The evening of March 10th, Richard Peverley of the NHL's Dallas Stars finished a shift during the first period, returned to the bench, lost consciousness and collapsed. Within seconds, a nurse from the stands rushed to him amongst his terrified and wildly gesturing teammates (imagine her launching herself over the glass into the bench, it's more fun that way). The talented and efficient medical teams present at any major professional sporting event immediately followed. He was given oxygen and an IV, and his heart was defibrillated back into a normal rhythm on the first attempt (a very positive sign). He regained consciousness immediately and was rushed to the hospital where he recovered without further sequelae.
His season is over and questions remain as to the future of his professional career, but his story is a positive one. He's alive and, all things considered, doing pretty damn well. Richard's cardiac condition was previously identified and I'd expect this allowed the Stars' medical staff to be even more prepared for this near tragedy than usual. Not everyone is so lucky.
Approximately 150 young athletes are victim to sudden cardiac death each year. The sudden death of a young person is always tragic, regardless of cause, but something about an asymptomatic and vibrant young athlete's heart betraying them demands even more attention. In 1990, Hank Gathers of Loyola Marymount University collapsed on the court shortly after a thunderous alley-oop. In 2011, Michigan high school student Wes Leonard collapsed shortly after hitting a game-winning shot to cap an undefeated season. Both were pronounced dead upon arrival at the hospital. The major issue these deaths raise is still an ongoing discussion today: what can the medical and scholastic athletic communities do to prevent them?
This topic was addressed in 2010 by Deadspin, 2011 by SI, and last November by NEJM. The usual conclusion is that while the most promising approach is some type of pre-participation screening, possibly with an electrocardiogram (ECG), the apparent benefits don't outweigh the costs (financial, health care resources, false positives, and others). I'd encourage you to take a quick read through all of those posts; both Barry's and SI's pieces will be better written than mine and the NEJM article is four short arguments from different physicians defending common takes on this issue. When you're done with that, the rest of this post will attempt to go through some of the science, specifically the problem of hypertrophic cardiomyopathy (the most common cause), how an ECG allows early detection, and the research currently driving the debate.
If you've got absolutely zero interest in anything but the public health side of this, go ahead and skip down to "Phew, that's it for the science," but you will be missing some pretty interesting stuff, I think.
The simplest description of hypertrophic cardiomyopathy (or HCM), and what you'll likely hear in news coverage, is an "enlarged heart." Like always, that's an oversimplification. An enlarged heart occurs in a huge variety of conditions, some dangerous and some healthy. Regular exercise, for example, causes "athlete's heart," an increase in size and contractility. This will be most extensive among high-intensity cardio athletes (swimmers, cross country skiers, cyclists) and serves to maximize cardiac output (more blood expelled from the heart per contraction).
HCM can arise at an early age due to genetic/congenital abnormalities or later in life via a variety of causes. That being said, we won't dive into the various mutations and accompanying research looking into the why/how of abnormal heart wall development. I'm sure it's fascinating but it's a bit too detailed considering the heart anatomy, physiology, and physics that HCM and ECG function are already going to require. So we'll jump past the how and get right to what actually happens when heart muscle abnormally expands.
Diagram of a normal and hypertrophic heart. Yes, right and left seem switched for the ventricles. Left/right is determined by the patient's viewpoint and the regular view of the heart is as if you were looking through the front of the patient's chest. Picture via.
It doesn't sound like more heart muscle is necessarily a bad thing. More heart should mean a stronger heart and a better chance of winning the 2006 World Series MVP. Doesn't quite work out like that though. The heart is a beautifully elegant organ specialized to its function in ways you'd never imagine. I'll do my best to quickly glaze over the required physiology/anatomy here and hopefully some of this will be review.
In the simplest sense, the heart is just a four chambered pyramid (it is not "heart shaped"), with two smaller chambers (the atria) sitting atop two larger chambers (the ventricles). It doesn't sit quite that neatly in your chest; it's actually tilted and twisted so the right side is mostly in front while the left side is mostly behind. Regardless, the important thing here is how blood pumps through it.
