Diving with a Stent

[DiveLvr]

I'm 57 yo male and been diving since I was 15. I am not in the best of shape but not a couch potato either. Due to feeling chest pains while cutting my grass (with a push mower) my doctor had me take a stress test which was cut short due to chest pains. I am to see a cardiologist to set up a review and consult prior to putting in a stent. How will having a stent affect my diving? I usually dive in the gulf, 40-100 ft deep, with nitrox.

Doug

 

[TSandM]

Our resident cardiologist here on SB, debersole (Dr. Doug Ebersole) has recommended that someone be able to exercise to 13 mets (a measure of exertional stress on a treadmill) before being cleared for diving after having stents put in. A lot depends on whether you have unscented disease and what your ejection fraction is, as well. When coronary artery disease is discovered before a frank heart attack has occurred, the likelihood of returning to all pre-procedure activities is pretty good.

 

[JohnN]

Our resident cardiologist here on SB, debersole (Dr. Doug Ebersole) has recommended that someone be able to exercise to 13 mets (a measure of exertional stress on a treadmill) before being cleared for diving after having stents put in. A lot depends on whether you have unscented disease and what your ejection fraction is, as well. When coronary artery disease is discovered before a frank heart attack has occurred, the likelihood of returning to all pre-procedure activities is pretty good.

I'll confess I'm not an expert in exercise physiology, but looking at the best study I can find (Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity - Jett[] - 2009 - Clinical Cardiology - Wiley Online Library),

I'm confused. . . I swim for exercise and using the study's reference for SCUBA diving (11 METs) to roughly the equivalent for swimming 3.5 km/hr. (11.5 METs) I get roughly 116 meters/minute of swimming is roughly the equivalent.

As a reference the World record is 100 meters in 46.91 seconds, so if someone could keep up that pace for the "extra" 16 meters, that would give 54.4 seconds for the 116 meters. So 116 meters/min is not quite world record status, but no way ANYONE diving puts out that much effort.

So what's up? What is the basis for the 13 MET limit (or the apparent BS 11 MET figure for SCUBA)?

 

[Ricky B]

Our resident cardiologist here on SB, debersole (Dr. Doug Ebersole) has recommended that someone be able to exercise to 13 mets (a measure of exertional stress on a treadmill) before being cleared for diving after having stents put in.

I too am surprised by this number. I checked a nomogram that I found on the Internet, which comes from the American Heart Assn. (Nomogram based on age, METs, and activity status (sedentary vs active) that provides a percent of age-expected exercise capacity in men.) 13 METS is at the bottom of the scale, and if I'm reading the nomogram right, 13 METS would be 100% of the age-expected exercise capacity of an active 40-year-old man.

In another source, titled "METs and Me," it indicates that a score of 12 METS would put a man in the above-average rank for men 20-39 (and for women, anything above 11 METS would put a woman in the highest rank for women 20-39). For men in their 40's, anything more than 12.5 METS would put the man in the highest rank. Granted, the source says that with this data "you are comparing yourself to a poorly conditioned group of Americans," but, still, lots of Americans dive. And most of them come nowhere close to 13 METS.

I understand that perhaps having a stent put in might require some extra conditioning, but I would imagine that most people who need a stent don't have 100% of the exercise capacity of an active 40-year-old man.

And, certainly, 11 METS as the energy expended for scuba doesn't seem right.

This is confusing to us layfolk. I hope someone can enlighten us.

 

[TSandM]

I thought it seemed high, as well. Doug has written it several times; I don't know what the basis for the recommendation is. I will ask him.

 

[Dr. Doug Ebersole]

The recommendation of "13 METS" comes from the textbook Diving Medicine by Alfred Bove, MD. Fred is Chief of Cardiology at Temple University and a past president of the American College of Cardiology. In chapter 21 entitled Cardiovascuar Disorders he writes " A diver with a maximum oxygen consumption of 40 ml/kg/min would be able to tolerate swimming at 1.3 knots for a few minutes, would then develop extreme hyperventilation to compensate for lactate production, and would fatigue rapidly. Swimming at 60% of maximum (about 24 ml/kg/min), a work level that is at or slightly below the anaerobic threshold can be sustained for long periods of time because it does not cause lactate accumulation in the blood. Safety considerations suggest that the sport diver should be able to tolerate a peak workload of about 40ml/kg/min and a sustained workload of 24 ml/kg/min (60% maximum) to ensure safety when in an adverse diving environment, when the need for rescuing another diver arises and when the need for swimming a long distance arises. A maximum capacity of 40ml/kg/min is equivalent to about 13 mets."

