In the July 2015 issue of Undercurrent, an article titled “A better heart-check tool than a stress test?” discusses the possible benefits of a coronary calcium scan for older divers to reduce the risk of experiencing a heart attack while diving.1 This article is a follow-up to a May 015 Undercurrent report about an overweight 65-year-old diver who died shortly into his dive while on a dive trip.2 That article, which considered preventive options such as a stress test, also presented views from Dr. Alfred Bove and DAN’s Dr. Petar Denoble and Dr. James Chimiak, who agreed with the American College of Physicians (ACP) guidelines that recommend a graded and individualized approach to preventive testing and diagnostics.
Another physician suggests in the July 2015 article, however, that older divers should have a coronary calcium scan, which he claims may provide information that will help them avoid a heart attack on their dive trips. Many walk-in clinics offer the test at a low price. “A coronary calcium scan can tell you years before a positive stress test that you are headed in that direction [of significant coronary disease] so that you can do some kind of intervention,” he said. While the statement has merit, it may be misleading in this context.
People can die from myocardial infarction (heart attack) while they sleep, play golf, jog, swim, snorkel, scuba dive or during any other activity. Physical activity during any exercise, including diving, may be a provocative factor, but physical inactivity as a lifestyle represents a greater risk. Coronary atherosclerosis, a cause for most heart attacks, is a chronic disease that starts asymptomatically and progresses with aging and exposure to risk factors. At an advanced stage it may begin to manifest symptoms or cause sudden death.
While people are asymptomatic, they can estimate their risk of major coronary heart disease in the future (usually in next 10 years) using calculators that consider their age, blood pressure, cholesterol level and lifestyle factors. Regardless of risk, adoption of a healthy lifestyle is generally recommended, blood pressure and cholesterol should be controlled, and any other abnormality should be corrected. Having a known and estimated risk does not prevent one’s participation in physical activities. Indeed, physical activity is a recommended lifestyle improvement.
On the other hand, people with symptoms should not exercise before they undergo necessary diagnostic testing and appropriate treatment. Post-treatment physical activities are encouraged. However, the recommended safe level of exercise intensity depends on the degree of restoration of cardiovascular functions, which a stress test can gauge.
All healthy people, asymptomatic people with a high estimated risk and people with diagnosed and treated coronary heart disease are encouraged to exercise within their physiological limits, with a goal to increase their functional capacity and slow down the progression of cardiovascular diseases. Increasing age, persistent risk factors and manifested coronary heart disease all increase the risk of dying, but it is not possible to predict when that might happen. How could a coronary calcium scan help determine it?
A coronary calcium scan usually refers to imaging methods — such as electron beam computed tomography (EBCT) and multidetector computed tomography (MDCT) — that can reveal any deposits of calcium present in blood vessels. This test may also be called a “calcium scan test” or “cardiac CT for calcium scoring.” Calcium deposits in the blood vessel wall are caused by atherosclerosis and inflammation. More deposits indicate longer-lasting and more advanced atherosclerosis. However, a coronary calcium scan may not reveal the patency of coronary arteries, which is a more important indicator for the functional capacity of the heart muscle.
Atherosclerotic plaques may burst suddenly and cause myocardial infarction before they receive the calcium deposits necessary for detection by a calcium scan. Because of this insidious nature of atherosclerosis, the value of a coronary calcium scan is limited. The calcium score alone is not sufficient to estimate risk 10 years from now — and especially not the risk of dying during the next month’s trip. In the best case the scan shows individuals how their score ranks among the distribution of scores within their age groups. When combined with standard risk calculators, the test may improve risk prediction for those people with moderate risk who already have received enough prompts for action, but it does not add any actionable information that standard methods don’t already provide.
In conclusion, the short answer to the question in the title is no, a coronary calcium scan cannot improve the prediction of a heart attack or death on one’s next dive trip and does not replace the standard methods of risk estimation and monitoring.
For more information about heart health and diving, see DAN’s medical reference on The Heart & Diving.
References
- A better heart-check tool than a stress test? July 2015; 30(7).
- Heart health in older divers: are stress tests and defibrillators really that helpful? Undercurrent. May 2015; 30(5).