Circulation through the heart. Deoxygenated blood comes through the venous system into the right atria, then into the right ventricle, then to the lungs where gas exchange occurs, then oxygenated blood flows back from the lungs into the left atria, then into the left ventricle, then out into the general circulation. Picture via.
(Quick aside, there's a good chance you've been told arteries hold oxygen-rich blood and veins hold oxygen-poor blood, that's false. Arteries hold blood moving away from the heart, veins hold blood moving toward it. You can see in the diagram above the pulmonary arteries carry deoxygenated blood to the lungs while the pulmonary veins carry oxygenated blood back to the heart. )
The above diagram is a nice simplified version of cardiac, pulmonary, and systemic circulation. It highlights both blood flow and the various chambers of the heart. While every step of the process is vital and regulated, we'll focus more on the ventricles, as they're responsible for most of the pumping function. The right ventricle is more muscular and thick walled than the atria and responsible for pumping to the lungs, a region of relatively low resistance. The left ventricle is even larger than the right ventricle, with walls up to three times thicker, as it's responsible for pumping blood to the rest of the body (sans lungs), through relatively larger resistance.
Not at all what you expected, huh? That's what the inside of your heart looks like. The left picture shows the opened left atria and ventricle. Don't worry about identifying the atria, but you should be able to see the thick, muscular walls around the ventricle and heart apex (rubbery-looking layer near the bottom). The right picture shows the opened right atria and ventricle. You can see these ventricular muscular walls are clearly thinner than those of the left (near the bottom again). Pictures via.
HCM can mess with this process, and most commonly does so via hypertrophy of the ventricles. There are two mechanisms in particular which often place patients at risk of sudden cardiac death. First, the tissue separating the left and right ventricles, the intraventricular septum, can enlarge. This process can obstruct blood flow from the left atrium into the left ventricle. Second, the enlarged ventricle can jumble the carefully ordered electrical circuitry of the heart. Fair bit of physiology to follow here, but wade through it; these carefully regulated charge differentials spontaneously and continuously keep you alive.
The electrical system of the heart flows through muscle cells specialized to conduct electrical impulses. Each heartbeat begins in the sinoatrial (SA) node (1), a portion of the right atrium which acts as your natural pacemaker. Charge then passes through the atrioventricular node (2) and into the ventricles. It spills into a right bundle (10) and a left bundle (4). These bundles run down each side of the intraventricular septum (8) and branch out into fibers which supply impulse to the rest of the ventricles. Picture via.
There's no end to details in this process (like pretty much all of medicine, the more deeply you delve into the workings of the heart, the more you find elegantly specialized cells, enzymes, ion channels, genes, etc). The following tidbits aren't necessary for understanding HCM or ECGs, but they're interesting so read them anyway.
Heartbeats don't have to start with the SA node, as once the current is begun anywhere along the conduction path it will continue to completion (this is how pacemakers work, by modulating the pace and location of electrical charges instigated in the heart). A healthy SA node normally serves as pacemaker via self-depolarization. This involves protein channels passing charged ions across cell membranes, gradually increasing an electrochemical difference (or gradient). Once this reaches a certain threshold, it triggers the opening of other voltage-gated ion channels. These new channels allow an even greater flood of charged ions to flood the cell. This wash of ions then spreads through specialized gap junctions between cells, causing neighboring cell membranes to reach their threshold charge difference which then triggers the opening of their voltage-gated ion channels, and so on and so on. The speed at which these charge differences (action potentials) are propagated through specialized muscle cells of the heart is also regulated. The AV node (2) is the slowest region, facilitating separation of atrial and ventricular contraction and maximizing heart output (in a sense, this is why you hear "lub-dub" instead of just "dub"; your heart doesn't contract in one giant, symmetrical squeeze5). Furthermore, even the individual chambers of the heart don't flex uniformly. The ventricles contract from the bottom up, again to maximize cardiac output (like getting every bit out of your toothpaste tube). The real experts of this electrical system are surgical electrophysiologists and if you get a chance to talk to one about his or her work, please do so. They're the electricians of the heart, undergo 7-8 years of training after medical school to become so, and their procedures sound like science fiction. In some cases of abnormal cardiac electrical conduction, they'll selectively damage regions of cardiac muscle cells to reroute charge down a healthier, functional path…effectively engineering a controlled heart attack as treatment.