Later in the chapter when discussing Coronary Bypass Surgery and Angioplasty he writes:
"If the diver can exercise to 13 mets with no ischemia or angina, with normal blood pressure response and with no serious arrhythmia, limited sport diving may be considered. Lesser capacity would require careful selection of nonstressful diving."

He and I discussed this issue at length several years ago at the DAN Fatality Conference. While he prefers divers with coronary artery disease to be able to achieve 13 mets on treadmill testing as above, he yielded to the "sustained 60% max" idea as an alternative. This would be the equivalent of being able to walk 2 miles in about 25 minutes. So, in patients with coronary artery disease I treadmill them to assess MAXIMUM exercise tolerance. If they are able to reach 12-13 mets, I clear them for diving without restrictions. If they are not able to reach this threshold, I advise them to exercise with a goal of being able to walk 2 miles in under 25 minutes. Once they are able to do this, I clear them to dive but recommend they limit themselves to low-stress diving situations.

Doug

 

[JohnN]

The recommendation of "13 METS" comes from the textbook Diving Medicine by Alfred Bove, MD. Fred is Chief of Cardiology at Temple University and a past president of the American College of Cardiology. In chapter 21 entitled Cardiovascuar Disorders he writes " A diver with a maximum oxygen consumption of 40 ml/kg/min would be able to tolerate swimming at 1.3 knots for a few minutes, would then develop extreme hyperventilation to compensate for lactate production, and would fatigue rapidly. Swimming at 60% of maximum (about 24 ml/kg/min), a work level that is at or slightly below the anaerobic threshold can be sustained for long periods of time because it does not cause lactate accumulation in the blood. Safety considerations suggest that the sport diver should be able to tolerate a peak workload of about 40ml/kg/min and a sustained workload of 24 ml/kg/min (60% maximum) to ensure safety when in an adverse diving environment, when the need for rescuing another diver arises and when the need for swimming a long distance arises. A maximum capacity of 40ml/kg/min is equivalent to about 13 mets."

Later in the chapter when discussing Coronary Bypass Surgery and Angioplasty he writes:
"If the diver can exercise to 13 mets with no ischemia or angina, with normal blood pressure response and with no serious arrhythmia, limited sport diving may be considered. Lesser capacity would require careful selection of nonstressful diving."

He and I discussed this issue at length several years ago at the DAN Fatality Conference. While he prefers divers with coronary artery disease to be able to achieve 13 mets on treadmill testing as above, he yielded to the "sustained 60% max" idea as an alternative. This would be the equivalent of being able to walk 2 miles in about 25 minutes. So, in patients with coronary artery disease I treadmill them to assess MAXIMUM exercise tolerance. If they are able to reach 12-13 mets, I clear them for diving without restrictions. If they are not able to reach this threshold, I advise them to exercise with a goal of being able to walk 2 miles in under 25 minutes. Once they are able to do this, I clear them to dive but recommend they limit themselves to low-stress diving situations.

Doug

Thanks,

Any insights to where the MET numbers in (Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity - Jett[] - 2009 - Clinical Cardiology - Wiley Online Library) came from?

Given that the swimming one is impossibly wrong, I wonder about the balance of the numbers. . .

 

[Ricky B]

Thank you for contributing.

to ensure safety when in an adverse diving environment, when the need for rescuing another diver arises and when the need for swimming a long distance arises.

In the context of diving in Northern California, I can see this, but in the context of diving in warm-water resort waters with a group of divers in calm seas, it seems like overkill. Many, many divers only dive in the latter conditions. As for rescue, I understood that one not trained in rescue should not attempt it, and many, many divers are not trained in rescue. So I can see limiting diving to low-stress diving (which is probably the kind of diving the patient needing the stent did in the first place), but it seems like he is using high-stress, emergency-situation diving as the basis for a general rule. (It seems from your post that you thought it was too stringent--but perhaps would not care for the use of my lay term "overkill.")

If the diver can exercise to 13 mets with no ischemia or angina, with normal blood pressure response and with no serious arrhythmia, limited sport diving may be considered.

