cardiovascular health

Can a coronary calcium scan improve the prediction of heart attacks in older divers?

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 2015 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.

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Diving and Endothelial Dysfunction

ImageEndothelium is a single cell layer lining the inner surface of blood vessels. It plays an important role in the regulation of circulation and reaction to various kinds of stress. Endothelial dysfunction is associated with the progression of atherosclerosis of blood vessels and heart disease.

Recently it has been shown that underwater diving may transiently decrease the post-ischemic flow mediated dilation (FMD), which is an indicator of endothelial function. This has caused some divers concern and raised questions in the media about the safety of various aspects of diving.

The FMD is a test that uses the ultrasound Doppler method to measure the diameter of brachial artery (the main artery in the upper arm) before and after a five-minute forearm ischemia caused by external compression with a blood pressure measurement cuff. The average diameter of the brachial artery in adults is about four to five millimeters. After the five minutes of circulation occlusion, the flow through the artery increases and the artery diameter increases for about seven to 10 percent of its initial value. This is called the flow mediated dilatation – FMD.

The extent of FMD may be decreased by various factors like exercise, obesity, hormonal status, diurnal changes, fatty meals, acute/chronic moderate to severe alcohol consumption, etc. On the other hand, dietary factors such as light alcohol consumption, chocolate, and various medications like nitroglycerine and statins may transiently increase FMD.

It has been also shown that FMD is transiently reduced after a single compressed air dive, breathing 60% oxygen at surface, a breath-hold dive and a nitrox dive. Both the increased partial pressure of oxygen and circulating gas bubbles have been suspected as possible causes. Oxygen does affect the metabolism and availability of nitric oxide (NO), which plays an important role in the relaxation of arteries, but the effects of it on the FMD are controversial.

What does it mean for divers?

In general, reported transient changes in FMD are not specific for diving. They appear to be a common endothelial response to a variety of stressors as a part of normal defense mechanisms including self-repair. If the stressors become excessive and exposure chronic, the endothelium may be harmed beyond repair. In extreme cases, dysfunctional endothelium in coronary artery disease may paradoxically cause narrowing of arteries in response to exercise and provoke angina or myocardial infarction. Nothing indicates that diving could reach significance of such an excessive and chronic stressor that it could acutely or in the long-term affect the health of divers through reduced FMD.

So far, only transient decreases of the brachial artery FMD after diving have been reported in asymptomatic divers. FMD is equally affected by repeated breath-hold diving and a single scuba dive on air. Nitrox diving reportedly causes a larger decrease of FMD than air diving. This would be consistent with the dose-dependent effects of hyperoxia; however, hyperbaric oxygen treatment which exposes patients to a much higher partial pressure of oxygen than diving does not appear to affect the FMD. The possible  dose-dependent effect of circulating gas bubbles has not been studied, but the greater decrease of FMD observed in nitrox, which is supposed to generate less bubbles, versus air diving is counterintuitive. Most importantly, there is no obvious acute or long-term harm (diseases, increased mortality) associated with reduced FMD after diving.

Having a bite of chocolate or large dose of vitamin C one hour before a dive may prevent the FMD decrease. However, the transient decrease of FMD described so far is not an injury and prevention is not necessary, regardless of how tempting the chocolate is.

Post written by: Petar Denoble, MD, D.Sc.

Placing the Risks and Benefits of Physical Activity Into Perspective

ImageGenerally, habitual physical activity reduces risk of death due to heart disease, but in susceptible persons vigorous activity can increase the risk of sudden cardiac death and acute myocardial infarction. Susceptible adult individuals are primarily those with atherosclerotic disease.

The incidence of both acute myocardial infarction and sudden death is greatest in habitually sedentary individuals. Habitually sedentary men are 56 times more likely to experience cardiac death during or after vigorous exercise than while resting; however, very physically active men are only five times more likely to die during or after vigorous exercise than at rest.2 Similarly acute myocardial infarction during or soon after vigorous physical exertion is 50 times more likely in least active than in most active subjects.3

Maintaining physical fitness through regular physical activity may help to reduce premature death because a disproportionate number of fatal cardiac events occur in the least physically active subjects performing unaccustomed physical activity. While sedentary people are advised to change their lifestyle and adopt regular physical exercise starting with low intensity and gradually increasing over time, they may need a preparticipation screening. Subjects with any health limitations need medical clearing and preferably a professional fitness coach. High-risk patients should be excluded from certain activities. For a brief set of guidelines, read “When to consult a health-care provider before engaging in physical activities.”

Even the most restrictive policies will never be able to completely prevent cardiovascular events associated with exercise. For individuals who exercise, it is important to recognize and report prodromal symptoms (symptoms preceding cardiac event). Prodromal symptoms were present in 50% of joggers, 75% of squash players, and 81% of distance runners who died during exercise. Prodromal symptoms may include chest pain/angina, increasing fatigue, indigestion/heartburn/gastrointestinal symptoms, excessive breathlessness, ear or neck pain, vague malaise, upper respiratory tract infection, dizziness/palpitations or severe headache. People who exercise have to be aware of this and physicians should inquire about exercise and these symptoms during exams.