Back to the important stuff. Potential problems caused by ventricular hypertrophy should be somewhat apparent here. The carefully aligned and specialized muscle cells facilitating electrical charge propagation get jumbled. The disrupted parallel cell alignment, or myocardial disarray, causes arrhythmia. Whether a region of conduction is slowed or rerouted, any deviance from the norm is going to change the timing of contractions and cause an abnormal heart beat. These ventricular arrhythmias can cause a variety of symptoms including palpitations (abnormal awareness of one's heartbeat), lightheadedness, dizziness, syncope (fainting), or death. If you just though to yourself, "Oh my God, I have heart palpitations sometimes," you're not alone. That's normal and not usually a sign of anything other than sometimes people have heart palpitations. If they're frequent, or come in runs, or are accompanied by other symptoms? Go to the doctor. If they're uncomfortable and you're still concerned even after I told you they're normal? Go to the doctor. If you know a young athlete who has complained of these symptoms, have them see a doctor before resuming athletic activity.
If it was that easy there wouldn't be a screening debate, just education and clear guidelines for proper handling of these warning signs. Unfortunately, a major problem with HCM is that it often presents asymptomatically until a catastrophic event. There's not a wealth of information concerning this, as sudden cardiac death is rare and retrospective looks into patient histories are prone to under reporting, but a significant portion (50% in a 1996 NEJM study1) of sufferers never reported antecedent symptoms beforehand.
So, we have a potentially fatal heart condition prone to catastrophic events during intense physical activity which often presents ahead of time with easily ignored symptoms or no symptoms at all. There are many tests capable of detecting abnormally thickened cardiac walls: echocardiograms, catheterization, ultrasound, MRI, but the most accurate procedure without prohibitive costs or availability is an electrocardiogram (ECG). That electrical current propagating through the heart? It's measurable with the proper equipment. A series of 12 leads are placed at specific locations around the body, and by looking at combinations of their readings, a 3-dimensional record of the heart's conduction path can be charted.
Six electrodes are placed on three limbs, the right leg serves as a ground, and six more electrodes partially encircle the heart, along the chest. As charge differentials pass through the heart, currents are created in extracellular fluid and generate small potential differences across the skin. By taking readings from the six limb leads, the current path along a certain vector can be measured, as shown in the diagram below.
The same process occurs with the leads place along the chest wall (far right). This allows for six vectors to be measure along a transverse plane perpendicular to the 6 limb leads. Normal readings from all 12 leads are pictured below. Taken together, they provide a surprisingly detailed story of the path electrical current takes through the heart.
Doesn't look like much though. Picture via.
Hopefully you've got a general idea of how these readings are taken, and hypothetically, how the information could be used to trace a path through the heart. Now, how's this information used to catch hypertrophic cardiomyopathy?
The boxes on the left show a four step sequence (A-D) of normal ventricular depolarization during a regular heartbeat with records from the V1 and V6 leads included. The middle diagram shows depolarization records from all six chest leads through regular ventricular depolarization. The upper right diagram shows right ventricular hypertrophy. The increased cardiac muscle takes longer to depolarize and presents abnormal V1 (red circles) and V6 (green circles) readings. Bottom right diagram shows left ventricular hypertrophy. The increased cardiac muscle presents abnormal V1 and V6 readings (circled in red and green again, though the differences are tougher to see as this presents as exaggerated spikes rather than easily distinguishable differences).
Phew, that it for the science. Everything here on out is epidemiology and public health concerns. There are three major studies of screening procedures serving as the predominant source of data in this argument.
