Gresham College Lectures

Rhythm Disturbances of the Heart

March 03, 2023 Gresham College
Gresham College Lectures
Rhythm Disturbances of the Heart
Show Notes Transcript

Our bodies depend on our hearts maintaining a steady beat, and increasing it appropriately in response to exercise. If the heart goes too fast, or too slowly, we have effects ranging from tiredness to unexpectedly passing out to death.

This lecture will consider the normal heartbeat, the causes of the heart going too fast or slowly and how it is treated when it does.


A lecture by Sir Chris Whitty recorded on 21 February 2023 at Barnard's Inn Hall, London.

The transcript and downloadable versions of the lecture are available from the Gresham College website: https://www.gresham.ac.uk/watch-now/rhythm-heart

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(swooshing music)- This evening I'm going to talk about one of the major groups of things that can go wrong with the heart, and that is the heart rhythm becoming abnormal. Now the heart in every mammal, and indeed birds beats with extraordinary regularity. It's a quite extraordinary mechanism by which it does that. And in humans it has a very steady beat, usually somewhere between 60 and 100 beats per minute, at rest. If people are extremely fit athletes, it'll go slower than that. So there's a variety of possibilities, but it can be designed in nature to be quite different points. So for example, blue whales, which are very large, can go down to four beats per minute when they're diving, whereas this Etruscan pygmy shrew on the lower part of this can have a beats per minute, which are over 1,000 beats per minute at rest. So the heart can essentially set its rate to the animal it's in, but the animal it's in in us is obviously humans, so that's the rate we have, between 60 and 100, at rest. Now this series of lectures I've been giving this year are the major conditions, which lead to heart disease in humans. And the first group, which I've talked about already are diseases of the coronary arteries, things that lead to angina, heart attacks, and problems of that sort. In this lecture I'm going to be talking about rhythm problems, the heart going too fast or going too slowly. And then in the last lecture, I'm going to talk about the structures of the heart, the heart valves, the heart muscle, and the structures. Now to understand how the rhythm works and what goes wrong, it is important to go back for those of you who are a little bit away from it to school biology, anatomy, because the anatomy helps to explain what goes wrong. And the heart is essentially two pumps smashed together, there's a left side and there's a right side, but in terms of the timing they work together at the same time. You have four chambers, the upper two chambers are called the atrium, and that beats first, go through the sequence several times. And then below that is the ventricle, which is a large muscle, which actually when it contracts it then pumps blood, either around the whole body on the left side or around the lungs on the right side. So that's the way that this works. And to make this work in sequence completely regularly, and then be able to speed up or slow down depending on whether you need it, the heart has what is for practical purposes a wiring system, and several pacemakers. So at the top of the heart where the number one there is something called the sinoatrial node, and that is your principal pacemaker. If everything is going right, then that will just go along with a regular rhythm, as I say, 60 to 100, and initiates the whole cascade I'm going to talk about. And what then happens is electrical wave spreads over the atrium very rapidly, and the atrium contracts, and then there's a delay, and the delay is built-in between it going from the atrium to the ventricle to give time for the blood essentially to get it to where it needs to be. And then the valves close, and then it goes through a very fast set of fibers, things called Purkinje fibers in the bundles of His, so that the whole of the lower part of the heart, it suddenly has an electrical impulse at virtually the same time because otherwise it'd be very inefficient. So the wiring system means that the electrical impulse goes around the whole thing incredibly quickly, then the heart, lower part contracts, and then it relaxes. That's the sequence, and you'll have seen that, and it's all of you, it's happening all the time. But this delay at the, what's called the atrioventricular the AV node is very important because if that delay didn't happen, then the atrium wouldn't beat before the ventricle in a nice, steady sequence. The SA node, the bit at the top of the heart can actually speed up or slow down under control of your body. And the sympathetic system... I'll come back to this again several times, the sympathetic system, the flight or fight system speeds it up, and it also speeds up the conduction through the AV node, and the parasympathetic node system slows it down. So for all of this, its intention, and we can speed up or slow down. If we have to climb that mountain, if we're very excited, if we're very stressed, if we've lost blood, it'll speed up. If we're at rest to conserve energy, it'll slow down. But there's also built-in redundancy. The body is unbelievably good at having... If something goes wrong, having something else, which will take over, if necessary. And below the SA node, the normal pacemaker, there's another pacemaker in the AV node as well, which if the SA node is not working can take over, but it beats more slowly because if it beat at the same speed, they'd be in competition. So it beats more slowly, but if the top one is eliminated, the AV node one would simply take over. And if the AV node doesn't work, there are other pacemakers lower down the system that are slower still, they're not capable of allowing you to climb Everest, but they will keep you alive. So if there's a temporary problem, they will take over until the temporary problem is fixed. So it's a very, very clever bit of built-in redundancy. Now the way that the sympathetic and the parasympathetic nervous system work, normally if you are just completely at rest, totally relaxed listening to a lecture, your parasympathetic system is actually driving the heart to go a bit slowly. The first thing that happens when you start to try and do some activity is the parasympathetic system switches off, and then the sympathetic system switches on, and that speeds the heart up up to maybe 150 beats per minute. So if you're a sprinter or something like that, it'll take off at an absolutely phenomenal rate. And that's under some degree your control. It's important