Comprehensive information about diving and undersea medicine for the non-medical diver, the non-diving physician and the specialist.
Scope of the Problem
There are about 2.5 million Americans with CAD ( coronary artery disease ) and this number will increase as our population ages. At the present time, the most likely cause for a diver over 40 to die suddenly while diving is a blocked artery to the heart (coronary occlusion) and a fatal ventricular fibrillation (rapid fluttering of the heart). This holds true for almost all other sports as well. The cause of this is the exertion that causes cardiac work beyond the capacity of the heart to obtain oxygen. This lack of O2 produces ischemia which leads to malfunction and arrhythmias (irregularities) following which there is a fatal heart attack.
In the latest report on Diving Fatalities over the past ten years put out by DAN, cardiovascular factors were found in 6-14% of diving fatalities, averaging about ten percent. Gas embolism caused an average of 8% while DCS caused an average of 1% fatalities. (Annual Review, 2000 Edition).
In a review of autopsies on recreational scuba divers 1989-1992 the DAN group (Mebane et al) reported 33 cases of sudden death while diving - 31 were attributed to coronary disease. One was from aortic stenosis and 1 was a CVA.
There is also a section on sudden cardiac death syndrome in Edmonds' 'Diving and Subaquatic Medicine', Chapter 26, p. 354. Most autopsies of victims revealed at least 50% stenosis of a coronary artery, with some showing 100% blockage and some had evidence of infarction. Those who did not have substantial arteriosclerosis often had pre-existing hypertension.
The nice part of all this
is that the risk factors for
CAD are for the most part controllable. Smoking, obesity, elevated
cholesterol, high blood pressure, lack of exercise and cocaine use are
all variables that are under your control; any of these or a
of them can cause heart attacks in the twenties. Cigarette smoking is
most common risk and is easily the most preventable. Family history is
important but the information derived from the knowledge can help you
CAD by closer attention to your health.
The Disease Process
The process of atherosclerosis (hardening of the arteries) causes narrowing and finally blockage of the arteries supplying the heart with oxygen. Damage is done to the lining of the vessels in a process poorly understood, a plaque is formed likened to rust in a pipe, and grows until it blocks the flow of blood. This blockage causes the heart muscle to die-and this in essence is a heart attack. About 1 million people have this to happen each year-and about half of them die suddenly from the attack.
Detection of CAD before it
causes trouble is done by stressing
the heart by exposure to exercise on a treadmill or a bicycle. In this
way we can detect loss of blood flow before it is totally lost and find
the hidden problem before it presents as symptoms at rest. Actual blood
flow distribution to the heart muscle can be measured by adding a small
amount of isotope to the test via an intravenous injection. This shows
up as a defect in the image on the subsequent scan of the heart. EKG
and drops in blood pressure can also be detected when there is a
in the oxygen to the heart. This stress test is the best way to be sure
that the heart is capable of performing during diving. By reproducing
similar to those that will be seen during diving, we can see whether
heart can handle the exercise of diving. An abnormal test suggests that
you could be at risk for a heart problem while diving, and you should
dive until further evaluation is done.
The most important choice for your long term health and diving is prevention. Family history should be a clue that you may be at risk for CAD. If a parent, brother or sister had a heart attack before the age of 55, you are likely at increased risk yourself. You should have your blood lipids (cholesterol, triglycerides, HDL, LDL) checked, and if abnormal, begin some program to get them back to a normal range (cholesterol---less than 200, triglycerides--less than 120, LDL-less than 130). Reduction in weight, saturated fat intake, alcohol intake and increase in exercise will improve these measurements. There are drugs that will also help reduce blood lipids to acceptable levels.
Discontinuance of smoking is probably the most important factor in the reduction of risk for CAD. This holds true for men and women.
Moderate exercise, such as walking, has been shown to contribute to lowering the risk for coronary disease. Exercise helps maintain a normal blood pressure, keep weight down, raises the HDL (good component of cholesterol), all of which lower the risks.
normal blood pressure is important, to do this requires a periodic
pressure check. Basic non-medical measures to reduce blood pressure
stress reduction, reduction in salt intake, reduction in alcohol
Diving With CAD
Most people with CAD should not dive without correction of their problem. The blocked arteries increase the risk of sudden death or unconsciousness due to arrhythmias due to the extra demand of the exercise involved. Exceptions to the rule occur as when successful bypass surgery or balloon angioplasty has totally corrected the problem with a normal exercise test. In these situations, diving can be permitted in warm water where heavy exercise will not be required. The person who has had a heart attack with extensive muscle death should not dive -again because of the inability to meet the pumping requirements of the increased exercise while diving.
should be obvious that diving is not the time to find out that you
coronary artery disease-the underwater environment would decrease your
chances by almost 100 percent.
Risk Factors for Coronary Heart Disease
Coronary artery disease (CAD), is the leading cause of death in the western world, resulting in close to a million deaths a year in the United States alone. DAN's latest report on diving fatalities shows that about a quarter of the deaths discussed cited heart disease as the primary factor or a significant contributing factor.
The importance of preventing, recognizing and treating cardiovascular diseases in scuba divers should be perfectly obvious. Functioning in an underwater environment in remote places far from advanced medical care, divers dramatically reduce their chances of survival should something happen. Therefore it would seem that prevention is our best weapon.
There are certain risk factors that increase the likelihood of CAD and subsequent problems. These are:
high blood pressure
age (over 45 for men, 55 for women)
Anyone who meets the age criteria or who has two or more of the other risk factors should have a complete physical evaluation, including an exercise stress test, prior to beginning or continuing diving.