Cardiovascular Health

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.

What is the practical significance of arterialization of gas bubbles after diving?

Decompression sickness (DCS) is a condition that may result from quick decompression, which may occur when diving or flying. One mechanism involved in DCS is the passage of venous gas emboli (VGE or “bubbles”) to the arterial side of circulation; this is known as arterialization.

Until recently, arterialization was considered a rare event except when there is a passage in the heart wall because of a patent foramen ovale, (PFO), atrial septal defect or ventricular septal defect. In people with normal hearts it was previously thought that when venous gas passed through the narrow pulmonary capillaries, the potential for VGE was eliminated. It is known that some pathways allow up to five percent of venous blood to bypass pulmonary capillary filters, but the caliber of these bypasses was considered too small to allow VGE to pass through. Occasionally, some bubbles would arterialize, but it was considered a rare event. Recently, however, several authors have reported postdive VGE arterialization, but the true incidence of this phenomenon was not known.

Our colleagues of University Split, Ljubkovic M., et al. studied VGE arterialization and published two papers. The first, “Determinants of arterial gas embolism after scuba diving” (http://jap.physiology.org/content/112/1/91.long), reports results of laboratory testing and postdive findings. They tested 34 subjects by injecting saline with air bubbles in an arm vein and used echocardiography to monitor for bubble passage to the left side of the heart. In 23 out of 34 subjects, the transpulmonary passage of bubbles was observed at rest or after mild exercise. Nine subjects with confirmed arterialization in lab conditions also experienced arterialization after a field dive. All nine had large amounts of VGE in their right heart (VGE grade of 4B or greater). In subjects with no arterialization in lab conditions, there was no arterialization postdive either despite five of them having VGE grade 4B.

Authors concluded that “Postdive VGE arterialization occurs in subjects that meet two criteria: 1) transpulmonary shunting of contrast bubbles at rest or at mild/moderate exercise and 2) VGE generation after a dive reaches the threshold grade.”

It is important to notice that none of the nine divers with echocardiographically detected arterialization had any symptoms or signs of DCS or cerebral arterial gas embolization (CAGE). There is also no clear evidence concerning long-term consequences of chronic embolization in divers without history of manifested DCS or CAGE. Read the Alert Diver article, “Effects of diving on the brain” to learn more.

The significance of these findings is dubious. In the first place, it is now clear that a certain level of arterialization occurs more often than previously assumed and proven. One of the reasons may be in increased resolution of new generations of echocardiography machines, which enables us to detect smaller VGE than before. Second, it is reasonable to assume that occurrence of DCS in cases of VGE arterialization depends on the size and quantity of VGE, but the threshold values are not known. Third, a loose relationship between the presence of PFO and DCS may be due to not accounting for transpulmonary bubble passage.

Thus, we are looking forward to results of a prospective study conducted by Germonpre, P. and colleagues, which relates to the presence of VGE in carotid artery (accounting for PFO and transpulmonary passage) to DCI.

Additional Readings:

PFO Research Foundation

“PFO and decompression illness in recreational divers”

“Effects of diving on the brain”

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

When to refer a diver for PFO screening?

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Postdive occurrence of bubbles in divers venous blood (venous gas emboli or VGE) is quite common. VGE are usually filtered out of circulation by the pulmonary capillary filter. However, in the case of PFO, transpulmonary passage of venous blood or other rare causes of right-to-left shunt (RLS), VGE may pass to the arterial circulation and cause damage of vital tissues manifesting decompression illness (DCI). Note that DCI includes both decompression sickness and cerebral arterial gas embolism. Because of high prevalence of RLS, mainly as a result of PFO, and low incidence of DCI, there is a general agreement that screening for RLS should not be done routinely on all divers. While in some cases screening may be useful, there is no consensus about when the screening is justified. In a recent paper by Oliver Sykes and James E. Clark titled, “Patent foramen ovale and scuba diving: a practical guide for physicians on when to refer for screening,” the authors detail clear guidelines for physicians as well as their definitions of safe diving practices, provocative dive profiles and factors suggestive of PFO. Their recommendations are very useful. Do not miss this paper. It is available for free from the above link.

Their recommendations are summarized in Figure 8 of Sykes and Clark’s paper:

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Figure 1. Flow chart on when to refer for screening by a cardiologist with an interest in diving. Courtesy of London Hyperbaric Medicine.