to know a little bit about the drugs by which the... Or the messengers by which the body does this because they're important for the drugs that I'll talk about later in how you treat it. So the rhythm effects for speeding things up, for the adrenal system is the beta system, that's what the sympathetic system uses. And the reason that's important is there is a drug class called beta blockers, which work directly on this system, but that's part of the way in which the body speeds things up. And the parasynthetic system uses a messenger called acetylcholine to a slightly different set of receptors. Now throughout this talk, I'm going to be talking quite a lot about ECGs, so I just want to talk a little bit about ECGs. An extraordinarily powerful bit of kit that is fundamentally incredibly simple. All it does is measures the electrical impulses on the outside of your body, but because your heart has got this electrical conduction happening, you can read it, and you can actually tell exactly which bit of the heartbeat is happening at any given point in time. It was developed right back in the 1880s originally, and they were originally large bits of equipment, like the one being demonstrated. This is just from the 1910s on the right, and the gentleman who is demonstrating it has one leg in a bucket, and both hands in the bucket. And those are the ways in which the electoral conduction was actually transmitted and measured. But what all of them have in common is that they just simply measure the electrical impulses on the surface of your body, which actually come from your heart, which gives you some idea about how strong these electrical impulses actually are. Now the ECG has a very standard shape, and last time in the last lecture when I was talking about coronary heart disease, I was talking about the right-hand side of the ECG, which tells you something about severe heart attacks. For understanding rhythms, you need to understand the left hand side of the ECG, and I'm just going to walk you through it in two different ways. So first of all, you get a small contraction, you see, so you get a small wave called the P wave, and that's when the electrical impulse is going across the atrium, which is a relatively small organ. And that's the initiation of the system. Then there's a delay because it then is held essentially at the AV node, and then it spreads incredibly fast around the whole heart, and that's what's cause the QRS thing, that's the main electrical impulse. Then there's another delay as the ventricle is contracting, and then you get the relaxation wave, which is something called the T wave. For understanding rhythm, you just need to understand the P and the QRS, forget the rest, those are the only two that matter. And so just to refresh that, so starting here on the left, nothing happening at all, you get the AV node... So the SA node fires, spreads over the atrium, you get the P wave, then you get contraction delay at the AV node at, then it spreads very rapidly through the ventricle QRS relaxation to the T wave, and repeat after a period of a delay. So that's under ordinary circumstances, and that gives rise to an ECG like this. And if any of you've gone into hospital or had friends or family in hospital, there's a high chance you'd have had one of these, and have looked to one of these, and seen what they show. And the ECG show a huge amount, they're very informative, but for purposes of this talk, I'm just going to be talking about the rhythm. So your heart can then do one of two things, which can cause problems for your ability to function. It can go too fast or too slowly. And ECGs everywhere in the world run at an exactly standard rate. So the number of squares you see on it, you can calculate from that exactly how fast this heart is going. So the heart on the left is going very slowly, that's a bradycardia, it's abnormally slow. The heart on the right is going very fast, that's a tachycardia. That's again abnormal, it's going too fast. Either of these will lead to your heart being much less efficient than it should be. Remember, it's designed to go at 60 to 100 normally, and then you speed up under certain circumstances. So this is bad news essentially, not necessarily catastrophic news, but this is the thing which I'm going to be talking about for the next few slides. Now if you have a rhythm problem, there are a variety of ways this can be picked up. It may be picked up simply because someone feels your pulse old-fashioned way, does an ECG before an operation, and they notice you got an abnormal rhythm. Though it wasn't doing you any harm, you had noticed it yourself, but they tell there's something going on, they want to investigate it further. So it may just be you're fine, the doctor or the nurse says,"Hang on a moment, we need to do something." It might be quite minimal symptoms, people having things called palpitations where they just feel the heart skipping beats, or it's a bit odd, but it can then go on to have a feeling of breathlessness, dizziness, faintness, absolute collapse, and in the extreme case, which I'll talk about at the end, cardiac arrest. To be clear, that's rare, none of you look as if you're about to have a cardiac arrest. That's right at the far end, but the relatively minor rhythm disturbances are relatively common. Now for many people, they will have symptoms that could be the heart doing that, or it could be a lot of other things, including nothing very worrying. And they go to the doctor or the nurse and they have an ECG, and at that point in time the ECG is normal, but they're also fine at that point. The problem is, you can have runs of heart going too fast or too slowly, particularly too fast, and it's not there at the time when you present to the doctor. So the way that that is then picked up is by a mechanism called a Holter monitor. It's named after this gentleman, Norman Holter, demonstrating early prototype. This would not be how we would normally do it now,(audience laughs) but engineering improves at all times, and they're now very, very small, and you wear them round your neck or on your belt, and you just go about your ordinary business. If you go running, you go running; if you go to work, you go to work, and they measure your pulse rate over a long period of time. They keep a record of it, and then you can analyze it subsequently and say, yes, there are runs where there's an abnormality, we need to take that further. Or they will say, "There's nothing wrong. No, that's not the problem." Now if there are, the heart, I'm going to start off in terms of the things which can look abnormal or be abnormal. The first group of things are when the heart goes too