**EP316: Understanding Heart Health**
**Dr. Auric Bishop:** Welcome, my name's Dr. Auric Bishop. I'm a cardiologist, an author, and a keynote speaker. I'm the CEO of the Healthy Heart Network. I'm all about trying to help people live as well as possible for as long as possible. Heart disease is huge in Australia. Every 20 minutes, someone suffers a heart attack. Most of these could probably have been avoided if only we knew what to do. This podcast is all about helping you understand blood pressure, weight, and cholesterol for better health. If you enjoy this podcast, I would be honoured for a five-star review. You can share it with your family and friends. It may well save someone you love.
Hi, my name is Dr. Eric Bishop, and welcome to my podcast and videocast station. I hope you're well. Patients often ask about heart rate, like what's normal, what's target, and what does it mean? So, look, I hope you enjoy this particular topic. I'll keep it reasonably short and sweet, but let's talk about heart rate.
Well, very simply, heart rate is the number of times the heart beats in a minute. It's a pretty straightforward measurement. Normally, we do it by feeling at the wrist, and that's pretty reliable. But interestingly, in some situations, it's unreliable, particularly with very irregular rhythms. Rhythms like atrial fibrillation, where the beats can be very close together, so that one beat could be felt at the wrist, but the next beat, because it's so close, the heart doesn't feel properly, and that beat is inadequate. If that beat is inadequate, then you may not feel it at the wrist, and you may get a distorted or reduced count for the actual heartbeat for that individual.
So, imagine someone's got a very fast atrial fibrillation and an irregularly irregular rhythm, and it's running at 200 beats a minute, which we can see on an ECG. That's the most accurate way for us to know what the rate of the heartbeat is because we look at each electrical signal of the heart contracting. Well, that heartbeat of 200 beats a minute, if there are lots of very fast and irregular close together beats, you may only feel a heart rate of 120 odd beats at the wrist. Something a bit variable, but it throws a bit of uncertainty into the exact number. So, the most accurate way is for us to measure it on ECG if there's ever any questions because that gives us the electrical beats and therefore the number of times the heart is actually contracting, not just the number of times there's a palpable pulse at the wrist.
Well, what is the normal heart rate? Most people's heart rate runs around about 60, 65, 70 odd beats a minute; that's a pretty normal rate. We talk about slow rates being less than 50 beats a minute, though sometimes people who are athletes may have slow heartbeats like that. Uncommonly, we would see heart rates over 100 beats a minute or approaching 100 beats a minute. If we see a heart rate of, say, 70 plus up to 80 or 90 beats a minute, generally this might be in the setting of a patient who's quite anxious. Importantly, though, if we were to see a patient at rest who had a resting heartbeat of over 100 beats a minute, it would certainly start to raise some questions as to what could be causing it. Might it be something like, well, could it be an infection? Could it be an arrhythmia giving a fast heartbeat?
So, somewhere around 70 odd is pretty common. Some people run down as low as 50 without any problems. Some people run 70, 80 plus to 90, but if you're over 100, it can be a problem. If you're under 50, it can occur if you're super fit, and particularly so overnight while you're asleep. I do see some families where the heart rate, particularly slow, is genetic, and that is simply due to the genes that have been, if you like, handed down, that give rise to that specific timepiece within the heart, that timekeeper. That's all related to the way the cells allow different salts through the membrane, which change the membrane and fire off an action potential that we call a beat. So, there can be genetic variants there, and sometimes we find some people with quite slow heart rates, 50 or just below, and they're perfectly normal, and they'll say, "Oh, Dad had a heartbeat like that."
Well, we talk about things like target heart rate, and there's lots of complexity around exactly where you should target your heart rate. Often, we'll talk about maximum heart rate as somewhere around 220 minus age. This is something that we've used for years. Not super robust, but it's not a bad guide. When we think about exercising and we want to get moderate intensity, we're looking at between 50 and 70% of maximum heart rate. So, you can figure that out for your own age if you like. If you're, for example, 20 years of age, you should pretty well be able to get your heart up close to 200 beats a minute. If you're looking for moderate intensity exercise, then 50 to 70 percent is going to be somewhere between 100 and probably 130 to 140 beats per minute.
We need to know those heart rate targets also when we're doing treadmill tests because a treadmill test needs to put the heart under strain. If you think about it, the whole reason we do a treadmill test is so that we see what the heart does when we put it under load. Well, just imagine your car. If you took your car to the mechanic and all they did was lift up the bonnet and have a look, it may not give the whole story. So, it's not until you take that car for a test drive, and it may not be until you rev that car up until a certain revs per minute—think heart rate—that the problem within the engine becomes apparent.
