April 15, 2013

expert reaction to resting heart rate and risk of death

Research published in the journal Heart tracked the cardiovascular health of just under 3000 men for 16 years, and found that after controlling for other health factors including fitness level, men with higher resting heart rates had a higher risk of death. A before the headlines analysis accompanied this roundup.

Dr Gavin Sandercock, Senior Lecturer in Clinical Physiology (Cardiology), University Of Essex, said:

“This is an interesting paper supporting a well-known phenomenon that having a lower heart rate means you are likely to live longer.

“The authors claim that this was irrespective of fitness level but there are three important things to note.

“1. Heart rate is the result of your heart’s ’intrinsic rate’, which varies between individuals but is more or less fixed, and the action of the two nerves (a ‘brake’ and  an ‘accelerator’) that change heart rate. The action of the nerves is not fixed, it varies greatly. The only way to lower your heart rate without the use of drugs like beta-blockers is to do regular aerobic exercise – this increases the action of the brake nerve.

“2. We all know that to be fit, you have to be active. When the authors took into account how fit the men were, the association all but disappeared except men with a very high rate >80bpm were more likely to have died than those with very low heart rate of <50bpm.

“3. People shouldn’t be put off doing exercise to increase longevity if they have a high heart rate; it’s still the best thing you can do to be healthy and we should bear in mind that the Danish men in this study were mostly very fit. Nearly half of them had heart rates <50 bpm which is pretty uncommon except in highly trained athletes – this makes the findings hard to generalise to normal middle aged men in the UK.”

Dr Tim Chico, Senior Clinical Lecturer and honorary Consultant Cardiologist, University of Sheffield / Sheffield Teaching Hospitals, said:

“It is important to put this research into context. This study measured fitness in 1971, and compared this to resting heart rate in 1985, but 14 years is more than long enough to get unfit and unhealthy. The message I take from this research is the importance of keeping fit as a lifelong habit. I often see patients who have previously been very fit. The important question is “how fit are you right now?”

Professor Patrick Wolfe, Royal Society Research Fellow and Professor of Statistics at University College London, said:

“This analysis starts with the assumption, supported by previous studies, that an elevated resting heart rate is associated with an increased risk of death overall.  It aims to determine whether this association is a marker related to currently known risk factors (poor physical fitness, smoking, etc.) or apparently independent of these in generally healthy individuals.  The authors conclude the association is independent of known risk factors, based on a long-term study of originally middle-aged men in Copenhagen who have remained healthy.

“We shouldn’t be surprised by this study – it tells us that factors other than those we currently understand may influence resting heart rate, which we already know can be related to risk of death.  The obvious candidate is physical fitness – and here the study does provide evidence for an increase in relative risk after physical activity levels (and other known factors) are taken into account.

“However, the numbers reported don’t tell us anything about how your heart rate directly influences your overall chances of dying.  Instead, they describe the amount of relative increase in this risk – relative to someone with similar known risk factors otherwise, but a very low resting heart rate.

“We don’t yet know what explains this apparent increase.  So, over the longer term, it will be important to identify other factors that contribute to higher resting heart rates, or possibly why such rates might represent some level of increased risk in and of themselves.  For now, there are plenty of steps we can all take to increase our chances of living longer – maintaining good physical fitness, aiming for a healthy balanced diet, and not smoking.”

Dr Valerie Gladwell, Senior Lecturer in Physiology, University of Essex, said:

“Heart rate is considered to be a marker of health. Generally if it is over 110 beats per minute it is considered to be tachycardic (i.e. beating faster than expected) and is likely to be due to a potential clinical problem. In this study the heart rates studied were below 100 beats per minute and so are considered within normal ranges. 

“Heart rate is managed by pacemaker cells in the heart.  Although these pacemakers can generate their own rhythm they are controlled by nerves from the nervous system. These nerves can speed up the heart (sympathetic nerve) or slow it down (parasympathetic nerve). Without input from the nerves the heart would beat at about 100 beats per minute. This means that normally at rest the parasympathetic nerve is firing to slow down the heart (greater at lower heart rates), with much less influence from the sympathetic nerves.  Although measuring heart rate is simple to do, it is really important that if a resting heart rate is required that it is carried out with the participant lying down with no nicotine, caffeine or food ingested for 2 hours prior to the measurement.  Physical activity, mental activity and stress increase heart rate due to a reduction in firing of the parasympathetic nerve and an increase in firing in the sympathetic nerve. If people wish to measure their own heart rate it is best to do it prior to getting out of bed in the morning.

“According to this study, those individuals with a heart rate measured above 90 beats per minute appear to have a 3-fold increase in risk of death. This is interesting and may suggest that individuals with heart rates greater than 90 may be more susceptible to death, maybe due to an imbalance of their nervous system. The authors suggest that the increase in risk of death occurs with elevated heart rate even when age, smoking, alcohol, physical activity, fitness and other clinical measures are considered. There were only 54 people in this group out of a total of 2798.  It may also be that within the group with higher heart rates, there were individuals who generally reacted more to unfamiliar situations and may have even found it more stressful to have their heart rate measured and thus recorded higher heart rates.  Thus, in these individuals it may be their increased reactivity to unfamiliar situations rather than a high heart per se that may be increasing their risk.

“Over time, exercise training has been shown to decrease heart rate, in part by increasing the influence of the parasympathetic nerve. However, in this study the authors suggest that death was more likely if heart rate was higher irrespective of fitness level. However these results should be considered with caution as fitness levels were measured 16 years prior to resting heart rate and fitness levels. They may be different if recorded at the same time and thus physical fitness may have a greater influence than is considered within this study.”

‘Elevated resting heart rate, physical fitness and all-cause mortality: a 16-year follow-up in the Copenhagen Male Study’ by Jensen MT et al., published in Heart on Monday 15th April.