Survival Rates of Sudden Cardiac Arrest in Young Athletes

Interview With Jonathan Drezner, MD

What made you decide to study this population of patients (i.e., young athletes who suffer SCA)? Why do you think this population has not been studied before? My interest in cardiac issues in young athletes goes back to my medical training; I was stimulated by this topic during medical school, my residency and my sports medicine fellowship. In fact, I have always had an interest in heart-related issues in young athletes. My initial work was studying automated external defibrillator (AED) prevalence in the collegiate athletic setting. In the first study, we surveyed Division I NCAA institutions, asking about the prevalence and location of AEDs and past utilization. It was not too surprising that AEDs were mostly used on the older, non-student population such as spectators, coaches and officials. However, there were a small number of cases in which the AED was used on the athlete, and there was a surprisingly big difference in the survival rate when we compared those two groups. The overall survival rate in 35 uses was 54 percent. There were five cases in athletes, but no athletes survived despite four receiving a shock. This information prompted a second look into a larger and more detailed study on those resuscitations and outcomes, to try to figure out the factors that affect survival in young athletes with sudden cardiac arrest. I think most previous studies only looked at sudden cardiac death and not outcomes of athletes with sudden cardiac arrest survivors or not. In the last 5 - 10 years, as AEDs have become more common, we now have an opportunity to study survival in cardiac arrest and not just study the etiology of sudden cardiac death. With the increasing placement of AEDs in athletic venues and in the athletic setting, there really is a mechanism in place now for secondary prevention of sudden cardiac death as well as hopefully a growing number of athletes who have survived an unexpected cardiac arrest during athletics.

Describe the study results. What are some of the factors that could have contributed to lower survival rates in this study? I think the major factor that contributes to lower survival in young athletes is the etiology of their cardiac arrest. In our study, the predominant cause of their cardiac arrest was the presence of a structural heart abnormality or hypertrophic cardiomyopathy. I can only hypothesize on why that would contribute to lower survival rates. Typically, during cardiac arrest in the older population, there is a decline in survival of approximately 10 percent per minute for every minute that defibrillation is delayed. I think that when you have abnormal heart muscle or cardiomyopathy, the rate of decline or the chance or survival decreases at a faster rate than traditional, so there may be a shorter window at which defibrillation may be effective in adequately shocking someone out of ventricular fibrillation and into a normal heart rhythm.

Is it possible that part of the risk factor is due to the patients being male? What I mean is, do you think we would find comparable results in female athletes? Should these risks factors also be studied in female athletes? Nine out of ten young athletes who experience cardiac arrest are male, as has been shown in other studies. I don't think that survival rates will differ specifically between males and females, assuming that the etiologies of their cardiac arrest are the same.

I noticed that the cause of SCA in several of the athletes was hypertrophic cardiomyopathy (HCM). Describe hypertrophic cardiomyopathy. Is it genetic? Do patients who have it generally experience symptoms? Hypertrophic cardiomyopathy is genetic, and has a prevalence in the general population of approximately 1 in 500, to possibly 1 in 1,000 persons. It involves abnormal and thickened heart muscle that has distorted architecture, or what we call cellular disarray. Therefore, the heart muscle fibers are aligned differently than normal. It comes in many shapes and sizes. Unfortunately, in athletes with HCM and other causes of structural heart disease, the majority of them are completely without symptoms until their cardiac arrest. Thus, most athletes with structural heart anomalies are not necessarily presenting with symptoms of chest pain, syncope, or palpitations, and often the sentinel event of their underlying cardiac disease is their cardiac arrest. This makes identification of these athletes who harbor potentially lethal cardiovascular abnormalities very difficult by history alone, since so many of them will be asymptomatic. On physical examination, most of these abnormalities will go undetected. In HCM, only approximately 25 percent of patients will have aortic outflow tract obstruction that causes a heart murmur that might be detected on exam. However, these are rare entities, usually with little symptoms, and they are difficult to detect on examination.

What is usually used to treat hypertrophic cardiomyopathy? As a family practitioner of sports medicine, if I detected that a patient had HCM, I would certainly refer them to a cardiologist with a specialty and interest in treating patients with HCM. It can be treated with medication or with implantable cardioverter defibrillators.

Should athletes be tested for this during a physical examination before being allowed to play sports? I do think that all athletes should have a comprehensive preparticipation sports evaluation prior to competing in athletics. This should involve a comprehensive history and physical examination by a physician who is trained and familiar with a sports screening evaluation. That said, I think we need to recognize the limitations of our screening process and exams, because many underlying occult heart illnesses will go undetected. There is a lot of debate about the use of additional screening techniques such as an EKG or echocardiogram to look for causes of sudden cardiac death (e.g., HCM) in young athletes. From what we know about studies performed in the United States as well as recommendations from the American Heart Association, implementation of standard screening processes with either EKG or echocardiogram is simply not cost-feasible or shown to be cost-effective in the United States. It may also likely identify a large number of athletes with false positives, with findings that border on abnormal although they in fact are normal, and unnecessarily limit their participation in athletics.