The findings in DAN’s PFO study coincide with most of the recommendations above. Retrospectively established incidence of various DCI manifestations in divers with PFO participating in our study is shown in following table:

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Multiorgan DCI manifestations were a frequent finding and we suggest adding it to the indications for RLS screening. In this context, multiorgan means coincidental occurrence of symptoms from two or more of the following symptom groups: skin, neurological (brain, spinal cord, ocular or inner ear), pulmonary and constitutional.

Learn more: Read about the dive and DCS history in divers who tested positive for PFO and pursue closure. http://www.alertdiver.com/Study_Update_PFO

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

Primary Prevention of Cardiovascular Disease with a Mediterranean Diet

ImageIn a recent article published in New England Journal of Medicine, Ramón Estruch and his colleagues present results of a multicenter trial in Spain conducted to evaluate the effects of a Mediterranean diet on myocardial infarction, stroke or death from cardiovascular causes in subjects who were at high cardiovascular risk, but with no cardiovascular disease at enrollment. Participants were randomly assigned to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet (advised to reduce dietary fat). The results of an interim analysis were so overwhelming that the trial was stopped after a median follow-up of 4.8 years.

Study enrolled 7,447 persons with an age range of 55 to 80. Severe cardiovascular events occurred in 288 participants.  More severe events occurred in control group (109) then in the  group assigned to a Mediterranean diet with extra virgin olive oil (96 events) and the group assigned to a Mediterranean diet with nuts (83 events), respectively.  It represented a 30% reduction for the groups with Mediterranean diet in comparison to the control group.

Researchers concluded that “among persons at high cardiovascular risk, a Mediterranean diet supplemented with extra virgin olive oil or nuts reduced the incidence of major cardiovascular events.”

How your diet compares to Mediterranean-style diet? Check it here:

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Estruch R, et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet.  NEJM, 2013; 368 (14):1279-1290

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

Obesity, The Heart & Diving

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How does obesity affect your heart and why can obese divers develop heart trouble at apparently low level of exertion?

Obesity is an escalating problem and is linked to a spectrum of cardiac dysfunctions that affect feeling of wellbeing, physical fitness and longevity. In a recent review paper Rider O.J. et al, summarize current knowledge about how obesity affects the heart. The most notable fact is the change of source of the fuel from which the heart derives its energy. By excluding glucose and relying mostly on fatty acids, the energy process becomes less efficient and the heart needs more oxygen for the same level of work. In the long run, lipids become toxic for heart cells and lead to structural changes and weakening of the heart muscles, which is disabling and life threatening. In case of divers who feel fit enough to dive, however, the danger comes from the increased needs of heart for oxygen even at rest. In some cases, even a small increase in exercise level may cause a significant hypoxia of heart muscles which can lead to major troubles.

The good thing is that the problem can be improved by moderate weight loss. However, weight regulation should be started sooner rather than later when changes may become irreversible.

Read the full paper: OJ Rider, P Cox, D Tyler, K Clarke and S Neubauer. Myocardial substrate metabolism in obesity. International Journal of Obesity (2013) 37, 972–979; doi:10.1038/ijo.2012.170; published online 16 October 2012

Learn more from DAN FAQs: Healthy But Overweight

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

Four Healthy Lifestyle Behaviors Slow Down Progression of Atherosclerosis and Lower Risk of Death

Gabriella FabbriThe Multi-Ethnic Study of Atherosclerosis (MESA) included 6,229 US adults aged 44 to 84. All patients were given one point for each of four behaviors they had option to follow: a Mediterranean-style diet, 150 minutes of moderate-intensity physical activity per week, maintaining a healthy body-mass index (BMI), and not smoking. All participants also underwent coronary artery calcium screening at baseline and three years later.

People with higher score (healthier lifestyle) had slower progression of atherosclerosis and 80% less risk of death in the observed period. Each of the healthy behaviors contributed independently to better outcome.

Of the behaviors investigated, however, smoking was the most devastating. Subjects who exercised, ate healthily and maintained normal weight, but smoked, were still worse off than people who did nothing else right but stayed away from cigarettes. Not smoking is the best individual thing people (including scuba divers) can do for their health.

Read full paper: Ahmed HM, Blaha MJ, Nasir K, et al. Low-risk lifestyle, coronary calcium, cardiovascular events, and mortality: results from MESA. Am J Epidemiol 2013; DOI:10.1093/aje/kws453. Available at: http://aje.oxfordjournals.org.

Learn more about cardiovascular health.

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