There are various problems associated with the conducting system. So a couple of issues with the SA node for example would be if the SA node is not firing fast enough, that's what we call bradycardia, a slower than normal heart rate. Often due to the SA node firing too slowly if the SA node fires very quickly that can cause tachycardia Which is an abnormally high heart rate higher than what it should be for the circumstances if the SA node becomes damaged or malfunctions or Sometimes the SA node is okay But the internodal pathways that take the signals from the SA node to the AV node become damaged.
So either way damaged SA node or internodal pathways, then the AV node can take over as the pacemaker for the heart and still cause the heart to beat. So it's like a backup in a way. Because remember the AV node still can fire on its own, but it's slower than the SA node, so the SA node is really what sets the pace. But with the damaged SA node or internodal pathways, AV node is the only thing that can fire correctly and sweep over the ventricles for contraction.
The problem with this is that the AV node is only going to fire 40 to 60 times per minute, right? 40 to 60 beats per minute or BPM. And so that's often a heart rate that's too low to be normal.
So we will call that a conduction deficit when you get damaged SA node or internodal pathways and the AV node is what is firing these signals. If you get electrical impulses that are generated from areas outside of the SA or AV nodes, right? So remember the SA node and AV nodes, they're the ones that have the pacemaker cells.
They're the ones that are supposed to be generating the impulses to make the heartbeat. But sometimes you can get conducting cells. Remember, conducting cells are just supposed to transmit the impulses.
Sometimes conducting cells can become abnormal and they can start firing their own impulses instead of just passing the message along. So you can have abnormal conducting cells that make their... fire their own signals when they're not supposed to be, or sometimes even contractile cells in the ventricle.
Contractile cells are just supposed to contract to pump the blood, right? Sometimes even contractile cells in the ventricle can fire their own electrical impulses and cause the heart to beat when it should not be. In this case, this is what's known as an ectopic pacemaker. Ectopic means an area outside of where it should be.
like an ectopic pregnancy is a pregnancy in an area outside of the uterus where you know it shouldn't be there so an ectopic pacemaker is a is an electrical impulse generating area outside of the SA node or AV node it's it's pacemaking what in parts of the heart where it shouldn't be pacemaking so if you get up ectopic pacemaker cells firing in different areas of the heart this can interfere with the normal timing of the heartbeat, it disrupts the activity of the SA node and AV node because now we're also getting contracting signals maybe in between SA node and AV node firings and it just causes abnormal contractions. One thing we can do to try to combat this problem is we can implant an artificial pacemaker to take over when the SA node isn't working, it's too slow and the AV nodes firing instead or if you get these topic pacemakers. Either way, if you have problems with the conduction system, too slow, irregular types of firings, then artificial pacemakers are an option. So with this, it's just a small electrical device that gets implanted in the wall of the chest with leads or wires that run to the heart. And so this artificial pacemaker fires electricity that travels to the wires like an electrical device.
and then it zaps different areas of the heart to stimulate it to contract correctly. There are several different ways that a heart could generate electrical impulses irregularly. So these are what are known as arrhythmias.
So with an arrhythmia, either the regular rhythm impulses that make the heart contract are irregular, or the force of the heartbeat is irregular. So ECGs are really good devices to diagnose different types of arrhythmias, and there are several different types. You do not need to know all the different types of arrhythmias.
Okay, here are explanations of different common types of arrhythmias that we can see. I will discuss just one type of arrhythmia. This is what we call ventricular fibrillation. So none of these ECGs are normal, okay? Right?
Either they're inconsistent in the rates that they're firing, or the electrical activity is abnormal, and that is... really obvious with what we call ventricular fibrillation, this type of arrhythmia. This looks nothing like what a typical ECG should look like. The reason ventricular fibrillation ECG looks like this is because the electrical activity that spreads over the ventricles is incredibly abnormal.
You get almost like random firings and contractions of the ventricle so that the heart muscle, the contractile cells in the ventricle sort of kind of quivers. So it's like if you were to drop a pebble in a lake and you see the nice ripples that come out from that one pebble that spread through the lake, that's like a normal electrical activity in a heartbeat. It kind of gets generated in one spot and it spreads over nice and even and everything works the way that it should. With ventricular fibrillations, it's like taking a handful of pebbles and just... throwing them all at the lake at one time, and you get lots of different areas of ripples being created.
This is like what happens in ventricular fibrillation. You get this really, the ventricle heart muscles just kind of quivering and randomly contracting all over the place, and it's not working together in a coordinated fashion to pump the blood correctly. So when somebody's in V-fib or ventricular fibrillation, the heart essentially stops pumping blood. There are a couple of ways to try to reset the conducting system and get rid of the V-fib. You can use drugs to do it or you can pass a very strong electrical current over the heart and that is often today what we do.
So if you're in ventricular fibrillation, fibrillation is the problem. To get rid of the fibrillation you need a defibrillator. And these devices here are sometimes it's, you know, paddles and it's the paddles and you put it on the chest and you shout clear and you shock the person, right? This is an automatic external defibrillator.
These are, you know, anybody can use these as long as you follow the simple directions. But this is what a defibrillator does. It passes a very large current across the chest, which means sweeping over the heart. And we cross our fingers and hope that it resets the conduction system.
And. Exit v-fib. Okay, they don't always work. I think if you watch movies and TV where they do this It's a lot more successful on TV than it is in real life.
But if you do it quickly The faster you do it the greater the chance that the person would survive