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Welcome to Doctor Warrick's Podcast Channel. Warrick is a practicing cardiologist and author with a passion for improving care by helping patients understand their heart health through education. Warrick believes educated patients get the best health care. Discover and understand the latest approaches and technology in heart care and how this might apply to you or someone you love. Hi, I'm Dr. Warrick and I'd like to welcome you to my consulting room. Today I'd like to speak with you about rate control in atrial fibrillation. When we see someone in the acute setting or someone who has had atrial fibrillation for the first time, often that rhythm is fast and rapid and really quite distressing for the patient. So, one of the things we want to do is to try and slow that heart rate down. It'll make the patient feel better. It'll make the heart work better and it's a good starting point. So, we're very keen to start to address this as soon as possible. There are a number of drugs that we use to control rate and I'd like to touch on each of those to give a little bit of an overview. Probably one of the most commonly-used drugs are a group of drugs called beta-blockers. Beta blockers are a class of drug that acts through the receptors that are associated with the sympathetic nervous system. And the sympathetic nervous system is the accelerating nervous system within the body. It's the process that gives us fight and flight. So, it increases heart rate, it increases blood pressure. The beta blockers act to block the receptors that drive that response. And so they actually act on receptors within the heart to slow the heart. Blocking what would be the accelerating features or factors that could act on the heart. The beta blockers can be given either via tablet or in through the vein. They're flexible and work very well. One of the things that we do want to be aware of when we give beta blockers is because they dampen down the sympathetic nervous system, they can also lower the blood pressure. So, we want to keep a close eye on blood pressure and occasionally if the blood pressure is low we may not be able to use beta-blockers in the way we want to. One of the other things that we know about beta blockers is that they can occasionally start asthma. So, in certain patients who may have sensitive airways, we would be very cautious about using beta blockers. But an agent such as Metoprolol which is a very commonly-used beta blocker is very often a first line agent in atrial fibrillation used either as a tablet form - We call that Aurelie or - as an in-the-vein injection. We call that intravenously. Sometimes we'll use beta-blockers in conjunction with other medications or we'll use other medications instead of beta-blockers depending on the heart rate response to the first line of therapy. One of the agents I like to use often in conjunction with beta-blockers is digoxin. Digoxin is from Digitalis and digitalis is from the foxglove plant. You might know a little bit more about plants than I do. But this has been around for many years and it's a tablet that has effects on the heart. Digoxin can actually be given orally as a tablet, but it can also be given in through the vein. The advantage of digoxin is it has an action on the node that is between the top of the heart and the bottom of the heart that regulates the electrical activity. Going from the atria to the ventricle. So, in atrial fibrillation when this chaotic electrical impulses bombarding the atria-ventricular node leading to ventricular excitation then digoxin acts at the node and slows transmission of electrical signals through the node, therefore meaning that the ventricular right can slow down and be better-controlled. One of the nice things about Digoxin is it doesn't tend to lower blood pressure and in the first instance is often very well-tolerated. One of the side effects or problems with digoxin is that if the kidneys are not working well it can accumulate. So it is a tablet or a medication, I should say, that we want to keep a close eye on. But in the first instance either alone or in combination with beta-blockers it can work very effectively to bring the heart rate down. One of the other agents that we use particularly if we choose not to use beta blockers, say in the situation of someone with asthma, is a centrally-acting calcium channel blocker. Well, that's a bit of a long description but that simply means a calcium channel blocker that acts predominantly on the heart and a calcium channel blocker is an agent that affects the way calcium flows through the cell membrane. One of the agents within this group is called verapamil, and one of the other agents is called Diltiazem. In general terms, verapamil is probably used slightly more than Diltiazem in this particular role. Verapamil and Diltiazem, it can both be given either by a tablet or in through the vein. Both have the benefit of regulating ventricular response or slowing the ventricular response down in atrial fibrillation. Both can have a bit of an impact on left ventricular function, so reduce how well the heart's pumping and this can be important for people who already have problems with their left ventricular function. But neither of these agents tend to be associated with worsening asthma, which is one of the reasons they might be chosen. Having discussed the beta blockers, Digoxin, the calcium channel blockers, they're the main agents for rate control, however in certain circumstances, in an acute setting occasionally Amiodaron might be used for rate regulation and Amiodaron is a separate sort of agent altogether with a different class of anti-arrhythmic effect. It can be given intravenously. It can also be given orally but because it takes a long time to really build up its levels in the body, it's far more effective in the acute setting, or in the immediate setting to give it in through the vein. This agent of its own can slow atrial fibrillation right down. It is also a fairly powerful reversion agent. So, it is a way to start to slow the heart with the possibility of returning the patient to normal rhythm. Amiodaron is not at the top of the list for controlling rate and that's because of a number of potential issues it has. It carries a lot of iodine in it and because of the iodine, it can certainly affect the thyroid gland in up to 20 to 25 percent of patients depending on geographical location. It can lead to some toxic toxicity with the lungs. It can even lead to some toxicity in the liver. So, it is one to keep up the sleeve, probably at the end of that list. In summary, then, we want to control rate when people present with rapid atrial fibrillation. We have beta blockers, we have calcium channel blockers, we have Digoxin, and we can fall back to an agent called Amiodaron if it's really needed. I hope that makes a bit of sense. I hope you've enjoyed today's discussion. As always, good health. You have been listening to another podcast from Dr. Warrick. Visit his website at www.drwarrickbishop.com for the latest news on heart disease. If you love this podcast, feel free to leave us a review.
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