For more details about risk/benefit and strategies to mitigate risks see the paper of Thompson PD et al.

References

  1. Thompson PD et al. Scientific Statement From the American Heart Association Council on Nutrition, Physical Exercise and Acute Cardiovascular Events: Placing the Risks Into Perspective: Physical Activity, and Metabolism and the Council on Clinical Cardiology. Circulation. 2007;115:2358-2368; originally published online April 27, 2007; http://circ.ahajournals.org/content/115/17/2358
  2. Siscovick DS, Weiss NS, Fletcher RH, Lasky T. The incidence of primary cardiac arrest during vigorous exercise. N Engl J Med. 1984;311: 874–877.
  3.  Mittleman MA, Maclure M, Tofler GH, Sherwood JB, Goldberg RJ, Muller JE. Triggering of acute myocardial infarction by heavy physical exertion: protection against triggering by regular exertion: Determinants of Myocardial Infarction Onset Study Investigators. N Engl J Med. 1993;329:1677–1683.

Post written by: Petar Denoble, MD, D.Sc.

The Safety of Sports for Athletes With Implantable Cardioverter-Defibrillators

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Current recommendations for patients with implantable cardioverter-defibrillators (ICDs) advise against participating in sport that are more vigorous than bowling or golf. These recommendations are based on reasonably estimated hazards of ICD failure to defibrillate, loss of control and injury caused by arrhythmia-related syncope or shock, and damage to the ICD system; however, the data about occurrence of these adverse events was not available. Medical conditions for which ICD is administered vary as well as the age of receivers. Many subjects with ICD are young and otherwise healthy. Participation in sports for some is an important quality of life factor and they choose to participate despite possible risks. The frequency of adverse events and risk of serious injury in such subjects was addressed in a prospective study based on a multinational registry.

Patient-centered care is a basic principle in which the patient establishes what brings quality to his/her life and challenges the physician to provide evidence so the patient can make an informed decision. In this case, that evidence is not established; this provided the ethical justification of a study that reviewed subjects who were enrolled in activities against medical advice. The study protocol had to ensure that it does not appear as an encouragement for subjects with ICD to engage in sports.

The study enrolled 372 athletes with ICDs (age: 10–60 years) already participating in organized (n=328) or high-risk (n=44) sports and followed them prospectively for a median of 30 months. Data was obtained via phone interviews and medical records at baseline, if a shock occurred and every 6 months. Of the enrolled subjects, 33% were women.  Sixty subjects were competitive athletes. Running, basketball, and soccer were the most common sports, but some also engaged in skiing (71) and surfing (13), which is considered high risk for syncope and ICD shock-related injuries.

This study found that shocks were not uncommon, but there were no injuries, deaths or need to externally defibrillate. Shocks occurred in 10% of study participants during competition/practice, in 8% during other physical activity and in 6% at rest. Lead malfunctions were not higher than in unselected populations.

In summary, many athletes with ICDs can engage in vigorous and competitive sports without physical injury or failure to terminate the arrhythmia, despite the occurrence of both inappropriate and appropriate shocks. This study also points out subgroups with likely higher risks; it also discusses specific tests and the process of patient evaluation necessary for informed physician advice and patient choices.

For my target audience, it is important to note that no scuba divers participated in this study. Scuba diving is considered a very high risk activity for subjects with ICD because the loss of control due to syncope or shock while underwater is likely to cause drowning. Some subjects with pacemaker, a device that does not provide shock, may be allowed to dive, but it appears that there are few out there since we had a lot difficulty recruiting participants for a survey-based study.

Lampert R, Olshansky B, Heidbuchel H, et al. Safety of Sports for Athletes With Implantable Cardioverter-Defibrillators. Results of a Prospective, Multinational Registry. Circulation. 2013;127:2021-2030.)

 More about DAN’s study on diving with pacemakers can be found here:

DAN Investigates Implanted Cardiac Devices: Volunteers Needed

Post written by: Petar Denoble, MD, D.Sc.

Effects of scuba diving on heart function

Recently, a group of Italian researchers conducted an underwater Doppler echocardiography study of 18 healthy scuba divers titled “Cardiovascular changes during SCUBA diving: an underwater Doppler echocardiographic study.” The rationale for the study was a concern that body immersion, which induces redistribution of blood from the periphery to the chest, may adversely affect subjects with previous heart disease. The aim of the study was to evaluate cardiovascular changes during immersion using underwater Doppler echocardiography. They found that the left ventricle is enlarged during immersion, an effect that is expected because there is more blood moving into the chest area. In addition, there were some changes in the velocity of the ventricle filling measured, but the significance of this is not clear. These changes were still noticeable when the Doppler echocardiography was repeated immediately after a dive; however, some older studies reported that most changes disappeared within one hour after the dive.