slowly, and the first of these is actually when the heart is going slowly, possibly abnormally slowly, but the heart rhythm itself is completely normal. So if you look at this ECG, you've got a P wave normally, a normal interval here, a normal QRS, and a normal T wave. This is a normal ECG in that sense, but it's just going too slowly, that's what's called sinus bradycardia. And there's lots of reasons for that, it could be someone who is an Olympic athlete, that's just their normal heart. It could be because they've got a number of reversible causes. For example, they might have a slightly low thyroid hormone level, that tends to lead to this. They might be hypothermic, if they've got very cold, that can lead to this. Quite a few drugs can potentially lead to this, even some infections, Lyme disease, for example, can sometimes do this. So there are a variety of things, which can lead to these kind of abnormalities. Most of these are reversible, and then occasionally it can be more severe things like a recent relatively small heart attack can lead to this. So several things can lead to this kind of presentation. Next thing that can go wrong is that the first pacemaker, the key initial pacemaker can get sick, and this is called sick sinus syndrome. And the node may fire either too fast, which can cause tachycardia. I'll come back to that. Or too slowly, too slowly being the one that I'm talking about now. Generally age related, it's more likely as we go on in age to happen, and the heart rhythm then kind of varies over time because the pacemaker is not sticking to its good steady rhythm under ordinary circumstances. It can be, there have been a variant, sino-atrial block. This what you see here is the P waves are normal all the way along, but you can see here between that normal P, QRS, and this one, there's a long delay. The sino-atrial node has basically gone to sleep, it's not doing its job, but it's not such a long delay that the rest of the heart takes over. So that's another problem with the sino-atrial node, so that's right at the top of the heart. More commonly in terms of people who got symptoms is where the problem is a bit lower down. It's what's called the AV node, that bit where there's a delay between the atrial contraction and then the ventricular contraction, the AV node, and you can get a block at that point. Now there are several different types of block, something called first degree block. It doesn't really matter that I'm just telling you for completeness. The key ones are second degree heart block, and third and complete heart block. So second degree heart block is made up of two different varieties. One of which is where the heart, but in a very regular rhythm drops a beat. And what actually happens when you look at the ECG is that the P wave gets longer and longer, then there's a drop beat, and then it resets, and it goes back to the beginning again. That's not dangerous. Dropping one beat completely predictably is not dangerous. It's odd, but it's not dangerous, but the more worrying one is where you get a beat that is dropped, doesn't go through the AV node properly, unpredictably. And this is second degree heart block, and this is something called Mobitz type II. And you can have it either irregularly, like this one, or you can have it regularly, where, for example, this one underneath, you can see the P waves going along a rate, and every other one the beat gets dropped. That's second degree heart block. And then you get complete heart block, also known as third degree heart block. And this is when the P wave is merrily beating along perfectly normally, the atrium is contracting, and unfortunately none of it's going through the AV node at all, so then the ventricle takes over. So one of the lower pacemakers takes over, and you have an atrium going along at one rhythm, and you have a ventricle going along at another rhythm much more slowly unrelated to one another. That's called complete heart block, and people usually have symptoms with, quite significant symptoms with that. So all of these things, secondary heart block, and complete heart block. If people who got symptoms, they're likely to need treatment because this can be debilitating. And if they're doing things like driving, this can actually be very dangerous. They can suddenly collapse, for example, when they're up a ladder, or under ordinary circumstances. So the first question always is, is this reversible? Is there some reason that you can simply switch off the reason, and it goes back to normal. And there are quite a few where that may be the case. So the most common of these is that people are taking drugs, which are designed to block the AV node, that's their job, but they got a bit too much of them. And therefore if you ease back on the drugs, the heart goes back to beating normally. So that's a doctor-induced block, in fact. They may have other reversible causes, but if there's any doubt, if you need to, you can actually either give temporary drugs, which will speed the heart up. Adrenaline is one, atropin is another, so there are some drugs you can do, but they only are appropriate to hold the line for a short period of time. They're not a long-term drug, you're not going to be taking them for the rest of your days. And this is not very comfortable, but it's doable. You can use what's called external pacing where you put pacing pads on people, and you basically give them a shock across the chest regularly to fire the heart up at a fast enough rate. Now no one is going to thank you for doing it, except you will still be alive at the end of it, which is a good outcome.(audience member laughs) But this is not... That is what external pacing is, but in general if you're doing these, what you're saying is, either this is very quickly reversible. I'm holding the line just for that, or I'm going straight to a pacemaker. And the final outcome for long-term bradycardias is always a pacemaker. There aren't drugs you can use to keep the heart going over long periods of time. So artificial pacemakers, again rather like the Holter monitor and the ECG I showed you, the miracles of engineering means that these have turned from large external boxes only used under extreme circumstances to smaller and smaller, and longer lasting, and increasingly sophisticated things that are tunneled generally under the skin with wires into the heart. So the early pacemakers, one shown here, would only have been used in very severe cases. Modern pacemakers are small, very durable, you can knock them about really quite a lot, and their batteries depending which type they are last generally between six and 10 years before they need a change. So once they're in, that gives you really quite a long period of support. So they come in several types, and it really depends on the problem, or which type. If you need one, you would get. All of them though do the same thing, which is in a regular way, they give a little electrical impulse, which is rather like the SA node or the AV node initiating a heart contraction. So it's essentially taken over from your natural pacemakers, and it's doing the job for them, but the rest of the system works normally. Most modern pacemakers now work what's called on-demand. So if you're someone of the people who 90% of the time your heart's beating normally, but 10% of the time it goes far too slowly. For the 90% it recognizes that and it doesn't beat at all, and it only kicks in at the point when your heart is going too slowly.