There was some discrepancy regarding resuming CPR after defibrillation. What does this say about the use of CPR and AEDs? What changes, if any, do you think are needed in CPR protocol when utilized in addition to AEDs? Let me comment on two things. You had asked me earlier about what I thought were the contributing factors as to why the survival rate in athletes was lower; the first reason being the presence of structural heart disease. I think the second contributing factor is really the recognition of sudden cardiac arrest in an athlete who has collapsed. Athletes can collapse from a variety of causes, and sometimes identifying those athletes who have collapsed who are actually in sudden cardiac arrest is difficult. It is a rare event, and people may not accurately diagnose a cardiac arrest because of the presence of agonal or occasional gasping they may misinterpret these for normal breathing. They may also falsely identify the presence of a pulse in both laypersons and medical professionals, rescuer assessment of a pulse in the setting of sudden cardiac arrest is notoriously inaccurate. In addition, these were witnessed accounts, and there were four cases where the rescuer reported presence of a pulse or respiration following collapse, before they thought the athlete was in full cardiopulmonary arrest. Of course there is no way of knowing what they were feeling or if it was really present. However, in many cases of cardiac arrest, I do think that there are often valuable and vital seconds lost in those confusing moments after collapse that may delay initiating CPR or getting a defibrillator before you fully identify that this person was in cardiac arrest. Therefore, one thing that will be helpful in improving survival rates is improved education on the recognition of cardiac arrest. One of my strong recommendations, stemming much from this study, would be that any athlete who has collapsed and is unresponsive should be assumed to have a cardiac cause of their collapse until proven otherwise. An AED, if readily available, should be retrieved as soon as possible, applied to the chest, and turned on for rhythm analysis. In many ways, the AED will be more accurate in correctly identifying the athlete in cardiac arrest than we will. It is also important to note that there is very little downside to applying an AED to an athlete who is not in cardiac arrest AEDs are very safe and accurate. However, there is an enormous downside to delaying the application or use of an AED for someone who is in cardiac arrest. The AED will only recommend a shock for the presence of ventricular fibrillation or rapid ventricular tachycardia. To get back to your specific question of CPR, I wanted to note that all of these athletes had received CPR. In November 2005, the American Heart Association released their new guidelines for CPR and emergency cardiovascular care. I think that these guidelines are terrific and include important changes for our CPR protocols. One of the changes is increased emphasis on chest compressions and immediately reinitiating chest compressions after deployment of the first shock. In the past, there was usually a series of three stacked shocks. The person would be shocked and then rescuers would wait for the AED to reanalyze the rhythm. A person might receive three shocks over a two-minute period, with very little or no CPR during that time. The new CPR guidelines recommend restarting chest compressions immediately after the first shock. In those early moments after a shock, the heart may go back into ventricular fibrillation or possibly into asystole. Therefore, if we can help the heart perfuse while that normal rhythm is beginning again in the early moments after shock, then we may have better survival rates. In my study, there were two athletes who received a shock and went into pulseless electrical activity and four other athletes who required repeat defibrillation. It is possible that they were shocked and went back into a normal rhythm very briefly but then fell back into ventricular fibrillation, requiring repeat defibrillation. I suppose we'll never know. However, I'm hopeful that the new CPR guidelines will be very helpful in improving survival in the young athletic population.

How is the one athlete who survived doing today? Is it true that no structural heart disease or cause of SCA was found? To my knowledge, the athlete is doing very well and had only very slight short-term cognitive deficits but otherwise is doing terrific. The cause of his cardiac arrest was never specifically found; however, sometimes athletes or individuals will have a cardiac arrest and a complete cardiac workup but no structural cause or clear arrhythmogenic cause will ever be found. These individuals are then classified by the term primary electrical disease as the source of their cardiac arrest. In addition, if the person had died in this population, for instance, if someone experienced sudden cardiac death but their autopsy results were normal and showed no structural heart disease, then they would be classified as sudden unexplained death (autopsy negative) or put into the SADS (sudden arrhythmia death syndrome) category.

Describe the National Registry for AED Use In Sports. Is this something that was newly developed? Who enters AED use data into it (e.g., athletic trainers or physicians)? The National Registry for AED Use In Sports was initially funded and supported by the NCAA. It was developed to monitor AED utilization, prevalence, location, and cost in the athletic setting. It is also a way of studying emergency planning in athletics. It involves a web-based questionnaire on a secure database and server; the fully operational website and survey was launched last year. We are currently involved in a prospective study of all NCAA colleges and high schools in the state of Washington regarding emergency planning and AED utilization. In addition, through a grant that I received by NOCSAE (National Operating Committee for Standards in Athletic Equipment), we will be expanding that survey to all high schools nationally to initially study their current level of emergency planning and AED prevalence. We hope to get a larger pool of schools to follow AED use in the athletic setting. Our surveys are generally sent out to the head athletic trainer at colleges or the athletic director at high schools. However, the website can also be accessed by anyone who is involved in AED use in sports so if there are other users who want to fill out the survey because they were involved in a case in the athletic setting, then there are ways to request the activation code, which will allow you to create your secure username and password. It can also be filled out by the athletic trainer, the athletic director, the principal, the physician, the school administrator, etc.

What is the next step for you in this research? Will you continue researching sudden cardiac arrest in young athletes? That is my plan. I have two main focuses: the first is to recognize that the study that we've done is small (nine cases total), and due to that, there are several limitations, including not fully representing all causes of sudden cardiac arrest in athletes and possibly misrepresenting the true survival rate in that age group. Therefore, one thing that is definitely needed that I'm planning is the acquisition of more cases over time to allow a larger study of this. We'll be pursuing this more in the college and high school setting primarily over the next many years. My second focus is working on both studying and putting together recommendations for emergency preparedness in the high school and college setting, both through this study and through a separate task force committee. I've been working as co-chair of a task force that is creating consensus recommendations for emergency planning and management of sudden cardiac arrest in athletics.

For more information about this research, please refer to: Drezner JA, Rogers KJ. Sudden cardiac arrest in intercollegiate athletes: Detailed analysis and outcomes of resuscitation in nine cases. Heart Rhythm. 2006;3(7):755-759. doi:10.1016/j.hrthm.2006.03.023