And after meeting the 13 METS minimum, only "limited sport diving"?

Given the nomogram that I looked at and the other source that I cited, it appears that most divers 40 or older would not be able to achieve 12-13 METS. And given America's obesity epidemic, there is no doubt that many 30- to 40-year-old divers would not either. Does this mean that all these divers are at meaningful risk of an adverse cardiovascular event? Or is the 12-13 METS a special rule for those who need a stent?

If it is a general rule that all divers should be able to achieve 12-13 METS, are there statistics that support this?

 

[scubadiver888]

Ricky B has expressed what I was thinking. I'm interested in this thread because I recently got a stent and my doctor okayed me for diving. In my area I dive in a 2 to 3 knot current. It is easy to get caught in the wrong current and swept to the American side of the river (St. Lawrence River). I was watching the students and not paying attention to where I was. Before I knew it I was caught in the wrong current and heading State-side. It was pretty hard swimming my way back to the Canadian side.

So in my area I can see a diver should be in pretty good shape. I'm 50 this year and considered young. There are a lot of divers in my area who are retired and exceeding 60. Some are approaching 70. That does not change the fact that dive conditions around here are tough.

On the other hand, I started diving in the Caribbean and it was a "walk in the park" compared to local diving. I dove dozens of places in the Caribbean and never got close to exerting myself. So if I stuck to Caribbean diving I probably wouldn't need to make 13 METS on my stress test.

Now mind you, I've been taking my health a lot more seriously since the heart attack and wonder if it isn't possible to get in better shape. Just because most guys in their fifties cannot do 13 METS doesn't mean I should do the best that I can for as long as I can. How else can I expect to make it to 100 if I don't start taking this more seriously now.

 

[Dr. Doug Ebersole]

The take home message is this for diving after coronary stenting which was the original question of the OP. If someone with CAD can reach 12-13 mets with no ischemia or arrhythmias on stress testing they are "good to go" in any sport diving activity. The point was that if someone cannot make 13 mets (about 11-12 min on a standard Bruce treadmill) but can get themselves to about 60% of that which would be the equivalent of walking 2 miles in under 25 minutes they should be able to safely dive in most sport diving situations. However, that level of fitness could still put someone with underlying heart disease at risk should they find themselves in the extremes of diving in terms of cold, current, rescue, etc situations. As diving is a leisure recreational activity, the medical community must err on the side of being conservative when it comes to making recommendations. After all, there are lots of other sports out there that people can participate in. Just because you want to learn to rock climb doesn't mean it's safe for you to do so. For certain individuals, just because they want to scuba dive that doesn't mean it's safe for them to do so. For the most part, scuba diving is a very easy low-stress activity. However, as everyone here knows, conditions can change quickly. If you start to have angina or symptoms of congestive heart failure while jogging, playing tennis, etc you can simply stop the activity. However, if you start to have these symptoms while fighting a strong current or large waves to get back to the dive boat, stopping to rest may not be as much as an option.

Every individual case is different in terms of the patient's age, physical condition, underlying coronary anatomy, degree of revasularization, left ventricular systolic function, and diving conditions they participate in. As such, each individual case should be managed on an individual basis between the diver and his cardiologist -- preferably one knowledgeable in diving medicine. Being able to achieve a maximum exercise level of 13 mets or sustain 60% of that is a benchmark to start each individual discussion. It would be really nice if in medicine we could just "cook-book" things. Unfortunately, that is simply not the case.

Doug

---------- Post added April 19th, 2014 at 05:09 PM ----------

Thanks,

Any insights to where the MET numbers in (Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity - Jett[] - 2009 - Clinical Cardiology - Wiley Online Library) came from?

Given that the swimming one is impossibly wrong, I wonder about the balance of the numbers. . .

Why do you say the "swimming one is impossibly wrong"? It says swimming 4.0 km/hr is 13.6 METS. 4.0 km/hr is swimming approximately 75 ft/min which is a pretty quick pace for an extended period of time. In cave diving (without flow) we usually plan a pace of about 50 ft/min. Adding some current and 75 feet/min is a good workout.

Dr. Bove gets his workload data and makes some of his recommendations from this reference:
Wasserman K, Whipp BJ, Koyal SM, Beaver WI:Anaerobic threshold and respiratory gas exchange during exercise. J Appl Physiol 35;236-243:1973.