That's got two advantages:

It's much more efficient, it's more physiological; and secondly the batteries last longer because you're not having to actually drive it in between times. Increasingly now they can also sense if the body is moving or you're breathing rapidly. And if that's the case, they'll speed up, and when you calm down, they'll slow down again, quite extraordinary really when you think about it. And as I'll show you in a second, they can be single chamber, you put them in just one chamber, two chambers, left, above the top and bottom, or what's called biventricular, which actually usually means three chambers. So there's a variety of ways that can be done. Lot of possible settings depends on what the problem is. If it's just a problem, for example, at the SA node, you might just have one just in the upper atrium, and the rest of the system goes normally. For many older people, we know it's much more common to have a wire in the top and a wire in the bottom, and it takes over the whole system. It provides the atrial thing, waits the correct amount of time, and then initiates the ventricular one. So it actually takes over the whole of the pacing system. And if someone's got heart failure, you might even have it in three different areas to make sure that the whole heart is contracting at exactly the right point. The developments of these are happening the whole time. So a new development is things called leadless pacemaker, so they don't actually have a box here with a lead into your heart, you put the pacemaker itself into the heart, it sits there. Those are mainly used as a way of reducing risks from infection in people who are particularly high-risk. And I'm sure whoever is giving a lecture on this in 20 years' time, they would have moved further, they'll be longer lasting, they'll be smaller, and they'll be more sophisticated. So this is a technology that's already good and continues to improve. So those are the bradycardias, I'm now going to move on to the slow things. I'm going to move on to things that mainly cause the heart to go too fast. And the commonest of these, and this is something which lots of people will have by the time they get to their older ages is atrial fibrillation. So atrial fibrillation is where the top bit of the heart, instead of beating in a nice steady way basically goes rogue, and just twitches like a kind of bag. It is moving, but it's not moving in any kind of coordinated way, it's not producing an impulse. Now that's got a number of implications. The first of them is that this means that the ventricle doesn't know what to do because sometimes basically the rate, the atrium is sending impulses through in a very irregular way, the way it's actually getting through the AV node, and you get what is called an irregularly irregular pulse. So you actually feel the pulse, and sometimes it's going fast, sometimes it's going slowly, and there's no way you can tell where the next beat is going to be, it just goes all over the place. That's quite often quite inefficient, and it often also goes too quickly. So as I'll come onto, you often need drugs to then slow the heart down. But there's a third issue, which is this twitching bag allows clots to form on the atrium. And if clots form, the risk of those is they go on and they flick off into the system, and the thing you really worry about is stroke. And atrial fibrillation, if you don't treat it with blood thinners, which we'll come onto, increase the risk of stroke quite significantly. So the ECG looks like this, it's a very irregular rhythm, and you can't see any P waves because there aren't any because it's just the atrium twitching. This graph here simply shows the age, which this tends to come on. Men get it a bit earlier than women, generally speaking. By your time you get to 100, for those of you who do, it's still only a third of people will have it, slightly less than women. So the majority will not have it, but it gets a lot more common as you get into your 80s and 90s. It just should be seen as one of the phenomenon of aging. And atrial fibrillation may be temporary. Quite a lot of people, if they have particularly an older age, if they have a big stress to the system, bad infection like a pneumonia, a big operation, the heart may flip into atrial fibrillation for a few days, and then just right itself as the body improves. So it can just be a temporary phenomenon. And one of the key things in medicine is to make a decision, are we going to treat this or are we going to let it run, protect the heart for a period and see if it goes back to normal? Several drugs, including alcohol, caffeine, cocaine for those who take it, amphetamines, all make it more likely to happen. So there are several things, which can actually trigger this off, either on a temporary or on a more permanent basis. And a hyperactive thyroid can make this more likely, as for example some valve diseases are, which I'll come onto in the next talk. If there's an obvious cause, you stop the cause. So if the problem is particular drugs, you stop that. If someone's got too much high thyroid, you bring the thyroid down, and it can often revert back to normal. If there's no cause, that's obvious, and particularly if someone's got problems, you can shock it out of the rhythm very frequently, at least if you catch it very early. And generally particularly in younger people. So here is someone where you can see the atrial rhythm going along atrial fibrillation, batting along at really quite a fast rate here. This spike here is someone putting pads across them and pressing the Go button, shock across the chest, and the heart is jolted back into a normal rhythm. So that's a quite common thing that might be done, either immediately or after a delay when, during which people have some anticoagulation for a period. And you can also try the same thing with drugs.

