Though myocarditis is relatively common the real incidence rate is completely unknown
By Dr. David Sawatzky
The most common cause of death in divers while they are diving is a heart attack. These heart attacks are usually the result of coronary artery disease (CAD), in which the arteries in the heart degenerate and eventually become blocked. Occasionally someone dies suddenly and there are no signs of CAD on autopsy. In young healthy people there is usually some other structural abnormality in the heart, but not always. The second most common cause of death in divers while diving is arterial gas embolism.
I work occasionally as an expert witness/consultant in cases of diving deaths and so have read a large number of autopsies performed on divers. Most pathologists have little or no training or experience in doing an autopsy on a diver. In the standard autopsy procedure, the chest is opened first and the heart removed. The lungs and brain are examined later. As a result, seeing a few gas bubbles in the heart, brain and lungs is common (air moved into the open blood vessels) but it is impossible to determine if the person suffered arterial gas embolism. In a diving autopsy, the chest should be opened underwater and the brain should be examined before the heart is removed.
During many autopsies, examination of the heart is limited to weighing it, measuring it, cutting it open and examining it. This is a good way to identify CAD and other structural problems. If nothing is found and the person died suddenly, it is usually assumed that they died from an arrhythmia (cause unknown). If they died in the water, it is often assumed that they ‘drowned’.
In 2008 a 38-year-old male, obese [5’8” (172 cm) and 212 pounds (96 kg)] diver did a routine CCR dive on a wreck at 240 fsw (73 msw) depth. The next day he jumped into the water to do a similar dive. He swam alongside the boat towards the downline and suddenly sank. His body was found eight hours later on the bottom. His computer showed a direct descent to the bottom and then no change in depth. Only minor equipment problems were found on exam, nothing that should have been fatal.
On autopsy there were no signs of CAD – surprising given his age and obesity – or other cardiac abnormalities. The pathologist noted microscopic myocyte necrosis, very small areas of dead heart cells, with infiltration of white blood cells into the tissue of the heart. They listed the cause of death as ‘myocarditis’. No mention of arterial gas embolism, oxygen toxicity, hypoxia, hypercarbia or even drowning was made. I would have written it off as the all too common poorly-done autopsy on a diver except that it was the best-written autopsy I have ever read, so I did a literature search on myocarditis. What I learned surprised me.
The Surprising Truth
Myocarditis simply means inflammation of heart cells. The most common causes are infections, toxic effects or autoimmune effects (the immune system mistakenly attacks the person’s own heart). This can result in serious damage to the heart, heart failure and death.
Myocarditis can present as cardiovascular collapse one to two days after infection of the heart by a virus (rare) or more typically symptoms present about two weeks after the heart is infected, while the virus is being cleared from the heart. In some cases the infection persists and a chronic process can occur.
I first learned about myocarditis when I was a medical student in the 1970s. I understood it to be rare and usually serious. I was shocked to discover that not only is it relatively common, the real incidence is completely unknown! It is now believed that the majority of cases are asymptomatic and in many other cases the symptoms are so mild that the diagnosis is never made (the person just feels a bit ‘off’ and assumes that they have the flu).
One autopsy series in a major US city showed myocarditis in one to 1.5 percent of all cases of sudden and unexpected death, usually viral or medication caused. Internationally, a parasitic infection called Chagas disease (18 million people infected) results in 50,000 deaths annually from myocarditis.
Studies have shown that in sudden cardiac death (SCD) in young people in North America, up to 20 percent are due to myocarditis. It also causes up to seven percent of SCD in competitive athletes, 20 percent of SCD in military recruits and up to 33 percent of cases of idiopathic ventricular tachycardia (a specific kind of rapid heart rate with no known cause).
We don’t know how sick most people with myocarditis get, because most cases are never diagnosed! In sick patients who manage to eliminate the virus, less than 4 percent die, compared with a 25 percent mortality rate if they do not eliminate the virus. In diagnosed cases, the average age is 42.
