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Cardiovascular System - Rhythm and Rate

Dr Jules Eden, dive medicine specialist and founder of e-med, answers divers' questions - as published in Sport Diver magazine:
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Q - Recently, I experienced six days of ectopic heart beats. For the first few days they were extremely frequent, up to 10 a minute, gradually decreasing on the sixth day to an infrequent two or three an hour. I have never experienced anything like this before in my life. I have seen a cardiologist and all my blood tests have been normal. A 24 hr ECG monitor showed up a number of ectopics but at a rate low enough to be considered normal. An echocardiogram was also normal, and so no explanation could be given for the "flare up".

Do these ectopics have any impact on my ability to dive?

A - The 2.5 billion beats a heart generates in an average lifespan are by and large regular as clockwork, thanks to the sino-atrial node, a little clump of cells that act as a natural pacemaker. Occasionally though, another bit of the heart tries to muscle in and fire off its own contraction; an ectopic is the result. Basically they’re extra beats out of sync with the regular heart rate. The vast majority are harmless and seen in many normal hearts, but if they occur too frequently or in long runs, they can indicate a diseased heart. Reassuringly in your case, the blood tests and echocardiogram were normal. Sometimes these ectopics can be due to excessive fatigue, caffeine, alcohol, nicotine or other drugs, so have a think if any of these factors are relevant. But if your cardiologist is happy that your heart is in good shape, then I think you’d be safe to dive again.

Q - As well as diving, I also fly light aircraft - why do I chose expensive hobbies?! My pilot's licence requires that I have an annual medical with an ECG. At the last medical it was discovered that I had Right Bundle Branch Block (RBBB). The Civil Aviation Authority then required that I be subjected to additional tests, namely, a stress ECG, an echocardiogram and a 24 hour monitor ECG. The results were deemed satisfactory and I get to keep my flying licence. It was my understanding from this, that the RBBB is of little consequence and shouldn't affect my health or life expectancy. I didn't think to ask the consultant if there is any problem diving with a RBBB. Is it safe to continue diving?

A - The heart beats about 35 million times a year, or over 2.5 billion times during an average lifespan, so you’d expect it to have a fairly foolproof control system. In fact the electrical wiring of the heart is quite simple. There are two “nodes” and specialised bundles of conducting tissue (much like normal electrical cable) that pass “current” through the heart muscle to make it contract. Electrical impulses begin at the sino-atrial (SA) node, which under normal conditions generates them roughly 60 to 100 times a minute. Each stimulus then passes to the atrioventricular (AV) node, and after a brief pause it splits and flows down the right and left “bundles of His” (pronounced as in the snake noise). The end result is that the atria (top 2 chambers) of the heart contract first, emptying their blood into the ventricles (bottom 2 chambers), which squeeze the blood all around the body just afterwards. Clear as cocoa? Hopefully the diagram will explain things.

For a variety of reasons, the bundles of His can stop conducting impulses, which is unsurprisingly termed Bundle Branch Block (BBB). This can be left or right-sided, or rarely both (in which case all sorts of bad things happen and you end up with a pacemaker). In general the left bundle does a lot more of the work than the right. Correspondingly, blockage of the left is far worse than the right. Left BBB requires an evaluation of exercise tolerance, such as you've just had, so it's reassuring that the results were all OK. If the right bundle blocks then the left often takes over (with minimal fuss but regular demands for overtime pay). So in your case I have no qualms about your continuing to dive.

Q - I am a 26 year old female with anorexia nervosa. Been diving since I was 14. Just got an ECG test back that said my heart rate was slower than normal (in the 50's). Does this put me at increased risk for diving? I am going away for the next two weeks and was hoping to dive - is it safe?

A - Anorexia nervosa is not a new illness. “Fasting girls”, a Victorian term for non-eating pre-adolescents, have been around since the Middle Ages, and were often claimed to have miraculous or magical powers, usually by exploitative museums. Sadly, whenever these claims were tested, the girls in question starved. Today the condition is a formal psychiatric diagnosis, an eating disorder that causes low body weight, body image distortion and an obsessive fear of gaining weight. In general terms, the problems that this would cause for diving are several. Reduced strength and exercise tolerance are common, meaning kit-carrying and hard finning may produce early fatigue. Psychological issues might jeopardise safety, with panic and phobic behaviours a prominent feature. Any medication taken for the disorder might have repercussions also.

As far as your specific heart rate query goes, a slow pulse can be a sign of a very fit heart. If the ECG is otherwise normal then the rate itself would not put you at any increased risk of diving problems. Nevertheless, I would suggest you are cleared by a diving doc, for the reasons outlined. The fact that you have been diving for 12 years should be in your favour though.

Q - I had an ECG in December 06 which has indicated possible enlargement of the left ventricle. My GP has also detected a heart murmur. I am due to have an ultrasound of the heart in Feb which will give more info about what is wrong. If I do have an enlarged left ventricle in addition to the heart murmur does this mean my diving career is over? I am 44 years old and an open water diver and at the moment I have stopped diving including swimming pool practice sessions. Grateful for your advice!