So, when we're doing a treadmill test, we actually are looking to try and get the heart rate up to about 85% of predicted heart rate maximum for that individual. So, that's pretty important too. It also raises the question about whether you do a treadmill test on medications that could slow your heart or off medications that could slow your heart. There are medications, like beta blockers, for example, or calcium channel blockers, which can slow the heart down. What's the answer to that?
Well, if you're doing a treadmill test and it's for evaluation of chest pain in an individual who's not been known to have problems with their arteries before, then you don't want heart rate regulating medication on board because it'll make it really, really hard to get to that 85% predicted heart rate max, which is where you need to rev the engine to get good sensitivity and specificity for the test. So, if we're doing a treadmill test for diagnostic purposes, stop the medications that slow your heartbeat. Of course, always check this with your doctor, but it's a good question to ask.
If we know that there's plaque in the arteries and we know there's high-risk plaque in particular, and we know that that person is going to be on heart rate regulating medications forever, and we're doing the test not for diagnostic purposes because we already have the diagnosis, but for prognostic purposes—understanding how well that person does in a day-to-day basis in their normal life, and those heart rate regulating medications are part of their normal life—then guess what? We want to do the test on their normal medications, even if it does reduce the chance of us getting to that 85%.
So, very interesting. When we think about heart rate changes, and this is a space that's really involved, and we will see more and more of it, we talk about heart rate variability. Heart rate variability looks very much at the variance beat to beat between the heart rate and gives us an indication of how responsive the heart can be to its external environment. So, heart rate variability is an indicator of how healthy the body is in responding to its need to accelerate or decelerate in response to external challenges.
Well, of course, if you've got some sort of arrhythmia, your heart would be running, say, a re-entrant arrhythmia, which gives you a regular heart rate at a certain set beat. As an example, if you've got an arrhythmia, then you would have no heart rate variability for a period of time of monitoring. The heart could be set at 150 beats a minute, which is obviously a bit of a problem. So, it's an arrhythmia you wouldn't want to stay in, but if the heart was set in that rhythm, then your heart rate variability would be zero because it's bang on 150 beats a minute because it's got a re-entrance circuit that continues to fire at the same rate over and over.
If so, lack of variability is obviously a problem. The flip side would be you could have extreme variability in someone who may have atrial fibrillation. Now, I've used two cardiac examples as impacts on heart rate variability, but it can be things like the autonomic nervous system or nervous problems, and individuals with Parkinson's disease or other neurological conditions can have changes in their heart rate variability.
Well, how do we monitor the heart rate? We're seeing more and more clever devices that you wear on wrists and have apps and the like. These are not too bad. The Apple Watch company, well Apple, with their watch as a company, ran probably one of the largest trials we've ever seen, which was the Apple Watch heart trial. They did demonstrate very small numbers of irregular rhythm, but the problem at this stage is that in their particular study, they were evaluating people who were otherwise well. So, they had a lot of false negatives. The very people who probably needed the watch were an older demographic who didn't have the watches.
And there's a little bit of uncertainty about the reproducibility and accuracy of particularly the PPG, which is the photo plethysmograph technology that uses lights and pulse to try and understand exactly what the heart rate is doing. So, there's a bit of uncertainty around this space, but I can almost assure you that we'll see more and more smart devices. What we do in our rooms is if we see someone who's got a heart rate we want to evaluate there and then, we'll do a 12-lead ECG, the very standard thing with the dots across the chest.
If we think there might be an arrhythmia there, getting a 12-lead ECG is the very best way to look at that. We may also put a monitor on people with three dots and send them away for 24, 48 hours, or even a little bit longer so that we've got a better idea of exactly what's happening. But watch this space because we're going to see more and more different ways of evaluating that heart rate and therefore the variability.
Remember that a normal heartbeat sits around about 70 odd beats a minute. If it's above 100 beats a minute, there's probably a problem. If it's below 50 or around 50, it may well be someone who's fit or has a genetic predisposition. But at 50 odd beats a minute, we'd also want an ECG and make sure that looked normal.
We've talked about some of the targets and particularly heart targets around what maximum would be for a given age, 220 minus age. We've talked about targets for exercise and also stress tests. We've talked about monitoring, and the future holds all sorts of opportunities there.
So, for now, I'm going to wrap up on heart rate. Keep an eye out because we will, with time, see heart rate variability as something that we probably bring into play more and more for general health. But there's your heart rate and a bit of a summary. If you have any queries or questions, drop us a note. Always happy to answer. If you have any ideas for any future podcasts, please let us know. The way to get hold of us is at info@drwarwickbishop.online.
For now, I'm going to say goodbye. I'm going to wish you the very best, and I hope you live as well as possible for as long as possible. Take care and bye for now.
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