Please note, although the motivating concerns for the study were about divers with pre-existing cardiovascular conditions like hypertension and coronary heart disease, the study involved 18 healthy subjects. While there are quite a few papers that report temporary changes in cardiovascular functions in healthy divers, there are no studies exploring how these temporary changes may acutely affect divers with pre-existing conditions or how long these changes may persist in such divers.

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DAN is conducting a study that aims to provide more answers. Cardiac function is evaluated by echocardiography after multiple days of diving. Possible arrhythmias are monitored with a continuous underwater electrocardiogram (ECG) using a specially adapted mini Holter recorder.

We just conducted our first field study involving 25 volunteers and plan to do five more trips to study up to 120 divers by the end of 2014.

Learn More

“Matters of the Heart.”

“Underwater Scan Finds Significant Heart Changes in Divers”

“Cardiovascular changes during SCUBA diving: an underwater Doppler echocardiographic study” 

Photography and post by: Petar Denoble, MD, D.Sc.

Trip Report: Left ventricular hypertrophy and risk of cardiac death in divers

We’ve just recently returned from the first field trip for the left ventricular hypertrophy and risk of cardiac death in divers study in Bonaire (August  31-September 7). For the first time, we field tested the study logistics and the protocol. The dive trip was organized by Down Under Surf & Scuba in Raleigh, N.C. Out of 36 subjects in the group, 25 were qualified participants over 40 years of age and actively participated in the study. Most of the baseline testing was completed prior to the trip in four sessions: two at DAN Headquarters and two at the dive shop. Five new subjects joined us from other parts of the country and were pre-screened upon arrival to Bonaire.

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The Buddy Dive Resort was our central study location. They were very accommodating and allowed us to use their main classroom as a lab. The classroom was at the waterfront where most divers enter and exit water or board the boat for the boat dives.

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 The plan was to get every participant scanned by echo twice after a full day of diving and once in the morning after a night’s rest. We took take a resting electrocardiogram (ECG) to monitor heart rate variability after a full day of diving on select dive days. All divers carried the Holter Monitor during at least one dive and were asked to record the depth and time of all their dives.

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The compliance was nearly perfect. In fact, the only delays were related to travel time back from some remote dive sites. We completed a total of:

  • 100 echo scans
  • 50 resting ECGs
  • 24 underwater Holters
  • Nearly 500 recorded dives

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The research team included cardiologist Dr. Douglas Ebersole, two professional echo cardiographers Brandy Emory of Lakeland Clinic and Lisa Caudill of Duke and myself. They did an excellent job maintaining the tight schedule and were well received by all of the participants. They even had time to join participants on some dives.

Scott Powell, the manager of Down Under Surf & Scuba and Rochelle Wright, a DAN Member Services specialist, managed all of the logistical challenges so we were able to complete our study. We’re very thankful for their support as well as the overwhelming support from the participants. We appreciate your participation and thank you for helping us to work toward improving diver safety.

Photography and Post by: Petar Denoble, MD, D.Sc.

Exercise and Acute Cardiovascular Events: Placing the Risks Into Perspective

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Do not ignore possible warning symptoms!

The American Heart Association’s Scientific Statement published in 2007 is still valid when it comes to exercise and acute cardiovascular events. While many sudden cardiac deaths related to exercise occur in subjects without obvious symptoms of heart disease, in many cases warning symptoms preceded death but were ignored by victims or their physician. Specifically, 50% of joggers, 75% of squash players, and 81% of distance runners who died during exercise had probable cardiac symptoms before death. Most reported these symptoms only to relatives and few sought medical attention. We have seen this also in scuba divers although not in such high percentages. Recommendation is that exercising adults should be aware of the nature of warning cardiac symptoms and the need for prompt medical attention.

 The most commons warning symptoms are:

  • Chest pain/angina                                                                        
  • Increasing fatigue                                                         
  • Indigestion/heartburn/gastrointestinal symptoms        
  • Excessive breathlessness                                           
  • Ear or neck pain                                                                         
  • Vague malaise                                                                                  
  • Upper respiratory tract infection                                         
  • Dizziness/palpitations                                                                     
  • Severe headache                                                                              

Suggestions for prudent risk mitigation measures brought forth in the same article could be modified and applied to diving as follows:

  • If your health changed recently, you are healthy and over 45, or you have two or more risks for heart disease, take your annual medical exam before resuming physical activities in preparation for diving.
  • If you have a known cardiac condition, you should be evaluated for diving according to published guidelines
  • Prepare physically for your dive trip by gradually increasing your exercise level and refreshing your skills in preceding months.
  • Know the nature of warning symptoms for heart disease and seek prompt medical care if such symptoms develop.
  • Modify your dive plan in response to variations in the environmental and general diving conditions. Learn to when to call a dive (this may be even before the dive starts).
  • Ask your dive provider where their staff is trained and equipped for resuscitation and if they conduct periodic drills.

Post written by: Petar Denoble, MD, D.Sc.