Rich et al
I saw the ER episode - sat down with my post-workout Chinese dinner only to see the student being brought in on a stretcher. The rescue squad tech rattles off the vitals, and mentions that the kid was hit in the chest with a kick during a karate demonstration and his heart stopped. "Commotio cordis" I rattled off as they brought him into the room. My medicine-practicing wife gives me a 'sure, you know-it-all' look. Then Anthony Edwards yells "Commotio cordis!" I gave a smug look to my wife who looked at me dumbfounded.
We talked about this one in the past both here and on the kyusho forum.
Several points I would like to make. In the end, I will defer to the comments of the good Dr. X. However I have cardioverted dogs in the lab about a thousand times or so. I have a little bit of experience on this one.
First of all, commotio cordis is a very rare phenomenon. You have to hit the chest of someone with a thin chest wall in a time interval no larger than several milliseconds (millisecond is 1/1000 of a second).This is the period of time in the ECG where you have the rising T wave.
There are several things going on here. I will use a crew boat full of athletes as a metaphor to explain what is going on here. First of all, cardiac cells depolarize and repolarize like neurons. With depolarization comes contraction. It is a bit like the fellow in the crew boat who decides to 'stroke' (the depolarization), and then pulls the oar that moves the boat (contraction). As long as he does it in synchrony with his neighbors, the boat moves fine and it is a thing of beauty.
There are a number of things going on in this boat. There is the coxswain that yells "Stroke!". That is the equivalent of the P wave in the ECG. A pacemaker in the atrium has fired and is communicating that signal to the rest of the heart (from the SA node to the AV node). Then each person on the boat hears the word "stroke" and thinks 'I must stroke'. That is the equivalent of the electrical wave hitting the individual cardiac cells. This is the QRS in the ECG. In general each cardiac cell gets this depolarizing signal from its neighbor. Well since this signal hits all people in the boat and all the cells in the heart *nearly* simultaneously, they all 'stroke' (or contract in the case of the heart) at the same time. Then everyone in the boat needs to get their oar back into position. This is the repolarization phase in the heart, and corresponds with the T wave in the ECG.
Now each time a person in the boat 'strokes', it takes him time to get his oar back in position. This latency period is called just that in the heart. An electrical charge across a cardiac cell membrane has just reversed and it takes some fraction of a second for the ion pumps to get it back to the starting position. In both the case of the person in the boat and the cardiac cell, no 'stroking' can happen at this interval in time.
So what is commotio cordis? Imagine if you will that some people in the boat get their oar back into position a fraction of a second before everyone else. This happens in the heart too. Then in this short interval of time, some jerk on the side of the river yells "STROKE" just to screw the boat up. Well a few of the folks who have their oars ready get fooled and 'stroke'. Those that don't have the oars up can't 'stroke', and so must wait until the real coxswain gives the command. The non-fooled and non-ready then pull their own oars at the proper time. You want to know what happens? Chaos! The oars clash and everybody loses the rhythm. The only way to get things right again is for somebody to yell "HEY, EVERYBODY GET YOUR OARS UP!!!!"
Well something similar would happen if your heart got a physical blow right in the few milliseconds of the rising of the T wave. Some cardiac cells are ready to depolarize, and others are not. A few that are ready to fire will do so, and they get out of synch with the rest of the cells that are ready to depolarize a fraction of a second later. You now have ventricular fibrillation. You MIGHT be able to get the heart back in synch with a big blow to the chest. Better yet, get the defibrillator out which will depolarize every single cell it can and hopefully get them all back in synch again.
Now for the practical side of things. First of all, it was my understanding that the problem they talked about in the ER was that the RESCUE SQUAD techs and NOT the karate folks did not have the defibrillator. Sure, a lot of people could probably put the paddles up against a chest and get lucky enough to do the cardioversion properly. But they also might hurt themselves or their neighbor in the process.
It is my understanding that 1) calling 911 and 2) doing the "process" of CPR is the treatment of choice in this situation. I know there is a movement to have defibrillators in airplanes and certain public places. But you really do need to know what you are doing. If you don't, best not to put a SECOND person in cardiac arrest by fooling around with a dangerous piece of equipment.
[This message has been edited by Bill Glasheen (edited 10-05-98).]