanced kidney disease as well as his heart troubles. A few hours after the surgery his blood pressure tanked, and his heart gave out. We started CPR. Now I was literally compressing his chest wall against his heart, forcing it to beat, willing a blood pressure. I could feel the ribs cracking under my compressions. Not good enough. We opened the chest with a slash of the scalpel and a few cuts of the wire-cutter. Now we could see the near lifeless, fibrillating heart. We squeezed it with our hearts in sequence (“cardiac massage”) a more direct form of CPR. A few shocks with the paddles…a tantalizing blood pressure…the cycles repeated…and then, nothing. No blood pressure, no pulse, no beating heart. Only death.


I walked in half-way through his autopsy the following morning. His chest cavity was spread open, empty. The heart and lung had already been removed – the perky pathologist gestured to their place on the table beside our patient. And his heart sat there, totally lifeless. There was no coming back this time.


It used to beat 60-100 times per minute. Now it was on a counter. It used to move oxygen all around his body. Soon it would be cut up into slides for the pathologist to review. It weighed over 300 grams, more than 100 times the weight of an average ruby-throated hummingbird.