There are two drugs in particular:

amiodarone and flecainide. I've talked about, but there are others. So there are ways you can try and basically bounce the heart back into normal rhythm. But for many people, particularly in older age, they will just get this, this is a permanent state. You might be able to flip them back for a short time, but they're going to go back into it. And so for them really the key things are firstly to slow the heart down to, or get the heart to a good rhythm. And then, secondly, to make sure they don't have any greater risk of stroke than can be avoided. The first person who developed a drug to help do this in atrial fibrillation slow the heart down was a doctor called William Withering in the 1780s. So this goes back a long way, and this was derived from foxgloves, and this is actually Withering's own illustration and his monograph on this, quite remarkable bit of science actually. Still used today, so this is an old drug, but still in the pharma(indistinct) it's actually a very good drug for the right people, but in general now we tend to use more two drug classes, which I'll talk about in slightly more detail now. Beta blockers and calcium channel blockers would do this to slow the heart down. And what all of them do is they slow the rate at which conduction occurs between the atrium, which is flickering away, firing off the whole time, and the ventricle, so that the heart rate overall slows down a bit. You don't want to slow down too far, and that's the art of this is you want them to slow down a bit, but not too much, and you're going to get the dose of the drug right to achieve that. Now I talked about these drugs in a different context, but I think it's worth just refreshing, but those who have not gone to my previous lecture, and also for those who have, to point out, these are drugs you can use for several purposes. They're remarkable drugs actually. The first class is what's called beta blockers. So remembering that adrenaline is the key to fight and flight. It speeds up the AV node, it speeds up the SA node, and therefore if you can block it. And the main transmitter in the heart is the beta, the beta receptors, if you block it, you reduce the essentially adrenaline like effect, and that slows the heart down. So this is a purposefully designed drug unlike the Withering's one, which was an observation from nature. This one was designed to do the job it was done. Sir James Black on the right, rightly got a Nobel prize for doing this. And that can slow the heart down, and you just adjust the dose to the right dose for the person in front of you. Another class of drugs unrelated to beta blockers does it a completely different way. The way in which many cells in the body signal is via calcium, and by calcium channel switching on and off the physiology, this is extraordinarily sophisticated. You'll be pleased to hear, I'm not going to go down there, but just to say that there are multiple forms of calcium channel, and there are different forms of calcium channel blocker drugs, and they are variably useful for different bits of the body. If you want to drop the blood pressure, you use one bit of them. If you want to slow the heart down, you use another. They're very slightly different, but they all work for blocking the calcium channel in the system. And some of them are optimized and the two that I'd highlighted, drugs called diltiazem and verapamil. So one of those drugs may well be used if someone's heart's going too fast. And then second thing which must always be considered, and usually initiated is blood thinning. And that is to reduce the risk of stroke, that's the principal risk. If you only have atrial fibrillation, nothing else, no other heart problems, no valve problems, no coronary artery disease, your risk of stroke is actually relatively low, but every single additional thing you get on top of that, the risk of a stroke goes up. And there are various scoring systems for this. And what this graph here shows is one of the scoring systems. This is the rate of stroke along this bit, and the more points you score, the more your risk of stroke goes up. So someone will do a scoring system and say, how high is your risk? And then the second question it'll ask is, how high is your risk of bleeding? Are you someone who is constantly falling over, and bashing their head, in which case the risk of bleeding becomes very high, or is this actually something where the risk is manageable? But most people will have treatment with blood thinners, the old-fashioned one was something called warfarin, it's still used. At very high doses, it's a rat killer, for those I'm sure you've heard that, but in the kind of doses we're talking about for humans, much, much lower doses, it just thins the blood. And here's a study which compares the rate of stroke in red in people on warfarin, and in blue people who do not have warfarin. It really pulls down the rate of stroke in people who got atrial fibrillation and other risk factors. You don't need it if you got almost no other risk factors, but if you've got other risk factors, that's what it's used for. Warfarin had a disadvantage, and many of you may have had to do this, you had to get it checked the whole time because it went up and down the whole time. It's a real pain in the neck, frankly. So there's a new class of drugs called the DOACs, directly-acting oral anticoagulants. And these are much simpler, you just take them, you don't have to be constantly measuring, and that makes it easier to manage. Now a new mechanism, which is very useful for some people with atrial fibrillation, particularly uncontrolled by drugs. When I say new, I'm talking newish, but developing the whole time is to stop it with what's called cardiac ablation. And in cardiac ablation what happens is, a catheter is put usually into the groin, put up into the heart, they test various bits of the heart to work out which is the very excitable bit of the heart