A doctor I know has some theories on Clint. Here's what he sent me:

Clint Dempsey’s Heart Condition: A Doctor’s Conjecture

Up front I want to be clear that although I am a practicing physician in a Seattle hospital I have no direct knowledge of Clint Dempsey’s condition, treatment, or prognosis. I am a hospital medicine physician, which means that I exclusively take care of adult patients who have an illness serious enough to require hospitalization, and part of my daily practice includes diagnosis and treatment of irregular heart rhythms. With my medical background, combined with the statements from Sounders’ representatives, I have formulated two highly probable scenarios regarding Clint Dempsey’s irregular heartbeat, also known in the broadest medical terminology as an arrhythmia.

Here’s what we know: On August 26th the Sounders announced that the 33 year old is undergoing medical tests for an irregular heartbeat. Garth Lagerwey reportedly said that the club has been monitoring this condition for "a while." This information is extremely limited, but allows a few inferences which narrow down possible diagnosis. 1) His condition is not so serious that it required him to be scratched earlier in the season and could just be monitored. Furthermore, MLS requires preseason EKGs and echocardiograms (heart ultrasounds) on every player, so any underlying structural or electrical abnormality would have been known not just to the Sounders, but to the league – a group risk averse enough to be unlikely to allow a marquee player to play through a condition that could have him collapse and die on national television. This inference likely eliminates many of the conditions with a marked risk of sudden death, such as hypertrophic cardiomyopathy (see Eddie Johnson’s retirement). 2) His condition is not so serious that he is announcing retirement even at this time, suggesting that while the irregularity is not as well controlled as it had been, there is a chance it could be controlled with additional procedures and/or medications. 3) Despite these encouraging inferences, this condition has proven serious enough that he has not returned after several weeks, which suggests that initial attempts to regain control have been unsuccessful.

With these three thoughts in mind we can narrow down the possibilities, but first, a quick biology refresher. Electrical signals normally start at a location at the top of the heart called the sinoatrial (SA) node which receives all of the chemical, hormonal, and nerve signals from the rest of the body to speed up or slow down the heart rate. From there the electrical signal travels in a concerted fashion to the atrioventricular (AV) node which sits between the atria at the top of the heart, and the ventricles at the bottom which pump the blood to the lungs and body. The AV node serves as a regulator to prevent abnormally fast signals from getting through and overworking the ventricles, but also has a backup electrical generator in case it doesn’t receive an electrical signal to pass on.

Anything that bypasses these systems can cause an irregular heartbeat. Sometimes these irregularities are self-limited, some require medications to reset, while still others require an intentional electrical shock to return to a normal rhythm. In each of these cases recurrence may or may not be preventable, even with medications or a procedure known as ablation in which the source of the electrical abnormality is scarred in such a way that it becomes electrically isolated and cannot spread its abnormal signal. Brian Schmetzer said that, "he had some issues a little earlier on. It was an incident that happened in a game, in a match, they went through some of the data they collected and that’s how they found it." This statement would suggest that Clint felt something abnormal yet transient during a match – perhaps chest pain, lightheadedness, or uncontrolled racing heart – and he brought it to the attention of the medical staff who then reviewed the monitors the players wear and they found a self-limited arrhythmia and have kept an eye on his monitor for recurrence. Whether it recurred in a self-limited fashion since then we don’t know, but it now appears to have recurred and persisted. With the inferences above and the insight from Schmetzer’s description we can narrow down the possibilities to one of two scenarios.

Scenario 1: Abnormal rhythms such as "AV node re-entrant tachycardia" and "atrioventricular reentrant tachycardia" are amongst the possibilities, and they share a similar underlying issue in which an electrical loop sends inappropriately rapid signals to the ventricles, the latter of which can generate heart rates well into the 200s. Both of these arrhythmias are highly amenable to the aforementioned ablation procedures, and if successful generally mean a return to competition in two to four weeks. The absence of this kind of a timeline from the Sounders could mean that the procedure was unsuccessful and is being repeated, with a timeline for return to be announced once they are able to successfully perform the ablation or adjust medications to prevent recurrence. From a fan’s perspective this is the best case scenario since it would mean a return before the end of the season.

Scenario 2: The other possibility, which becomes increasingly likely the longer he is out, is that he has a more complex arrhythmia. Atrial fibrillation or atrial flutter are conditions with rapid electrical signal generated from the SA node, but from the atria themselves, and are therefore not as responsive to the body’s signals to speed up or slow down, running the risk of unmitigated rapid heart rate even at rest. If uncontrolled, this nonstop rapid rate can lead to heart failure, and the abnormal blood flow patterns that result within the heart can increase the risk of stroke. The prevention of stroke in these situations frequently necessitates blood thinners that would be incompatible with professional soccer. Treatments to stop these arrhythmias include medications, cardioversion (electrical shock to reset the heart), and/or ablation procedures, but if initially unsuccessful then control of the arrhythmia becomes less likely with each passing attempt. When the arrhythmia cannot be eliminated, the next step is to use medication to prevent the heart from going too fast, which would then make elite level performance nearly impossible.

The lack of information from the Sounders is entirely appropriate. This is Clint Dempsey’s medical issue and it is up to him how much he wishes to share. On September 13th a photograph reportedly showing Clint jogging was posted, which suggests that the he may have had a successful ablation for one of the less complex arrhythmias (scenario 1) and is being monitored for recurrence as he gradually increases exertion to match levels. If this proves correct, and he remains without recurrence for 2-4 weeks (a timeline his return to exertion suggests he may already be partway down), then he could potentially be back on the pitch in time for the match against LA on the 25th. However, the longer the Sounders go without providing a timeline for return, the more likely scenario 2 becomes. As both a physician and a fan I wish him the best of health, as I know we all do.