Incomplete Right Bundle Branch Block in Endurance Athletes

During this test, a resting ECG readout suggested an incomplete right bundle branch block (IRBBB):

Note the "rabbit ears"/M-shape during V1, and W during V6.  I do not have an exact measurement of the QRS complex, but she said "incomplete" and it looks to my very untrained eye to be close to 100ms (>120 ms would be suggestive of a complete block).  I appreciated the initial reading, and appreciate other suggestions, and fortunately have access to some very smart cardiology fellows.

Essentially, this is a representation of the electrophysiology of the right side of the heart.  A "block" isn't scary, but is more of a re-routing of how and when the right side is polarized/depolarized.  This is not "normal," but the real question: Is it pathological?

Athletic Heart Syndrome

Based on my (limited) understanding and research and suggested interpretation (no further followup or concern was suggested), I believe this is likely an artifact of the athletic heart syndrome.  People that train, especially for a longer duration and especially for endurance events, exhibit a characteristically remodeled heart that is physically larger than normal, mostly from a hypertrophied left ventricle (which supplies oxygenated blood to the rest of the body).  Technology such as ECG's and echocardiograms provide good, raw data on physical measurements, but an ultimate diagnosis of pathology needs to include further contextual information.  In fact, some heart measurements are similar between certain forms of heart disease, and a well-trained athlete.  Most importantly, the outcomes for trained athletes and diseased patients are vastly different, which is why further information is needed for diagnosis.  In fact, as ECG screening becomes more prevalent (and its importance appreciated) for young athletes, understanding of the experience and level of activity of the athlete is important for accurate diagnosis.


Alene (who cheated by being a nurse! =)  ), then, had a very astute guess regarding the most common phenotypic characteristics of the athlete's heart.

"hypertrophic left ventricle, resting sinus bradycardia, and sinus arrhythmia, where your heart rate slows on expiration and increases with inspiration phases of the respiratory cycle"

The latter two can be quickly appreciated from the comfort of your own home: a resting heart rate below 60, that also slows on expiration and increased when breathing in, are considered symptoms of athletic heart syndrome.  I had previously observed these myself, but have not had any imaging done to suggest left ventricular hypertrophy (although it would be a reasonable hypothesis).  So these weren't necessarily "novel" suggestions during this research visit -- only the IRBBB was.

While considered "abnormal" amongst the general population, there appears to be reasonable evidence that it is not concerning for endurance-trained athletes.  With respect to 12-lead ECG's, here's a good differential summary between pathology and trained physiology.  In fact, IRBBB was found to have a relative risk of 3.5-5 compared to young, healthy controls -- and showed an even stronger effect for endurance athletes.

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In summary, it's important to understand and appreciate differences between populations based on history.  This means it's important for you and your doctor for accurate diagnoses -- many runners and cyclists have already "surprised" medical staff with very low resting heart rates.  It's equally (if not more) important for all people to "own" your own health and fitness -- your doctors and nurses can tell you what's wrong, and it's up to you and only you to fix it.  Lastly, our understanding of all of this comes from participatory research studies: consider signing up for clinical trials!  You learn something, science learns something...and you get paid!

CU Denver Clinical Trials