that's triggering this off. And they basically blast it with radio frequency to cause a scar to cause that bit of the heart to die. And the hope then is that the rest of the heart will go back to normal because this rogue bit of the heart is no longer working. It's extremely sophisticated, it's getting better the whole time. For people who have atrial fibrillation, they may need one or more than one go at this. Some of the other things I'll talk about later, usually it's much more common, you can do it in just one go. It is a relatively crude idea, in one sense, scarring the heart, but fundamentally if the difference is between this or being atrial fibrillation with a heart much less efficient being on drugs, the risk of stroke, this is for many people the right answer, not by any means all. And if they get it wrong, and they prang the pacemaker, which is entirely possible, there maybe a need for an artificial pacemaker afterwards to keep the heart going. So this is just you have to think about some of these issues. Some people don't have steady atrial fibrillation, but they do flip in and out of it the whole time, this is called paroxysmal atrial fibrillation. And there are several ways this can be dealt with. They may be given drugs continuously, so that it's much less likely they go into atrial fibrillation, they just keep a normal rhythm because of the drugs. They may, and this is quite common now be given what's called a pill in the pocket. They know when they're getting atrial fibrillation, they feel they're suddenly short of breath, they can maybe feel their own pulse in some cases, they have the antirrhythmic drug in their pocket, they take the pill, that flips things back to normal. Or again, we may use ablation as before, and some of them may need anticoagulation, some may not. So this is a variant of atrial fibrillation when it's intermittent. And then the final group of arrhythmias I want to talk about, and then I want to talk at the end just a bit about cardiac arrest, is the tachycardias, which are not atrial fibrillation. And these are from one of two forms, they're either above the AV node, it's called supraventricular tachycardia, and it's driven from the atrium, or it's driven from below the node, and it's called ventricular tachycardia. And the treatment for those is importantly different, both of them lead to the heart going too fast. Under ordinary circumstances, you might have a sinus tachycardia. Sinus tachycardia is rather like a sinus bradycardia. The P waves, the QRS, they're all going along in the ordinary sequence, but the rate is too quick. Now this can be for lots of reasons. It could be, you've just gone on a run and you're just, that's your heart's just batting along. You might have had a really exciting time or you might be incredibly stressed, you're having public exams, or something of that sort. It also may be things like sepsis or infection, pulse goes up in those situations. It might be blood loss, you've dropped your blood pressure, the heart compensates by speeding up. There's lots of reasons, and things like hypothyroidism can also do this hormonal changes. If you've got sinus tachycardia, then normally there's a cause for it. And if there isn't an obvious reason for it, like someone who has just been exercising, then you need to find the cause and treat the cause. The problem isn't the heart here, the heart is responding as the heart should respond, the problem is elsewhere, and you need to look elsewhere. But sometimes the problem is the heart has gone too fast, and a common one of these is something called atrial flutter. In atrial flutter, the atrium is not twitching like a bag, but is beating at typically somewhere between 280 and 300 beats per minute, which is very fast for a human. And then what you can get in response is the ventricle might go along at the same rate. This poor person has got a heartbeat where their heart is going at 300 beats per minute, that's very, very fast. Or it might be two to one block, or three to one block, or a four to one block. So this one is a four to one block, and what you can see is the atrial flutter going along what's called a sore tooth pattern here. And once every four flutters, you get a ventricular tachycardia. Sorry, ventricular contraction rather. So there are a variety of ways this can present. It's usually a lot easier to terminate than atrial fibrillation. If you shock someone, you need less electricity; if you use drugs, you often need less powerful drugs. And ablation is appropriate for people who get it the whole time or have it lots of times repeatedly. It's usually much more effective than an atrial fibrillation. So actually treatment to this is more straightforward in general. And then a variety of other forms of supraventricular tachycardia when it comes from above the AV node. And they normally cause what in medics called a narrow complex tachycardia. This basically means that the QRS complex looks completely normal. And that's because once it's gone through the AV node, the ventricle contracts completely normally. So it's a normal contraction, it's just going far too fast. There are lots of reasons for that. They include, you can have an area of the atrium that's firing abnormally fast, so it's going too quickly, but there can also be various forms of reentry where instead of going in a stately progression over the atrium delays, it goes through the AV node contraction, and then a long delay. The electrical impulse around the ventricle goes back up again into at some part along the pathway back into the atrium and restarts the thing. So essentially taking over from the pacemaker in a continuous loop. So, and then there's some genetic forms of this as well. Treatment can be very simple in some cases, so the simplest thing to do is to make the parasympathetic system cause an AV block. And the simplest way to do that is, you get someone to just close their nose and just breathe against resistance, and