A - And much to tell you here. Left ventricular enlargement is not a bar to diving per sae. But rather like the fading male porn star, it’s all about the failure of the organ to pump properly. Bring out the fluffers I say.

A few things can cause the left ventricle to get bigger. High blood pressure and floppy or tight heart valves are but three of them. Now if the heart is compromised as it can’t send the blood round the body properly, you can imagine the effects on the body demanding fuel as it dives. Likewise there can be effects on the ability to push out the blood returning from the venous side and the lungs. Pulmonary oedema or wet lungs that be, me hearties. So, it depends on how big the enlargement is, and how much it compromises the heart’s function. As a ball park, 20% loss would be a problem and disqualify you. So get your cardiologist to check something called ejection fraction. A bit like our porn star on the wane. Well just a misplaced consonant.

Q - On March 9th this year I was admitted to hospital with a severe virus infection and I was kept in for four weeks. The virus was never identified but it caused me to become seriously ill and affected most of my organs.

Blood potassium and sodium were extremely low and my kidneys started to fail. However, with good nursing, I have made a good recovery from the viral infection. While I was in hospital, I developed atrial fibrillation with a pulse rate of 156. This has now been brought back to normal and I am taking Amiodorone. I am told I have hypertrophic cardiomyopathy, HOCUM, which must have been present all my life and only caused problems when the virus struck. I am still on Warfarin but this will be stopped quite soon now. I have never had any previous illness and am a keen diver, diving twice a year for two weeks at a time. I have always been keen on tennis, swimming and walking.

I am seventy. Do you think I could dive again next year? Would I be a bad buddy? Can one dive while taking Amiodorone? I now have no atrial fibrillation and my pulse rate is 70.

Please could you give me your opinion.

A - You sound fit, fun and are obviously active. But sadly I have to be the bearer of sad news. I think diving is going to be beyond your medical capabilities.

Even if you are off the warfarin. Even though your pulse is a normal rate and not fibrillating. [ A kind of irregular irregularity in the pulse, imagine a monkey on a piano for the beat.]

The bottom line is that you have HOCUM, and that can cause the heart to flip into an odd rhythm. This could cause a faint or collapse above the water. Imagine what would happen below.

I know you might think, I've been diving all my life, never had a problem, until this darn virus did it's worst. And I know you are also thinking, the heart is fine without the virus, so why not just carry on especially as the amiodarone has put me in the safe zone. And I know you are thinking, if I went to some dive resort and just said I never had a problem, they would never know and let me dive anyway. But rules is rules.

Q - During the last 2-3 years I have suffered an increased frequency of irregular heart beat. The frequency was such that I consulted my doctor soon after Christmas about the condition. I have been referred to a consultant who has diagnosed atrial fibrillation from the results of a 24 hour ECG. Initially the irregular heart beats occurred when I was at rest, but latterly came on as well during vigorous exercise. I do not experience any other symptoms like shortage of breath during an attack.

At present I swim 1 km in a local pool most mornings without detrimental effect. A recent unmedicated ECG on a running machine conducted by the consultant did not not bring on an attack even with the heart rate at 156.

In the middle of July I am due to holiday in Cuba when I planned to scuba dive. (I have PADI Advanced Open Water Certification) My current medication is 25 mg of Metoprolol twice daily. With my current situation is it safe to dive or would I be a risk to myself and others?

Your guidance would be appreciated.

A - This is an interesting question. Atrial fibrillation or AF is a condition where the heart beat becomes irregular, but in an irregular sort of way. Unsurprisingly doctors describe the rhythm as "irregularly irregular". Diagnosing it is easy but what is harder is finding out why this has happened. It can be due to valve problems in the heart or even thyroid disorders too. So it is important that your cardiologist has excluded the causes of this problem.

If no cause is found then it is known as "lone atrial fibrillation" as it can occur with increasing age on its own. If it is this variety then you have to look at how often it occurs and what happens to your heart and lung function when it is happening. It seems that you are able to exercise well without it coming on but your consultant did not, it seems, check your lung function at the same time, as AF can rarely cause fluid build up in the lungs which would be catastrophic underwater.

The other thing that is a problem in your case is that you are taking a medication known as a beta blocker. Metoprolol will slow your heart rate down, however it also affects your response to exercise [I see you were not on it during the ECG] again leading to a fluid build up in the lungs called pulmonary oedema.

So at this stage I would say that you are at risk and should not dive. There are other treatments for AF that are not beta blockers such as digoxin or disopyramide which it would be fine to dive on, but the medication switch is something you need to discuss with your consultant.

Also to be able to dive you need to prove that the exercise test you do will never bring on a run of AF that would then bring on this pulmonary oedema. You also need an echocardigram to exclude all other heart valve problems. So there's a bit of work to be done before you go, but with non beta blocker well controlled AF you should be fine in the end.

Lastly it has been shown that AF can cause little clots to shoot off around the body called emboli. These are caused by the fact that the blood is not flowing normally around the heart chambers and can clot in the atria. Therefore is a good idea to take an aspirin daily to prevent these clots from forming.

(other dive medical questions)



   


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