Symptoms and Causes
Many cases of myocarditis have no symptoms. When symptoms are present, the most common are fatigue, mild shortness of breath at rest, sore joints, shortness of breath on exertion, irregular heartbeat and, in 20 percent of cases, fever. Up to 35 percent of people have chest pain, but it tends to be sharp and stabbing (not like a heart attack) and may be due to inflammation of the sack around the heart (pericarditis). If one of the very small areas of necrosis is in an electrically sensitive area of the heart, the person can suddenly develop a fatal arrhythmia and die.
If the infecting virus is parvovirus B19, the myocarditis might present like a lateral wall heart attack. Up to 50 percent of people who are diagnosed with myocarditis have a history of a viral-like illness about 2 weeks before the symptoms of myocarditis.
In North America, and presumably in Europe and Australia, myocarditis is usually due to a viral infection of the heart. A very wide range of viruses can cause myocarditis. HIV is unique in that it reduces the ability of the heart muscle to contract without inflammation. Myocarditis is present in more than 50 percent of people with HIV infections. Worldwide, the most common bacterial cause of myocarditis is diphtheria. Other bacteria that cause myocarditis are strep, staph, bartonella, brucella, letospira, salmonella and lyme disease.
The most common cause of myocarditis in South America is the parasite trypanosomiasis (Chagas). Trichinosis (from pork) can also cause myocarditis. Many drugs (clozapine, penicillin, ampicillin, hydrochlorothiazide, methyldopa, sulfonamide) and medications (lithium, doxorubicin, cocaine, catecholamines, acetaminophen, zidovudine) can cause myocarditis. Common toxic causes include lead, arsenic, carbon monoxide and Chinese sumac. Wasp and scorpion stings, spider bites (black widow) and radiation therapy can cause myocarditis, as can connective tissue disorders like SLE (lupus), RA (rheumatoid arthritis) and PSS (scleroderma).
Myocarditis is difficult to diagnose. Cardiac enzymes are only elevated in 35 percent of cases (the areas of necrosis are often very small) and the white count is only up 25 percent of the time. There are a wide variety of EKG abnormalities. MRI is quite useful and MRI-targeted biopsy is diagnostic. However, no one is going to do an MRI or stick a needle into the heart to take a tissue sample in a person with mild symptoms!
Most people with myocarditis require no treatment or simple supportive care. More severely ill patients require cardiac monitoring, oxygen and fluid management. Some require pacing. Stimulants like sympathomimetic drugs seem to increase the heart damage and risk of dying. After the person recovers, they should avoid ALL strenuous activity, including diving for at least six months (risk of recurrence). In people who present with heart failure, 50 percent recover, 25 percent stabilize and do well, while 25 percent progress and do poorly.
In the western world the most common cause of myocarditis is a viral infection. Vaccination against measles, mumps, rubella (MMR), polio and influenza has greatly reduced these causes of myocarditis. Meat inspection has almost eliminated trichinellosis and the resultant myocarditis. Many other viruses can cause myocarditis and in animals, vaccination against these viruses has been shown to prevent myocarditis.
This is all very interesting but exactly what does it have to do with diving? Animal studies have clearly shown that exercise and swimming increase replication of the virus in the heart, increase the weight of the heart (not a good thing) and increase the risk of dying. One autopsy series of 22 children who had drowned, with no symptoms of being ill or other cause, found that 5/22 (23 percent) had myocarditis! In all cases the heart was grossly normal at autopsy and the diagnosis could only be made microscopically.
Swimming and simply being in the water increase the risk of having a fatal arrhythmia. Having myocarditis also increases the risk of a fatal arrhythmia. The combined effect may be more than additive.
So, what is the bottom line? Myocarditis is common, usually caused by a viral infection of the heart, and often has minimal symptoms. Most people recover fully without problem. Anyone with diagnosed myocarditis or even suspected myocarditis should be restricted from all activities, including diving, for at least 6 months after they appear to have made a complete recovery. If you are feeling ‘off’ or like you have the flu, you should avoid strenuous activity, including swimming and diving.
In all cases of sudden cardiac death and all cases of ‘drowning’ (basically anyone who dies while in the water), a very careful microscopic examination of the heart tissue should be done at autopsy looking for myocarditis. It is highly probable that myocarditis is a much more common cause of death in divers (and others) than has been recognized historically.
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