Italy implemented a national pre-participation athletic screening requirement in 1982. Data was collected concerning screening results, sudden deaths in youths, and the nature of those deaths from 1979-2004.2 This study found a significant decrease in sudden cardiac death in young athletes, from 3.6 per 100 000 person-years in '79-'80 to 0.4 per 100 000 person-years in '03-'04. Person-years refer to the number of years of data per subject: 1 subject monitored for 4 years provides 4 person-years of data, while 2 subjects monitored for 2 years also provides 4 person-years of data. Throughout this study, 9% of screened athletes either screened positively or equivocally, with 2% continuing on to disqualification from activity (a 7% false-positive rate).2 Cost for ECG screening alone was around $40 per athlete, although financial burden increases for the 9% requiring further testing.2 Seems like fairly clean cut improvements for relatively reasonable prices.
Israel implemented a similar screening requirement in 1997, although this program required both an ECG and an exercise stress test (which should theoretically decrease the number of false negatives over ECGs alone). Data was gathered concerning sudden cardiac deaths in young athletes from 1985-2009.3 This study found no significant change with the introduction of screening requirements, from 2.54 per 100 000 person-years in '85-'97 to 2.66 per 100 000 person-years in '97-'09.3
Minnesota implemented a statewide screening involving only a standardized questionnaire and physical evaluation without ECG or further specialized procedures. Monitored from 1993-2012, this study found a consistent low level of sudden cardiac death in young athletes, 0.24 per 100 000 person-years over the 19 years studied (with relatively little deviation).4
Diagram summarizing the death rates per 100 000 person-years data compiled above.3
While Italy's study taken alone seems to paint a fairly clear picture, the introduction of Minnesota's and Israel's death rates muddy the waters. Three studies showing a variety of death rates from different population: largely homogenous Italians with and without mandated ECG screening, largely homogenous Israelis with and without mandated ECG/stress screening, and largely homogenous Minnesotans without any ECG/stress screening (the MN study doesn't present any information on the diversity of their high school athlete population, but as a former MN high school student, I feel safe assuming it wasn't the most diverse crowd). Taking all the information together, the two years monitored before the implementation of Italy's study don't necessarily provide the clearest "before" picture and it's difficult to be sure that 3.6 per 100 000 person-years value is an accurate baseline from which to measure improvement. Furthermore, the Israeli study doesn't show an improvement with mandatory screening and the widely disparate death rates across all three make it difficult to apply a screening methodology to a huge and diverse young athletic population like the United States'.
It seems that, for now, more data and screening will need to be implemented in small scale environments until we nail down an approach that maximizes benefit and minimizes cost. Given the research, possibly asymptomatic nature of these heart conditions, and sensitivity of ECGs, I'd expect this screening will require at least an ECG to effectively benefit the pre-participation athlete. Uncomfortably, the debate at this point gets into "how much money is a young athlete's life worth?" territory. This is more than just a cut-and-dried "it would take this much money to save this many person-years" situation, the cost of the death of a youth expands beyond a victim's lost years to family, friends, school and town.
I don't have an answer here. I wouldn't even know where to begin in placing a dollar value on that type of tragedy. For now, I don't have to. Hopefully we'll have more data in the near future and ongoing research will clarify a screening process to efficiently catch this silent killer. Then the debate over the cost-benefit analysis of widespread efforts to reduce this rare and tragic condition can begin. Today, like 23 years ago when Hank Gathers died and two years ago when Wes Leonard died, there's simply not enough data supporting implementation of a mandatory screening process for young athletes.
- 1. Liberthson, R. Sudden Death from Cardiac Causes in Children and Young Adults. NEJM 1996;334:1039-1044.
- 2. Corrado D, Basso C, et al. Trends in sudden cardiovascular death in young competitive athletes after implementation of a preparticipation screening program. JAMA 2006;296:1593-601.
- 3. Steinvil A, Chundadze T, et al. Mandatory electrocardiographic screening of athletes to reduce their risk for sudden death: proven fact or wishful thinking? J Am Coll Cardiol 2011;57:1291-6.
- 4. Roberts W, Stovitz, S. Incidence of Sudden Cardiac Death in Minnesota High School Athletes 1993-2012 Screened With a Standardized Pre-Participation Evaluation. J Am Coll Cardiol 2013;62:1298-301.
- 5. Technically, heart sounds are caused by blood turbulence as heart valves slam shut. But the pressure differentials which shut those valves are driven by contracting regions of the heart so I'm going to stand by this sentence as accurate enough for this audience.