then suddenly release it. And that can give enough of a parasympathetic jolt that you may break the cycle. When you do that, it's unbelievably satisfying for the patient,(audience laughs) and pretty satisfying for the doctor or the nurse. I have to say it doesn't happen very often, but when it does, it's great. No drugs involved, this is normal physiology, it's done the job it should do. If that fails, there are quite a lot of drugs, and I'm not going to go through them, but if you are doctors or nurses, paramedics, you deal with this the whole time, which temporarily block the AV node, and essentially break the cycle of this. And if you need to, someone's gone into shock, they're in deep trouble, you can't control it any other way, you give them a shock across the heart, and that usually jumps the heart back into an ordinary rhythm. So that's kind of the progression down the more and more invasive things. And then they might need drugs for the long-term, this might be just a one-off occasion for a particular reason, it's the first time they've taken cocaine, they promise never to do it again. It's a whole variety of different things, but if they're getting it repeatedly, they may need ablation where you actually find the area, which is causing the problem and scar it in the way I've talked about. So that tends to be the longer term solution for many people. And then below the atrium, you then get ventricular tachycardia, and this is coming from the wrong bit of the ventricle, So it's getting conducted the wrong way, and the result is you get that nice QRS, and really, really sharp. It's over a much broader area. This is generally more dangerous than supraventricular tachycardia. The rate may be the same, but the ventricle itself is going in a very inefficient way, and these people tend to need treatment pretty rapidly. Sometimes they will be possible to treat with drugs. And the most commonly used one still is a drug called amiodarone. It's a fantastic drug actually, it works really well against paroxysmal atrial fibrillation against supraventricular tachycardia, against ventricular tachycardia, but it has side effects. And some of them come from the fact it's got two iodines here, which mean it causes problems with thyroid gland, it can cause problems with the lung, it can make your skin look a rather strange gray color. So it's not a drug, it's a drug you use to care, but it is an incredibly effective drug. In an emergency, it's a really good drug if you have time. But if you don't have time, and for ventricular tachycardia you often don't have time, it's shock, that's the thing you default to, if things are going wrong, or if all other things fail. Shock across the heart, so-called synchronized DC cardioversion. Occasionally you do also need pacemakers when people have got a tachycardia, and the situations you do them are, you might do what's called block and pace. You give someone a drug to slow the heart down, and you give them a pacemaker in case you go too far. So it basically provides a ceiling and a floor on the rate of the heart. Sometimes when cardiac ablation hits the wrong bit of the system, the heart may go too slowly, so you may ablate and pace. And then some people have a rhythm that needs shocking, and they have an implantable defibrillator. They looks actually not particularly different to the untrained eye from an ordinary pacemaker, it has thicker leads in a variety... This is a implantable defibrillator here. And that actually when it senses that someone's going into ventricular tachycardia, it gives them a shock straight into the heart, and terminates it. So those are a variety of ways pacemakers can be useful even in a tachycardia. Finally in terms of the rhythms, I'd just like to obviously go onto the most severe of these, which is cardiac arrest. And cardiac arrest can happen for multiple reasons. Not all of them coming in fact in practice from the heart itself, but when it does coming from the heart, what people have is they collapse, and you feel their pulse and they have no pulse, and you can actually see them walking along and suddenly they collapse, or they're often in ICCU if they just had a heart attack because heart attacks are one of the commonest causes that precede cardiac arrest. And they may well have what's called a shockable rhythm, and the shockable rhythms are usually either something called a ventricular fibrillation. It's like atrial fibrillation, but on a grand scale. Now the ventricle is twitching like a bag, so the whole system is no longer working properly. Or they might have what's called pulseless ventricular tachycardia. It is beating along, but there isn't a... It is not, it's so inefficient that there isn't a pulse to feel. In either of those situations, a paramedic or a doctor or a nurse is going to put a shock across the heart. That's basically the way you try and terminate this. It doesn't always work, but it does in a significant number of cases, if it's caught early. So what you do if you come across this? Well, the key skill is CPR. This is a first aid skill, is actually pretty easy. And I would strongly recommend anybody, you can go on a St. John's ambulance or other course, and learn the basics of CPR because if someone collapses, this can be literally lifesaving. There are relatively few things that are literally lifesaving, this is one of them. And what you do is you are pumping the chest as a way of causing enough blood to circulate around the body to keep the brain, the kidneys, the vital organs alive whilst waiting for help. So stage one call for help or call to someone else to call for help. Stage two, you start pumping on the chest. And if you've recently done your refresher course, and you feel confident, you can do what we used to call "The Breath of Life" where you breathe in and out of the chest, but I wouldn't recommend that if you've never done it except watching a YouTube video. Pumping the chest is easy, coordinating it with the breathing is a bit more difficult. But the CPR is really critical and can keep people alive for really quite a long period of time. So it's a very effective holding maneuver. And then what we are holding for in most cases is a combination of drugs, in some cases and shocking. Now if a paramedic turns up in an ambulance, if you're in a hospital and you're dealing with doctors and nurses, they will do this, they're very used to it. People who are doctors or nurses are used to crash teams the whole time. It's a very, very standardized, we're all taught in an incredibly regimented way, whether it's me or the first day house officer, we're all taught exactly the same thing. So we can go to any hospital, cardiac arrest, you all do the same thing. It's very, very regimented, and usually taught by paramedics, they're much better than doctors at emergencies. That's just a reality. If there are any doctors, you can hit me afterwards, but it's true, speaking as one. They may use drugs, but what you can also have in outdoor settings is you can have defibrillators, which are in many public buildings, and they're usually well-marked, and they're not... What they're designed for is you just need to know where to put the pads, which is one side of the heart and the other, and you turn the thing on, and it will talk to you, and it'll tell you, "Stand Back."(audience member laughs) When it says that, please do what it says. (laughs) And then it will give a shock, if it thinks a shock is appropriate. So these are really clever bits of kit actually, and they mean that you don't have to have training in using them. The main thing you ought to do is CPR, and then stand away when the shock's going to happen because you don't want the shock to go through you. That's not a good outcome. And this can be, if it's done quickly, highly effective, but most people who have cardiac arrest who've had a long period between collapse and starting CPR will have very, very bad outcomes. So it's all about speed, essentially. Important to say that many people in hospital worry when someone says to them, do you want your relative to have a resuscitation? And the conversation can be for lots of reasons, but usually it's because you think someone who has not got going to have one of these. If they die, they've died. And shocking someone who's dead does not do them any good at all. It just is undignified as a way for someone to end their days. So it's really a conversation about, this isn't just after a heart attack, but we think a cardiac arrest is likely, this is a different pathway because things are not looking too great, so there's a reason for those conversations. In the great majority of the films, the shock is 100% successful.(audience laughs) In reality, it's only under a narrow range of circumstances that it is likely to work. And that conversation is an important one to have, all of us will reach this stage at some stage. And then I haven't talked very much about prevention, I'm only going to do one slide on prevention before I summarize. And that's because I covered really in the last talk a whole lot about prevention. The things that prevent coronary heart disease are also the things that make these rhythms much less likely. So avoid the drugs, which are going to make things worse. So if you're getting lots of arrhythmias, alcohol is not a good idea to have in excess, it does make rhythms more likely. Some recreational drugs, you'll find out soon enough, if you are on them.(audience member laughs) But the main thing is to do a whole bunch of different things which can speed up the heart, so it can make them improve the heart. Stopping smoking, these are all evidence-based, these are not just dragged out of a hat, these are evidence-based things. Stop smoking, exercise is really good for keeping the heart young in a body, which is chronologically getting older. Reducing hypertension, if that's an issue; reducing cholesterol, if that's an issue. These are the same things as I say that were important for coronary heart disease. So things that are good for your body, things are good for your heart, are also good for reducing the risk of arrhythmia, pushing the probability of you getting it off to the right. And with all of these things, my view is, you're pushing it off to the right. If we live long enough, we'll all get an arrhythmia, but if you're going to get an arrhythmia and you can push it off to, you want 110 and you die at 99, it's not a problem for you. So it's all about delaying it(audience member laughs) beyond the point of inevitability. And at that point, it doesn't really cause you any trouble. So my summary really, bradycardias and tachycardias, to understand it, you need to understand the structure of the heart wiring. It's a very impressive bit of biology. The system's got a lot of the redundancy. In general, if you have symptomatic bradycardia, you are going to end up with a pacemaker in the great majority of cases. Drugs are not going to help you. If you end up with a tachycardia, you are generally going to be treated with drugs, but increasingly ablation is helpful for some people to stop this, and then basically be off drugs completely or back to normal. And you may well need to have some combination of ablation drugs and pacing in more complicated situations, but the outlook for people with arrhythmias, whether too fast or too slow is transformationally different than it was when I was a first-year house officer, first-year doctor, and will undoubtedly improve. I consider we're nowhere near the end of the stage in terms of drugs to slow the heart, and pacemakers to speed it up as needed. And I think ablation is going to go quite a lot further in terms of this ability, its sophistication than its speed. So I think there's a bunch of things that are going to continue to get better, but as I say we are in reasonably good shape now compared to where we were before. Thanks very much.(audience applauds)